In vivo antisense oligonucleotide reduction of NPC1 expression as a novel mouse model for Niemann Pick type C– associated liver disease

Niemann-Pick type C (NPC) is an autosomal recessive lysosomal storage disease with an estimated prevalence of 1:150,000, which is characterized by cellular accumulation of cholesterol and glycosphingolipids in all tissues of the body.1 The majority of patients with NPC have mutations in the NPC1 gene and a small number have mutations in NPC2.2 Symptoms of NPC include vertical gaze palsy, ataxia, dystonia, and progressive neurodegeneration. The majority of patients with NPC die as a consequence of their neurological disease; however, approximately 45%−65% of patients with NPC also suffer from cholestasis, prolonged jaundice, and hepatosplenomegaly.2-4 Ten percent of these patients die from liver failure before they reach 6 months of age.3 NPC disease is the second most common cause of neonatal cholestasis.5 Multiple cases have reported patients suffering from liver failure.4,6-11 Thus, liver disease in patients with NPC is more common than previously perceived. A key function of the liver is to maintain the whole-body cholesterol balance.12 The liver is responsible for clearing cholesterol circulating in the blood in the form of low-density lipoproteins (LDL), high-density lipoproteins (HDL), and chylomicron remnants. Both chylomicron remnants and LDL particles are internalized via a clathrin-mediated endocytic pathway in which the cholesteryl ester core is hydrolyzed in endosomes to unesterified cholesterol. NPC1 and NPC2 encode proteins found in late endosomes and lysosomes and are hypothesized to participate in cholesterol egress from those organelles.13 The cholesterol can then be sent to the endoplasmic reticulum for re-esterification or utilized for bile acid synthesis, leading to its elimination from the body. When NPC1 or NPC2 is mutated, cholesterol transport out of endosomes and lysosomes is impaired, leading to the formation of storage bodies. Previous studies investigating NPC liver disease have used the NPCnih mouse model, which lacks a functional NPC1 protein.14 These studies report that NPCnih mice exhibit a liver disease phenotype similar to that seen in the NPC infant.15-19 Characteristic features include hepatomegaly, liver cholesterol accumulation, increased plasma liver enzymes, and apoptotic cells.16 Fibrosis occurs when the mice are fed a high-cholesterol diet.17 Although liver disease is observed in NPCnih mice, the neurodegeneration is overwhelming, causing declining body weight and a lifespan shortened to approximately 60−80 days.17,20-22 To study NPC liver disease without the confounding effects of neurodegeneration, we have developed a mouse model in which the liver disease is predominant. In this study, we used second-generation 2′-O-methoxyethyl–modified antisense oligonucleotides (ASOs) to block NPC1 expression. We show that ASO treatment causes reduced NPC1 expression in liver and lung, but not in brain or other tissues. This leads to changes in liver histology and physiology that are characteristic of NPC disease.