Clusterin (7. Heart)

In the normal heart, abundant clusterin mRNA and protein are expressed in atrial myocytes; no expression is detected in ventricular myocytes. To provide clues about the role of clusterin in the heart, the response of clusterin to heart disease, including three models of myocarditis and two models of in vivo pressure overload hypertrophy, were examined. In the disease model studied extensively, myosin-induced myocarditis, in situ hybridization detected induction of clusterin mRNA in ventricular myocytes immediately before histological evidence of injury. Clusterin message in ventricular myocytes reached high levels as myocarditis became more severe. Evidence of early clusterin induction, before inflammation and injury, also occurred in viral myocarditis. Clusterin mRNA was not present in the inflammatory or interstitial cells during myocarditis. In areas of severe inflammation and myocardial fiber degeneration, clusterin showed a gradient of expression, with highest levels in myocytes immediately surrounding the lesion and diminishing with increasing distance. Clusterin protein also accumulated in myocytes at the interface between degenerated myocardial tissue and the surrounding cardiac tissue. During cardiac hypertrophy that occurred without associated inflammation or cell damage, ventricular clusterin mRNA was not detected. When ischemic damage accompanied hypertrophy, clusterin was induced in the ventricular myocytes near the lesion borders. The correlation of clusterin induction with ventricular tissue damage, but not hypertrophy, suggests that clusterin is a repair response protein. It is proposed that clusterin functions to limit tissue injury and/or promote tissue remodeling ^Ref .

Clusterin-deficient and wild-type mice exhibited similar initial onset of myocarditis, as evidenced by the induction of two early markers of the t cell-mediated immune response, MHC-II and TNF receptor p55. Furthermore, autoantibodies against the primary antigen cardiac myosin were induced to the same extent. Although the same proportion of challenged animals exhibited some degree of inflammatory infiltrate, inflammation was more severe in clusterin-deficient animals. Inflammatory lesions were more diffuse and extensive in clusterin-deficient mice, particularly in females. In marked contrast to wild-type animals, the development of a strong generalized secondary response against cardiac antigens in clusterin-deficient mice was predictive of severe myocarditis.Wild-type mice with a strong Ab response to secondary antigens appeared to be protected from severe inflammation.After resolution of inflammation, clusterin-deficient, but not wild-type, mice exhibited cardiac function impairment and severe myocardial scarring. These results suggest that clusterin limits progression of autoimmune myocarditis and protects the heart from postinflammatory tissue destruction ^Ref .

Clusterin is selectively deposited in the infarcted areas of human myocardium. Clusterin deposits were observed in the heart tissue of 10 patients whose infarcted lesions were 8 hr to 14 days old, but not in patients who died from other causes. Clusterin co-localized with the komplement membrsne attack complex on the surface of damaged cardiomyocytes. In normal myocardium, only endothelial lining of blood vessels occasionally stained positive for clusterin.the 80,000 MW clusterin was also detected by Western blot analysis in extracts of myocardial infarction lesions, but only faintly in extracts of normal heart. As clusterin has apparently failed in protecting myocardium against complement-mediated cell injury its main role might be to participate in the clearance of damaged and necrotic tissue ^Ref .

Sprague-Dawley rats underwent permanent coronary ligation or sham operation. Hearts were harvested at 6 hours and at 2, 14, and 28 days after infarction. Cardiac clusterin expression was examined by immunohistoche­mistry and in situ hybridization. Left ventricular clusterin staining was evident at 6 hours and 2 days after myocardial infarction, although not at later time periods. Clusterin was localized to peri-infarct zone myocytes and endothelial cells of this region, and local synthesis of clusterin by myocytes was confirmed by in situ hybridization. Clusterin was not present in inflammatory cells or in left ventricular tissue distant from the infarct.the distribution of clusterin was different from the membrane attack complex of complement (C5b-9), with the latter being present diffusely throughout the infarct zone. Although the role of cardiac clusterin is not known, we speculate that clusterin‘s co­hesive properties serve to promote myocyte interactions that are perturbed in the peri-infarct zone after myocardial infarction ^Ref .

The relationship between clusterin and activated complement in human heart infarction was examined and the effect of this protein on ischemic rat neonatal cardiomyoblasts (H9c2) and isolated adult ventricular rat cardiomyocytes as in vitro models of acute myocardial infarction was evaluated. Clusterin protects cells by inhibiting complement and colocalizes with complement on jeopardized human cardiomyocytes after infarction. The distribution of clusterin and complement factor C3d was evaluated in the infarcted human heart. The protein expression of clusterin in ischemic H9c2 cells was also analyzed. The binding of endogenous and purified human clusterin on H9c2 cells was analyzed by flow cytometry. Furthermore, the effect of clusterin on the viability of ischemically challenged H9c2 cells and isolated adult ventricular rat cardiomyocytes was analyzed. In human myocardial infarcts, clusterin was found on scattered, morphologically viable cardiomyocytes within the infarcted area that were negative for complement. In H9c2 cells, clusterin was rapidly expressed after ischemia. Its expression was reduced after reperfusion. Clusterin bound to single annexin V-positive or annexin V and propidium iodide-positive H9c2 cells. Clusterin inhibited ischemia-induced death in H9c2 cells as well as in isolated adult ventricular rat cardiomyocytes in the absence of complement.We conclude that ischemia induces the upregulation of clusterin in ischemically challenged, but viable, cardiomyocytes. These data suggest that clusterin protects cardiomyocytes against ischemic cell death via a complement-independent pathway ^Ref .

EtOH-exposed canine fetal myoblasts underwent apoptosis in a concentration- and time-dependent manner. Expression of clusterin by cDNA transfection markedly reduced EtOH-induced apoptosis in the cells. Clusterin expression also restored partially the mitochondrial membrane potential and prevented the release of cytochrome-c from mitochondria into cytoplasma. Thus, clusterin serves as a cytoprotective protein that protects cardiac stem cells against EtOH cytotoxicity ^Ref .