Abstract: Objective To investigate the role and mechanism of CX3C chemokine receptor 1 (CX3CR1) in regulating microglial polarization via the MFGE8/Janus kinase 2 (JAK2)/signal transducer and activator of transcription 3 (STAT3) signaling pathway in cerebral ischemia/reperfusion injury (CI/RI). Methods A transient middle cerebral artery occlusion (tMCAO) model was established in mice, which were randomly divided into the following groups: sham operation, tMCAO, shNC, shCX3CR1, and shCX3CR1+shMFGE8. Infarct volume was assessed by TTC staining; neurological deficits were evaluated using the Longa scoring system; and histopathological changes in brain tissue were observed via HE staining and Nissl staining. Western blot and RT-qPCR were used to detect the expression of proteins related to the MFGE8/JAK2/STAT3 pathway and marker genes of microglial polarization. The levels of inflammatory cytokines (TNF-α, IL-6, IL-1β, etc.) in brain tissue were measured by ELISA. Results Compared with the sham group, the tMCAO group showed significantly increased infarct volume and neurological scores, accompanied by increased neuronal necrosis, nuclear pyknosis, and structural disruption, as well as elevated pro-inflammatory cytokine levels. The mRNA and protein levels of Cx3cr1 were up-regulated, while those of Mfge8 were down-regulated (P＜0.05). Compared with the shNC group, the shCX3CR1 group exhibited reduced infarct volume and neurological scores, decreased neuronal necrosis, and lower pro-inflammatory cytokine levels. Additionally, the expression of M2-type microglial marker genes (Arg1, Cd206, YM1/2) was increased, whereas M1-type marker genes (Nos2, Tnf, Il1b) were decreased. MFGE8 protein levels were elevated, while total JAK2 and STAT3 protein levels remained unchanged, with reduced phosphorylation levels of p-JAK2 and p-STAT3 (P＜0.05). Compared with the shCX3CR1 group, the shCX3CR1+shMFGE8 group showed opposite trends in the above indicators (P＜0.05). Conclusions CX3CR1 may aggravate neuronal necrosis and CI/RI by inhibiting MFGE8 to activate the JAK2/STAT3 signaling pathway, thereby promoting M1-type microglial polarization.

Key words: cerebral ischemia/reperfusion, microglia polarization, CX3C chemokine receptor 1, milk fat globule-EGF factor 8/janus activated kinase / signal transducer and activator of transcription 3 signaling pathway