Increased expression of the lysosomal cholesterol transporter NPC1 in Alzheimer's disease

https://doi.org/10.1016/j.bbalip.2010.05.005Get rights and content

Abstract

The Niemann-Pick type C1 (NPC1) protein mediates the trafficking of cholesterol from lysosomes to other organelles. Mutations in the NPC1 gene lead to the retention of cholesterol and other lipids in the lysosomal compartment, and such defects are the basis of NPC disease. Several parallels exist between NPC disease and Alzheimer's disease (AD), including altered cholesterol homeostasis, changes in the lysosomal system, neurofibrillary tangles, and increased amyloid-beta generation. How the expression of NPC1 in the human brain is affected in AD has not been investigated so far. In the present study, we measured NPC1 mRNA and protein expression in three distinct regions of the human brain, and we revealed that NPC1 expression is upregulated at both mRNA and protein levels in the hippocampus and frontal cortex of AD patients compared to control individuals. In the cerebellum, a brain region that is relatively spared in AD, no difference in NPC1 expression was detected. Similarly, murine NPC1 mRNA levels were increased in the hippocampus of 12-month-old transgenic mice expressing a familial AD form of human amyloid-beta precursor protein (APP) and presenilin-1 (APP/PS1tg) compared to 12-month-old wild type mice, whereas no change in NPC1 was detected in mouse cerebellum. Immunohistochemical analysis of human hippocampus indicated that NPC1 expression was strongest in neurons. However, in vitro studies revealed that NPC1 expression was not induced by transfecting SK-N-SH neurons with human APP or by treating them with oligomeric amyloid-beta peptide. Total cholesterol levels were reduced in hippocampus from AD patients compared to control individuals, and it is therefore possible that the increased expression of NPC1 is linked to perturbed cholesterol homeostasis in AD.

Introduction

Alzheimer's disease (AD) is the most common form of dementia. It is characterized by deposition in the brain of amyloid plaques, mainly constituted of amyloid β (Aβ) peptide and dystrophic neurites rich in phosphorylated tau. The strongest known risk factor influencing the incidence of sporadic AD is the ApoE genotype, where homozygosity for ApoE4 increases the risk of developing AD 12-fold [1]. Elevated midlife serum cholesterol has been associated with risk of AD later in life [2], and it has been observed that subjects treated with statins have a significantly decreased prevalence of AD [3], [4]. However, conflicting data regarding statin treatment in relation to AD have been published [5]. Aβ is produced by sequential cleavage of the amyloid precursor protein (APP) by β-secretase followed by γ-secretase. The fact that APP, β-, and γ-secretases are localized in cholesterol-rich lipid rafts, suggests that alterations in cholesterol homeostasis may affect the development of AD via modulation of Aβ production and accumulation [6]. Elevated cholesterol levels increase Aβ levels in cellular and animal models [7]. Cholesterol homeostasis and Aβ are also linked via the ATP-binding cassette A1 and A7 (ABCA1 and ABCA7) membrane transporters, where increased ABCA1 or ABCA7 expression stimulates cholesterol efflux from lipid rafts and decreases Aβ secretion [8], [9], [10], [11], [12], [13].

It has been shown that neurons of AD patients contain enlarged endosomes and increased numbers of lysosomes and are characterized by an enhanced gene expression and synthesis of lysosomal enzymes [14], [15], [16]. Interestingly, components of the γ-secretase complex such as presenilin-1 and nicastrin have been detected in the lysosomal membrane [17]. β-Secretase has also been observed in the endosomal/lysosomal system [18] and has an acidic pH optimum [19].

Cholesterol is delivered to lysosomes subsequent to receptor-mediated endocytosis of extracellular lipoprotein particles. [20]. Exit of cholesterol from lysosomes requires two proteins, lysosomal membrane-bound Niemann-Pick type C1 (NPC1) and lysosomal soluble NPC2. NPC disease is an inherited neurodegenerative lipid storage disorder. Mutations in the NPC genes lead to the retention of cholesterol and other lipids in late endosomes and lysosomes [21]. Clinical and biochemical studies suggest that cholesterol imbalance and failure of homeostatic responses in the brain can lead to the development of both AD and NPC [6], [22]. Moreover, there are several pathological similarities between AD and NPC such as the presence of neurofibrillary tangles and taupathy, endosomal and lysosomal abnormalities, and increased Aβ generation [22], [23].

