Niemann-Pick type C1 (NPC1) mediates low-density cholesterol transport from late endosomes and lysosomes to other areas of the cell via receptor mediation endocytosis. Although cholesterol moves freely inside the cell, it cannot independently export out of the lysosome, which is where NPC1 steps in. After NPC1 interacts with lipoproteins and removes or delivers them to their destined compartments, they are hydrolyzed and released as free cholesterol. Mutations in the NPC1 gene cause Niemann-Pick type C disease, a rare autosomal recessive neurodegenerative disorder characterized by over accumulation of cholesterol in lysosomes and is characterized by both neural and liver degeneration.
Niemann-Pick C1 Antibody [NB400-148] - Staining of human brain, cortex, neurons and astrocytes.
The effects of poor cholesterol regulation vary greatly. Bartz et al used a NPC1 antibody as part of a cholesterol regulating gene screening in order to further understand plasma cholesterol dynamics. Plasma cholesterol in particular was of interest to this group given its implications in cardiovascular disease and mortality, and also its role in potentially helping to elucidate cellular cholesterol homeostasis. They observed that sterol depleted cells caused TMEM97 to localize to the lysosome, endosome and plasma membrane. This finding suggests that TMEM97 has a function at these compartments. After using a NPC1 antibody in immunoprecipitation, it was discovered that TMEM97 colocalizes with NPC1, further implying that TMEM97 regulates LDL cholesterol trafficking in lysosomes working directly or indirectly with NPC1.
Kanerva et al established a fluorescent cholesterol analog as a tool to visualize sterol movement in living cells as compared to endogenous cholesterol. Their overarching goal was to follow the pathway of LDL sterol delivery and to identify key regulators of this process. Using a NPC1 antibody, they found that efflux of their cholesterol analog from the late endosome and lysosome is dependent on LAL, NPC1 and Microtubules. The NPC1 antibody was used in immunofluorescence in NPC1 depleted cells, and resulted in defective arrival of LDL at the plasma membrane. Concurrently, cells that were treated with the microtubule depolymerizer nocodazole showed defective exit of LDL from the late endosome/lysosome. Further experiments pointed to Rab8 as a regulator of this post endosomal sterol transport, and overall this analog based method of LDL screening has allowed for in detail tracking of this pathway in a living cell.
In addition to using NPC1 antibodies as a marker of LDL transport pathways and function, Li et al used an NPC1 antibody to determine whether NPC1 is required to transport LDL across glycocalyx lined lysosomes (glycocalyx is a compound that lines lysosomes and in turn protects their membranes from degradation enzymes). Initially, this group saw that lysosome cholesterol was 30% less after NPC1 deficient human fibroblasts were treated with an inhibitor of o-linked glycosylation. This finding shows that altering the glycosylation of glycoproteins changes the level of cholesterol found in lysosomes, however more research needs to be done to determine the specific role of glycocalyx and LDL transport.
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