Tetrandrine, an agonist of aryl hydrocarbon receptor, reciprocally modulates the activities of STAT3 and STAT5 to suppress Th17 cell differentiation.

Tetrandrine, a bisbenzylisoquinoline alkaloid constituent of the root of Stephania tetrandra S. Moore, was previously shown to suppress the differentiation of T helper 17 (Th17) cells and consequently ameliorate the collagen-induced arthritis (CIA) in mice by activating the aryl hydrocarbon receptor (AhR), but its underlying mechanism is incompletely understood. Here, we investigated how tetrandrine suppressed Th17 cell differentiation through the AhR pathway. The naïve CD4+ T cells were stimulated with anti-CD3/CD28 for 72 hrs in the presence or absence of tetrandrine under the Th17-polarizing condition. Tetrandrine inhibited the phosphorylation of signal transducer and activator of transcription-3 (STAT3) and boosted the phosphorylation of STAT5, while it did not alter the expression levels of phospho-Janus kinase-1 (p-JAK1), p-JAK2, p-JAK3, and suppressor of cytokine signalling-3 (SOCS3). The tetrandrine-mediated inhibition of the Th17 cell differentiation could be diminished by the activator of STAT3 and the inhibitor of STAT5. Meanwhile, the effect of tetrandrine on the either STAT3 or STAT5 phosphorylation was almost completely reversed by the AhR antagonist CH223191 and the AhR knockdown. In CIA mice, tetrandrine decreased p-STAT3 levels and increased p-STAT5 levels, which could also be reversed by the AhR antagonist resveratrol administration. Furthermore, tetrandrine promoted the AhR binding to the STAT5, but not to the STAT3. The tetrandrine-induced inhibition of the STAT3 phosphorylation was diminished by the inhibitor of STAT5. Taken together, tetrandrine suppressed Th17 cell differentiation by reciprocally modulating the activities of STAT3 and STAT5 in an AhR-dependent manner.

Yuan X ，Dou Y ，Wu X ，Wei Z ，Dai Y ... -  《-》

Tetrandrine ameliorates collagen-induced arthritis in mice by restoring the balance between Th17 and Treg cells via the aryl hydrocarbon receptor.

Tetrandrine is an alkaloid constituent of the root of Stephania tetrandra S. Moore. The long-term clinical uses of tetrandrine for treatments of rheumatalgia and arthralgia as well as the inhibition of rat adjuvant-induced arthritis imply that tetrandrine may have therapeutic potential in rheumatoid arthritis (RA). Here, we explored its anti-RA mechanism in collagen-induced arthritis (CIA) in relation to the balance between T helper (Th) 17 cells and regulatory T (Treg) cells. DBA/1 mice were immunized with chicken type II collagen and were orally administered tetrandrine for 14 consecutive days. Then, the mice were sacrificed, their joints were removed for histological analysis, and spleens and mesenteric lymph nodes (MLNs) were removed to examine the Th17 and Treg cells. Tetrandrine markedly alleviated the severity of arthritis, reduced the serum levels of pro-inflammatory cytokines, and restored the Th17/Treg balance, as demonstrated by the serum levels of their related cytokines (IL-17 and IL-10) and the proportion of each cell type. Tetrandrine inhibited Th17 cell differentiation and induced Treg cell differentiation in vitro . Notably, aryl hydrocarbon receptor (AhR) was proven to play a crucial role in tetrandrine-mediated T cell differentiation. The correlation between AhR activation, regulation of Th17/Treg and amelioration of arthritis by tetrandrine was verified in the CIA mice. Moreover, tetrandrine might be a ligand of AhR because it facilitated the expression of the AhR target gene cytochrome P450 1A1 (CYP1A1) and the activation of its downstream signaling pathways. Taken together, tetrandrine exerts its anti-arthritis efficacy by restoring Th17/Treg balance via AhR.

Yuan X ，Tong B ，Dou Y ，Wu X ，Wei Z ，Dai Y ... -  《-》

The role of STAT3 and AhR in the differentiation of CD4+ T cells into Th17 and Treg cells.

