Continuous contractile activity induces fiber type specific
expression of hsp70 in skeletal muscle.
Neufer, P. Darrell, George A. Ordway, Gregory A. Hand, John M.
Shelton, James A. Richardson, Ivor J. Benjamin, and R. Sanders
Williams.
Departments of Internal Medicine, Biochemistry, Physiology, and
Pathology, University of Texas Southwestern Medical Center, Dallas,
TX 75235
APStracts 3:0200C, 1996.
Continuous contractile activity of skeletal muscle elicits an early
and dramatic increase in ribosomal RNA, suggesting that translational
efficiency and/or capacity is enhanced during the adaptive response
to increased metabolic demand. In view of the important role heat
shock or stress proteins (Hsps) play as molecular chaperones during
protein synthesis, we examined whether expression of the inducible
Hsp70 and/or mitochondrial Hsp60 is altered in rabbit tibialis
anterior muscle during continuous low frequency motor nerve
stimulation. Induction of the Hsp70 gene was evident within 24 h
after the onset of stimulation as reflected by increases in Hsp70
transcription (>20 fold) and mRNA (>50 fold). Hsp70 protein
levels were significantly elevated (10-12 fold) after 14 and 21 d of
stimulation. Mitochondrial Hsp60 mRNA and protein also increased
during stimulation (>18 and >5-fold after 21 d,
respectively). In situ hybridization and immunohistochemistry coupled
with myosin ATPase staining revealed that expression of Hsp70 was
restricted to oxidative type I and IIa fibers during the first 3 d of
stimulation, but shifted to primarily type II fibers after 21 d of
stimulation. These findings demonstrate that induction of Hsp70
during the adaptive response to chronic motor nerve stimulation
proceeds from type I/IIa to type IId(x)/b fibers, suggesting that the
expression of hsps may be required to support the folding and
compartmentalization of nascent proteins during the transformation
process.
Received 28 March 1996; accepted in final form 13 June 1996.
APS Manuscript Number C176-6.
Article publication pending Am. J. Physiol. (Cell Physiology).
ISSN 1080-4757 Copyright 1996 The American Physiological Society.
Published in APStracts on 4 July 96