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Casanova F, Tian Q, Atkins JL, Wood AR, Williamson D, Qian Y, Zweibaum D, Ding J, Melzer D, Ferrucci L, Pilling LC. Iron and risk of dementia: Mendelian randomisation analysis in UK Biobank. J Med Genet 2024; 61:435-442. [PMID: 38191510 DOI: 10.1136/jmg-2023-109295] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/23/2023] [Accepted: 11/28/2023] [Indexed: 01/10/2024]
Abstract
BACKGROUND Brain iron deposition is common in dementia, but whether serum iron is a causal risk factor is unknown. We aimed to determine whether genetic predisposition to higher serum iron status biomarkers increased risk of dementia and atrophy of grey matter. METHODS We analysed UK Biobank participants clustered into European (N=451284), African (N=7477) and South Asian (N=9570) groups by genetic similarity to the 1000 genomes project. Using Mendelian randomisation methods, we estimated the association between genetically predicted serum iron (transferrin saturation [TSAT] and ferritin), grey matter volume and genetic liability to clinically defined dementia (including Alzheimer's disease [AD], non-AD dementia, and vascular dementia) from hospital and primary care records. We also performed time-to-event (competing risks) analysis of the TSAT polygenic score on risk of clinically defined non-AD dementia. RESULTS In Europeans, higher genetically predicted TSAT increased genetic liability to dementia (Odds Ratio [OR]: 1.15, 95% Confidence Intervals [CI] 1.04 to 1.26, p=0.0051), non-AD dementia (OR: 1.27, 95% CI 1.12 to 1.45, p=0.00018) and vascular dementia (OR: 1.37, 95% CI 1.12 to 1.69, p=0.0023), but not AD (OR: 1.00, 95% CI 0.86 to 1.15, p=0.97). Higher TSAT was also associated with increased risk of non-AD dementia in participants of African, but not South Asian groups. In survival analysis using a TSAT polygenic score, the effect was independent of apolipoprotein-E ε4 genotype (with adjustment subdistribution Hazard Ratio: 1.74, 95% CI 1.33 to 2.28, p=0.00006). Genetically predicted TSAT was associated with lower grey matter volume in caudate, putamen and thalamus, and not in other areas of interest. DISCUSSION Genetic evidence supports a causal relationship between higher TSAT and risk of clinically defined non-AD and vascular dementia, in European and African groups. This association appears to be independent of apolipoprotein-E ε4.
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Affiliation(s)
- Francesco Casanova
- Department of Clinical and Biomedical Sciences, University of Exeter, Exeter, UK
| | - Qu Tian
- Translational Gerontology Branch Longitudinal Studies Section, National Institute on Aging, Bethesda, Maryland, USA
| | - Janice L Atkins
- Department of Clinical and Biomedical Sciences, University of Exeter, Exeter, UK
| | - Andrew R Wood
- Department of Clinical and Biomedical Sciences, University of Exeter, Exeter, UK
| | | | - Yong Qian
- Translational Gerontology Branch Longitudinal Studies Section, National Institute on Aging, Bethesda, Maryland, USA
| | - David Zweibaum
- Translational Gerontology Branch Longitudinal Studies Section, National Institute on Aging, Bethesda, Maryland, USA
| | - Jun Ding
- Translational Gerontology Branch Longitudinal Studies Section, National Institute on Aging, Bethesda, Maryland, USA
| | - David Melzer
- Department of Clinical and Biomedical Sciences, University of Exeter, Exeter, UK
| | - Luigi Ferrucci
- Translational Gerontology Branch Longitudinal Studies Section, National Institute on Aging, Bethesda, Maryland, USA
| | - Luke C Pilling
- Department of Clinical and Biomedical Sciences, University of Exeter, Exeter, UK
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Dar NJ, John U, Bano N, Khan S, Bhat SA. Oxytosis/Ferroptosis in Neurodegeneration: the Underlying Role of Master Regulator Glutathione Peroxidase 4 (GPX4). Mol Neurobiol 2024; 61:1507-1526. [PMID: 37725216 DOI: 10.1007/s12035-023-03646-8] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/16/2023] [Accepted: 09/05/2023] [Indexed: 09/21/2023]
Abstract
Oxytosis/ferroptosis is an iron-dependent oxidative form of cell death triggered by lethal accumulation of phospholipid hydroperoxides (PLOOHs) in membranes. Failure of the intricate PLOOH repair system is a principle cause of ferroptotic cell death. Glutathione peroxidase 4 (GPX4) is distinctly vital for converting PLOOHs in membranes to non-toxic alcohols. As such, GPX4 is known as the master regulator of oxytosis/ferroptosis. Ferroptosis has been implicated in a number of disorders such as neurodegenerative diseases (amyotrophic lateral sclerosis (ALS), Alzheimer's disease (AD), Parkinson's disease (PD), and Huntington's disease (HD), etc.), ischemia/reperfusion injury, and kidney degeneration. Reduced function of GPX4 is frequently observed in degenerative disorders. In this study, we examine how diminished GPX4 function may be a critical event in triggering oxytosis/ferroptosis to perpetuate or initiate the neurodegenerative diseases and assess the possible therapeutic importance of oxytosis/ferroptosis in neurodegenerative disorders. These discoveries are important for advancing our understanding of neurodegenerative diseases because oxytosis/ferroptosis may provide a new target to slow the course of the disease.
