MSC-EVs carrying PD-L1 rescue glycolytic hyperactivation and neuroinflammation via the PD-1/ERK/HIF-1a pathway in fragile X syndrome

Fragile X syndrome (FXS) is an X-linked inherited disorder characterized by intellectual disability, social impairments, anxiety, and impulsivity. Recent studies have demonstrated impaired glucose metabolism in FXS patients, leading to disruption of energy homeostasis. As the most abundant glial cells, astrocytes are pivotal to neuronal metabolic homeostasis, structural integrity, and neuroprotection. Accumulating evidence indicates that reactive astrocytes and pro-inflammatory cytokines are notably elevated in the cortex of FXS patients and Fmr1 −/y mice, suggesting that neuroinflammation constitutes a prominent pathological feature of FXS. Here, we reported that the programmed cell death 1 (PD-1) overexpression, hyperactivated glycolysis, and elevated neuroinflammatory mediators in primary astrocytes derived from Fmr1 −/y mice. Capitalizing on the immunomodulatory functions, minimal immunogenicity properties and PD-L1, the principal ligand of PD-1, enrichment of mesenchymal stem cell-derived extracellular vesicles (MSC-EVs), we demonstrated that intranasal MSC-EVs delivery could rescue social deficits, anxiety, and repetitive behaviors of Fmr1 −/y mice. Mechanistic investigations identified that PD-L1-expressing MSC-EVs engage astrocytic PD-1 to suppress the ERK/HIF-1α pathway, concurrently normalizing glycolysis and neuroinflammation. Critically, pharmacological blockade of PD-1 diminished MSC-EV-mediated therapeutic effects while exacerbating astrocyte activation and metabolic perturbations. Our study revealed that PD-L1-expressing MSC-EVs exhibited metabolic support and immunomodulation, collectively driving therapeutic efficacy.