(A) The O-linked attachment of the monosaccharide N-acetylglucosamine (GlcNAc) moiety to nuclear and cytosolic proteins is a cell signalling process that is similar to and can interact with phosphorylation; this is referred to as protein O-GlcNAcylation, to contrast it with traditional N- and O-glycosylation within the secretory pathways. In contrast to the hundreds of kinases and phosphatases that add and remove phosphate, attachment of O-GlcNAc to proteins is catalyzed by a single enzyme, O-GlcNAc transferase (OGT), and the removal catalyzed by O-GlcNAcase (OGA). Similar to phosphorylation, O-GlcNAc modification of proteins alters their function, activity, subcellular localization, and stability. Synthesis of O-GlcNAc is regulated by the hexosamine biosynthetic pathway; consequently, O-GlcNAc levels are regulated by substrate availability. In addition, however, O-GlcNAcylation is also upregulated in response to cellular stress and this can occur independent of substrate availability.
(B) Chronic upregulation of O-GlcNAcylation in conditions such as diabetes and hypertension is often associated with adverse effects on the cardiovascular system. However, there is increasing evidence demonstrating that O-GlcNAcylation is an essential mediator of cardiac and vascular function, and that acute activation of pathways increasing O-GlcNAc levels are cardioprotective.
Abbreviations:G, GlcNAc; P, phosphate; OGT, O-GlcNAc transferase; OGA, O-GlcNAcase; CV, cardiovascular; I/R, ischemia/reperfusion; ER, endoplasmic reticulum; Ang II, angiotensin II.
The process of mitochondrial fission is under the control of the mitochondrial fission proteins Drp1 and Fis1. Drp1 is located mainly in the cytosol and comprises a GTPase, a central region, and a GTPase effector domain (GED) or assembly domain. Fis1 is localized in the outer mitochondrial membrane with most of the protein facing into the cytosol, acting as a docking station for Drp1. On activation, Drp1 translocates to the mitochondria (a process which is regulated by phosphorylation and sumoylation), oligomerizes, and constricts the mitochondrial scission site, a process which requires GTPase, thereby resulting in mitochondrial fission.
The process of mitochondrial fusion is under the control of the mitochondrial fusion proteins Mfn1 and 2 and OPA-1. Mitochondrial membrane fusion has been shown to be a distinct two-step process which occurs separately for the inner and outer membrane, but in chronology. Both the outer and inner membranes of the mitochondria must fuse properly in order for the matrix contents to mix properly. (A) The mitochondrial fusion proteins Mfn1 and Mfn2 are located on the outer mitochondrial membrane with a cytosolic GTPase domain and two hydrophobic heptad repeat (HR) regions separated by a transmembrane repeat. The C-terminal HR region (HR2) mediates oligomerization between Mfn molecules on adjacent mitochondria, allowing the membranes to fuse. GTP hydrolysis facilitates the fusion process. (B) The mitochondrial fusion protein OPA1 comprises an N-terminal mitochondrial import sequence (MIS), hydrophobic heptad repeat (HR) segments, coiled-coil domain (C C), a GTPase domain, a central domain, and a GTPase effector domain (GED) at the C-terminus. OPA1 mediates the fusion of the inner mitochondrial membranes.
Vasodilator-stimulated phosphoprotein: crucial for activation of Rac1 in endothelial barrier maintenance
VASP stabilizes endothelial barrier functions by regulation of small GTPase Rac1.
It is well established in the meantime that vasodilator-stimulated phosphoprotein (VASP) is required to maintain endothelial barrier properties. Under conditions of acute inflammation and hypoxia, VASP was shown to be down-regulated, leading to increased endothelial permeability. Recent data provide evidence for a completely new mechanism by which VASP stabilizes the endothelial barrier, i.e. by facilitating activation of Rac1 downstream of PKA and PKG. According to this model VASP-dependent endothelial barrier stabilization was shown to act via cAMP- and cGMP-mediated signalling pathways. VASP is associated with actin filaments via zyxin and vinculin while paxillin is linked to endothelial adherens junctions via β-catenin. We found that VASP was required for cAMP-mediated Rac1 activation and barrier enhancement. Serine-157 phosphorylation of VASP via PKA induced translocation of VASP to cell junctions and binding of VASP to ZO-1. In line with this, PKG-mediated serine-239 phosphorylation was also shown to be required for Rac1 activation. Thus, we propose that cAMP- and cGMP-mediated signalling facilitates Rac1 activation close to cell junctions in VASP-dependent manner, which in turn appears to be crucial for endothelial barrier stabilization.