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Affiliation(s)
- Nawab John Dar
- School of Medicine, University of Texas Health San Antonio, San Antonio, TX, 78229, USA.
| | - Urmilla John
- School of Studies in Neuroscience, Jiwaji University, Gwalior, India
- School of Studies in Zoology, Jiwaji University, Gwalior, India
| | - Nargis Bano
- Faculty of Life Sciences, Department of Zoology, Aligarh Muslim University, Aligarh, U.P, India
| | - Sameera Khan
- Faculty of Life Sciences, Department of Zoology, Aligarh Muslim University, Aligarh, U.P, India
| | - Shahnawaz Ali Bhat
- Faculty of Life Sciences, Department of Zoology, Aligarh Muslim University, Aligarh, U.P, India.
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Revisiting the Role of Vitamins and Minerals in Alzheimer's Disease. Antioxidants (Basel) 2023; 12:antiox12020415. [PMID: 36829974 PMCID: PMC9952129 DOI: 10.3390/antiox12020415] [Citation(s) in RCA: 8] [Impact Index Per Article: 8.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/16/2023] [Revised: 02/02/2023] [Accepted: 02/03/2023] [Indexed: 02/11/2023] Open
Abstract
Alzheimer's disease (AD) is the most common type of dementia that affects millions of individuals worldwide. It is an irreversible neurodegenerative disorder that is characterized by memory loss, impaired learning and thinking, and difficulty in performing regular daily activities. Despite nearly two decades of collective efforts to develop novel medications that can prevent or halt the disease progression, we remain faced with only a few options with limited effectiveness. There has been a recent growth of interest in the role of nutrition in brain health as we begin to gain a better understanding of what and how nutrients affect hormonal and neural actions that not only can lead to typical cardiovascular or metabolic diseases but also an array of neurological and psychiatric disorders. Vitamins and minerals, also known as micronutrients, are elements that are indispensable for functions including nutrient metabolism, immune surveillance, cell development, neurotransmission, and antioxidant and anti-inflammatory properties. In this review, we provide an overview on some of the most common vitamins and minerals and discuss what current studies have revealed on the link between these essential micronutrients and cognitive performance or AD.
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Qiu J, Lian F, Fang X. Iron status and mental disorders: A Mendelian randomization study. Front Nutr 2022; 9:1084860. [PMID: 36590208 PMCID: PMC9797506 DOI: 10.3389/fnut.2022.1084860] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/31/2022] [Accepted: 12/01/2022] [Indexed: 12/23/2022] Open
Abstract
Background Mental disorders account for an enormous global burden of disease, and has been associated with disturbed iron metabolism in observational studies. However, such associations are inconsistent and may be attributable to confounding from environmental factors. This study uses a two-sample Mendelian randomization (MR) analysis to investigate whether there is any causal effect of systemic iron status on risk of 24 specific mental disorders. Methods Genetic variants with concordant relations to 4 biomarkers of iron status (serum iron, ferritin, transferrin saturation, and transferrin) were obtained from a genome-wide association study performed by the Genetics of Iron Status (GIS) consortium. Summary-level data for mental disorders were obtained from the UK Biobank. An inverse-variance weighted (IVW) approach was used for the main analysis, and the simple median, weighted median and MR-Egger methods were used in sensitivity analyses. Results Genetically predicted serum iron, ferritin, and transferrin saturation were positively associated with depression and psychogenic disorder, and inversely associated with gender identity disorders. A higher transferrin, indicative of lower iron status, was also associated with increased risk of gender identity disorders and decreased risk of psychogenic disorder. Results were broadly consistent when using multiple sensitivity analyses to account for potential genetic pleiotropy. Conclusion Our findings offer a novel insight into mental health, highlighting a detrimental effect of higher iron status on depression and psychogenic disorder as well as a potential protective role on risk of gender identity disorders. Further studies regarding the underlying mechanisms are warranted for updating preventative strategies.
