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Cvekl A, Vijg J. Aging of the eye: Lessons from cataracts and age-related macular degeneration. Ageing Res Rev 2024; 99:102407. [PMID: 38977082 DOI: 10.1016/j.arr.2024.102407] [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: 03/11/2024] [Revised: 06/18/2024] [Accepted: 07/01/2024] [Indexed: 07/10/2024]
Abstract
Aging is the greatest risk factor for chronic human diseases, including many eye diseases. Geroscience aims to understand the effects of the aging process on these diseases, including the genetic, molecular, and cellular mechanisms that underlie the increased risk of disease over the lifetime. Understanding of the aging eye increases general knowledge of the cellular physiology impacted by aging processes at various biological extremes. Two major diseases, age-related cataract and age-related macular degeneration (AMD) are caused by dysfunction of the lens and retina, respectively. Lens transparency and light refraction are mediated by lens fiber cells lacking nuclei and other organelles, which provides a unique opportunity to study a single aging hallmark, i.e., loss of proteostasis, within an environment of limited metabolism. In AMD, local dysfunction of the photoreceptors/retinal pigmented epithelium/Bruch's membrane/choriocapillaris complex in the macula leads to the loss of photoreceptors and eventually loss of central vision, and is driven by nearly all the hallmarks of aging and shares features with Alzheimer's disease, Parkinson's disease, cardiovascular disease, and diabetes. The aging eye can function as a model for studying basic mechanisms of aging and, vice versa, well-defined hallmarks of aging can be used as tools to understand age-related eye disease.
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Affiliation(s)
- Ales Cvekl
- Departments of Genetics and Ophthalmology and Visual Sciences, Albert Einstein College of Medicine, Bronx, NY 10461, USA.
| | - Jan Vijg
- Departments of Genetics and Ophthalmology and Visual Sciences, Albert Einstein College of Medicine, Bronx, NY 10461, USA.
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Greiling TM, Clark JM, Clark JI. The significance of growth shells in development of symmetry, transparency, and refraction of the human lens. FRONTIERS IN OPHTHALMOLOGY 2024; 4:1434327. [PMID: 39100140 PMCID: PMC11294239 DOI: 10.3389/fopht.2024.1434327] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 05/17/2024] [Accepted: 06/27/2024] [Indexed: 08/06/2024]
Abstract
Human visual function depends on the biological lens, a biconvex optical element formed by coordinated, synchronous generation of growth shells produced from ordered cells at the lens equator, the distal edge of the epithelium. Growth shells are comprised of straight (St) and S-shaped (SSh) lens fibers organized in highly symmetric, sinusoidal pattern which optimizes both the refractile, transparent structure and the unique microcirculation that regulates hydration and nutrition over the lifetime of an individual. The fiber cells are characterized by diversity in composition and age. All fiber cells remain interconnected in their growth shells throughout the life of the adult lens. As an optical element, cellular differentiation is constrained by the physical properties of light and its special development accounts for its characteristic symmetry, gradient of refractive index (GRIN), short range transparent order (SRO), and functional longevity. The complex sinusoidal structure is the basis for the lens microcirculation required for the establishment and maintenance of image formation.
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Affiliation(s)
- Teri M. Greiling
- Department of Dermatology, School of Medicine, Oregon Health & Science University, Portland, OR, United States
| | - Judy M. Clark
- Department of Biological Structure, University of Washington, Seattle, WA, United States
| | - John I. Clark
- Department of Biological Structure, University of Washington, Seattle, WA, United States
- Department of Biological Structure & Ophthalmology, School of Medicine, University of Washington, Seattle, WA, United States
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De Guia IL, Eslick S, Naismith SL, Kanduri S, Shah TM, Martins RN. The Crosstalk Between Amyloid-β, Retina, and Sleep for the Early Diagnosis of Alzheimer's Disease: A Narrative Review. J Alzheimers Dis Rep 2024; 8:1009-1021. [PMID: 39114553 PMCID: PMC11305848 DOI: 10.3233/adr-230150] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/20/2023] [Accepted: 05/17/2024] [Indexed: 08/10/2024] Open
Abstract
Alzheimer's disease (AD) is the most common type of dementia, which is characterised by progressive memory loss and accumulation of hallmark markers amyloid-β (Aβ) and neurofibrillary tangles in the diseased brain. The current gold standard diagnostic methods have limitations of being invasive, costly, and not easily accessible. Thus, there is a need for new avenues, such as imaging the retina for early AD diagnosis. Sleep disruption is symptomatically frequent across preclinical and AD subjects. As circadian activity, such as the sleep-wake cycle, is linked to the retina, analysis of their association may be useful additions for achieving predictive AD diagnosis. In this narrative review, we provide an overview of human retina studies concerning the deposition of Aβ, the role of the retina in sleep-wake cycle, the disruption of sleep in AD, and to gather evidence for the associations between Aβ, the retina, and sleep. Understanding the mechanisms behind the associations between Aβ, retina, and sleep could assist in the interpretation of retinal changes accurately in AD.