Abbreviations: FAK= focal adhesion kinase; PKA= cAMP-dependent protein kinase A; PKG= cGMP-dependent protein kinase G; EPAC= exchange protein directly activated by cAMP; ZO-1/2/3= zonula occludens protein1/2/3; α, β = α- and β-catenin; ECM= extracellular matrix.
Schematic representation of a hypothetical pathway by which the splice variants of ENH could promote or prevent hypertrophy.
The Enigma proteins (ENH) are cytoplasmic proteins that bind to the cytoskeleton and serve as a platform for binding many proteins such as protein kinases. Four ENH isoforms have been described. ENH1, which contains the LIM motif, is expressed in the embryonic and neonatal heart. In the adult heart it is replaced by ENH3, which does not contain this binding motif (Yamazaki et al. Cardiovasc Res 2010,86:374-382). Based upon previously published data showing that the LIM domain anchors PKC and PKD and taking into account the well-described molecular pathways implicated in the hypertrophic effect of these kinases, it is tempting to propose that the LIM domains of ENH1 act as a new signalling platform that mediates the PKC and PKD hypertrophic pathways.
Abbreviations: ENH1-PDZ, enigma homologue 1 PDZ (PSD-95, DLG, ZO-1) domain; ENH1-Lim, enigma homologue 1 Lim (LIN-11, Isl-1, MEC-3) domains; LTCC, L-type voltage-gated Ca2+ channel; PKD1, protein kinase D1; PKC, protein kinase C; Id, inhibitor of differentiation/DNA binding; CaMK, Ca2+/calmodulin kinase; 14-3-3, chaperone protein 14-3-3; HDAC4,5,9, histone deacetylase type 4, 5, and 9; MEF2, myocyte enhancing factor 2; P, phosphorylation.
High glucose, NO, and adenosine: a vicious circle in chronic hyperglycaemia.
HUVEC isolated from gestational diabetic pregnancies show a reduced adenosine transport activity via hENT1. This effect of gestational diabetes leads to extracellular accumulation and a higher bioavailability of this nucleoside to activate the A2a adenosine receptor subtype. The intracellular signalling cascade triggered by A2a purinoreceptor activation by adenosine results in an increased l-arginine transport activity via hCATs and increased NO synthesis by eNOS. The intracellular second messengers involved in the effect of adenosine include activation of protein kinase C (PKC) and 42/44 kDa mitogen-activated protein kinases (P42/44mapk), which then activate (+) l-arginine transport. The up-regulation in the endothelial l-arginine/NO pathway by adenosine is associated with an increase in NO. NO activates hCHOP and C/EBPα transcription factor complex formation, which migrates to the nucleus of the endothelial cells and binds, as a complex, to a consensus sequence located on the promoter region of the SLC29A1 gene (for hENT1).
This phenomenon results in reduced transcriptional activity of the SLC29A1 promoter, leading to reduced levels of the hENT1 mRNA and protein. As a consequence, a decreased hENT1 transport-like activity could result in reducing the removal of the endogenous nucleoside adenosine from the extracellular medium in HUVEC. The reduced adenosine transport via hENT1 detected in HUVEC from gestational diabetes could also result from the inhibition (−) by PKC or P42/44mapk. Notably, hyperglycaemia (glucose) may be proposed as a regulator of the illustrated vicious circle since it might increase (+) both eNOS and NO levels. hCHOP, a key transcriptional regulator of the SLC29A1 gene, has been demonstrated to be increased (+) by high glucose and diabetes.
MMP-2 is present in discrete intracellular compartments within the cardiac myocyte (sarcomere, nuclei, caveolae, and mitochondria) as a 72 kD zymogen. It can be activated in two ways that likely dictate its diverse biological roles. Its secretion and proteolytic removal of its autoinhibitory propeptide domain by MT1-MMP together with TIMP-2 results in a 64 kD form that targets extracellular matrix proteins. Oxidative stress, particularly as ONOO- in the presence of glutathione, causes the S-glutathiolation of a critical cysteine residue in the propeptide and conformational change and activation of the 72 kD form, allowing access of intracellular substrates (troponin I, α-actinin, myosin light chain-1, and titin are thus far known) to its catalytic zinc centre. MMP-2 is also a phosphoprotein (both 72 and 64 kD forms) and phosphorylation markedly reduces its activity (FASEB J 2007;21:2486). The kinases and phosphatases that regulate its activity in vivo are unknown; however, PKC can phosphorylate MMP-2 in vitro. Thus, MMP-2 can ‘remodel’ both intracellular and extracellular protein substrates. The cleavage of intracellular substrates by MMP-2 is an early response to enhanced oxidative stress that results in acute contractile dysfunction.
