SERINE PROTEINASE-INHIBITORS IN HUMAN SKELETAL-MUSCLE - EXPRESSION OFBETA-AMYLOID PROTEIN-PRECURSOR AND ALPHA(1)-ANTICHYMOTRYPSIN IN-VIVO AND DURING MYOGENESIS IN-VITRO

The balance of serine proteases and inhibitors in nerve and muscle is altered during programmed- and injury-induced remodeling. A serpin, al pha(1)-antichymotrypsin (alpha(1)-ACT), and Kunitz-inhibitor containin g forms of the beta-amyloid precursor protein (beta APP) may be import ant components of this balance. In the present study, we analyzed thei r expression in primary cultures of human myogenic (satellite) cells t hat mimic myogenic differentiation using Western blotting and immunocy tochemistry. In vitro results were compared to in vivo results from no rmal adult human skeletal muscle biopsies. Using an anti-alpha(1)-ACT polyclonal antibody, we detected a 62 kDa immunoreactive band both in cultured human myogenic cells (mononucleated myoblasts as well as mult i-nucleated myotubes) and in extracts of human muscle biopsies. With a polyclonal anti-beta APP antibody we found two bands (105 and 120 kDa ) in myoblasts and myotubes in culture. However, the same antibody rec ognized only a single band at 92 kDa in biopsies. By immunocytochemist ry both alpha(1)-ACT and beta APP were indistinctly present on localiz ed to the surface of myoblasts in culture. In contrast, these inhibito rs were dense on myotube surfaces, where they often formed distinct ag gregates and frequently co-localized. In permeabilized muscle cells, a lpha(1)-ACT and beta APP appeared to be localized to the perikarya of both myoblasts and myotubes. Confirming previous results, both alpha(1 )-ACT and beta APP were present at the neuromuscular junction in human muscle sections. These developmental changes found during in vitro my ogenesis for alpha(1)-ACT and beta APP, both serine protease inhibitor s, reinforce the hypothesis that regulation of the serine proteases an d serine protease inhibitors plays an important role in neuromuscular differentiation. (C) 1995 Wiley-Liss, Inc.