Omega-3 polyunsaturated fatty acids protect peritoneal mesothelial cells from hyperglycolysis and mesothelial-mesenchymal transition through the FFAR4/CaMKKS/AMPK/mTOR signaling pathway

Peritoneal fibrosis is a severe clinical complication associated with peritoneal dialysis (PD) and impacts its efficacy and patient outcomes. The process of mesothelial-mesenchymal transition (MMT) in peritoneal mesothelial cells plays a pivotal role in fibrogenesis, whereas metabolic reprogramming, characterized by excessive glycolysis, is essential in MMT development. No reliable therapies are available despite substantial progress made in understanding the mechanisms underlying peritoneal fibrosis. Protective effect of omega-3 polyunsaturated fatty acids (co3 PUFAs) has been described in PD-induced peritoneal fibrosis, although the detailed mechanisms remain unknown. It is known that co3 PUFAs bind to and activate the free fatty acid receptor 4 (FFAR4). However, the expression and role of FFAR4 in the peritoneum have not been investigated. Thus, we hypothesized that co3 PUFAs would alleviate peritoneal fibrosis by inhibiting hyperglycolysis and MMT through FFAR4 activation. First, we determined FFAR4 expression in peritoneal mesothelium in humans and mice. FFAR4 expression was abnormally decreased in patients on PD and mice and HMrSV5 mesothelial cells exposed to PD fluid (PDF); this change was restored by the co3 PUFAs (EPA and DHA). co3 PUFAs significantly inhibited peritoneal hyperglycolysis, MMT, and fibrosis in PDF-treated mice and HMrSV5 mesothelial cells; these changes induced by co3 PUFAs were blunted by treatment with the FFAR4 antagonist AH7614 and FFAR4 siRNA. Additionally, co3 PUFAs induced FFAR4, Ca2+/calmodulin-dependent protein kinase kinase S (CaMKKS), and AMPK and suppressed mTOR, leading to the inhibition of hyperglycolysis, demonstrating that the co3 PUFAsmediated FFAR4 activation ameliorated peritoneal fibrosis by inhibiting hyperglycolysis and MMT via CaMKKS/AMPK/mTOR signaling. As natural FFAR4 agonists, co3 PUFAs may be considered for the treatment of PD-associated peritoneal fibrosis.