Abbreviations: matrix metalloproteinase-2 (MMP-2); tissue inhibitor of metalloproteinase-2 (TIMP-2); membrane-type-1 matrix metalloproteinase (MT1-MMP); glutathione (GSH); peroxynitite (ONOO-); protein kinase A (PKA); protein kinase C (PKC)
PQC is carried out by chaperones, the ubiquitin proteasome system (UPS), and the autophagy-lysosome pathway. Chaperones facilitate the folding of nascent polypeptides and the unfolding/refolding of misfolded proteins, prevent the misfolded proteins from aggregating, and escort terminally misfolded proteins for degradation by the UPS. The UPS degrades misfolded proteins and unneeded native proteins in the cell through two general steps: first, covalent attachment of ubiquitin to a target protein by a cascade of chemical reactions catalysed by the ubiquitin-activating enzyme (E1), ubiquitin-conjugating enzymes (E2), and ubiquitin ligase (E3); second, the degradation of the target protein by the proteasome. The autophagy-lysosomal pathway helps remove protein aggregates formed by the misfolded proteins that have escaped from the surveillance of chaperones and the UPS. Protein aggregates or defective organelles are first segregated by an isolated double membrane (phagophore) to form autophagosomes, which later fuse with lysosomes to form autophagolysosomes, where the segregated content is degraded by lysosomal hydrolases. p62/SQSTM1 and NBR1 (neighbour of BRCA1 gene 1) may mediate the activation of autophagy by aggregated ubiquitinated proteins. The legend for symbols used is shown in the box at the lower left.
Free ubiquitin proteins are generated from the processing of ubiquitin precursors or ubiquitin chains by deubiquitylation enzymes (DUBs). An enzymatic cascade involving the E1 (ubiquitin activase), E2 (ubiquitin conjugase), and E3 (ubiquitin ligase) enzymes covalently conjugates ubiquitin chains to lysine residues in target proteins. Proteins deemed for degradation are singled out by E3 enzymes through the presence of a degradation signal (degron). The ubiquitylated substrate is recognized by a large proteolytic complex, the proteasome. The proteasome contains of 19S regulatory particles and the 20S core particle, which contains several proteolytic active subunits. The 19S regulatory particle binds, deubiquitylates, unfolds, and translocates the substrate into the proteolytic chamber of the 20S particle where the protein is degraded into short peptide fragments.
MYBPC3 is one of the most frequently mutated genes in hypertrophic cardiomyopathy (HCM). Most mutations result in a frameshift and a premature termination codon (PTC) and should produce truncated proteins, which were never detected in myocardial tissue of patients. Recent data showed that the nonsense-mediated mRNA decay (NMD) is involved in the degradation of nonsense mRNA in a mouse model of HCM (Vignier, Schlossarek et al., Circ Res 2009). NMD is an evolutionarily conserved pathway existing in all eukaryotes that detects and eliminates PTC-containing transcripts. NMD apparently evolved to protect the organism from the deleterious dominant-negative or gain-of-function effects of resulting truncated proteins.
(A) NMD occurs when a PTC is located more than 50–55 nucleotides (nt) upstream of the last exon–exon junction within the mRNA (green region), whereas mRNAs with PTCs downstream of this boundary (red region) escape NMD. (B) During pre-mRNA splicing, exon junction complexes (EJC) are deposited upstream of every exon–exon junction. In normal transcripts, EJCs are displaced by the ribosome during the pioneer round of translation, and translation stops when the ribosome reaches the normal stop codon. In contrast, in PTC-bearing mRNAs, the ribosome is blocked at the PTC and the EJC downstream of the PTC remains associated with the mRNA. This results in attachment of the SURF complex to the ribosome. Subsequent phosphorylation of UPF1 by SMG-1 drives dissociation of eRF1 and eRF3 and binding of SMG7. Ultimately, the mRNA is degraded by different pathways including decapping or deadenylation.
