Lysosomal vitamin E accumulation in Niemann–Pick type C disease

Niemann-Pick Disease Type C (NPDC) by Mutation of NPC1 and NPC2: Aberrant Lysosomal Cholesterol Trafficking and Oxidative Stress

Cholesterol trafficking is initiated by the endocytic pathway and transported from endo/lysosomes to other intracellular organelles. Deficiencies in cholesterol-sensing and binding proteins NPC1 and NPC2 induce accumulation in lysosomes and the malfunction of trafficking to other organelles. Each organelle possesses regulatory factors to induce cholesterol trafficking. The mutation of NPC1 and NPC2 genes induces Niemann-Pick disease type C (NPDC), which is a hereditary disease and causes progressive neurodegeneration, developmental disability, hypotonia, and ataxia. Oxidative stress induces damage in NPDC-related intracellular organelles. Although studies on the relationship between NPDC and oxidation are relatively rare, several studies have reported the therapeutic potential of antioxidants in treating NPDC. Investigating antioxidant drugs to relieve oxidative stress and cholesterol accumulation is suggested to be a powerful tool for developing treatments for NPDC. Understanding NPDC provides challenging issues in understanding the oxidative stress-lysosome metabolism of the lipid axis. Thus, we elucidated the relationship between complexes of intracellular organelles and NPDC to develop our knowledge and suggested potential antioxidant reagents for NPDC therapy.

Mitochondrial cholesterol: Metabolism and impact on redox biology and disease

Cholesterol is a crucial component of membrane bilayers by regulating their structural and functional properties. Cholesterol traffics to different cellular compartments including mitochondria, whose cholesterol content is low compared to other cell membranes. Despite the limited availability of cholesterol in the inner mitochondrial membrane (IMM), the metabolism of cholesterol in the IMM plays important physiological roles, acting as the precursor for the synthesis of steroid hormones and neurosteroids in steroidogenic tissues and specific neurons, respectively, or the synthesis of bile acids through an alternative pathway in the liver. Accumulation of cholesterol in mitochondria above physiological levels has a negative impact on mitochondrial function through several mechanisms, including the limitation of crucial antioxidant defenses, such as the glutathione redox cycle, increased generation of reactive oxygen species and consequent oxidative modification of cardiolipin, and defective assembly of respiratory supercomplexes. These adverse consequences of increased mitochondrial cholesterol trafficking trigger the onset of oxidative stress and cell death, and, ultimately, contribute to the development of diverse diseases, including metabolic liver diseases (i.e. fatty liver disease and liver cancer), as well as lysosomal disorders (i.e. Niemann-Pick type C disease) and neurodegenerative diseases (i.e. Alzheimer's disease). In this review, we summarize the metabolism and regulation of mitochondrial cholesterol and its potential impact on liver and neurodegenerative diseases.

α-Tocopherol transfer protein (α-TTP)

α-Tocopherol transfer protein (α-TTP) is so far the only known protein that specifically recognizes α-tocopherol (α-Toc), the most abundant and most biologically active form of vitamin E, in higher animals. α-TTP is highly expressed in the liver where α-TTP selects α-Toc among vitamin E forms taken up via plasma lipoproteins and promotes its secretion to circulating lipoproteins. Thus, α-TTP is a major determinant of plasma α-Toc concentrations. Familial vitamin E deficiency, also called Ataxia with vitamin E deficiency, is caused by mutations in the α-TTP gene. More than 20 different mutations have been found in the α-TTP gene worldwide, among which some missense mutations provided valuable clues to elucidate the molecular mechanisms underlying intracellular α-Toc transport. In hepatocytes, α-TTP catalyzes the vectorial transport of α-Toc from the endocytotic compartment to the plasma membrane (PM) by targeting phosphatidylinositol phosphates (PIPs) such as PI(4,5)P₂. By binding PIPs at the PM, α-TTP opens the lid covering the hydrophobic pocket, thus facilitating the release of bound α-Toc to the PM.