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Affiliation(s)
- Jiaqi Qiu
- Department of Nutrition and Toxicology, School of Public Health, Hangzhou Normal University, Hangzhou, China
| | - Fuzhi Lian
- Department of Nutrition and Toxicology, School of Public Health, Hangzhou Normal University, Hangzhou, China
| | - Xuexian Fang
- Department of Nutrition and Toxicology, School of Public Health, Hangzhou Normal University, Hangzhou, China,Key Laboratory of Elemene Class Anti-Cancer Chinese Medicines of Zhejiang Province, Hangzhou Normal University, Hangzhou, China,*Correspondence: Xuexian Fang,
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Ou M, Jiang Y, Ji Y, Zhou Q, Du Z, Zhu H, Zhou Z. Role and Mechanism of Ferroptosis in Neurological Diseases. Mol Metab 2022; 61:101502. [PMID: 35447365 PMCID: PMC9170779 DOI: 10.1016/j.molmet.2022.101502] [Citation(s) in RCA: 38] [Impact Index Per Article: 19.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 03/29/2022] [Revised: 04/14/2022] [Accepted: 04/15/2022] [Indexed: 02/08/2023] Open
Abstract
Background Ferroptosis, as a new form of cell death, is different from other cell deaths such as autophagy or senescence. Ferroptosis involves in the pathophysiological progress of several diseases, including cancers, cardiovascular diseases, nervous system diseases, and kidney damage. Since oxidative stress and iron deposition are the broad pathological features of neurological diseases, the role of ferroptosis in neurological diseases has been widely explored. Scope of review Ferroptosis is mainly characterized by changes in iron homeostasis, iron-dependent lipid peroxidation, and glutamate toxicity accumulation, of which can be specifically reversed by ferroptosis inducers or inhibitors. The ferroptosis is mainly regulated by the metabolism of iron, lipids and amino acids through System Xc−, voltage-dependent anion channels, p53, p62-Keap1-Nrf2, mevalonate and other pathways. This review also focus on the regulatory pathways of ferroptosis and its research progress in neurological diseases. Major conclusions The current researches of ferroptosis in neurological diseases mostly focus on the key pathways of ferroptosis. At the same time, ferroptosis was found playing a bidirectional regulation role in neurological diseases. Therefore, the specific regulatory mechanisms of ferroptosis in neurological diseases still need to be further explored to provide new perspectives for the application of ferroptosis in the treatment of neurological diseases.
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Affiliation(s)
- Mengmeng Ou
- The affiliated Wuxi Mental Health Center of JiangNan University, Wuxi Tongren International Rehabilitation Hospital, Wuxi, Jiangsu, 214151, China
| | - Ying Jiang
- The affiliated Wuxi Mental Health Center of JiangNan University, Wuxi Tongren International Rehabilitation Hospital, Wuxi, Jiangsu, 214151, China
| | - Yingying Ji
- The affiliated Wuxi Mental Health Center of JiangNan University, Wuxi Tongren International Rehabilitation Hospital, Wuxi, Jiangsu, 214151, China
| | - Qin Zhou
- The affiliated Wuxi Mental Health Center of JiangNan University, Wuxi Tongren International Rehabilitation Hospital, Wuxi, Jiangsu, 214151, China
| | - Zhiqiang Du
- The affiliated Wuxi Mental Health Center of JiangNan University, Wuxi Tongren International Rehabilitation Hospital, Wuxi, Jiangsu, 214151, China
| | - Haohao Zhu
- The affiliated Wuxi Mental Health Center of JiangNan University, Wuxi Tongren International Rehabilitation Hospital, Wuxi, Jiangsu, 214151, China.
| | - Zhenhe Zhou
- The affiliated Wuxi Mental Health Center of JiangNan University, Wuxi Tongren International Rehabilitation Hospital, Wuxi, Jiangsu, 214151, China.