Viral myocarditis is an inflammatory disease of the myocardium caused by virus infection. The disease progression occurs in three distinct stages: viral infection, immune response, and cardiac remodelling. Recent evidence suggests that the host proteolytic systems play crucial roles in the regulation of the pathogenesis of viral myocarditis in all three stages. During the viral infection stage, the virus evolves different strategies to utilize the host ubiquitin/proteasome system and the autophagy machinery to facilitate its replication. At the immune response stage, viral infection induces the formation of an immunoproteasome to increase MHC class I antigen presentation. Meanwhile, production of pro-inflammatory cytokines is enhanced, partially through the ubiquitin/proteasome system-mediated NFκB activation. Autophagy may also contribute to immune-mediated pathogenesis by modulating MHC class II antigen presentation. During the cardiac remodelling phase, increased accumulation of abnormal ubiquitin-protein conjugates/aggregates and elevated oxidative stress lead to the eventual impairment of the ubiquitin/proteasome function, subsequently resulting in abnormal regulation of contractile apparatus expression and also triggering apoptosis and autophagic cell death. As a result of myocyte loss and decreased contractile properties, the left ventricle of the heart begins to dilate to compensate for impaired cardiac function.
Activation of the survivor activating factor enhancement (SAFE) pathway, as represented by the binding of a low concentration of endogenous or exogenous tumour necrosis factor alpha (TNFα) to its TNF receptor 2 (TNFR2) at the onset of reperfusion with the subsequent activation of the transcription factor signal transducer and activator of transcription-3 (STAT-3), initiates a cardioprotective signalling cascade in both ischaemic pre- and postconditioning that is activated independently of the well-known reperfusion injury salvage kinases (RISK) pathway. The delineation of the SAFE pathway further emphasizes the importance of RISK-independent pathways in cardioprotection, which may have potential therapeutic application in the mitigation of ischaemic-reperfusion injury.
Abbreviations: RISK: Reperfusion Injury Salvage Kinases; SAFE: Survivor Activating Factor Enhancement; S1P: sphingosine-1-phosphate; TNFα: tumour necrosis factor alpha; GPCR: green protein coupled receptors; S1P R1/R3: sphingosine-1-phosphate receptors 1 or 3; TNFR2: tumour necrosis factor alpha receptor 2; MEK: mitogen-activated protein kinase; PI3K: phosphoinositide 3- kinase; Erk1/2: extracellular regulated kinases 1/2; Akt: protein kinase B; GSK-3β: glycogen synthase kinase-3 beta; JAK: janus kinase; STAT-3: signal transducer and activator of transcription-3; mPTP: mitochondrial permeability transition pore; P: phosphorylation.
The core structure of the mPTP remains unresolved. Known mPTP regulatory elements are depicted on the left side of the figure, whereas the right side indicates symbolically the threshold for mPTP-induction by oxidant stress. The middle row (horizontally) depicts the basal state of ANT and CyP-D as they relate to the basal threshold for mPTP induction by oxidant stress. The top row reflects factors that facilitate mPTP induction: atractyloside, Ca2+, and indirect effects of Pi. The bottom row includes factors that are known to inhibit mPTP induction: genetic deletion of ANT (ANT is dispensable for mPTP formation per se; inhibition of CyP-D by CsA remains protective), ADP, or bongkrekic acid (requirement/role of CyP-D under these conditions is unknown), CsA and genetic deletion of CyP-D in the presence of Pi (atractyloside, CsA and Ca2+ are no longer effective when compared with WT). Note the opposing mechanisms of Pi in mPTP induction: (i) Pi as a direct mPTP desensitizer (bottom row) is opposed by CyP-D binding (top row), whereas (ii) Pi may also act as an indirect mPTP sensitizer (through regulation of Mg2+ and/or polyphosphate levels; top row). Note that Ca2+ is not a major factor in mPTP induction in intact cardiomyocytes and neurons.
mPTP mitochondrial permeability transition pore
ANT adenine nucleotide translocator
BKA bongkrekic acid
CyP-D cyclophilin D
Pi inorganic phosphate
CsA cyclosporin A
ADP adenosine diphosphate
Ppif gene encoding CyP-D in mouse
There are three major signalling cascades of protein kinase activation in cardioprotection: (A) the GPCR/NPR-AKT-eNOS-PKG pathway, (B) the reperfusion-injury salvage kinase (RISK) pathway, and (C) the survival activating factor enhancement (SAFE) pathway, which centrally involves gp130-JAK-STAT signalling. In each system, there are molecules that are decreased in expression and/or activity with advancing age (marked in yellow) and possibly contribute to the loss of cardioprotection with aging. Such loss of cardioprotection with aging is one major problem in the translation of experimental data from (usually young and healthy) animals to the clinical situation in elderly humans.
