PD-1 mediates microglia polarization via the MAPK signaling pathway to protect blood-brain barrier function during cerebral ischemia/reperfusion

• Published in: Brain research bulletin 2024-10, Vol.216, p.111055, Article 111055
• Main Authors: Huang, Linqiang, Li, Xinping, Li, Zhuo, Zhu, Huishan, Han, Yongli, Zeng, Juhao, Wen, Miaoyun, Zeng, Hongke
• Format: Article
• Language: English
• Subjects: Animals; Apoptosis - physiology; Blood-brain barrier; Blood-Brain Barrier - metabolism; Blood-Brain Barrier - pathology; Brain injury; Brain Ischemia - metabolism; Cell Polarity - physiology; Cerebral ischemia; Inflammation; Male; MAP Kinase Signaling System - physiology; Mice; Mice, Inbred C57BL; Microglia - metabolism; Microglia polarization; Programmed Cell Death 1 Receptor - metabolism; Reperfusion Injury - metabolism
• ISSN: 0361-9230; 1873-2747; 1873-2747
• DOI: 10.1016/j.brainresbull.2024.111055

Cerebral ischemia is characterized by its rapid onset and high rates of recurrence, morbidity, and mortality, with blood-brain barrier (BBB) permeability playing a vital role in brain injury. Therefore, it is important to understand the molecular mechanism which regulates the BBB during cerebral ischemia. An in vitro model of oxygen-glucose deprivation (OGD) and an in vivo model of cerebral ischemia/reperfusion (I/R) were constructed. PD-1 overexpression vectors and vectors containing si-RNA were transfected and injected into in vitro and in vivo models. Western blotting, real-time quantitative PCR (qPCR), immunofluorescence (IF) analysis, and immunohistochemical staining were employed to evaluate the expression levels of programmed cell death-1 (PD-1), microglia M1 and M2 biomarkers, and tight junction proteins. Flow cytometry and ELISA were used to measure the levels of pro-inflammatory cytokines. The BBB permeability of brain tissues was evaluated by Evans blue dye (EBD) extravasation and transendothelial electrical resistance (TEER). Brain water content was measured to assess the extent of inflammatory exudation. The infarct volume and neurological severity score (NSS) were used to assess the severity of brain injury. Brain cell apoptosis was assessed by the TUNEL assay and hematoxylin-eosin (H&E) staining. PD-1 helped to convert the microglia M1 phenotype to the M2 phenotype and to reduce BBB permeability both in vitro and in vivo. Overexpression of PD-1 promoted a shift of the M1 phenotype to the M2 phenotype and reduced BBB permeability via the ERK and p38 MAPK signaling pathways. PD-1 reduced inflammatory exudation, BBB permeability, cell apoptosis, and brain injury in vivo. Our present study verified that PD-1 exerts an anti-inflammatory effect by converting the microglia M1 phenotype to the M2 phenotype, reducing BBB permeability, and thereby relieves brain injury caused by cerebral ischemia. PD-1 is potential therapeutic target for brain injury caused by cerebral ischemia. •PD-1 promotes anti-inflammation function by converting microglia M1 to M2 phenotype.•PD-1 reduces BBB permeability in cerebral ischemia.•PD-1 releases brain injury of cerebral ischemia.