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Cardiovascular Research 2001 50(3):516-524; doi:10.1016/S0008-6363(01)00237-1
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Copyright © 2001, European Society of Cardiology

Cardiac remodeling after myocardial infarction is impaired in IGF-1 deficient mice

M. Palmena, M.J.A.P. Daemenc, R. Bronsaera, W.R.M. Dassena, H.R. Zandbergena, M. Kockxd, J.F.M. Smitsb, R. van der Zeea and P.A. Doevendansa,*

aDepartment of Cardiology, Cardiovascular Research Institute, Maastricht, University of Maastricht, The Netherlands
bDepartment of Pharmacology, Cardiovascular Research Institute, Maastricht, University of Maastricht, The Netherlands
cDepartment of Pathology, Cardiovascular Research Institute, Maastricht, University of Maastricht, The Netherlands
dDepartment of Pathology, APCAM, AZ Middelheim, Antwerp, Belgium

* Corresponding author. Department of Cardiology, Academic Hospital Maastricht, PO Box 5800, 6202 AZ Maastricht, the Netherlands. Tel.: +31-43-387-5095; fax: +31-43-387-5104 p.doevendans{at}cardio.azm.nl

Received 19 September 2000; accepted 23 January 2001


   Abstract
Top
 Abstract
1 Introduction/background
 2 Methods
 3 Results
 4 Discussion
 5 Conclusions
 References
 
Objective: To obtain more insight in the role of IGF-1 in cardiac remodeling and function after experimental myocardial infarction. We hypothesized that cardiac remodeling is altered in IGF-1 deficient mice, which may affect cardiac function. Methods: A myocardial infarction was induced by surgical coronary artery ligation in heterozygous IGF-1 deficient mice. One week after surgery, left ventricular function was analyzed, and parameters of cardiac remodeling were measured. Results: No significant difference in cardiac function was found between infarcted wildtype and knock-out animals, despite a marked reduction in capillarization and blunting of the hypertrophic response of the interventricular septum in the IGF-1 deficient group. Furthermore, decreased DNA synthesis and increased apoptosis rates were observed in the IGF-1 knock-out mice. Conclusion: IGF-1 deficient mice show preservation of cardiac function 1 week after MI, despite an altered cardiac remodeling process.

KEYWORDS BrdU, 5-Bromo-deoxyuridine; BW, Body weight; CD, Capillary density; C/F ratio, Capillary to fiber ratio; GH, Growth hormone; HW, Heart weight; HR, Heart rate; HZ, Heterozygous (IGF-1+/–); IGF-1, Insulin-like growth factor-1; IGF-1R, IGF-1 receptor; IGF-2, Insulin-like growth factor-2; LVEDP, Left ventricular end diastolic pressure; LVFW, Left Ventricular Free Wall; MD, Myocyte density; MI, Myocardial infarction; PBS, Phosphate Buffered Saline; +dP/dt, Maximal rate of positive pressure development (contractility); –dP/dt, Maximal rate of negative pressure development (relaxation); SLVP, Systolic left ventricular pressure; TLF, Total Labeling Fraction; TUNEL, Terminal Transferase dUTP Nick End Labeling; WT, Wildtype (non-transgenic littermate)


   1 Introduction/background
Top
 Abstract
 1 Introduction/background
2 Methods
 3 Results
 4 Discussion
 5 Conclusions
 References
 
IGF-1 (Insulin-like Growth Factor-1) is a pleiotrophic growth promoting peptide which is produced in the liver upon stimulation with growth hormone (GH) [1]. In addition to circulating IGF-1 levels, local production in several tissues also serves as a source of IGF-1. After release into the circulation IGF-1 is bound to specific IGF binding proteins that regulate the interactions of IGF-1 with the IGF-1 receptors (IGF-1R) in distant tissues. IGF-1 has a myriad of distinct, but interrelated growth-inducing effects on the organism.

During adult life, IGF-1 plays a role in many pathological processes involved in cardiovascular disease. IGF-1 induces cardiomyocyte hypertrophy, both after exogenous administration under physiologic conditions [2], and following an acute augmentation of cardiac workload [3], for instance after myocardial infarction (MI) [4]. Recent studies suggest a role for IGF-1 in the protection of cardiomyocytes against apoptosis both in vitro and in vivo [5,6]. In concert with several other growth promoting peptides like VEGF and FGF-1/2, IGF-1 stimulates angiogenesis [7].

