Contractile Protein and Extracellular Matrix Secretion of Cell Monolayer Sheets Following Cyclic Stretch

Abstract

Cell therapy treatment of post-myocardial infarction patients aims to regenerate tissue to improve function and prevent scarring. Although scaffold-free cell sheets offer an attractive solution, the monolayers are limited currently in their integrity as the individual layers do not cyclically stretch and cannot match the mechanical force transduction of the myocardium. In this study, we have explored stretching HL-1 mouse cardiomyocytes and embryonic stem cells derived into cardiomyocytes cultured in monolayers, and on temperature-responsive substrates to increase contractile protein and extracellular matrix (ECM) secretion for the purpose of reinforcing the baseline proteins and ECM. Sheets of HL-1 cells were stretched at 3 conditions (5, 10, 19%) along with static, unstretched controls at 1 Hz for 24 h. Embryonic stem cells derived into cardiomyocytes were stretched at 0 and 10% at 1 Hz for 24 h. Contractile proteins α- and β-myosin heavy chain (αMHC and βMHC) and sarcomeric α-actinin exhibited a significant increase in protein expression at 10% elongation strain. Atrial natriuretic factor (ANF) and connexin43 (Cx43) mRNA expression increased between static and conditioned cells; however, mRNA and protein expression at 19% strain increased less than cyclically strained cells at 5% strain. ECM secretion was not found to increase with conditioning. Effective engineering of cell monolayers with improved mechanical integrity may require an optimal strain condition to achieve maximum expression.