Role of healing-specific-matricellular proteins and matrix metalloproteinases in age-related enhanced early remodeling after reperfused STEMI in dogs

We assessed whether aging augments left ventricular (LV) damage, remodeling, and dysfunction and alters expression of healing-specific-matricellular proteins (HSMPs), matrix metalloproteinases (MMPs) and other pertinent proteins after acute reperfused-ST-segment-elevation myocardial infarction (RSTEMI) in the dog model. The findings suggest a novel role for HSMPs, MMPs, and the other proteins in the age-related increase in LV damage, remodeling, and dysfunction. Potentially detrimental effects of the altered proteins appear to outweigh beneficial effects and contribute to adverse outcome. Deleterious changes include the increase in matrix-degrading MMPs, inducible nitric oxide synthase (iNOS) and pro-inflammatory cytokines interleukin (IL)-6 and tumor necrosis factor (TNF)-alpha, HSMPs such as secreted-protein-acidic-and-rich-in-cysteine (SPARC) and osteopontin (OPN), the blunted increase in endothelial-NOS (eNOS), and the decrease in IL-10 and neuronal NOS (nNOS). Potentially beneficial changes include increases in the HSMP secretory-leucocyte-protease-inhibitor (SLPI) and cytokine transforming growth factor (TGF)-beta(1). Targeting these proteins may mitigate enhanced LV remodeling and dysfunction with aging.     

Isothiocyanates sensitize the effect of chemotherapeutic drugs via modulation of protein kinase C and telomerase in cervical cancer cells

We determined effects of the vasopeptidase inhibitor (VPI) omapatrilat and angiotensin II type 1 receptor (AT(1)R) blocker (ARB) candesartan in rats during healing between day-2 and day-21 after reperfused myocardial infarction (RMI) on left ventricular (LV) remodeling and function, and regional matrix metalloproteinase (MMP)-9, tissue inhibitor of MMP (TIMP)-3, inducible-nitric-oxide-synthase (iNOS), oxidant-generating myeloperoxidase (MPO), and cytokines tumor-necrosis-factor (TNF)-alpha, interleukin (IL)-6 and IL-10, and transforming-growth-factor (TGF)-beta(1), and collagens. Compared to RMI-placebo, both agents reversed adverse LV remodeling and systolic and diastolic dysfunction, improved collagen remodeling, and normalized MMP-9 (activity, protein, and mRNA), TIMP-3 (protein and mRNA), and iNOS, MPO, TNF-alpha, IL-6, and TGF-beta(1) proteins, and improved MMP-9/TIMP-3 balance and IL-10 levels in previously ischemic zones. The results suggest that modulation of matrix proteases, oxidants, cytokines, and NOSs with omapatrilat and candesartan contribute to reversal of adverse collagen and LV remodeling and attenuation of LV dysfunction during healing after RMI.     

Activation and inactivation of volume-sensitive taurine efflux from rat mammary gland

Persistent left ventricular (LV) dysfunction after reperfused myocardial infarction (RMI) is a significant problem and angiotensin II (AngII) type 1 receptor (AT1R) blockers (ARBs) may limit reperfusion injury involving upregulation of AngII type 2 receptors (AT2R). To determine whether ARBs valsartan and irbesartan limit reperfusion injury and upregulate AT2R protein during RMI, we randomized dogs with anterior RMI (90 min ischemia; 120 min reperfusion) to 4 groups [valsartan (n = 6); irbesartan (n = 9); vehicle controls (n = 8); and sham (n = 6)] and measured serial in vivo hemodynamics, LV systolic and diastolic function, and inhibition of AngII pressor responses to the ARBs, and ex vivo infarct size, and regional AT1R and AT2R protein expression at the end of the reperfusion. Compared to the control group, both ARBs significantly limited the increase in left atrial pressure, promptly limited the deterioration of LV dP/dtmax, dP/dtmin, ejection fraction and diastolic function, limited infarct expansion and thinning, and limited infarct size. Importantly, both ARBs increased AT2R protein in the postischemic reperfused zone, with no change in AT1R protein. There were no changes in the sham group. The results suggest that limitation of myocardial injury associated with AT1R blockade combined with upregulation of AT2R protein expression contributes to the cardioprotective effects of ARBs during RMI. This beneficial effect of ARBs on persistent LV dysfunction after RMI should be evaluated in the clinical setting to determine the relative benefit of ARBs in patients who undergo reperfusion therapy for acute coronary syndromes.     

