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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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2
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Giblin FJ, Anderson DMG, Han J, Rose KL, Wang Z, Schey KL. Acceleration of age-induced proteolysis in the guinea pig lens nucleus by in vivo exposure to hyperbaric oxygen: A mass spectrometry analysis. Exp Eye Res 2021; 210:108697. [PMID: 34233175 PMCID: PMC8429224 DOI: 10.1016/j.exer.2021.108697] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/31/2021] [Revised: 06/21/2021] [Accepted: 06/30/2021] [Indexed: 11/19/2022]
Abstract
Hyperbaric oxygen (HBO) treatment of animals or ocular lenses in culture recapitulates many molecular changes observed in human age-related nuclear cataract. The guinea pig HBO model has been one of the best examples of such treatment leading to dose-dependent development of lens nuclear opacities. In this study, complimentary mass spectrometry methods were employed to examine protein truncation after HBO treatment of aged guinea pigs. Quantitative liquid chromatography-mass spectrometry (LC-MS) analysis of the membrane fraction of guinea pig lenses showed statistically significant increases in aquaporin-0 (AQP0) C-terminal truncation, consistent with previous reports of accelerated loss of membrane and cytoskeletal proteins. In addition, imaging mass spectrometry (IMS) analysis spatially mapped the acceleration of age-related αA-crystallin truncation in the lens nucleus. The truncation sites in αA-crystallin closely match those observed in human lenses with age. Taken together, our results suggest that HBO accelerates the normal lens aging process and leads to nuclear cataract.
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Affiliation(s)
- Frank J Giblin
- Eye Research Institute, Oakland University, Rochester, MI, 48309, USA
| | - David M G Anderson
- Department of Biochemistry and Mass Spectrometry Research Center, Vanderbilt University, Nashville, TN, 37242, USA
| | - Jun Han
- Genome BC Proteomics Centre, University of Victoria, Victoria, British Columbia, Canada
| | - Kristie L Rose
- Department of Biochemistry and Mass Spectrometry Research Center, Vanderbilt University, Nashville, TN, 37242, USA
| | - Zhen Wang
- Department of Biochemistry and Mass Spectrometry Research Center, Vanderbilt University, Nashville, TN, 37242, USA
| | - Kevin L Schey
- Department of Biochemistry and Mass Spectrometry Research Center, Vanderbilt University, Nashville, TN, 37242, USA.
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3
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Wang L, Zhang L, Gong X, Fu J, Gan Y, Hou M, Nie Q, Xiang J, Xiao Y, Wang Y, Zheng S, Yang L, Chen H, Xiang M, Liu Y, Li DW. PP-1β and PP-2Aα modulate cAMP response element-binding protein (CREB) functions in aging control and stress response through de-regulation of αB-crystallin gene and p300-p53 signaling axis. Aging Cell 2021; 20:e13458. [PMID: 34425033 PMCID: PMC8441381 DOI: 10.1111/acel.13458] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/04/2020] [Revised: 07/04/2021] [Accepted: 08/06/2021] [Indexed: 02/06/2023] Open
Abstract
The function of the transcription factor, cAMP response element‐binding protein (CREB), is activated through S133 phosphorylation by PKA and others. Regarding its inactivation, it is not well defined. cAMP response element‐binding protein plays an essential role in promoting cell proliferation, neuronal survival and the synaptic plasticity associated with long‐term memory. Our recent studies have shown that CREB is an important player in mediating stress response. Here, we have demonstrated that CREB regulates aging process through suppression of αB‐crystallin and activation of the p300‐p53‐Bak/Bax signaling axis. First, we determined that two specific protein phosphatases, PP‐1β and PP‐2Aα, can inactivate CREB through S133 dephosphorylation. Subsequently, we demonstrated that cells expressing the S133A‐CREB, a mutant mimicking constant dephosphorylation at S133, suppress CREB functions in aging control and stress response. Mechanistically, S133A‐CREB not only significantly suppresses CREB control of αB‐crystallin gene, but also represses CREB‐mediated activation of p53 acetylation and downstream Bak/Bax genes. cAMP response element‐binding protein suppression of αB‐crystallin and its activation of p53 acetylation are major molecular events observed in human cataractous lenses of different age groups. Together, our results demonstrate that PP‐1β and PP‐2Aα modulate CREB functions in aging control and stress response through de‐regulation of αB‐crystallin gene and p300‐p53‐Bax/Bak signaling axis, which regulates human cataractogenesis in the aging lens.
