Annexin-A5 monomer as a membrane repair agent for the treatment of renal ischemia-reperfusion injury

Background: Renal ischemia-reperfusion injury (IRI) is one of the causes of acute kidney injury. Annexin A5 (AnxA5) as a calcium-dependent cell membrane binding protein has shown good protective effects in various organ IRI models. This study explored the therapeutic effect of exogenous AnxA5 monomer protein on renal IRI and its potential mechanism. Methods: In vivo, different doses of AnxA5 were injected intravenously to treat bilateral renal IRI models in SD rats. This model confirms the protective effect of AnxA5 on the structure and function of the kidneys. In vitro, HK-2, the renal tubular epithelial cells, was subjected to hypoxia for 12 hours, followed by restoration of normal oxygen supply to simulate IRI. In vitro experiments have demonstrated the mechanism of action of AnxA5 by measuring cell activity and permeability. The comparison of the mutant AnxA5 protein M23 and the application of calcium-free culture medium further validated the protective effect of AnxA5 by forming a network structure. Results: In vivo, AnxA5 monomer improved kidney function damage caused by IRI and prevented the deterioration of the pathological structure. In vitro, AnxA5 protected cell viability, reduced cell membrane permeability, and inhibited cell apoptosis induced by IRI treatment. However, AnxA5 lost its protective effect in the calcium-free culture medium and the M23 that lack the ability of forming a two-dimensional network structure could not reduce cell membrane permeability and lost its protective effect on cell viability, indicating that the formation of a two-dimensional network structure of AnxA5 is critical to the repair of the cell membrane. Conclusions: Exogenous AnxA5 monomer could prevent renal IRI by binding to the damaged renal tubular epithelial cell membrane, forming a two-dimensional network structure to maintain cell membrane integrity, and ultimately prevent cell death.