Therapeutic hypothermia protects the ischemic penumbra via Xkr8.

Salvage of the ischemic penumbra is critical for improving outcomes after stroke, yet effective molecular targets remain elusive. Therapeutic hypothermia (TH) is a promising neuroprotective strategy, but its precise mechanisms, particularly concerning penumbral salvage, are not fully understood. Here, we demonstrate that TH significantly reduces infarct volume and limits the expansion of the ischemic penumbra in a murine model of transient middle cerebral artery occlusion. Mechanistically, TH exerted its protective effects primarily by suppressing apoptosis rather than other forms of regulated cell death. We identified phosphatidylserine (PS) exposure-a key "eat-me" signal for apoptosis-as a critical target of TH. TH selectively attenuated ischemia-induced PS externalization in neurons both in vivo and in vitro. Furthermore, we found that TH downregulated the expression of the scramblase Xkr8, a major regulator of PS exposure. Inhibition of Xkr8 mimicked the neuroprotective effects of TH, reducing PS exposure and improving neuronal survival, whereas overexpression of Xkr8 mitigated TH-mediated protection in the mouse model. Collectively, our findings reveal that TH protects the ischemic penumbra by inhibiting Xkr8-dependent PS exposure and subsequent apoptotic neuronal death, highlighting Xkr8 as a novel therapeutic target for ischemic stroke.