Mitochondrial Management of Reactive Oxygen Species

Mitochondria in aerobic eukaryotic cells are both the site of energy production and the formation of harmful species, such as radicals and other reactive oxygen species, known as ROS. They contain an efficient antioxidant system, including low-molecular-mass molecules and enzymes that specialize in removing various types of ROS or repairing the oxidative damage of biological molecules. Under normal conditions, ROS production is low, and mitochondria, which are their primary target, are slightly damaged in a similar way to other cellular compartments, since the ROS released by the mitochondria into the cytosol are negligible. As the mitochondrial generation of ROS increases, they can deactivate components of the respiratory chain and enzymes of the Krebs cycle, and mitochondria release a high amount of ROS that damage cellular structures. More recently, the feature of the mitochondrial antioxidant system, which does not specifically deal with intramitochondrial ROS, was discovered. Indeed, the mitochondrial antioxidant system detoxifies exogenous ROS species at the expense of reducing the equivalents generated in mitochondria. Thus, mitochondria are also a sink of ROS. These observations highlight the importance of the mitochondrial antioxidant system, which should be considered in our understanding of ROS-regulated processes. These processes include cell signaling and the progression of metabolic and neurodegenerative disease.

RedEfish: Generation of the Polycistronic mScarlet: GSG-T2A: Ttpa Zebrafish Line

The vitamin E regulatory protein, the alpha-tocopherol transfer protein (Ttpa), is necessary for zebrafish embryo development. To evaluate zebrafish embryo Ttpa function, we generated a fluorescent-tagged zebrafish transgenic line using CRISPR-Cas9 technology. One-cell stage embryos (from Casper (colorless) zebrafish adults) were injected the mScarlet coding sequence in combination with cas9 protein complexed to single guide RNA molecule targeting 5′ of the ttpa genomic region. Embryos were genotyped for proper insertion of the mScarlet coding sequence, raised to adulthood and successively in-crossed to produce the homozygote RedEfish (mScarlet: GSG-T2A: Ttpa). RedEfish were characterized by in vivo fluorescence detection at 1, 7 and 14 days post-fertilization (dpf). Fluorescent color was detectable in RedEfish embryos at 1 dpf; it was distributed throughout the developing brain, posterior tailbud and yolk sac. At 7 dpf, the RedEfish was identifiable by fluorescence in olfactory pits, gill arches, pectoral fins, posterior tail region and residual yolk sac. Subsequently (14 dpf), the mScarlet protein was found in olfactory pits, distributed throughout the digestive tract, along the lateral line and especially in caudal vertebrae. No adverse morphological outcomes or developmental delays were observed. The RedEfish will be a powerful model to study Ttpa function during embryo development.

Genistein Activates Transcription Factor EB and Corrects Niemann-Pick C Phenotype

Niemann-Pick type C disease (NPCD) is a lysosomal storage disease (LSD) characterized by abnormal cholesterol accumulation in lysosomes, impaired autophagy flux, and lysosomal dysfunction. The activation of transcription factor EB (TFEB), a master lysosomal function regulator, reduces the accumulation of lysosomal substrates in LSDs where the degradative capacity of the cells is compromised. Genistein can pass the blood-brain barrier and activate TFEB. Hence, we investigated the effect of TFEB activation by genistein toward correcting the NPC phenotype. We show that genistein promotes TFEB translocation to the nucleus in HeLa TFEB-GFP, Huh7, and SHSY-5Y cells treated with U18666A and NPC1 patient fibroblasts. Genistein treatment improved lysosomal protein expression and autophagic flux, decreasing p62 levels and increasing those of the LC3-II in NPC1 patient fibroblasts. Genistein induced an increase in β-hexosaminidase activity in the culture media of NPC1 patient fibroblasts, suggesting an increase in lysosomal exocytosis, which correlated with a decrease in cholesterol accumulation after filipin staining, including cells treated with U18666A and NPC1 patient fibroblasts. These results support that genistein-mediated TFEB activation corrects pathological phenotypes in NPC models and substantiates the need for further studies on this isoflavonoid as a potential therapeutic agent to treat NPCD and other LSDs with neurological compromise.

