Mast cells promote proliferation and migration and inhibit differentiation of mesenchymal stem cells through PDGF.

BACKGROUND: Mast cells (MCs) dynamically participate in wound healing after myocardial infarction (MI) by releasing cytokines. Indeed, MC-deficient mice undergo rapid left ventricular dilation post-MI. Mesenchymal stem cells (MSCs) are recruited to the injured region following an MI and have potential for cardiac repair. In the current study, we evaluate the effect of MCs on MSC proliferation and myogenic differentiation. METHODS AND RESULTS: MCs were cultured from mouse bone marrow and MC granulate (MCG) was extracted from MCs via freeze-thaw cycles followed by filtration. α-SMA (smooth muscle actin) expression was examined as an indicator of myogenic differentiation. MSC/MC co-culture resulted in decreased MSC differentiation indicated by α-SMA suppression in MSCs. MCG also suppressed α-SMA expression and increased MSC migration and proliferation in a dose-dependent manner. Removal of MCG rescued α-SMA expression and MSC differentiation. Platelet derived growth factor (PDGF) receptor blockade using AG1296 also rescued MSC differentiation even after MCG treatment. Real-time PCR and Western blot showed that MCG exerted its effects on MSCs via downregulation of miR-145 and miR-143, downregulation of myocardin, upregulation of Klf4, and increased Erk and Elk1 phosphorylation. CONCLUSIONS: MCs promote MSC proliferation and migration by suppressing their myogenic differentiation. MCs accomplish this via activation of the PDGF pathway, downregulation of miR-145/143, and modulation of the myocardin-Klf4 axis. These data suggest a potential role for MSC/MC interaction in the infarcted heart where MCs may inhibit MSCs from differentiation and promote their proliferation whereby increased cardiac MSC accumulation promotes eventual cardiac regeneration after MCs cease activity.

The cardiac repair benefits of inflammation do not persist: evidence from mast cell implantation.

Multiple mechanisms contribute to progressive cardiac dysfunction after myocardial infarction (MI) and inflammation is an important mediator. Mast cells (MCs) trigger inflammation after MI by releasing bio-active factors that contribute to healing. c-Kit-deficient (Kit(W/W-v) ) mice have dysfunctional MCs and develop severe ventricular dilatation post-MI. We explored the role of MCs in post-MI repair. Mouse wild-type (WT) and Kit(W/W-v) MCs were obtained from bone marrow (BM). MC effects on fibroblasts were examined in vitro by proliferation and gel contraction assays. MCs were implanted into infarcted mouse hearts and their effects were evaluated using molecular, cellular and cardiac functional analyses. In contrast to WT, Kit(W/W-v) MC transplantation into Kit(W/W-v) mice did not improve cardiac function or scar size post-MI. Kit(W/W-v) MCs induced significantly reduced fibroblast proliferation and contraction compared to WT MCs. MC influence on fibroblast proliferation was Basic fibroblast growth factor (bFGF)-dependent and MC-induced fibroblast contractility functioned through transforming growth factor (TGF)-ß. WT MCs transiently rescue cardiac function early post-MI, but the benefits of BM cell implantation lasted longer. MCs induced increased inflammation compared to the BM-injected mice, with increased neutrophil infiltration and infarct tumour necrosis factor-α (TNF-α) concentration. This augmented inflammation was followed by increased angiogenesis and myofibroblast formation and reduced scar size at early time-points. Similar to the functional data, these beneficial effects were transient, largely vanishing by day 28. Dysfunctional Kit(W/W-v) MCs were unable to rescue cardiac function post-MI. WT MC implantation transiently enhanced angiogenesis and cardiac function. These data suggest that increased inflammation is beneficial to cardiac repair, but these effects are not persistent.

Uterine-derived progenitor cells are immunoprivileged and effectively improve cardiac regeneration when used for cell therapy.

Cell therapy to prevent cardiac dysfunction after myocardial infarction (MI) is less effective in aged patients because aged cells have decreased regenerative capacity. Allogeneic transplanted stem cells (SCs) from young donors are usually rejected. Maintaining transplanted SC immunoprivilege may dramatically improve regenerative outcomes. The uterus has distinct immune characteristics, and we showed that reparative uterine SCs home to the myocardium post-MI. Here, we identify immunoprivileged uterine SCs and assess their effects on cardiac regeneration after allogeneic transplantation. We found more than 20% of cells in the mouse uterus have undetectable MHC I expression by flow cytometry. Uterine MHC I((neg)) and MHC I((pos)) cells were separated by magnetic cell sorting. The MHC I((neg)) population expressed the SC markers CD34, Sca-1 and CD90, but did not express MHC II or c-kit. In vitro, MHC I((neg)) and ((pos)) SCs show colony formation and endothelial differentiation capacity. In mixed leukocyte co-culture, MHC I((neg)) cells showed reduced cell death and leukocyte proliferation compared to MHC I((pos)) cells. MHC I((neg)) and ((pos)) cells had significantly greater angiogenic capacity than mesenchymal stem cells. The benefits of intramyocardial injection of allogeneic MHC I((neg)) cells after MI were comparable to syngeneic bone marrow cell transplantation, with engraftment in cardiac tissue and limited recruitment of CD4 and CD8 cells up to 21 days post-MI. MHC I((neg)) cells preserved cardiac function, decreased infarct size and improved regeneration post-MI. This new source of immunoprivileged cells can induce neovascularization and could be used as allogeneic cell therapy for regenerative medicine.

c-Ski, Smurf2, and Arkadia as regulators of TGF-beta signaling: new targets for managing myofibroblast function and cardiac fibrosis.

Recent studies demonstrate the critical role of the extracellular matrix in the organization of parenchymal cells in the heart. Thus, an understanding of the modes of regulation of matrix production by cardiac myofibroblasts is essential. Transforming growth factor beta (TGF-beta) signaling is transduced through the canonical Smad pathway, and the involvement of this pathway in matrix synthesis and other processes requires precise control. Inhibition of Smad signaling may be achieved at the receptor level through the targeting of the TGF-beta type I receptors with an inhibitory Smad7/Smurf2 complex, or at the transcriptional level through c-Ski/receptor-Smad/co-mediator Smad4 interactions. Conversely, Arkadia protein intensifies TGF-beta-induced effects by marking c-Ski and inhibitory Smad7 for destruction. The study of these TGF-beta mediators is essential for future treatment of fibrotic disease, and this review highlights recent relevant findings that may impact our understanding of cardiac fibrosis.