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Affiliation(s)
| | - Shaun Eslick
- Macquarie University, North Ryde, NSW, Australia
| | - Sharon L. Naismith
- Faculty of Science, Charles Perkins Centre, The University of Sydney, Camperdown, NSW, Australia
| | | | | | - Ralph N. Martins
- Macquarie University, North Ryde, NSW, Australia
- Edith Cowen University, Joondalup, WA, Australia
- Australian Alzheimer’s Research Foundation, Nedlands, WA, Australia
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Glaesser D, Iwig M. Increased molar ratio of free fatty acids to albumin in blood as cause and early biomarker for the development of cataracts and Alzheimer's disease. Exp Eye Res 2024; 243:109888. [PMID: 38583754 DOI: 10.1016/j.exer.2024.109888] [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: 10/25/2023] [Revised: 03/29/2024] [Accepted: 04/04/2024] [Indexed: 04/09/2024]
Abstract
Cataracts and Alzheimer's disease (AD) are closely linked and are associated with aging and with systemic diseases that increase the molar ratio of free fatty acids to albumin (mFAR) in the blood. From the results of our earlier studies on the development of senile cataracts and from results recently published in the literature on the pathogenesis of Alzheimer's disease, we suggest that there is a common lipotoxic cascade for both diseases, explaining the strong connection between aging, an elevated mFAR in the blood, cataract formation, and AD. Long-chain free fatty acids (FFA) are transported in the blood as FFA/albumin complexes. In young people, vascular albumin barriers in the eyes and brain, very similar in their structure and effect, reduce the FFA/albumin complex concentration from around 650 μmol/l in the blood to 1-3 μmol/l in the aqueous humour of the eyes as well as in the cerebrospinal fluid of the brain. At such low concentrations the fatty acid uptake of the target cells - lens epithelial and brain cells - rises with increasing FFA/albumin complex concentrations, especially when the fatty acid load of albumin molecules is mFAR>1. At higher albumin concentrations, for instance in blood plasma or the interstitial tissue spaces, the fatty acid uptake of the target cells becomes increasingly independent of the FFA/albumin complex concentration and is mainly a function of the mFAR (Richieri et al., 1993). In the blood plasma of young people, the mFAR is normally below 1.0. In people over 40 years old, aging increases the mFAR by decreasing the plasma concentration of albumin and enhancing the plasma concentrations of FFA. The increase in the mFAR in association with C6-unsaturated FFA are risk factors for the vascular albumin barriers (Hennig et al., 1984). Damage to the vascular albumin barrier in the eyes and brain increases the concentration of FFA/albumin complex in the aqueous humour as well as in the cerebrospinal fluid, leading to mitochondrial dysfunction and the death of lens epithelial and brain cells, the development of cataracts, and AD. An age-dependent increase in the concentration of FFA/albumin complex has been found in the aqueous humour of 177 cataract patients, correlating with the mitochondria-mediated apoptotic death of lens epithelial cells, lens opacification and cataracts (Iwig et al., 2004). Mitochondrial dysfunction is also an early crucial event in Alzheimer's pathology, closely connected with the generation of amyloid beta peptides (Leuner et al., 2012). Very recently, amyloid beta production has also been confirmed in the lenses of Alzheimer's patients, causing cataracts (Moncaster et al., 2022). In view of this, we propose that there is a common lipotoxic cascade for senile cataract formation and senile AD, initiated by aging and/or systemic diseases, leading to an mFAR>1 in the blood.
