Quantitation of the rates of hepatic and intestinal cholesterol synthesis in lysosomal acid lipase-deficient mice before and during treatment with ezetimibe
Esterified cholesterol (EC) and triglycerides, contained within lipoproteins taken up by cells, are hydrolysed by lysosomal acid lipase (LAL) in the late endosomal/lysosomal (E/L) compartment. The resulting unesterified cholesterol (UC) is transported via Niemann-Pick type C2 and C1 into the cytosolic compartment where it enters a putative pool of metabolically active cholesterol that is utilized in accordance with cellular needs. Loss-of-function mutations in LIPA, the gene encoding LAL, result in dramatic increases in tissue concentrations of EC, a hallmark feature of Wolman disease and cholesteryl ester storage disease (CESD). The lysosomal sequestration of EC causes cells to respond to a perceived deficit of sterol by increasing their rate of cholesterol synthesis, particularly in the liver. A similar compensatory response occurs with treatments that disrupt the enterohepatic movement of cholesterol or bile acids. Here we measured rates of cholesterol synthesis in vivo in the liver and small intestine of a mouse model for CESD given the cholesterol absorption inhibitor ezetimibe from weaning until early adulthood. Consistent with previous findings, this treatment significantly reduced the amount of EC sequestered in the liver (from 132.43 ± 7.35 to 70.07 ± 6.04 mg/organ) and small intestine (from 2.78 ± 0.21 to 1.34 ± 0.09 mg/organ) in the LAL-deficient mice even though their rates of hepatic and intestinal cholesterol synthesis were either comparable to, or exceeded those in matching untreated Lal−/− mice. These data reveal the role of intestinal cholesterol absorption in driving the expansion of tissue EC content and disease progression in LAL deficiency.