Triptolide Inhibits Preformed Fibril-Induced Microglial Activation by Targeting the MicroRNA155-5pSHIP1 Pathway

Abstract EN

Evidence suggests that various forms of α-synuclein- (αSyn-) mediated microglial activation are associated with the progression of Parkinson’s disease.

MicroRNA-155-5p (miR155-5p) is one of the most important microRNAs and enables a robust inflammatory response.

Triptolide (T10) is a natural anti-inflammatory component, isolated from a traditional Chinese herb.

The objective of the current study was to identify the role and potential regulatory mechanism of T10 in αSyn-induced microglial activation via the miR155-5p mediated SHIP1 signaling pathway.

Mouse primary microglia were exposed to monomers, oligomers, and preformed fibrils (PFFs) of human wild-type αSyn, respectively.

The expressions of TNFα and IL-1β, measured by enzyme-linked immunosorbent assay (ELISA) and qPCR, demonstrated that PFFs initiated the strongest immunogenicity in microglia.

Application of inhibitors of toll-like receptor (TLR) 1/2, TLR4, and TLR9 indicated that PFFs activated microglia mainly via the NF-κB pathway by binding TLR1/2 and TLR4.

Treatment with T10 significantly suppressed PFF-induced microglial activation and attenuated the release of proinflammatory cytokines including TNFα and IL-1β.

Levels of IRAK1, TRAF6, IKKα/β, p-IKKα/β, NF-κB, p-NF-κB, PI3K, p-PI3K, t-Akt, p-Akt and SHIP1 were measured via Western blot.

Levels of miR155-5p were measured by qPCR.

The results demonstrated that SHIP1 acted as a downstream target molecule of miR155-5p.

Treatment with T10 did not alter the expression of IRAK1 and TRAF6, but significantly decreased the expression of miR155-5p, resulting in upregulation of SHIP1 and repression of NF-κB activity, suggesting inhibition of inflammation and microglial activation.

The protective effects of T10 were abolished by the use of SHIP1 siRNA and its inhibitor, 3AC, and miR155-5p mimics.

In conclusion, our results demonstrated that treatment with T10 suppressed microglial activation and attenuated the release of proinflammatory cytokines by suppressing NF-κB activity via targeting the miR155-5p/SHIP1 pathway in PFFs-induced microglial activation.