Inhibition of class IIa HDACs reduces neuroinflammation via NEU1-LAMP1 regulation and promotes M2 macrophage polarization in ischemic stroke.

Neuroinflammation plays a crucial role in ischemic injury. Macrophages contribute to post-stroke inflammation through activation and polarization into pro-inflammatory (M1) or anti-inflammatory (M2) phenotypes. Class IIa histone deacetylases (HDACs) have been implicated in inflammatory regulation. Neuraminidase 1 (NEU1) serves as a negative regulator of lysosomal-associated membrane protein 1 (LAMP1). This study investigates whether class IIa HDACs inhibition mitigates neuroinflammation by modulating macrophage polarization and lysosomal exocytosis via the NEU1-LAMP1. A total of 74 adult male Sprague-Dawley rats were subjected to 2 h middle cerebral artery occlusion (MCAO). The selective class IIa HDACs inhibitor TMP269 (4 mg/kg) was administered 30 min before MCAO. Brain damage was evaluated at 48 h reperfusion, while the long-term functional outcomes were examined at days 3 and 7 after stroke. Pro-inflammatory cytokines, macrophage polarization, class IIa HDACs, CD68, NEU1, LAMP1 and lysosomal exocytosis were assessed at 24 h reperfusion. TMP269 treatment significantly reduced infarct volume, CD68+ microglia/macrophage accumulation and pro-inflammatory cytokine levels. TMP269 promoted M2 macrophage polarization while suppressing M1 markers in the brain but not blood. Improved functional recovery was observed on days 3 and 7 post-stroke. Among class IIa HDACs, HDAC9 exhibited the most significant upregulation following stroke and was effectively inhibited by TMP269. Furthermore, TMP269 increased NEU1 expression, leading to LAMP1 down-regulation and suppression of lysosomal exocytosis, in association with reduced neuroinflammation. These findings highlight the neuroprotective effect of class IIa HDACs inhibition, particularly HDAC9, in reducing neuroinflammation by promoting M2 macrophage polarization and regulating lysosomal exocytosis via NEU1-LAMP1.