S1P 2 -Gα 12 signaling inhibits astrocytic glutamate uptake and mitochondrial oxygen consumption.

Glutamate is the principal excitatory neurotransmitter in the human brain. Following neurotransmission, astrocytes remove excess extracellular glutamate to prevent neurotoxicity. Glutamate neurotoxicity has been reported in multiple neurological diseases including multiple sclerosis (), representing a shared neurodegenerative mechanism. A potential modulator of glutamate neurotoxicity is the bioactive lysophospholipid sphingosine 1-phosphate () that signals through five cognate G protein-coupled receptors (), S1P - S1P, however, a clear link between glutamate homeostasis and S1P signaling has not been established. Here, S1P receptor knock-out mice, primary astrocyte cultures, and receptor-selective chemical tools were used to examine the effects of S1P on glutamate uptake. S1P inhibited astrocytic glutamate uptake in a dose-dependent manner and increased mitochondrial oxygen consumption, primarily through S1P Primary cultures of wild-type mouse astrocytes expressed S1P transcripts, and selective deletion of S1P and/or S1P in cerebral cortical astrocytes, did not alter S1P-mediated, dose-dependent inhibition of glutamate uptake. Pharmacological antagonists, S1P-null astrocytes, and Gα hemizygous-null astrocytes indicated that S1P-Gα-Rho/ROCK signaling was primarily responsible for the S1P-dependent inhibition of glutamate uptake. In addition, S1P exposure increased mitochondrial oxygen consumption rates () in wild-type astrocytes, and reduced OCRs in S1P-null astrocytes, implicating receptor selective metabolic consequences of S1P-mediated glutamate uptake inhibition. Astrocytic S1P-S1P signaling increased extracellular glutamate, which could contribute to neurotoxicity. This effect was not observed with the FDA-approved S1P receptor modulators, siponimod and fingolimod. Development and use of S1P-selective antagonists may provide a new approach to reduce glutamate neurotoxicity in neurological diseases.Extracellular glutamate is excitotoxic and its levels are controlled by astrocyte uptake. Sphingosine 1-phosphate (S1P) is a bioactive lipid originating from cell membrane sphingolipids that associates with carrier molecules like albumin, ApoM, and ApoA4 to produce cellular effects. S1P signals extracellularly through five GPCRs and it is found in higher concentrations in neurological diseases like multiple sclerosis where excitotoxic neurodegeneration has been implicated. Here we show that astrocytic S1P activation by S1P results in glutamate uptake inhibition to promote excitotoxic damage. S1P receptor modulators, including approved drugs for treating multiple sclerosis ( fingolimod (FTY720) and siponimod (BAF312)), do not engage S1P, thus avoiding glutamate uptake inhibition. S1P antagonists may provide a means to reduce S1P-induced glutamate neurotoxicity and ameliorate neurological diseases.