Recently, it was shown that increased IGF-1 levels in the heart improve cardiac performance both in normal hearts and after MI [8], either by an increased local expression of IGF-1 or after exogenous administration. Also in the failing human heart, GH and IGF-1 administration enhance cardiac performance [4,5,9]. IGF-1 deficiency was, however, also shown to augment cardiac function and increase conscious blood pressure in a physiologic non-MI setting [10], illustrating the apparently conflicting data on the effects of IGF-1 on hemodynamics.

We hypothesized that IGF-1 deficiency results in altered cardiac remodeling and a decrease in cardiac function following induction of MI. To gain more insight into the effects of IGF-1 on cardiac function and structure, the effects of reduced IGF-1 levels on functional and structural aspects of cardiac remodeling following chronic myocardial infarction were assessed in a mouse model.


   2 Methods
Top
 Abstract
 1 Introduction/background
 2 Methods
3 Results
 4 Discussion
 5 Conclusions
 References
 
Heterozygous IGF-1 deficient mice (with a C57blJ6 background) were generated by Genentech (San Francisco, USA) and kindly provided by L. Powell-Braxton [10,11]. The animals were genotyped by PCR and Southern Blotting. Measurement of IGF-1 plasma levels was performed independently by Genentech, using ELISA. Heterozygous (IGF+/–) animals were used, because nearly all of the homozygous (IGF–/–) animals die in utero or shortly after birth. The mice that survived surgery were subsequently assigned to one of four experimental groups:

1. Heterozygous animals with SHAM surgery (HZ/SHAM) (n=10)
2. Heterozygous animals with experimental MI (HZ/MI) (n=13)
3. Wildtype littermates with SHAM surgery (WT/SHAM) (n=8)
4. Wildtype littermates with experimental MI (WT/MI) (n=8)

2.1 Induction of a myocardial infarction
Male and female heterozygous IGF-1+/– were included. All experiments were conducted with permission of the Animal Welfare Committee of the University of Maastricht. The surgical procedure and technical aspects of MI-induction in mice have recently been published by Lutgens et al. [12]. Briefly, adult mice were anesthetized with pentobarbital (100 mg/kg) and artificially ventilated. After opening the chest, the anterior descending coronary artery was ligated at the junction with 6-0 prolene. After ligation, the chest wall was closed and a BrdU-filled osmotic minipump (Alzet 2001, Alza Corporation, Palo Alto, CA; Serva, Heidelberg, Germany; infusion rate 13 mg/kg/day for 7 days) was introduced subcutanously between the scapulae. SHAM animals underwent the same procedure without ligation of the artery.

2.1.1 Assessment of LV function parameters
After 1 week animals were reanesthetized and a catheter tip manometer (Microtip 1.4 F; Millar Instruments, Houston, TX, USA) was inserted in the left carotid artery and advanced into the left ventricle, where continuous registrations of the left ventricular pressure signal were made. After stabilization of LV function and heart rate, left ventricular systolic pressure (sLVP) and maximal positive (+dP/dt) and negative (–dP/dt) rates of pressure development were recorded for processing. Data were sampled at a rate of 2 KHz.

2.2 Assessment of structural parameters
2.2.1 Tissue processing
Following LV function measurements, the thorax was opened and the heart was arrested in diastole by infusion of cadmium chloride (0.1 M) into the left atrium. The heart and circulation were perfused antegradely with phosphate buffered saline (PBS, pH 7.4, 1 mg/ml sodium nitroprusside) and 5% formalin in PBS at physiologic pressures. After perfusion, heart (except the atria), lungs and liver were dissected and weighed. Subsequently, the tissues were immersion-fixed in 10% formalin in PBS for 24 h, processed and embedded in paraffin for morphologic and histologic analysis.

The heart was cut longitudinally, perpendicular to the infarcted area and aortic root (left ventricular outflow tract), resulting in an anterior and a posterior part. From both parts 2- and 4-µm sections were cut. Both tissue sections were analyzed. In a separate group of animals, the posterior part of the heart was cut transversely, to obtain transverse sections of the papillary muscle.

2.2.2 Morphometry
Infarct size was determined on Azan-stained 4-µm sections. Infarct size was assessed by computerized morphometry (Quantimet 570, Leica, The Netherlands) and expressed as a percentage of the total left ventricular wall circumference. In addition, changes in interventricular septum and left ventriular free wall (LVFW) thickness were measured. All animals had a transmural infarct. Infarcts encompassing <30% of the left ventricular circumference (typical apical infarcts) were excluded from the study.

