Adaptations of Energy Metabolism Associated with Increased Levels of Mitochondrial Cholesterol in Niemann-Pick Type C1-deficient Cells
Bibliographic record
Abstract
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.
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How this classification was reachedexpand
Full frame machine prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. The Gemma side is a direct model label for every work in the frame, read from the title-only record. The Codex side is a classifier learned from the 10,348 direct Codex labels and calibrated to design-weighted sample rates; fields without enough sample support carry no Codex call. Candidate is the union of the two sides; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels.
Distilled classifier scores by category (both heads)
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.000 | 0.000 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.001 | 0.000 |
| Bibliometrics | 0.000 | 0.000 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.001 | 0.000 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.001 | 0.001 |
| Insufficient payload (model declined to judge) | 0.001 | 0.000 |
Machine scores (provisional)
The two teacher heads of the student model, read on this work. A score orders the frame for review; it never asserts a category, and the validation status ships verbatim with every row.
Baseline scores from an immature model (maturity gate not passed, 7 training rounds). Scores rank; they never assert a category.
score_only:v0-immature-baseline · verbatim from the scoring run: score_only means the number may rank works, and no category label ships from itClassification
machine, unvalidatedMachine predicted; a candidate call from one source (direct Gemma or distilled Codex), not a consensus.
How this classification was reached, model by model and score by score, is at the end of the page under "How this classification was reached".