LPA₃-mediated lysophosphatidic acid signaling promotes postnatal heart regeneration in mice

Background: Lysophosphatidic acid (LPA) is a small glycerophospholipid that acts as a potent extracellular signal in various biological processes and diseases. Our previous work demonstrated that the expression of the LPA receptors LPA₁ and LPA₃ is elevated in the early postnatal heart. However, the role of this stage-specific expression of LPA₁ and LPA₃ in the heart is unknown. Methods and Results: By using LPA₃ and LPA₁ knockout mice, and neonatal SD rats treated with Ki16425 (LPA₁/LPA₃ inhibitor), we found that the number of proliferating cardiomyocytes, detected by coimmunostaining pH3, Ki67 or BrdU with cardiac troponin T, was significantly decreased in the LPA₃ knockout mice and the Ki16425-treated rats but not in the LPA₁ knockout mice during the first week of postnatal life. Using a myocardial infarction (MI) model, we found that cardiac function and the number of proliferating cardiomyocytes were decreased in the neonatal LPA₃ KO mice and increased in the AAV9-mediated cardiac-specific LPA₃ overexpression mice. By using lineage tracing and AAV9-LPA₃, we further found that LPA₃ overexpression in adult mice enhances cardiac function and heart regeneration as assessed by pH3-, Ki67-, and Aurora B-positive cardiomyocytes and clonal cardiomyocytes after MI. Genome-wide transcriptional profiling and additional mechanistic studies showed that LPA induces cardiomyocyte proliferation through the PI3K/AKT, BMP-Smad1/5, Hippo/YAP and MAPK/ERK pathways in vitro, whereas only ERK was confirmed to be activated by LPA-LPA₃ signaling in vivo. Conclusion: Our study reports that LPA₃-mediated LPA signaling is a crucial factor for cardiomyocyte proliferation in the early postnatal heart. Cardiac-specific LPA₃ overexpression improved cardiac function and promoted cardiac regeneration after myocardial injury induced by MI. This finding suggested that activation of LPA₃ potentially through AAV-mediated gene therapy might be a therapeutic strategy to improve the outcome after MI.