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Lupton MK, Robinson GA, Adam RJ, Rose S, Byrne GJ, Salvado O, Pachana NA, Almeida OP, McAloney K, Gordon SD, Raniga P, Fazlollahi A, Xia Y, Ceslis A, Sonkusare S, Zhang Q, Kholghi M, Karunanithi M, Mosley PE, Lv J, Borne L, Adsett J, Garden N, Fripp J, Martin NG, Guo CC, Breakspear M. A prospective cohort study of prodromal Alzheimer's disease: Prospective Imaging Study of Ageing: Genes, Brain and Behaviour (PISA). NEUROIMAGE-CLINICAL 2020; 29:102527. [PMID: 33341723 PMCID: PMC7750170 DOI: 10.1016/j.nicl.2020.102527] [Citation(s) in RCA: 9] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 06/24/2020] [Revised: 11/11/2020] [Accepted: 12/04/2020] [Indexed: 12/20/2022]
Abstract
This prospective cohort study, "Prospective Imaging Study of Ageing: Genes, Brain and Behaviour" (PISA) seeks to characterise the phenotype and natural history of healthy adult Australians at high future risk of Alzheimer's disease (AD). In particular, we are recruiting midlife and older Australians with high and low genetic risk of dementia to discover biological markers of early neuropathology, identify modifiable risk factors, and establish the very earliest phenotypic and neuronal signs of disease onset. PISA utilises genetic prediction to recruit and enrich a prospective cohort and follow them longitudinally. Online surveys and cognitive testing are used to characterise an Australia-wide sample currently totalling over 3800 participants. Participants from a defined at-risk cohort and positive controls (clinical cohort of patients with mild cognitive impairment or early AD) are invited for onsite visits for detailed functional, structural and molecular neuroimaging, lifestyle monitoring, detailed neurocognitive testing, plus blood sample donation. This paper describes recruitment of the PISA cohort, study methodology and baseline demographics.
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Affiliation(s)
| | - Gail A Robinson
- School of Psychology, The University of Queensland, St. Lucia, Brisbane, Australia; Queensland Brain Institute, The University of Queensland, St. Lucia, Brisbane, Australia
| | - Robert J Adam
- QIMR Berghofer Medical Research Institute, Brisbane, Australia; Centre for Clinical Research (UQCCR), The University of Queensland, Brisbane, Australia; Royal Brisbane and Women's Hospital Mental Health Services, University of Queensland, Brisbane, Australia; Faculty of Medicine, University of Queensland, Brisbane, Australia
| | - Stephen Rose
- CSIRO Health and Biosecurity, Australian E-Health Research Centre, Brisbane, Australia
| | - Gerard J Byrne
- Royal Brisbane and Women's Hospital Mental Health Services, University of Queensland, Brisbane, Australia; Faculty of Medicine, University of Queensland, Brisbane, Australia
| | - Olivier Salvado
- CSIRO Health and Biosecurity, Australian E-Health Research Centre, Brisbane, Australia
| | - Nancy A Pachana
- School of Psychology, The University of Queensland, St. Lucia, Brisbane, Australia
| | - Osvaldo P Almeida
- Medical School, University of Western Australia, Perth, Australia; WA Centre for Health and Ageing of the University of Western Australia, Australia
| | - Kerrie McAloney
- QIMR Berghofer Medical Research Institute, Brisbane, Australia
| | - Scott D Gordon
- QIMR Berghofer Medical Research Institute, Brisbane, Australia
| | - Parnesh Raniga
- CSIRO Health and Biosecurity, Australian E-Health Research Centre, Brisbane, Australia
| | - Amir Fazlollahi
- CSIRO Health and Biosecurity, Australian E-Health Research Centre, Brisbane, Australia
| | - Ying Xia
- CSIRO Health and Biosecurity, Australian E-Health Research Centre, Brisbane, Australia
| | - Amelia Ceslis
- School of Psychology, The University of Queensland, St. Lucia, Brisbane, Australia
| | | | - Qing Zhang
- CSIRO Health and Biosecurity, Australian E-Health Research Centre, Brisbane, Australia
| | - Mahnoosh Kholghi
- CSIRO Health and Biosecurity, Australian E-Health Research Centre, Brisbane, Australia
| | - Mohan Karunanithi
- CSIRO Health and Biosecurity, Australian E-Health Research Centre, Brisbane, Australia
| | - Philip E Mosley
- QIMR Berghofer Medical Research Institute, Brisbane, Australia; Queensland Brain Institute, The University of Queensland, St. Lucia, Brisbane, Australia; Neurosciences Queensland, Brisbane, Queensland, Australia
| | - Jinglei Lv
- Sydney Imaging & School of Biomedical Engineering, The University of Sydney, Sydney, Australia
| | - Léonie Borne
- The University of Newcastle, Newcastle, Australia
| | - Jessica Adsett
- QIMR Berghofer Medical Research Institute, Brisbane, Australia
| | - Natalie Garden
- QIMR Berghofer Medical Research Institute, Brisbane, Australia
| | - Jurgen Fripp