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Affiliation(s)
- Dietmar Glaesser
- Institute of Physiological Chemistry, Martin-Luther-University Halle-Wittenberg, D-06097, Halle, Germany.
| | - Martin Iwig
- Institute of Physiological Chemistry, Martin-Luther-University Halle-Wittenberg, D-06097, Halle, Germany
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Palko SI, Benoit MR, Yao AY, Mohan R, Yan R. ER-stress response in retinal Müller glia occurs significantly earlier than amyloid pathology in the Alzheimer's mouse brain and retina. Glia 2024; 72:1067-1081. [PMID: 38497356 PMCID: PMC11006574 DOI: 10.1002/glia.24514] [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: 01/10/2023] [Revised: 02/01/2024] [Accepted: 02/05/2024] [Indexed: 03/19/2024]
Abstract
Alzheimer's Disease (AD) pathogenesis is thought to begin up to 20 years before cognitive symptoms appear, suggesting the need for more sensitive diagnostic biomarkers of AD. In this report, we demonstrated pathological changes in retinal Müller glia significantly earlier than amyloid pathology in AD mouse models. By utilizing the knock-in NLGF mouse model, we surprisingly discovered an increase in reticulon 3 (RTN3) protein levels in the NLGF retina as early as postnatal day 30 (P30). Despite RTN3 being a canonically neuronal protein, this increase was noted in the retinal Müller glia, confirmed by immunohistochemical characterization. Further unbiased transcriptomic assays of the P30 NLGF retina revealed that retinal Müller glia were the most sensitive responding cells in this mouse retina, compared with other cell types including photoreceptor cells and ganglion neurons. Pathway analyses of differentially expressed genes in glia cells showed activation of ER stress response via the upregulation of unfolded protein response (UPR) proteins such as ATF4 and CHOP. Early elevation of RTN3 in response to challenges by toxic Aβ likely facilitated UPR. Altogether, these findings suggest that Müller glia act as a sentinel for AD pathology in the retina and should aid for both intervention and diagnosis.
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Affiliation(s)
| | | | - Annie Y. Yao
- Department of Neuroscience, University of Connecticut Health Center, Farmington CT 06030 USA
| | - Royce Mohan
- Department of Neuroscience, University of Connecticut Health Center, Farmington CT 06030 USA
| | - Riqiang Yan
- Department of Neuroscience, University of Connecticut Health Center, Farmington CT 06030 USA
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Serebryany E, Martin RW, Takahashi GR. The Functional Significance of High Cysteine Content in Eye Lens γ-Crystallins. Biomolecules 2024; 14:594. [PMID: 38786000 PMCID: PMC11118217 DOI: 10.3390/biom14050594] [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: 03/28/2024] [Revised: 05/07/2024] [Accepted: 05/14/2024] [Indexed: 05/25/2024] Open
Abstract
Cataract disease is strongly associated with progressively accumulating oxidative damage to the extremely long-lived crystallin proteins of the lens. Cysteine oxidation affects crystallin folding, interactions, and light-scattering aggregation especially strongly due to the formation of disulfide bridges. Minimizing crystallin aggregation is crucial for lifelong lens transparency, so one might expect the ubiquitous lens crystallin superfamilies (α and βγ) to contain little cysteine. Yet, the Cys content of γ-crystallins is well above the average for human proteins. We review literature relevant to this longstanding puzzle and take advantage of expanding genomic databases and improved machine learning tools for protein structure prediction to investigate it further. We observe remarkably low Cys conservation in the βγ-crystallin superfamily; however, in γ-crystallin, the spatial positioning of Cys residues is clearly fine-tuned by evolution. We propose that the requirements of long-term lens transparency and high lens optical power impose competing evolutionary pressures on lens βγ-crystallins, leading to distinct adaptations: high Cys content in γ-crystallins but low in βB-crystallins. Aquatic species need more powerful lenses than terrestrial ones, which explains the high methionine content of many fish γ- (and even β-) crystallins. Finally, we discuss synergies between sulfur-containing and aromatic residues in crystallins and suggest future experimental directions.
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Affiliation(s)
- Eugene Serebryany
- Department of Physiology & Biophysics, Stony Brook University, SUNY, Stony Brook, NY 11794, USA
- Laufer Center for Physical & Quantitative Biology, Stony Brook University, SUNY, Stony Brook, NY 11794, USA
| | - Rachel W. Martin
- Department of Chemistry, UCI Irvine, Irvine, CA 92697-2025, USA
- Department of Molecular Biology & Biochemistry, UCI Irvine, Irvine, CA 92697-3900, USA
| | - Gemma R. Takahashi
- Department of Molecular Biology & Biochemistry, UCI Irvine, Irvine, CA 92697-3900, USA
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Sarangi S, Minaeva O, Ledoux DM, Parsons DS, Moncaster JA, Black CA, Hollander J, Tripodis Y, Clark JI, Hunter DG, Goldstein LE. In vivo quasi-elastic light scattering detects molecular changes in the lenses of adolescents with Down syndrome. Exp Eye Res 2024; 241:109818. [PMID: 38422787 DOI: 10.1016/j.exer.2024.109818] [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: 05/24/2023] [Revised: 12/08/2023] [Accepted: 01/30/2024] [Indexed: 03/02/2024]
Abstract
Down syndrome (DS) is the most common chromosomal disorder in humans. DS is associated with increased prevalence of several ocular sequelae, including characteristic blue-dot cerulean cataract. DS is accompanied by age-dependent accumulation of Alzheimer's disease (AD) amyloid-β (Aβ) peptides and amyloid pathology in the brain and comorbid early-onset Aβ amyloidopathy and colocalizing cataracts in the lens. Quasi-elastic light scattering (QLS) is an established optical technique that noninvasively measures changes in protein size distributions in the human lens in vivo. In this cross-sectional study, lenticular QLS correlation time was decreased in adolescent subjects with DS compared to age-matched control subjects. Clinical QLS was consistent with alterations in relative particle hydrodynamic radius in lenses of adolescents with DS. These correlative results suggest that noninvasive QLS can be used to evaluate molecular changes in the lenses of individuals with DS.
