Lysophosphatidic Acid Receptor 5 (LPA(5)) Knockout Ameliorates the Neuroinflammatory Response In Vivo and Modifies the Inflammatory and Metabolic Landscape of Primary Microglia In Vitro

Systemic inflammation induces alterations in the finely tuned micromilieu of the brain that is continuously monitored by microglia. In the CNS, these changes include increased synthesis of the bioactive lipid lysophosphatidic acid (LPA), a ligand for the six members of the LPA receptor family (LPA(1-6)). In mouse and human microglia, LPA(5) belongs to a set of receptors that cooperatively detect danger signals in the brain. Engagement of LPA(5) by LPA polarizes microglia toward a pro-inflammatory phenotype. Therefore, we studied the consequences of global LPA(5) knockout ((-/-)) on neuroinflammatory parameters in a mouse endotoxemia model and in primary microglia exposed to LPA in vitro. A single endotoxin injection (5 mg/kg body weight) resulted in lower circulating concentrations of TNF alpha and IL-1 beta and significantly reduced gene expression of IL-6 and CXCL2 in the brain of LPS-injected LPA(5)(-/-) mice. LPA(5) deficiency improved sickness behavior and energy deficits produced by low-dose (1.4 mg LPS/kg body weight) chronic LPS treatment. LPA(5)(-/-) microglia secreted lower concentrations of pro-inflammatory cyto-/chemokines in response to LPA and showed higher maximal mitochondrial respiration under basal and LPA-activated conditions, further accompanied by lower lactate release, decreased NADPH and GSH synthesis, and inhibited NO production. Collectively, our data suggest that LPA(5) promotes neuroinflammation by transmiting pro-inflammatory signals during endotoxemia through microglial activation induced by LPA.