Cornel iridoid glycoside alleviates microglia-mediated inflammatory response via NLRP3/calpain pathway

OBJECTIVE Vascular dementia(VaD) is associated with cerebral hypoperfusion, which results in long-term cognitive impairment and memory loss. Neuroinflammation is an important mechanism of vascular dementia. Cornel iridoid glycoside(CIG) is the major active constituent isolated from the ripe fruit of Cornus officinalis.Previous studies have shown that CIG enhances neurological function in Va D rats. In the present research, we attempted to clarify the molecular processes underlying the role of CIG on neuroinflammation in Va D. METHODS In vivo, we created a chronic cerebral ischemia rat model by ligation of the bilateral common carotid arteries(2VO).The rats were divided into sham operation, 2VO, 2VO +CIG(60 and120 mg·kg-1·d-1), and 2VO + butylphthalide(100 mg·kg-1·d-1) groups and then treated rats with different concentrations of CIG. In vitro, BV2 microglia cells were induced with bacterial lipopolysaccharide(LPS) and interferon-γ(IFN-γ) to construct the model of microglias with analog neuroinflammation. Histopathology and bielschowsky silver staining were used to detect myelin integrity and neuronal loss. Immunofluorescence was used to observe changes in microglia. Magnetic Luminex Assay was used to detect changes in inflammatory factors. Western blotting, ELISA or calpain activity assay was used to measure the expression and activity of calpain, as well as the expression of NLRP3 inflammasome protein. Furthermore, NLRP3 overexpressing cells were used to further elucidate the potential anti-inflammatory molecular mechanism of CIG. RESULTS(1) CIG improved neuronal impairment in the brain of 2VO rats.(2) CIG increased white matter(WM) integrity in 2VO rats.(3) CIG reduced microglia inflammatory response in the cortex and hippocampus of 2VO rats.(4) CIG inhibited calpain activity in the cortex and hippocampus of 2VO rats.(5) CIG exerted anti-inflammatory effects on BV2cells stimulated by LPS and IFN-γ.(6) CIG Inhibited the expression and activity of calpain in LPS/IFN-γ-activated BV2 cells.(7) The main component of CIG had a weak binding force to calpain1.(8) CIG inhibited the activation of the NLRP3 inflammasome.(9) CIG reduced the activity of calpain induced by NLRP3 overexpression. CONCLUSION CIG inhibits microglial polarization into a proinflammatory state by attenuating the assembly of the NLRP3inflammasome and calpain activation, thus reducing brain inflammation, WM injury, and the loss of neurons.To sum up, the present study suggests that CIG inhibits neuroinflammation. The NLRP3/calpain pathway may be the main pathway by which CIG protects against neuroinflammation.