DAPC modulation with resistance training in young and older men 1 MODULATION OF THE DYSTROPHIN-ASSOCIATED PROTEIN COMPLEX IN RESPONSE TO RESISTANCE TRAINING IN YOUNG AND OLDER MEN

The dystrophin associated protein complex (DAPC) is a scaffold of proteins linking the intracellular cytoskeleton with the extracellular matrix that is integral to structural stability/integrity, signaling/mechanotransduction, and force transmission. We hypothesized that the expression of DAPC component proteins would be altered by resistance loading during progressive resistance training (PRT)-mediated myofiber hypertrophy, and we investigated whether aging influenced these changes. Seventeen young (27 yr) and 13 older (65 yr) men completed 16 wk of PRT with muscle biopsies at baseline (T1), 24 h after bout one (T2), and 24 h after the final bout at wk 16 (T3). Myofiber hypertrophy in young (type I 31%, P<0.005; type II 40%, P<0.001) far exceeded hypertrophy in old (type II only, 19.5%, P<0.05). PRT altered protein expression for caveolin-3 (decreased 24% by T3, P<0.01); alpha-1 syntrophin (increased 16% by T3, P<0.05); alpha dystrobrevin (fell 23% from T2 to T3, P<0.01); and dystrophin (rose acutely (30% by T2, P<0.05) and returned to baseline by T3). The phosphorylation state of membrane nNOS (Ser 1417) decreased 70% (P<0.005) by T3, particularly in old (81%), while p38 MAPK phosphorylation increased 2-fold by T3 in old (P<0.01). We conclude that component proteins of the DAPC are modulated by PRT, which may serve to improve both structural and signaling functions during load-mediated myofiber hypertrophy. The blunted hypertrophic adaptation seen in old vs. young men may have resulted from over-stress as suggested by marked p38 MAPK activation in old only.