Systems Mechanobiology of Cardiac Myocytes

Abstract

Cardiac myocytes are sensitive to specific and distinct mechanical stimuli. We examined the effect of the major axis of biaxial mechanical stretch on cardiac myocyte gene expression and reconstructed a stretch signaling model to identify pathways and transcription factors regulating these responses. Neonatal cardiac myocytes were cultured on a micropatterned substrate, and the primary stretch axis was applied either parallel or transverse to the myofibril direction. RNA sequencing (RNA-Seq) after acute myocyte stretch showed a more robust response to longitudinal than to transverse stretch. After 30 minutes of stretch, 53 and 168 genes were significantly up- or down-regulated by transverse or longitudinal stretch, respectively. After 4 hours, the number of differentially expressed genes increased to 795 with longitudinal stretch but only 35 with transverse stretch. Genes regulated by both stretches showed significant enrichment of transcription factor activity and protein kinase activity, whereas longitudinal but not transverse stretch specifically activated genes involved in sarcomere organization and cytoskeletal protein binding. Network analysis using logic-based signaling model constructed from published data identified serum response factor (SRF) and myocyte enhancer factor-2 (MEF2) as critical regulators of longitudinal stretch-induced changes mediated by protein kinase C (PKC). cAMP response element-binding protein (CREB) was found to be activated by both longitudinal and transverse stretch. Inhibitor experiments were used to validate these model predictions. Cardiac myocytes activate different pathways in response to transverse and longitudinal mechanical strain; these responses may underlie differential whole organ responses to pressure versus volume overload.