![]() ![]() (A) Diagram shows tamoxifen (Tam) and EdU injection scheme. All analyses were performed with 3-4 month stage hearts. Lats1/2 and Salv were conditionally deleted in cardiomyocytes using the inducible Myh6-Cre/Esr line via tamoxifen injection. These results show that cardiomyocytes re-enter the cell cycle upon Hippo pathway disruption and support the hypothesis that Hippo signaling is a negative regulator of adult cardiomyocyte renewal.Īdult cardiomyocyte renewal via deletion of Hippo pathway genes. Average cardiomyocyte size in these hearts was significantly smaller than that of controls ( Fig. Moreover, total cardiomyocyte number was increased with more mononuclear cardiomyocytes in Lats1/2 and Salv CKO hearts than in controls ( Fig. Both Lats1/2 CKO and Salv CKO cardiomyocyte nuclei had increased numbers of Ki-67 (Mki67)-expressing cardiomyocytes compared with controls ( Fig. Cell cycle re-entry was also quantified in isolated cardiomyocyte nuclei using fluorescence-activated cell sorting (FACS) analysis ( Fig. Quantification of EdU-positive cells showed significant induction of DNA synthesis in Hippo-deficient hearts with a greater increase in Lats1/2 mutants compared with Salv CKO cardiomyocytes ( Fig. In contrast to Hippo mutant hearts, control hearts only incorporated EdU in cardiac fibroblasts ( Fig. Nuclear EdU incorporation, indicating de novo DNA synthesis, was detected in both Salv conditional knockout (CKO) and Lats1/2 CKO mutant cardiomyocytes revealing an endogenous cardiomyocyte renewal capacity when Hippo signaling is deleted. To determine whether Hippo deficiency results in cell cycle re-entry, we also injected mice with 5-ethynyl-2’-deoxyuridine (EdU). Efficient deletion of Hippo components was determined by immunohistochemistry with antibodies for phosphoYap (pYap) and Salv ( Fig. We generated adult cardiomyocytes that were mutant for Salv and Lats1/2 by injecting three-month-old mice with tamoxifen ( Fig. Targeting the Hippo pathway in human disease might be beneficial for the treatment of heart disease. Our findings reveal that Hippo signaling is an endogenous repressor of adult cardiomyocyte renewal and regeneration. In damaged hearts, Hippo mutant cardiomyocytes also have elevated proliferation. Moreover, Hippo deficiency enhances cardiomyocyte regeneration with functional recovery after adult myocardial infarction as well as after postnatal day eight (P8) cardiac apex resection and P8 myocardial infarction. ![]() We found that unstressed Hippo-deficient adult mouse cardiomyocytes re-enter the cell cycle and undergo cytokinesis. Here, we investigated Hippo signaling in adult cardiomyocyte renewal and regeneration. Hippo signaling, an ancient organ size control pathway, is a kinase cascade that inhibits developing cardiomyocyte proliferation but it has not been studied postnatally or in fully mature adult cardiomyocytes. ![]() The endogenous mechanisms preventing mammalian cardiomyocyte regeneration are poorly understood. Heart failure due to cardiomyocyte loss after ischemic heart disease is the leading cause of death in the United States in large part because heart muscle regenerates poorly. ![]()
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