Skip Navigation

Cardiovascular Research 2007 75(4):669-678; doi:10.1016/j.cardiores.2007.06.001
This Article
Right arrow Abstract Freely available
Right arrow FREE Full Text (PDF) Freely available
Right arrow Alert me when this article is cited
Right arrow Alert me if a correction is posted
Services
Right arrow Email this article to a friend
Right arrow Similar articles in this journal
Right arrow Similar articles in PubMed
Right arrow Alert me to new issues of the journal
Right arrow Add to My Personal Archive
Right arrow Download to citation manager
Right arrowRequest Permissions
Google Scholar
Right arrow Articles by Auger, F. A.
Right arrow Articles by Germain, L.
Right arrow Search for Related Content
PubMed
Right arrow PubMed Citation
Right arrow Articles by Auger, F. A.
Right arrow Articles by Germain, L.
Social Bookmarking
Add to CiteULike   Add to Connotea   Add to Del.icio.us  
What's this?

Copyright © 2007, European Society of Cardiology

Adventitia contribution to vascular contraction: Hints provided by tissue-engineered substitutes

François A. Augera,b,*, Pédro D'Orléans-Justec and Lucie Germaina,b

aLaboratoire d'Organogénèse Expérimentale (LOEX), Hôpital du Saint-Sacrement du CHA, Québec, Canada
bDepartment of Surgery, Laval University, Québec, Canada
cInstitute of Pharmacology, Medical School, Sherbrooke University, Sherbrooke, Québec, Canada

* Corresponding author. Laboratoire d'Organogénèse Expérimentale (LOEX), Hôpital du Saint-Sacrement du CHA, 1050, chemin Sainte-Foy, Québec, Canada G1S 4L8. Tel.: +1 418 682 7663; fax: +1 418 682 8000. Francois.Auger{at}chg.ulaval.ca

Received 23 January 2007; revised 29 May 2007; accepted 1 June 2007


   Abstract
Top
 Abstract
1. Introduction
 2. Vascular tone control:...
 3. The value of...
 4. Tissue-engineered vascular...
 5. Perspectives and conclusions
 References
 
It is well accepted that the adventitia is much more than a simple elastic membrane which surrounds the media. However, the extent of its contribution to vascular physiology, as well as the mechanisms involved, remains to be clearly established and characterised. Investigation into these topics is hampered by a few technical challenges, like the paucity of available healthy human vascular samples and the variability such samples can display. Another challenge is the isolation and preparation of intact adventitia without contaminating cells from the media. For those reasons, although other models have proved useful to address these questions, data from tissue-engineered vascular substitutes can also provide quite valuable answers. Results from such substitutes indicate that a reconstructed adventitial layer can respond to classic vasoactive agents such as endothelin and sodium nitroprusside.

KEYWORDS Adventitia; Tissue engineering; Blood vessel; Vascular tone

Abbreviations: TEBV, tissue-engineered blood vessel • TEVM, tissue-engineered vascular media • TEVA, tissue-engineered vascular adventitia • VSMC, vascular smooth muscle cells • VF, vascular fibroblasts • ET, endothelin • ECM, extracellular matrix • NO, nitric oxide • SNP, sodium nitroprusside.


   1. Introduction
Top
 Abstract
 1. Introduction
2. Vascular tone control:...
 3. The value of...
 4. Tissue-engineered vascular...
 5. Perspectives and conclusions
 References
 
The contribution of the adventitia in vascular tone is a complex yet highly important parameter to consider towards a better understanding of the physiological function of each component of the blood vessel wall. Investigators are even more challenged if these experiments are to be done by utilising human tissues. The difficulties lie in the problematic access to human tissues and blood vessels combined with the significant variance in many parameters between different donors such as age, sex, previous diseases and life habits. It is in such a context that utilisation of tissue-engineered blood vessel (TEBV) may shed some light on some particular and complex issues in cardiovascular pharmacology. Organ constructs created by tissue engineering have the following advantages: 1) obtaining a more consistent culture process resulting in complex 3D reconstructed tissues, 2) achieving an acceptable level of reproducibility, 3) access to human cells, 4) individual tailoring of the various components of the construct can be achieved for special experiments, 5) the nature of the donor can be well defined, such as young, old or hypertensive.

The role of the media in cardiovascular tone control is well established [1]. A lingering question is the evident yet poorly explored significance of the adventitia in that very same function. Many previous studies have used elegant and interesting techniques to investigate specific vascular layers. For example, isolated cells in culture offer a powerful system to investigate many cellular mechanisms, as shown by An et al. to investigate how adventitial fibroblasts could express endothelin-1 in response to angiotensin-II [2]. Other groups have used analytical tools such as immunohistochemistry to unravel tissue-specific and cell-specific mechanisms [3–6], or ingenious devices such as microelectrodes to assess changes in specific layers of whole vessels [7]. Finally, other approaches have worked with native vascular samples, mostly from animal models, to which various stripping procedures were applied [8–14]. However, this last approach has been hampered by the technical difficulty of clearly separating the adventitia from the media [15]. Thus, current knowledge can be obfuscated by experimental drawbacks. The use of tissue-engineered vascular substitutes should introduce a novel and additional approach that can bring additional insight to the field.

Our research group, amongst others, has been a proponent of tissue-engineered tissues and organs substitutes as in vitro models for more than 14 years [1,16–33]. Thus, we believe such an approach can provide relevant answers to address the various functions of specific vascular wall components: intima, media and adventitia [1,21,22,29,30]. Admittedly, tissue-engineered vascular substitutes lack some of the more complex features found in native vessels, such as vasa vasorum, resident immune cells and nerve endings. However, they offer a useful intermediate level of complexity between monolayer cell cultures and native human blood vessels. Previous publications have shown that our tissue-engineered vascular substitutes display a number of characteristics that are similar or close to those observed in native small diameter blood vessels. These similarities support the physiological relevance of tissue-engineered constructs of this type for investigating vascular components [1,17,22,25].


   2. Vascular tone control: putting the role of the adventitia in perspective
Top
 Abstract
 1. Introduction
 2. Vascular tone control:...
3. The value of...
 4. Tissue-engineered vascular...
 5. Perspectives and conclusions
 References
 
The role of the adventitia has long been considered mostly limited to its structural and mechanical functions, with some involvement of the perivascular innervation in overall vascular responses [34]. Until the early eighties, the adventitial layer had been known to be involved in the anchoring of the blood vessel to extravascular matrices (e.g. connective tissue). Aside from fibroblasts, other cell types can be found in the adventitia. Endothelial cells are present in the adventitia of blood vessels containing a vasa vasorum. Aside from the possibility that they could provide the adventitia with a close source of vasoactive factors such as nitric oxide (NO), published evidence indicates that the vasa vasorum could be involved in various vascular pathologies such as atherosclerosis [35,36]. Other, experimental results indicate the adventitia can be a source of NO [6,11,13]. This could be related to adventitial resident mastocytes and nerve cells, which display close contacts and have been suggested to be involved in the local release of vasoactive compounds [3,5,37,38]. Furthermore, previous results show that the adventitial fibroblasts themselves can also be involved in the local release of NO [6,10,39].

