Increased expression of IGF-binding protein-5 in Duchenne Muscular Dystrophy (DMD) fibroblasts correlates with the fibroblast-induced downregulation of DMD myoblast growth: An in vitro analysis

In DMD the progressive loss of muscle ability and concomitant increasing fi brosis might originate from, besides other causes, the fibroblast paracrine inhibition of satellite cell "growth." In this study we report that in myo blast/fibroblast coculture experiments, the presence of DMD fibroblasts neg atively interfered with DMD myoblast growth to an extent directly proportio nal to the percentage of DMD fibroblasts present in the mixed-cell cultures . Moreover, the observation that media conditioned with proliferating DMD f ibroblasts inhibited the growth of DMD myoblasts more seriously than did co ntrol fibroblast-conditioned media suggested a paracrine effect by diffusib le factors. IGF-binding proteins could act as such diffusible factors; in f act, IGFBP-5 transcript increased threefold in DMD fibroblasts proliferatin g in DMD muscle extracts, whereas IGFBP-3 mRNA decreased. In addition, high levels of IGFBP-5 protein were detected in DMD fibroblast-conditioned medi a. In neutralizing IGFBP-5 in DMD fibroblast-conditioned media by means of specific antibodies, or inhibiting IGFBP-5 gene expression in DMD fibroblas ts by means of oligo antisense, the fibroblast-conditioned media lost inhib itory power over DMD myoblast proliferation. (C) 2000 Wiley-Liss, Inc.