saponins (PNS) attenuate Th17 cell differentiation in CIA mice via inhibition of nuclear PKM2-mediated STAT3 phosphorylation.

CONTEXT

Rheumatoid arthritis (RA) is an autoimmune disease with aberrant Th17 cell differentiation. (Burk.) F. H. Chen (Araliaceae) saponins (PNS) have an anti-inflammatory effect and can suppress Th17 cell differentiation.

OBJECTIVE

To investigate mechanisms of PNS on Th17 cell differentiation in RA, and the role of pyruvate kinase M2 (PKM2).

MATERIALS AND METHODS

Naive CD4T cells were treated with IL-6, IL-23 and TGF-β to induce Th17 cell differentiation. Apart from the Control group, other cells were treated with PNS (5, 10, 20 μg/mL). After the treatment, Th17 cell differentiation, PKM2 expression, and STAT3 phosphorylation were measured flow cytometry, western blots, or immunofluorescence. PKM2-specific allosteric activator (Tepp-46, 50, 100, 150 μM) and inhibitor (SAICAR, 2, 4, 8 μM) were used to verify the mechanisms. A CIA mouse model was established and divided into control, model, and PNS (100 mg/kg) groups to assess an anti-arthritis effect, Th17 cell differentiation, and PKM2/STAT3 expression.

RESULTS

PKM2 expression, dimerization, and nuclear accumulation were upregulated upon Th17 cell differentiation. PNS inhibited the Th17 cells, RORγt expression, IL-17A levels, PKM2 dimerization, and nuclear accumulation and Y705-STAT3 phosphorylation in Th17 cells. Using Tepp-46 (100 μM) and SAICAR (4 μM), we demonstrated that PNS (10 μg/mL) inhibited STAT3 phosphorylation and Th17 cell differentiation by suppressing nuclear PKM2 accumulation. In CIA mice, PNS attenuated CIA symptoms, reduced the number of splenic Th17 cells and nuclear PKM2/STAT3 signaling.

DISCUSSION AND CONCLUSIONS

PNS inhibited Th17 cell differentiation through the inhibition of nuclear PKM2-mediated STAT3 phosphorylation. PNS may be useful for treating RA.