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Affiliation(s)
- Srikant Sarangi
- Molecular Aging & Development Laboratory, Boston University Chobanian and Avedisian School of Medicine, Boston, MA, USA; Boston University Photonics Center, Boston University, Boston, MA, USA; Department of Biomedical Engineering, Boston University, Boston, MA, USA
| | - Olga Minaeva
- Molecular Aging & Development Laboratory, Boston University Chobanian and Avedisian School of Medicine, Boston, MA, USA; Boston University Photonics Center, Boston University, Boston, MA, USA; Department of Biomedical Engineering, Boston University, Boston, MA, USA; Boston University Alzheimer's Disease Research Center, Boston University Chobanian and Avedisian School of Medicine, Boston, MA, USA; Department of Ophthalmology, Boston Children's Hospital, Boston, MA, USA
| | - Danielle M Ledoux
- Department of Ophthalmology, Boston Children's Hospital, Boston, MA, USA; Department of Ophthalmology, Harvard Medical School, Boston, MA, USA
| | - Douglas S Parsons
- Molecular Aging & Development Laboratory, Boston University Chobanian and Avedisian School of Medicine, Boston, MA, USA; Boston University Photonics Center, Boston University, Boston, MA, USA
| | - Juliet A Moncaster
- Molecular Aging & Development Laboratory, Boston University Chobanian and Avedisian School of Medicine, Boston, MA, USA; Boston University Photonics Center, Boston University, Boston, MA, USA; Boston University Alzheimer's Disease Research Center, Boston University Chobanian and Avedisian School of Medicine, Boston, MA, USA
| | - Caitlin A Black
- Department of Ophthalmology, Boston Children's Hospital, Boston, MA, USA
| | - Jeffrey Hollander
- Department of Ophthalmology, Boston Children's Hospital, Boston, MA, USA
| | - Yorghos Tripodis
- Department of Biostatistics, Boston University School of Public Health, Boston, MA, USA
| | - John I Clark
- Department of Biological Structure, University of Washington, Seattle, WA, USA
| | - David G Hunter
- Department of Ophthalmology, Boston Children's Hospital, Boston, MA, USA; Department of Ophthalmology, Harvard Medical School, Boston, MA, USA
| | - Lee E Goldstein
- Molecular Aging & Development Laboratory, Boston University Chobanian and Avedisian School of Medicine, Boston, MA, USA; Boston University Photonics Center, Boston University, Boston, MA, USA; Department of Biomedical Engineering, Boston University, Boston, MA, USA; Boston University Alzheimer's Disease Research Center, Boston University Chobanian and Avedisian School of Medicine, Boston, MA, USA.
