Quantitation of the rates of hepatic and intestinal cholesterol synthesis in lysosomal acid lipase-deficient mice before and during treatment with ezetimibe

Abstract

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.

Lysosomal Acid Lipase: From Cellular Lipid Handler to Immunometabolic Target

“…Some reports indicate the use of ezetimibe in CESD patients, but robust data are not yet available on its lipid-lowering efficacy alone or in combination with statins [55,72]. However, in lal -/mice, ezetimibe significantly reduces the amount of CE sequestered in the liver and small intestine, thus improving liver steatosis and suggesting that intestinal cholesterol absorption could also play a role in cellular lipid accumulation observed in LAL-D [73]. In line with this, an amelioration of liver disease was observed in young CESD patients treated with ezetimibe alone or in association with statins [72,74,75].…”

Cholesterol auxotrophy and intolerance to ezetimibe in mice with SREBP-2 deficiency in the intestine

“…Together, SREBPs control the synthesis of both cholesterol and fatty acids. Whereas SREBP-2 preferentially activates genes required for cholesterol synthesis and SREBP-1c primarily activates genes required for fatty acid and triglyceride synthesis, drug that blocks apical cholesterol uptake in enterocytes by inhibiting the cholesterol transporter Niemann-Pick C1-like 1 protein (NPC1L1), potently activates proteolysis of SREBP-2 (12), and stimulates a compensatory increase in intestinal sterol synthesis (13,14). In mice with intestinal deficiency of Insigs, feedback inhibition of SREBP-2 by cholesterol derived from the gut lumen was abolished, leading to massive increases in intestinal sterol synthesis (15).…”

Long term substrate reduction therapy with ezetimibe alone or associated with statins in three adult patients with lysosomal acid lipase deficiency

“…More recently, Chuang measured rates of cholesterol synthesis in vivo in the liver and in small intestine of lal−/− mice treated with ezetimibe; he demonstrated a reduction of esterified cholesterol storage in the liver and in the small intestine, even though the rates of liver and small intestine cholesterol synthesis were comparable or exceeded those in matching untreated lal−/− mice. These data show the importance of cholesterol intestinal absorption for the storage of cholesteryl esters in the liver of lal−/− mice [ 14 ]. Furthermore, in animal models ezetimibe ameliorates steatohepatitis by autophagy induction through AMP protein kinase activation, transcriptional EB nuclear factor translocation, and NLRP3 inflammasome inhibition [ 15 ].…”