Single-cell RNA sequencing reveals profibrotic roles of distinct epithelial and mesenchymal lineages in pulmonary fibrosis.

Pulmonary fibrosis (PF) is a form of chronic lung disease characterized by pathologic epithelial remodeling and accumulation of extracellular matrix (ECM). To comprehensively define the cell types, mechanisms, and mediators driving fibrotic remodeling in lungs with PF, we performed single-cell RNA sequencing of single-cell suspensions from 10 nonfibrotic control and 20 PF lungs. Analysis of 114,396 cells identified 31 distinct cell subsets/states. We report that a remarkable shift in epithelial cell phenotypes occurs in the peripheral lung in PF and identify several previously unrecognized epithelial cell phenotypes, including a KRT5- /KRT17 + pathologic, ECM-producing epithelial cell population that was highly enriched in PF lungs. Multiple fibroblast subtypes were observed to contribute to ECM expansion in a spatially discrete manner. Together, these data provide high-resolution insights into the complexity and plasticity of the distal lung epithelium in human disease and indicate a diversity of epithelial and mesenchymal cells contribute to pathologic lung fibrosis.

Epigenetically altered wound healing in keloid fibroblasts.

Keloids are benign dermal tumors that form during wound healing in genetically susceptible individuals. The mechanism(s) of keloid formation is unknown and there is no satisfactory treatment. We have reported differences between fibroblasts cultured from normal scars and keloids that include a pattern of glucocorticoid resistance and altered regulation of genes in several signaling pathways associated with fibrosis, including Wnt and IGF/IGF-binding protein 5 (IGFBP5). As previously reported for glucocorticoid resistance, decreased expression of the Wnt inhibitor secreted frizzled-related protein 1 (SFRP1), matrix metalloproteinase 3 (MMP3), and dermatopontin (DPT), and increased expression of IGFBP5 and jagged 1 (JAG1) are seen only in fibroblasts cultured from the keloid nodule. In vivo, decreased expression of SFRP1 and SFRP2 and increased expression of IGFBP5 proteins are observed only in proliferative keloid tissue. There is no consistent difference in the replicative life span of normal and keloid fibroblasts, and the altered response to hydrocortisone (HC) and differential regulation of a subset of genes in standard culture medium are maintained throughout at least 80% of the culture lifetime. Preliminary studies using ChIP-chip analysis, Trichostatin A, and 5-aza-2'-deoxycytidine further support an epigenetically altered program in keloid fibroblasts that includes an altered pattern of DNA methylation and histone acetylation.