2.2.3 Immunohistochemistry
Capillarization was assessed on 2-µm BS-1 Isolectin B4 (Sigma, L2140, USA) stained sections of the non-infarcted papillary muscle and the interventricular septum. Staining techniques are described elsewhere [13]. Capillary to fiber ratio (C/F ratio) was determined microscopically in the septum and the papillary muscle, by dividing the total number of capillaries by the total number of cardiomyocytes. C/F ratio was measured with an eyepiece grid (400xmagnification) in six microscopic fields. For capillary density (CD), total tissue area was detected morphometrically, using a calibrated grid, after which the number of capillaries was assessed in that same field. In that way, the number of capillaries per square µm of tissue could be calculated. Moreover, from identical fields the total number of cardiomyocytes was counted to calculate myocyte density (MD) per square µm of tissue [14]. Since there were no differences between the C/F ratio's in the papillary muscle and the interventricular septum, subsequent measurements of the MD and CD were performed in the interventricular septum.

To detect 5-Bromo-deoxyuridine (BrdU) incorporation, the Total Labeling Fraction (TLF, number of BrdU-positive/total number of counted nucleix100%) for BrdU was calculated in the borderzone of the infarcted left ventricle, the center of the non-infarcted right ventricle and the non-infarcted septum. Cell numbers were determined microscopically with an eyepiece grid (400xmagnification). A total of 3000 nuclei per heart were counted in two tissue sections (1000 nuclei at the borders of the infarcted area and 1000 nuclei in the center of the non-infarcted septum, all in the same section). All measurements were performed by one investigator (M.P.), and intra-observer variation was less than 10%. The investigator was blinded for the experimental group.

In order to assess the amount of apoptosis, a modified TUNEL assay (Terminal transferase dUTP Nick End Labeling) was performed [15]. The percentage of TUNEL positive nuclei was expressed as percentage of total nuclei as described above (TLF for TUNEL). TUNEL positive labeled nuclei were counted in the infarcted area, the borderzone and the non-infarcted septum and expressed as a percentage of the total amount of nuclei in those areas. The TUNEL technique is very sensitive and therefore needs a careful titration of proteolytic pretreatment and Tdt concentration, otherwize a high fraction of non-apoptotic nuclei will be labeled. In a recent study, a molecular explanation for this phenomenon was found [16,17]. It was demonstrated in this study that besides apoptotic nuclei, non-apoptotic nuclei that show signs of active gene transcription are labeled by the TUNEL technique. These cells are still active and are transcribing genes that might be related or completely unrelated to the apoptotic cell death pathway. In a true apoptotic cell the nuclear DNA is cleaved in oligonucleosomal sized fragments and caspase activation can be demonstrated. In the present study we used a stringent TUNEL technique to exclude the aspecific labeling and activated caspase-3 staining was performed. Activated caspase was detected by an antibody against cleaved caspase-3 (Pharmingen, USA). The polyclonal antibody of Pharmingen is raised against the 17 kd cleaved fragment of the human caspase-3 and was used at a dilution of 1/200 after citrate microwave pretreatment of the sections. Tonsil tissue was used as positive control. DNA laddering was not performed because of the low apoptosis rates in the infarcted area [18]. The total number of caspase positive cells was divided by the total number of nuclei in the infarcted area.

2.3 Statistics
Data are expressed as means±S.E.M. The effects of surgery and genotype were evaluated with the Mann–Whitney test. The level of statistical significance was considered to be at P<0.05. Intra-observer variability was smaller than 10% for all the parameters measured.


   3 Results
Top
 Abstract
 1 Introduction/background
 2 Methods
 3 Results
4 Discussion
 5 Conclusions
 References
 
3.1 General
Body weights and organ weights of IGF-1+/– animals were lower than those in their non-transgenic littermates. No changes in HW/BW ratios were observed, neither between SHAM and MI groups, nor between both genotypes (Table 1). IGF-1 plasma levels in IGF+/– animals were 65% of normal WT plasma levels. No statistical significant differences could be observed between male and female animals in both genotype groups.


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  		Table 1 Weight parametersa

 
Surgical mortality was approximately 40%. The majority of deaths was seen in the MI groups, in equal amounts in both groups (eight out of 18 in the WT/MI group and 10 out of 26 the HZ/MI group). Only six SHAM animals died, due to anesthesia. During cardiac function measurements, two WT/MI mice and three animals in the HZ/MI group died before function measurements were completed.

3.2 Infarct size and structural ventricular chamber parameters
Coronary artery ligation resulted in a MI encompassing 30–50% of the left ventricular wall circumference. No significant differences were observed in infarct size between the IGF-1+/– animals and their non-transgenic littermates (WT/MI: 43.6±9.3% vs. HZ/MI: 40.3±8.7%). LV diameter increased in both MI-groups.

