Sphingosine Kinase 2 Inhibition Ameliorates Neuroinflammation in Diet-Induced Obese Mice.

Obesity is associated with low-grade inflammation and microgliosis, contributing to brain dysfunction and cognitive decline. Sphingosine-1-phosphate (S1P) and its generating enzymes sphingosine kinase 1/2 (SphK1/2) have been implicated in metabolic and inflammatory regulation. Plasma S1P levels are elevated in obese mice and humans, and genetic ablation of SphK2 in mice protects from age- and diet-induced weight gain. As SphK2 is the predominant isoform in the brain, the present study examined whether pharmacological SphK2 inhibition mitigates obesity-associated microgliosis. Male C57BL/6J mice were fed either a high-fat diet (HFD; 60% fat) or control diet (CD; 10% fat) for 9 weeks. After 7 weeks, mice received the SphK2 inhibitor ABC294640 (SphK2i; 5 mg/kg, s.c.) or vehicle every other day for two weeks. Brain tissue was analyzed for microglial morphology (classification of ramified, intermediate, and amoeboid phenotypes, as well as branch length and endpoints), profiling of pro-inflammatory cytokines and S1P pathway components, and S1P concentrations. SphK2 inhibition attenuated HFD-induced microgliosis in cortex and dentate gyrus, with partial restoration of microglial arborization and branch length in cortex, in the absence of pro-inflammatory cytokine expression alterations. S1P pathway responses showed regional specificity, including elevated cortical S1P levels after HFD feeding accompanied by reduced S1P receptor 1 (S1PR1) expression, whereas hippocampal S1P levels and S1PR1 expression remained unchanged. SphK2 was undetectable in cortical microglia, while hippocampal microglia were SphK2-positive. Despite regional specificities of HFD-induced S1P/S1PR1 alterations, pharmacological SphK2 inhibition reduced microglial activation across regions, highlighting its potential relevance for obesity-associated neuroinflammation in a brain region-specific manner.