Signaling via the TGF-beta type I receptor Alk5 in heart development

University of Michigan, Department of Biologic and Materials Sciences, Ann Arbor, MI 48109, USA.
Developmental Biology (Impact Factor: 3.55). 09/2008; 322(1):208-18. DOI: 10.1016/j.ydbio.2008.07.038
Source: PubMed


Trophic factors secreted both from the endocardium and epicardium regulate appropriate growth of the myocardium during cardiac development. Epicardially-derived cells play also a key role in development of the coronary vasculature. This process involves transformation of epithelial (epicardial) cells to mesenchymal cells (EMT). Similarly, a subset of endocardial cells undergoes EMT to form the mesenchyme of endocardial cushions, which function as primordia for developing valves and septa. While it has been suggested that transforming growth factor-betas (Tgf-beta) play an important role in induction of EMT in the avian epi- and endocardium, the function of Tgf-betas in corresponding mammalian tissues is still poorly understood. In this study, we have ablated the Tgf-beta type I receptor Alk5 in endo-, myo- and epicardial lineages using the Tie2-Cre, Nkx2.5-Cre, and Gata5-Cre driver lines, respectively. We show that while Alk5-mediated signaling does not play a major role in the myocardium during mouse cardiac development, it is critically important in the endocardium for induction of EMT both in vitro and in vivo. Moreover, loss of epicardial Alk5-mediated signaling leads to disruption of cell-cell interactions between the epicardium and myocardium resulting in a thinned myocardium. Furthermore, epicardial cells lacking Alk5 fail to undergo Tgf-beta-induced EMT in vitro. Late term mutant embryos lacking epicardial Alk5 display defective formation of a smooth muscle cell layer around coronary arteries, and aberrant formation of capillary vessels in the myocardium suggesting that Alk5 is controlling vascular homeostasis during cardiogenesis. To conclude, Tgf-beta signaling via Alk5 is not required in myocardial cells during mammalian cardiac development, but plays an irreplaceable cell-autonomous role regulating cellular communication, differentiation and proliferation in endocardial and epicardial cells.

