Background Cardiomyopathy is among the leading causes of death in systemic sclerosis (SSc). Endothelial cell apoptosis with reduced capillary density, perivascular inflammation, myofibroblast differentiation and accumulation of collagen are typical histopathological features observed in the myocardium of SSc patients without clinically manifest cardiac involvement . Experimental evidence indicates that manifestations of SSc-related cardiomyopathy may be mimicked by murine models of SSc, especially Fra-2 transgenic mice . Urokinase-type plasminogen activator receptor (uPAR)-deficient mice are a recently described animal model displaying important histopathological hallmarks of SSc, such as dermal fibrosis, reduced dermal capillary density and pulmonary fibrosis .
Objectives In the present study, we investigated whether uPAR-deficient mice could display the histopathological features of SSc-related cardiomyopathy.
Methods Left ventricular myocardium sections from uPAR-deficient mice (n=14) and wild-type littermates (n=13) at 12 and 24 weeks of age were stained with hematoxylin-eosin for routine histology and Picrosirius red for the analysis of collagen content. Myofibroblast and microvessel counts in myocardium sections were determined by immunofluorescence for alpha-smooth muscle actin and the pan-endothelial cell marker CD31, respectively. Endothelial cell apoptosis was assessed by a combined TUNEL/CD31 immunofluorescence assay. The expression of the native full-length form of uPAR in left ventricular myocardium samples from SSc patients (n=5) and age-matched and sex-matched controls (n=7) was determined by immunohistochemistry and immunofluorescence.
Results The myocardium of 24-week-old uPAR-deficient mice displayed focal ischemic lesions with hypertrophy of cardiomyocytes, severe myofibril rarefaction and contraction band necrosis. At 24 weeks of age, interstitial and perivascular collagen deposition (Picrosirius red-positive area) and myofibroblast counts were significantly greater in myocardial tissue of uPAR-deficient mice than in wild-type littermates (both p<0.001). In 24-week-old uPAR-deficient mice, myocardial fibrosis was paralleled by endothelial cell apoptosis and reduced capillary density, as shown by a significant increase in the percentage of apoptotic endothelial cells and a significant decrease in microvessel counts compared with wild-type littermates (both p<0.001). Full-length uPAR expression was significantly downregulated in the stromal compartment of SSc myocardium compared with controls (p<0.001), especially in microvessels and fibroblasts.
Conclusions Typical histopathological features of SSc-related cardiomyopathy, including foci of contraction band necrosis, endothelial cell apoptosis with reduced capillary density, profibrotic myofibroblast differentiation and collagen accumulation, are mimicked by uPAR-deficient mice. Moreover, the downregulation of uPAR in the myocardium of SSc patients may suggest similar underlying pathogenetic mechanisms. Thus, uPAR-deficient mice might be a preclinical model to study the mechanisms and therapeutic approaches of myocardial involvement in SSc.
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Disclosure of Interest None declared
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