Question:

Mechanotransduction means the transduction of physical forces into biochemical signals enabling skeletal muscles (SkM) to adapt to exercise - a mechanism that is often disturbed in SkM diseases. Focal adhesion (FA) and costamere (CSTM) protein assemblies are important structures assuring proper SkM adaptations to exercise. Only little knowledge exists, however, on effects of exercise on FAs CSTMs, although this question is of high relevance to understand regulatory potentials of exercise on SkM. We hypothesized that FAs and CSTMs and downstream signaling cascades are regulated exercise-dependently in SkM.

Methods:

Sprague-Dawley rats were assigned to the following groups: sedentary (CON,n=7), 6-wks lasting level exercise (Level,n=7,5d/wk,1h/d,20 m/min,0°decline) or 6-wks lasting downhill exercise (Dh,n=7,see Level,but -20°decline). Quadriceps femoris (QUF) and gastrocnemius (GAS) muscles were investigated. RT-PCR/WB analyses were performed to investigate FAs and CSTMs in both SkM after exercise interventions.

Results:

FAs and CSTMs were jointly regulated in dependence on exercise mode and SkM type. Interestingly, Level increased all targets only in QUF, whereas Downhill had no effects. Conversely, Downhill increased all targets only in GAS and no effect was observed in QUF. Downstream signaling cascades, e.g. pp38, pERK, and pAkt were activated in the same manner.

Conclusion:

Our data are the first to demonstrate that the type of in vivo muscle contraction has divergent effects on FAs and CSTMs in a SkM type-dependent manner. As FAs/CSTMs are involved in a variety of SkM diseases, these data are important to understand SkM adaptations and to evaluate exercise models as therapeutic interventions in SkM diseases.