Mechanisms controlling the acquisition of a cardiac phenotype by liver stem cells

Abstract

The mechanisms underlying stem cell acquisition of a cardiac phenotype are unresolved. We studied early events during the acquisition of a cardiac phenotype by a cloned adult liver stem cell line (WB F344) in a cardiac microenvironment. WB F344 cells express a priori the transcription factors GATA4 and SRF, connexin 43 in the cell membrane, and myoinositol 1,4,5-triphosphate receptor in the perinuclear region. calcium signal transduction ͉ cardiomyogenesis ͉ gap junctions E xtracardiac stem cell use in early phase clinical trials and animal experiments has raised the possibility that stem cell therapy may be able to repair the damaged heart (for review see refs. 1 and 2). The mechanisms underlying the acquisition of a cardiac phenotype by stem cells have not been elucidated. In some cases, fusion between stem cells and cardiomyocytes has been proposed as the basis for the apparent ''transdifferentiation'' (3). We (4) and others (5, 6) have demonstrated that extracardiac stem cells can acquire a cardiac phenotype when placed in a cardiac microenvironment without the benefit of fusion with surrounding myocytes.We have found that cells from a stem cell line (WB F344) derived from a cloned single nonparenchymal epithelial cell isolated from the liver of a young adult rat (for review see ref.7) respond in vivo (8) and in culture (4) to signals from a cardiac microenvironment and acquire a cardiomyocyte phenotype. Understanding the mechanisms that regulate the acquisition of a cardiac phenotype by a clone-derived stem cell (for example, WB F344 cells) may prove valuable in selecting and manipulating stem cells from other sources, e.g., autologous stem cells, and so enhance their potential for successful use in cell therapy.In the current study we examined the earliest events associated with the acquisition of a cardiomyocyte phenotype by WB F344 cells cocultured with rat neonatal heart cells, a cardiac environment model system (4). We find that cell-cell communication through shared and functional gap junction channels is estab- ] nu oscillations require myoinositol 1,4,5-triphosphate receptor (IP3R) stimulation and are associated with de novo expression of cardiac transcription factors in the WB F344 cells. We hypothesize that collectively these events usher in the acquisition of a cardiac phenotype in the WB F344 stem cell line. Results Early Intercellular Communication Between Neonatal Myocytes andWB F344 Cells. Because WB F344 cells express connexin 43 (Cx43), the predominant isoform expressed in ventricular myocytes, we examined whether myocytes and WB F344 cells develop shared Cx43-derived gap junctions. Twenty-four hours after dsRed fluorescent WB F344 cells were cocultured with heart cells, functional cell-cell communication between their cytoplasm and juxtaposed neonatal cardiomyocytes was demonstrated by fluorescence recovery after photobleaching (Fig. 1). When in older cocultures (4-6 days old) WB F344 cells had acquired a cardiac phenotype, Cx43 was preferentially localized at the interface between neonata...

In vivo forced expression of myocardin in ventricular myocardium transiently impairs systolic performance in early neonatal pig heart

“…In this regard, myocd can initiate the expression of cardiac muscle-specified genes in cultured fibroblasts, but only in the presence of the co-expressed small ubiquitinlike modifier, SUMO-1 . Undifferentiated liverderived stem cells acquire a cardiomyocyte phenotype when cocultivated in vitro with neonatal cardiomyocytes which, in turn, results in the de novo activation of cardiac transcriptional factors including myocd (Muller-Borer et al, 2007). These and other data (Oh et al, 2004;Callis et al, 2005;Creemers et al, 2006a) strongly suggest that additional factors are required to promote myocardin's role in cardiogenic gene expression.…”

Gap Junctional Coupling with Cardiomyocytes is Necessary but Not Sufficient for Cardiomyogenic Differentiation of Cocultured Human Mesenchymal Stem Cells

“…Interestingly, these fetal AM hMSCs were able to differentiate, in coculture with nrCMCs, into functional CMCs, while adult AT hMSCs were not [19]. Other investigators using cocultures with CMCs to induce cardiomyogenic differentiation in stem cells have also proposed that intercellular communication through gap junctions might be essential in this differentiation process [33,34]. However, the role of gap junctional communication in the transfer of cardiomyogenic signals from CMCs to other cell types has not yet been investigated.…”

“…In line with these findings are the observations by Muller-Borer et al who found that in coculture with nrCMCs, rat liver stem cells obtain CMC-like properties and display [Ca 2þ ] oscillations synchronous with those of adjoining CMCs. The [Ca 2þ ] oscillations in the liver stem cells were dependent on gap junctional communication with neighboring CMCs and their inhibition led to a decrease in the expression of CMC-specific genes by the liver stem cells [34]. The recent observation that hyperpolarization is sufficient to induce cardiomyogenic differentiation of human CMC progenitor cells underlines the importance of gap junctional coupling in this process [12].…”

Early Cell Loss Associated with Mesenchymal Stem Cell Cardiomyoplasty

“…We chose this model to maximize our ability to differentiate between host and transplanted cells using species specific markers.While we used GFP to label cells, other methods such as antibodies to human mitochondria could have been used as well [35]. Concern may be raised about the xenogenic immune response that could be elicited from these injections.…”