Zexi Jia

Background and purpose: The role of PD-L1/PD-1 axis in IS remains controversial, with conflicting outcomes from systemic PD-1 or PD-L1 knockout models. These discrepancies underscore the complexity of PD-L1/PD-1 signaling and highlight the need to explore its cell-specific functions, particularly in neurons and microglia. Neurons, as the primary functional cells in the CNS, play a critical role in modulating local immune responses, yet their contribution to PD-L1/PD-1 signaling in IS is unknown. Furthermore, the mechanisms linking PD-L1/PD-1 to microglial polarization remain unclear. This study investigates whether targeted suppression of neuronal PD-L1 alleviates IS injury by modulating the PD-1/RFX1 axis and driving microglial polarization toward an anti-inflammatory phenotype. Methods: Middle cerebral artery occlusion (MCAO) was performed in mice to model IS. Neuronal PD-L1 was selectively suppressed using AAV. Microglial polarization, PD-1 and RFX1 expression, and neuroinflammation were assessed via flow cytometry, immunofluorescence, 4D-FastDIA proteomics, and qPCR/ELISA. In vitro, PD-1 knockdown BV2 cells and RFX1 overexpression models were established to validate mechanistic interactions. Results: Neuronal PD-L1 suppression reduced infarct volume, improved cerebral blood flow, and alleviated neurological deficits in ischemic stroke mice. Microglial PD-1 expression decreased significantly, accompanied by a phenotypic shift from pro-inflammatory to anti-inflammatory states. RFX1, exclusively expressed in microglia, was downregulated and identified as a key regulator of PD-1 and microglial polarization. In vitro, RFX1 overexpression reversed the anti-inflammatory effects of PD-1 knockdown, restoring pro-inflammatory cytokine levels. Critically, neuronal PD-L1 suppression spared peripheral immune cells, avoiding systemic immune disruption. These findings establish the PD-1/RFX1 axis as a central mediator of neuron-microglia crosstalk in IS neuroinflammation. Conclusion: Neuronal PD-L1 suppression attenuates IS injury by modulating the PD-1/RFX1 axis to promote anti-inflammatory microglial polarization. This study reveals a novel neuron-microglia crosstalk mechanism and highlights RFX1 as a therapeutic target for IS. The neuron-specific strategy overcomes limitations of systemic PD-L1/PD-1 inhibition, offering a precise and clinically translatable approach to mitigate neuroinflammation while preserving peripheral immune homeostasis.

Interleukin 33 (IL-33) belongs to the IL-1 family and is localized in the nucleus. IL-33 is primarily composed of three distinct domains, namely the N-terminal domain responsible for nuclear localization, the intermediate sense protease domain, and the C-terminal cytokine domain. Its specific receptor is the suppression of tumorigenicity 2 (ST2), which is detected in serum-stimulated fibroblasts and oncogenes. While most other cytokines are actively produced in cells, IL-33 is passively produced in response to tissue damage or cell necrosis, thereby suggesting its role as an alarm following cell infection, stress, or trauma. IL-33 plays a crucial role in congenital and acquired immunity, which assists in the response to environmental stress and maintains tissue homeostasis. IL-33/ST2 interaction further produces many pro-inflammatory cytokines. Moreover, IL-33 is crucial for central nervous system (CNS) homeostasis and the pathogenic mechanisms underlying CNS degenerative disorders. The present work summarizes the structure of IL-33, its fundamental activities, and its role in immunoregulation and neurodegenerative diseases. Therefore, this work proposes that IL-33 may play a role in the pathogenic mechanism of diseases and can be used in the development of treatment strategies.

Neural inflammatory response is a crucial pathological change in intracerebral hemorrhage (ICH) which accelerates the formation of perihematomal edema and aggravates neural cell death. Although surgical and drug treatments for ICH have advanced rapidly in recent years, therapeutic strategies that target and control neuroinflammation are still limited. Exosomes are important carriers for information transfer among cells. They have also been regarded as a promising therapeutic tool in translational medicine, with low immunogenicity, high penetration through the blood-brain barrier, and ease of modification. In our previous research, we have found that exogenous administration of miRNA-124-overexpressed microglial exosomes (Exo-124) are effective in improving post-injury cognitive impairment. From this, we evaluated the potential therapeutic effects of miRNA-124-enriched microglial exosomes on the ICH mice in the present study. We found that the gene-edited exosomes could attenuate neuro-deficits and brain edema, improve blood–brain barrier integrity, and reduce neural cell death. Moreover, the protective effect of Exo-124 was abolished in mice depleted of Gr-1⁺ myeloid cells. It suggested that the exosomes exerted their functions by limiting the infiltration of leukocyte into the brain, thus controlling neuroinflammation following the onset of ICH. In conclusion, our findings provided a promising therapeutic strategy for improving neuroinflammation in ICH. It also opens a new avenue for intranasal delivery of exosome therapy using miRNA-edited microglial exosomes.