Cellular Players in Gastrointestinal Involvement of Systemic Sclerosis: Insights into Pathogenesis

: Background: Gastrointestinal (GI) involvement is the most frequent visceral complication of systemic sclerosis (SSc), affecting up to 90% of patients, yet it remains poorly understood compared to pulmonary or cutaneous manifestations. The aim of this review is to integrate current knowledge on the cellular mechanisms underlying GI disease in SSc and to identify research priorities. Methods: A narrative literature review was conducted through a systematic PubMed search up to September 2025, complemented by manual reference screening. Results: Histopathological and functional evidence consistently demonstrates that neuromuscular alterations, including degeneration of enteric neurons, loss of interstitial cells of Cajal, and smooth muscle atrophy, can precede fibrosis, challenging the traditional "fibrosis-first" paradigm. Fibroblast and myofibroblast activation are present in gastric and colonic samples, sustained by profibrotic mediators such as TGF-β, CTGF, and endothelin-1, although the cellular origins of these stromal cells remain uncertain. Additional pathogenic contributions include autonomic dysfunction, barrier dysfunction with dysbiosis, impaired vascular reserve of vessels perfusing the gut, and functional autoantibodies targeting interneural and neuromuscular function and communication. Compared with skin and lung, the GI tract displays less fibrosis and fewer inflammatory infiltrates, but immune-derived mediators and autoantibodies suggest distinct immunopathogenic pathways are activated. Conclusions: Collectively, these findings depict GI involvement in SSc as a multi-compartmental process integrating neural, epithelial, endothelial, stromal, and immune alterations. Addressing the lack of validated biomarkers, mechanistic models, and biomarker-stratified trials will be essential to move beyond symptomatic care and toward precision medicine approaches for SSc-related GI disease.