Sex-dependent protective effects of microglial tumor necrosis factor on post-stroke inflammation and myelin injury

Tumor necrosis factor (TNF) is rapidly induced after ischemic stroke, but its proposed cell-specific and sex-dependent functions during post-stroke inflammation remain insufficiently understood. Here, we investigated the role of microglia-derived TNF in the acute and subacute response to permanent middle cerebral artery occlusion (pMCAO). Tnf expression was transiently upregulated after stroke, becoming significant at 4 h, peaking at 12-24 h, and returning to baseline by 5 days. In situ hybridization confirmed strong Tnf expression in the infarct and peri-infarct regions. Whole-brain transcriptomic profiling showed that global TNF deficiency reshaped the early post-ischemic response, shifting it from microglia-associated phagocytic and wound-healing pathways toward an interferon-related inflammatory signature. To define the specific contribution of microglial TNF, we used inducible Cx3cr1^CreER:Tnf^fl/fl mice. Microglial TNF deletion had no effect on infarct volume in males at 24 h or 5 days after pMCAO, but significantly increased infarct size in females at both time points. In both sexes, brain TNF levels peaked at 24 h and were significantly reduced in Cx3cr1^CreER:Tnf^fl/fl mice, confirming microglia as a major source of early post-ischemic TNF. However, downstream consequences diverged by sex. At 5 days, male Cx3cr1^CreER:Tnf^fl/fl mice showed reduced microglial reactivity and 18 kDa translocator protein (TSPO) signal, with no change in T-cell infiltration, and exhibited increased density of mature oligodendrocytes. In contrast, female Cx3cr1^CreER:Tnf^fl/fl mice displayed enhanced microglial reactivity, increased TSPO binding, higher peri-infarct T-cell infiltration, and reduced oligodendrocyte density and myelin integrity. Together, these findings identify microglial TNF as a sex-dependent regulator of post-stroke inflammation and myelin injury.