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Affiliation(s)
- Ling Wang
- The State Key Laboratory of Ophthalmology Zhongshan Ophthalmic Center Sun Yat‐sen University Guangzhou China
| | - Lan Zhang
- The State Key Laboratory of Ophthalmology Zhongshan Ophthalmic Center Sun Yat‐sen University Guangzhou China
| | - Xiao‐Dong Gong
- The State Key Laboratory of Ophthalmology Zhongshan Ophthalmic Center Sun Yat‐sen University Guangzhou China
| | - Jia‐Ling Fu
- The State Key Laboratory of Ophthalmology Zhongshan Ophthalmic Center Sun Yat‐sen University Guangzhou China
| | - Yu‐Wen Gan
- The State Key Laboratory of Ophthalmology Zhongshan Ophthalmic Center Sun Yat‐sen University Guangzhou China
| | - Min Hou
- The State Key Laboratory of Ophthalmology Zhongshan Ophthalmic Center Sun Yat‐sen University Guangzhou China
| | - Qian Nie
- The State Key Laboratory of Ophthalmology Zhongshan Ophthalmic Center Sun Yat‐sen University Guangzhou China
| | - Jia‐Wen Xiang
- The State Key Laboratory of Ophthalmology Zhongshan Ophthalmic Center Sun Yat‐sen University Guangzhou China
| | - Yuan Xiao
- The State Key Laboratory of Ophthalmology Zhongshan Ophthalmic Center Sun Yat‐sen University Guangzhou China
| | - Yan Wang
- The State Key Laboratory of Ophthalmology Zhongshan Ophthalmic Center Sun Yat‐sen University Guangzhou China
| | - Shu‐Yu Zheng
- The State Key Laboratory of Ophthalmology Zhongshan Ophthalmic Center Sun Yat‐sen University Guangzhou China
| | - Lan Yang
- The State Key Laboratory of Ophthalmology Zhongshan Ophthalmic Center Sun Yat‐sen University Guangzhou China
| | - Huimin Chen
- The State Key Laboratory of Ophthalmology Zhongshan Ophthalmic Center Sun Yat‐sen University Guangzhou China
| | - Meng‐Qing Xiang
- The State Key Laboratory of Ophthalmology Zhongshan Ophthalmic Center Sun Yat‐sen University Guangzhou China
| | - Yizhi Liu
- The State Key Laboratory of Ophthalmology Zhongshan Ophthalmic Center Sun Yat‐sen University Guangzhou China
| | - David Wan‐Cheng Li
- The State Key Laboratory of Ophthalmology Zhongshan Ophthalmic Center Sun Yat‐sen University Guangzhou China
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4
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Gong XD, Wang Y, Hu XB, Zheng SY, Fu JL, Nie Q, Wang L, Hou M, Xiang JW, Xiao Y, Gao Q, Bai YY, Liu YZ, Li DWC. Aging-dependent loss of GAP junction proteins Cx46 and Cx50 in the fiber cells of human and mouse lenses accounts for the diminished coupling conductance. Aging (Albany NY) 2021; 13:17568-17591. [PMID: 34226295 PMCID: PMC8312418 DOI: 10.18632/aging.203247] [Citation(s) in RCA: 6] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/09/2021] [Accepted: 06/12/2021] [Indexed: 06/13/2023]
Abstract
The homeostasis of the ocular lens is maintained by a microcirculation system propagated through gap junction channels. It is well established that the intercellular communications of the lens become deteriorative during aging. However, the molecular basis for this change in human lenses has not been well defined. Here, we present evidence to show that over 90% of Cx46 and Cx50 are lost in the fiber cells of normal human lenses aged 50 and above. From transparent to cataractous lenses, while Cx43 was upregulated, both Cx46 and Cx50 were significantly down-regulated in the lens epithelia. During aging of mouse lenses, Cx43 remained unchanged, but both Cx46 and Cx50 were significantly downregulated. Under oxidative stress treatment, mouse lenses develop in vitro cataractogenesis. Associated with this process, Cx43 was significantly upregulated, in contrast, Cx46 and Cx50 were sharply downregulated. Together, our results for the first time reveal that downregulation in Cx46 and Cx50 levels appears to be the major reason for the diminished coupling conductance, and the aging-dependent loss of Cx46 and Cx50 promotes senile cataractogenesis.
