Microglial LNK regulates metabolic reprogramming via competitively inhibiting OTUB1 binding to PKM2 and mitigates ischemic stroke

Microglia-mediated neuroinflammation plays a key role in the process of ischemic stroke. Lymphocyte adaptor protein (LNK) negatively regulates cytokine signaling in peripheral immune cells, but its roles in neuroinflammation and ischemic stroke remain unknown. Here, we demonstrated that LNK expression was decreased in peripheral blood mononuclear cells and microglia after stroke in humans and mice, respectively. Microglia-specific knockout of LNK in mice promoted neuroinflammation and exacerbated ischemia‒reperfusion (I/R) injury in a mouse model of ischemic stroke. Mechanistically, LNK and pyruvate kinase M2 (PKM2) can competitively bind to the OTU deubiquitinase, ubiquitin aldehyde binding 1 (OTUB1), and promote the ubiquitination and degradation of PKM2. In the case of LNK deficiency, OTUB1 can bind to PKM2 and increase its stability, which promotes microglial glycolysis and lactate secretion, enhances the expression of H4K12la and proinflammatory cytokines, and ultimately, worsens brain I/R injury. On the basis of these findings, a PKM2 inhibitor was shown to reduce brain I/R injury exacerbated by LNK deficiency. Moreover, adenovirus-mediated LNK overexpression significantly protected against brain I/R injury in a mouse model of ischemic stroke. Therefore, our study reveals a new function of LNK, which acts as a competitive inhibitory molecule to exert negative regulation, thereby determining stroke outcomes.