Niemann-Pick C liver-specific proteostasis and pathology

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ABSTRACT Niemann-Pick disease type C is an invariably fatal autosomal recessive neurovisceral lipid storage disease affecting all ages. Approximately 85% of patients have hepatomegaly which can develop into hepatic steatosis, cirrhosis, hepatocellular carcinoma, and liver failure. Liver defects are especially detrimental in patients with neonatal onset, with 10% dying from liver failure by 6 months of age. Although the liver is a significant contributor to disease, the cellular drivers and pathophysiology are incompletely understood. Niemann-Pick C is caused by over 300 loss-of-function point mutations in the late endosomal/lysosomal cholesterol-exporting protein NPC1. We have previously shown that the most common of these mutations, I1061T, is primarily degraded by FAM134B-dependent ER-selective autophagy (ER-phagy), but there is a crucial need to understand how this pathway works for other disease-causing mutations. Furthermore, preliminary data indicates that the brain and liver express two different isoforms of FAM134B with potentially divergent functions. Consequently, there is a need to understand Niemann-Pick C liver proteostasis and pathogenesis. The next step in addressing these needs is to pursue the overall objectives of this application: (i) determine the effectors mediating tissue-specific NPC1 proteostasis and (ii) define the contribution of different cell types to Niemann-Pick C liver pathology. Here we will test our central hypothesis is that cell type-specific pathways regulate NPC1 proteostasis and drive Niemann-Pick C liver pathology. We will test our hypothesis using induced hepatocytes and neurons from isogenic human iPSCs containing a panel of Niemann-Pick C disease-causing mutations. We will leverage biochemical and genetic assays to establish the extent to which NPC1 proteostasis and FAM134B isoform function are tissue-dependent (Aim 1). Additionally, we will take advantage of Npc1 loxP mice to delete Npc1 globally, in Kupffer cells/macrophages, or hepatocytes to study how these cells contribute to liver pathology, function, and inflammation (Aim 2). These studies are expected to identify novel pathways that significantly contribute to manifestations of Niemann-Pick C-related liver disease across many disease-causing mutations. This will set the stage for the future discovery efforts to identify and test new therapeutic strategies which correct both liver and brain. Our rationale for this project is that defining influence of Kupffer cells/macrophages on tissue-specific proteostasis and liver cell types on disease pathology will provide a strong scientific framework to develop new liver targeted Niemann-Pick C therapeutics. In addition, we outline a career development plan to increase liver biology knowledge by leveraging mentorship, technical training, seminars, liver conferences, and R01 grant writing boot camps. The University of Michigan has committed its support and facilities to allow Dr. Schultz to complete the proposed research and participate in their extensive training seminars. Completion of the proposed 5-year research and training plans will prepare Dr. Schultz for an independent research career and assist in securing an R01 from NIDDK.