AT1 Receptor blockade limits myocardial injury and upregulates AT2 receptors during reperfused myocardial infarction

Persistent left ventricular (LV) dysfunction after reperfused myocardial infarction (RMI) is a significant problem and angiotensin II (AngII) type 1 receptor (AT₁R) blockers (ARBs) may limit reperfusion injury involving upregulation of AngII type 2 receptors (AT₂R). To determine whether ARBs valsartan and irbesartan limit reperfusion injury and upregulate AT₂R protein during RMI, we randomized dogs with anterior RMI (90 min ischemia; 120 min reperfusion) to 4 groups [valsartan (n = 6); irbesartan (n = 9); vehicle controls (n = 8); and sham (n = 6)] and measured serial in vivo hemodynamics, LV systolic and diastolic function, and inhibition of AngII pressor responses to the ARBs, and ex vivo infarct size, and regional AT₁R and AT₂R protein expression at the end of the reperfusion. Compared to the control group, both ARBs significantly limited the increase in left atrial pressure, promptly limited the deterioration of LV dP/dt_max, dP/dt_min, ejection fraction and diastolic function, limited infarct expansion and thinning, and limited infarct size. Importantly, both ARBs increased AT₂R protein in the postischemic reperfused zone, with no change in AT₁R protein. There were no changes in the sham group. The results suggest that limitation of myocardial injury associated with AT₁R blockade combined with upregulation of AT₂R protein expression contributes to the cardioprotective effects of ARBs during RMI. This beneficial effect of ARBs on persistent LV dysfunction after RMI should be evaluated in the clinical setting to determine the relative benefit of ARBs in patients who undergo reperfusion therapy for acute coronary syndromes.     

AT1 receptor blockade alters metabolic, functional and structural proteins after reperfused myocardial infarction: detection using proteomics

Angiotensin II (AngII) type 1 receptor (AT1R) blockers (ARBs) limit left ventricular (LV) dysfunction and necrosis after reperfused myocardial infarction (RMI) and proteomics can detect changes in protein levels after injury. We applied proteomics to detect changes in levels of specific protein in the ischemic zone (IZ) and non-ischemic zone (NIZ) of dog hearts after in vivo RMI (90 min of anterior ischemia; 120 min of reperfusion) and treatment with intravenous vehicle (control) and the ARBs valsartan or irbesartan (10 mg/kg) over 30 min before RMI. We also assessed LV function, infarction and apoptosis. Both ARBs limited the RMI-induced LV dysfunction, infarct size and apoptosis. Proteomics detected differential expression of 5 randomly selected proteins in the IZ compared to the NIZ after RMI: decrease in a subunit of ATP synthase isoform precursor (consistent with increased conversion to a subunit under metabolic stress), M chain creatine kinase (consistent with cellular damage) and ventricular myosin light chain-1 (consistent with structural damage and decreased contractility); and increase in NAD+ -isocitrate dehydrogenase (ICDH) and alpha subunit and ATP synthase D chain (mitochondrial, consistent with metabolic dysfunction). Importantly, changes in NAD+ -ICDH and ATP synthase D chain were reversed by ARB therapy. Thus, proteomics can detect regional changes in metabolic, contractile, and structural proteins after RMI and several of these proteins are favorably modified by ARBs, suggesting that they may be novel therapeutic targets.     