After MI, septum thickness in the WT/MI group increased as compared to the WT/SHAM group, indicating a compensatory hypertrophic response to the acute increase in workload in the non-infarcted interventricular septum. In the IGF-1+/– animals, septum thickness did not change significantly after MI, indicating a blunted compensatory hypertrophic response after MI. The thickness of the infarcted area of the LVFW decreased in both MI groups (P<0.05). In the IGF+/– group, infarct thickness was smaller when compared to WT mice (P<0.05). However, the difference in LVFW thickness was also present between both SHAM groups (P<0.05) (Table 2a).


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  		Table 2 Left ventricular morphometry

 
3.3 Capillarization of the non-infarcted myocardium
No significant differences were found in baseline MD values between both genotypes, although a trend was observed towards increased MD in IGF+/– mice. Induction of MI did not change myocyte diameter significantly, although a trend toward decreased MD was observed in both genotypes after MI. Myocytes were smaller in IGF+/– animals after infarction when compared to the WT/MI group (Fig. 1a and b), as indicated by the increased MD in this group (P<0.05). CD did not differ neither between genotypes, nor between infarct and SHAM group, although a trend was observed to decreased CD after MI in both genotypes. C/F ratio's of both IGF-1+/– groups were lower than those obtained in their wildtype littermates (1.89±0.053 for WT/SHAM vs. 1.36±0.041 for HZ/SHAM, P<0.05). Induction of MI did not change the C/F ratio in both genotypes. Altogether, these data indicate that the lower C/F ratio's in IGF-1+/– animals can be explained largely by changes in MD, not by changes in CD (Table 2b).


Figure 1
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  		Fig. 1 (a and b) This is a representative lectin stained tissue section in the non-infarcted septum of a WT/MI mouse (a) compared to the same area in a HZ/MI mouse (b) (100x). Cardiomyocytes are clearly larger in the WT group after MI. (c) shows the anti-BrdU staining in the non-infarcted interventricular septum (250x). Anti-BrdU positivity is confined to non-cardiomyocytes and not to cardiomyocytes. (d) shows an anti-BrdU stained section of the non-infarcted septum of a HZ/SHAM animal (160x). (e and f) These pictures show an example of a TUNEL [(e), 160x] and an activated caspase 3 staining [(f), 250x] in the infarcted area of a HZ/MI mouse.

 
3.3.1 Cellular DNA synthesis and apoptosis in the heart
A very low basal rate of DNA synthesis was seen in SHAM animals, with no differences between two genotypes (Fig. 2b). After MI, BrdU incorporation increased in the interventricular septum and, even more pronounced, in the borderzone of the infarcted ventricle (Fig. 1c and d). Septum BrdU labeling fraction in the HZ/MI group was only 60% when compared to the values in infarcted wildtype animals (P<0.05). In the borderzone of the infarcted area, no differences in BrdU labeling between both genotypes were found. With light microscopy, we investigated the interventricular septum where the plane of section was perpendicular to the axis of the myocytes, and counted the BrdU positive nuclei that were not defined to cardiac myocytes. In fact, >99% of BrdU positive nuclei were localized in non-cardiomyocytes. In the borderzone of the infarcted area, similar results were obtained.


Figure 2
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  		Fig. 2 (a) Apoptosis in the heart. This figure shows the Tunel labeling fraction for TUNEL (closed bars) and activated caspase-3 staining (open bars) in the infarcted left ventricular free wall (LVFW) 1 week after myocardial infarction (MI). In both genotypes, very low basal apoptosis rates are found. After MI, TUNEL and activated caspase-3 labeling fraction increase in both genotypes, but in IGF-1+/– animals, significantly more apoptosis was detected (P<0.05, Mann–Whitney). (b) DNA synthesis in the heart. This figure shows the BrdU labeling fraction, indicating DNA synthesis, 1 week after MI, both in the borderzone of the infarcted LVFW and in the interventricular septum. After MI, there is a significant increase in DNA synthesis in both regions of the heart and in both genotypes (*, P<0.05 for WT/MI vs. HZ/MI). In IGF-1 deficient animals, DNA synthesis in the borderzone and septum is lower when compared to WT animals. WT, wildtype littermate; HZ, heterozygous (IGF-1+/–).

 
A very low basal rate of apoptosis was found in the non-infarcted hearts, with no differences between the two SHAM groups (Fig. 2a). MI induction in wild types increased TUNEL labeling from <0.01 to 0.4%. In the infarcted LVFW of IGF+/– animals, TUNEL labeling fraction increased to 1.7% (P<0.05) (Fig. 1e and f). In the non-infarcted area no differences were observed between the genotypes. The staining for cleaved caspase-3 showed a similar pattern in the infarcted area, with significantly more positive nuclei in IGF-1 deficient hearts (3.20±0.73%) when compared with WT (1.35±0.59%, P<0.05). TUNEL and cleaved caspase-3 labeling in the infarcted area was confined to non-cardiomyocytes, although in the borderzone, several positive cardiomyocytes were detected.

