The exercise-induced expression of heat shock proteins in human skeletal muscle : the role of evaluated muscle and core temperature and the influence of training status
Skeletal muscle adapts to the stress of contractile activity with a change in gene
expression to yield a family of highly conserved cytoprotective proteins known as
heat shock proteins (HSPs). These proteins function to restore cellular homeostasis
and to protect the cell against further insults. The exercise-induced stress response of
rodent muscle is now relatively well defined. Comparable data from human studies,
however, are extremely limited and the stress response of human skeletal muscle is far
from understood. The main aims of this thesis were to characterise the time-course
and magnitude of response of the exercise-induced production of the major HSP
families in human skeletal muscle. The role of increased muscle and core temperature
in contributing to the exercise-induced production of HSPs was also investigated.
Finally, the effects of training status on baseline muscle content of the major HSP
families and on the magnitude of the exercise-induced stress response was also
All of the exercise related studies undertaken in this thesis employed a 45 min running
exercise protocol on a motorised treadmill at an intensity corresponding to the lactate
threshold. This protocol was characterised as `non-damaging' in nature as it resulted
in no overt structural or functional damage to the muscle of young untrained (27 ±5
years), recreationally active (25 ±2 years) or aerobically trained male subjects (27 ±6
years), as evidenced by indirect indicators of muscle damage such as circulating
levels of creatine kinase and maximal quadriceps isometric muscle force.
The time-course and magnitude of the exercise-induced response of the major HSP
families were characterised in an active young (24 ±4 years) male population.
Muscle biopsies were obtained from the vastus lateralis muscle immediately prior to
and at 24 h, 48 h, 72 h and 7 days post-exercise. Exercise induced significant and
individually variable increases in HSP70, HSC70 and HSP60 content with peak
increases typically occurring at 48 h post-exercise. In contrast, exercise did not induce
significant increases in either HSP27, aB-crystallin, manganese superoxide dismutase
(MnSOD) protein content or the activity of superoxide dismutase (SOD) and catalase.
When examining baseline protein levels, HSC70, HSP27 and aB-crystallin appeared
consistently expressed between subjects whereas HSP70 and MnSOD displayed
marked individual variation of up to 3 and 1.5 fold, respectively. These data
demonstrate a differential effect of aerobic exercise on specific HSPs. Data also
demonstrate an individual variation in both basal HSP levels and in the magnitude of
the stress response to acute exercise, which may be related to individual differences in
The role of increased muscle and core temperature in contributing to the exerciseinduced
production of HSPs were subsequently investigated. Active young males (23
A: 3 years) underwent a passive heating protocol of 1h duration during which the
temperature of the core and vastus lateralis muscle were increased to similar levels as
that occurring during exercise. One limb was immersed in a tank containing warm
water whilst the contra-lateral limb remained outside the tank and was not exposed to
heat stress. Muscle biopsies were obtained from the vastus lateralis of both legs
immediately prior to and at 48 h and 7 days post-heating. The heating protocol
induced significant increases in rectal and muscle temperature of the heated leg whilst
muscle temperature of the non-heated limb showed no significant change followingheating. The heating protocol failed to induce significant increases in muscle content
of HSP70, HSC70, HSP60, HSP27, aB-crystallin, MnSOD protein content or the
activity of SOD and catalase in either the heated or non-heated leg. Data demonstrate
that increases in both systemic and local muscle temperature per se appear not to be
mediating the exercise-induced production of HSPs and suggest that non-heat-stress
factors associated with muscle contractile activity are of more importance in
mediating this response.
The influences of aerobic training status on the basal levels of HSPs and on the
magnitude of the exercise-induced stress response were also investigated. Muscle
biopsies were obtained from the vastus lateralis of young trained (28 ±6 years) and
untrained (29 ±6 years) male subjects immediately prior to and at 48 h and 7 days
post-exercise. When comparing muscles at rest, trained subjects had significantly
higher levels of aB-crystallin, HSP60 and MnSOD compared with untrained subjects.
Trained subjects also had a tendency for higher levels of HSP70, HSC70 and total
SOD activity compared with untrained subjects. In contrast to the active population
examined earlier, neither the trained nor untrained subjects exhibited a stress response
to exercise. The absence of a stress response in trained subjects is likely due to the
increase in baseline defences and the customary nature of the exercise protocol. The
absence of a stress response in untrained subjects may be due to the failure of the
exercise protocol to elicit a proposed critical threshold intensity that is required to
induce increases in muscle HSP content.
This thesis has provided novel data for the literature and has significantly advanced
our understanding of the exercise-induced stress response of human skeletal muscle.
Future research should examine the effects of exercise intensity on muscle HSP
production and investigate the role of reactive oxygen species in contributing to the
response. The wider implications of the exercise-induced production of HSPs, such
as their potential cytoprotective properties against related and non-related stressors,
should also be examined.
Key Words: molecular chaperones, oxidative stress, hyperthermia, stress proteins