Identification of pro-fibrotic cellular subpopulations in fascia of gluteal muscle contracture using single-cell RNA sequencing

Fibrosis is a common and integral pathological feature in various chronic diseases, capable of affecting any tissue or organ. Fibrosis within deep fascia is implicated in many myofascial disorders, including gluteal muscle contracture (GMC), Dupuytren's disease, plantar fasciitis, iliotibial band syndrome, and chronic muscle pain. Despite its clinical significance, deep fascia fibrosis remains considerably under-researched compared to other fibrotic conditions. Single-cell RNA-sequencing (scRNA-seq) has been used to investigate cellular heterogeneity in fibrotic tissues. However, to our knowledge, only a few studies have applied scRNA-seq to explore cellular heterogeneity in deep fascia, and none have specifically examined fibrotic fascia. In this study, we performed scRNA-seq analysis on fibrotic fascia associated with GMC and compared them to nonfibrotic control fascial samples. Our findings show that fibroblast and macrophage cells play critical roles in pathological tissue remodeling within fibrotic deep fascia. We observed an upregulation of various collagens, proteoglycans, and extracellular matrix (ECM) glycoproteins in contracture deep fascia, attributed to the widespread activation of fibroblast subclusters. Additionally, two pro-fibrotic macrophage subpopulations, SPP1⁺ MP and ECM-like MP, appear to facilitate ECM deposition in fibrotic deep fascia by either regulating fibroblast activation or directly contributing to ECM production. The SPP1⁺ MP and ECM-like MP cells, as well as the signal interaction between SPP1⁺ MP and fibroblast cells, present potential therapeutic target for treating GMC and other related myofascial disorders.