Blocking S1P signaling attenuates brain injury in mice with ischemic stroke.

Introduction: The functions of S1P receptors have been revealed using genetic and pharmacological tools, including the potent non-selective modulator FTY720. However, studies on subtype-specific agonists and antagonists are limited; hence, the role of S1P remains unclear.

Objectives: To identify a novel function of S1P as a pathogenic factor in stroke using a newly developed S1P-selective modulator and S1P knockdown.

Methods: Heteroaromatic analogs of FTY720 were synthesized, a β-arrestin assay was conducted against S1P receptors, and the developed compound (NXC736) was characterized as a functional S1P antagonist. To clarify the function of S1P, the therapeutic potential of NXC736 in ischemic stroke was determined using a transient middle cerebral artery occlusion (tMCAO) mouse model, which was validated using S1P knockdown. The S1P-dependent pathogenic mechanisms were determined using immunohistochemical and biochemical analyses.

Results: Molecular modeling studies provide valuable clues for understanding S1P selectivity of NXC736. NXC736 contains a triazole ring instead of a phenyl ring and exhibits S1P-selective activity as a functional antagonist. Its action on S1P does not require phosphorylation by sphingosine kinase 2. Notably, NXC736 exhibited substantial therapeutic activity against ischemic stroke by attenuating tMCAO-induced acute brain injuries, including brain infarction, neurological deficits, and neuronal apoptosis. This suggested that S1P is a pathogenic factor in ischemic stroke. This function was confirmed using AAV-based S1P knockdown. NXC736 or S1P knockdown attenuated blood-brain barrier disruption, neutrophil infiltration, microglial activation and proliferation, and the upregulation of pro-inflammatory cytokines, thereby demonstrating that S1P influences neuroinflammatory responses in ischemic stroke. The underlying mechanisms were activation of NLRP3 inflammasome, NF-κB, and MAPKs. S1P also contributed to chronic brain injuries caused by ischemic stroke because NXC736 exerted long-term neuroprotective effects against tMCAO challenge.

Conclusion: Using a functional S1P antagonist (NXC736) and a genetic tool for S1P knockdown, we identified S1P as a novel pathogenic factor in ischemic stroke.