Hsp70 accumulation in tissues of heat-stressed rats is blunted with
advancing age.
Kregel, Kevin C., Pope L. Moseley, Rebecca Skidmore, Jesus A.
Gutierrez, and Vince Guerriero, Jr.
Departments of Exercise Science and Internal Medicine, The
University of Iowa, Iowa City, Iowa 52242 and Department of Exercise
and Sport Sciences and Department of Animal Sciences, University of
Arizona, Tucson, Arizona 85721
APStracts 2:0289A, 1995.
The purpose of this study was to determine whether aging results in
reduced accumulation of the 70-kDa heat shock protein (HSP70) in
response to a thermal challenge. Experiments were conducted in mature
(MAT; 12-mo-old) and senescent (SEN; 24-mo-old) male Fischer 344 rats
that were conscious and freely-moving. Rats were randomly assigned to
either a euthermic control group (thermoneutral conditions) or a
nonexertionally heated group that was exposed to an ambient
temperature of 42 C until colonic temperature reached 41 C (n=6-7 per
group for each age). In the latter group, heating rates were similar
in the MAT and SEN rats (0.092 +/- 0.006 vs. 0.094 +/- 0.010 C/min).
Tissue samples were subsequently obtained from the liver and left
ventricle and an enzyme-linked immunosorbent assay specific for both
the constitutive and inducible forms of HSP70 was used to directly
quantitate absolute levels of the protein in each tissue. Heat
stressed rats had significantly elevated HSP70 levels in the liver
compared with the euthermic control groups (i.e., main effect of
heating). Post-hoc comparisons revealed that heat stress elicited
marked elevations in liver HSP70 in MAT rats compared with the age
-matched control group (11.1 +/- 0.98 vs 2.6 +/- 0.54 ng/[mu]g total
protein; P<0.05). In contrast, HSP70 values were unchanged in the SEN
heated and control groups (6.7 +/- 0.79 vs. 4.6 +/- 0.54 ng/[mu]g).
In the left ventricle, there was also a significant main effect of
heating on HSP70 concentration. The levels of HSP70 accumulation were
greater in the heat stressed MAT (+182%) and SEN (+67%) groups in
comparison with age-matched controls. In addition, HSP70 levels were
29% higher in the hyperthermic MAT group compared with SEN rats that
underwent a similar heating protocol. Liver and ventricle samples
probed for the accumulation of the highly-inducible 72-kDa HSP showed
an age-related decrease in HSP72 levels with heating. Thus the
increases in liver and myocardial HSP70 accumulation in response to
nonexertional heat stress are attenuated with senescence. Since these
proteins are postulated to protect cells from injury and enhance
cellular recovery from heat stress, the data suggest that an aging
organism has a reduced ability to properly maintain cellular function
and integrity after a thermal challenge.
Received 27 March 1995; accepted in final form 22 June 1995.
APS Manuscript Number A340-5.
Article publication pending Journal of Applied Physiology.
ISSN 1080-4757 Copyright 1995 The American Physiological Society.
Published in APStracts on 11 July 1995.