Coordinated CRYAB phosphorylation and desmin expression indicate adaptation and de-adaptation 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, CRYAB is phosphorylated at serine 59 (pCRYABS59) by P38, acutely protecting the cytoskeleton. To reveal adaptation and de-adaptation of these myofibrillar sub-systems to CiL, we examined CRYAB-, P38- and desmin regulation following resistance exercise at diverse timepoints of a chronic training period. Mechano-sensitive JNK phosphorylation (pJNKT183/Y185) was determined to indicate the presence of mechanical components in CiL. Within six weeks, subjects performed 13 resistance exercise bouts at the 8-12 repetition maximum, followed by ten days detraining and a final 14th bout. Biopsies were taken at baseline, 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 were not regulated over the time course. pCRYABS59 and pJNKT183/Y185 strongly increased following the unaccustomed 1st bout. This exercise-induced pCRYABS59/pJNKT183/Y185 increase disappeared with the 10th till 13th bout. As response to the detraining-period, the 14th bout led to a renewed increase in pCRYABS59. Desmin content followed pCRYABS59 inversely, i.e. was up- when pCRYABS59 was downregulated and vice versa. In conclusion, pCRYABS59-responseindicates increase and decrease in resistance to CiL, in which a reinforced desmin network could play an essential role by structurally stabilizing the cells.