Question: 

Focal adhesions are crucial for mechanotransduction and thus skeletal muscle integrity. The IPP complex constituted by Ilk, Pinch and parvins is crucial for these processes. However, only little knowledge exists regarding IPP regulation byin vivomechanical stimulation. Therefore, it was hypothesized that IPP members are regulated by both concentric (Conc) and eccentric (Ecc) stimulation in rat lateralis and gastrocnemius muscles.

Methodology: 

13 wks old female Sprague-Dawley rats were assigned to the following groups: Age-matched control (AC, n=10), Conc (n=10, running bouts, 6 wks, 5d/wk, 20m*min-1, 0° decline), and Ecc (n=10, running bouts, 6 wks, 5d/wk, 20m*min-1, –20° decline). Lateralis and gastrocnemius were dissected 4h post last bout and either conserved in 4% PFA or liquid nitrogen until further analyses. IPP members were investigated by WB and confocal microscopy.

Results: 

In lateralis Ilk shows highest protein levels in the Conc group, whereas in gastrocnemius Ilk is highest in the Ecc group. In both muscles, Ilk localized to focal adhesion sites. Comparable data were obtained for Pinch1 and alpha-parvin by the mentioned methods and respective muscles.

Conclusion: 

These data lead to the conclusion that chronic in vivo mechanical stimulations possess the ability to regulate focal adhesion constituents. Thereby, protein levels of focal adhesion constituents seem to be critically regulated by the type of muscle contractions (Conc vs. Ecc) and the skeletal muscle type (lateralis vs. gastrocnemius). Therefore, Conc and Ecc stimulations might have a different impact on skeletal muscle integrity.