Adaptation Within Embryonic and Neonatal Heart Environment Reveals Alternative Fates for Adult c-Kit+ Cardiac Interstitial Cells

Cardiac interstitial cells (CIC) perform essential roles in myocardial biology through preservation of homeostasis as well as response to injury or stress. Studies of murine CIC biology reveal remarkable plasticity in terms of transcriptional reprogramming and ploidy state with important implications for function. Despite over a decade of characterization and in vivo utilization of adult c-Kit+ CIC (cCIC), adaptability and functional responses upon delivery to adult mammalian hearts remain poorly understood. Limitations of characterizing cCIC biology following in vitro expansion and adoptive transfer into the adult heart were circumvented by delivery of the donated cells into early cardiogenic environments of embryonic, fetal, and early postnatal developing hearts. These three developmental stages were permissive for retention and persistence, enabling phenotypic evaluation of in vitro expanded cCICs after delivery as well as tissue response following introduction to the host environment. Embryonic blastocyst environment prompted cCIC integration into trophectoderm as well as persistence in amniochorionic membrane. Delivery to fetal myocardium yielded cCIC perivascular localization with fibroblast-like phenotype, similar to cCICs introduced to postnatal P3 heart with persistent cell cycle activity for up to 4 weeks. Fibroblast-like phenotype of exogenously transferred cCICs in fetal and postnatal cardiogenic environments is consistent with inability to contribute directly toward cardiogenesis and lack of functional integration with host myocardium. In contrast, cCICs incorporation into extra-embryonic membranes is consistent with fate of polyploid cells in blastocysts. These findings provide insight into cCIC biology, their inherent predisposition toward fibroblast fates in cardiogenic environments, and remarkable participation in extra-embryonic tissue formation.

Pericytes in the infarcted heart

The adult mammalian heart lacks regenerative capacity and heals through activation of an inflammatory cascade that leads to the formation of a collagen-based scar. Although scar formation is important to preserve the structural integrity of the ventricle, unrestrained inflammation and excessive fibrosis have been implicated in the pathogenesis of adverse post-infarction remodeling and heart failure. Interstitial cells play a crucial role in the regulation of cardiac repair. Although recent studies have explored the role of fibroblasts and immune cells, the cardiac pericytes have been largely ignored by investigators interested in myocardial biology. This review manuscript discusses the role of pericytes in the regulation of inflammation, fibrosis and angiogenesis following myocardial infarction. During the inflammatory phase of infarct healing, pericytes may regulate microvascular permeability and may play an important role in leukocyte trafficking. Moreover, pericyte activation through Toll-like receptor-mediated pathways may stimulate cytokine and chemokine synthesis. During the proliferative phase, pericytes may be involved in angiogenesis and fibrosis. To what extent pericyte to fibroblast conversion and pericyte-mediated growth factor synthesis contribute to the myocardial fibrotic response remains unknown. During the maturation phase of infarct healing, coating of infarct neovessels with pericytes plays an important role in scar stabilization. Implementation of therapeutic approaches targeting pericytes in the infarcted and remodeling heart remains challenging, due to the lack of systematic characterization of myocardial pericytes, their phenotypic heterogeneity and the limited knowledge on their functional role.

A Light Wand to Untangle the Myocardial Cell Network

The discovery of optogenetics has revolutionized research in neuroscience by providing the tools for noninvasive, cell-type selective modulation of membrane potential and cellular function in vitro and in vivo. Rhodopsin-based optogenetics has later been introduced in experimental cardiology studies and used as a tool to photoactivate cardiac contractions or to identify the sites, timing, and location most effective for defibrillating impulses to interrupt cardiac arrhythmias. The exploitation of cell-selectivity of optogenetics, and the generation of model organisms with myocardial cell type targeted expression of opsins has started to yield novel and sometimes unexpected notions on myocardial biology. This review summarizes the main results, the different uses, and the prospective developments of cardiac optogenetics.