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    • "Indeed, consistent with our work in diabetes induced cardiac fibrosis [15,16,30,34,47], elevated TGF-β1 expression is consistently found during the transition from stable hypertrophy to heart failure in both experimental models and human heart failure [14,41]. As a result, strategies to reduce TGF-β activity remain an important therapeutic target, however current attempts have been limited by toxicity or off target effects [48-50]. In the present paper, we focused upon inhibition of Smad2, which mediates the intracellular actions of TGF-β receptor activation. "
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    ABSTRACT: Background Despite advances in the treatment of heart failure, mortality remains high, particularly in individuals with diabetes. Activated transforming growth factor beta (TGF-β) contributes to the pathogenesis of the fibrotic interstitium observed in diabetic cardiomyopathy. We hypothesized that high glucose enhances the activity of the transcriptional co-activator p300, leading to the activation of TGF-β via acetylation of Smad2; and that by inhibiting p300, TGF-β activity will be reduced and heart failure prevented in a clinically relevant animal model of diabetic cardiomyopathy. Methods p300 activity was assessed in H9c2 cardiomyoblasts under normal glucose (5.6 mmol/L—NG) and high glucose (25 mmol/L—HG) conditions. 3H-proline incorporation in cardiac fibroblasts was also assessed as a marker of collagen synthesis. The role of p300 activity in modifying TGF-β activity was investigated with a known p300 inhibitor, curcumin or p300 siRNA in vitro, and the functional effects of p300 inhibition were assessed using curcumin in a hemodynamically validated model of diabetic cardiomyopathy – the diabetic TG m(Ren-2)27 rat. Results In vitro, H9c2 cells exposed to HG demonstrated increased p300 activity, Smad2 acetylation and increased TGF-β activity as assessed by Smad7 induction (all p < 0.05 c/w NG). Furthermore, HG induced 3H-proline incorporation as a marker of collagen synthesis (p < 0.05 c/w NG). p300 inhibition, using either siRNA or curcumin reduced p300 activity, Smad acetylation and TGF-β activity (all p < 0.05 c/w vehicle or scrambled siRNA). Furthermore, curcumin therapy reduced 3H-proline incorporation in HG and TGF-β stimulated fibroblasts (p < 0.05 c/w NG). To determine the functional significance of p300 inhibition, diabetic Ren-2 rats were randomized to receive curcumin or vehicle for 6 weeks. Curcumin treatment reduced cardiac hypertrophy, improved diastolic function and reduced extracellular matrix production, without affecting glycemic control, along with a reduction in TGF-β activity as assessed by Smad7 activation (all p < 0.05 c/w vehicle treated diabetic animals). Conclusions These findings suggest that high glucose increases the activity of the transcriptional co-regulator p300, which increases TGF-β activity via Smad2 acetylation. Modulation of p300 may be a novel strategy to treat diabetes induced heart failure.
    Cardiovascular Diabetology 05/2014; 13(1):89. DOI:10.1186/1475-2840-13-89 · 4.02 Impact Factor
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    • "We found that only a small percentage of cells expressing WT1 were present in the epicardium, the subepicardium and the infarcted area; however, the number of WT1 pos cells within the infarcted area was increased in AICAR-treated hearts (Supplemental Fig. 2). As TGF-β1 stimulates epicardial-to-mesenchymal transition (EMT) [33] and AICAR augments TGF-β1 signaling [9], the activated TGF-β1/AMPK pathway may account for the elevated EMT in AICAR-treated hearts. Because of the small portion of WT1 pos cells in the infracted area they might be contributing to a minor extent to fibroblast formation in the aging heart as suggested by others [32] "
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    ABSTRACT: We have demonstrated that scar formation after myocardial infarction (MI) is associated with an endogenous pool of CD44(pos)CD45(neg) multipotential mesenchymal stem cells (MSC). MSC differentiate into fibroblasts secreting collagen that forms a scar and mature into myofibroblasts that express alpha smooth muscle actin (α-SMA) that stabilizes the scar. In the aging mouse, cardiac repair after MI is associated with impaired differentiation of MSC; MSC derived from aged hearts form dysfunctional fibroblasts that deposit less collagen in response to transforming growth factor beta-1 (TGF-β1) and poorly mature into myofibroblasts. We found in vitro that the defect in myofibroblast maturation can be remedied by AICAR, which activates non-canonical TGF-β signaling through AMP-activated protein kinase (AMPK). In the present study, we injected aged mice with AICAR and subjected them to 1h occlusion of the left anterior descending artery (LAD) and then reperfusion for up to 30 days. AICAR-dependent AMPK signaling led to mobilization of an endogenous CD44(pos)CD45(neg) MSC and its differentiation towards fibroblasts and myofibroblasts in the infarct. This was accompanied by enhanced collagen deposition and collagen fiber maturation in the scar. The AICAR-treated group has demonstrated reduced adverse remodeling as indicated by improved apical end diastolic dimension but no changes in ejection fraction and cardiac output were observed. We concluded that these data indicate the novel, previously not described role of AMPK in the post-MI scar formation. These findings can potentially lead to a new therapeutic strategy for prevention of adverse remodeling in the aging heart.
    Journal of Molecular and Cellular Cardiology 07/2013; 63. DOI:10.1016/j.yjmcc.2013.07.005 · 4.66 Impact Factor
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    • "In addition to these postnatal defects we, and others, have previously shown Tgfbr2 is also important in ECs for vascular integrity during development of the embryonic brain [20], [21]. Furthermore, endothelial specific depletion of the TGFβ type I receptor Alk5 leads to a similar cerebral haemorrhagic phenotype and embryonic lethality [21], [33], consistent with a requirement for both Tgfbr1 and Tgfbr2 proteins as a heteromeric receptor complex during TGFβ signalling in ECs. "
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    ABSTRACT: TGFβ signalling in endothelial cells is important for angiogenesis in early embryonic development, but little is known about its role in early postnatal life. To address this we used a tamoxifen inducible Cre-LoxP strategy in neonatal mice to deplete the TypeII TGFβ receptor (Tgfbr2) specifically in endothelial cells. This resulted in multiple micro-haemorrhages, and glomeruloid-like vascular tufts throughout the cerebral cortices and hypothalamus of the brain as well as in retinal tissues. A detailed examination of the retinal defects in these mutants revealed that endothelial adherens and tight junctions were in place, pericytes were recruited and there was no failure of vascular smooth muscle differentiation. However, the deeper retinal plexus failed to form in these mutants and the angiogenic sprouts stalled in their progress towards the inner nuclear layer. Instead the leading endothelial cells formed glomerular tufts with associated smooth muscle cells. This evidence suggests that TGFβ signalling is not required for vessel maturation, but is essential for the organised migration of endothelial cells as they begin to enter the deeper layers of the retina. Thus, TGFβ signalling is essential in vascular endothelial cells for maintaining vascular integrity at the angiogenic front as it migrates into developing neural tissues in early postnatal life.
    PLoS ONE 09/2012; 7(6):e39336. DOI:10.1371/journal.pone.0039336 · 3.23 Impact Factor
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