Smurf1: A possible therapeutic target in dry age-related macular degeneration

Smad ubiquitylation regulatory factor-1 (Smurf1) is one of C2-WW-HECT domain E3 ubiquitin ligases, it can regulate BMP pathway by mediating ubiquitylation degradation of Smad1/Smad5. Many functions about Smurf1 also are still unknown, especially in retina. This research is about to explore the role of Smurf1 in retina degeneration. Tail vein injection of sodium iodate (NaIO3) in C57BL/6J mice was the animal model of retina degeneration. In NaIO3 model, Smurf1 had more expression than normal mice. Specific Smurf1 inhibitor, A01, was injected into vitreous cavity. Results showed that inhibiting Smurf1 could alleviate acute retina injury, such as keeping a better retina structure in living imaging and histologic sections, less cell death and inflammation activation. Tert-butyl hydroperoxide (TBH) was used to establish oxidative stress injury in human retinal pigments epithelial cell line (ARPE-19). Oxidative stress injury gradually caused co-upregulation of Smurf1, TGF-β1 and phosphorylated NF-κB (pNF-κB). TGF-β1 could directly induce Smurf1 expression. Inhibiting Smurf1 had an anti-epithelial mesenchymal transition (anti-EMT) function. Similarly, A01 also could inhibit the expression of pNF-κB, NLRP3 and IL-1β. At last, after searching bioinformatics database, Smurf1 had a possible interaction with beta-transducin repeat containing E3 ubiquitin protein ligase (β-TrCP), another E3 ubiquitin ligases. β-TrCP can mediate ubiquitination degradation of p-IκBα. Lentivirus-SMURF1 was used to overexpress Smurf1, and GS143 was used to inhibit β-TrCP. The results showed Smurf1 could directly induce NF-κB, pNF-κB, and NLRP3 expression, and keep a stable β-TrCP expression. However, inhibiting β-TrCP could cause more NF-κB activation and NLRP3 expression. Therefore, β-TrCP may play a negative role in NF-κB pathway activation. In summary, Smurf1 plays a role in exacerbating oxidative stress injury and inflammation in retina and may become a potential therapeutic target in ROS injury of retina.