Recombinant canine NT-proBNP (aa85,>95%)

Lipid Phosphate phosphatase 3 (LPP3), encoded by the PIpp3 gene, is an enzyme that dephosphorylates the bioactive lipid mediator lysophosphatidic acid (LPA). To study the role of LPP3 in the myocardium, we generated a cardiac specific PIpp3 deficient mouse strain. Although these mice were viable at birth in contrast to global PIpp3 knockout mice, they showed increased mortality similar to 8 months. LPP3 deficient mice had enlarged hearts with reduced left ventricular performance as seen by echocardiography. Cardiac specific Plpp3 deficient mice had longer ventricular effective refractory periods compared to their Plpp3 littermates. We observed that lack of Lpp3 enhanced cardiomyocyte hypertrophy based on analysis of cell surface area. We found that lack of Lpp3 signaling was mediated through the activation of Rho and phospho-ERK pathways. There are increased levels of fetal genes Natriuretic Peptide A and B (Nppa and Nppb) expression indicating myocardial dysfunction. These mice also demonstrate mitochondrial dysfunction as evidenced by a significant decrease (P < 0.001) in the basal oxygen consumption rate, mitochondrial ATP production, and spare respiratory capacity as measured through mitochondrial bioenergetics. Histology and transmission electron microscopy of these hearts showed disrupted sarcomere organization and intercalated disc, with a prominent disruption of the cristae and vacuole formation in the mitochondria. Our findings suggest that LPA/LPP3-signaling nexus plays an important role in normal function of cardiomyocytes.

There is great interest in identifying signaling mechanisms by which cardiomyocytes (CMs) can enter the cell cycle and promote endogenous cardiac repair. We have previously demonstrated that IL-13 stimulated cell cycle activity of neonatal CMs in vitro. However, the signaling events that occur downstream of IL-13 in CMs and the role of IL-13 in CM proliferation and regeneration in vivo have not been explored. Here, we tested the role of IL-13 in promoting neonatal CM cell cycle activity and heart regeneration in vivo and investigated the signaling pathway(s) downstream of IL-13 specifically in CMs. Compared with control, CMs from neonatal IL-13 knockout (IL-13(-/-)) mice showed decreased proliferative markers and coincident upregulation of the hypertrophic marker brain natriuretic peptide (Nppb) and increased CM nuclear size. After apical resection in anesthetized newborn mice, heart regeneration was significantly impaired in IL-13(-/-) mice compared with wild-type mice. Administration of recombinant IL-13 reversed these phenotypes by increasing CM proliferation markers and decreasing Nppb expression. RNA sequencing on primary neonatal CMs treated with IL-13 revealed activation of gene networks regulated by ERK1/2 and Akt. Western blot confirmed strong phosphorylation of ERK1/2 and Akt in both neonatal and adult cultured CMs in response to IL-13. Our data demonstrated a role for endogenous IL-13 in neonatal CM cell cycle and heart regeneration. ERK1/2 and Akt signaling are important pathways known to promote CM proliferation and protect against apoptosis, respectively; thus. targeting transmembrane receptor signaling or administering recombinant IL-13 may be therapeutic approaches for activating proregenerative and survival pathways in the heart. NEW & NOTEWORTHY Here, we demonstrate, for the first time, that IL-13 is involved in neonatal cardiomyocyte cell cycle activity and heart regeneration in vivo. Prior work has shown that IL-13 promotes cardiomyocyte cell cycle activity in vitro; however, the signaling pathways were unknown. We used RNA sequencing to identify the signaling pathways activated downstream of IL-13 in cardiomyocytes and found that ERK1/2 and Akt signaling was activated in response to IL-13.