Pericytes represent another cell type that can be found in the adventitia. Although some evidence points towards their implication in the calcification commonly associated with atherosclerosis [40–42], their role in vascular stability and angiogenesis is also well accepted [43,44]. There are indications that pericytes could also, in addition to their role in the neovascular structures, provide progenitor cells for other lineages in wound repair [45,46]. Finally, although not morphologically part of the adventitia itself, perivascular adipocytes are another anatomically specialised cell type in close contact with the outer region of blood vessels, and some results convincingly point to their contribution towards vascular tone regulation and remodelling [47–49].

2.1 Role of the adventitia in vascular compliance
The involvement of the adventitia has been proposed in angiogenesis and arteriosclerosis [3,36,37,39,50]. Indeed, vascular remodelling occurring in advanced arteriosclerosis causes loss of vascular compliance (i.e. enhanced rigidity) and triggers intimal thickening. The latter pathology may involve adventitial progenitor cell migration towards the more intraluminal compartments of the vasculature [50–53]. These and other results point towards the significant contribution of the adventitia in post-transplant or post-injury vascular remodelling [14,52,54]. The triggering mechanisms for adventitial myofibroblast migration are yet to be fully understood and controlled, albeit part of the answer might be found in the stimulation of toll-like receptors and inflammatory responses [55,56] as well as in the combined role of TGF-β and the Connective Tissue Growth Factor (CTGF) [57]. It has also been proposed that reactive oxygen species generated by adventitial fibroblasts through NAD(P)H oxidase activity can modulate pathological fibroblast proliferation, stimulate medial hypertrophy and affect vascular tone [39]. Finally, it has been shown that balloon injury causes an overall reduction in vascular {alpha}-adrenoceptors expression [58]. This reduction is associated with an enhanced growth-factor-like activity of catecholamines on vascular smooth muscle cells and adventitial fibroblasts which leads to vascular wall hypertrophy [58].

2.2 Role of the adventitia in autocrine control of vascular function
The overall contribution of the adventitial layer in the biomechanical characteristics and responsiveness of the blood vessel, under physiological conditions, was not abundantly explored in the literature until recently. Actually, not only does the adventitia respond to hormones such as endothelin-1 [21–23] but adventitial fibroblasts can secrete ET-1 under certain stimuli such as hypoxia or angiotensin-II [2,59]. Furthermore, the vascular outer layer can release vasoactive factors such as the adventitial-derived relaxing factor (ADRF) [60,61]. Calcium entry-dependent activation of tyrosine kinase and protein kinase is the suggested mechanism of action of ADRF. Its physiological role remains, however, largely undocumented in in vivo settings and the readers are referred to the elegant study of Gao et al. for further details [62]. On the other hand, Singhal et al. [63] have successfully correlated the role of adipocyte-derived leptin release as one of the cardinal causes of atherosclerosis. This group demonstrated that in obese subjects an overproduction of leptin from perivascular adipocytes was positively correlated with significant changes in vascular distensibility of brachial arteries from healthy adolescent subjects independently of other obesity-related factors such as body weight, mass index or LDL/cholesterol index [63,64]. Another group used leptin-deficient hyperlipidemic mice to provide more evidence that leptin can accelerate atherosclerosis [65]. Considering that perivascular adipocytes are predominantly located close to the adventitial layer of blood vessels, studies support the concept that secretion of factors such as leptin and ADRF from the adventitial layer may greatly influence vascular compliance either acutely (i.e. short term response to biomechanical stimuli) or chronically (i.e. long term angiogenic, remodelling and/or atherosclerotic and arteriosclerotic processes) [62–64]. Additional concepts, based on some in vitro studies and deductive reasoning, have been suggested regarding the influence of periarteriolar fat adipocytokines, such as tumor necrosis factor alpha and interleukin-6, on local vascular signalling [49]. The authors of this study hypothesised a role for these adipocytokines in obese subjects in the relation between insulin resistance and arteriolar vasoconstriction in skeletal muscles.

2.3 Role of the adventitia in neurogenic control of vascular tone
Vascular innervation of the adventitia and neurogenic control of vascular tone have been well documented in coronary [3,66–68] and cerebral [5,69–72] vasculature for many years. The presence and role of vascular nerve endings have also been investigated in various blood vessels [73–76]. Vascular autonomic and sensory nerves of various types inclusive of cholinergic, adrenergic, peptidergic or nitrergic are found in different proportions and density depending on the specific anatomical site [37,66,71,72,75,77,78]. The variety of nerves which can be found in the adventitia is underlined by the presence of many neuron-related peptides and molecules such as acetylcholine [72], noradrenaline [12,79], neuropeptide Y [67,80], substance P [67,80], calcitonin gene-related peptide [67], neurotensin [81] and vasoactive intestinal peptide [67,72,80]. Nerve stimulation may elicit different responses, either in type or amplitude, in different parts of the vascular system [71,80]. Neurogenic vasocontrol can thus follow different patterns depending on which molecules are released and local reactions they trigger. For example, active molecules released locally from adventitial nerves may diffuse and act directly on the adventitia and the media or act on the endothelium which in turn will release factors such as NO which will then influence the media [37,70,75,76,78,79]. Yet another component of this complex question is the presence of resident mast cells, which can be affected by neurons. Such a link has been proposed by Dimitriadou et al. based on data from temporal arteries of cluster headache patients in which adventitial mast cells showed signs of progressive degranulation compared to normal controls [82]. Another example of possible mast cell involvement has been proposed for atherosclerosis by Laine et al. [3]. Sensitive C-fibers richly innervate the medial-adventitial interface [78] and neuropeptides (such as substance P and Calcitonin Gene Related Peptide) released from C-fibers can interact with resident mast cells. In pathological conditions, Laine et al. [3] demonstrated increased mast cell/C-fiber contacts. They conclude that activated mast cells may release pro-inflammatory molecules such as leukotrienes and histamine leading, perhaps, to exaggerated vasospastic responses of the injured blood vessel wall. The authors do not identify which specific leukotrienes are involved in this process. Substance P, however, has been shown to induce murine mast cells to generate leukotriene c4 in vitro, although it did not also elicit granule release in the given experimental conditions [83].

2.4 Role of the adventitia in overall vascular reactivity to hormones and autacoids
Very few studies have addressed the topic of adventitial reactivity to exogenous, let alone endogenous, hormones, perhaps because of the technical difficulties of dissecting this particular vascular compartment in the overall vascular responsiveness. Surgical layer stripping is one way to address this problem, although much care needs to be exercised to ensure the integrity and purity of the separated layers [13,15]. In one such study, adventitia-denuded rabbit carotid artery rings showed a lower response to noradrenaline than control rings [14]. Other experiments, based on rat aorta, carotid and iliac arteries which also used surgical separation of the vascular layers, have provided more evidence that the adventitia is involved in vascular contraction and relaxation [8–14]. Those results showed differences in the in vitro contractile and relaxation capacity of vascular samples devoid of adventitia and, in some cases, also of endothelium. In a number of experiments using agents such as noradrenalin, forskolin, urotensin-II, LPS, KCl, acetylcholine and sodium nitroprusside (SNP), adventitial control of NO release has been shown to have an important influence on vascular tone [8–14]. In contrast, it should also be noted that superoxide anions generated in the adventitia may reduce the bioavailability of NO and thus counteract the modulation of adventitial tone by the later labile factor [39,84].

