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1 Schoolf of Mechanical Engineering, Georgia Institute of Technology, Atlanta, GA, USA; Interdisciplinary Bioengineering Program in Bioengineering, Georgia Institute of Technology, Atlanta, GA, USA
2 School of Applied Physiology, Georgia Institute of Technology, Atlanta, GA, USA
3 School of Applied Physiology, Georgia Institute of Technology, Atlanta, GA, USA; Interdisciplinary Bioengineering Program in Bioengineering, Georgia Institute of Technology, Atlanta, GA, USA
* To whom correspondence should be addressed. E-mail: thomas.burkholder{at}ap.gatech.edu.
Mechanotransduction is critical to the maintenance and growth of skeletal muscle, but the mechanism by which cellular deformations are converted to biochemical signals remains unclear. Among the earliest and most ubiquitous responses to mechanical stimulation is the phosphorylation and activation of mitogen activated protein kinases, in particular ERK-2. Caveolin-3 (CAV-3) binds ERK 2 and its upstream activators in inactive states on the caveolae of resting muscle. Caveolae are deformed by stretch, and it was hypothesized that this deformation might disrupt the CAV-3 dependent inhibition of ERK2 to effect stretch-induced activation. Stretch induced phosphorylation of ERK2 in myotubes was both amplitude and velocity dependent, consistent with a viscoelastic mechanism, such as deformation of caveolae. Chemical disruption of caveolae by cholesterol depletion increased ERK2 activation by up to 176%. Small interfering RNA oligomers were then used to knock down expression of CAV-3 in cultured myotubes prior to mechanical stimulation, with the expectation that reducing CAV-3 expression would eliminate the stretch induced activation of ERK2. Knockdown reduced CAV-3 protein content by 55%, but did not significantly alter the stretch-induced increase in ERK-2 phosphorylation, suggesting that CAV-3 is not an essential element of the mechanotransduction pathway, although the limited extent of knockdown limits the strength of this conclusion.
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