The Role of Extracellular Matrix Stiffness on Cardiac Metabolic Activity

Abstract

The cardiac L-type Ca2+ channel (LTCC) can regulate mitochondrial metabolic activity via calcium-independent mechanisms. The sarcomeric network plays an important role in this response. Hypertrophic cardiomyopathy (HCM) occurs due to mutations in sarcomeric proteins. Using murine models of human HCM, we have shown that mutations in sarcomeric proteins are associated with altered LTCC kinetics, impaired structural-functional communication between LTCC and mitochondria, and increased metabolic activity (consistent with the human phenotype). However, the mechanisms by which mutations in sarcomeric proteins lead to alterations in metabolic activity remain unknown. Cardiomyocytes can ‘sense’ extracellular matrix (ECM) mechanics via a process called mechanotransduction. This involves conversion of mechanical stimuli into biochemical events that can alter myocardial function. Since human HCM is characterised by a stiff myocardium, we developed an in vitro model to determine the role of increased ECM stiffness on metabolic activity. Wild-type cardiomyocytes were cultured on hydrogels with stiffnesses mimicking healthy (10 kPa) or HCM (40 kPa) myocardium. Cardiomyocytes on 40 kPa hydrogels exhibited increased stiffness versus 10 kPa (atomic force microscopy; 3.8 ± 0.4 kPa, n = 53 versus 1.5 ± 0.2 kPa, n = 31; p < 0.05). Cardiomyocytes on 40 kPa hydrogels also exhibited a larger increase in metabolic activity in response to activation of LTCC (flavoprotein autofluorescence; 40 kPa: 64.6 ± 4.3% increase, n = 35 versus 10 kPa: 20.3 ± 1.8%, n = 27 p < 0.05), that was attenuated by sarcomeric protein depolymerising agents latrunculin A (F-actin) or colchicine (β-tubulin). We conclude that ECM stiffness may regulate cardiac metabolic activity. Increased ECM stiffness may contribute to increased metabolic activity and development of HCM.