Intracerebral hemorrhage complicated by diabetes mellitus (DM-ICH) is characterized by severe secondary injury of the blood-brain barrier (BBB) and poor clinical outcomes; however, targeted therapies remain limited. Using single-cell RNA sequencing (scRNA-seq) in a dynamic rat model of ICH, we observed that brain microvascular endothelial cells (BMECs) exhibited a robust type I interferon (IFN-I)-mediated innate immune response at the peak of injury (day 3), paradoxically accompanied by decreased expression of interferon-stimulated gene 15 (Isg15). This study aimed to investigate the role of Isg15 deficiency in mitophagy impairment and IFN-β dysregulation in DM-ICH, and to evaluate the therapeutic potential of the GLP-1 receptor agonist semaglutide. An in vivo DM-ICH model was established in male rats, alongside an in vitro model using the human cerebral microvascular endothelial cell line hCMEC/D3 exposed to high glucose and hemin (HG+Hemin). Brain injury was evaluated by measuring brain water content and neurological scores, while BBB integrity was assessed through Evans blue (EB) extravasation and transmission electron microscopy (TEM). ScRNA-seq, adeno-associated virus (AAV)- and siRNA-mediated interventions, co-immunoprecipitation (Co-IP), and cycloheximide (CHX) chase assays were utilized to systematically explore the molecular role of Isg15 and assess the effects of semaglutide on Isg15 regulation and BBB protection. ScRNA-seq data demonstrated that although IFN-I-related pathways were activated in BMECs at the injury peak, the key negative regulator Isg15 was specifically downregulated. This suppression was further exacerbated under DM-ICH conditions and was associated with severe BBB damage. Isg15 deficiency destabilized the mitophagy receptor FUNDC1, impairing mitophagy, triggering mitochondrial DNA (mtDNA) leakage into the cytosol, and subsequently inducing robust IFN-I-mediated inflammation. Mechanistically, Isg15 stabilized FUNDC1 by inhibiting proteasomal degradation independently of ISGylation. Semaglutide effectively upregulated Isg15 expression, reversing this pathological cascade, attenuating BBB disruption, and improving neurological function. This study provides the first evidence that the Isg15-FUNDC1-mitophagy axis protects BBB homeostasis following DM-ICH. Isg15 downregulation drives IFN-I-mediated vascular injury, whereas semaglutide protects the BBB by upregulating Isg15, offering a translational therapeutic strategy. However, the applicability of these findings to females warrants further research.
Wang et al. (2026) studied this question.