Intracellular cholesterol trafficking is dependent upon NPC2 interaction with lysobisphosphatidic acid.

Leslie A Mccauliff,Debosreeta Bose,Judith Storch,Annette Langan,Peter C Kahn,Olga Ilnytska,Kimberly Lai,Ran Li,Miriam Waghalter

doi:10.7554/elife.50832

Leslie A Mccauliff, Debosreeta Bose + Show 7 more

Open Access

https://doi.org/10.7554/elife.50832

Copy DOI

Journal: eLife	Publication Date: Oct 3, 2019
Citations: 48	License type: CC BY 4.0

Affiliation: Rutgers, The State University of New Jersey

Abstract

Unesterified cholesterol accumulation in the late endosomal/lysosomal (LE/LY) compartment is the cellular hallmark of Niemann-Pick C (NPC) disease, caused by defects in the genes encoding NPC1 or NPC2. We previously reported the dramatic stimulation of NPC2 cholesterol transport rates to and from model membranes by the LE/LY phospholipid lysobisphosphatidic acid (LBPA). It had been previously shown that enrichment of NPC1-deficient cells with LBPA results in cholesterol clearance. Here we demonstrate that LBPA enrichment in human NPC2-deficient cells, either directly or via its biosynthetic precursor phosphtidylglycerol (PG), is entirely ineffective, indicating an obligate functional interaction between NPC2 and LBPA in cholesterol trafficking. We further demonstrate that NPC2 interacts directly with LBPA and identify the NPC2 hydrophobic knob domain as the site of interaction. Together these studies reveal a heretofore unknown step of intracellular cholesterol trafficking which is critically dependent upon the interaction of LBPA with functional NPC2 protein.

Highlights

Cholesterol is a small, hydrophobic molecule that is a vital building block of cell membranes and a precursor for steroid hormones, bile salts, vitamin D, and oxysterol ligands for transcription factors.Intracellular transport of cholesterol is a highly regulated but, as yet, incompletely understood process.Perturbations can lead to detrimental outcomes such as in the lysosomal storage disorder Niemann PickType C (NPC) disease, where LDL-derived cholesterol becomes trapped within the late endosomal/lysosomal (LE/LY) system
In the present studies we discovered an unanticipated impact of lysobisphosphatidic acid (LBPA) incorporation into membranes, in which some NPC2 mutants that were highly defective in sterol transfer to phosphatidylcholine membranes, were essentially normalized when LBPA was present
In this study we demonstrate for the first time that functional and likely direct interaction of NPC2 protein with LBPA is a required step in normal cholesterol trafficking through the endosomal/lysosomal compartment

Summary

Introduction

Type C (NPC) disease, where LDL-derived cholesterol becomes trapped within the late endosomal/lysosomal (LE/LY) system. The sterol enriches LE/LY inner membranes, which develop during endosome maturation as a means of compartmentalizing its contents (Gruenberg, 2001; Gruenberg, 2003; Matsuo et al, 2004). The accumulation of cholesterol in NPC disease is associated with amassing of other lipids in the LE/LY, disruption of post-lysosomal cholesterol metabolism, and clinical manifestations including organomegaly and neurological deterioration. In 95% of NPC cases, mutations in the large LE/LY transmembrane protein, NPC1, prevent proper export of cholesterol from the LE/LY to other cellular compartments. The remaining 5% of cases are caused by mutations in the small, 132-amino acid, soluble LE/LY protein, NPC2 (Peake & Vance, 2010; Sokol et al, 2010)

Methods

Results

Conclusion