This process involves the binding of TGF-β to its receptor, phosphorylation of the downstream Smad3 protein, and subsequent nuclear translocation of Smad3 to regulate the transcription and expression of fibrosis-related genes, such as fibronectin (Fn), Snail, and collagen I, thereby contributing to the onset and progression of PF [21,22]. The gene discussed is FN1; the disease is pemphigus foliaceus.