Chronic Prestress Regulation of Micro-Heart Muscle Physiology

Engineered heart tissues have been created to study cardiac biology and disease in a setting that more closely mimics in-vivo heart muscle than 2D monolayer culture. Previously published studies suggest that geometrically anisotropic micro-environments are crucial for inducing "in vivo-like" physiology from immature cardiomyocytes. We hypothesized that such anisotropic tissue geometries regulate tissue prestress, and that in turn this prestress is a major factor regulating cardiomyocytes electrophysiological development. Thus, we studied the effects of tissue geometry on electrophysiology of micro-heart muscle arrays (HM) engineered from human induced pluripotent stem cells (iPSC). Geometries predicted to increase tissue prestress not only affected cardiomyocyte structure, but also had profound effects on electrophysiology. Elongated geometries led to adaptations that yielded increased calcium intake during each contraction cycle. Strikingly, pharmacologic studies revealed a prestress threshold is required for sodium channel function, whereas L-type calcium and rapidly-rectifying potassium channels were largely insensitive. Analysis of RNA and protein levels suggest sodium channel activity changes were related to post-transcriptional, and potentially post-translational, changes. HM formed from Plakophilin 2 (PKP2) knockout iPSC had a cellular structure similar to isogenic controls. However, these tissues exhibited no functional sodium current and an overall lesser degree of electrical remodeling in response to prestress. These results suggest that PKP2, a key component of the nascent desmosome, is crucial to transducing tissue prestress into physiologically beneficial electrical remodeling via activation of sodium channels.