Metabolic and epigenetic regulation of skin Tregs

CD4+Foxp3+ regulatory T cells (Tregs) maintain immune tolerance and suppress autoimmunity. Recent studies reveal that Tregs not only reside in secondary lymphoid organs (SLOs) but also enrich in various non-lymphoid tissues. Our lab and others have characterized a unique population of Tregs in the skin with distinctive transcriptional and epigenetic profile that maintain tissue homeostasis and suppress local inflammation. In response to antigen stimuli and environmental cues, T cells adapt their metabolism such as aerobic glycolysis and mitochondrial oxidative phosphorylation (OXPHOS) to facilitate their activation and differentiation. While studies on SLO Tregs and in vitro- induced Tregs revealed a strong dependency on OXPHOS and fatty acid oxidation, the metabolic profiles of Tregs residing in non-lymphoid tissues like the skin are still poorly understood. This knowledge gap is partly due to limited numbers of Tregs from non-lymphoid tissues for traditional metabolic assays and the lack of robust genetic tools for tissue-Treg specific targeting of key metabolic enzymes and transporters. To address this issue, we utilize single-cell energetic metabolism by profiling translation inhibition (SCENITH), a robust assay to assess metabolic dependencies and capacities of freshly isolated cells at single-cell resolution, alongside CRISPR/Cas9-based in vivo screening/validation and skin-Treg specific genetic knockout mouse models. Our preliminary results indicate that skin Tregs experience hypoxia and dramatically upregulate the aerobic glycolysis pathway to support their homeostasis, metabolic fitness, and transcriptional reprogramming in the skin microenvironment. Ablation of key transporters and enzymes in this pathway reduces the skin-Treg compartment, decreases their Foxp3 levels and expression of skin-Treg gene signatures, and exacerbates skin inflammation in a mouse model of contact hypersensitivity (CHS). Recent studies have revealed an intricate link between metabolism and epigenetic remodeling as many metabolites act as substrates for epigenetic modifications. The overall goal of this project is to dissect the specific metabolic program governing the homeostasis of skin Tregs in their microenvironment and to elucidate how this metabolic adaptation impacts their transcriptional and epigenetic reprogramming. First, we will use various tissue and cell type specific genetic targeting approaches to dissect how glycolysis promotes skin-Treg homeostasis within and outside of their tissue microenvironment and delineate hypoxia as a key environmental signal driving the glycolytic program in skin Tregs. Next, we will use CUT&Tag and ATAC-seq to define the molecular mechanisms by which glycolysis modulates the transcriptional and epigenetic reprogramming of skin Tregs. Lastly, we will investigate how Treg glycolysis impacts the severity of various inflammatory skin diseases. This work will transform our understanding of how Tregs adapt to tissue-specific cues, especially metabolites, to support their homeostasis and function. Project Number: 1R01AI190202-01 | Fiscal Year: 2025 | NIH Institute/Center: National Institute of Allergy and Infectious Diseases (NIAID) | Principal Investigator: Chaoran Li | Institution: EMORY UNIVERSITY, ATLANTA, GA | Award Amount: $597,542 | Activity Code: R01 | Study Section: Skin and Connective Tissue Sciences Study Section[SCTS] View on NIH RePORTER: https://reporter.nih.gov/project-details/1R01AI19020201