- CSIRO Health and Biosecurity, Australian E-Health Research Centre, Brisbane, Australia
| | | | - Christine C Guo
- QIMR Berghofer Medical Research Institute, Brisbane, Australia
| | - Michael Breakspear
- QIMR Berghofer Medical Research Institute, Brisbane, Australia; The University of Newcastle, Newcastle, Australia
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Yan N, Zhang J. Iron Metabolism, Ferroptosis, and the Links With Alzheimer's Disease. Front Neurosci 2020; 13:1443. [PMID: 32063824 PMCID: PMC7000453 DOI: 10.3389/fnins.2019.01443] [Citation(s) in RCA: 147] [Impact Index Per Article: 36.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/24/2019] [Accepted: 12/24/2019] [Indexed: 12/17/2022] Open
Abstract
Iron is an essential transition metal for numerous biologic processes in mammals. Iron metabolism is regulated via several coordination mechanisms including absorption, utilization, recycling, and storage. Iron dyshomeostasis can result in intracellular iron retention, thereby damaging cells, tissues, and organs through free oxygen radical generation. Numerous studies have shown that brain iron overload is involved in the pathological mechanism of neurodegenerative disease including Alzheimer’s disease (AD). However, the underlying mechanisms have not been fully elucidated. Ferroptosis, a newly defined iron-dependent form of cell death, which is distinct from apoptosis, necrosis, autophagy, and other forms of cell death, may provide us a new viewpoint. Here, we set out to summarize the current knowledge of iron metabolism and ferroptosis, and review the contributions of iron and ferroptosis to AD.
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Affiliation(s)
- Nao Yan
- Department of Neurology, Zhongnan Hospital of Wuhan University, Wuhan, China
| | - JunJian Zhang
- Department of Neurology, Zhongnan Hospital of Wuhan University, Wuhan, China
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Winchester LM, Powell J, Lovestone S, Nevado-Holgado AJ. Red blood cell indices and anaemia as causative factors for cognitive function deficits and for Alzheimer's disease. Genome Med 2018; 10:51. [PMID: 29954452 PMCID: PMC6022699 DOI: 10.1186/s13073-018-0556-z] [Citation(s) in RCA: 39] [Impact Index Per Article: 6.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/13/2018] [Accepted: 06/07/2018] [Indexed: 02/07/2023] Open
Abstract
BACKGROUND Studies have shown that low haemoglobin and anaemia are associated with poor cognition, and anaemia is known to be associated with Alzheimer's disease (AD), but the mechanism of this risk is unknown. Here, we first seek to confirm the association between cognition and anaemia and secondly, in order to further understand the mechanism of this association, to estimate the direction of causation using Mendelian randomisation. METHODS Two independent cohorts were used in this analysis: AddNeuroMed, a longitudinal study of 738 subjects including AD and age-matched controls with blood cell measures, cognitive assessments and gene expression data from blood; and UK Biobank, a study of 502,649 healthy participants, aged 40-69 years with cognitive test measures and blood cell indices at baseline. General linear models were calculated using cognitive function as the outcome with correction for age, sex and education. In UK Biobank, SNPs with known blood cell measure associations were analysed with Mendelian randomisation to estimate direction of causality. In AddNeuroMed, gene expression data was used in pathway enrichment analysis to identify associations reflecting biological function. RESULTS Both sample sets evidence a reproducible association between cognitive performance and mean corpuscular haemoglobin (MCH), a measure of average mass of haemoglobin per red blood cell. Furthermore, in the AddNeuroMed cohort, where longitudinal samples were available, we showed a greater decline in red blood cell indices for AD patients when compared to controls (p values between 0.05 and 10-6). In the UK Biobank cohort, we found lower haemoglobin in participants with reduced cognitive function. There was a significant association for MCH and red blood cell distribution width (RDW, a measure of cell volume variability) compared to four cognitive function tests including reaction time and reasoning (p < 0.0001). Using Mendelian randomisation, we then showed a significant effect of MCH on the verbal-numeric and numeric traits, implying that anaemia has causative effect on cognitive performance. CONCLUSIONS Lower haemoglobin levels in blood are associated to poor cognitive function and AD. We have used UK Biobank SNP data to determine the relationship between cognitive testing and haemoglobin measures and suggest that haemoglobin level and therefore anaemia does have a primary causal impact on cognitive performance.
