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Cardiac repair depends on angiogenesis and cell proliferation. Previously we identified Canopy 2 (CNPY2) as a secreted angiogenic growth factor which promotes neovascularization. We investigated the role of CNPY2 in cardiac repair following myocardial infarction (MI) and the possible mediators involved using Cnpy2 knockout (KO) mice and human cardiac tissue. Cardiac tissue from patients with end-stage heart failure had significantly lower endogenous CNPY2 expression compared to samples from control patients. CNPY2 expression in mouse hearts significantly decreased following MI. Significantly less leukocyte and endothelial cell proliferation was found in Cnpy2 KO than wild-type (WT) mice post MI which contributed to impaired angiogenesis, tissue repair, and decreased cardiac function (fractional shortening: WT: 21.1 ± 2.1% vs. KO: 16.4 ± 1.6%, p <.01 at day 28 post MI). RT-qPCR revealed significantly increased p16INK4a expression in Cnpy2 KO mouse hearts (WT: 1.0 ± 0.04 vs. KO: 2.33 ± 0.11 [relative expression of p16 INK4a], p <.01) which was confirmed by immunostaining (WT: 8.47 ± 1.22 vs. KO: 12.9 ± 1.22 [% total cells], p <.05) for the p16INK4a protein. Expression of cell cycle-related proteins, cyclin D1, cyclin-dependent kinases 4 and 6, and phosphorylated retinoblastoma protein (pRb) was significantly decreased in Cnpy2 KO mouse hearts. The up-regulation of the p16INK4a/cyclin D1/Rb pathway by knockout of Cnpy2 was accompanied by attenuation of PDK1/Akt phosphorylation. MI exacerbated the detrimental effects of p16INK4a on tissue repair in Cnpy2 KO mice. Overexpression of CNPY2 in the cardiac tissue of transgenic mice reversed the inhibition of cell proliferation through suppression of the p16INK4a pathway. Cardiac injury and progressive heart failure were associated with decreased CNPY2 levels in both humans and mice. Knockout of Cnpy2 resulted in up-regulation of p16INK4a which impaired cardiac function and tissue repair. These data suggest that CNPY2 is an important regulator of p16INK4a and promotes cell proliferation and tissue repair through inhibition of the p16INK4a pathway. CNPY2 treatment may offer a new approach to restore cardiac function after an MI. • Lower CNPY2 expression in cardiac tissue from patients with end-stage heart failure. • CNPY2 expression in mouse hearts decreased significantly following an MI. • Cnpy2 KO mice showed impaired functional recovery post MI. • Cnpy2 KO upregulated p16INK4a to hinder leukocyte and endothelial cell proliferation and heart repair. • Overexpressing CNPY2 reversed inhibited cell proliferation by suppressing p16INK4a. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]