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LeVine SM. The Azalea Hypothesis of Alzheimer Disease: A Functional Iron Deficiency Promotes Neurodegeneration. Neuroscientist 2024; 30:525-544. [PMID: 37599439 PMCID: PMC10876915 DOI: 10.1177/10738584231191743] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 08/22/2023]
Abstract
Chlorosis in azaleas is characterized by an interveinal yellowing of leaves that is typically caused by a deficiency of iron. This condition is usually due to the inability of cells to properly acquire iron as a consequence of unfavorable conditions, such as an elevated pH, rather than insufficient iron levels. The causes and effects of chlorosis were found to have similarities with those pertaining to a recently presented hypothesis that describes a pathogenic process in Alzheimer disease. This hypothesis states that iron becomes sequestered (e.g., by amyloid β and tau), causing a functional deficiency of iron that disrupts biochemical processes leading to neurodegeneration. Additional mechanisms that contribute to iron becoming unavailable include iron-containing structures not undergoing proper recycling (e.g., disrupted mitophagy and altered ferritinophagy) and failure to successfully translocate iron from one compartment to another (e.g., due to impaired lysosomal acidification). Other contributors to a functional deficiency of iron in patients with Alzheimer disease include altered metabolism of heme or altered production of iron-containing proteins and their partners (e.g., subunits, upstream proteins). A review of the evidence supporting this hypothesis is presented. Also, parallels between the mechanisms underlying a functional iron-deficient state in Alzheimer disease and those occurring for chlorosis in plants are discussed. Finally, a model describing the generation of a functional iron deficiency in Alzheimer disease is put forward.
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Affiliation(s)
- Steven M. LeVine
- Department of Cell Biology and Physiology, University of Kansas Medical Center, Kansas City, KS, US
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He K, Zhao Z, Zhang J, Li D, Wang S, Liu Q. Cholesterol Metabolism in Neurodegenerative Diseases. Antioxid Redox Signal 2024. [PMID: 38842175 DOI: 10.1089/ars.2024.0674] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 06/07/2024]
Abstract
Significance: Cholesterol plays a crucial role in the brain, where it is highly concentrated and tightly regulated to support normal brain functions. It serves as a vital component of cell membranes, ensuring their integrity, and acts as a key regulator of various brain processes. Dysregulation of cholesterol metabolism in the brain has been linked to impaired brain function and the onset of neurodegenerative diseases such as Alzheimer's disease (AD), Parkinson's disease, and Huntington's disease. Recent Advances: A significant advancement has been the identification of astrocyte-derived apoliprotein E as a key regulator of de novo cholesterol biosynthesis in neurons, providing insights into how extracellular signals influence neuronal cholesterol levels. In addition, the development of antibody-based therapies, particularly for AD, presents promising opportunities for therapeutic interventions. Critical Issues: Despite significant research, the association between cholesterol and neurodegenerative diseases remains inconclusive. It is crucial to distinguish between plasma cholesterol and brain cholesterol, as these pools are relatively independent. This differentiation should be considered when evaluating statin-based treatment approaches. Furthermore, assessing not only the total cholesterol content in the brain but also its distribution among different types of brain cells is essential. Future Direction: Establishing a causal link between changes in brain/plasma cholesterol levels and the onset of brain dysfunction/neurodegenerative diseases remains a key objective. In addition, conducting cell-specific analyses of cholesterol homeostasis in various types of brain cells under pathological conditions will enhance our understanding of cholesterol metabolism in neurodegenerative diseases. Manipulating cholesterol levels to restore homeostasis may represent a novel approach for alleviating neurological symptoms.