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Affiliation(s)
| | - John Powell
- Institute of Psychiatry, Psychology and Neuroscience, Kings College London, London, UK
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Gene-gene interactions among coding genes of iron-homeostasis proteins and APOE-alleles in cognitive impairment diseases. PLoS One 2018. [PMID: 29518107 PMCID: PMC5843269 DOI: 10.1371/journal.pone.0193867] [Citation(s) in RCA: 35] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022] Open
Abstract
Cognitive impairments of different aetiology share alterations in iron and lipid homeostasis with mutual relationships. Since iron and cholesterol accumulation impact on neurodegenerative disease, the associated gene variants are appealing candidate targets for risk and disease progression assessment. In this light, we explored the role of common single nucleotide polymorphisms (SNPs) in the main iron homeostasis genes and in the main lipoprotein transporter gene (APOE) in a cohort of 765 patients with dementia of different origin: Alzheimer’s disease (AD) n = 276; vascular dementia (VaD), n = 255; mild cognitive impairment (MCI), n = 234; and in normal controls (n = 1086). In details, four genes of iron homeostasis (Hemochromatosis (HFE: C282Y, H63D), Ferroportin (FPN1: -8CG), Hepcidin (HAMP: -582AG), Transferrin (TF: P570S)), and the three major alleles of APOE (APOE2, APOE3, APOE4) were analyzed to explore causative interactions and synergies. In single analysis, HFE 282Y allele yielded a 3-fold risk reduction in the whole cohort of patients (P<0.0001), confirmed in AD and VaD, reaching a 5-fold risk reduction in MCI (P = 0.0019). The other iron SNPs slightly associated with risk reduction whereas APOE4 allele resulted in increased risk, reaching more than 7-fold increased risk in AD homozygotes (P = 0.001), confirmed to a lower extent in VaD and MCI (P = 0.038 and P = 0.013 respectively) as well as in the whole group (P<0.0001). Comparisons of Mini Mental State Examination (MMSE) among AD showed appreciable lowering in APOE4 carriers (P = 0.038), confirmed in the whole cohort of patients (P = 0.018). In interaction analysis, the HFE 282Y allele completely extinguished the APOE4 allele associated risk. Conversely, the coexistence in patients of a substantial number of iron SNPs accrued the APOE4 detrimental effect on MMSE. Overall, the analysis highlighted how a specific iron-allele burden, defined as different combinations of iron gene variants, might have different effects on cognitive impairment and might modulate the effects of established genetic risk factors such as APOE4. Our results suggest that established genetic risk factors might be affected by specific genetic backgrounds, making patients differently suited to manage iron accumulation adding new genetic insights in neurodegeneration. The recently recognized interconnections between iron and lipids, suggest that these pathways might share more than expected. We therefore extended to additional iron gene variants the newly proposed influencing mechanisms that HFE gene has on cholesterol metabolism. Our results have a strong translational potential promoting new pharmacogenetics studies on therapeutic target identification aimed at optimally tuning brain iron levels.
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