Peptide DR8 suppresses epithelial-to-mesenchymal transition via the TGF-β/MAPK signaling pathway in renal fibrosis

Aims: Renal fibrosis is a progressive disease that leads to renal dysfunction and end-stage renal failure, and there is currently no specific treatment. Our previous study showed that the 8-residue peptide DR8 (DHNNPQIR) exhibits potent antioxidant and antifibrotic properties, and accumulating evidence suggests that oxidative stress contributes greatly to fibrosis. The effects and mechanisms of DR8 on renal fibrosis remain unknown. Materials and methods: The effects of DR8 were assessed in a unilateral ureteral obstruction mouse model that received a daily, single-dose subcutaneous injection of 500 pg/kg DR8 for 14 days and in cultured cells (HK-2 and NIH-3T3 cells) treated with 5 ng/mL TGF-beta 1 and 80 p.M DR8. Western blotting, immunohistochemical staining, real-time qPCR and other tools were conducted to study the molecular mechanisms underlying antifibrotic effects. Key findings: DR8 improved renal function and reduced injury and extracellular matrix (ECM) deposition. Inflammation and oxidative stress were alleviated by DR8 in vivo. DR8 also inhibited the activation of fibroblasts and ECM deposition in HK-2 and NIH-3T3 cells induced by TGF-beta 1. In addition, epithelial-to-mesenchymal transition (EMT) was inhibited by DR8 both in vivo and in vitro. Mechanistic studies supported that DR8 inhibited ERK and p38 mitogen-activated protein kinase (MAPK) activation. These results indicate that DR8 attenuates renal fibrosis via suppression of EMT by antagonizing the MAPK pathway. Significance: We provide mechanistic details for a potential therapeutic agent and establish a foundation for peptide therapeutics.