Question: 

The extracellular matrix characterizes dense scaffolds of broad diversities of protein classes and thus provides mechanical stability to tissues, including skeletal muscle. The composition of the extracellular matrix determines structural and mechanical characteristics and thus regulates skeletal muscle integrity. It is described that short-term exercise bouts (of both concentric and eccentric nature) lead to short-term responses in changes of diverse constituents' mRNA profiles. However, only limited knowledge exists on effects of long-term stimulation on both mRNA and protein profiles. Thus, changes in collagen I and III, integrin a7 and prolyl 4-hydroxylases (P4ha1, Paha2) were investigated in response to long-term stimulation.

Methodology: 

32 Sprague-Dawley rats were assigned to one of following groups: age-matched control (AC, sedentary), concentric (Conc, 0° decline) or eccentric (Ecc, -20° decline) exercise (each exercise lasted six weeks). RNA and tissue homogenates were prepared from both medial gastrocnemius and vastus lateralis.

Results: 

No changes were observed in both muscles for collagen I and III as well as P4ha1 and P4ha2 mRNAs. Integrin alpha7 increased in Lat muscle after both interventions. However, all targets showed marked regulations at the functional protein level after both interventions.

Discussion: 

The present study investigated for the first time chronic effects of mechanical stimuli on ECM constituents in muscle at both transcriptional and translational level. It was demonstrated that both muscle show differently regulated adaptations to the applied stimulus models. The obtained data reveal a high biological significance of chronic mechanical stimuli in remodeling processes and integrity of ECM that establishes new tissue equilibriums of functional protein classes. The results highlight the enormous plasticity of skeletal muscle tisses.