Abbreviations: AMPK, AMP-activated kinase; ANP, atrial natriuretic peptide; BNP, brain natriuretic peptide; CB-R, cannabinoid receptor; Cx43, connexin 43; eNOS, endothelial NO synthase; ERK, extracellular regulated kinase; FGF-2, fibroblast growth factor 2; gp130, glycoprotein 130; GPCR, G-protein-coupled receptor; GSK3β, glycogen synthase kinase 3 β; H11K, H11 kinase; IGF, insulin-like growth factor 1; IL-6, interleukin 6; iNOS, inducible NO synthase; JAK, janus kinase; KATP, ATP-dependent potassium channel, MnSOD, manganese superoxide dismutase; MPTP, mitochondrial permeability transition pore; NO, nitric oxide; NPR, natriuretic peptide receptor; p38, p38 mitogen activated protein kinase; P70S6K, p70 ribsosomal S6 protein kinase; pGC, particulate guanylyl cyclase; PI3K, phosphoinositide 3-kinase; PKC, protein kinase C; PKG, protein kinase G; ROS, reactive oxygen species; sGC, soluble guanylyl cyclase; SIRT1, sirtuin 1; STAT3, signal transducer and activator of transcription 3; TNF-R, tumour necrosis factor receptor; UCN, urocortins.
This schematic provides a simplified overview of the intracellular transduction pathways underlying cardioprotection elicited by the growth factors: transforming growth factor-β1 (TGF-β1), cardiotrophin-1 (CT-1), fibroblast growth factor (FGF), vascular endothelial growth factor (VEGF), insulin, insulin-like growth factor (IGF), and urocortin. Ligand binding to their respective cell-surface receptors on the cardiomyocyte activates intracellular signalling kinase cascades including Raf-Ras-Mek1/2-Erk1/2 and PI3K-Akt of the reperfusion injury salvage kinase (RISK) pathway, the JAK-STAT pathway, and various anti-apoptotic mechanisms (including the phosphorylation and inhibition of Bax and BAD as well as the inhibition of cytochrome C release).
Many of the acute cardioprotective mechanisms manifested at the time of reperfusion converge on the mitochondria and include the inhibition of the mitochondrial permeability transition pore (mPTP), which can be achieved through several different mechanisms including the phosphorylation and inhibition of GSK3β; the opening of the ATP-sensitive mitochondrial potassium (Mito KATPM) channel by the eNOS-NO-PKG-PKC-ε cascade which produces mitochondrial ROS, which inhibits mitochondrial permeability transition pore opening; and the intracellular calcium modulation due to augmented SERCA uptake of calcium into the sarcoplasmic reticulum. More long-term cardioprotection may be achieved through the genetic transcription of various cardioprotective mediators such as iNOS, NFκB, MMP-1, phospholipase-1, and so on (not shown on diagram, see text for details).
Nitrite homeostasis is determined by nitric oxide (NO) generation from NO synthases and dietary consumption of nitrate. Nitrate enters the stomach and then circulates in the blood and is converted into nitrite via salivary bacteria containing nitrate reductase. Nitrite derived from the diet and NOS activity rapidly accumulates in the plasma and is transported into tissues such as the heart. Nitrite is then stored in the myocardium and is metabolized into NO during hypoxia or ischaemia.
A schematic representation of the cardiomyocyte VEGF signalling pathway. Flt-1 and KDR are the two major VEGF receptors. In cardiomyocytes, VEGF drives cardiac hypertrophy or its regression, depending on the prevalent binding to KDR or Flt-1, respectively. Copper (Cu) supplementation determines a switch in the VEGF signalling pathway, increasing the ratio of Flt-1 to KDR. By this mechanism, copper induces regression of cardiomyocyte hypertrophy.
