Pathophysiological Cardiac Remodeling And The Potential Of Cellular And Molecular Therapy

Pathological cardiac remodeling occurs following myocardial injury and results in impaired cardiac function. Cellular therapy involving stem cell transplantation has been shown to attenuate the effects of cardiac remodeling and improve cardiac function. Mesenchymal stem cells (MSCs) are known to alleviate arrhythmias and improve conduction when transplanted into cardiac tissue; however, the mechanism was not yet determined. Therefore, the first objective of the study was aimed to determine the mechanism by which MSCs modulate the excitability and conduction in cardiac tissue after transplantation by testing the hypothesis that MSCs modulate conduction i. by intercellular coupling with cardiomyocytes or ii. by paracrine signaling. Multi-electrode arrays (MEAs) were used to monitor beating frequency and conduction velocity (θ) in HL-1 cardiomyocyte monolayers in vitro. Co-culture of MSCs with HL-1 cells significantly attenuated the beating frequency over time with no significant change in θ. However, treatment of HL-1 cells with MSC-conditioned media/tyrode (ConM/ConT) significantly enhanced θ over time with no change in excitability. Further results demonstrated that connexin 43 (Cx43) expression was upregulated after treatment with ConM/ConT. This upregulation was dependent on the activation of Wnt signaling pathway in part through MSC-dependent Wnt secretion. Overall the results indicate that MSCs decrease cardiomyocyte excitability via hetero-cellular coupling and increase cardiac conduction by upregulation of Cx43 via paracrine signaling. The second objective of the thesis involved studying transverse-tubule (T-tubule) remodeling during pathological cardiac remodeling. T-tubules are cellular structures that enable synchronous calcium release and uniform contraction across the entire myocyte. Although it is known that t-tubules undergo remodeling under pathological conditions such as hypertrophy and heart failure (HF), the mechanisms underlying this are not clearly understood. Therefore, we aimed to determine the mechanism by which t-tubule remodeling occurs. T-tubule integrity was assessed using confocal microscopy. The initial experimental results indicate that inhibition of NADPH oxidase, a reactive oxygen species (ROS) producer, attenuates t-tubular remodeling. Therefore, this initial study demonstrates ROS as a potential target to attenuate t-tubular remodeling during pathological conditions.