Liu X ，Hu H ，Fan H ，Zuo D ，Shou Z ，Liao Y ，Nan Z ，Tang Q ... -  《-》

T-bet over-expression regulates aryl hydrocarbon receptor-mediated T helper type 17 differentiation through an interferon (IFN)γ-independent pathway.

Various transcription factors are also known to enhance or suppress T helper type 17 (Th17) differentiation. We have shown previously that the development of collagen-induced arthritis was suppressed in T-bet transgenic (T-bet Tg) mice, and T-bet seemed to suppress Th17 differentiation through an interferon (IFN)-γ-independent pathway, although the precise mechanism remains to be clarified. The present study was designed to investigate further the mechanisms involved in the regulation of Th17 differentiation by T-bet over-expression, and we found the new relationship between T-bet and aryl hydrocarbon receptor (AHR). Both T-bet Tg mice and IFN-γ-/- -over-expressing T-bet (T-bet Tg/IFN-γ-/- ) mice showed inhibition of retinoic acid-related orphan receptor (ROR)γt expression and IL-17 production by CD4+ T cells cultured under conditions that promote Th-17 differentiation, and decreased IL-6 receptor (IL-6R) expression and signal transducer and activator of transcription-3 (STAT-3) phosphorylation in CD4+ T cells. The mRNA expression of ahr and rorc were suppressed in CD4+ T cells cultured under Th-17 conditions from T-bet Tg mice and T-bet Tg/IFN-γ-/- mice. CD4+ T cells of wild-type (WT) and IFN-γ-/- mice transduced with T-bet-expressing retrovirus also showed inhibition of IL-17 production, whereas T-bet transduction had no effect on IL-6R expression and STAT-3 phosphorylation. Interestingly, the mRNA expression of ahr and rorc were suppressed in CD4+ T cells with T-bet transduction cultured under Th17 conditions. The enhancement of interleukin (IL)-17 production from CD4+ T cells by the addition of AHR ligand with Th17 conditions was cancelled by T-bet over-expression. Our findings suggest that T-bet over-expression-induced suppression of Th17 differentiation is mediated through IFN-γ-independent AHR suppression.

Yokosawa M ，Kondo Y ，Tahara M ，Iizuka-Koga M ，Segawa S ，Kaneko S ，Tsuboi H ，Yoh K ，Takahashi S ，Matsumoto I ，Sumida T ... -  《-》

Low dose CP-690,550 (tofacitinib), a pan-JAK inhibitor, accelerates the onset of experimental autoimmune encephalomyelitis by potentiating Th17 differentiation.

Th17 cells, which have been implicated in autoimmune diseases, require STAT3 signaling activated by IL-6 or IL-23 for their development. Other Th1 and Th2 cytokines such as IL-2, IFN-γ and IL-4 strongly suppress Th17 development. Recently, CP-690,550 (tofacitinib), originally developed as a JAK3 inhibitor, has been shown to be effective in phase III clinical trials of rheumatoid arthritis and collagen-induced arthritis (CIA) models, but the precise mechanism of the effect, especially with respect to Th17 cells, is poorly understood. To our surprise, a low dose CP-690,550 was found to accelerate the onset of experimental autoimmune encephalomyelitis (EAE) at a concentration that suppressed CIA. At an early stage after immunization, more IL-17 production was observed in 15mg/kg body weight CP-690,550-treated mice than in untreated mice. In vitro, CP-690,550 inhibited both Th1 and Th2 development, while promoting Th17 differentiation at 10-50nM concentrations. Enhancement of Th17 by CP-690,550 is probably due to suppression of IL-2 signaling, because anti-IL-2 antibodies cancel the Th17-promoting effect of CP-690,550. CP-690,550 selectively inhibited IFN--induced STAT1, IL-4-induced STAT6 and IL-2-induced STAT5 at 3-30nM, while suppression of IL-6-induced STAT3 phosphorylation required a concentration greater than 100nM. In HEK293T cells, CP-690,550 less effectively suppressed JAK1-mediated STAT3 phosphorylation compared with JAK3. These results suggest that CP-690,550 has a different effects among JAKs and STATs, thereby affecting helper T cell differentiation, and murine autoimmune disease models.

Yoshida H ，Kimura A ，Fukaya T ，Sekiya T ，Morita R ，Shichita T ，Inoue H ，Yoshimura A ... -  《-》