Long Non-Coding RNA XIST and TSIX Modulate TGF-β-Mediated Cellular Transdifferentiation and Fibrosis in Systemic Sclerosis

<title>Abstract</title> <p> <bold>Background</bold> Systemic sclerosis (SSc) is a complex autoimmune disease characterized by immune dysregulation, microvascular injury, and progressive fibrosis, with transforming growth factor-β (TGF-β) serving as a central driver of fibrotic responses. Although the long non-coding RNAs (lncRNAs) XIST and TSIX are recognized as important epigenetic regulators, their contribution to TGF-β-mediated fibrosis in SSc remains poorly defined. <bold>Method</bold> Tissue- and gender based XIST and TSIX expression was evaluated in SSc patients and healthy controls (HCs). Functional analyses were performed <italic>in-vitro</italic> , using Differential serum induction (Autologous or Patients’ serum) and Synthetic TGF-β stimulation on PBMCs from healthy individuals. siRNA-based knockdown analyses were performed to evaluate their regulatory influence on fibrotic markers and TGF-β expression. <bold>Result</bold> Both lncRNAs were significantly upregulated in patients with SSc, regardless of tissue type or sex, in contrast to the physiologically female-biased expression of XIST observed in healthy controls. Exposure of healthy PBMCs to SSc serum promoted fibrocyte transdifferentiation and increased the expression of fibrosis-associated markers. XIST and TSIX expression positively correlated with profibrotic genes and was further induced following TGF-β stimulation. Conversely, silencing either lncRNA reduced TGF-β expression together with downstream fibrotic mediators, supporting their involvement in TGF-β-associated profibrotic signalling. <bold>Conclusion</bold> XIST and TSIX are the upstream regulators of TGF-β and are also associated with the immune-fibrotic pathophysiological axis of systemic sclerosis, highlighting their potential as biomarkers of disease activity. Targeting them may offer a selective, safer alternative to direct TGF-β inhibition. Further mechanistic studies are required to define their precise roles in SSc pathogenesis. </p>