Studies from Dr. Ting Chen Laboratory reveal the cellular and molecular mechanism that fibroblast orchestrates patterned auto-immune activities in vitiligo

On Dec 16th, study from Dr. Ting Chen Laboratory at National institute of Biological Sciences, Beijing/Tsinghua Institute of Multidisciplinary Biomedical Research entitled “Anatomically distinct fibroblast subsets determine skin autoimmune patterns” is published online in the journal Nature. This work reveals that anatomically distinct dermal fibroblasts exhibit heterogeneity in regulating immunoactivity reflected in intrinsic differences in response to IFNγ. These dermal fibroblasts are uniquely required to recruit and activate CD8+ cytotoxic T cells through secreted chemokines and drive the organ level lesion patterns in this autoimmune disease vitiligo.

Vitiligo is an acquired polygenetic autoimmune disease. Its defining feature is skin depigmentation, owing to auto-reactive CD8+ T cells cause a loss of epidermal melanocytes. Vitiligo afflicts 0.5% to 2% of the population worldwide. More than 80% vitiligo patients have bilateral symmetric depigmentation patterns across the central body axis, which is classified as non-segmental vitiligo. Previous studies have shown that IFNγ is important for T cell-induced depigmentation in skin. However, the identity of IFNγ-responsive cells that mediated this important function is largely unknown. Hypotheses about the reason behind the bilateral symmetric patterns that are observed in vitiligo pathology include regional variations in microbiota distribution, the pattern of antigen expression in melanocyte, and different distributions of neuropeptides released by nerve endings. Despite these studies, the cellular and molecular mechanisms that orchestrate patterned immune cell activities in vitiligo patients’ skin remain elusive.

Dr. Chen and her team has long been devoted to the mechanism of skin regional pattern. Their previous study identified skin mesenchymal niches controlled regional epithelial stem cell activation via Hoxc-Wnt signaling. This time, they turned attention to the regional pattern of skin autoimmune disease vitiligo. They analysed skin biopsies from patients with vitiligo and found the majority of the infiltrated CD8+ T cells were concentrated at the junction area between lesion and perilesion skin, which implied a local recruitment mechanism. To test this hypothesis, they carried out single cell RNA-seq to analyse skin local cells. Among eight different cell types, they identified dermal fibroblasts accounted for most of the IFNγ responses and T cell migration. Through a robust mouse model of vitiligo, they demonstrated IFNγ signalling is essential for local recruitment and cytotoxicity of CD8+ T cells. Furthermore, by a skin graft experiment, they found IFNγ-responsive skin stromal cells were required to drive CD8+ T cell-mediated vitiligo in a paracrine manner.

After an elaborate experimental design, Dr. Chen and her team used conditional knockout (cKO) in specific cell types and in vivo mosaic fibroblast knockdown techniques, and finally identified that IFNγ-responsive fibroblasts mediated local aggregation of CD8+ T cells through the CXCL9/CXCL10–CXCR3 axis. Three sets of parallel experiments were used. Firstly, they ablated Ifngr1 gene in six different candidate cell types respectively, and found only in the fibroblast Pdgfra^CreER;Ifngr1^fl/fl cKO mice was vitiligo progression blocked. Secondly, by a fibroblast transplantation assay, they found intradermal injection of wild-type fibroblasts into the tail skin of Ifngr1 KO mice resulted in significant local aggregation of CD8+ T cells after the induction of vitiligo, which means IFNγ-responsive fibroblasts is sufficient to mediate the local recruitment of CD8+ T cells. Thirdly, by RNA-seq analysis and lentivirus mediated shRNA knockdown in dermal fibroblast, they demonstrated dermal fibroblasts mediated CD8+ T cells aggregation and vitiligo pathogenesis through the CXCL9/CXCL10–CXCR3 axis.

By quantification of the frequencies of vitiligo lesions at different anatomic regions of 2,265 patients, Dr. Chen and her team found large variations in the frequency, with the hand back and the chest being the most susceptible to vitiligo, while the palm and arm the least. They also found that the numbers and types of upregulated genes in response to IFNγ varied significantly among regional-specific fibroblasts using RNA-seq. Multiple IFNγ-induced chemokine genes, including CXCL9, CXCL10 and CXCL11, were significantly upregulated in fibroblasts that were isolated from anatomic regions with a higher incidence of vitiligo. Further correlation analysis showed that the percentage of vitiligo incidence positively correlated with the intrinsic IFNγ response of dermal fibroblasts at different anatomic regions. Finally, In the mouse model of vitiligo, they demonstrated regional variation in fibroblasts IFNγ-responsive abilities could result in patterned T cell activity and vitiligo progression.

The discovery provides a general paradigm through which the regional pattern of skin autoimmune diseases is regulated. It also provides new insights for the regulatory mechanism of many other autoimmune skin diseases in addition to vitiligo, which exhibits regional preference with symmetric distributions. Besides the skin, fibroblasts are ubiquitously present in essentially all organs of our body; the study also provides avenues for investigation of the potentially broad application of this cellular cross-talk.

Dr. Zijian Xu and Dr. Daoming Chen are the co-first authors of this article. Other authors of the paper include Dr. Yucheng Hu at Capital Normal University; Huanwei Huang, Kaiju Jiang, YingXue Du, Dr. Wenbo Wu, and Dr. Jianhua Sui at National institute of Biological Sciences; Dr. Wenhui Wang and Dr. Long Zhang at Peking University Third Hospital; Dr. Shuli Li and Dr. Chunying Li at Xijing Hospital; Dr. Yong Yang at Institute of Dermatology, Chinese Academy of Medical Sciences. Dr. Ting Chen and Dr. Jianmin Chang are the corresponding authors of this article. This work was carried out at National Institute of Biological Sciences, Beijing.

Article link: https://doi.org/10.1038/s41586-021-04221-8