Ezetimibe-sensitive cholesterol uptake by NPC1L1 protein does not require endocytosis

Area of Science:

• Biochemistry
• Cell Biology
• Pharmacology

Background:

• Human NPC1L1 protein facilitates cholesterol absorption in the intestine and liver.
• NPC1L1 is the molecular target of ezetimibe, a medication for hypercholesterolemia.
• Prior research suggested ezetimibe inhibits NPC1L1 function by blocking its endocytosis.

Purpose of the Study:

• To investigate the mechanism by which ezetimibe affects NPC1L1 protein function.
• To determine if ezetimibe inhibits NPC1L1-mediated cholesterol uptake by blocking endocytosis.

Main Methods:

• Cell surface biotinylation was employed to track NPC1L1-GFP endocytosis in cultured rat hepatocytes.
• The effect of ezetimibe on NPC1L1-GFP endocytosis rate was assessed.
• Small-molecule inhibitors of general endocytosis were used to evaluate their impact on ezetimibe-sensitive cholesterol uptake.

Main Results:

• Ezetimibe did not alter the rate of NPC1L1-GFP endocytosis in cultured rat hepatocytes.
• NPC1L1-GFP endocytosis was partially dependent on C-terminal cytoplasmic sequences but not on N-terminal cholesterol binding.
• Inhibitors of general endocytosis did not block ezetimibe-sensitive [(3)H]cholesterol uptake.

Conclusions:

• Cholesterol uptake mediated by NPC1L1 protein does not necessitate endocytosis.
• Ezetimibe interferes with the cholesterol adsorption activity of NPC1L1 without inhibiting its internalization.
• These findings challenge previous understandings of ezetimibe's mechanism of action on NPC1L1.