AT2 receptor and apoptosis during AT1 receptor blockade in reperfused myocardial infarction in the rat

We assessed whether upregulation of the angiotensin II (AngII) type 2 receptor (AT2R) during AngII type 1 receptor (AT1R) blockade might induce apoptosis in the in vivo rat model of reperfused myocardial infarction (RMI) and whether addition of an AT2R blocker abolishes that effect. We measured in vivo hemodynamics and left ventricular (LV) systolic and diastolic function (echocardiograms/Doppler), and ex vivo infarct size (triphenyl tetrazolium chloride), regional AT1R and AT2R proteins (immunoblots), and apoptosis (TUNEL assay and DNA ladder) after regional anterior RMI (60 min ischemia, 90 min reperfusion) in Sprague-Dawley rats randomized to intravenous AT1R blockade with candesartan (1 mg/kg, n = 9) or saline (controls, n = 14) over 30 min before RMI, and sham (n = 8). We also assessed the effect of AT2R blockade (PD123319, 10 mg/kg i.v.) plus candesartan on infarct size and apoptosis. Compared to controls, candesartan significantly (p < 0.001) limited increases in left atrial pressure, improved positive LV dP/dtmax and negative dP/dtmin, normalized LV ejection fraction, improved LV diastolic function, limited infarct expansion, decreased infarct size and apoptosis, and increased AT2R protein (not AT1R) in the reperfused ischemic zone. There were no changes in sham hearts. PD123319 abolished the candesartan-induced decrease in infarct size and LV dysfunction but not the decrease in apoptosis. Thus, during AT1R blockade in the in vivo rat model of RMI, regional AT2R upregulation contributes to the beneficial effect on infarct size and LV dysfunction but not on apoptosis, suggesting that the apoptosis is AT1R not AT2R-mediated.     

AT1receptor blockade alters metabolic,functional and structural proteins after reperfused myocardial infarction: Detection using proteomics

Angiotensin II (AngII) type 1 receptor (AT₁R) blockers (ARBs) limit left ventricular (LV) dysfunction and necrosis after reperfused myocardial infarction (RMI) and proteomics can detect changes in protein levels after injury. We applied proteomics to detect changes in levels of specific protein in the ischemic zone (IZ) and non-ischemic zone (NIZ) of dog hearts after in vivo RMI (90 min of anterior ischemia; 120 min of reperfusion) and treatment with intravenous vehicle (control) and the ARBs valsartan or irbesartan (10 mg/kg) over 30 min before RMI. We also assessed LV function, infarction and apoptosis. Both ARBs limited the RMI-induced LV dysfunction, infarct size and apoptosis. Proteomics detected differential expression of 5 randomly selected proteins in the IZ compared to the NIZ after RMI: decrease in subunit of ATP synthase isoform precursor (consistent with increased conversion to subunit under metabolic stress), M chain creatine kinase (consistent with cellular damage) and ventricular myosin light chain-1 (consistent with structural damage and decreased contractility); and increase in NAD⁺-isocitrate dehydrogenase (ICDH) and subunit and ATP synthase D chain (mitochondrial, consistent with metabolic dysfunction). Importantly, changes in NAD₊-ICDH and ATP synthase D chain were reversed by ARB therapy. Thus, proteomics can detect regional changes in metabolic, contractile, and structural proteins after RMI and several of these proteins are favorably modified by ARBs, suggesting that they may be novel therapeutic targets. (Mol Cell Biochem 263: 179–188, 2004)     

Atrial natriuretic peptide-dependent modulation of hypoxia-induced pulmonary vascular remodeling