Vitamin E Supplementation and Mitochondria in Experimental and Functional Hyperthyroidism: A Mini-Review

Mitochondria are both the main sites of production and the main target of reactive oxygen species (ROS). This can lead to mitochondrial dysfunction with harmful consequences for the cells and the whole organism, resulting in metabolic and neurodegenerative disorders such as type 2 diabetes, obesity, dementia, and aging. To protect themselves from ROS, mitochondria are equipped with an efficient antioxidant system, which includes low-molecular-mass molecules and enzymes able to scavenge ROS or repair the oxidative damage. In the mitochondrial membranes, a major role is played by the lipid-soluble antioxidant vitamin E, which reacts with the peroxyl radicals faster than the molecules of polyunsaturated fatty acids, and in doing so, protects membranes from excessive oxidative damage. In the present review, we summarize the available data concerning the capacity of vitamin E supplementation to protect mitochondria from oxidative damage in hyperthyroidism, a condition that leads to increased mitochondrial ROS production and oxidative damage. Vitamin E supplementation to hyperthyroid animals limits the thyroid hormone-induced increases in mitochondrial ROS and oxidative damage. Moreover, it prevents the reduction of the high functionality components of the mitochondrial population induced by hyperthyroidism, thus preserving cell function.

α-Tocopherol transfer protein does not regulate the cellular uptake and intracellular distribution of α- and γ-tocopherols and -tocotrienols in cultured liver cells

Liver cells express a cytosolic α-tocopherol transfer protein (αTTP) with high binding affinity for α-tocopherol (αT) and much lower affinities for the non-αT congeners. The role of αTTP in the intracellular distribution of the different vitamin E forms is currently unknown. We therefore investigated the intracellular localization of αT, γ-tocopherol (γT), α-tocotrienol (αT3), and γ-tocotrienol (γT3) in cultured hepatic cells with and without stable expression of αTTP. We first determined cellular uptake of the four congeners and found the methylation of the chromanol ring and saturation of the sidechain to be important factors, with tocotrienols being taken up more efficiently than tocopherols and the γ-congeners more than the α-congeners, irrespective of the expression of αTTP. This, however, could perhaps also be due to an observed higher stability of tocotrienols, compared to tocopherols, in culture media rather than a higher absorption. We then incubated HepG2 cells and αTTP-expressing HepG2 cells with αT, γT, αT3, or γT3, isolated organelle fractions by density gradient centrifugation, and determined the concentrations of the congeners in the subcellular fractions. All four congeners were primarily associated with the lysosomes, endoplasmic reticulum, and plasma membrane, whereas only αT correlated with mitochondria. Neither the chromanol ring methylation or sidechain saturation, nor the expression of αTTP were important factors for the intracellular distribution of vitamin E. In conclusion, αTTP does not appear to regulate the uptake and intracellular localization of different vitamin E congeners in cultured liver cells.

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We studied how αTTP affects intracellular distribution of αT, γT, αT3, γT3 in HepG2 cells.

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All congeners associated with lysosomes, endoplasmic reticulum and the plasma membrane.

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Only αT significantly correlated with mitochondria.

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Neither the chemical structure, nor αTTP were important for intracellular localization.

Vitamin E and Phosphoinositides Regulate the Intracellular Localization of the Hepatic α-Tocopherol Transfer Protein

α-Tocopherol (vitamin E) is an essential nutrient for all vertebrates. From the eight naturally occurring members of the vitamin E family, α-tocopherol is the most biologically active species and is selectively retained in tissues. The hepatic α-tocopherol transfer protein (TTP) preferentially selects dietary α-tocopherol and facilitates its transport through the hepatocyte and its secretion to the circulation. In doing so, TTP regulates body-wide levels of α-tocopherol. The mechanisms by which TTP facilitates α-tocopherol trafficking in hepatocytes are poorly understood. We found that the intracellular localization of TTP in hepatocytes is dynamic and responds to the presence of α-tocopherol. In the absence of the vitamin, TTP is localized to perinuclear vesicles that harbor CD71, transferrin, and Rab8, markers of the recycling endosomes. Upon treatment with α-tocopherol, TTP- and α-tocopherol-containing vesicles translocate to the plasma membrane, prior to secretion of the vitamin to the exterior of the cells. The change in TTP localization is specific to α-tocopherol and is time- and dose-dependent. The aberrant intracellular localization patterns of lipid binding-defective TTP mutants highlight the importance of protein-lipid interaction in the transport of α-tocopherol. These findings provide the basis for a proposed mechanistic model that describes TTP-facilitated trafficking of α-tocopherol through hepatocytes.