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Affiliation(s)
- Xiao-Dong Gong
- The State Key Laboratory of Ophthalmology, Zhongshan Ophthalmic Center, Sun Yat-Sen University, Guangzhou, Guangdong 510230, China
| | - Yan Wang
- The State Key Laboratory of Ophthalmology, Zhongshan Ophthalmic Center, Sun Yat-Sen University, Guangzhou, Guangdong 510230, China
| | - Xue-Bin Hu
- The State Key Laboratory of Ophthalmology, Zhongshan Ophthalmic Center, Sun Yat-Sen University, Guangzhou, Guangdong 510230, China
| | - Shu-Yu Zheng
- The State Key Laboratory of Ophthalmology, Zhongshan Ophthalmic Center, Sun Yat-Sen University, Guangzhou, Guangdong 510230, China
| | - Jia-Ling Fu
- The State Key Laboratory of Ophthalmology, Zhongshan Ophthalmic Center, Sun Yat-Sen University, Guangzhou, Guangdong 510230, China
| | - Qian Nie
- The State Key Laboratory of Ophthalmology, Zhongshan Ophthalmic Center, Sun Yat-Sen University, Guangzhou, Guangdong 510230, China
| | - Ling Wang
- The State Key Laboratory of Ophthalmology, Zhongshan Ophthalmic Center, Sun Yat-Sen University, Guangzhou, Guangdong 510230, China
| | - Min Hou
- The State Key Laboratory of Ophthalmology, Zhongshan Ophthalmic Center, Sun Yat-Sen University, Guangzhou, Guangdong 510230, China
| | - Jia-Wen Xiang
- The State Key Laboratory of Ophthalmology, Zhongshan Ophthalmic Center, Sun Yat-Sen University, Guangzhou, Guangdong 510230, China
| | - Yuan Xiao
- The State Key Laboratory of Ophthalmology, Zhongshan Ophthalmic Center, Sun Yat-Sen University, Guangzhou, Guangdong 510230, China
| | - Qian Gao
- The State Key Laboratory of Ophthalmology, Zhongshan Ophthalmic Center, Sun Yat-Sen University, Guangzhou, Guangdong 510230, China
| | - Yue-Yue Bai
- The State Key Laboratory of Ophthalmology, Zhongshan Ophthalmic Center, Sun Yat-Sen University, Guangzhou, Guangdong 510230, China
| | - Yi-Zhi Liu
- The State Key Laboratory of Ophthalmology, Zhongshan Ophthalmic Center, Sun Yat-Sen University, Guangzhou, Guangdong 510230, China
| | - David Wan-Cheng Li
- The State Key Laboratory of Ophthalmology, Zhongshan Ophthalmic Center, Sun Yat-Sen University, Guangzhou, Guangdong 510230, China
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5
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Rocha MA, Sprague-Piercy MA, Kwok AO, Roskamp KW, Martin RW. Chemical Properties Determine Solubility and Stability in βγ-Crystallins of the Eye Lens. Chembiochem 2021; 22:1329-1346. [PMID: 33569867 PMCID: PMC8052307 DOI: 10.1002/cbic.202000739] [Citation(s) in RCA: 17] [Impact Index Per Article: 5.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/26/2020] [Revised: 12/17/2020] [Indexed: 11/10/2022]
Abstract