In the present study, we investigated if AD has an impact on human NPC1 expression. Our data demonstrate for the first time that NPC1 mRNA and protein expression is significantly upregulated in the AD frontal cortex and hippocampus, but not in the cerebellum when compared to healthy subjects.

Section snippets

Human brain tissues

Human brain tissues were obtained from the Australian Brain Donor Programs Prince of Wales Medical Research Institute Tissue Resource Centre (supported by the Australian National Health and Medical Research Council, NHMRC) and the NSW Tissue Resource Centre (supported by The University of Sydney, NHMRC, Schizophrenia Research Institute, National Institute of Alcohol Abuse and Alcoholism, and NSW Department of Health). Ethics approval was from the University of New South Wales Human Research

NPC1 expression in human brain

To investigate the potential impact of AD on NPC1 expression, we measured NPC1 mRNA and protein expression in human brain. NPC1 mRNA was increased significantly in the frontal cortex and in the CA1 field of the hippocampus in the AD cases. This increase in NPC1 was not detected in the cerebellar cortex (a brain region that is relatively spared in AD; Fig. 1A). Analysis of NPC1 protein levels by Western blotting confirmed that NPC1 was selectively upregulated in AD in the frontal cortex and CA1

Discussion

Although AD and NPC disease are distinct neuropathological disorders, certain commonalities involving lysosomal changes, altered cholesterol homeostasis, and Aβ generation prompted us to investigate if changes in NPC1 expression occur in the AD brain. Our results demonstrate for the first time that NPC1 mRNA and protein levels are significantly upregulated in the frontal cortex and in the CA1 field of the hippocampus in AD cases compared to controls. This upregulation appears to be associated

Acknowledgments

This study was supported by a fellowship from the Swedish Research Council and grants from the foundations of Nilsson, Engkvist and Wiberg (KK) and project grant 510148 from the Australian National Health and Medical Research Council (BG). We are very grateful to Assoc Prof Andrew Hill for provision of the CHO-APP cell line and to Prof Colin Masters and Dr Qiao-Xin Li for providing WO2 antibody. Human brain tissues were obtained from the Australian Brain Donor Programs Prince of Wales Medical

References (58)

  • G.C. Gregory et al.

    Differences in regional brain atrophy in genetic forms of Alzheimer's disease

    Neurobiol. Aging

    (2006)
  • S. Mexal et al.

    Brain pH has a significant impact on human postmortem hippocampal gene expression profiles

    Brain Res.

    (2006)
  • A.R. White et al.

    Degradation of the Alzheimer disease amyloid beta-peptide by metal-dependent up-regulation of metalloprotease activity

    J. Biol. Chem.

    (2006)
  • R.P. Erickson et al.

    Variation in NPC1, the gene encoding Niemann-Pick C1, a protein involved in intracellular cholesterol transport, is associated with Alzheimer disease and/or aging in the Polish population

    Neurosci. Lett.

    (2008)
  • T. Yamamoto et al.

    Increased NPC1 mRNA in skin fibroblasts from Niemann-Pick disease type C patients

    Brain Dev.

    (2004)
  • K. Simons et al.

    Jamming the endosomal system: lipid rafts and lysosomal storage diseases

    Trends Cell Biol.

    (2000)
  • R.P. Mason et al.

    Evidence for changes in the Alzheimer's disease brain cortical membrane structure mediated by cholesterol

    Neurobiol. Aging

    (1992)
  • M. Heverin et al.

    Changes in the levels of cerebral and extracerebral sterols in the brain of patients with Alzheimer's disease

    J. Lipid Res.

    (2004)
  • E.E. Millard et al.

    Niemann-Pick type C1 (NPC1) overexpression alters cellular cholesterol homeostasis

    J. Biol. Chem.

    (2000)
  • W. Yu et al.

    Neurodegeneration in heterozygous Niemann-Pick type C1 (NPC1) mouse: implication of heterozygous NPC1 mutations being a risk for tauopathy

    J. Biol. Chem.

    (2005)
  • A. Akram et al.

    Increased expression of cholesterol transporter ABCA1 is highly correlated with severity of dementia in AD hippocampus

    Brain Res.

    (2010)
  • W. Chen et al.

