Adaptations of energy metabolism associated with increased levels of mitochondrial cholesterol in Niemann-Pick type C1-deficient cells.
Niemann-Pick type C1 (NPC1) is a late endosomal transmembrane protein, which, together with NPC2 in the endosome lumen, mediates the transport of endosomal cholesterol to the plasma membrane and endoplasmic reticulum. Loss of function of NPC1 or NPC2 leads to cholesterol accumulation in late endosomes and causes neuronal dysfunction and neurodegeneration. Recent studies indicate that cholesterol also accumulates in mitochondria of NPC1-deficient cells and brain tissue and that NPC1 deficiency leads to alterations in mitochondrial function and energy metabolism. Here, we have investigated the effects of increased mitochondrial cholesterol levels on energy metabolism, using RNA interference to deplete Chinese hamster ovary cells of NPC1 alone or in combination with MLN64, which mediates endosomal cholesterol transport to mitochondria. Mitochondrial cholesterol levels were also altered by depletion of NPC2 in combination with the expression of NPC2 mutants. We found that the depletion of NPC1 increased lactate secretion, decreased glutamine-dependent mitochondrial respiration, and decreased ATP transport across mitochondrial membranes. These metabolic alterations did not occur when transport of endosomal cholesterol to mitochondria was blocked. In addition, the elevated mitochondrial cholesterol levels in NPC1-depleted cells and in NPC2-depleted cells expressing mutant NPC2 that allows endosomal cholesterol trafficking to mitochondria were associated with increased expression of the antioxidant response factor Nrf2. Antioxidant treatment not only prevented the increase in Nrf2 mRNA levels but also prevented the increased lactate secretion in NPC1-depleted cells. These results suggest that mitochondrial cholesterol accumulation can increase oxidative stress and in turn cause increased glycolysis to lactate and other metabolic alterations.
From the Department of Biochemistry and Molecular Biology, Dalhousie University, Halifax, Nova Scotia B3H 4R2, Canada and.
Barry E
BE
Kennedy
the Institute of Molecular Biology and Biochemistry, Center of Molecular Medicine, Medical University Graz, 8010 Graz, Austria.
Corina T
CT
Madreiter
the Institute of Molecular Biology and Biochemistry, Center of Molecular Medicine, Medical University Graz, 8010 Graz, Austria.
Neelanjan
N
Vishnu
the Institute of Molecular Biology and Biochemistry, Center of Molecular Medicine, Medical University Graz, 8010 Graz, Austria.
Roland
R
Malli
the Institute of Molecular Biology and Biochemistry, Center of Molecular Medicine, Medical University Graz, 8010 Graz, Austria.
Wolfgang F
WF
Graier
From the Department of Biochemistry and Molecular Biology, Dalhousie University, Halifax, Nova Scotia B3H 4R2, Canada and bkarten@dal.ca.
Barbara
B
Karten
D000818:Animals; D016466:CHO Cells; D002352:Carrier Proteins / Q000235:genetics / Q000378:metabolism*; D002460:Cell Line; D002784:Cholesterol / Q000378:metabolism*; D006224:Cricetinae; D003412:Cricetulus; D004734:Energy Metabolism; D005947:Glucose / Q000378:metabolism; D005973:Glutamine / Q000378:metabolism; D006801:Humans; D047908:Intracellular Signaling Peptides and Proteins; D019344:Lactic Acid / Q000378:metabolism; D008562:Membrane Glycoproteins / Q000235:genetics / Q000378:metabolism*; D008928:Mitochondria / Q000378:metabolism*; D000077296:Niemann-Pick C1 Protein; D034622:RNA Interference
D002352:Carrier Proteins; D047908:Intracellular Signaling Peptides and Proteins; D008562:Membrane Glycoproteins; C106881:NPC1 protein, human; D000077296:Niemann-Pick C1 Protein; D005973:Glutamine; D019344:Lactic Acid; D002784:Cholesterol; D005947:Glucose
Cholesterol Metabolism; Glucose Metabolism; Glutamine; Mitochondrial Cholesterol; Niemann-Pick Type C; Oxidative Stress; Respiration