Engineering post-infarct extracellular matrix remodeling in vitro for understanding cardiac fibroblast fate and function

Abstract

Myocardial fibrosis is associated with vast majority of cardiovascular diseases which is one of the most common disease afflicting adults around the world. During myocardial infarction, myocytes die and are replaced by a specialized fibrotic extracellular matrix (ECM), otherwise known as scarring. The transdifferentiation to myofibroblasts is essential for wound healing of the heart. This cell type influences the secretion of cytokines, deposition of extracellular matrix proteins, structural support, and filling of the mechanical load caused by myocyte necrosis. However, the fibrosis influenced by myofibroblasts can lead to progressive heart failure. Fibrotic scarring presents a tremendous hemodynamic burden on the heart, as it creates a stiff substrate which resists diastolic filling. Fibrotic mechanisms result in permanent scarring which often leads to hypertrophy, arrhythmias, and a rapid progression to failure. Despite the deep understanding of fibrosis in other tissues, acquired through previous investigations, the mechanisms of cardiac fibrosis remain unclear. Recent studies suggest that biochemical cues as well as mechanical cues regulate cells in myocardium. However, the steps in myofibroblast transdifferentiation, as well as the molecular mechanisms of such transdifferentiation in vivo are poorly understood. This dissertation is focused on addressing the limited understanding of myofibroblast transdifferentiation cues and pathways that transduce those cues for cellular response, especially those mechanical in nature. Previously p38 has been reported to govern cardiac myofibroblast fate in response to various cues such as TGF, substrate stiffness, and mechanical stretch. We investigated the myofibroblast fate regulation through p38 in response to topographic cue. Moreover, YAP was known to lend itself to heart regeneration and myofibroblast phenotype. In this dissertation, we show that p38 and YAP are also responsible for transducing mechanical signals related to topography and works in conjunction to tensin 1 to regulate transdifferentiation to myofibroblast. These results help to elucidate the pathway by which mechanical cues are transduced, leading to transdifferentiation. This study has addressed the limited understanding of myofibroblast transdifferentiation by identifying the novel topographic regulation and pathways that transduce such signals. Taken together, this research demonstrates the utility of bioengineering strategies to develop in vitro platforms to better understand the mechanism of cardiac fibrosis which would aid in discovering solutions to assist patients with hearts affected by fibrosis.