    Preferential ATP-binding cassette transporter A1-mediated cholesterol efflux from late endosomes/lysosomes

    J. Biol. Chem.

    (2001)
  • H.Y. Choi et al.

    Impaired ABCA1-dependent lipid efflux and hypoalphalipoproteinemia in human Niemann-Pick type C disease

    J. Biol. Chem.

    (2003)
  • E.B. Neufeld et al.

    The ABCA1 transporter modulates late endocytic trafficking: insights from the correction of the genetic defect in Tangier disease

    J. Biol. Chem.

    (2004)
  • W. Chen et al.

    A PEST deletion mutant of ABCA1 shows impaired internalization and defective cholesterol efflux from late endosomes

    J. Biol. Chem.

    (2005)
  • E.B. Neufeld et al.

    Cellular localization and trafficking of the human ABCA1 transporter

    J. Biol. Chem.

    (2001)
  • E.H. Corder et al.

    Gene dose of apolipoprotein E type 4 allele and the risk of Alzheimer's disease in late onset families

    Science

    (1993)
  • M.A. Pappolla et al.

    Mild hypercholesterolemia is an early risk factor for the development of Alzheimer amyloid pathology

    Neurology

    (2003)
  • B. Wolozin et al.

    Decreased prevalence of Alzheimer disease associated with 3-hydroxy-3-methyglutaryl coenzyme A reductase inhibitors

    Arch. Neurol.

    (2000)
  • Cited by (36)

    • The lysosomal storage disease continuum with ageing-related neurodegenerative disease

      2016, Ageing Research Reviews
      Citation Excerpt :

      Interestingly, tau deletion has been shown to exacerbate NPC phenotypes (Pacheco et al., 2009), suggesting an interaction between the two proteins, and overexpression of APP in the absence of NPC1 leads to further defects in the clearance of amyloid-β and the accumulation of APP-CTFs (Maulik et al., 2015). These findings, suggesting a link between NPC disease and AD, are supported by the observation that levels of the NPC1 protein are elevated in the hippocampus and cortex, but not the cerebellum (which is spared), of post-mortem AD patients (Kagedal et al., 2010). This process may not just be a result of the increased lysosomal biogenesis in AD as there is evidence of upregulation of NPC1 levels as a result of deficient endolysosomal cholesterol transport (Puri et al., 1999) or in response to altered sterol metabolism (Gevry et al., 2008).

    • Bidirectional links between Alzheimer's disease and Niemann-Pick type C disease

      2014, Neurobiology of Disease
      Citation Excerpt :

      We recently found increased CSF levels of six endosomal and lysosomal proteins (EEA1, LAMP-1, LAMP-2, LC3, Rab3, and Rab7) in AD patients compared to controls, and most of these (with the exception of EEA1) appeared to be specifically increased in AD, rather than general markers of neurodegeneration (Armstrong et al., 2014). In contrast to NPC1 gene downregulation observed in MCI/AD CA1 neurons in post mortem brains by Ginsberg et al. (2010), two additional reports described its increased mRNA and protein levels in both AD human brains and AD transgenic mouse models (Kågedal et al., 2010; Yao et al., 2012). Kågedal et al. (2010) analyzed mRNA/protein levels of NPC1 in different brain regions of AD patients and APP/PS1-tg mice (APPsw/Ps1∆E9) and revealed, in both models, a significantly increased NPC1 mRNA/protein expression in the hippocampus and frontal cortex, the two most affected brain areas in AD.

    • NPC1, intracellular cholesterol trafficking and atherosclerosis

      2014, Clinica Chimica Acta
      Citation Excerpt :

      Our recent investigation has demonstrated that oxidized low-density lipoprotein (oxLDL) can enhance the expression of NPC1 mRNA and protein in macrophages, and the mechanisms are associated with the extracellular signal-regulated kinase 1/2 (ERK1/2)/cyclooxygenase-2 (COX-2)/peroxisome proliferator-activated receptor α (PPARα) pathway [57]. It is suggested that NPC1 expression is upregulated at both the mRNA and protein levels in the hippocampus and frontal cortex of Alzheimer's disease patients as compared to control individuals [58]. Bambace and co-workers observed that NPC1 mRNA is significantly elevated in the subcutaneous and omental white adipose tissues of obese individuals, and is reduced by weight loss [59].

    View all citing articles on Scopus
    View full text