Hypoxic stress upsets the balance in the normal relationships between mitogenic and growth inhibiting pathways in lung, resulting in pulmonary vascular remodeling characterized by hyperplasia of pulmonary arterial smooth muscle cells (PASMCs) and fibroblasts and enhanced deposition of extracellular matrix. Atrial natriuretic peptide (ANP) reduces pulmonary vascular resistance and attenuates hypoxia-induced pulmonary hypertension in vivo and PASMC proliferation and collagen synthesis in vitro. The current study utilized an ANP null mouse model (Nppa-/-) to test the hypothesis that ANP modulates the pulmonary vascular and alveolar remodeling response to normobaric hypoxic stress. Nine-10 wk old male ANP null (Nppa-/-) and wild type nontransgenic (NTG) mice were exposed to chronic hypoxia (10% O(2), 1 atm) or air for 6 wks. Measurement: pulmonary hypertension, right ventricular hypertrophy, and pulmonary arterial and alveolar remodeling were assessed. Hypoxia-induced pulmonary arterial hypertrophy and muscularization were significantly increased in Nppa-/- mice compared to NTG controls. Furthermore, the stimulatory effects of hypoxia on alveolar myofibroblast transformation (8.2 and 5.4 fold increases in Nppa-/- and NTG mice, respectively) and expression of extracellular matrix molecule (including osteopontin [OPN] and periostin [PN]) mRNA in whole lung were exaggerated in Nppa-/- mice compared to NTG controls. Combined with our previous finding that ANP signaling attenuates transforming growth factor (TGF)-beta-induced expression of OPN and PN in isolated PASMCs, the current study supports the hypothesis that endogenous ANP plays an important anti-fibrogenic role in the pulmonary vascular adaptation to chronic hypoxia.     

Secreted protein acidic and rich in cysteine (SPARC/osteonectin/BM-40) binds to fibrinogen fragments D and E, but not to native fibrinogen.

Secreted protein acidic and rich in cysteine (SPARC/osteonectin/BM-40) is a matricellular protein that functions in wound healing. Fibrinogen is a plasma protein involved in many aspects of wound healing, such as inflammation, fibrosis and thrombosis. In this study, the binding of SPARC to both native and plasmin-cleaved fibrinogen under physiological conditions was examined by the use of a surface plasmon resonance (SPR) biosensor. We show that SPARC binds to plasmin-cleaved fibrinogen, but not to native fibrinogen. SPARC binds to both fibrinogen fragments D and E fg D and fg E with similar dissociation constants (8.67 x 10(-8) M for Fg D and 1.61 x 10(-7) M for Fg E). Results from endothelial cell proliferation assays show that the binding of SPARC to Fg E suppressed the inhibition of proliferation by SPARC, whereas the binding of SPARC to Fg D did not influence the activity of SPARC on the cell cycle. The interaction of SPARC with fibrinogen fragments D and E, which are produced as a result of proteolytic activation of fibrinolysis, reveals potential storage sites in provisional extracellular matrix for SPARC during the wound healing process and indicates a regulatory role of SPARC in fibrinolysis and angiogenesis.     

TGF-β1 induces the expression of type I collagen and SPARC,and enhances contraction of collagen gels,by fibroblasts from young and aged donors

Fibroblasts have a major role in the synthesis and reorganization of extracellular matrix that occur during wound repair. An impaired biosynthetic or functional response of these cells to stimulation by growth factors might contribute to the delayed wound healing noted in aging. We, therefore, compared the responses of dermal fibroblasts from young and elderly individuals (26, 29, 65, 89, 90, and 92 years of age) to transforming growth factor-β1 (TGF-β1) with respect to: (1) the synthesis of type I collagen and SPARC (two extracellular matrix proteins that are highly expressed by dermal fibroblasts during the remodeling phase of wound repair) and (2) the contraction of collagen gels, an in vitro assay of wound contraction. With the exception of one young donor, all cultures exposed for 44 hours to 10 ng/ml TGF-β1 exhibited a 1.6- to 5.5-fold increase in the levels of secreted type 1 collagen and SPARC, relative to untreated cultures, and exhibited a 2.0- to 6.2-fold increase in the amounts of the corresponding mRNAs. Moreover, the dose-response to TGF-β1 (0.1–10 ng/ml), as determined by synthesis of type I collagen and SPARC mRNA, was as vigorous in cells from aged donors as in cells from a young donor. In assays of collagen gel contraction, fibroblasts from all donors were stimulated to a similar degree by 10 ng/ml TGF-β1. In conclusion, cells from both young and aged donors exhibited similar biosynthetic and contractile properties with exposure to TGF-β1. It therefore appears that the impaired wound healing noted in the aged does not result from a failure of their dermal fibroblasts to respond to this cytokine. © 1994 Wiley-Liss, Inc.     

