Sex Differences in the Initiation and Progression of Necroptosis Following Kidney Ischemia-Reperfusion Injury.

Background: Ischemia-reperfusion injury (IRI) is a major contributor to acute kidney injury (AKI). While the precise mechanisms of AKI are still incompletely defined, extensive evidence highlights tubular cell injury and death as key factors in its development. Necroptosis has recently emerged as a critical pathway in the pathogenesis of ischemia-reperfusion-induced AKI (IR-AKI). Although sex differences in susceptibility to IR-AKI have been reported, it remains unclear whether there are sex differences in necroptosis dynamics and whether these differences underlie the observed sexual dimorphism in kidney IRI. This study aimed to address these questions. Methods: male and female C57BL/6 J mice were subjected to AKI via ischemia induced by bilateral renal pedicle clamping for 18 min at 37 °C. Plasma, urine, and kidney samples were collected at 0 h, 3 h, 6 h, 12 h, 24 h, 48 h, and 72 h post-reperfusion. Kidney injury and function were assessed by measuring plasma creatinine (PCr), blood urea nitrogen (BUN) levels, and histological damage (PAS and cleaved caspase3 staining). Necroptosis activation was assessed by quantifying phosphorylated forms of key markers: p-RIPK1 and p-MLKL. To explore the role of sex hormones in regulating necroptosis dynamics, ovariectomized female mice were subjected to the same IR-AKI protocol, and their kidney injury and functional outcomes were compared with those of intact counterparts. Results: The PCr was 0.35 ± 0.04 and 0.32 ± 0.06 mg/dL for males and females, respectively, at 3 h of IR. The levels exponentially increased to 2.05 ± 0.18 at 48 h post-reperfusion in the males but only gradually to 0.94 ± 0.13 mg/dL in females. Necroptosis activation began as early as 3 h post-IR in males but was delayed until ~6 h in females. Males exhibited stronger and more sustained necroptosis activation than females, showing elevated phosphorylation levels of pRIPK1 and pMLKL in Western blot. Female sex hormone deficiency exacerbated the female response to IR-induced injury, which reduced the sex difference in the dynamic of the necroptotic activation and subsequent kidney injury. To our knowledge, this is the first study to characterize sex differences in the initiation and progression of necroptosis and subsequent injury in a mouse model of IR-AKI. Conclusions: Our findings reveal distinct temporal patterns of programmed cell death between sexes. Necroptosis-targeted therapies require early intervention in males, which can be delayed in females after IR-AKI, highlighting the need for sex-specific therapeutic windows.