3.3.2 Cardiac function (Table 3)
Left ventricular function measurements revealed no significant baseline differences between the two SHAM-operated groups. However, after infarction a significant reduction of sLVP (from 82.1±5.5 to 62.4±7.7 in WT animals, from 77.7±8.2 to 63.6±9.3 in IGF-1 deficient animals, P<0.05) was found when compared to the SHAM groups (Table 3). Similar results were obtained for cardiac contractility and cardiac relaxation values with a decrease in both positive and negative dP/dt values after MI in both genotypes (Table 3). No significant changes were seen between the IGF-1 deficient and the WT infarct groups.


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  		Table 3 Left ventricular performancea,bGo

 

   4 Discussion
Top
 Abstract
 1 Introduction/background
 2 Methods
 3 Results
 4 Discussion
5 Conclusions
 References
 
The major finding in this study is that following MI, cardiac performance in IGF+/– animals was not affected, despite a blunted cardiac remodeling response. IGF-1+/– animals had a blunted hypertrophic response of the interventricular septum, in addition to a general decrease in C/F ratio, mainly due to an increased MD. Furthermore, DNA synthesis was decreased, in conjunction with a 4-fold increase in apoptosis rates.

4.1 Role of IGF-1 in cardiac remodeling
Although IGF-1+/– animals had lower body and organ weights, their HW/BW ratio was not disturbed, which underscores the general growth promoting effects attributed to IGF-1 [10]. Data in this study indicate that IGF-1 deficiency is associated with smaller cardiomyocytes and a blunted hypertrophic response of the interventricular septum after MI. In both genotype groups, a non-significant decrease in MD was observed after MI. In WT/MI animals, MD was lower compared to animals in the HZ/MI group and occurred concomitantly with an increase in septum thickness. In HZ/MI animals, a nonsignificant decrease in MD was accompanied by only a modest increase in septum thickness. This phenomenon of myocyte hypertrophy and thinning of the septum could be explained by side to side slippage of cardiomyocytes [19] or by early apoptosis [20] of cardiomyocytes in the interventricular septum in the HZ/MI group. If so, the early apoptosis peak potentially has been missed.

In literature, overwhelming evidence is present for a role of IGF-1 in cardiac hypertrophy. Both administration of IGF-1 to healthy animals and excessive production of GH in humans with acromegaly leads to cardiac hypertrophy without structural signs of cardiomyopathy [2,21]. Also in the infarcted heart, IGF-1 has been shown to play a major role in reactive hypertrophy after acute coronary artery occlusion. GH [9], IGF-1 administration [2,4] and IGF-1 overexpression [5] augment the hypertrophic response of the non-infarcted contractile tissue and preserve cardiac performance after myocardial infarction. The data presented in this study provide further evidence for a role of IGF-1 in the regulation of the compensatory hypertrophic response of the non-infarcted area of the heart.

Furthermore, IGF-1 has been shown to regulate angiogenesis in vivo. Duerr et al. [4] showed in a rat model of MI and Kluge et al. [7] in a porcine model of cardiac microembolization, that IGF-1 administration increased cardiac angiogenesis. Here we report that IGF-1 deficiency is associated with decreased C/F ratios of the non-infarcted myocardium, both under physiologic conditions and after MI. As explained above, C/F ratios did not change after MI in both genotypes, albeit because of different mechanisms. In wildtype animals, the unchanged C/F ratio was due to a decrease in MD and a matching decrease in capillary numbers, while the unchanged C/F ratio in IGF-1+/– animals can be explained by the blunted hypertrophic response of cardiomyocytes and lack of angiogenesis. This suggests a balance between cardiac hypertrophy and cardiac angiogenesis in both mouse models.

IGF-1 deficiency was associated with decreased DNA synthesis in the interventricular septum and infarct borderzone and increased rates of apoptosis in the infarcted area of the heart. The increased apoptosis rates in the infarcted area may account for the augmented thinning of the infarcted area of IGF-1+/– hearts, compared to WT infarcts. Part of this difference might be explained by the baseline difference in LVFW thickness that was observed between both SHAM groups. (Table 2a) In our study, the majority of BrdU incorporation in the infarcted area was not confined to cardiomyocytes, but rather detected in non-cardiomyocytes. This was also found by Kuizinga et al. [22] in rats and by Lutgens et al. [12] in mice.

