Cytoskeletal disruption and small heat shock protein translocation immediately after lengthening contractions

Abstract

The purposes of this study were to determine whether, immediately after lengthening contractions, 1) levels of specific force-transmitting cytoskeletal elements are reduced in skeletal muscle cells and 2) cytosolic small heat shock proteins (HSPs) translocate to structures prone to disruption. Western blot analysis demonstrated decreased concentrations of z-disk proteins alpha-actinin and plectin and membrane scaffolding proteins dystrophin and beta-spectrin in muscle exposed to lengthening contractions compared with contralateral control muscle. Lengthening contractions also resulted in immediate translocation of constitutively expressed HSP25 and alphaB-crystallin from the soluble to the insoluble fraction of muscle homogenates, and cryosections showed translocation from a diffuse, cytosolic localization to striations that corresponded to z-disks. Lengthening contraction-induced translocation of HSP25 and alphaB-crystallin was associated with phosphorylation of these small HSPs, which may trigger their protective activity. In summary, these findings demonstrate loss of z-disk and membrane scaffolding proteins immediately after lengthening contractions, and concomitant translocation of HSP25 and alphaB-crystallin to the z-disk, which may help to stabilize or repair cytoskeletal elements at this site.