LDLR and Hypercholesterolemia: Proprotein convertase subtilisin kexin 9 (PCSK9), as a neuronal apoptotic regulatory invertase, not only participates in liver regeneration and regulates neuronal apoptosis, but also affects low-density lipoprotein (LDL) internalization by reducing the number of LDL-receptor (LDLR) on hepatocytes, so that the LDL in blood cannot be cleared, leading to hypercholesterolemia [7].