βγ-Crystallins are the primary structural and refractive proteins found in the vertebrate eye lens. Because crystallins are not replaced after early eye development, their solubility and stability must be maintained for a lifetime, which is even more remarkable given the high protein concentration in the lens. Aggregation of crystallins caused by mutations or post-translational modifications can reduce crystallin protein stability and alter intermolecular interactions. Common post-translational modifications that can cause age-related cataracts include deamidation, oxidation, and tryptophan derivatization. Metal ion binding can also trigger reduced crystallin solubility through a variety of mechanisms. Interprotein interactions are critical to maintaining lens transparency: crystallins can undergo domain swapping, disulfide bonding, and liquid-liquid phase separation, all of which can cause opacity depending on the context. Important experimental techniques for assessing crystallin conformation in the absence of a high-resolution structure include dye-binding assays, circular dichroism, fluorescence, light scattering, and transition metal FRET.
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Affiliation(s)
- Megan A. Rocha
- Department of Chemistry, University of California, Irvine, 1102 Natural Sciences 2, Irvine, CA 92697-2025 (USA)
| | - Marc A. Sprague-Piercy
- Department of Molecular Biology and Biochemistry, University of California Irvine, 3205 McGaugh Hall, Irvine, CA 92697-2525
| | - Ashley O. Kwok
- Department of Chemistry, University of California, Irvine, 1102 Natural Sciences 2, Irvine, CA 92697-2025 (USA)
| | - Kyle W. Roskamp
- Department of Chemistry, University of California, Irvine, 1102 Natural Sciences 2, Irvine, CA 92697-2025 (USA)
| | - Rachel W. Martin
- Department of Chemistry, University of California, Irvine, 1102 Natural Sciences 2, Irvine, CA 92697-2025 (USA)
- Department of Molecular Biology and Biochemistry, University of California Irvine, 3205 McGaugh Hall, Irvine, CA 92697-2525
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Tau Is Truncated in Five Regions of the Normal Adult Human Brain. Int J Mol Sci 2021; 22:ijms22073521. [PMID: 33805376 PMCID: PMC8036332 DOI: 10.3390/ijms22073521] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/10/2020] [Revised: 03/24/2021] [Accepted: 03/25/2021] [Indexed: 01/01/2023] Open
Abstract
The truncation of Tau is thought to be important in promoting aggregation, with this feature characterising the pathology of dementias such as Alzheimer disease. Antibodies to the C-terminal and N-terminal regions of Tau were employed to examine Tau cleavage in five human brain regions: the entorhinal cortex, prefrontal cortex, motor cortex, hippocampus, and cerebellum. These were obtained from normal subjects ranging in age from 18 to 104 years. Tau fragments of approximately 40 kDa and 45 kDa with an intact N-terminus retained were found in soluble and insoluble brain fractions. In addition, smaller C-terminal Tau fragments ranging in mass from 17 kDa to 25 kDa were also detected. These findings are consistent with significant Tau cleavage taking place in brain regions from 18 years onwards. It appears that site-specific cleavage of Tau is widespread in the normal human brain, and that large Tau fragments that contain the N-terminus, as well as shorter C-terminal Tau fragments, are present in brain cells across the age range.
