Altered Cholesterol Metabolism in Niemann-Pick Type C1 Mouse Brains Affects Mitochondrial Function

Yu, Wei; Gong, Jian-Sheng; Ko, Mi-Hee; Garver, William S.; Yanagisawa, Katsuhiko; Michikawa, Makoto

doi:10.1074/jbc.m412898200

Cited by 185 publications

(191 citation statements)

References 47 publications

(47 reference statements)

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“…Proteins were solubilized with CHAPS, separated by size exclusion chromatography, and the elution profile of Bax was analyzed by immunoblotting. For each condition, even-numbered fractions were loaded on two separate gels; a short exposure time was chosen for the low molecular weight fractions (30-44), and a longer one for the high molecular weight fractions (14)(15)(16)(17)(18)(19)(20)(21)(22)(23)(24)(25)(26)(27)(28) and its sensitivity to trypsin digestion were analyzed by immunoblotting. The presence of tBid was required for the recruitment of Bax to liposomes and led to the appearance of a Tr-Bax fragment (Figure 1d).…”

Section: Resultsmentioning

confidence: 99%

“…It interferes with the trafficking of cholesterol, causing its increase in late endosomes/lysosomes, 23,24 and inhibits its neosynthesis in the ER. 25 A recent study reported the accumulation of cholesterol in the mitochondria of neurons isolated from an Niemann-Pick Type C1 mouse model, 26 raising the possibility that U18666A might also increase mitochondrial cholesterol content. We therefore incubated HeLa cells with U18666A, isolated mitochondria, and analyzed their lipid composition by thin-layer chromatography (Figure 3a and b).…”

Section: Resultsmentioning

confidence: 99%

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Bax activation and stress-induced apoptosis delayed by the accumulation of cholesterol in mitochondrial membranes

2007

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Activation of Bax or Bak is essential for the completion of many apoptotic programmes. Under cytotoxic conditions, these proteins undergo a series of conformational rearrangements that end up with their oligomerization. We found that unlike inactive monomeric Bax, active oligomerized Bax is partially resistant to trypsin digestion, providing a convenient read out to monitor Bax activation. Using this assay, we studied how the lipid composition of membranes affects tBid-induced Bax activation in vitro with pure liposomes. We report that Bax activation is inhibited by cholesterol and by decreases in membrane fluidity. This observation was further tested in vivo using the drug U18666A, which we found increases mitochondrial cholesterol levels. When incubated with tBid, mitochondria isolated from U18666A-treated cells showed a delay in the release of Smac/Diablo and Cytochrome c, as well as in Bax oligomerization. Moreover, pre-incubation with U18666A partially protected cells from stressinduced apoptosis. As many tumours display high mitochondrial cholesterol content, inefficient Bax oligomerization might contribute to their resistance to apoptosis-inducing agents. Among the stimuli that lead to apoptosis, a series of stress conditions trigger the permeabilization of the mitochondrial outer membrane (MOM) and the release of pro-apoptotic factors that will activate caspases in the cytosol. This so-called intrinsic apoptotic pathway is tightly regulated by proteins of the Bcl-2 family, among which the pro-apoptotic members Bax and Bak are essential. They seem to be the central players whose activation results in MOM permeabilization.Under resting conditions, whereas Bak essentially resides in the MOMs, Bax is found in loose association with membranes (mainly the MOMs) or as a soluble protein in the cytosol. Following many cytotoxic signals, Bax and Bak undergo a series of conformational rearrangements. 1 Bax translocates to mitochondria and inserts into the MOMs in a form that cannot be detached by alkali treatment. Bax and Bak then uncover N-terminal epitopes and oligomerize. Oligomerization, shown by size exclusion chromatography, 2 crosslinking experiments 3,4 and native gel electrophoresis, 5 appears as the critical step resulting in MOM permeabilization. However, despite many efforts, it remains unclear how each of these conformational rearrangements is regulated, and how Bax/Bak oligomerization leads to the release of mitochondrial apoptogenic factors. Both processes are undoubtedly regulated by other members of the Bcl-2 family, 6,7 but the participation of many unrelated proteins was also proposed. 8 While a BH3-only protein appears to be sufficient for Bax to oligomerize in synthetic liposomes, 9,10 additional proteins could be required for its activation in isolated mitochondria. 11 These might directly interact with Bax, and/or modify the membrane properties to allow its oligomerization. Interaction with mitochondrial lipids is indeed an important parameter to consider as the final conformational rearrange...

