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Endotoxin‐Stimulated Hepatic Stellate Cells Increase Suppressive Potential of Regulatory T Cells via IDO‐Mediated AhR Activation: Therapeutic Implications
Author(s) -
Kumar Sudhir,
Dangi Anil,
Gandhi Chandrashekhar R
Publication year - 2016
Publication title -
the faseb journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.709
H-Index - 277
eISSN - 1530-6860
pISSN - 0892-6638
DOI - 10.1096/fasebj.30.1_supplement.57.7
Subject(s) - foxp3 , hepatic stellate cell , in vivo , aryl hydrocarbon receptor , ex vivo , chemistry , indoleamine 2,3 dioxygenase , immune system , immune tolerance , microbiology and biotechnology , downregulation and upregulation , signal transduction , cancer research , immunology , biology , biochemistry , endocrinology , transcription factor , tryptophan , amino acid , gene
Due to adverse effects of the pharmacological drugs, use of immunosuppressive CD4 + Foxp3 + regulatory T cells (Tregs) is an attractive and preferred approach to promote immunological tolerance. However, poor in vivo stability of the ex vivo expanded Tregs, and their conversion to injurious effector immune cells are major drawbacks. We reported earlier that hepatic stellate cells (HSCs) cause expansion and increase suppressive function of allogeneic Tregs; lipopolysaccharide (LPS) pretreatment of HSCs augment the expansion of Tregs. The aim of this study was to delineate the mechanisms underlying HSC‐induced expansion, increased potency and in vivo stability of Tregs. HSCs and Tregs were isolated from allogeneic mouse livers and spleens, respectively. Following co‐culture with untreated or LPS‐pretreated HSCs, proliferation of Tregs was measured by CFSE‐dilution method, and Foxp3 expression and its acetylation were determined via immunoprecipitation and Western blotting analyses. Expression of various genes was determined via quantitative RT‐PCR. Ex vivo HSC‐expanded Tregs were highly stable in vivo following adoptive transfer into mice and retained their increased suppressive property. LPS increased the expression and activity of immunoregulatory enzyme indoleamine 2,3‐dioxygenase 1 (IDO1) in HSCs, and LPS‐pretreated HSCs stimulated aryl hydrocarbon receptor (AhR) signaling in Tregs. Compared to WT HSCs, IDO1 −/− HSCs were much inferior in stimulating expansion of Tregs and their Foxp3 expression. Pharmacologic blocking of IDO by 1‐methyl tryptophan in HSCs prevented AhR signaling, Foxp3 expression and expansion of Tregs. The HSC/IDO‐dependent increased acetylation of lysine residues of Foxp3 was associated with stability and competitive fitness of Tregs. Finally, HSCs stored frozen following 2–3 subcultures were much more potent than freshly isolated HSCs in expanding Tregs, thus providing a mode for clinical application. We conclude that HSCs cause expansion of allogeneic Tregs through IDO‐dependent AhR‐mediated signaling mechanism, and increase their stability through lysine‐acetylation of Foxp3. Importantly, availability of frozen HSCs for ex vivo expansion of Tregs provides an exciting therapeutic opportunity for immunological disorders. Support or Funding Information Supported by a VA Merit Review Award (1IO1BX001174) and grants from NIH (PO1AIO81678 and R21AA020846) to CRG.