IGF-1 is known to play an important role in apoptosis, both in vitro and in vivo. In vitro, stretch-induced apoptosis of cardiomyocytes was attenuated by IGF-1 administration [23]. In a murine model of ischemia reperfusion [24] and in a chronic MI study in mice overexpressing IGF-1 [5], IGF-1 was shown to protect against apoptosis and reduced myocyte death. In the present study, we used a stringent TUNEL technique to exclude the aspecific labeling. DNA laddering was not performed because of the low apoptosis rates in the infarcted area [18]. Therefore, an activated caspase-3 staining method was done, which confirmed the TUNEL results. In literature, acute MI induces apoptosis of cardiac myocytes in the borderzone [25]. In this study, apoptosis was detected mainly in non-myocytes, rather than in cardiomyocytes, although several apoptotic myocytes were detected in the borderzone of the infarcted area. In the center of the infarcted area, myocyte necrosis occurred and nuclei were absent in these ghost cells.

In literature, there is an ongoing discussion about the mechanism of IGF-1 induced protection from apoptosis. Apoptosis is decreased by IGF-1 by interference with known pro-apoptotic pathways. Leri et al. [23] showed that IGF-1 overexpression induced increased levels of p53-Mdm2 complexes leading to decreased p53 transcriptional activity and conversely to decreased bax, angiotensinogen and AT-I receptor type 1 transcription, all of which are associated with increased apoptosis levels of cardiac myocytes. Furthermore, Chen et al. [26] showed that IGF-1-induced attenuation of apoptosis could be prevented by inhibition of PI-3K.

We showed that induction of MI resulted in left ventricular dysfunction. Since liver and lung weigths did not increase due to MI induction and no late (>24 h post-MI) mortality occurred, we conclude that no overt heart failure was present. Furthermore, no differences in cardiac function parameters were found between WT and IGF-1 deficient animals, which is in agreement with the data presented by Lembo et al. [10] This group reported no baseline changes in cardiac contractility in these IGF-1+/– mice, using comparable methods for LV performance measurements. Here we show that also in the infarcted IGF-1 deficient heart, cardiac performance was not altered, although obvious changes in the architecture of the ventricle were observed. One of the explanations for the lack of functional changes might be the timing of the measurements. Potentially, early changes and late remodeling may have been missed. When we compare the + and –dP/dt data obtained with the Millar 1.4F catheter and compare these with values in literature, several groups obtained higher values, using comparable techniques [10,27]. Reported dP/dt values by other groups are in the same magnitude [28,29]. Differences could be explained by the use of other anesthetics (penthotal vs. ketamine/thiobutabarbital) [27], and strain differences. In literature, conflicting data on the role of IGF-1 on cardiac function have been reported. Both reduced and increased IGF-1 levels have been reported to enhance left ventricular performance. Li et al. [5] showed that IGF-1 overexpression in mice increased cardiac performance following MI. In contrast, GH [30] and IGF-1 deficient mice (the latter producing only 30% of normal IGF-1 levels) [10], showed an overall increase in LV performance, in addition to increased conscious blood pressure. These, apparently contradicting, observations have been explained by increased beta adrenergic receptor density with GH deficiency and increased adenyl cyclase activity in IGF-1 deficiency.

The role of IGF-1 in cardiac remodeling is investigated thoroughly in literature. This study provides further evidence for a pivotal role of IGF-1 in cardiac remodeling following myocardial infarction. IGF-1 deficiency leads to a blunted cardiac remodeling following MI, as indicated by the attenuation of the hypertrophic response, increased apoptosis and decreased cellular proliferation. However, this is not accompanied by a further decreased cardiac performance for reasons mentioned above.

This study further underlines the need for evaluation of the role of IGF-1 in human myocardial infarction remodeling and function in order to come to a better therapy for patients suffering from heart failure.


   5 Conclusions
Top
 Abstract
 1 Introduction/background
 2 Methods
 3 Results
 4 Discussion
 5 Conclusions
References
 
In this study we showed that heterozygous IGF-1 deficiency in mice leads to a blunted cardiac remodeling response following myocardial infarction, while cardiac function appears not to be further affected, 1 week after MI, as compared to controls. These data suggest a stimulatory role of IGF-1 in cardiac hypertrophy, DNA synthesis and apoptosis. IGF+/– mice have a modest phenotype post-MI, leading to preservation of cardiac function.

Time for primary review 21 days.


