| Summary: | Receptor-mediated lysophosphatidic acid (LPA) signaling has come to be considered an important event for various diseases. In cerebral ischemia, LPA<sub>1</sub> has recently been identified as a receptor subtype that mediates brain injury, but the roles of other LPA receptor subtypes remain unknown. Here, we investigated the potential role of LPA<sub>5</sub> as a novel pathogenic factor for cerebral ischemia using a mouse model of transient middle cerebral artery occlusion (tMCAO). LPA<sub>5</sub> was upregulated in the ischemic core region after tMCAO challenge, particularly in activated microglia. When TCLPA5, a selective LPA<sub>5 </sub>antagonist, was given to tMCAO-challenged mice immediately after reperfusion, brain damage, including brain infarction, functional neurological deficit, and neuronal and non-neuronal apoptosis, was reduced in mice. Similarly, delayed TCLPA5 administration (at three hours after reperfusion) reduced brain infarction and neurological deficit. The histological results demonstrated that TCLPA5 administration attenuated microglial activation, as evidenced by the decreased Iba1 immunoreactivities, the number of amoeboid cells, and proliferation in an injured brain. TCLPA5 administration also attenuated the upregulation of the expression of pro-inflammatory cytokines at mRNA levels in post-ischemic brain, which was also observed in lipopolysaccharide-stimulated BV2 microglia upon LPA<sub>5</sub> knockdown. Overall, this study identifies LPA<sub>5</sub> as a novel pathogenic factor for cerebral ischemia, further implicating it as a promising target for drug development to treat this disease.
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