AhR Ligands Differentially Regulate miRNA-132 Which Targets HMGB1 and to Control the Differentiation of Tregs and Th-17 Cells During Delayed-Type Hypersensitivity Response

Abstract

Aryl hydrocarbon receptor (AhR), is a transcription factor and an environmental sensor that has been shown to regulate T cell differentiation. Interestingly, AhR ligands exert varying effects from suppression to exacerbation of inflammation through induction of Tregs and Th-17 cells, respectively. In the current study, we investigated whether the differential effects of AhR ligands on T cell differentiation are mediated by miRNA during delayed-type hypersensitivity (DTH) reaction against methylated Bovine Serum Albumin (mBSA). Treatment of C57BL/6 mice with TCDD attenuated mBSA-mediated DTH response, induced Tregs, decreased Th-17 cells, and caused upregulation of miRNA-132. TCDD caused an increase in several Treg subsets including inducible peripheral, natural thymic, and Th3 cells. Also, TCDD increased TGF-β and Foxp3 expression. In contrast, treating mice with FICZ exacerbated the DTH response, induced inflammatory Th17 cells, induced IL-17, and RORγ. Analysis of miRNA profiles from draining lymph nodes showed that miR-132 was upregulated in the TCDD group and downregulated in the FICZ group. Transfection studies revealed that miRNA-132 targeted High Mobility Group Box 1 (HMGB1). Downregulation of HMGB1 caused an increase in FoxP3+ Treg differentiation and suppression of Th-17 cells while upregulation of HMGB1 caused opposite effects. Moreover, TCDD was less effective in suppressing DTH response and induction of Tregs in mice that were deficient in miR-132. In summary, this study demonstrates that TCDD and FICZ have divergent effects on DTH response and T cell differentiation, which is mediated through, at least in part, regulation of miRNA-132 that targets HMGB1.

The Ability of AhR Ligands to Attenuate Delayed Type Hypersensitivity Reaction Is Associated With Alterations in the Gut Microbiota

“…inflammation associated with the DTH response. Our study demonstrated that AhR ligands, such as TCDD and FICZ, have opposite effects on DTH response mediated by mBSA, with the former suppressing DTH while the latter, enhancing this response, consistent with our recent studies (34). Interestingly, in our previous report (34) on mBSA-induced DTH response, we focused on T-cell responses in the draining popliteal lymph nodes while in the current study, because we were interested in studying gut-associated microbiota and inflammation, resorted to MLNs.…”

“…Our study demonstrated that AhR ligands, such as TCDD and FICZ, have opposite effects on DTH response mediated by mBSA, with the former suppressing DTH while the latter, enhancing this response, consistent with our recent studies (34). Interestingly, in our previous report (34) on mBSA-induced DTH response, we focused on T-cell responses in the draining popliteal lymph nodes while in the current study, because we were interested in studying gut-associated microbiota and inflammation, resorted to MLNs. Thus, we were surprised to note that the changes brought about by AhR ligands in the MLNs were similar to that seen in the draining lymph nodes (34) in that TCDD caused induction of Tregs while suppressing Th17 cells, whereas FICZ had the opposite effects on these T cells.…”

“…Additionally, our previous studies also demonstrated that TCDD may induce Tregs through regulation of miRNA-132 which targets HMGB1 (34).…”

“…All mice were then separated into four groups: control (PBS), vehicle (corn oil), TCDD (10 µg/kg body weight), and FICZ (50 µg/kg body weight). These doses of TCDD and FICZ used in this study were based on the differential effects of these ligands on Tregs and Th17 cells as shown in our previous studies ( 34 ) and those from others ( 10 , 35 ). On day 5, each group of mice was treated with vehicle, TCDD, or FICZ by intraperitoneal (i.p.)…”

“…On day 5, each group of mice was treated with vehicle, TCDD, or FICZ by intraperitoneal (i.p.) route as described previously ( 34 , 36 ). The footpad thickness of the mice was measured using an engineer’s calipers 48 h after the secondary challenge on day 8.…”