Neuronal gene repression in Niemann-Pick type C models is mediated by the c-Abl/HDAC2 signaling pathway

BACKGROUND

Niemann-Pick type C (NPC) disease is a fatal neurodegenerative disorder characterized by the accumulation of free cholesterol in lysosomes. There are currently no effective FDA-approved treatments for NPC, although in the last years the inhibition of histone deacetylases (HDACs) has emerged as a potential treatment for this disease. However, the molecular mechanisms that deregulate HDAC activity in NPC disease are unknown. Previously our group had shown that the proapoptotic tyrosine kinase c-Abl signaling is activated in NPC neurons. Here, we demonstrate that c-Abl activity increases HDAC2 levels inducing neuronal gene repression of key synaptic genes in NPC models.

RESULTS

Our data show that: i) HDAC2 levels and activity are increased in NPC neuronal models and in Npc1(-/-) mice; ii) inhibition of c-Abl or c-Abl deficiency prevents the increase of HDAC2 protein levels and activity in NPC neuronal models; iii) c-Abl inhibition decreases the levels of HDAC2 tyrosine phosphorylation; iv) treatment with methyl-β-cyclodextrin and vitamin E decreases the activation of the c-Abl/HDAC2 pathway in NPC neurons; v) in vivo treatment with two c-Abl inhibitors prevents the increase of HDAC2 protein levels in the brain of Npc1(-/-) mice; and vi) c-Abl inhibition prevents HDAC2 recruitment to the promoter of neuronal genes, triggering an increase in their expression.

CONCLUSION

Our data show the involvement of the c-Abl/HDAC2 signaling pathway in the regulation of neuronal gene expression in NPC neuronal models. Thus, inhibition of c-Abl could be a pharmacological target for preventing the deleterious effects of increased HDAC2 levels in NPC disease.

Drug Delivery Innovations for Enhancing the Anticancer Potential of Vitamin E Isoforms and Their Derivatives

Vitamin E isoforms have been extensively studied for their anticancer properties. Novel drug delivery systems (DDS) that include liposomes, nanoparticles, and micelles are actively being developed to improve Vitamin E delivery. Furthermore, several drug delivery systems that incorporate Vitamin E isoforms have been synthesized in order to increase the bioavailability of chemotherapeutic agents or to provide a synergistic effect. D-alpha-tocopheryl polyethylene glycol succinate (Vitamin E TPGS or TPGS) is a synthetic derivative of natural alpha-tocopherol which is gaining increasing interest in the development of drug delivery systems and has also shown promising anticancer effect as a single agent. This review provides a summary of the properties and anticancer effects of the most potent Vitamin E isoforms and an overview of the various formulations developed to improve their efficacy, with an emphasis on the use of TPGS in drug delivery approaches.

Vitamin E: Curse or Benefit in Alzheimer's Disease? A Systematic Investigation of the Impact of α-, γ- and δ-Tocopherol on Aß Generation and Degradation in Neuroblastoma Cells

OBJECTIVES

The E vitamins are a class of lipophilic compounds including tocopherols, which have high antioxidative properties. Because of the elevated lipid peroxidation and increased reactive oxidative species in Alzheimer's disease (AD) many attempts have been made to slow down the progression of AD by utilizing the antioxidative action of vitamin E. Beside the mixed results of these studies nothing is known about the impact of vitamin E on the mechanisms leading to amyloid-β production and degradation being responsible for the plaque formation, one of the characteristic pathological hallmarks in AD. Here we systematically investigate the influence of different tocopherols on Aβ production and degradation in neuronal cell lines.

MEASUREMENTS

Beside amyloid-β level the mechanisms leading to Aβ production and degradation are examined.

RESULTS

Surprisingly, all tocopherols have shown to increase Aβ level by enhancing the Aβ production and decreasing the Aβ degradation. Aβ production is enhanced by an elevated activity of the involved enzymes, the β- and γ-secretase. These secretases are not directly affected, but tocopherols increase their protein level and expression. We could identify significant differences between the single tocopherols; whereas α-tocopherol had only minor effects on Aβ production, δ-tocopherol showed the highest potency to increase Aβ generation. Beside Aβ production, Aβ clearance was decreased by affecting IDE, one of the major Aβ degrading enzymes.

