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 LPA(1) and LPA(3) is elevated in the early postnatal heart. However, the role of this stage-specific expression of LPA(1) and LPA(3) in the heart is unknown. Methods and Results: By using LPA(3) and LPA(1) knockout mice, and neonatal SD rats treated with Ki16425 (LPA(1)/LPA(3) 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 LPA(3) knockout mice and the Ki16425-treated rats but not in the LPA(1) 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 LPA(3) KO mice and increased in the AAV9-mediated cardiac-specific LPA(3) overexpression mice. By using lineage tracing and AAV9-LPA(3), we further found that LPA(3) 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-LPA(3) signaling in vivo. Conclusion: Our study reports that LPA(3)-mediated LPA signaling is a crucial factor for cardiomyocyte proliferation in the early postnatal heart. Cardiac-specific LPA(3) overexpression improved cardiac function and promoted cardiac regeneration after myocardial injury induced by MI. This finding suggested that activation of LPA(3) potentially through AAV-mediated gene therapy might be a therapeutic strategy to improve the outcome after MI.