   Acknowledgements
 
We are indebted to Jacques Debets, Peter Leenders, Anique Jansen and Dr. Jack Cleutjens for their technical support. We thank Genentech for determination of the IGF-1 serum levels and the Cardiovascular Biology Foundation, the Netherlands for financial support.


   References
Top
 Abstract
 1 Introduction/background
 2 Methods
 3 Results
 4 Discussion
 5 Conclusions
 References
 

  1. Schmid C. Insulin-like growth factors. Cell Biol Int (1995) 19:445–457.[CrossRef][ISI][Medline]
  2. Cittadini A., Strömer H., Katz S.E., Clark R., Moses A.C., Morgan J.P., Douglas P.S. Differential cardiac effects of growth hormone and Insulin-like growth factor-1 in the rat. Circulation (1996) 93:800–809.[Abstract/Free Full Text]
  3. Donohue T.J., Dworkin L.D., Lango M.N., Fliegner K., Lango R.P., Benstein J.A., Slater W.R., Catanese V.M. Induction of myocardial insulin-like growth factor-1 gene expression in left ventricular hypertrophy. Circulation (1994) 89:799–809.[Abstract/Free Full Text]
  4. Duerr R.L., Huang S., Miraliakbar H.R., Clark R., Chien K.R., Ross J.J.R. Insulin-like growth factor-1 enhances ventricular hypertrophy and function during the onset of experimental cardiac failure. J Clin Invest (1995) 95:619–627.[ISI][Medline]
  5. Li Q., Li B., Wang X., Leri A., Jana K.P., Liu Y., Kajstura J., Baserga R., Anversa P. Overexpression of insulin-like growth factor-1 in mice protects from myocyte death after infarction, attenuating ventricular dilatation, wall stress, and cardiac hypertrophy. J Clin Invest (1997) 100:1991–1999.[ISI][Medline]
  6. Wang L., Weiqiong M., Markovich R., Chen J.-W., Wang P.H. Regulation of cardiomyocyte apoptotic signaling by insulin-like growth factor 1. Circ Res (1998) 83:516–522.[Abstract/Free Full Text]
  7. Kluge A., Zimmermann R., Munkel B., Mohri M., Sack S., Schaper J., Schaper W. Insulin-like growth factor 1 is involved in inflammation linked angiogenic processes after microembolisation in porcine heart. Cardiovasc Res (1995) 29:407–415.[Abstract/Free Full Text]
  8. Reiss K., Kajstura J., Zhang X., Li P., Szoke E., Olivetti G., Anversa P. Acute myocardial infarction leads to upregulation of the IGF-1 autocrine system. DNA replication, and nuclear mitotic division in the remaining viable cardiac myocytes. Exp Cell Res (1994) 213:463–472.[CrossRef][ISI][Medline]
  9. Cittadini A., Grossman J.D., Napoli R., Katz S.E., Stroemer H., Smith R.J., Clark R., Morgan J.P., Douglas P.S. Growth hormone attenuates early left ventricular remodeling and improves cardiac function in rats with large myocardial infarction. J Am Coll Cardiol (1997) 29:1109–1116.[Abstract]
  10. Lembo G., Rockman H.A., Hunter J.J., Steinmetz H., Koch W.J., Ma L., Prinz M.P., Ross J.J., Chien K.R., Powell-Braxton L. Elevated blood pressure and enhanced myocardial contractility in mice with severe IGF-1 deficiency. J Clin Invest (1996) 98:2648–2655.[ISI][Medline]
  11. Powell-Braxton L., Hollingshead P., Warburton C., Dowd M., Pitts-Meek S., Dalton D., Gillett N., Steward T.A. IGF-1 is required for normal embryonic growth in mice. Gen Dev (1993) 7:2909–2917.
  12. Lutgens E., Daemen M.J.A.P., de Muinck E.D., Debets J., Leenders P., Smits J.F.M. Chronic myocardial infarction in the mouse: cardiac functional and structural changes. Cardiovasc Res (1999) 41:586–593.[Abstract/Free Full Text]
  13. Nelissen-Vrancken H.J.M., Kuizinga M.C., Daemen M.J.A.P., Smits J.F.M. Early captopril treatment inhibits DNA synthesis in endothelial cells and normalization of maximal coronary flow in infarcted rat hearts. Cardiovasc Res (1998) 40:156–164.[Abstract/Free Full Text]
