thymosin-beta(4) and Muscular-Dystrophy--Duchenne

Thymosin beta-4 (Tbeta4) is a ubiquitous protein with many properties relating to cell proliferation and differentiation that promotes wound healing and modulates inflammatory mediators. We studied the effects of chronic administration of Tbeta4 on the skeletal and cardiac muscle of dystrophin deficient mdx mice, the mouse model of Duchenne muscular dystrophy. Female wild type (C57BL10/ScSnJ) and mdx mice, 8-10 weeks old, were treated with 150 microg of Tbeta4 twice a week for 6 months. To promote muscle pathology, mice were exercised for 30 minutes twice a week. Skeletal and cardiac muscle function were assessed via grip strength and high frequency echocardiography. Localization of Tbeta4 and amount of fibrosis were quantified using immunohistochemistry and Gomori's tri-chrome staining, respectively. Mdx mice treated with Tbeta4 showed a significant increase in skeletal muscle regenerating fibers compared to untreated mdx mice. Tbeta4 stained exclusively in the regenerating fibers of mdx mice. Although untreated mdx mice had significantly decreased skeletal muscle strength compared to untreated wild type, there were no significant improvements in mdx mice after treatment. Systolic cardiac function, measured as percent shortening fraction, was decreased in untreated mdx mice compared to untreated wild type and there was no significant difference after treatment in mdx mice. Skeletal and cardiac muscle fibrosis were also significantly increased in untreated mdx mice compared to wild type, but there was no significant improvement in treated mdx mice. In exercised dystrophin deficient mice, chronic administration of Tbeta4 increased the number of regenerating fibers in skeletal muscle and could have a potential role in treatment of skeletal muscle disease in Duchenne muscular dystrophy.

Topics: Animals; Dystrophin; Female; Heart; Immunohistochemistry; Mice; Mice, Inbred C57BL; Muscle, Skeletal; Muscular Dystrophy, Duchenne; Thymosin

In the dystrophin-deficient mdx mice, an animal model of Duchenne muscular dystrophy (DMD), damaged skeletal muscles are efficiently regenerated and thus the animals thrive. The phenotypic differences between DMD patients and mdx mice suggest the existence of factors that modulate the muscle wasting in the mdx mice. To identify these factors, we searched for mRNAs affected by the mdx mutation using cDNA microarrays with newly established skeletal muscle cell lines derived from mdx and normal mice. We found that genes encoding thymosin beta4, frizzled related protein 2 (FRP2), and regeneration-associated muscle protease (RAMP) are up-regulated in skeletal muscle of mdx mice. Thymosin beta4 was induced in both regenerating muscle fibers and inflammatory cells after muscle injury. It stimulated migration and chemotaxis of myoblasts. FRP2 was dramatically induced upon muscle injury. RNA interference-mediated knockdown of FRP2 mRNA in myoblasts resulted in a massive cell death. Thus FRP2 may enhance the survival rate of myoblasts in the regenerative regions. RAMP mRNA was specifically induced in the regenerating areas of injured skeletal muscle. Expression of RAMP and FRP2 was much lower in individual muscle cell lines derived from biopsy specimens from several DMD patients compared to in a normal muscle cell line. Above results suggest that thymosin beta4, FRP2, and RAMP may play roles in the regeneration of skeletal muscle and that down-regulation of these molecules could be involved in the progression of DMD in humans.

Topics: Animals; Cells, Cultured; Gene Expression; Humans; Membrane Proteins; Metalloendopeptidases; Mice; Mice, Inbred mdx; Muscle, Skeletal; Muscular Dystrophy, Duchenne; Myoblasts; Regenerative Medicine; RNA, Messenger; Serine Endopeptidases; Serine Proteases; Thymosin