One group reported that removal of the adventitia caused a notable proliferation of the media [14]. This raises the question of whether the stripping procedure might trigger rapid modifications in the smooth muscle cells that could influence contractile capacity [85]. The reduction in contractile response of vascular samples from which the adventitia has been stripped might thus not be entirely attributed to the absence of this layer. In order to have a model in which no tissue stripping is necessary, tissue-engineered vascular constructs are an interesting tool to elucidate adventitial involvement in vascular tone. Indeed, 3D vessels constructed with adventitial cells provided by human donors [23] introduce a new approach that has allowed to determine the overall responsiveness of a reconstructed layer to potent vasoactive agents and to estimate an adventitia versus media intrinsic activity ratio in such constructs. Recent data show that apparent affinities and maximal contractility responses can be estimated in comparative fashion. Furthermore, the adventitial layer may account for about 50% of overall vessel constrictive response to endothelin-1 in engineered adventitia/media vessels [21].


   3. The value of tissue-engineered substitutes as in vitro models
Top
 Abstract
 1. Introduction
 2. Vascular tone control:...
 3. The value of...
4. Tissue-engineered vascular...
 5. Perspectives and conclusions
 References
 
Animal cell culture, either in 2D (monolayer) or 3D (engineered tissues), and animal models share many biological functions with human tissues, including blood vessels, and have been of great value in numerous experiments. However, beyond their common characteristics, human and animal cells have some inherent differences which have to be taken into account when selecting models and analysing experimental results [86–90]. The use of tissue-engineered constructs as in vitro models has recently undergone a significant resurgence of interest due to distinct advantages. One important advantage of using human cells is to avoid any inter species differences, subtle or not, that can affect the experimental results. Alternatively, human tissue-engineered constructs may be profitably used to validate results obtained in animal models prior to more expensive and ethically restricted clinical assays. On the other hand, even when generated from human cells, tissue-engineered constructs are still simplified versions of the actual physiological tissues they aim to represent and they may not perfectly reflect all the mechanisms present in vivo. Despite these limitations, tissue-engineered models have advantages worth exploiting in various applications [1,16–18,20–24,26,27,29–33,91,92]. Overall, it is possible to generate tissue-engineered vascular constructs with characteristics which, although not perfectly identical to native tissues, provide enough similarities to become useful experimental models [1,17,21–23,25,29,30,85]. Two recent and interesting reviews of the value of tissue-engineered 3D models can be suggested to the reader [93,94], as this aspect is beyond the scope of the present review.


   4. Tissue-engineered vascular constructs: a novel approach to the functional analysis of the vascular wall
Top
 Abstract
 1. Introduction
 2. Vascular tone control:...
 3. The value of...
 4. Tissue-engineered vascular...
5. Perspectives and conclusions
 References
 
4.1 Tissue engineering of vascular constructs
The tissue-engineered vascular models generated by the self-assembly approach are entirely made from human cells and achieve their mechanical properties without the addition of exogenous synthetic biomaterial. As described for a tissue-engineered blood vessel, the cells produce and organize their own extracellular matrix [25]. The development of tissue-engineered vascular models with three different "architectures" generated with this approach has recently been reported [21]. The first vascular construct contained only an adventitial component assembled uniquely with vascular fibroblasts (VF) (4 layers) (TEVA), the second vascular construct contained only a medial component with vascular smooth muscle cells (VSMC) (4 layers) (TEVM) and the third one was a combination of adventitial (2 layers) and medial (2 layers) components (TEVMA) (Fig. 1). This last construct was the one closest to native small diameter human constricting blood vessels. Although the technique has evolved to include an intima [25] when necessary, its absence is not a drawback when specific comparison of media to adventitia is desired.


Figure 1
View larger version (28K):
[in this window]
[in a new window]
[Download PowerPoint slide]
  		Fig. 1 Tissue engineering of three vascular constructs with medial component alone, adventitial component alone, or comprising both media and adventitia. Each cell type is extracted and cultured from the same biopsy of human saphenous vein and assessed for phenotype homogeneity. Cell sheets are produced by culturing either vascular smooth muscle cells (VSMC) or vascular fibroblast (VF) in conditions that stimulate extracellular matrix synthesis. To obtain vascular substitutes with only media or adventitia, sheets of VSMC or VF are wrapped around a tubular support until a four-layer construct is obtained. For the substitutes with both media and adventitia, two layers of VSMC sheet and two layers of VF sheet were successively wrapped over the tubular support to obtain a construct which had the same number of layers (four) as the final TEVM and the TEVA constructs.

 
Obviously, our vascular constructs are devoid of nerves, vasa vasorum, mast cells and perivascular adipose layer. Although elastin has been detected in the reconstructed adventitia, the constructs did not display elastic laminae. The absence of these components, however, did not seem to compromise the similarity of the pharmacological responses to those elicited in native human vessels. Accumulated observations of the various vascular constructs from histological, immunohistochemical and ultrastructural analyses have shown that, although notable differences can be seen, they show interesting similarities to native human arteries of small diameter [1,17,21–23,25,29,92]. Histological analysis revealed cells embedded in a self-generated extracellular matrix (ECM). In a TEBV, VSMC expressing {alpha}-smooth muscle actin ({alpha}SMA) and desmin were seen as elongated cells in an orientation resembling that in human media [25]. Vascular VSMC density, although high for an in vitro model, was still lower than in a normal vascular media [25]. However, when treated with classic agents such as KCl, SNP, endothelin, histamine and bradykinin the constructs nonetheless displayed vasomotor responses similar to normal human blood vessels [1,17,21–23,30]. TEVM contained a high percentage of cells expressing {alpha}SMA. In contrast, only a low number of {alpha}SMA-expressing cells were detected in TEVA, reflecting that the differences between VF and VSMC were preserved in the reconstructed vascular tissues (Fig. 2) [21]. As studied in the TEBV, fibroblasts synthesized high amounts of elastin assembled in small fibers, which were organized in large circular arrays [25]. Immunostaining also indicated that the ECM contained type I, III, and IV collagens as well as laminin, fibronectin, and chondroitin sulfates [25,95].


Figure 2
View larger version (46K):
[in this window]
[in a new window]
[Download PowerPoint slide]
  		Fig. 2 Immunofluorescence staining of {alpha}SMA on TEVM (A) and TEVA (C). (B and D) Nuclei staining with Hoechst 33258 of A and C, respectively. Scale bars: 100 µm. (From Laflamme, K. et al. FASEB J 2006; 20: E516–24. Used with permission.)

