Coordinated alpha-crystallin B phosphorylation and desmin expression indicate adaptation and deadaptation to resistance exercise-induced loading in human skeletal muscle

Skeletal muscle is a target of contraction-induced loading (CiL), leading to protein unfolding or cellular perturbations, respectively. While cytoskeletal desmin is responsible for ongoing structural stabilization, in the immediate response to CiL, alpha-crystallin B (CRYAB) is phosphorylated at serine 59 ( p CRYAB S59 ) by P38, acutely protecting the cytoskeleton. To reveal adaptation and deadaptation of these myofibrillar subsystems to CiL, we examined CRYAB, P38, and desmin regulation following resistance exercise at diverse time points of a chronic training period. Mechanosensitive JNK phosphorylation ( p JNK T183/Y185 ) was determined to indicate the presence of mechanical components in CiL. Within 6 wk, subjects performed 13 resistance exercise bouts at the 8–12 repetition maximum, followed by 10 days detraining and a final 14th bout. Biopsies were taken at baseline and after the 1st, 3rd, 7th, 10th, 13th, and 14th bout. To assess whether potential desensitization to CiL can be mitigated, one group trained with progressive and a second with constant loading. As no group differences were found, all subjects were combined for statistics. Total and phosphorylated P38 was not regulated over the time course. p CRYAB S59 and p JNK T183/Y185 strongly increased following the unaccustomed first bout. This exercise-induced p CRYAB S59 / p JNK T183/Y185 increase disappeared with the 10th until 13th bout. As response to the detraining period, the 14th bout led to a renewed increase in p CRYAB S59 . Desmin content followed p CRYAB S59 inversely, i.e., was up- when p CRYAB S59 was downregulated and vice versa. In conclusion, the p CRYAB S59 response indicates increase and decrease in resistance to CiL, in which a reinforced desmin network could play an essential role by structurally stabilizing the cells.