Soluble urokinase plasminogen activator receptor promotes endoplasmic reticulum stress and apoptosis susceptibility through RAGE in sepsis acute kidney injury

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BACKGROUND: Acute kidney injury (AKI) is a common complication among critically ill patients, associated with an increased risk of adverse outcomes. There is an urgent need for novel biomarkers to assist in the early detection and management of AKI. Soluble urokinase plasminogen activator receptor (suPAR) is an inflammation-related, immune-derived molecule implicated in the pathogenesis of several diseases, including kidney diseases. METHODS: We characterized the ability of serum suPAR levels to diagnose AKI in 124 patients admitted to the intensive care unit (ICU). Additionally, in vivo and in vitro experiments were performed to explore the underlying mechanisms between suPAR and the development of AKI. We stimulated HK-2 cells with suPAR to investigate its effects on HK-2 cells. Additionally, Methods such as receptor inhibitors, protein docking, and co—immunoprecipitation were used to study how suPAR acts on HK-2 cells. We further explored whether the uPAR monoclonal antibody could alleviate acute kidney injury in septic mice. RESULTS: We found that serum suPAR levels were significantly elevated in patients with AKI. In addition, total suPAR/uPAR was elevated in the renal cortex of AKI mice, and serum suPAR levels were also increased. In vitro cell experiments demonstrated that suPAR stimulation promoted endoplasmic reticulum stress (ER stress) and the expression of apoptosis—related proteins in HK-2 cells and increased intracellular reactive oxygen species (ROS). Consistently, mice injected intraperitoneally with recombinant suPAR also exhibited elevated ER stress in the renal cortex. Furthermore, we discovered that suPAR was immunoprecipitated with the receptor of advanced glycation end products (RAGE), and recombinant suPAR labeled with FITC was fluorescently colocalized with RAGE on HK-2 cells, indicating that RAGE was involved in the signal transduction of suPAR. Additionally, protein docking results showed that suPAR can form a protein–protein complex with RAGE through hydrogen bonds. Pretreatment with uPAR monoclonal antibody alleviated kidney injury in septic mice and reduced the levels of ROS, apoptosis, and endoplasmic reticulum stress in the kidneys of septic AKI mice. CONCLUSIONS: Our study demonstrates that high levels of suPAR are positively correlated with the occurrence of AKI. suPAR promotes endoplasmic reticulum stress and increases susceptibility to apoptosis in renal tubular epithelial cells. RAGE on the cell membrane can bind to suPAR, participating in the activation of suPAR-mediated endoplasmic reticulum stress pathways and the expression of apoptosis-related proteins. Pretreatment with uPAR monoclonal antibody alleviates acute kidney injury in septic mice.

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