 
4.2 Pharmacodynamic characterisation of tissue-engineered vascular constructs
4.2.1 Pharmacological responses of the TEVA to the endothelin peptides and precursors
The tissue-engineered adventitial vessel (TEVA) responds to isoforms of the endothelin peptides, with the notable exception of ET-3 and its precursor big-ET-3 (Table 1). Even if both ET-1 and ET-2 have similar apparent affinities (i.e. pD2 and EC50) in the nanomolar range, the former peptide is slightly more potent that the latter one, while both peptides have similar intrinsic activities (i.e. {alpha}E). The lack of response of the TEVA to ET-3 suggests that this particular engineered vessel does not possess functional ETB receptors. RT-PCR demonstrated the presence and absence, respectively, of mRNA for ETA and ETB receptors in TEVA [21]. This observation correlates with results from other groups, where ETB was mostly present in the media and absent from the adventitia [4,96]. The TEVA response to the precursors of ET-1 and ET-2, namely big-ET-1 and -2, demonstrates the presence of a functional endothelin-converting enzyme (ECE) in these engineered vessels. If the presence of such an enzyme in the adventitia of normal blood vessels can be molecularly confirmed, it would be interesting to explore how it is compatible with the observations that ET-1 can be produced by adventitial fibroblasts [2,59], thus suggesting a possible paracrine role for this molecule in the vascular wall. It is, on the other hand, important to point out that we were unable to confirm the capacity of the ECE to convert big-ET-3 to ET-3 because of the lack of intrinsic activity of the later peptides in the TEVA. Thus, a vessel constructed from cultured cells of a particular vascular tunica, such as the adventitia, possesses functional integrity, in terms of receptors and maturing enzymes, in a similar fashion as to what has been shown in intact human blood vessels [21–23].


View this table:
[in this window]
[in a new window]

  		Table 1 Pharmacodynamic characterisation of endothelins in TEVA

 
4.2.2 Contribution of the adventitial layer in the overall vasoactive response to endothelins
To the best of our knowledge, Laflamme et al. [21–23] are the first to report data generated with adventitia alone, showing measurable contractile properties which may contribute to the overall vascular compliance in response to endogenous hormones and autacoids. Overall, the adventitia contributes to a lesser extent than the media to the contractile response of the tissue to ET-1, in our vascular substitutes. Indeed, potency of ET-1 is markedly enhanced in TEVM, in terms of maximal response, when compared to vessels composed of adventitial as well as adventitial/medial cells.

The presence of an ETB-dependent contraction in both TEVM and TEVMA engineered vessels when compared to TEVA constructs is another striking result (Table 2). Indeed, whereas ET-3 is inactive in TEVA, this particular peptide possesses a weaker relative affinity (40 to 50 times less potent than ET-1), yet shows a similar intrinsic activity in both TEVM and TEVMA. This ETB-dependent component has been described in more detail by Laflamme et al., both at the functional (via the use of selective ETA and ETB receptor antagonists and ETB agonist) as well as at the molecular level, either with a system expressing both ETA and ETB [23] or ETA alone [22]. Finally, although ET-3 contracts both TEVM and TEVMA, its precursor big-ET-3 is inactive (Table 2). It is therefore possible to conclude that the above-mentioned vessels allow the study of the specificity of action of the endothelin-converting enzyme. In these vessels, ECE discriminates between the precursors of ET-1 and ET-3, is sensitive to the ECE inhibitor phosphoramidon [21] and therefore possesses the selective proteolytic characteristics of the ECE-1 isoform extensively detailed in the literature [97–99]]. This is relevant to the in vivo situation for two reasons. Firstly, the endothelium which possesses the ETB receptor type will respond equally well to ET-1 or ET-3 since it possesses the same affinity for both peptides. Secondly, is that it has been previously shown that the ECE possesses substrate specificity for big-ET-1 and big-ET-2 but does not convert big-ET-3 [100]. This suggests that the engineered vessels express a functional ECE of the ECE-1 type, as indicated by the fact that big-ET-3 is inactive in all three constructs. By analogy, the lack of hemodynamic properties of big-ET-3, as opposed to ET-3, would also suggest that in vivo the predominant ECE isoform is of the ECE-1 type [100].


View this table:
[in this window]
[in a new window]

  		Table 2 Comparison of relative affinities and intrinsic activities of ET-1, ET-3 and precursors in engineered vessels

 
4.2.3 Does the adventitia respond to endothelium-dependent or independent vasorelaxant factors?
L'Heureux et al. [25] were the first to demonstrate the presence of a functional endothelium in engineered vessels. Indeed, this particular study showed that the addition of an endothelial layer in TEBVs contributed to an inhibition of platelet deposition on the vascular wall. On the other hand, little is known about the vasoactive functionality of the endothelium seeded on the luminal portion of engineered vessels. One of the first steps towards measurement of this important function of the endothelium was to assess whether the underlying smooth muscle cells of engineered vessels would respond to activators of guanylate cyclase, the main mechanism involved in the vasodilatory response of endothelial derived relaxant factor, nitric oxide (NO). Indeed, all three engineered vessels, namely TEVA, TEVM and TEVMA, dilate in a concentration-dependent fashion to the guanylate cyclase activator, SNP [1,21].

These results demonstrate that the adventitia, similarly to the media, may be able to respond to endothelium-dependent vasoactive factors such as nitric oxide. Since NO is extremely labile, we suggest that the luminally-released autacoid may not be the major contributor in the relaxation of the distantly localized adventitial layers, in conductance or resistance vessels. In contrast, Somoza et al. [101] have shown an important contribution of the adventitia to the production of vasoconstrictive superoxide anions in animal vessels mechanically denuded for the above-mentioned layer. Whether tissue-engineered vessels composed of adventitial cells generate superoxide anions as well remains to be determined. At the current stage, our group also has yet to identify if the adventitia, or even the media for that matter, responds to stimulators of adenylate cyclase such as endothelium-derived prostacyclin. On the other hand, the release of NO by vessels of the vasa vasorum, located in the distant portion of the medial area, and by adventitial cells themselves [6,11,13], may be involved in the vasodilatation of the adventitial layer of vasculatures.


   5. Perspectives and conclusions
Top
 Abstract
 1. Introduction
 2. Vascular tone control:...
 3. The value of...
 4. Tissue-engineered vascular...
 5. Perspectives and conclusions
References
 
Two major additions can be envisioned to improve the value of tissue-engineered vascular substitutes as experimental models (and for transplantation). Firstly, intrinsic neuronal networks are crucially involved in the control of vascular compliance in response to factors which influence hemodynamic parameters either acutely (MAP variation, hypovolemia, hypothermia, ischemia/reperfusion episodes) or chronically (arteriosclerosis, atherosclerosis, heart failure, cardiac hypertrophy). The ideal TEBVs should have built in, similarly to normal blood vessels, a neural network composed of sympathetic and parasympathetic as well as non-adrenergic non-cholinergic fibers. To address the difficulty of growing mature nerve cells within the TEBV, the strategy of using stem cell technology may be attractive. Along these lines, Klein et al. [102] have recently reported the use of embryonic hyppocampal neuronal cells in post-surgical regeneration of trauma. Furthermore, Ikeda et al. [103] have developed a strategy using MASH-1 transfected mouse embryonic stems cells towards reconstitution of damaged neuronal networks in the mouse central nervous system. Finally, Berthod et al. have also reported new approaches towards nerve regeneration in skin constructs [104,105]. Strategies such as those put forward by Ikeda et al. and Berthod et al. [103–105] could be adapted using human adult stem cells in the engineered blood vessels. This latter concept emphasises what one may consider as another advantage of engineered blood vessels as it becomes therefore feasible to apply gene transfer technologies to selective cell types and at optimal stages of cellular culture. These experimental conditions are obviously difficult to attain in intact blood vessels undergoing gene therapy.