SPARC (osteonectin/BM-40)

SPARC (Secreted ProteinAcidic and Rich in Cysteine) is a prototype of a family of biologically active glycoproteins that bind to cells and to extracellular matrix (ECM) components. It is expressed spatially and temporally during embryogenesis, tissue remodeling and repair. SPARC is a modular protein (34 kDa) comprised of three structural domains, one or more of which are implicated in the regulation of cell adhesion, proliferation, matrix synthesis/turnover. Rapid proteolysis of SPARC by extracellular proteases accounts for its transient detection in the extracellular environment. The proposed roles of SPARC in the development of cataracts and the regulation of angiogenesis during wound healing and tumor growth account for the recent attention it has received from the biomedical community.     

Angiotensin receptor blockade and angiotensin-converting-enzyme inhibition limit adverse remodeling of infarct zone collagens and global diastolic dysfunction during healing after reperfused ST-elevation myocardial infarction

To determine whether therapy with the angiotensin II type 1 receptor blocker (ARB) candesartan and the comparator angiotensin-converting-enzyme inhibitor (ACEI) enalapril during healing after reperfused ST-elevation myocardial infarction (RSTEMI) limit adverse remodeling of infarct zone (IZ) collagens and left ventricular (LV) diastolic dysfunction, we randomized 24 dogs surviving anterior RSTEMI (90-min coronary occlusion) to placebo, candesartan, and enalapril therapy between day 2 and 42. Six other dogs were sham. We measured regional IZ and non-infarct zone (NIZ) collagens (hydroxyproline; types I/III; cross-linking), transforming growth factor-β (TGF-β) and topography at 6 weeks, and hemodynamics, LV diastolic and systolic function, and remodeling over 6 weeks. Compared to sham, placebo-RSTEMI differentially altered regional collagens, with more pronounced increase in TGF-β, hydroxyproline, and type I, insoluble, and cross-linked collagens in the IZ than NIZ, and increased IZ soluble and type III collagens at 6 weeks, and induced persistent LV filling pressure elevation, diastolic and systolic dysfunction, and LV remodeling over 6 weeks. Compared to placebo-RSTEMI, candesartan and enalapril limited adverse regional collagen remodeling, with normalization of type III, soluble and insoluble collagens and decrease in pyridinoline cross-linking in the IZ at 6 weeks, and attenuation of LV filling pressure, diastolic dysfunction, and remodeling over 6 weeks. The results suggest that candesartan and enalapril during healing after RSTEMI prevent rather than worsen adverse remodeling of IZ collagens and LV diastolic dysfunction, supporting the clinical use of ARBs and ACEIs during subacute RSTEMI.     

Inhibition of matrix metalloproteinases improves left ventricular function in mice lacking osteopontin after myocardial infarction

Osteopontin (OPN) plays an important role in left ventricular (LV) remodeling after myocardial infarction (MI) by promoting collagen synthesis and accumulation. This study tested the hypothesis that MMP inhibition modulates post-MI LV remodeling in mice lacking OPN. Wild-type (WT) and OPN knockout (KO) mice were treated daily with MMP inhibitor (PD166793, 30 mg/kg/day) starting 3 days post-MI. LV functional and structural remodeling was measured 14 days post-MI. Infarct size was similar in WT and KO groups with or without MMP inhibition. M-mode echocardiography showed greater increase in LV end-diastolic (LVEDD) and end-systolic diameters (LVESD) and decrease in percent fractional shortening (%FS) and ejection fraction in KO-MI versus WT-MI. MMP inhibition decreased LVEDD and LVESD, and increased %FS in both groups. Interestingly, the effect was more pronounced in KO-MI group versus WT-MI (P < 0.01). MMP inhibition significantly decreased post-MI LV dilation in KO-MI group as measured by Langendorff-perfusion analysis. MMP inhibition improved LV developed pressures in both MI groups. However, the improvement was significantly higher in KO-MI group versus WT-MI (P < 0.05). MMP inhibition increased heart weight-to-body weight ratio, myocyte cross-sectional area, fibrosis and septal wall thickness only in KO-MI. Percent apoptotic myocytes in the non-infarct area was not different between the treatment groups. Expression and activity of MMP-2 and MMP-9 in the non-infarct area was higher in KO-MI group 3 days post-MI. MMP inhibition reduced MMP-2 activity in KO-MI with no effect on the expression of TIMP-2 and TIMP-4 14 days post-MI. Thus, activation of MMPs contributes to reduced fibrosis and LV dysfunction in mice lacking OPN.     

