CHANGES IN THE CONTENT OF HEAT SHOCK PROTEIN 72, IN RAT SKELETAL MUSCLE FOLLOWING ECCENTRIC EXERCISE

Induction of the chaperone heat shock protein 72 (HSP72) through heat treatment (HT), exercise, or overexpression improves glucose tolerance and mitochondrial function in skeletal muscle. Less is known about HSP72 function in the liver where lipid accumulation can result in insulin resistance and nonalcoholic fatty liver disease (NAFLD). The purpose of this study was 1) to determine whether weekly in vivo HT induces hepatic HSP72 and improves glucose tolerance in rats fed a high-fat diet (HFD) and 2) to determine the ability of HSP72 to protect against lipid accumulation and mitochondrial dysfunction in primary hepatocytes. Male Wistar rats were fed an HFD for 15 wk and were given weekly HT (41°C, 20 min) or sham treatments (37°C, 20 min) for the final 7 wk. Glucose tolerance and insulin sensitivity were assessed, along with HSP72 induction and triglyceride storage, in the skeletal muscle and liver. The effect of an acute loss of HSP72 in primary hepatocytes was examined via siRNA. Weekly in vivo HT improved glucose tolerance, elevated muscle and hepatic HSP72 protein content, and reduced muscle triglyceride storage. In primary hepatocytes, mitochondrial morphology was changed, and fatty acid oxidation was reduced in small interfering HSP72 (siHSP72)-treated hepatocytes. Lipid accumulation following palmitate treatment was increased in siHSP72-treated hepatocytes. These data suggest that HT may improve systemic metabolism via induction of hepatic HSP72. Additionally, acute loss of HSP72 in primary hepatocytes impacts mitochondrial health as well as fat oxidation and storage. These findings suggest therapies targeting HSP72 in the liver may prevent NAFLD.

Download Full-text

Elevation in heat shock protein 72 mRNA following contractions in isolated single skeletal muscle fibers

AJP Regulatory Integrative and Comparative Physiology ◽

10.1152/ajpregu.00852.2007 ◽

2008 ◽

Vol 295 (2) ◽

pp. R642-R648 ◽

Cited By ~ 8

Author(s):

Creed M. Stary ◽

Brandon J. Walsh ◽

Amy E. Knapp ◽

David Brafman ◽

Michael C. Hogan

Keyword(s):

Skeletal Muscle ◽

Heat Shock ◽

Heat Shock Protein ◽

Muscle Fibers ◽

Stable Model ◽

Heat Shock Protein 72 ◽

Skeletal Muscle Fibers ◽

Single Bout ◽

Mrna Content ◽

Fatiguing Contractions

The purpose of the present study was 1) to develop a stable model for measuring contraction-induced elevations in mRNA in single skeletal muscle fibers and 2) to utilize this model to investigate the response of heat shock protein 72 (HSP72) mRNA following an acute bout of fatiguing contractions. Living, intact skeletal muscle fibers were microdissected from lumbrical muscle of Xenopus laevis and either electrically stimulated for 15 min of tetanic contractions (EX; n = 26) or not stimulated to contract (REST; n = 14). The relative mean developed tension of EX fibers decreased to 29 ± 7% of initial peak tension at the stimulation end point. Following treatment, individual fibers were allowed to recover for 1 ( n = 9), 2 ( n = 8), or 4 h ( n = 9) prior to isolation of total cellular mRNA. HSP72, HSP60, and cardiac α-actin mRNA content were then assessed in individual fibers using quantitative PCR detection. Relative HSP72 mRNA content was significantly ( P < 0.05) elevated at the 2-h postcontraction time point relative to REST fibers when normalized to either HSP60 (18.5 ± 7.5-fold) or cardiac α-actin (14.7 ± 4.3-fold), although not at the 1- or 4-h time points. These data indicate that 1) extraction of RNA followed by relative quantification of mRNA of select genes in isolated single skeletal muscle fibers can be reliably performed, 2) HSP60 and cardiac α-actin are suitable endogenous normalizing genes in skeletal muscle following contractions, and 3) a significantly elevated content of HSP72 mRNA is detectable in skeletal muscle 2 h after a single bout of fatiguing contractions, despite minimal temperature changes and without influence from extracellular sources.

Download Full-text