Cessation of rapid late endosomal tubulovesicular trafficking in Niemann–Pick type C1 disease

Abstract

Niemann-Pick type C1 (NPC1) disease results from a defect in the NPC1 protein and is characterized by a pathological accumulation of cholesterol and glycolipids in endocytic organelles. We followed the biosynthesis and trafficking of NPC1 with the use of a functional green fluorescent protein-fused NPC1. Newly synthesized NPC1 is exported from the endoplasmic reticulum and requires transit through the Golgi before it is targeted to late endosomes. NPC1-containing late endosomes then move by a dynamic process involving tubulation and fission, followed by rapid retrograde and anterograde migration along microtubules. Cell fusion studies with normal and mutant NPC1 cells show that exchange of contents between late endosomes and lysosomes depends upon ongoing tubulovesicular late endocytic trafficking. In turn, rapid endosomal tubular movement requires an intact NPC1 sterol-sensing domain and is retarded by an elevated endosomal cholesterol content. We conclude that the neuropathology and cellular lysosomal lipid accumulation in NPC1 disease results, at least in part, from striking defects in late endosomal tubulovesicular trafficking. D efects of the NPC1 gene cause a severe endocytic accumulation of cholesterol in a variety of cellular and animal models of Niemann-Pick C1 (NPC1) disease (1, 2). The fatal damage in NPC1 disease is neurodegeneration starting from early life. The product of the NPC1 gene (NPC1) is composed of 1,278 aa and is predicted to contain 13 transmembrane domains (2, 3). NPC1 possesses a sterol-sensing domain (SSD) that is also found in two other proteins critical to maintaining cellular cholesterol homeostasis, the sterol response elementbinding protein cleavage-activating protein and the enzyme 3-hydroxy-3-methylglutaryl-CoA reductase (2, 4). The cDNA encoding human NPC1 corrects the defect in NPC1 mutant cells and facilitates clearance of the extensive lysosomal pools of cholesterol (2, 5). After biosynthesis of NPC1 in the endoplasmic reticulum, the protein is processed further in the Golgi apparatus (6); at steady state, it is associated with late endosomes. Cellular cholesterol enrichment, through endocytic uptake of low-density lipoprotein (LDL), alters the intracellular distribution of NPC1 protein from a finely dispersed granular pattern to sequestration in prominent cytoplasmic vesicles (7,8). These NPC1-containing vesicles are positive for lysosomal-associated membrane protein 2 (LAMP2) (7, 9), are not enriched in lysosomal hydrolases (7), and are positive for the late endosomal marker proteins Rab7 (7) and Rab 9 (10). NPC1-containing late endosomes are critical for the retroendocytic trafficking of multiple lysosomal cargo (4, 9). Retroendocytic clearance of fluid phase markers, such as sucrose, from late endosomes is retarded by LDL-derived cellular enrichment of cholesterol (9). We have recently shown that cholesterol modulates glycolipid sorting from NPC1-containing late endosomes into lysosomes (7). In this report, we have visualized functional green fluorescent protein-labeled...

High susceptibility to fatty liver disease in two-pore channel 2-deficient mice

“…5f). Filipin [39][40][41][42] stainings further confirmed a strong accumulation of cholesterol in TPC2 À / À hepatocytes after CD treatment (Fig. 6a).…”

Apolipoprotein E Promotes β-Amyloid Trafficking and Degradation by Modulating Microglial Cholesterol Levels

“…In Niemann-Pick C disease, dysfunction of NPC1 results in missorting and accumulation of cholesterol in the late endosomes. The cholesterol loading decreases the capacity of GDI to extract membrane-associated Rab7, thus inhibiting these vesicles from switching from minus-to plusend-directed motility, eventually resulted in a loss of bi-directional motility and paralysis (35,85). Failure to recycle Rab7 to the membrane interferes with the switch in early-to-late endosome maturation and ultimately results in the paralysis of the endocytic system (29,35,60).…”

Niemann-Pick C1 Functions Independently of Niemann-Pick C2 in the Initial Stage of Retrograde Transport of Membrane-impermeable Lysosomal Cargo

“…Indeed, it has been shown that the ability of late endosomes and lysosomes to fuse can depend on lipid accumulation in these compartments (21). To examine this, we evaluated dextran release in cells that had functional NPC proteins but had lysosomal lipid storage disorders.…”