Familial Hypercholesterol Homeostasis

Low-density lipoproteins (LDL), known as bad cholesterol, are carrier vesicles that transport cholesterol in the bloodstream. Receptor-mediated endocytosis refers to system in which these LDL bind to receptors, which engulf the ligand into the cell (Alberts, et al., 2010). A protein-coding gene called proprotein convertase subtilisin/kexin type 9 (PCSK9) helps regulate the number of low-density lipoprotein receptors (LDLR) located on the plasma membrane of a cell (Duan, et al., 2012). This, in turn, balances the amount of LDL that are released from the bloodstream via receptor-mediated endocytosis to maintain cholesterol homeostasis (Tavori, et al., 2013). Cholesterol homeostasis relies strictly on the correlated function of two proteins; LDLR and PCSK9, which can cause familial hypercholesterolemia due to function abnormalities.

LDLR play a significant role in cholesterol homeostasis, in which it allows the shuttling of LDL from the bloodstream to nearby cells to control cholesterol levels in the human body (Mousavi, et al., 2009). When there is a dysfunctional mutation in this receptor, its function for clearing out the LDL will

This protein binds to the LDLR, which undergoes the exact same receptor-mediated endocytosis pathway. This leads to PCSK9 and LDLR being degraded in the lysosome of the cell (Tavori, et al., 2013). In this process, PCSK9 is actually decreasing the number of opportunities for LDL to leave the bloodstream due to the decreased number of LDLR available that it can bind to. There can be a gain-of-function mutation on the PCSK9, which is a very rare form of hypercholesterolemia (Tavori, et al, 2013). This mutation causes an increased regulation rate of PCSK9, which means there is more availability for PCSK9 to bind to LDLR and less availability for LDL to bind to LDLR, thus increasing cholesterol concentration in the