Single-cell profiling of scleroderma-like syndromes: Identifying key molecular pathways in skin fibrosis

Summary: Abstract Body: Scleroderma-like syndromes (SLS) are a group of disorders characterized by skin hardening due pathological fibrosis. However, their pathogenesis and mechanism of fibrosis remain unclear. Here, we performed single-cell, bulk and spatial profiling of 3 cases of Stiff Skin Syndrome, a disease caused by a mutation in the fibrillin 1 (FBN1) gene and characterized by progressive fibrosis, contractures and hypertrichosis. We contrasted the data against single-cell data from 4 systemic sclerosis (SSc) and 4 healthy controls (HC). We identified 52,420 cells across seventeen major cell type across all skin samples capturing all major stromal, epithelial and immune cell types. Patients with Stiff Skin Syndrome had increased hair follicle but lower immune cell proportions, particularly myeloid cells, compared to SSc. COL1A1 mRNA expression was markedly increased in both Stiff Skin Syndrome and Systemic Sclerosis (9.7-fold, p=8.8x10-11, and 13.5-fold, p-1.6x10-8, respectively) and shared enriched Biological Processes including Extracellular Matrix Organization, Integrin Cell Surface Interactions, and Smooth Muscle Contraction. Myofibroblasts (COL8A1+) were enriched in both Stiff Skin Syndrome and SSc but had strikingly different distribution on spatial sequencing with myofibroblasts in Stiff Skin Syndrome being prominent in the upper dermis and around adnexal structures including hair follicles and eccrine glands, whereas myofibroblasts in SSc were denser in the deeper dermis. Notably, prominent receptor-ligand interactions specific to Stiff Skin Syndrome were seen, with hair follicle cells being a major sender and receiver of cell communication. These data outline distinct compartmentalization of fibrotic processes in different fibrotic diseases and provide a deeper understanding of the molecular and cellular mechanisms involved. Jesus A. Gutierrez Brito¹, Vincent van Drongelen¹, Rachael Bogle¹, Lin Zhang¹, J M. Kahlenberg^{1, 2}, Lam C. Tsoi¹, John Varga², Paul W. Harms^{1, 3}, Dinesh Khanna², Allison C. Billi¹, Johann E. Gudjonsson^{1, 2} 1. Dermatology, University of Michigan, Ann Arbor, MI, United States. 2. Rheumatology, University of Michigan, Ann Arbor, MI, United States. 3. Pathology, University of Michigan, Ann Arbor, MI, United States. Translational Studies: Cell and Molecular Biology