Secondly, NO released by vessels of the vasa vasorum, located in the distant portion of the medial area, may be important in the overall reactivity of the adventitial layer of blood vessels. The inclusion of a transmural vasa vasorum network within the TEBV remains to be performed. However, our own experience in creating endothelialized skin substitutes may prove useful to achieve this goal [16,33,106]. On the other hand, the optimisation of an intima located within the lumen of the TEBV and in which the endothelial layer presents vasodilatory properties is certainly achievable and will be included in future experiments.

In conclusion, the present review strives to summarize and interpret the most recent observations derived from tissue engineering strategies towards the development and optimisation of functional blood vessels. Clearly, several important aspects still need to be addressed. Nonetheless, tissue-engineered vascular substitutes have and will hopefully continue to play a significant role in the experimental (in vitro) and also the clinical (in vivo) settings.

Time for primary review 27 days


   Acknowledgements
 
We wish to extend our appreciation to Alexandre Deschambeault for his work on Fig. 1 as well as to Dr Dan Lacroix for editing the manuscript.


   References
Top
 Abstract
 1. Introduction
 2. Vascular tone control:...
 3. The value of...
 4. Tissue-engineered vascular...
 5. Perspectives and conclusions
 References
 

  1. L'Heureux N., Stoclet J.C., Auger F.A., Lagaud G.J., Germain L., Andriantsitohaina R. A human tissue-engineered vascular media: a new model for pharmacological studies of contractile responses. Faseb J (2001) 15:515–524.[Abstract/Free Full Text]
  2. An S.J., Boyd R., Zhu M., Chapman A., Pimentel D.R., Wang H.D. NADPH oxidase mediates angiotensin II-induced endothelin-1 expression in vascular adventitial fibroblasts. Cardiovasc Res (2007) 75:702–709.[Abstract/Free Full Text]
  3. Laine P., Naukkarinen A., Heikkila L., Penttila A., Kovanen P.T. Adventitial mast cells connect with sensory nerve fibers in atherosclerotic coronary arteries. Circulation (2000) 101:1665–1669.[Abstract/Free Full Text]
  4. Wendel M., Kummer W., Knels L., Schmeck J., Koch T. Muscular ETB receptors develop postnatally and are differentially distributed in specific segments of the rat vasculature. J Histochem Cytochem (2005) 53:187–196.[Abstract/Free Full Text]
  5. Yoshida K., Okamura T., Kimura H., Bredt D.S., Snyder S.H., Toda N. Nitric oxide synthase-immunoreactive nerve fibers in dog cerebral and peripheral arteries. Brain Res (1993) 629:67–72.[CrossRef][ISI][Medline]
  6. Zhang H., Du Y., Cohen R.A., Chobanian A.V., Brecher P. Adventitia as a source of inducible nitric oxide synthase in the rat aorta. Am J Hypertens (1999) 12:467–475.[CrossRef][ISI][Medline]
  7. Mochizuki S., Goto M., Chiba Y., Ogasawara Y., Kajiya F. Flow dependence and time constant of the change in nitric oxide concentration measured in the vascular media. Med Biol Eng Comput (1999) 37:497–503.[ISI][Medline]
  8. Beranova P., Schott C., Chalupsky K., Kleschyov A.L., Stoclet J.C., Muller B. Role of the adventitia in the cyclic GMP-mediated relaxant effect of N-hydroxy-L-arginine in rat aorta. J Vasc Res (2005) 42:331–336.[CrossRef][ISI][Medline]
  9. Gonzalez M.C., Arribas S.M., Molero F., Fernandez-Alfonso M.S. Effect of removal of adventitia on vascular smooth muscle contraction and relaxation. Am J Physiol Heart Circ Physiol (2001) 280:H2876–H2881.[Abstract/Free Full Text]
  10. Kleschyov A.L., Muller B., Keravis T., Stoeckel M.E., Stoclet J.C. Adventitia-derived nitric oxide in rat aortas exposed to endotoxin: cell origin and functional consequences. Am J Physiol Heart Circ Physiol (2000) 279:H2743–H2751.[Abstract/Free Full Text]
  11. Kleschyov A.L., Muller B., Schott C., Stoclet J.C. Role of adventitial nitric oxide in vascular hyporeactivity induced by lipopolysaccharide in rat aorta. Br J Pharmacol (1998) 124:623–626.[CrossRef][ISI][Medline]
  12. Levin J.A., Wilson S.E. Effect of inhibitors of neuronal and extraneuronal uptake on the accumulation and metabolism of 3H-L-norepinephrine in rabbit aorta. Blood Vessels (1983) 20:234–244.[ISI][Medline]
  13. Lin L., Ding W.H., Jiang W., Zhang Y.G., Qi Y.F., Yuan W.J., et al. Urotensin-II activates L-arginine/nitric oxide pathway in isolated rat aortic adventitia. Peptides (2004) 25:1977–1984.[CrossRef][ISI][Medline]
  14. Mu H.M., Zhu Z.M., Wang H.Y., Wang L.J. [Effect of removal of the adventitia on vascular remodeling and vasoconstriction in rabbits]. Sheng Li Xue Bao (2003) 55:290–295.[Medline]
  15. Kemler M.A., Kolkman W.F., Slootweg P.J., Kon M. Adventitial stripping does not strip the adventitia. Plast Reconstr Surg (1997) 99:1626–1631.[ISI][Medline]
  16. Black A.F., Berthod F., L'Heureux N., Germain L., Auger F.A. In vitro reconstruction of a human capillary-like network in a tissue-engineered skin equivalent. Faseb J (1998) 12:1331–1340.[Abstract/Free Full Text]
  17. Diebolt M., Germain L., Auger F.A., Andriantsitohaina R. Mechanism of potentiation by polyphenols of contraction in human vein-engineered media. Am J Physiol Heart Circ Physiol (2005) 288:H2918–H2924.[Abstract/Free Full Text]
  18. Dube J., Chakir J., Laviolette M., Saint Martin S., Boutet M., Desrochers C., et al. In vitro procollagen synthesis and proliferative phenotype of bronchial fibroblasts from normal and asthmatic subjects. Lab Invest (1998) 78:297–307.[ISI][Medline]
  19. Germain L., Auger F.A., Grandbois E., Guignard R., Giasson M., Boisjoly H., et al. Reconstructed human cornea produced in vitro by tissue engineering. Pathobiology (1999) 67:140–147.[CrossRef][ISI][Medline]
  20. Germain L., Jean A., Auger F.A., Garrel D.R. Human wound healing fibroblasts have greater contractile properties than dermal fibroblasts. J Surg Res (1994) 57:268–273.[CrossRef][ISI][Medline]
