Cytoskeletal disruption and small heat shock protein translocation immediately after lengthening contractions.
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.
Koh
Timothy J
TJ
School of Kinesiology, University of Illinois at Chicago, Chicago, Illinois 60608, USA. tjkoh@uic.edu
Escobedo
Joel
J
D000818:Animals; D003599:Cytoskeleton / Q000378:metabolism*; D005455:Fluorescent Antibody Technique; D006360:Heat-Shock Proteins; D008297:Male; D051379:Mice; D008810:Mice, Inbred C57BL; D018832:Molecular Chaperones; D009119:Muscle Contraction / Q000502:physiology*; D018485:Muscle Fibers, Skeletal / Q000502:physiology*; D009363:Neoplasm Proteins / Q000378:metabolism*; D010766:Phosphorylation; D013047:Specific Pathogen-Free Organisms; D038203:alpha-Crystallin B Chain / Q000378:metabolism*
D006360:Heat-Shock Proteins; C486113:Hsbp1 protein, mouse; D018832:Molecular Chaperones; D009363:Neoplasm Proteins; D038203:alpha-Crystallin B Chain