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7
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Liu F, Fu J, Wang L, Nie Q, Luo Z, Hou M, Yang Y, Gong X, Wang Y, Xiao Y, Xiang J, Hu X, Zhang L, Wu M, Chen W, Cheng B, Luo L, Zhang X, Liu X, Zheng D, Huang S, Liu Y, Li DW. Molecular signature for senile and complicated cataracts derived from analysis of sumoylation enzymes and their substrates in human cataract lenses. Aging Cell 2020; 19:e13222. [PMID: 32827359 PMCID: PMC7576240 DOI: 10.1111/acel.13222] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/15/2020] [Revised: 07/14/2020] [Accepted: 07/26/2020] [Indexed: 11/30/2022] Open
Abstract
Sumoylation is one of the key regulatory mechanisms in eukaryotes. Our previous studies reveal that sumoylation plays indispensable roles during lens differentiation (Yan et al. 2010. Proc Natl Acad Sci USA. 107:21034-21039; Gong et al. 2014. Proc Natl Acad Sci USA. 111:5574-5579). Whether sumoylation is implicated in cataractogenesis, a disease largely derived from aging, remains elusive. In the present study, we have examined the changing patterns of the sumoylation ligases and de-sumoylation enzymes (SENPs) and their substrates including Pax6 and other proteins in cataractous lenses of different age groups from 50 to 90 years old. It is found that compared with normal lenses, sumoylation ligases 1 and 3, de-sumoylation enzymes SENP3/7/8, and p46 Pax6 are clearly increased. In contrast, Ubc9 is significantly decreased. Among different cataract patients from 50s to 70s, male patients express more sumoylation enzymes and p46 Pax6. Ubc9 and SENP6 display age-dependent increase. The p46 Pax6 displays age-dependent decrease in normal lens, remains relatively stable in senile cataracts but becomes di-sumoylated in complicated cataracts. In contrast, sumoylation of p32 Pax6 is observed in senile cataracts and increases its stability. Treatment of rat lenses with oxidative stress increases Pax6 expression without sumoylation but promotes apoptosis. Thus, our results show that the changing patterns in Ubc9, SENP6, and Pax6 levels can act as molecular markers for senile cataract and the di-sumoylated p46 Pax6 for complicated cataract. Together, our results reveal the presence of molecular signature for both senile and complicated cataracts. Moreover, our study indicates that sumoylation is implicated in control of aging and cataractogenesis.
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Affiliation(s)
- Fang‐Yuan Liu
- State Key Laboratory of Ophthalmology Zhongshan Ophthalmic CenterSun Yat‐Sen University Guangzhou China
| | - Jia‐Ling Fu
- State Key Laboratory of Ophthalmology Zhongshan Ophthalmic CenterSun Yat‐Sen University Guangzhou China
| | - Ling Wang
- State Key Laboratory of Ophthalmology Zhongshan Ophthalmic CenterSun Yat‐Sen University Guangzhou China
| | - Qian Nie
- State Key Laboratory of Ophthalmology Zhongshan Ophthalmic CenterSun Yat‐Sen University Guangzhou China
| | - Zhongwen Luo
- State Key Laboratory of Ophthalmology Zhongshan Ophthalmic CenterSun Yat‐Sen University Guangzhou China
| | - Min Hou
- State Key Laboratory of Ophthalmology Zhongshan Ophthalmic CenterSun Yat‐Sen University Guangzhou China
| | - Yuan Yang
- State Key Laboratory of Ophthalmology Zhongshan Ophthalmic CenterSun Yat‐Sen University Guangzhou China
| | - Xiao‐Dong Gong
- State Key Laboratory of Ophthalmology Zhongshan Ophthalmic CenterSun Yat‐Sen University Guangzhou China
| | - Yan Wang
- State Key Laboratory of Ophthalmology Zhongshan Ophthalmic CenterSun Yat‐Sen University Guangzhou China
| | - Yuan Xiao
- State Key Laboratory of Ophthalmology Zhongshan Ophthalmic CenterSun Yat‐Sen University Guangzhou China
| | - Jiawen Xiang
- State Key Laboratory of Ophthalmology Zhongshan Ophthalmic CenterSun Yat‐Sen University Guangzhou China