  21. Laflamme K., Roberge C.J., Grenier G., Remy-Zolghadri M., Pouliot S., Baker K., et al. Adventitia contribution in vascular tone: insights from adventitia-derived cells in a tissue-engineered human blood vessel. Faseb J (2006) 20:1245–1247.[Abstract/Free Full Text]
  22. Laflamme K., Roberge C.J., Labonte J., Pouliot S., D'Orleans-Juste P., Auger F.A., et al. Tissue-engineered human vascular media with a functional endothelin system. Circulation (2005) 111:459–464.[Abstract/Free Full Text]
  23. Laflamme K., Roberge C.J., Pouliot S.P., D'Orleans-Juste P., Auger F.A., Germain L. Tissue-engineered human vascular media produced in vitro by the self-assembly approach present functional properties similar to those of their native blood vessels. Tissue Eng (2006) 12:2275–2281.[CrossRef][ISI][Medline]
  24. Laplante A.F., Germain L., Auger F.A., Moulin V. Mechanisms of wound reepithelialization: hints from a tissue-engineered reconstructed skin to long-standing questions. Faseb J (2001) 15:2377–2389.[Abstract/Free Full Text]
  25. L'Heureux N., Paquet S., Labbe R., Germain L., Auger F.A. A completely biological tissue-engineered human blood vessel. Faseb J (1998) 12:47–56.[Abstract/Free Full Text]
  26. Moulin V., Auger F.A., Garrel D., Germain L. Role of wound healing myofibroblasts on re-epithelialization of human skin. Burns (2000) 26:3–12.[CrossRef][ISI][Medline]
  27. Paquette J.S., Moulin V., Tremblay P., Bernier V., Boutet M., Laviolette M., et al. Tissue-engineered human asthmatic bronchial equivalents. Eur Cell Mater (2004) 7:1–11.[Medline]
  28. Pouliot R., Germain L., Auger F.A., Tremblay N., Juhasz J. Physical characterization of the stratum corneum of an in vitro human skin equivalent produced by tissue engineering and its comparison with normal human skin by ATR-FTIR spectroscopy and thermal analysis (DSC). Biochim Biophys Acta (1999) 1439:341–352.[Medline]
  29. Remy-Zolghadri M., Laganiere J., Oligny J.F., Germain L., Auger F.A. Endothelium properties of a tissue-engineered blood vessel for small-diameter vascular reconstruction. J Vasc Surg (2004) 39:613–620.[CrossRef][ISI][Medline]
  30. Stoclet J.C., Andriantsitohaina R., L'Heureux N., Martinez C., Germain L., Auger F. Use of human vessels and human vascular smooth muscle cells in pharmacology. Cell Biol Toxicol (1996) 12:223–225.[CrossRef][ISI][Medline]
  31. Talbot M., Carrier P., Giasson C.J., Deschambeault A., Guerin S.L., Auger F.A., Bazin R., et al. Autologous transplantation of rabbit limbal epithelia cultured on fibrin gels for ocular surface reconstruction. Mol Vis (2006) 12:65–75.[ISI][Medline]
  32. Tremblay P.L., Berthod F., Germain L., Auger F.A. In vitro evaluation of the angiostatic potential of drugs using an endothelialized tissue-engineered connective tissue. J Pharmacol Exp Ther (2005) 315:510–516.[Abstract/Free Full Text]
  33. Tremblay P.L., Hudon V., Berthod F., Germain L., Auger F.A. Inosculation of tissue-engineered capillaries with the host's vasculature in a reconstructed skin transplanted on mice. Am J Transplant (2005) 5:1002–1010.[CrossRef][ISI][Medline]
  34. Rhodin J.A.G. Handbook of physiology. Section 2: the cardiovascular system. Vol. II: vascular smooth muscle. Bohr D.F., Somlyo A.P., Sparks H.V.J., eds. (1980) Bethesda, MD: Am Physiol Soc. 1–31.
  35. Plante G.E. Vascular response to stress in health and disease. Metabolism (2002) 51:25–30.[ISI][Medline]
  36. Scotland R.S., Vallance P.J., Ahluwalia A. Endogenous factors involved in regulation of tone of arterial vasa vasorum: implications for conduit vessel physiology. Cardiovasc Res (2000) 46:403–411.[Abstract/Free Full Text]
  37. Gutterman D.D. Adventitia-dependent influences on vascular function. Am J Physiol (1999) 277:H1265–H1272.[ISI][Medline]
  38. MacMicking J., Xie Q.W., Nathan C. Nitric oxide and macrophage function. Annu Rev Immunol (1997) 15:323–350.[CrossRef][ISI][Medline]
  39. Rey F.E., Pagano P.J. The reactive adventitia: fibroblast oxidase in vascular function. Arterioscler Thromb Vasc Biol (2002) 22:1962–1971.[Abstract/Free Full Text]
  40. Shao J.S., Cai J., Towler D.A. Molecular mechanisms of vascular calcification: lessons learned from the aorta. Arterioscler Thromb Vasc Biol (2006) 26:1423–1430.[Abstract/Free Full Text]
  41. Canfield A.E., Doherty M.J., Wood A.C., Farrington C., Ashton B., Begum N., et al. Role of pericytes in vascular calcification: a review. Z Kardiol (2000) 89(Suppl_2):20–27.[CrossRef][ISI][Medline]
  42. Wilkinson F.L., Liu Y., Rucka A.K., Jeziorska M., Hoyland J.A., Heagerty A.M., et al. Contribution of VCAF-positive cells to neovascularization and calcification in atherosclerotic plaque development. J Pathol (2007) 211:362–369.[CrossRef][ISI][Medline]
  43. Lamalice L., Le Boeuf F., Huot J. Endothelial cell migration during angiogenesis. Circ Res (2007) 100:782–794.[Abstract/Free Full Text]
  44. von Tell D., Armulik A., Betsholtz C. Pericytes and vascular stability. Exp Cell Res (2006) 312:623–629.[CrossRef][ISI][Medline]
  45. Farrington-Rock C., Crofts N.J., Doherty M.J., Ashton B.A., Griffin-Jones C., Canfield A.E. Chondrogenic and adipogenic potential of microvascular pericytes. Circulation (2004) 110:2226–2232.[Abstract/Free Full Text]
  46. Yamashima T., Tonchev A.B., Vachkov I.H., Popivanova B.K., Seki T., Sawamoto K., et al. Vascular adventitia generates neuronal progenitors in the monkey hippocampus after ischemia. Hippocampus (2004) 14:861–875.[CrossRef][ISI][Medline]
  47. Engeli S. Is there a pathophysiological role for perivascular adipocytes? Am J Physiol Heart Circ Physiol (2005) 289:H1794–H1795.[Free Full Text]
  48. Ford C.A., Mong K., Tabrizchi R. Influence of tangential stress on mechanical responses to vasoactive agents in human saphenous vein with and without perivascular adipose tissue. Can J Cardiol (2006) 22:1209–1216.[ISI][Medline]
  49. Yudkin J.S., Eringa E., Stehouwer C.D. "Vasocrine" signalling from perivascular fat: a mechanism linking insulin resistance to vascular disease. Lancet (2005) 365:1817–1820.[CrossRef][ISI][Medline]
