Restoration of Resting Sarcomere Length After Uniaxial Static Strain Is Regulated by Protein Kinase Cε and Focal Adhesion Kinase

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Abstract
Physiological or pathological stresses and strains produce longer or wider muscle cells, but resting sarcomere length remains constant. Our goal was to investigate the cellular mechanisms for controlling this optimal, resting sarcomere length. To do so, we cultured neonatal rat cardiomyocytes on microfabricated peg-and-groove, laminin-coated silicone surfaces and applied a uniaxial static strain of 10%. Sarcomere length was accurately measured by fast Fourier transform analysis of images before, within 5 minutes of, and 4 to 6 hours after imposition of the strain. Sarcomere length of aligned cardiomyocytes (1.94±0.07 μm) was lengthened acutely (2.06±0.06 μm), and recovered (1.95±0.07 μm) by 4 hours. Puromycin, an mRNA translational inhibitor, prevented recovery of resting sarcomere length by 4 hours, thus indicating a requirement for new protein synthesis in the recovery process. Furthermore, activation of protein kinase Cε (PKCε) was necessary for length recovery, as nonselective PKC inhibitors [staurosporine (5 μmol/L) and chelerythrine chloride (10 μmol/L)], and a replication-defective adenovirus (Adv) encoding a dominant-negative mutant of PKCε prevented the restoration of sarcomere length. To assess the importance of focal adhesion complexes, cardiomyocytes were infected with an Adv encoding a dominant-negative inhibitor of focal adhesion kinase (FAK) (Adv-GFP-FRNK). Adv-GFP-FRNK also prevented resting sarcomere length recovery, whereas a control Adv encoding only GFP did not. In conclusion, using our novel culture system, we provide evidence indicating that the length remodeling process requires new protein synthesis, PKCε and FAK.