Abbreviations: VEGF, vascular endothelial growth factor; Flt-1, FMS-like tyrosine kinase-1; KDR, kinase insert domain receptor; PKG-1, cGMP-dependent protein kinase-1; Cu, copper; DAG, diacylglycerol; IP3, inositol trisphosphate; Sos, Son of Sevenless; Shc, Src-homology collagen protein; Grb-2, growth factor receptor-bound protein 2; MEK1/2, mitogen activated protein kinase (MAPK)/extracellular-regulated kinase (ERK) kinase 1/2; PKC, protein kinase C; PLC-γ, phospholipase C-γ; PD98059 (PD) and UO126 are selective ERK1/2 inhibitors.
Prior research has identified major changes in cardiac metabolism during the development of pathological hypertrophy. The hallmark of these changes is a reduction in the contribution of fatty acids to oxidative metabolism. As a result, the hypertrophied heart shifts to increased reliance on glucose metabolism. Specifically, increased glucose uptake and accelerated glycolysis occur in cardiac hypertrophy with increased activity of LDH and lactate efflux. Despite this, oxidation of pyruvate is not increased, which demonstrates an “uncoupling” of glycolysis and glucose oxidation. However, the potential of excess pyruvate to enter the TCA cycle through anaplerosis, specifically via malic enzyme, has been recently shown. Although the glycolytic pathway is upregulated, studies have not shown a consistent upregulation of accessory pathways of glucose metabolism in pathological cardiac hypertrophy. Glycogen content and its contribution to metabolism remain unchanged. Although increased activity of G6PD has been found, no changes in flux or enzymes involved in the pentose phosphate pathway have been identified. Additionally, the role of the aldose reductase pathway in cardiac hypertrophy has not been elucidated. Considerable work has identified increased expression of GFAT as well as increased flux through the hexosamine biosynthetic pathway in pressure-overload hypertrophy and heart failure.
Legend: Key changes in the metabolic pathway have been colour coded. Green: increased; Red: decreased; Blue: no change; Black: unknown.
Abbreviations: F-6-P, fructose-6-phosphate; G-6-P, glucose-6-phosphate; G6PD, glucose-6-phosphate dehydrogenase; GFAT, glutamine fructose-6-phosphate amidotransferase; GLUT, glucose transporter; LDH, lactate dehydrogenase; ME, malic enzyme; NADH, reduced nicotinamide adenine dinucleotide; OMC, oxoglutarate-malate carrier; TCA, tricarboxylic acid.
KATP channel-dependent metaboproteome decoded: systems approaches to heart failure prediction, diagnosis, and therapy
Forecasting cardiac outcome from a presymptomatic proteomic signature. (A) At baseline, no differences were observed in cardiac structure or function between age- and sex-matched wild-type and Kir6.2 KATP channel knockout cohorts. Left ventricular tissue was extracted for proteomic analysis by comparative 2D gel electrophoresis resolution. (B) Statistical analysis of quantified 2D gel images indicated significant differences in 9% of detected protein species, subsequently isolated and identified by tandem mass spectrometry and categorized by primary protein function, revealing a metabolism-centric theme of protein change. (C) Altered proteins served as focus proteins for network analysis, with Ingenuity Pathways Knowledge Base expanding the KATP channel-dependent changes into a broader network neighbourhood, which reinforced the metabolic focus of measured changes both by ontological function (shown) and by ontological assessment of overrepresented biological processes (not shown).34
(D) Bioinformatic interrogation of proteome changes and their expanded network, for the presence of potential adverse effects, indicated an overrepresentation of markers associated with susceptibility to cardiac disease. Subsequent experimental imposition of graded stress validated disease susceptibility, with the Kir6.2 deficient cohort exhibiting progressively deleterious structural and functional cardiac defects, ultimately decreasing survival. *P< 0.05 vs. WT counterparts; **P< 0.01 vs. WT counterparts.
Parathyroid hormone is a DPP-IV inhibitor and increases SDF-1-driven homing of CXCR4+ stem cells into the ischaemic heart
Mechanism of PTH-mediated cardioprotection. PTH administration after MI induces mobilization of stem cells from the BM to the peripheral blood. These stem cells circulate to the damaged heart, where they are incorporated by interaction of intact myocardial SDF-1 and the homing receptor CXCR4. PTH inhibits DPP-IV activity and thereby prevents the degradation of intact SDF-1. Thus, an increased amount of SDF-1 improves homing of mobilized CXCR4+ cells. Altogether, PTH reduced cardiac remodelling after MI and enhanced cardiac function by attenuating the development of ischaemic cardiomyopathy.
