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Fibroblast growth factor 10 gene regulation in the second heart field by Tbx1, Nkx2-5, and Islet1 reveals a genetic switch for down-regulation in the myocardium.

ABSTRACT: During cardiogenesis, Fibroblast Growth Factor (Fgf10) is expressed in the anterior second heart field. Together with Fibroblast growth factor 8 (Fgf8), Fgf10 promotes the proliferation of these cardiac progenitor cells that form the arterial pole of the heart. We have identified a 1.7-kb region in the first intron of Fgf10 that is necessary and sufficient to direct transgene expression in this cardiac context. The 1.7-kb sequence is directly controlled by T-box transcription factor 1 (Tbx1) in anterior second heart field cells that contribute to the outflow tract. It also responds to both NK2 transcription factor related, locus 5 (Nkx2-5) and ISL1 transcription factor, LIM/homeodomain (Islet1), acting through overlapping sites. Mutation of these sites reduces transgene expression in the anterior second heart field where the Fgf10 regulatory element is activated by Islet1 via direct binding in vivo. Analysis of the response to Nkx2-5 loss- and Isl1 gain-of-function genetic backgrounds indicates that the observed up-regulation of its activity in Nkx2-5 mutant hearts, reflecting that of Fgf10, is due to the absence of Nkx2-5 repression and to up-regulation of Isl1, normally repressed in the myocardium by Nkx2-5. ChIP experiments show strong binding of Nkx2-5 in differentiated myocardium. Molecular and genetic analysis of the Fgf10 cardiac element therefore reveals how key cardiac transcription factors orchestrate gene expression in the anterior second heart field and how genes, such as Fgf10, normally expressed in the progenitor cell population, are repressed when these cells enter the heart and differentiate into myocardium. Our findings provide a paradigm for transcriptional mechanisms that underlie the changes in regulatory networks during the transition from progenitor state to that of the differentiated tissue.

SUBMITTER: Watanabe Y

PROVIDER: S-EPMC3494960 | biostudies-literature |

REPOSITORIES: biostudies-literature

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Project description:BACKGROUND:Activated fibroblasts (myofibroblasts) play a critical role in cardiac fibrosis; however, their origin in the diseased heart remains unclear, warranting further investigation. Recent studies suggest the contribution of bone marrow fibroblast progenitor cells (BM-FPCs) in pressure overload-induced cardiac fibrosis. We have previously shown that interleukin-10 (IL10) suppresses pressure overload-induced cardiac fibrosis; however, the role of IL10 in inhibition of BM-FPC-mediated cardiac fibrosis is not known. We hypothesized that IL10 inhibits pressure overload-induced homing of BM-FPCs to the heart and their transdifferentiation to myofibroblasts and thus attenuates cardiac fibrosis. METHODS:Pressure overload was induced in wild-type (WT) and IL10 knockout (IL10KO) mice by transverse aortic constriction. To determine the bone marrow origin, chimeric mice were created with enhanced green fluorescent protein WT mice marrow to the IL10KO mice. For mechanistic studies, FPCs were isolated from mouse bone marrow. RESULTS:Pressure overload enhanced BM-FPC mobilization and homing in IL10KO mice compared with WT mice. Furthermore, WT bone marrow (from enhanced green fluorescent protein mice) transplantation in bone marrow-depleted IL10KO mice (IL10KO chimeric mice) reduced transverse aortic constriction-induced BM-FPC mobilization compared with IL10KO mice. Green fluorescent protein costaining with ?-smooth muscle actin or collagen 1? in left ventricular tissue sections of IL10KO chimeric mice suggests that myofibroblasts were derived from bone marrow after transverse aortic constriction. Finally, WT bone marrow transplantation in IL10KO mice inhibited transverse aortic constriction-induced cardiac fibrosis and improved heart function. At the molecular level, IL10 treatment significantly inhibited transforming growth factor-?-induced transdifferentiation and fibrotic signaling in WT BM-FPCs in vitro. Furthermore, fibrosis-associated microRNA (miRNA) expression was highly upregulated in IL10KO-FPCs compared with WT-FPCs. Polymerase chain reaction-based selective miRNA analysis revealed that transforming growth factor-?-induced enhanced expression of fibrosis-associated miRNAs (miRNA-21, -145, and -208) was significantly inhibited by IL10. Restoration of miRNA-21 levels suppressed the IL10 effects on transforming growth factor-?-induced fibrotic signaling in BM-FPCs. CONCLUSIONS:Our findings suggest that IL10 inhibits BM-FPC homing and transdifferentiation to myofibroblasts in pressure-overloaded myocardium. Mechanistically, we show for the first time that IL10 suppresses Smad-miRNA-21-mediated activation of BM-FPCs and thus modulates cardiac fibrosis.

Project description:BACKGROUND:Transforming growth factor-?s regulate a wide range of cellular responses by activating Smad-dependent and Smad-independent cascades. In the infarcted heart, Smad3 signaling is activated in both cardiomyocytes and interstitial cells. We hypothesized that cell-specific actions of Smad3 regulate repair and remodeling in the infarcted myocardium. METHODS:To dissect cell-specific Smad3 actions in myocardial infarction, we generated mice with Smad3 loss in activated fibroblasts or cardiomyocytes. Cardiac function was assessed after reperfused or nonreperfused infarction using echocardiography. The effects of cell-specific Smad3 loss on the infarcted heart were studied using histological studies, assessment of protein, and gene expression levels. In vitro, we studied Smad-dependent and Smad-independent actions in isolated cardiac fibroblasts. RESULTS:Mice with fibroblast-specific Smad3 loss had accentuated adverse remodeling after reperfused infarction and exhibited an increased incidence of late rupture after nonreperfused infarction. The consequences of fibroblast-specific Smad3 loss were not a result of effects on acute infarct size but were associated with unrestrained fibroblast proliferation, impaired scar remodeling, reduced fibroblast-derived collagen synthesis, and perturbed alignment of myofibroblast arrays in the infarct. Polarized light microscopy in Sirius red-stained sections demonstrated that the changes in fibroblast morphology were associated with perturbed organization of the collagenous matrix in the infarcted area. In contrast, ?-smooth muscle actin expression by infarct myofibroblasts was not affected by Smad3 loss. Smad3 critically regulated fibroblast function, activating integrin-mediated nicotinamide adenine dinucleotide phosphate (NADPH) oxidase-2 (NOX-2) expression. Smad3 loss in cardiomyocytes attenuated remodeling and dysfunction after infarction. Cardiomyocyte-specific Smad3 loss did not affect acute infarct size but was associated with attenuated cardiomyocyte apoptosis in the remodeling myocardium, accompanied by decreased myocardial NOX-2 levels, reduced nitrosative stress, and lower matrix metalloproteinase-2 expression. CONCLUSIONS:In healing myocardial infarction, myofibroblast- and cardiomyocyte-specific activation of Smad3 has contrasting functional outcomes that may involve activation of an integrin/reactive oxygen axis.

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Fibroblast growth factor 10 gene regulation in the second heart field by Tbx1, Nkx2-5, and Islet1 reveals a genetic switch for down-regulation in the myocardium.

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