REN and brain ischemia: In addition, the renin-angiotensin-aldosterone system (RAAS) in the body is activated after brain injury, which stimulates the release of renin and angiotensin II, causing vasoconstriction of brain and kidney, aggravating cerebral ischemia and hypoxia damage, and reducing glomerular filtration rate, leading to the increase of β2MG in vivo [13].