Oxidative stress is a major driver of neuroinflammation, yet the molecular redox mechanisms that shape microglial activation remain incompletely defined. Among reversible redox modifications, protein S-glutathionylation has emerged as a key regulator of signaling cascades under conditions of elevated Reactive Oxygen Species (ROS). While IFNγ is known to activate STAT1 and promote a pro-inflammatory microglial phenotype, the contribution of oxidative stress to this process is poorly understood. Here, we investigated the interplay between ROS and STAT1 signaling in IFNγ-stimulated microglial cells. We demonstrate that ROS not only enhance STAT1 phosphorylation but also promote its S-glutathionylation, a modification that sustains STAT1 transcriptional activity. This dual regulation leads to prolonged expression of pro-inflammatory mediators, including iNOS, COX2, TNFα, and IL-6. Importantly, STAT1-deficient cells fail to mount these responses, confirming STAT1 as a central redox-sensitive hub in microglial polarization. Our findings identify S-glutathionylation as a molecular switch that links oxidative stress to persistent STAT1 activation and M1 polarization. These results suggest that targeting STAT1 redox regulation could help control microglial overactivation and may offer new opportunities for therapeutic intervention in neuroinflammatory and neurodegenerative diseases.

Extracellular Vesicles (EVs) have been proposed as a promising tool for drug delivery because of their natural ability to cross biological barriers, protect their cargo, and target specific cells. Moreover, EVs are not recognized by the immune system as foreign, reducing the risk of an immune response and enhancing biocompatibility. Herein, we proposed an alternative therapeutic strategy to restore STAT3 signaling exploiting STAT3 loaded EVs. This approach could be useful in the treatment of Autosomal Dominant Hyper-IgE Syndrome (AD-HIES), a rare primary immunodeficiency and multisystem disorder due to the presence of mutations in STAT3 gene. These mutations alter the signal transduction of STAT3, thereby impeding Th17 CD4⁺ cell differentiation that leads to the failure of immune response. We set up a simple and versatile method in which EVs were loaded with fully functional STAT3 protein. Moreover, our method allows to follow the uptake of STAT3 loaded vesicles inside cells due to the presence of EGFP in the EGFP-STAT3 fusion protein construct. Taken together, the data presented in this study could provide the scientific background for the development of new therapeutic strategy aimed to restore STAT3 signaling in STAT3 misfunction associated diseases like AD-HIES. In the future, the administration of fully functional wild type STAT3 to CD4+ T cells of AD-HIES patients might compensate its loss of function and would be beneficial for these patients, lowering the risk of infections, the use of medications, and hospitalizations.