Phosphorylation of αβ-crystallin and its cytoskeleton association differs in skeletal myofiber types depending on resistance exercise intensity and volume

alpha beta-crystallin (CRYAB) is an important actor in the immediate cell stabilizing response following mechanical stress in skeletal muscle. Yet, only little is known regarding myofiber type-specific stress responses of CRYAB. We investigated whether the phosphorylation of CRYAB at serine 59 ((p)CRYAB(Ser59)) and its cytoskeleton association are influenced by varying load-intensity and -volume in a fiber type-specific manner. Male subjects were assigned to 1, 5, and 10 sets of different acute resistance exercise protocols: hypertrophy (HYP), maximum strength (MAX), strength endurance (SE), low intensity (LI), and three sets of maximum eccentric resistance exercise (ECC). Skeletal muscle biopsies were taken at baseline and 30 min after exercise. Western blot revealed an increase in (p)CRYAB(Ser59) only following 5 and 10 sets in groups HYP. MAX, SE. and LI as well as following 3 sets in the ECC group. In type I fibers, immunohistochemistry determined increased p CRYAB' in all groups. In type II fibers, (p)CRYAB(Ser59) only increased in MAX and ECC groups, with the increase in type II fibers exceeding that of type I fibers in ECC. Association of CRYAB and (p)CRYAB(Ser59)with the cytoskeleton reflected the fiber type-specific phosphorylation pattern. Phosphorylation of CRYAB and its association with the cytoskeleton in type I and II myofibeis is highly specific in terms of loading intensity and volume. Most likely, this is based on specific recruitment patterns of the different myofiber entities due to the different resistance exercise loadings. We conclude that (p)CRYAB(Ser59) indicates contraction-induced mechanical stress exposure of single myoribers in consequence of resistance exercise. NEW & NOTEWORTHY We determined that the phosphorylation of alpha beta-crystallin at seine 59 ((p)CRYAB(Ser59)) after resistance exercise differs between myofiber types in a load- and intensity-dependent manner. The determination of(p)CRYAB(Ser59) could serve as a marker indirectly indicating contractile involvement and applied mechanical stress on individual fibers. By that, it is possible to retrospectively assess the impact of resistance exercise loading on skeletal muscle fiber entities.