REN and acute kidney injury: The complex and unclear pathophysiological mechanisms of SA-AKI, mainly including systemic and renal immune inflammation, complement activation, renin-angiotensin-aldosterone system (RAAS) dysregulation, mitochondrial dysfunction, metabolic reprogramming, microcirculatory dysfunction, and macrocirculatory abnormalities, account for the diverse clinical phenotypes and challenging clinical management of SA-AKI [21,27,32,76].