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Tost F. A Wide Range of Eye Diseases. DEUTSCHES ARZTEBLATT INTERNATIONAL 2023; 120:488. [PMID: 37661325 PMCID: PMC10487677 DOI: 10.3238/arztebl.m2023.0075] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 09/05/2023]
Affiliation(s)
- Frank Tost
- *Klinik und Poliklinik für Augenheilkunde Universitätsmedizin Greifswald
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Man S, Chen B, Zhang Y, Xu H, Liu Y, Gao Y, Chen Y, Chen Q, Zhang M. The Associations Between Cataracts and Alzheimer's Disease: A Bidirectional Two-Sample Mendelian Randomization Study. J Alzheimers Dis 2023; 92:1451-1458. [PMID: 36911941 DOI: 10.3233/jad-221137] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 03/12/2023]
Abstract
BACKGROUND The relationship between cataracts and Alzheimer's disease (AD) has been reported in recent observational studies. However, it is still unclear whether a causal effect of cataracts on AD or reverse causation exists. OBJECTIVE To explore the association between cataracts and AD genetically, we performed a bidirectional two-sample Mendelian randomization study. METHODS We obtained genetic instrumental variables related to cataracts and AD from recently published genome-wide association studies (GWASs). SNP-outcome associations for AD were obtained from a GWAS with 111,326 cases and 677,663 controls. SNP-outcome associations for cataracts were drawn from two sources: a GWAS with 67,844 cases and 517,399 controls and the FinnGen consortium (42,843 cases and 262,698 controls). Inverse variance weighted (IVW) was used as the primary method for Mendelian randomization (MR) analyses. RESULTS No genetic evidence suggested that cataracts were associated with the risk of AD (IVW odds ratio =1.04, 95% confidence interval: 0.98-1.10, p=0.199). In contrast, an effect of genetically determined AD on a decreased risk of cataract was observed with suggestive evidence (IVW odds ratio =0.96, 95% confidence interval: 0.93-0.99, p=0.004). However, this result might be distorted by survival bias. CONCLUSION Genetically determined cataracts were not related to AD, as demonstrated by our study. In contrast, there was suggestive evidence that AD might prevent cataract development, but there might be potential survival bias. To define the exact association between the two diseases, more prospective research and studies on the pathogenesis are needed.
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Affiliation(s)
- Shulei Man
- Department of Ophthalmology, West China Hospital, Sichuan University, Chengdu, China
| | - Boran Chen
- Department of Neurosurgery, West China Hospital, Sichuan University, Chengdu, China
| | - Yifan Zhang
- Department of Ophthalmology, West China Hospital, Sichuan University, Chengdu, China
| | - Hanyue Xu
- Department of Ophthalmology, West China Hospital, Sichuan University, Chengdu, China
| | - Yu Liu
- Department of Neurosurgery, West China Hospital, Sichuan University, Chengdu, China
| | - Yuzhu Gao
- Department of Ophthalmology, West China Hospital, Sichuan University, Chengdu, China
| | - Yi Chen
- Department of Ophthalmology, West China Hospital, Sichuan University, Chengdu, China
| | - Qing Chen
- Department of Ophthalmology, West China Hospital, Sichuan University, Chengdu, China
| | - Ming Zhang
- Department of Ophthalmology, West China Hospital, Sichuan University, Chengdu, China
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Quinlan RA, Clark JI. Insights into the biochemical and biophysical mechanisms mediating the longevity of the transparent optics of the eye lens. J Biol Chem 2022; 298:102537. [PMID: 36174677 PMCID: PMC9638808 DOI: 10.1016/j.jbc.2022.102537] [Citation(s) in RCA: 14] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/31/2021] [Revised: 09/20/2022] [Accepted: 09/22/2022] [Indexed: 11/18/2022] Open
Abstract
In the human eye, a transparent cornea and lens combine to form the "refracton" to focus images on the retina. This requires the refracton to have a high refractive index "n," mediated largely by extracellular collagen fibrils in the corneal stroma and the highly concentrated crystallin proteins in the cytoplasm of the lens fiber cells. Transparency is a result of short-range order in the spatial arrangement of corneal collagen fibrils and lens crystallins, generated in part by post-translational modifications (PTMs). However, while corneal collagen is remodeled continuously and replaced, lens crystallins are very long-lived and are not replaced and so accumulate PTMs over a lifetime. Eventually, a tipping point is reached when protein aggregation results in increased light scatter, inevitably leading to the iconic protein condensation-based disease, age-related cataract (ARC). Cataracts account for 50% of vision impairment worldwide, affecting far more people than other well-known protein aggregation-based diseases. However, because accumulation of crystallin PTMs begins before birth and long before ARC presents, we postulate that the lens protein PTMs contribute to a "cataractogenic load" that not only increases with age but also has protective effects on optical function by stabilizing lens crystallins until a tipping point is reached. In this review, we highlight decades of experimental findings that support the potential for PTMs to be protective during normal development. We hypothesize that ARC is preventable by protecting the biochemical and biophysical properties of lens proteins needed to maintain transparency, refraction, and optical function.
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Affiliation(s)
- Roy A Quinlan
- Department of Biosciences, Durham University, South Road Science Site, Durham, United Kingdom; Department of Biological Structure, University of Washington, Seattle, Washington, USA.
| | - John I Clark
- Department of Biological Structure, University of Washington, Seattle, Washington, USA.
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