  50. Zalewski A., Shi Y., Johnson A.G. Diverse origin of intimal cells: smooth muscle cells, myofibroblasts, fibroblasts, and beyond? Circ Res (2002) 91:652–655.[Free Full Text]
  51. Hu Y., Zhang Z., Torsney E., Afzal A.R., Davison F., Metzler B., et al. Abundant progenitor cells in the adventitia contribute to atherosclerosis of vein grafts in ApoE-deficient mice. J Clin Invest (2004) 113:1258–1265.[CrossRef][ISI][Medline]
  52. Shi Y., O'Brien J.E., Fard A., Mannion J.D., Wang D., Zalewski A. Adventitial myofibroblasts contribute to neointimal formation in injured porcine coronary arteries. Circulation (1996) 94:1655–1664.[Abstract/Free Full Text]
  53. Torsney E., Hu Y., Xu Q. Adventitial progenitor cells contribute to arteriosclerosis. Trends Cardiovasc Med (2005) 15:64–68.[CrossRef][ISI][Medline]
  54. Michel J.B., Thaunat O., Houard X., Meilhac O., Caligiuri G., Nicoletti A. Topological determinants and consequences of adventitial responses to arterial wall injury. Arterioscler Thromb Vasc Biol (2007) 27:1259–1268.[Abstract/Free Full Text]
  55. Schoneveld A.H., Oude Nijhuis M.M., van Middelaar B., Laman J.D., de Kleijn D.P., Pasterkamp G. Toll-like receptor 2 stimulation induces intimal hyperplasia and atherosclerotic lesion development. Cardiovasc Res (2005) 66:162–169.[Abstract/Free Full Text]
  56. Vink A., Schoneveld A.H., van der Meer J.J., van Middelaar B.J., Sluijter J.P., Smeets M.B., et al. In vivo evidence for a role of toll-like receptor 4 in the development of intimal lesions. Circulation (2002) 106:1985–1990.[Abstract/Free Full Text]
  57. Jiang Z, Yu P, Tao M, Fernandez C, Ifantides C, Moloye O, et al. TGF-{beta}/CTGF mediated fibroblast recruitment influences early outward vein graft remodeling. Am J Physiol Heart Circ Physiol in press, doi:10.1152/ajpheart.01372.2006 (available online 16 March 2007).
  58. Faber J.E., Yang N. Balloon injury alters alpha-adrenoceptor expression across rat carotid artery wall. Clin Exp Pharmacol Physiol (2006) 33:204–210.[CrossRef][ISI][Medline]
  59. Davie N.J., Gerasimovskaya E.V., Hofmeister S.E., Richman A.P., Jones P.L., Reeves J.T., et al. Pulmonary artery adventitial fibroblasts cooperate with vasa vasorum endothelial cells to regulate vasa vasorum neovascularization: a process mediated by hypoxia and endothelin-1. Am J Pathol (2006) 168:1793–1807.[Abstract/Free Full Text]
  60. Dubrovska G., Verlohren S., Luft F.C., Gollasch M. Mechanisms of ADRF release from rat aortic adventitial adipose tissue. Am J Physiol Heart Circ Physiol (2004) 286:H1107–H1113.[Abstract/Free Full Text]
  61. Lohn M., Dubrovska G., Lauterbach B., Luft F.C., Gollasch M., Sharma A.M. Periadventitial fat releases a vascular relaxing factor. Faseb J (2002) 16:1057–1063.[Abstract/Free Full Text]
  62. Gao Y.J., Zeng Z.H., Teoh K., Sharma A.M., Abouzahr L., Cybulsky I., et al. Perivascular adipose tissue modulates vascular function in the human internal thoracic artery. J Thorac Cardiovasc Surg (2005) 130:1130–1136.[Abstract/Free Full Text]
  63. Singhal A., Farooqi I.S., Cole T.J., O'Rahilly S., Fewtrell M., Kattenhorn M., et al. Influence of leptin on arterial distensibility: a novel link between obesity and cardiovascular disease? Circulation (2002) 106:1919–1924.[Abstract/Free Full Text]
  64. Whincup P.H., Gilg J.A., Donald A.E., Katterhorn M., Oliver C., Cook D.G., et al. Arterial distensibility in adolescents: the influence of adiposity, the metabolic syndrome, and classic risk factors. Circulation (2005) 112:1789–1797.[Abstract/Free Full Text]
  65. Chiba T, Shinozaki S, Nakazawa T, Kawakami A, Ai M, Kaneko E, et al. Leptin deficiency suppresses progression of atherosclerosis in apoE-deficient mice. Atherosclerosis in press, doi:10.1016/j.atherosclerosis.2007.01.040 (available 28 March 2007).
  66. Cavallotti C., Bruzzone P., Mancone M. Catecholaminergic nerve fibers and beta-adrenergic receptors in the human heart and coronary vessels. Heart Vessels (2002) 17:30–35.[CrossRef][ISI][Medline]
  67. Crick S.J., Wharton J., Sheppard M.N., Royston D., Yacoub M.H., Anderson R.H., Polak J.M. Innervation of the human cardiac conduction system. A quantitative immunohistochemical and histochemical study. Circulation (1994) 89:1697–16708.[Abstract/Free Full Text]
  68. Dahlstrom A., Mya-Tu M., Fuxe K., Zetterstrom B.E. Observations on adrenergic innervation of dog heart. Am J Physiol (1965) 209:689–692.[Abstract/Free Full Text]
  69. Aubineau P. [Role of the adventitial innervation in establishing and maintaining the structural and functional properties of the arterial wall. Effects during aging]. Ann Cardiol Angeiol (Paris) (1991) 40:285–291.[Medline]
  70. Gonzalez C., Barroso C., Martin C., Gulbenkian S., Estrada C. Neuronal nitric oxide synthase activation by vasoactive intestinal peptide in bovine cerebral arteries. J Cereb Blood Flow Metab (1997) 17:977–984.[CrossRef][ISI][Medline]
  71. Okamura T., Ayajiki K., Fujioka H., Shinozaki K., Toda N. Neurogenic cerebral vasodilation mediated by nitric oxide. Jpn J Pharmacol (2002) 88:32–38.[CrossRef][Medline]
  72. Yu J.G., Kimura T., Chang X.F., Lee T.J. Segregation of vipergic–nitric oxidergic and cholinergic–nitric oxidergic innervation in porcine middle cerebral arteries. Brain Res (1998) 801:78–87.[CrossRef][ISI][Medline]
  73. Kadowitz P.J., Knight D.S., Hibbs R.G., Ellison J.P., Joiner P.D., Brody M.J., et al. Influence of 5- and 6-hydroxydopamine on adrenergic transmission and nerve terminal morphology in the canine pulmonary vascular bed. Circ Res (1976) 39:191–199.[Abstract/Free Full Text]
  74. Knoche H., Walther-Wenke G., Addicks K. [The fine structure of baroreceptor's nerve endings in the wall of carotid sinus in cats]. Acta Anat (Basel) (1977) 97:403–418.[ISI][Medline]
  75. Okamura T., Ayajiki K., Uchiyama M., Kagami K., Toda N. Mechanisms underlying constrictor and dilator responses to perivascular nerve stimulation in canine lingual arteries. Eur J Pharmacol (1998) 354:43–50.[CrossRef][ISI][Medline]
