Thrombin receptor induction by injury-related factors in human skeletal muscle cells

Thrombin is involved in tissue repair through its proteolytic activation of a specific thrombin receptor (PAR-1), Previous studies have shown that ser ine proteases and their inhibitors are involved in neuromuscular junction p lasticity. We hypothesized that thrombin could also be involved during skel etal muscle inflammation, Thus we investigated the expression of PAR-1 in h uman myoblasts and myotubes in vitro and its regulation by injury-related f actors. The functionality of this receptor was tested by measuring thrombin 's ability to elicit Ca2+ signals. Western blot analysis and immunocytochem istry demonstrated the presence of PAR-1 in myoblasts but not in myotubes u nless they were treated by tumor necrosis factor-alpha (10 ng/ml), interleu kin-1 beta (5 ng/ml), or transforming growth factor-beta (1) (10 ng/ml), Th e addition of 10 nM alpha -thrombin evoked a strong Ca2+ signal in myoblast s while a limited response in myotubes was observed, However, in the additi onal presence of injury-related factors, the amplitude of the Ca2+ response was significantly enhanced, representing 88, 65, 48% of their respective b asal level, compared to 27% of that obtained in controls. Moreover, immunoc hemical studies on human skeletal muscle biopsies of patients suffering fro m inflammatory myopathies showed an overexpression of PAR-1, These results suggest that PAR-1 synthesis may be induced in response to muscle injury, t hereby implicating thrombin signaling in certain muscle inflammatory diseas es. (C) 2001 Academic Press.