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Section: Resultsmentioning

confidence: 99%

Section: Resultsmentioning

confidence: 99%

Bax activation and stress-induced apoptosis delayed by the accumulation of cholesterol in mitochondrial membranes

2007

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“…15) via the modulation of amyloid-␤ synthesis (16,17). Other lines of evidence suggest that cholesterol plays essential roles in the modulation of tau phosphorylation (6,18,19), neurofibrillary tangle formation (20), and neuronal survival (21,22). These lines of evidence suggest that Alzheimer disease pathologies preferentially developing in specific brain regions may be explained by a region-specific difference in the lipid profile.…”

mentioning

confidence: 94%

Cholesterol-mediated Neurite Outgrowth Is Differently Regulated between Cortical and Hippocampal Neurons

Zou

Minagawa

et al. 2005

Journal of Biological Chemistry

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The acquisition of neuronal type-specific morphogenesis is a central feature of neuronal differentiation and has important consequences for region-specific nervous system functions. Here, we report that the cell type-specific cholesterol profile determines the differential modulation of axon and dendrite outgrowths in hippocampal and cerebral cortical neurons in culture. The extent of axon and dendrite outgrowths is greater and the polarity formation occurs earlier in cortical neurons than in hippocampal neurons. The cholesterol concentrations in total homogenate and the lipid rafts from hippocampal neurons are significantly higher than those from cortical neurons. Cholesterol depletion by ␤-cyclodextrin markedly enhanced the neurite outgrowth and accelerated the establishment of neuronal polarity in hippocampal neurons, which were similarly observed in nontreated cortical neurons, whereas cholesterol loading had no effects. In contrast, both depletion and loading of cholesterol decreased the neurite outgrowths in cortical neurons. The stimulation of neurite outgrowth and polarity formation induced by cholesterol depletion was accompanied by an enhanced localization of Fyn, a Src kinase, in the lipid rafts of hippocampal neurons. A concomitant treatment with ␤-cyclodextrin and a Src family kinase inhibitor, PP2, specifically blocked axon outgrowth but not dendrite outgrowth (both of which were enhanced by ␤-cyclodextrin) in hippocampal neurons, suggesting that axon outgrowth modulated by cholesterol is induced in a Fyn-dependent manner. These results suggest that cellular cholesterol modulates axon and dendrite outgrowths and neuronal polarization under culture conditions and also that the difference in cholesterol profile between hippocampal and cortical neurons underlies the difference in neurite outgrowth between these two types of neurons.Neurons contain two types of processes, axons and dendrites, which are structurally and functionally distinct and play different roles in the maintenance of brain functions. There are studies showing the significant role of lipids in the formation of neuronal polarity; it has been shown that phospholipids regulate neurite outgrowth in cultured neurons (1) and that the correct distribution of axonal membrane proteins requires the formation of sphingomyelin/cholesterol-rich microdomains, lipid rafts, and the maturation of the axonal plasma membrane requires the up-regulation of sphingomyelin synthesis (2, 3). Cholesterol also plays a prominent role in raft-mediated trafficking and sorting, because cholesterol depletion by methyl-␤-cyclodextrin impedes trafficking from the trans-Golgi network to the apical membrane (4). It has been shown that cholesterol modulates dendrite outgrowth (5), that its deficiency enhances phosphorylation of tau and axonal depolymerization (6), and that axonal regeneration is dependent on local cholesterol reutilization in vivo (7). In addition, cholesterol supplied as glial lipoproteins stimulates the axon outgrowth of central nervous system neurons...

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“…These associations raise the possibility that oxidative stress is a signifi cant factor contributing to the etiology of NPC disease. Indeed, NPCaffected cells exhibit mitochondrial dysfunctions ( 83 ), increased expression of reactive oxygen species (ROS)-producing and oxidative stress-responsive genes ( 84 ), and elevated plasma levels of oxidized cholesterol ( 85 ). Recent studies demonstrated that plasma samples from human NPC patients exhibit compromised ex-vivo antioxidant capacity ( 86 ).…”

Section: Vitamin E Status In Npc-affected Micementioning

confidence: 99%

Altered vitamin E status in Niemann-Pick type C disease

Ulatowski

Parker

Davidson

et al. 2011

Journal of Lipid Research

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Altered Cholesterol Metabolism in Niemann-Pick Type C1 Mouse Brains Affects Mitochondrial Function

Cited by 185 publications

References 47 publications

Bax activation and stress-induced apoptosis delayed by the accumulation of cholesterol in mitochondrial membranes

Bax activation and stress-induced apoptosis delayed by the accumulation of cholesterol in mitochondrial membranes

Cholesterol-mediated Neurite Outgrowth Is Differently Regulated between Cortical and Hippocampal Neurons

Altered vitamin E status in Niemann-Pick type C disease

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