CONCLUSIONS

Our results suggest that beside the beneficial antioxidative effects of vitamin E, tocopherol has in respect to AD also a potency to increase the amyloid-β level, which differ for the analysed tocopherols. We therefore recommend that further studies are needed to clarify the potential role of these various vitamin E species in respect to AD and to identify the form which comprises an antioxidative property without having an amyloidogenic potential.

Vitamin E and neurodegeneration

Alpha-tocopherol (vitamin E) is a plant-derived antioxidant that is essential for human health. Studies with humans and with animal models of vitamin E deficiency established the critical roles of the vitamin in protecting the central nervous system, and especially the cerebellum, from oxidative damage and motor coordination deficits. We review here the established roles of vitamin E in protecting cerebellar functions, as well as emerging data demonstrating the critical roles of alpha-tocopherol in preserving learning, memory and emotive responses. We also discuss the importance of vitamin E adequacy in seemingly unrelated neurological disorders.

Vitamin E dietary supplementation improves neurological symptoms and decreases c-Abl/p73 activation in Niemann-Pick C mice

Niemann-Pick C (NPC) disease is a fatal neurodegenerative disorder characterized by the accumulation of free cholesterol in lysosomes. We have previously reported that oxidative stress is the main upstream stimulus activating the proapoptotic c-Abl/p73 pathway in NPC neurons. We have also observed accumulation of vitamin E in NPC lysosomes, which could lead to a potential decrease of its bioavailability. Our aim was to determine if dietary vitamin E supplementation could improve NPC disease in mice. NPC mice received an alpha-tocopherol (α-TOH) supplemented diet and neurological symptoms, survival, Purkinje cell loss, α-TOH and nitrotyrosine levels, astrogliosis, and the c-Abl/p73 pathway functions were evaluated. In addition, the effect of α-TOH on the c-Abl/p73 pathway was evaluated in an in vitro NPC neuron model. The α-TOH rich diet delayed loss of weight, improved coordination and locomotor function and increased the survival of NPC mice. We found increased Purkinje neurons and α-TOH levels and reduced astrogliosis, nitrotyrosine and phosphorylated p73 in cerebellum. A decrease of c-Abl/p73 activation was also observed in the in vitro NPC neurons treated with α-TOH. In conclusion, our results show that vitamin E can delay neurodegeneration in NPC mice and suggest that its supplementation in the diet could be useful for the treatment of NPC patients.

New Niemann-Pick type C1 gene mutation associated with very severe disease course and marked early cerebellar vermis atrophy

Niemann-Pick type C is an autosomal recessive lipid storage disease caused by mutations in the NPC1 or NPC2 gene. In childhood-onset Niemann-Pick type C, the usual course is slowly progressive, with normal cerebral magnetic resonance at onset. Here the authors present the case of a patient carrying 2 compound heterozygous NPC1 mutations: the known nonsense mutation (p.Trp833X) in exon 16 and a novel missense mutation (p.Ile609Phe) in exon 12. At onset, the patient presented ataxia, cognitive decline, and epilepsy, with early cerebral atrophy and marked cerebellar vermis atrophy. The course of the disease was rapid, and the patient died within 1-2 years of onset. A possible phenotype-genotype correlation is discussed. This case further expands the clinical spectrum and the genetic heterogeneity of Niemann-Pick type C due to NPC1 mutations.

Kinetic modeling of low density lipoprotein oxidation in arterial wall and its application in atherosclerotic lesions prediction

Oxidation of low-density lipoprotein (LDL) is one of the major factors in atherogenic process. Trapped oxidized LDL (Ox-LDL) in the subendothelial matrix is taken up by macrophage and leads to foam cell generation creating the first step in atherosclerosis development. Many researchers have studied LDL oxidation using in vitro cell-induced LDL oxidation model. The present study provides a kinetic model for LDL oxidation in intima layer that can be used in modeling of atherosclerotic lesions development. This is accomplished by considering lipid peroxidation kinetic in LDL through a system of elementary reactions. In comparison, characteristics of our proposed kinetic model are consistent with the results of previous experimental models from other researches. Furthermore, our proposed LDL oxidation model is added to the mass transfer equation in order to predict the LDL concentration distribution in intima layer which is usually difficult to measure experimentally. According to the results, LDL oxidation kinetic constant is an important parameter that affects LDL concentration in intima layer so that existence of antioxidants that is responsible for the reduction of initiating rates and prevention of radical formations, have increased the concentration of LDL in intima by reducing the LDL oxidation rate.