Proteins mediating collagen biosynthesis and accumulation in arterial repair: novel targets for anti-restenosis therapy
Effects of matrix metalloproteinases (MMPs) in the vessel wall.
Proteins mediating collagen biosynthesis and accumulation in arterial repair: novel targets for anti-restenosis therapy
Receptor signaling pathways affecting extracellular matrix synthesis in the arterial wall in response to vascular injury. See text for details.
Red arrow indicates inhibition, green arrow indicates activation, yellow arrow indicates signal transduction to the nucleus. VSMC, vascular smooth muscle cell. TGF-β, transforming growth factor beta, PDGF, platelet-derived growth factor. MMPs, matrix metalloproteinases, ET, endotheline
Endothelial cell-borne platelet bridges selectively recruit monocytes in human and mouse models of vascular inflammation
The mechanisms by which secretory SMCs promote the recruitment of monocytes from flowing blood.
The routes by which inflammatory leucocytes are recruited to the artery wall and are enriched within the atherosclerotic environment are poorly described. Here, observations using co-culture and animal models of the diseased artery wall, allied with data from previous studies, show that interactions between cells of the diseased artery wall can generate signals that coordinate the preferential recruitment of monocytes from flowing blood. This process depends upon crosstalk between secretory smooth muscle cells (SMCs) and endothelial cells (ECs), which leads to the plasmin-dependent generation of active transforming growth factor-β1 (TGF-β1). This agent induces von Willebrand factor (vWF) expression on ECs so that platelets are recruited and activated and act as an adhesive bridge between the EC surface and the flowing blood. Monocytes are preferentially recruited from blood by tethering to platelet P-selectin and preferentially activated by CCL2 (MCP-1), which is released from ECs by the action of the platelet chemokine CXCL4 (PF4; platelet factor 4), stimulating the endothelial cell receptor CXCR3b.
This process greatly enriches for monocytes at the EC surface and supports monocyte transmigration. Thus, a series of cellular and molecular interactions initiated by cells resident within the diseased artery are shown to result in the specific recruitment of the predominant population of inflammatory leucocytes recruited during atherogenesis.
Function and regulation of phosphatase-1-inhibitor-1 (I-1) and constitutively active I-1c.
Control of protein phosphorylation/dephosphorylation events occurs through regulation of protein kinases and phosphatases. The phosphatase type 1 comprises the main activity of Ser/Thr phosphatases in the heart. Inhibitor-1 (I-1) specifically inhibits phosphatase-1. I-1 was found to be downregulated in human heart failure but hyperactive in human atrial fibrillation, implicating I-1 in the pathogenesis of heart failure and arrhythmias. (A) I-1 represents a distal element of Β-adrenoceptor (AR) signalling, which allows amplification of protein kinase A (PKA)-mediated effects on the phosphorylation state of regulatory proteins. (B) I-1 consists of 171 amino acids (aa) and an N-terminal consensus motif (KIQF) that is essential for I-1 binding to phosphatase-1. I-1 becomes activated upon phosphorylation by cAMP-dependent PKA at Thr35, resulting in a potent inhibition of phosphatase-1. In contrast, phosphorylation at Ser67 by protein kinase Cα (PKCα) attenuates its inhibitory activity towards phosphatase-1. Phosphatase-2A (PP-2A) and Ca2+-dependent phosphatase-2B (PP-2B, calcineurin) dephosphorylate I-1 at Thr35 and thus reverses its inhibitory activity on phosphatase-1. (C) Replacement of Thr35 by phosphomimetic aspartic acid (T35D) and C-terminal truncation to 65 aa yields a constitutively active form of I-1 (I-1c) that is independent of PKA, PP-2A, and PP-2B.
Disruption of fuel servicing in the myocardium: from ‘eutaxy and efficiency’ to ‘ataxy and inefficiency’
Deletion of PGC-1β leads to disruption of mitohormesis and arrhythmias in cardiomyocytes.
A tentative scheme is shown that depicts how PPAR-γ or PGC-1s stimulation and suppression modulate electrical activity in cardiomyocytes. For biological activity, PPAR-γ needs coactivation by PGC-1α/β. These coactivators are inducible and play a vital role in cellular ATP production and mitochondrial function.