  14. Nelissen-Vrancken H.J.M.G., Debets J.J.M., Snoeckx L.H.E.H., Daemen M.J.A.P., Smits J.F.M. Time-related normalisation of maximal coronary flow in isolated perfused hearts of rats with myocardial infarction. Circulation (1996) 93:349–355.[Abstract/Free Full Text]
  15. Kockx M.M., Muhring J., Bortier H., De Meyer G.R.H., Jacob W. Biotin-or digoxigenin-conjugated nucleotides bind to matrix vesicles in atherosclerotic plaques. Am J Pathol (1996) 148:1771–1777.[Abstract]
  16. Kockx M.M., Muhring J., Knaapen M.W.M., De Meyer G.R.Y. RNA synthesis and splicing interferes with DNA synthesis in situ and labeling techniques used to detect apoptosis. Am J Pathol (1998) 152:885–888.[Abstract]
  17. Yaoita H., Ogawa K., Maehara K., Maruyama Y. Apoptosis in relevant clinical situations: contribution of apoptosis in myocardial infarction. Cardiovasc Res (2000) 45:630–641.[Abstract/Free Full Text]
  18. van Heerde W.L., Robert-Offerman S., Dumont E., Hofstra L., Doevendans P.A., Smits J.F.M., Daemen M.J.A.P., Reutelingsperger C.P.M. Markers of apoptosis in cardiovascular tissues; focus on Annexin V. Cardiovasc Res (2000) 45:549–559.[Abstract/Free Full Text]
  19. Olivetti G., Quaini F., Lagastra C., Cigola E., Ricci R., Maestri R., Anversa P. Cellular basis of ventricular remodeling after myocardial infarction in rats. Cardioscience (1995) 6:101–106.[ISI][Medline]
  20. Anversa P., Cheng W., Liu Y., Leri A., Redaelli G., Kajstura J. Apoptosis and myocardial infarction. Bas Res Cardiol (1998) 93:8–12.[CrossRef][ISI][Medline]
  21. Tanaka N., Ryoke T., Hongo M., Mao L., Rockman H.A., Clark R.G., Ross J. Effects of growth hormone and IGF-1 on cardiac hypertrophy and gene expression in mice. Am J Physiol (1998) 275:393–399.
  22. Kuizinga M.C., Smits J.F.M., Arends J.W., Daemen M.J.A.P. AT2 receptor blockade reduces cardiac interstitial cell DNA synthesis and cardiac function after rat myocardial infarction. J Mol Cell Cardiol (1998) 30:425–434.[CrossRef][ISI][Medline]
  23. Leri A., Liu Y., Claudio P.P., Kajstura J., Wang X., Wang S., Kang P., Malhotra A., Anversa P. Insulin-like growth factor-1 induces Mdm2 and down-regulates p53, attenuating the myocyte renin–angiotensin system and stretch-mediated apoptosis. Am J Pathol (1999) 154:567–580.[Abstract/Free Full Text]
  24. Buerke M., Murohara T., Skurk C., Nuss C., Tomaselli K., Lefer A.M. Cardioprotective effect of insulin-like growth factor 1 in myocardial ischemia followed by reperfusion. Proc Natl Acad Sci USA (1995) 92:8031–8035.[Abstract/Free Full Text]
  25. Saraste A., Pulkki K., Kallajoki M., Hendriksen K., Parvinen M., Voipio-Pulkki L.-M. Apoptosis in human acute myocardial infarction. Circulation (1997) 95:320–323.[Abstract/Free Full Text]
  26. Chen D.B., Wang L., Wang P.H. Insulin-like growth factor 1 retards apoptotic signaling induced by ethanol in cardiomyocytes. Life Sci (2000) 67:1683–1693.[CrossRef][ISI][Medline]
  27. Lorenz J.N., Robbins J. Measurement of intraventricular pressure and cardiac performance in the intact closed-chest anesthetized mouse. Am J Physiol (1997) 272:H1137–H1146.[ISI][Medline]
  28. Koch W.J., Rockman H.A., Samana P., Hamilton R.A., Bond R.A., Milano C.A., Lefkowitz R.J. Cardiac function in mice overexpressing the beta-adrenergic receptor kinase or a beta-ARK inhibitor. Science (1995) 268:1350–1353.[Abstract/Free Full Text]
  29. Milano C.A., Allen L.F., Rockman H.A., Dolber P.C., Mcminn T.C., Chien K.R., Johnson T.D., Bond R.A., Lefkowitz R.J. Enhanced myocardial function in transgenic mice overexpressing the beta-2 adrenergic receptor. Science (1994) 264:582–586.[Abstract/Free Full Text]
  30. Brown L., Wyse B., Sernia C. Adrenoceptor-mediated cardiac and vascular responses in genetically growth hormone deficient rats. Biochem Pharmacol (1993) 45:2223–2229.[CrossRef][ISI][Medline]

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