Vitamin E trafficking in neurologic health and disease

Vitamin E was identified almost a century ago as a botanical compound necessary for rodent reproduction. Decades of research since then established that of all members of the vitamin E family, α-tocopherol is selectively enriched in human tissues, and it is essential for human health. The major function of α-tocopherol is thought to be that of a lipid-soluble antioxidant that prevents oxidative damage to biological components. As such, α-tocopherol is necessary for numerous physiological processes such as permeability of lipid bilayers, cell adhesion, and gene expression. Inadequate levels of α-tocopherol interfere with cellular function and precipitate diseases, notably ones that affect the central nervous system. The extreme hydrophobicity of α-tocopherol poses a serious thermodynamic barrier for proper distribution of the vitamin to target tissues and cells. Although transport of the vitamin shares some steps with that of other lipids, selected tissues evolved dedicated transport mechanisms involving the α-tocopherol transfer protein (αTTP). The critical roles of this protein and its ligand are underscored by the debilitating pathologies that characterize human carriers of mutations in the TTPA gene.

Oxidative stress: a pathogenic mechanism for Niemann-Pick type C disease

Niemann-Pick type C (NPC) disease is a neurovisceral atypical lipid storage disorder involving the accumulation of cholesterol and other lipids in the late endocytic pathway. The pathogenic mechanism that links the accumulation of intracellular cholesterol with cell death in NPC disease in both the CNS and the liver is currently unknown. Oxidative stress has been observed in the livers and brains of NPC mice and in different NPC cellular models. Moreover, there is evidence of an elevation of oxidative stress markers in the serumof NPC patients. Recent evidence strongly suggests that mitochondrial dysfunction plays an important role in NPC pathogenesis and that mitochondria could be a significant source of oxidative stress in this disease. In this context, the accumulation of vitamin E in the late endosomal/lysosomal compartments in NPC could lead to a potential decrease of its bioavailability and could be another possible cause of oxidative damage. Another possible source of reactive species in NPC is the diminished activity of different antioxidant enzymes. Moreover, because NPC is mainly caused by the accumulation of free cholesterol, oxidized cholesterol derivatives produced by oxidative stress may contribute to the pathogenesis of the disease.

Alteration of gene expression profile in Niemann-Pick type C mice correlates with tissue damage and oxidative stress

BACKGROUND

Niemann-Pick type C disease (NPC) is a neurovisceral lipid storage disorder mainly characterized by unesterified cholesterol accumulation in lysosomal/late endosomal compartments, although there is also an important storage for several other kind of lipids. The main tissues affected by the disease are the liver and the cerebellum. Oxidative stress has been described in various NPC cells and tissues, such as liver and cerebellum. Although considerable alterations occur in the liver, the pathological mechanisms involved in hepatocyte damage and death have not been clearly defined. Here, we assessed hepatic tissue integrity, biochemical and oxidative stress parameters of wild-type control (Npc1(+/+); WT) and homozygous-mutant (Npc1(-/-); NPC) mice. In addition, the mRNA abundance of genes encoding proteins associated with oxidative stress, copper metabolism, fibrosis, inflammation and cholesterol metabolism were analyzed in livers and cerebella of WT and NPC mice.

METHODOLOGY/PRINCIPAL FINDINGS

We analyzed various oxidative stress parameters in the liver and hepatic and cerebellum gene expression in 7-week-old NPC1-deficient mice compared with control animals. We found signs of inflammation and fibrosis in NPC livers upon histological examination. These signs were correlated with increased levels of carbonylated proteins, diminished total glutathione content and significantly increased total copper levels in liver tissue. Finally, we analyzed liver and cerebellum gene expression patterns by qPCR and microarray assays. We found a correlation between fibrotic tissue and differential expression of hepatic as well as cerebellar genes associated with oxidative stress, fibrosis and inflammation in NPC mice.

CONCLUSIONS/SIGNIFICANCE

In NPC mice, liver disease is characterized by an increase in fibrosis and in markers associated with oxidative stress. NPC is also correlated with altered gene expression, mainly of genes involved in oxidative stress and fibrosis. These findings correlate with similar parameters in cerebellum, as has been previously reported in the NPC mice model.