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Oettinger D, Yamamoto A. Autophagy Dysfunction and Neurodegeneration: Where Does It Go Wrong? J Mol Biol 2025:169219. [PMID: 40383464 DOI: 10.1016/j.jmb.2025.169219] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/30/2025] [Revised: 04/24/2025] [Accepted: 05/13/2025] [Indexed: 05/20/2025]
Abstract
An infamous hallmark of neurodegenerative diseases is the accumulation of misfolded or unfolded proteins forming inclusions in the brain. The accumulation of these abnormal structures is a mysterious one, given that cells devote significant resources to integrate complementary pathways to ensure proteome integrity and proper protein folding. Aberrantly folded protein species are rapidly targeted for disposal by the ubiquitin-proteasome system (UPS), and even if this should fail, and the species accumulates, the cell can also rely on the lysosome-mediated degradation pathways of autophagy. Despite the many safeguards in place, failure to maintain protein homeostasis commonly occurs during, or preceding, the onset of disease. Over the last decade and a half, studies suggest that the failure of autophagy may explain the disruption in protein homeostasis observed in disease. In this review, we will examine how the highly complex cells of the brain can become vulnerable to failure of aggregate clearance at specific points during the processive pathway of autophagy, contributing to aggregate accumulation in brains with neurodegenerative disease.
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Affiliation(s)
- Daphne Oettinger
- Doctoral Program for Neurobiology and Behavior, Columbia University, New York, NY, USA
| | - Ai Yamamoto
- Departments of Neurology and Pathology and Cell Biology, Columbia University, New York, NY, USA.
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Tu H, Yeo XY, Zhang ZW, Zhou W, Tan JY, Chi L, Chia SY, Li Z, Sim AY, Singh BK, Ma D, Zhou Z, Bonne I, Ling SC, Ng ASL, Jung S, Tan EK, Zeng L. NOTCH2NLC GGC intermediate repeat with serine induces hypermyelination and early Parkinson's disease-like phenotypes in mice. Mol Neurodegener 2024; 19:91. [PMID: 39609868 PMCID: PMC11603791 DOI: 10.1186/s13024-024-00780-2] [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] [Received: 05/07/2024] [Accepted: 11/13/2024] [Indexed: 11/30/2024] Open
Abstract
BACKGROUND The expansion of GGC repeats (typically exceeding 60 repeats) in the 5' untranslated region (UTR) of the NOTCH2NLC gene (N2C) is linked to N2C-related repeat expansion disorders (NREDs), such as neuronal intranuclear inclusion disease (NIID), frontotemporal dementia (FTD), essential tremor (ET), and Parkinson's disease (PD). These disorders share common clinical manifestations, including parkinsonism, dementia, seizures, and muscle weakness. Intermediate repeat sizes ranging from 40 to 60 GGC repeats, particularly those with AGC-encoded serine insertions, have been reported to be associated with PD; however, the functional implications of these intermediate repeats with serine insertion remain unexplored. METHODS Here, we utilized cellular models harbouring different sizes of N2C variant 2 (N2C2) GGC repeat expansion and CRISPR-Cas9 engineered transgenic mouse models carrying N2C2 GGC intermediate repeats with and without serine insertion to elucidate the underlying pathophysiology associated with N2C intermediate repeat with serine insertion in NREDs. RESULTS Our findings revealed that the N2C2 GGC intermediate repeat with serine insertion (32G13S) led to mitochondrial dysfunction and cell death in vitro. The neurotoxicity was influenced by the length of the repeat and was exacerbated by the presence of the serine insertion. In 12-month-old transgenic mice, 32G13S intensified intranuclear aggregation and exhibited early PD-like characteristics, including the formation of α-synuclein fibers in the midbrain and the loss of tyrosine hydroxylase (TH)-positive neurons in both the cortex and striatum. Additionally, 32G13S induced neuronal hyperexcitability and caused locomotor behavioural impairments. Transcriptomic analysis of the mouse cortex indicated dysregulation in calcium signaling and MAPK signaling pathways, both of which are critical for mitochondrial function. Notably, genes associated with myelin sheath components, including MBP and MOG, were dysregulated in the 32G13S mouse. Further investigations using immunostaining and transmission electron microscopy revealed that the N2C intermediate repeat with serine induced mitochondrial dysfunction-related hypermyelination in the cortex. CONCLUSIONS Our in vitro and in vivo investigations provide the first evidence that the N2C-GGC intermediate repeat with serine promotes intranuclear aggregation of N2C, leading to mitochondrial dysfunction-associated hypermyelination and neuronal hyperexcitability. These changes contribute to motor deficits in early PD-like neurodegeneration in NREDs.