Role of matricellular proteins in cardiac tissue remodeling after myocardial infarction

After onset of myocardial infarction (MI), the left ventricle (LV) undergoes a continuum of molecular, cellular, and extracellular responses that result in LV wall thinning, dilatation, and dysfunction. These dynamic changes in LV shape, size, and function are termed cardiac remodeling. If the cardiac healing after MI does not proceed properly, it could lead to cardiac rupture or maladaptive cardiac remodeling, such as further LV dilatation and dysfunction, and ultimately death. Although the precise molecular mechanisms in this cardiac healing process have not been fully elucidated, this process is strictly coordinated by the interaction of cells with their surrounding extracellular matrix (ECM) proteins. The components of ECM include basic structural proteins such as collagen, elastin and specialized proteins such as fibronectin, proteoglycans and matricellular proteins. Matricellular proteins are a class of non-structural and secreted proteins that probably exert regulatory functions through direct binding to cell surface receptors, other matrix proteins, and soluble extracellular factors such as growth factors and cytokines. This small group of proteins, which includes osteopontin, thrombospondin-1/2, tenascin, periostin, and secreted protein, acidic and rich in cysteine, shows a low level of expression in normal adult tissue, but is markedly upregulated during wound healing and tissue remodeling, including MI. In this review, we focus on the regulatory functions of matricellular proteins during cardiac tissue healing and remodeling after MI.     

Selective spatiotemporal induction of matrix metalloproteinase-2 and matrix metalloproteinase-9 transcription after myocardial infarction

Myocardial remodeling after myocardial infarction (MI) is associated with increased levels of the matrix metalloproteinases (MMPs). Levels of two MMP species, MMP-2 and MMP-9, are increased after MI, and transgenic deletion of these MMPs attenuates post-MI left ventricular (LV) remodeling. This study characterized the spatiotemporal patterns of gene promoter induction for MMP-2 and MMP-9 after MI. MI was induced in transgenic mice in which the MMP-2 or MMP-9 promoter sequence was fused to the beta-galactosidase reporter, and reporter level was assayed up to 28 days after MI. Myocardial localization with respect to cellular sources of MMP-2 and MMP-9 promoter induction was examined. After MI, LV diameter increased by 70% (P < 0.05), consistent with LV remodeling. beta-Galactosidase staining in MMP-2 reporter mice was increased by 1 day after MI and increased further to 64 +/- 6% of LV epicardial area by 7 days after MI (P < 0.05). MMP-2 promoter activation occurred in fibroblasts and myofibroblasts in the MI region. In MMP-9 reporter mice, promoter induction was detected after 3 days and peaked at 7 days after MI (53 +/- 6%, P < 0.05) and was colocalized with inflammatory cells at the peri-infarct region. Although MMP-2 promoter activation was similarly distributed in the MI and border regions, activation of the MMP-9 promoter was highest at the border between the MI and remote regions. These unique findings visually demonstrated that activation of the MMP-2 and MMP-9 gene promoters occurs in a distinct spatial relation with reference to the MI region and changes in a characteristic time-dependent manner after MI.     

Cardiomyocyte-restricted restoration of nitric oxide synthase 3 attenuates left ventricular remodeling after chronic pressure overload

