Osteoactivin upregulates expression of MMP-3 and MMP-9 in fibroblasts infiltrated into denervated skeletal muscle in mice

Abstract

. Osteoactivin upregulates expression of MMP-3 and MMP-9 in fibroblasts infiltrated into denervated skeletal muscle in mice. Am J Physiol Cell Physiol 289: C697-C707, 2005; doi:10.1152/ajpcell.00565.2004.-In this study, we examined pathophysiological roles of osteoactivin, a functionally unknown type I membrane glycoprotein, in mouse skeletal muscle atrophied by denervation (sciatic neurectomy). Denervation increased the amounts of osteoactivin, vimentin, matrix metalloproteinase-3 (MMP-3), and MMP-9 in mouse gastrocnemius muscle. Interestingly, immunohistochemical analysis revealed that vimentin, MMP-3, and MMP-9 were mainly present in fibroblast-like cells infiltrated into denervated mouse gastrocnemius muscle, whereas osteoactivin was expressed in the sarcolemma of myofibers adjacent to the fibroblast-like cells. On the basis of these findings, we reasoned that osteoactivin in myocytes was involved in activation of the infiltrated fibroblasts. To address this issue, we examined effects of osteoactivin on expression of MMPs in fibroblasts in vitro and in vivo. Overexpression of osteoactivin in NIH-3T3 fibroblasts induced expression of MMP-3, but not in mouse C 2C12 myoblasts, indicating that osteoactivin might functionally target fibroblasts. Treatment with recombinant mouse osteoactivin increased the amounts of collagen type I, MMP-3, and MMP-9 in mouse NIH-3T3 fibroblasts. The upregulated expression of these fibroblast marker proteins was significantly inhibited by heparin, but not by an integrin inhibitor, indicating that a heparin-binding motif in the extracellular domain might be an active site of osteoactivin. In osteoactivin-transgenic mice, denervation further enhanced expression of MMP-3 and MMP-9 in fibroblasts infiltrated into gastrocnemius muscle, compared with wild-type mice. Our present results suggest that osteoactivin might function as an activator for fibroblasts infiltrated into denervated skeletal muscles and play an important role in regulating degeneration/regeneration of extracellular matrix. sciatic neurectomy; Gpnmb family; C2C12 cells; NIH-3T3 cells; osteoactivin-transgenic mice DENERVATION (sciatic neurectomy) causes numerous changes in contractile, electrical, metabolic, and molecular properties of the muscle fiber membrane and sarcoplasm in hindlimb skeletal muscles (6, 10). Previous studies (21,22,32) have shown evidence that denervation alters interstitial spaces between muscle fibers: mononucleated cells are infiltrated into interstitial spaces of muscle fibers, and fibrosis occasionally occurs in the muscle. These findings suggest that the interaction between muscle fiber membrane and infiltrated cells might play an important role in degeneration or regeneration of denervated skeletal muscle. However, information on the interaction between the muscle fiber membrane and infiltrated cells is very little.To address this issue, we previously examined the expression of ϳ26,000 genes in rat gastrocnemius muscle atrophied by denervation or spaceflight using an Affymetrix DNA microarray...

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