Proteomic Analysis of Niemann-Pick Type C Hepatocytes Reveals Potential Therapeutic Targets for Liver Damage

Abstract

Niemann-Pick type C disease (NPCD) is a lysosomal storage disorder caused by mutations in the NPC1 gene. The most affected tissues are the central nervous system and liver, and while significant efforts have been made to understand its neurological component, the pathophysiology of the liver damage remains unclear. In this study, hepatocytes derived from wild type and Npc1−/− mice were analyzed by mass spectrometry (MS)-based proteomics in conjunction with bioinformatic analysis. We identified 3832 proteins: 416 proteins had a p-value smaller than 0.05, of which 37% (n = 155) were considered differentially expressed proteins (DEPs), 149 of them were considered upregulated, and 6 were considered downregulated. We focused the analysis on pathways related to NPC pathogenic mechanisms, finding that the most significant changes in expression levels occur in proteins that function in the pathways of liver damage, lipid metabolism, and inflammation. Moreover, in the group of DEPs, 30% (n = 47) were identified as lysosomal proteins and 7% (n = 10) were identified as mitochondrial proteins. Importantly, we found that lysosomal DEPs, including CTSB/D/Z, LIPA, DPP7 and GLMP, and mitocondrial DEPs, AKR1B10, and VAT1 had been connected with liver fibrosis, damage, and steatosis in previous studies, validiting our dataset. Our study found potential therapeutic targets for the treatment of liver damage in NPCD.

Alterations in Lysosome Homeostasis in Lipid-Related Disorders: Impact on Metabolic Tissues and Immune Cells

“…Concerning NPC disease, proteomic analysis from hepatocytes of Npc1 −/− mice, performed by our group, showed an increase in the levels of CD36 protein levels (Balboa et al, 2021). Increased transcript levels of the CD36 in hepatocytes of Npc1 −/− mice have been observed by our group and others (Vázquez et al, 2011;Dos Reis et al, 2020).…”

“…This section will focus on the role of cathepsins and autophagy in hepatocytes in the context of NPC and Gaucher diseases, considering that most of the studies have been performed in the liver. An increase in the expression of CTSB, CTSD, CTSS, and CTSZ were recently observed in the liver and hepatocytes of Npc1 −/− mice (Balboa et al, 2021;van der Lienden et al, 2021), suggesting that lysosomal proteases were increased. However, Npc1 −/− mouse embryonic fibroblasts showed increased levels of mature CTSB and CTSD and normal lysosomal proteolytic functions, suggesting that they remained unaffected (Sarkar et al, 2013).…”

“…This sterol transporter, also located in the lysosomal membrane, has been studied in the context of cholesterol transfer towards ER through MCSs formation (Alpy et al, 2013). Interestingly, we have shown that STARD3 protein levels in NPC were increased in hepatocytes, correlating with elevated cholesterol levels in mitochondria purified from livers of NPC mice, which might contribute to mitochondrial dysfunction (Balboa et al, 2017(Balboa et al, , 2021.…”

“…Interestingly, in Gaucher and NPC cells there is a secondary accumulation of lipids besides glucosylceramide and cholesterol, respectively. In addition, NPC cells show mitochondrial damage and mitochondrial cholesterol accumulation (Balboa et al, 2017). Hence, it is possible to speculate that there is an increase in the transfer of lipids between lysosome and mitochondria, through MCSs that contributes to mitochondrial damage in NPC and Gaucher cells.…”

NPC1 Deficiency Contributes to Autophagy-Dependent Ferritinophagy in HEI-OC1 Auditory Cells

“…NPCD is mainly characterized by cholesterol accumulation, and it affects multiple organelles such as the central nervous system (CNS), visceral organelles, and auditory system (King, 2014a;Wheeler and Sillence, 2020). Current research show more interests on the former (Vanier, 2010;Santos-Lozano et al, 2015;Balboa et al, 2021;Van Hoecke et al, 2021), but fewer studies have focused on the effect of NPCD related to genetic hearing loss and the molecular mechanism has not been fully understood to date.…”