Although nitric oxide synthase (NOS)3 is implicated as an important modulator of left ventricular (LV) remodeling, its role in the cardiac response to chronic pressure overload is controversial. We examined whether selective restoration of NOS3 to the hearts of NOS3-deficient mice would modulate the LV remodeling response to transverse aortic constriction (TAC). LV structure and function were compared at baseline and after TAC in NOS3-deficient (NOS3(-/-)) mice and NOS3(-/-) mice carrying a transgene directing NOS3 expression specifically in cardiomyocytes (NOS3(-/-TG) mice). At baseline, echocardiographic assessment of LV dimensions and function, invasive hemodynamic measurements, LV mass, and myocyte width did not differ between the two genotypes. Four weeks after TAC, echocardiographic and hemodynamic indexes of LV systolic function indicated that contractile performance was better preserved in NOS3(-/-TG) mice than in NOS3(-/-) mice. Echocardiographic LV wall thickness and cardiomyocyte width were greater in NOS3(-/-) mice than in NOS3(-/-TG) mice. TAC-induced cardiac fibrosis did not differ between these genotypes. TAC increased cardiac superoxide generation in NOS3(-/-TG) but not NOS3(-/-) mice. The ratio of NOS3 dimers to monomers did not differ before and after TAC in NOS3(-/-TG) mice. Restoration of NOS3 to the heart of NOS3-deficient mice attenuates LV hypertrophy and dysfunction after TAC, suggesting that NOS3 protects against the adverse LV remodeling induced by prolonged pressure overload.     

Targeting the upregulation of reactive oxygen species subsequent to hyperglycemia prevents type 1 diabetic cardiomyopathy in mice

Cardiac oxidative stress is an early event associated with diabetic cardiomyopathy, triggered by hyperglycemia. We tested the hypothesis that targeting left-ventricular (LV) reactive oxygen species (ROS) upregulation subsequent to hyperglycemia attenuates type 1 diabetes-induced LV remodeling and dysfunction, accompanied by attenuated proinflammatory markers and cardiomyocyte apoptosis. Male 6-week-old mice received either streptozotocin (55 mg/kg/day for 5 days), to induce type 1 diabetes, or citrate buffer vehicle. After 4 weeks of hyperglycemia, the mice were allocated to coenzyme Q₁₀ supplementation (10 mg/kg/day), treatment with the angiotensin-converting-enzyme inhibitor (ACE-I) ramipril (3 mg/kg/day), treatment with olive oil vehicle, or no treatment for 8 weeks. Type 1 diabetes upregulated LV NADPH oxidase (Nox2, p22^phox, p47^phox and superoxide production), LV uncoupling protein UCP3 expression, and both LV and systemic oxidative stress (LV 3-nitrotyrosine and plasma lipid peroxidation). All of these were significantly attenuated by coenzyme Q₁₀. Coenzyme Q₁₀ substantially limited type 1 diabetes-induced impairments in LV diastolic function (E:A ratio and deceleration time by echocardiography, LV end-diastolic pressure, and LV −dP/dt by micromanometry), LV remodeling (cardiomyocyte hypertrophy, cardiac fibrosis, apoptosis), and LV expression of proinflammatory mediators (tumor necrosis factor-α, with a similar trend for interleukin IL-1β). Coenzyme Q_10's actions were independent of glycemic control, body mass, and blood pressure. Coenzyme Q₁₀ compared favorably to improvements observed with ramipril. In summary, these data suggest that coenzyme Q₁₀ effectively targets LV ROS upregulation to limit type 1 diabetic cardiomyopathy. Coenzyme Q₁₀ supplementation may thus represent an effective alternative to ACE-Is for the treatment of cardiac complications in type 1 diabetic patients.     

SPARC, a matricellular protein: at the crossroads of cell–matrix communication: [Matrix Biology (2000) 569–580]

The publisher regrets that the above article was published with several typographical errors. The corrected version appears on the following pages. SPARC is a multifunctional glycoprotein that belongs to the matricellular group of proteins. It modulates cellular interaction with the extracellular matrix (ECM) by its binding to structural matrix proteins, such as collagen and vitronectin, and by its abrogation of focal adhesions, features contributing to a counteradhesive effect on cells. SPARC inhibits cellular proliferation by an arrest of cells in the G1 phase of the cell cycle. It also regulates the activity of growth factors, such as platelet-derived growth factor (PDGF), fibroblast growth factor (FGF)-2, and vascular endothelial growth factor (VEGF). The expression of SPARC in adult animals is limited largely to remodeling tissue, such as bone, gut mucosa, and healing wounds, and it is prominent in tumors and in disorders associated with fibrosis. The crystal structure of two of the three domains of the protein has revealed a novel follistatin-like module and an extracellular calcium-binding (EC) module containing two EF-hand motifs. The follistatin-like module and the EC module are shared by at least four other proteins that comprise a family of SPARC-related genes. Targeted disruption of the SPARC locus in mice has shown that SPARC is important for lens transparency, as SPARC-null mice develop cataracts shortly after birth. SPARC is a prototypical matricellular protein that functions to regulate cell–matrix interactions and thereby influences many important physiological and pathological processes.     

