Connexin43 Modulates Cell Polarity and Directional Cell Migration by Regulating Microtubule Dynamics

Knockout mice deficient in the gap junction gene connexin43 exhibit developmental anomalies associated with abnormal neural crest, primordial germ cell, and proepicardial cell migration. These migration defects are due to a loss of directional cell movement, and are associated with abnormal actin stress fiber organization and a loss of polarized cell morphology. To elucidate the mechanism by which Cx43 regulates cell polarity, we used a wound closure assays with mouse embryonic fibroblasts (MEFs) to examine polarized cell morphology and directional cell movement. Studies using embryonic fibroblasts from Cx43 knockout (Cx43KO) mice showed Cx43 deficiency caused cell polarity defects as characterized by a failure of the Golgi apparatus and the microtubule organizing center to reorient with the direction of wound closure. Actin stress fibers at the wound edge also failed to appropriately align, and stabilized microtubule (Glu-tubulin) levels were markedly reduced. Forced expression of Cx43 with deletion of its tubulin-binding domain (Cx43dT) in both wildtype MEFs and neural crest cell explants recapitulated the cell migration defects seen in Cx43KO cells. However, forced expression of Cx43 with point mutation causing gap junction channel closure had no effect on cell motility. TIRF imaging revealed increased microtubule instability in Cx43KO cells, and microtubule targeting of membrane localized Cx43 was reduced with expression of Cx43dT construct in wildtype cells. Together, these findings suggest the essential role of Cx43 gap junctions in development is mediated by regulation of the tubulin cytoskeleton and cell polarity by Cx43 via a nonchannel function

Targeting Cx43 and N-Cadherin, Which Are Abnormally Upregulated in Venous Leg Ulcers, Influences Migration, Adhesion and Activation of Rho GTPases

Venous leg ulcers can be very hard to heal and represent a significant medical need with no effective therapeutic treatment currently available

eXtraembryonic ENdoderm (XEN) Stem Cells Produce Factors that Activate Heart Formation

Initial specification of cardiomyocytes in the mouse results from interactions between the extraembryonic anterior visceral endoderm (AVE) and the nascent mesoderm. However the mechanism by which AVE activates cardiogenesis is not well understood, and the identity of specific cardiogenic factors in the endoderm remains elusive. Most mammalian studies of the cardiogenic potential of the endoderm have relied on the use of cell lines that are similar to the heart-inducing AVE. These include the embryonal-carcinoma-derived cell lines, END2 and PYS2. The recent development of protocols to isolate eXtraembryonic ENdoderm (XEN) stem cells, representing the extraembryonic endoderm lineage, from blastocyst stage mouse embryos offers new tools for the genetic dissection of cardiogenesis.Here, we demonstrate that XEN cell-conditioned media (CM) enhances cardiogenesis during Embryoid Body (EB) differentiation of mouse embryonic stem (ES) cells in a manner comparable to PYS2-CM and END2-CM. Addition of CM from each of these three cell lines enhanced the percentage of EBs that formed beating areas, but ultimately, only XEN-CM and PYS2-CM increased the total number of cardiomyocytes that formed. Furthermore, our observations revealed that both contact-independent and contact-dependent factors are required to mediate the full cardiogenic potential of the endoderm. Finally, we used gene array comparison to identify factors in these cell lines that could mediate their cardiogenic potential.These studies represent the first step in the use of XEN cells as a molecular genetic tool to study cardiomyocyte differentiation. Not only are XEN cells functionally similar to the heart-inducing AVE, but also can be used for the genetic dissection of the cardiogenic potential of AVE, since they can be isolated from both wild type and mutant blastocysts. These studies further demonstrate the importance of both contact-dependent and contact-independent factors in cardiogenesis and identify potential heart-inducing proteins in the endoderm

Novel therapeutic strategies targeting fibroblasts and fibrosis in heart disease

Our understanding of cardiac fibroblast functions has moved beyond their roles in heart structure and extracellular matrix generation, and now includes contributions to paracrine, mechanical and electrical signalling during ontogenesis and normal cardiac activity. Fibroblasts have central roles in pathogenic remodelling during myocardial ischaemia, hypertension and heart failure. As key contributors to scar formation, they are crucial for tissue repair after interventions including surgery and ablation. Novel experimental approaches targeting cardiac fibroblasts are promising potential therapies for heart disease. Indeed, several existing drugs act, at least partially, through effects on cardiac connective tissue. This Review outlines the origins and roles of fibroblasts in cardiac development, homeostasis and disease; illustrates the involvement of fibroblasts in current and emerging clinical interventions; and identifies future targets for research and development