Exercise attenuates stress-related signaling as sensed by higher phosphorylation of small heat shock proteins in skeletal muscle from older individuals.

BACKGROUND: Heat shock proteins (HSPs) are key molecular chaperones that help maintain protein homeostasis by stabilizing or removing damaged proteins during cellular stress. Aging weakens these stress-response systems, disrupting proteostasis and increasing vulnerability to sarcopenia. High-intensity training (HIT) can counteract these declines by activating protective pathways such as the HSP response. HSPs are highly responsive to stress, examining their regulation during aging is important, as altered HSP activity is linked to the progressive loss of muscle mass. METHODS: This study investigated the abundance and phosphorylation of HSPs in skeletal muscle from healthy, active young and older adults (n = 7 per group), assessed at baseline and again in the older group following 12 weeks of HIT. Using calibrated Western blotting on both whole-muscle homogenates and pooled single muscle fibres, we quantified HSP content and phosphorylation to determine how aging and exercise influence stress-responsive protein regulation at both the tissue and cellular levels. RESULTS: In whole muscle homogenates, HSPs (HSP72, HSP27, and αB-crystallin) did not differ between young and older adults, while higher phosphorylation of small HSPs (sHSPs): phospho-HSP27 at Serine15 (pHSP27 Ser15) and phospho-αB-crystallin at Serine59 (pαB-crystallin Ser59) (∼1.8-fold and ∼2.9-fold, respectively) were found in muscle from older adults, indicating higher cellular stress associated with aging. A 12-week HIT intervention in older adults reduced homogenate pHSP27 Ser15 and pαB-crystallin Ser59 abundances to similar levels found in young adults. Total HSPs typically displayed a distinct fiber-type profile in both age groups, with more in type I compared to type II fibers, distinguished by the presence of myosin heavy chain I (MHCI) or MHCII. Phosphorylation at pHSP27 Ser15 and pαB-crystallin Ser59 was not different between type I and type II fibers. The HIT in older adults decreased total and phosphorylated sHSPs in both type I and type II fibers but increased HSP72 in type I fibers. CONCLUSION: HIT has the potential to mitigate age-related cellular stress and modulate protein expression patterns in aging skeletal muscle and, perhaps, has the potential to delay age-related muscle decline, thereby improving muscle health in older adults.