Lysophosphatidic acid signaling regulates the KLF9-PPARγ axis in human induced pluripotent stem cell-derived neurons

Lysophosphatidic acid (LPA) is a lipid signaling molecule that plays several significant roles in the nervous system during development and injury. In this study, we differentiated human induced pluripotent stem cells (iPSCs) into neurons as an in vitro model to examine the specific effects of LPA. We demonstrated that LPA activates peroxisome proliferator-activated receptor gamma (PPARγ), a ligand-activated nuclear receptor, as well as its cognate receptor LPA₁ on human iPSC-derived neurons to enhance proliferation and neurite outgrowth. Furthermore, we found that the gene expression of Kruppel-like factor 9 (KLF9), a member of the large KLF transcription factor family, was induced by LPA treatment. Knockdown of KLF9 decreased proliferation and neurite outgrowth in vehicle- and LPA-treated IPSC-derived neurons compared to cells expressing KLF9. In conclusion, LPA plays dual roles as a ligand mediator through the activation of cell surface G-coupled protein receptors and as an intracellular second messenger through the activation of PPARγ. We discuss the contribution of the LPA₁-PPARγ-KLF9 axis to neurite outgrowth and proliferation in human iPSC-derived neurons.