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Affiliation(s)
- Keqiang He
- Department of Anesthesiology, The First Affiliated Hospital of USTC, Center for Advanced Interdisciplinary Science and Biomedicine of IHM, Division of Life Sciences and Medicine, University of Science and Technology of China, Hefei 230001, China
| | - Zhiwei Zhao
- Department of Cardiovascular Surgery, the First Affiliated Hospital of USTC, Hefei National Laboratory for Physical Sciences at the Microscale, Division of Life Sciences and Medicine, University of Science and Technology of China
| | - Juan Zhang
- Department of Neurology, The First Affiliated Hospital of USTC, Division of Life Sciences and Medicine, Hefei National Research Center for Physical Sciences at the Microscale, University of Science and Technology of China, Hefei, China
- CAS Key Laboratory of Brain Function and Diseases, Division of Life Sciences and Medicine, University of Science and Technology of China, Hefei, China
- Institute on Aging and Brain Disorders, The First Affiliated Hospital of USTC, University of Science and Technology of China, Hefei, China
| | - Dingfeng Li
- Department of Neurology, The First Affiliated Hospital of USTC, Division of Life Sciences and Medicine, Hefei National Research Center for Physical Sciences at the Microscale, University of Science and Technology of China, Hefei, China
- CAS Key Laboratory of Brain Function and Diseases, Division of Life Sciences and Medicine, University of Science and Technology of China, Hefei, China
- Institute on Aging and Brain Disorders, The First Affiliated Hospital of USTC, University of Science and Technology of China, Hefei, China
| | - Sheng Wang
- Department of Anesthesiology, The First Affiliated Hospital of USTC, Center for Advanced Interdisciplinary Science and Biomedicine of IHM, Division of Life Sciences and Medicine, University of Science and Technology of China, Hefei 230001, China
| | - Qiang Liu
- Department of Anesthesiology, The First Affiliated Hospital of USTC, Center for Advanced Interdisciplinary Science and Biomedicine of IHM, Division of Life Sciences and Medicine, University of Science and Technology of China, Hefei 230001, China
- Department of Neurology, The First Affiliated Hospital of USTC, Division of Life Sciences and Medicine, Hefei National Research Center for Physical Sciences at the Microscale, University of Science and Technology of China, Hefei, China
- CAS Key Laboratory of Brain Function and Diseases, Division of Life Sciences and Medicine, University of Science and Technology of China, Hefei, China
- Institute on Aging and Brain Disorders, The First Affiliated Hospital of USTC, University of Science and Technology of China, Hefei, China
- Neurodegenerative Disorder Research Center, Anhui Province Key Laboratory of Biomedical Aging Research, University of Science and Technology of China, Hefei, China
- Key Laboratory of Immune Response and Immunotherapy, University of Science and Technology of China, Hefei, China
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Ayyubova G. APOE4 is a Risk Factor and Potential Therapeutic Target for Alzheimer's Disease. CNS & NEUROLOGICAL DISORDERS DRUG TARGETS 2024; 23:342-352. [PMID: 36872358 DOI: 10.2174/1871527322666230303114425] [Citation(s) in RCA: 4] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/01/2022] [Revised: 12/20/2022] [Accepted: 01/12/2023] [Indexed: 03/07/2023]
Abstract
Alzheimer's disease (AD) is a progressive neurodegenerative disease, the main pathological hallmark of which is the loss of neurons, resulting in cognitive and memory impairments. Sporadic late-onset AD is a prevalent form of the disease and the apolipoprotein E4 (APOE4) genotype is the strongest predictor of the disease development. The structural variations of APOE isoforms affect their roles in synaptic maintenance, lipid trafficking, energy metabolism, inflammatory response, and BBB integrity. In the context of AD, APOE isoforms variously control the key pathological elements of the disease, including Aβ plaque formation, tau aggregation, and neuroinflammation. Taking into consideration the limited number of therapy choices that can alleviate symptoms and have little impact on the AD etiology and progression to date, the precise research strategies guided by apolipoprotein E (APOE) polymorphisms are required to assess the potential risk of age-related cognitive decline in people carrying APOE4 genotype. In this review, we summarize the evidence implicating the significance of APOE isoforms on brain functions in health and pathology with the aim to identify the possible targets that should be addressed to prevent AD manifestation in individuals with the APOE4 genotype and to explore proper treatment strategies.
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Affiliation(s)
- Gunel Ayyubova
- Department of Cytology, Embryology and Histology, Azerbaijan Medical University, Baku, Azerbaijan
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