End-stage renal disease (ESRD) can be effectively treated with peritoneal dialysis (PD), and over 272,000 ESRD patients worldwide are currently receiving this form of therapy, representing about 11 % of all dialysis patients (Li et al., 2017). PD offers several advantages over hemodialysis, including lower cost, home-based therapy, and better preservation of residual renal function. As a result, the number of PD patients has been steadily increasing, particularly in developing countries, from 1997 to 2008 (Wang et al., 2020a). However, despite these benefits, long-term exposure to high-glucose peritoneal dialysate can have detrimental effects on the structure and function of peritoneal tissue. This may lead to peritoneal fibrosis, which in turn can result in ultrafiltration failure and discontinuation of PD (Balzer, 2020). Therefore, it is crucial to find ways to delay or reverse peritoneal fibrosis, and this has been a major focus of research over the past two decades. Peritoneal mesothelial cells play a crucial role as the first line of defense and physiological barrier against peritoneal dialysate. The formation of peritoneal fibrosis has been linked to the epithelial-mesenchymal transition (EMT) of peritoneal mesothelial cells (Yáñez-Mó et al., 2003). Understanding the mechanisms underlying EMT may provide a theoretical foundation for the treatment of peritoneal fibrosis. Various factors and signaling pathways, such as the transforming growth factor-β1 (TGF-β1)/Smad-dependent pathway, TGF-β1/Smad-independent pathway, and non-coding RNAs, strictly regulate the occurrence of EMT in peritoneal mesothelial cells (Guo et al., 2020a).

A distinct class of endogenous non-coding RNAs known as circular RNAs (circRNAs) is defined by its closed circular structure, which lacks the 5′ cap and 3′ poly(A) tail typical of linear RNAs (Chen et al., 2020). CircRNAs are formed through a process called back-splicing of precursor mRNAs and are known to have enhanced stability compared with linear RNA molecules. Previous studies have highlighted the essential role of circRNAs in EMT and the development of organ fibrosis (Wang et al., 2020b; Yao et al., 2018). However, their specific contribution to the progression of peritoneal fibrosis remains unclear. Therefore, this study aimed to explore the functions of circRNAs and to uncover their potential mechanisms in the progression of peritoneal fibrosis.