Keratinocytes initiate fibroblast reprogramming in autoimmune skin fibrosis

Summary: Fibrosis is a hallmark of select autoimmune skin diseases such as discoid lupus erythematosus. Few animal models of autoimmune disease recapitulate fibrosis, limiting mechanistic and therapeutic discovery. Here, we integrate data from our previously described <i>K5-Vgll3 </i>murine lupus model and human lupus patients to establish a role for keratinocytes in initiating autoimmune skin fibrosis through altering fibroblast transcriptional states. Single-cell RNA-sequencing of pre-lesional transgenic mouse skin suggests that epidermal VGLL3 overexpression initiates inflammation through keratinocyte hypersecretion of cytokines such as TNF and CCL20 and generation of an interferon-rich environment. Pre-lesional fibroblasts respond with induction of a profibrotic, proinflammatory transcriptional program characterized by enhanced expression of extracellular matrix genes and upregulation of chemokines like <i>CCL2</i>, implicated in multiple fibrotic diseases. Primary human fibroblasts cultured in conditioned media from VGLL3-overexpressing keratinocytes show <i>CCL2</i> induction, confirming a direct effect. Subclustering of murine fibroblasts reveals expansion of a profibrotic fibroblast subset in both pre-lesional and lesional skin. Ligand-receptor analysis identifies this subset as one of the most differentially activated cellular communicators in both pre-lesional and lesional versus control skin. In lesional skin, fibroblasts show induction of classic fibrotic transcripts including targets of TGFB and YAP-TEAD. Comparison of our murine and human single-cell data corroborated many of these findings in human lupus. These results suggest that keratinocytes play a dual role in early autoimmune skin fibrosis through both fibroblast reprogramming and immune cell recruitment and support the use of the <i>K5-Vgll3</i> model of sex-biased autoimmune disease for investigation of autoimmune skin fibrosis. Mehrnaz Gharaee-Kermani², Poulami Dey¹, Vincent van Drongelen¹, Joanna Rew¹, Rachael Bogle¹, Marisa C. Hildebrandt¹, Benjamin Klein¹, Rezvan Moallemian¹, Monique Verhaegen¹, Andrzej Dlugosz¹, Michelle Kahlenberg¹, Johann E. Gudjonsson¹, Allison C. Billi¹ 1. Dermatology, University of Michigan Michigan Medicine, Ann Arbor, MI, United States. 2. Dermatology, University of Michigan, Ann Arbor, MI, United States. Adaptive and Auto-Immunity