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Affiliation(s)
- Haitao Tu
- Neural Stem Cell Research Lab, Research Department, National Neuroscience Institute, Singapore, 308433, Singapore
| | - Xin Yi Yeo
- Department of Psychological Medicine, Yong Loo Lin School of Medicine, National University of Singapore, Singapore, 119228, Singapore
| | - Zhi-Wei Zhang
- Neural Stem Cell Research Lab, Research Department, National Neuroscience Institute, Singapore, 308433, Singapore
| | - Wei Zhou
- Research Department, National Neuroscience Institute, Singapore General Hospital (SGH) Campus, Singapore, 169856, Singapore
| | - Jayne Yi Tan
- Department of Neurology, National Neuroscience Institute, Singapore, 308433, Singapore
| | - Li Chi
- Neural Stem Cell Research Lab, Research Department, National Neuroscience Institute, Singapore, 308433, Singapore
- Hospital of Stomatology, Guanghua School of Stomatology, Guangdong Provincial Key Laboratory of Stomatology, Institute of Stomatology, Sun Yat-Sen University, Guangzhou, Guangdong, 510080, China
| | - Sook-Yoong Chia
- Neural Stem Cell Research Lab, Research Department, National Neuroscience Institute, Singapore, 308433, Singapore
| | - Zhihong Li
- Neural Stem Cell Research Lab, Research Department, National Neuroscience Institute, Singapore, 308433, Singapore
| | - Aik Yong Sim
- Electron Microscopy Unit, Yong Loo Lin School of Medicine, National University of Singapore, Singapore, 117549, Singapore
| | - Brijesh Kumar Singh
- Laboratory of Hormonal Regulation, Cardiovascular and Metabolic Disorders, Duke-NUS Medical School, Singapore, 169857, Singapore
| | - Dongrui Ma
- Department of Neurology, Singapore General Hospital, Singapore, 169609, Singapore
| | - Zhidong Zhou
- Research Department, National Neuroscience Institute, Singapore General Hospital (SGH) Campus, Singapore, 169856, Singapore
- Neuroscience & Behavioural Disorders Program, DUKE-NUS Graduate Medical School, Singapore, 169857, Singapore
| | - Isabelle Bonne
- Electron Microscopy Unit, Yong Loo Lin School of Medicine, National University of Singapore, Singapore, 117549, Singapore
- Department of Microbiology and Immunology, Yong Loo Lin School of Medicine, National University of Singapore, Singapore, 117545, Singapore
- Immunology Translational Research Programme, Life Sciences Institute, National University of Singapore, Singapore, 117456, Singapore
| | - Shuo-Chien Ling
- Neuroscience & Behavioural Disorders Program, DUKE-NUS Graduate Medical School, Singapore, 169857, Singapore
- Department of Physiology, Yong Loo Lin School of Medicine, National University of Singapore, Singapore, 119077, Singapore
| | - Adeline S L Ng
- Department of Neurology, National Neuroscience Institute, Singapore, 308433, Singapore
- Neuroscience & Behavioural Disorders Program, DUKE-NUS Graduate Medical School, Singapore, 169857, Singapore
| | - Sangyong Jung
- Department of Medical Science, College of Medicine, CHA University, Seongnam, 13488, Republic of Korea
| | - Eng-King Tan
- Research Department, National Neuroscience Institute, Singapore General Hospital (SGH) Campus, Singapore, 169856, Singapore.
- Department of Neurology, National Neuroscience Institute, Singapore, 308433, Singapore.
- Neuroscience & Behavioural Disorders Program, DUKE-NUS Graduate Medical School, Singapore, 169857, Singapore.
| | - Li Zeng
- Neural Stem Cell Research Lab, Research Department, National Neuroscience Institute, Singapore, 308433, Singapore.
- Neuroscience & Behavioural Disorders Program, DUKE-NUS Graduate Medical School, Singapore, 169857, Singapore.
- Centre for Molecular Neuropathology, Lee Kong Chian School of Medicine, Nanyang Technology University, Singapore, Novena Campus, 308232, Singapore.
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