SPARC-thrombospondin-2-double-null mice exhibit enhanced cutaneous wound healing and increased fibrovascular invasion of subcutaneous polyvinyl alcohol sponges.

Secreted protein acidic and rich in cysteine (SPARC) and thrombospondin-2 (TSP-2) are structurally unrelated matricellular proteins that have important roles in cell-extracellular matrix (ECM) interactions and tissue repair. SPARC-null mice exhibit accelerated wound closure, and TSP-2-null mice show an overall enhancement in wound healing. To assess potential compensation of one protein for the other, we examined cutaneous wound healing and fibrovascular invasion of subcutaneous sponges in SPARC-TSP-2 (ST) double-null and wild-type (WT) mice. Epidermal closure of cutaneous wounds was found to occur significantly faster in ST-double-null mice, compared with WT animals: histological analysis of dermal wound repair revealed significantly more mature phases of healing at 1, 4, 7, 10, and 14 days after wounding, and electron microscopy showed disrupted ECM at 14 days in these mice. ST-double-null dermal fibroblasts displayed accelerated migration, relative to WT fibroblasts, in a wounding assay in vitro, as well as enhanced contraction of native collagen gels. Zymography indicated that fibroblasts from ST-double-null mice also produced higher levels of matrix metalloproteinase (MMP)-2. These data are consistent with the increased fibrovascular invasion of subcutaneous sponge implants seen in the double-null mice. The generally accelerated wound healing of ST-double-null mice reflects that described for the single-null animals. Importantly, the absence of both proteins results in elevated MMP-2 levels. SPARC and TSP-2 therefore perform similar functions in the regulation of cutaneous wound healing, but fine-tuning with respect to ECM production and remodeling could account for the enhanced response seen in ST-double-null mice.     

Loss of insulin-like growth factor I receptor-dependent expression of p107 and cyclin A in cells that lack the extracellular matrix protein secreted protein acidic and rich in cysteine.

The extracellular matrix-associated glycoprotein secreted protein acidic and rich in cysteine (SPARC) has been implicated in the control of cell proliferation during tissue remodeling, wound healing, and malignant development. Here, we describe a novel mechanism through which SPARC influences cell cycle progression in embryonic fibroblasts derived from Sparc-nullizygous (-/-) mice. SPARC-deficient cells were indistinguishable from wild-type cells in their ability to initiate DNA synthesis after treatment with either fetal bovine serum or platelet-derived growth factor. In contrast, Sparc -/- cells responded poorly to activation of the insulin-like growth factor receptor (IGFI-R) by insulin. This defect was traced to reduced expression of the IGFI-R in Sparc -/- cells. Consistent with impaired cell cycle progression through S-phase, insulin-stimulated Sparc -/- cells also revealed reduced expression of two key regulators of S phase progression (cyclin A and thymidine kinase), whereas expression of the G1 phase progression regulators cmyc or cyclin D1 was unaffected. An examination of the status of retinoblastoma family pocket proteins in Sparc -/- cells revealed a selective and dramatic reduction in levels of the retinoblastoma-related protein p107. Exogenous platelet-derived growth factor restored expression of the IGFI-R and IGFI-R dependent DNA synthesis as well as induction of cyclin A, thymidine kinase, and p107 in insulin-stimulated Sparc -/- cells. These results suggest that SPARC-dependent matrix to cell interactions contribute to the regulation of p107 and cyclin A through IGFI-R dependent pathway(s).