Cholesterol movement in Niemann-Pick type C cells and in cells treated with amphiphiles

Cholesterol accumulates to massive levels in cells from Niemann-Pick type C (NP-C) patients and in cells treated with class 2 amphiphiles that mimic N P-C disease. This behavior has been attributed to the failure of cholestero l released from ingested low density lipoproteins to exit the lysosomes. Ho wever, we now show that the rate of movement of cholesterol from lysosomes to plasma membranes in NP-C cells is at least as great as normal, as was al so found previously for amphiphiletreated cells. Furthermore, the lysosomes in these cells filled with plasma membrane cholesterol in the absence of l ipoproteins. In addition, we showed that the size of the endoplasmic reticu lum cholesterol pool and the set point of the homeostatic sensor of cell ch olesterol were approximately normal in NP-C cells. The plasma membrane chol esterol pools in both NP-C and amphiphiletreated cells were also normal. Fu rthermore, the build up of cholesterol in NP-C lysosomes was not a physiolo gical response to cholesterol overload. Rather, it appeared that the accumu lation in NP-C lysosomes results from an imbalance in the brisk now of chol esterol among membrane compartments. In related experiments, we found that NP-C cells did not respond to class 2 amphiphiles (e,g, trifluoperazine, im ipramine, and U18666A); these agents may therefore act directly on the NPC1 protein or on its pathway. Finally, we showed that the lysosomal cholester ol pool in NP-C cells was substantially and preferentially reduced by incub ating cells with the oxysterols, 25-hydroxycholesterol and 7-ketocholestero l; these findings suggest a new pharmacological approach to the treatment o f NP-C disease.