Exogenous stress stimulates the expression of chemokines and adhesion molecules in the heart. These molecules promote atrial fibrosis on the one hand, and macrophage recruitment and inflammation on the other, which result in heart failure and arrhythmias substrate formation.
The suppression or deletion of PGC-1β seems to result in variable electrical instabilities and arrhythmias, especially during adrenergic stress. An imbalance of mitochondrial ATP production is noted as well, which is arrhythmogenic by itself. The stimulation of PPARγ; blocks stress-induced expression of chemokines and adhesion molecules. The recruitment of macrophages from storage sites such as splenic red pulp (red bar) is also suppressed, resulting in an improvement of atrial fibrosis and mitochondrial function. Details of signaling cascades mediated by the PPARγ-PGC-1 axis that leads to electrical instability are waiting to be elucidated.
Schematic diagram showing the proposed mechanisms by which calpains participate in reperfusion injury and in the cardioprotective effects of preconditioning and postconditioning. NCX, Na+/Ca2+ exchanger; NBC, Na+/HCO3− cotransporter; NHE, Na+/H+ exchanger.
Mechanisms and consequences of altered Ca2+ handling in cardiomyocytes during initial reperfusion. Main events are connected through black lines, whereas red lines indicate important modulating factors. GCPR, G-coupled protein receptors; IP3, inositol trisphosphate; NOS, nitric oxide synthase; ROS, reactive oxygen species.
Pathophysiological role of SR–mitochondria functional units on lethal reperfusion injury. Calcium overload and re-energization cause calcium oscillations. ROS favour oscillations and trigger MPT. mNCX, mitochondrial Na/Ca exchanger; MCU: mitochondrial calcium uniporter.
Myocardial injury in ischemia–reperfusion develops in two phases. Reperfusion injury adds to the injury developed during initial ischemia (resulting in the red curve). The extent of reperfusion injury can be influenced by protective procedures, such as postconditioning or protective agents, applied during the first minutes of reperfusion (resulting in the blue curve). When the myocardium is not reperfused, it becomes entirely subject to ischemic cell death (broken black curve). While the past dogma was that protection against ischemia–reperfusion injury achieved by the pre-ischemic application of preconditioning is solely achieved by an effect on ischemic injury, it is now thought that this protection is also largely due to an effect on the causes of reperfusion injury (blue arrows).
Mitochondrial connexin43 as a new player in the pathophysiology of myocardial ischaemia–reperfusion injury
Scheme summarizing the potential roles of Cx43 in the pathophysiology of ischaemia–reperfusion. Solid lines indicate roles for which there is experimental evidence. Broken lines indicate phenomena for which available evidence has been obtained under conditions other than ischaemia–reperfusion. PK, protein kinases; Src, Src tyrosine kinase.
Mitochondrial connexin43 as a new player in the pathophysiology of myocardial ischaemia–reperfusion injury
Potential mechanisms by which mitochondrial Cx43 could participate in ischaemic pharmacological (diazoxide) preconditioning. Monomeric Cx43 (in blue) could modulate mitochondrial K+ATP channels (in brown), but also the effects of diazoxide on the respiratory chain (in dark gray).103 Cx43 hemichannels could favor H+ and K+ leak resulting in protective mild uncoupling104 and swelling.105,106
Scheme of the pathogenesis of acute reperfusion injury. Reperfusion reactivates ATP production in mitochondria (Mito). Recovering energy production (High ATP) activates the Ca2+ pump (SERCA) of the sarcoplasmic reticulum (SR), which clears the cytosol from Ca2+ overload accumulated during ischemia. Repetitive release of Ca2+ through the ryanodine receptor Ca2+ release channel (RyR) and reuptake into the SR leads to Ca2+ oscillations with high cytosolic peak Ca2+ concentrations. This high Ca2+ together with ATP provokes myofibrillar hypercontracture (Ca2+ contracture) and subsequent disruption of cells (Necrosis). Ca2+ uptake through the uniporter into mitochondria causes the opening of mitochondrial permeability transition pores (mPTP) and cytochrome c (Cyt c) release. The former leads to failure of energy production (low ATP), and the latter activates apoptosis. Low ATP induces rigor contracture of the myofibrils, again leading to cell disruption. Protection by reperfusion injury salvage kinase pathways (RISK) may interfere favourably at the SR or at mitochondria.