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 LPA 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 LPA-PPARγ-KLF9 axis to neurite outgrowth and proliferation in human iPSC-derived neurons.
We previously showed that an alkyl-ether analog of lysophosphatidic acid, AGP (alkyl-glycerophosphate), accumulates in human atherosclerotic plaques and is a potent agonist of peroxisome proliferator-activated receptor-gamma (PPARγ). On the other hand, cyclic phosphatidic acid (cPA), similar in structure to AGP, can negatively regulate PPARγ. However, in this study, cPA had no effect on the expression and secretion of C-C motif chemokine 2 (CCL-2), a chemokine that is also linked to inflammatory responses and atherosclerosis. We showed that AGP enhances CCL-2 mRNA expression and secretion in a dose-dependent manner. Furthermore, oxidative stress plays a major role in the pathology of cardiovascular diseases; we showed that AGP triggers ROS generation and lipid peroxidation and that ROS and 8-isoprostane generation can be suppressed by a PPARγ antagonist. These results suggest that an imbalance of the PPARγ agonist-antagonist equilibrium is involved in changes in cellular functions, including ROS generation and lipid peroxidation.
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