Tinosinenside A inhibits neuroinflammation and protects HT22 cells by suppressing the TLR4/NF-κB/NLRP3 signaling pathway in BV2 cells

Abstract

Microglia-mediated neuroinflammation plays a crucial role in Alzheimer's disease (AD). Tinosinenside A (Tis A) is a novel sesquiterpene glycoside isolated from the dried rattan stem of Tinospora sinensis (Lour.) Merr. Tis A exhibited anti-inflammatory and neuroprotective activities in vitro. However, the mechanism underlying the inhibition of neuroinflammation and protection of nerve cells remains obscure. This study used lipopolysaccharide (LPS)-induced inflammatory response in BV2 cells to simulate a neuroinflammatory model and used Aβ_1-42-induced HT22 cells to establish an AD cell model, aiming to investigate the efficacy and mechanism of Tis A through anti-neuroinflammation to protect nerve cells. Tis A had no effect on the proliferation of BV2 and HT22 cells at the tested concentrations. The time- and dose-dependent effects of Tis A on the LPS-induced inflammatory response of BV2 cells demonstrated that the best anti-inflammatory efficacy appeared after 12 h of pretreatment. Tis A inhibited the gene levels of TNF-α, IL-6, IL-1β, iNOS, and IL-10 while enhancing the gene levels of IL-4 and TGF-β. Additionally, Tis A reduced the gene expression levels of CD16 and CD32 and increased the CD36 and CD206 gene expression levels. It also downregulated the protein expression of Iba-1 and iNOS while upregulating CD206. Tis A obviously inhibited NLRP3 gene and protein expression in LPS-stimulated BV2 cells. The inhibitory effect of Tis A on NLRP3 was counteracted by the NLRP3 activator nigericin and overexpression plasmid GV358. Tis A inhibits NLRP3 protein expression to reduce the assembly of NLRP3/ASC/Caspase-1 inflammasome, then regulates the TLR4/NF-κB/NLRP3 signaling pathway. It regulates microglia activation and M1/M2 phenotypic polarization, then inhibits the production of inflammatory factors, and reduces the apoptosis rate of HT22 cells under inflammatory conditions, improving the survival rate of nerve cells to protect neurons.

Keywords: Microglia; Neuroinflammation; TLR4/NF-κB/NLRP3; Tinosinenside A.