  76. Toda N., Kimura T., Yoshida K., Bredt D.S., Snyder S.H., Yoshida Y., et al. Human uterine arterial relaxation induced by nitroxidergic nerve stimulation. Am J Physiol (1994) 266:H1446–H1450.[ISI][Medline]
  77. Bevan R.D., Dodge J., Nichols P., Penar P.L., Walters C.L., Wellman T., et al. Weakness of sympathetic neural control of human pial compared with superficial temporal arteries reflects low innervation density and poor sympathetic responsiveness. Stroke (1998) 29:212–221.[Abstract/Free Full Text]
  78. Ralevic V., Burnstock G. Neural-endothelial interactions in the control of local vascular tone. (1993) Austin, TX: Landes.
  79. Bennett M.R., Farnell L., Gibson W.G., Blair D. A quantitative description of the diffusion of noradrenaline in the media of blood vessels following its release from sympathetic varicosities. J Theor Biol (2004) 226:359–372.[CrossRef][ISI][Medline]
  80. Edvinsson L., Gulbenkian S., Wharton J., Jansen I., Polak J.M. Peptide-containing nerves in the rat femoral artery and vein. An immunocytochemical and vasomotor study. Blood Vessels (1989) 26:254–271.[ISI][Medline]
  81. Reinecke M., Weihe E., Carraway R.E., Leeman S.E., Forssmann W.G. Localization of neurotensin immunoreactive nerve fibers in the guinea-pig heart: evidence derived by immunohistochemistry, radioimmunoassay and chromatography. Neuroscience (1982) 7:1785–1795.[CrossRef][ISI][Medline]
  82. Dimitriadou V., Henry P., Brochet B., Mathiau P., Aubineau P. Cluster headache: ultrastructural evidence for mast cell degranulation and interaction with nerve fibres in the human temporal artery. Cephalalgia (1990) 10:221–228.[CrossRef][ISI][Medline]
  83. Karimi K., Kool M., Nijkamp F.P., Redegeld F.A. Substance P can stimulate prostaglandin D2 and leukotriene C4 generation without granule exocytosis in murine mast cells. Eur J Pharmacol (2004) 489:49–54.[CrossRef][ISI][Medline]
  84. Wang H.D., Pagano P.J., Du Y., Cayatte A.J., Quinn M.T., Brecher P., Cohen R.A. Superoxide anion from the adventitia of the rat thoracic aorta inactivates nitric oxide. Circ Res (1998) 82:810–818.[Abstract/Free Full Text]
  85. Grenier G., Remy-Zolghadri M., Bergeron F., Guignard R., Baker K., Labbe R., Auger F.A., Germain L. Mechanical loading modulates the differentiation state of vascular smooth muscle cells. Tissue Eng (2006) 12:3159–3170.[CrossRef][ISI][Medline]
  86. Balakumar P., Singh A.P., Singh M. Rodent models of heart failure. J Pharmacol Toxicol Methods (2007) 56:1–10.[CrossRef][Medline]
  87. Davidson M.K., Lindsey J.R., Davis J.K. Requirements and selection of an animal model. Isr J Med Sci (1987) 23:551–555.[ISI][Medline]
  88. Loisel S., Ohresser M., Pallardy M., Dayde D., Berthou C., Cartron G., Watier H. Relevance, advantages and limitations of animal models used in the development of monoclonal antibodies for cancer treatment. Crit Rev Oncol Hematol (2007) 62:34–42.[CrossRef][ISI][Medline]
  89. Rangarajan A., Hong S.J., Gifford A., Weinberg R.A. Species- and cell type-specific requirements for cellular transformation. Cancer Cell (2004) 6:171–183.[CrossRef][ISI][Medline]
  90. Tkacs N.C., Thompson H.J. From bedside to bench and back again: research issues in animal models of human disease. Biol Res Nurs (2006) 8:78–88.[Abstract/Free Full Text]
  91. Auger F.A. The LOEX perspective on the role of tissue engineering in regenerative medicine. Biomed Mater Eng (2006) 16:S19–S25.[Medline]
  92. Diebolt M, Laflamme K, Labbé R, Germain L, Auger FA, Andriantsitohaina R. Polyphenols modulate calcium-independent mechanisms in human arterial tissue-engineered vascular media. J Vasc Surg 2007; in press.
  93. Griffith L.G., Swartz M.A. Capturing complex 3D tissue physiology in vitro. Nat Rev Mol Cell Biol (2006) 7:211–224.[CrossRef][ISI][Medline]
  94. Suuronen E.J., Sheardown H., Newman K.D., McLaughlin C.R., Griffith M. Building in vitro models of organs. Int Rev Cytol (2005) 244:137–173.[CrossRef][ISI][Medline]
  95. Germain L., Remy-Zolghadri M., Auger F. Tissue engineering of the vascular system: from capillaries to larger blood vessels. Med Biol Eng Comput (2000) 38:232–240.[CrossRef][ISI][Medline]
  96. Onoue H., Tsutsui M., Smith L., O'Brien T., Katusic Z.S. Adventitial expression of recombinant endothelial nitric oxide synthase gene reverses vasoconstrictor effect of endothelin-1. J Cereb Blood Flow Metab (1999) 19:1029–1037.[CrossRef][ISI][Medline]
  97. Davenport A.P., Maguire J.J. Endothelin. Handb Exp Pharmacol (2006) 295–329.
  98. Turner A.J., Tanzawa K. Mammalian membrane metallopeptidases: NEP, ECE, KELL, and PEX. Faseb J (1997) 11:355–364.[Abstract]
  99. Turner A.J., Murphy L.J. Molecular pharmacology of endothelin converting enzymes. Biochem Pharmacol (1996) 51:91–102.[CrossRef][ISI][Medline]
  100. D'Orleans-Juste P., Plante M., Honore J.C., Carrier E., Labonte J. Synthesis and degradation of endothelin-1. Can J Physiol Pharmacol (2003) 81:503–510.[CrossRef][ISI][Medline]
  101. Somoza B., Gonzalez M.C., Gonzalez J.M., Abderrahim F., Arribas S.M., Fernandez-Alfonso M.S. Modulatory role of the adventitia on noradrenaline and angiotensin II responses role of endothelium and AT2 receptors. Cardiovasc Res (2005) 65:478–486.[Abstract/Free Full Text]
  102. Klein C.L., Scholl M., Maelicke A. Neuronal networks in vitro: formation and organization on biofunctionalized surfaces. J Mater Sci Mater Med (1999) 10:721–727.[CrossRef][ISI][Medline]
  103. Ikeda R., Kurokawa M.S., Chiba S., Yoshikawa H., Hashimoto T., Tadokoro M., et al. Transplantation of motoneurons derived from MASH1-transfected mouse ES cells reconstitutes neural networks and improves motor function in hemiplegic mice. Exp Neurol (2004) 189:280–292.
  104. Gingras M., Paradis I., Berthod F. Nerve regeneration in a collagen–chitosan tissue-engineered skin transplanted on nude mice. Biomaterials (2003) 24:1653–1661.