Abstract 280: Cardiac Fibroblast Specific Deletion of Gsk3α Alleviate From Cardiac Dysfunction and Fibrotic Remodeling in Ischemic Heart

Heart failure is the leading cause of mortality, morbidity and healthcare expenditures worldwide. Numerous studies from our lab and others have implicated GSK-3 as a promising therapeutic target for cardiovascular diseases. Recently, we reported that cardiomyocyte-specific deletion of GSK3α limits adverse remodeling and preserves cardiac function, post-MI. However, the role of cardiac fibroblast GSK3α (CF-GSK-3α) in myocardial biology is unknown. To determine the role of CF-GSK-3α in MI-induced fibrotic remodeling, we created CF-GSK-3α KO mice in which Cre recombinase is driven by Postn (periostin) promoter. WT and CF-GSK-3α-KO mice were subjected to MI or sham surgery at 2 months age and cardiac function were monitored by serial echocardiography. Interestingly, at four weeks post-MI, CF-GSK-3α-KO mice showed preserved chamber dimensions and LV functions as reflected by preserved ejection fraction and fractional shortening as compared to littermate controls. The preserved LV dimensions and cardiac function were remained significantly better up to the end of the study i.e., 8 weeks post-MI. At 8 weeks post MI, hearts were excised, and Masson trichrome staining was performed. LV scar circumference was measured and expressed as a percentage of total area of LV myocardium. Scar tissue percent circumference was significantly reduced in CF-GSK-3α-KO hearts. Furthermore, GSK3α KO heart scars were thicker with much higher numbers of viable cardiomyocytes as compared to WT. To gain the mechanistic insights of observed GSK-3α mediated fibrotic remodeling, we examined profibrotic TGFβ signaling and myofibroblast transformation. WT and GSK-3α KO mouse embryonic fibroblasts (MEFs) were treated with TGF-β1 (10 ng/mL) for 1 hour, and phosphorylation of SMAD-3 (Ser423/25) was determined. Indeed, TGF-β1 induced activation of SMAD3 was significantly reduced in GSK3α KO cells. Consistently, deletion of GSK-3α leads to reduced myofibroblast transformation as reflected by significantly reduced expression of α-SMA in GSK-3α KO cells. These findings suggest that CF-specific deletion of GSK3α is protective in ischemic heart and GSK3α could be a novel therapeutic target for management of adverse fibrotic remodeling in the diseased heart.

Abstract 1: Chemical Biology of Cardiac Regeleration: an Instructive Hydrogel-based Platform for Heart Repair

Regeleration is the myocardium’s natural adaptive remodeling response to implanted biopolymer hydrogels, a new heart failure treatment modality with promising success in early clinical trials. Classified as a medical device capable of long-term myocardial engraftment, implanted hydrogels of varying molecular composition provide mechanical bulking and scaffolding support that can stabilize or reverse adverse ventricular remodeling. Additionally, natural or synthetically designed hydrogels encoding specific bioactivities or signaling functions can directly regulate myocardial biology to mediate heart repair. To gain mechanistic insight into the molecular and cellular biology and biochemistry of the biopolymer-myocardial interface, we studied two clinically relevant hydrogels - seaweed-derived alginate (Alg) and myomatrix (MMx), extracellular matrix molecules prepared from decellularized pig heart - in a mouse model. Alg and MMx differentially activated signal transduction cascades, recruited different cell types and produced distinctive gene expression signatures and patterns of cardiomyocyte hypertrophy, including muscle enhancer factor-2 (MEF2) and fetal gene program (re)activation. Chemically modifying Alg’s backbone structure correspondingly altered myocardium’s biological response, demonstrating the synthetic tunability of this repair process. These observations demonstrate that implanted biopolymer hydrogels drive unexpectedly robust and versatile regelerative responses in myocardium, transducing physical and biochemical signals to the cardiac genome that contribute to hydrogel function, providing a potential therapeutic target for enhancing hydrogel-mediated heart repair without stem cells.