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Regulatory T cells in skin are uniquely poised to suppress profibrotic immune responses

Lokesh A. Kalekar,Jarish N. Cohen,N. Prevel,P. Sandoval,A. Mathur,J. Moreau,Margaret M. Lowe,Audrey Nosbaum,P. Wolters,A. Haemel,F. Boin,M. Rosenblum

Published 2019 in Science immunology

ABSTRACT

Skin Tregs depend on GATA3 to attenuate immune cell–stimulated cutaneous fibrosis. See the related Focus by Bal and Stadhouders. Skin Tregs rely on Gata3 to curb fibrosis Hyperactive fibroblasts that overproduce extracellular matrix components are a root cause of tissue fibrosis, a shared feature of many chronic inflammatory diseases. Kalekar et al. found that depletion of regulatory T cells (Tregs) in mice resulted in increased skin fibrosis, prompting them to investigate the mechanisms by which skin-resident Tregs normally prevent excess fibroblast activation. RNA sequencing analysis of skin Tregs revealed preferential expression of transcription factors typically associated with TH2 differentiation, including GATA3 and IRF4. Genetic deletion of Gata3 in Tregs resulted in increases in TH2 cytokine production and excessive dermal fibrosis. These findings reveal that GATA3 expression by skin-resident Tregs is an adaptation to the cutaneous microenvironment that enables these specialized Tregs to maintain homeostatic control of fibroblast activity. See the related Focus by Bal and Stadhouders. At the center of fibrosing diseases is the aberrant activation of tissue fibroblasts. The cellular and molecular mechanisms of how the immune system augments fibroblast activation have been described; however, little is known about how the immune system controls fibroblast function in tissues. Here, we identify regulatory T cells (Tregs) as important regulators of fibroblast activation in skin. Bulk cell and single-cell analysis of Tregs in murine skin and lungs revealed that Tregs in skin are transcriptionally distinct and skewed toward T helper 2 (TH2) differentiation. When compared with Tregs in lung, skin Tregs preferentially expressed high levels of GATA3, the master TH2 transcription factor. Genes regulated by GATA3 were highly enriched in skin “TH2 Treg” subsets. In functional experiments, Treg depletion resulted in a preferential increase in TH2 cytokine production in skin. Both acute depletion and chronic reduction of Tregs resulted in spontaneous skin fibroblast activation, profibrotic gene expression, and dermal fibrosis, all of which were exacerbated in a bleomycin-induced murine model of skin sclerosis. Lineage-specific deletion of Gata3 in Tregs resulted in an exacerbation of TH2 cytokine secretion that was preferential to skin, resulting in enhanced fibroblast activation and dermal fibrosis. Together, we demonstrate that Tregs play a critical role in regulating fibroblast activation in skin and do so by expressing a unique tissue-restricted transcriptional program that is mediated, at least in part, by GATA3.

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