| | - Xuebin Hu
- State Key Laboratory of Ophthalmology Zhongshan Ophthalmic CenterSun Yat‐Sen University Guangzhou China
| | - Lan Zhang
- State Key Laboratory of Ophthalmology Zhongshan Ophthalmic CenterSun Yat‐Sen University Guangzhou China
| | - Mingxing Wu
- State Key Laboratory of Ophthalmology Zhongshan Ophthalmic CenterSun Yat‐Sen University Guangzhou China
| | - Weirong Chen
- State Key Laboratory of Ophthalmology Zhongshan Ophthalmic CenterSun Yat‐Sen University Guangzhou China
| | - Bing Cheng
- State Key Laboratory of Ophthalmology Zhongshan Ophthalmic CenterSun Yat‐Sen University Guangzhou China
| | - Lixia Luo
- State Key Laboratory of Ophthalmology Zhongshan Ophthalmic CenterSun Yat‐Sen University Guangzhou China
| | - Xinyu Zhang
- State Key Laboratory of Ophthalmology Zhongshan Ophthalmic CenterSun Yat‐Sen University Guangzhou China
| | - Xialin Liu
- State Key Laboratory of Ophthalmology Zhongshan Ophthalmic CenterSun Yat‐Sen University Guangzhou China
| | - Danying Zheng
- State Key Laboratory of Ophthalmology Zhongshan Ophthalmic CenterSun Yat‐Sen University Guangzhou China
| | - Shengsong Huang
- State Key Laboratory of Ophthalmology Zhongshan Ophthalmic CenterSun Yat‐Sen University Guangzhou China
| | - Yizhi Liu
- State Key Laboratory of Ophthalmology Zhongshan Ophthalmic CenterSun Yat‐Sen University Guangzhou China
| | - David Wan‐Cheng Li
- State Key Laboratory of Ophthalmology Zhongshan Ophthalmic CenterSun Yat‐Sen University Guangzhou China
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Truscott RJW, Friedrich MG. Molecular Processes Implicated in Human Age-Related Nuclear Cataract. Invest Ophthalmol Vis Sci 2020; 60:5007-5021. [PMID: 31791064 PMCID: PMC7043214 DOI: 10.1167/iovs.19-27535] [Citation(s) in RCA: 26] [Impact Index Per Article: 6.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/21/2022] Open
Abstract
Human age-related nuclear cataract is commonly characterized by four biochemical features that involve modifications to the structural proteins that constitute the bulk of the lens: coloration, oxidation, insolubility, and covalent cross-linking. Each of these is progressive and increases as the cataract worsens. Significant progress has been made in understanding the origin of the factors that underpin the loss of lens transparency. Of these four hallmarks of cataract, it is protein-protein cross-linking that has been the most intransigent, and it is only recently, with the advent of proteomic methodology, that mechanisms are being elucidated. A diverse range of cross-linking processes involving several amino acids have been uncovered. Although other hypotheses for the etiology of cataract have been advanced, it is likely that spontaneous decomposition of the structural proteins of the lens, which do not turn over, is responsible for the age-related changes to the properties of the lens and, ultimately, for cataract. Cataract may represent the first and best characterized of a number of human age-related diseases where spontaneous protein modification leads to ongoing deterioration and, ultimately, a loss of tissue function.
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Affiliation(s)
- Roger J W Truscott
- Illawarra Health and Medical Research Institute, University of Wollongong, Australia
| | - Michael G Friedrich
- Illawarra Health and Medical Research Institute, University of Wollongong, Australia
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Schey KL, Wang Z, Friedrich MG, Garland DL, Truscott RJW. Spatiotemporal changes in the human lens proteome: Critical insights into long-lived proteins. Prog Retin Eye Res 2019; 76:100802. [PMID: 31704338 DOI: 10.1016/j.preteyeres.2019.100802] [Citation(s) in RCA: 27] [Impact Index Per Article: 5.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/05/2019] [Revised: 10/24/2019] [Accepted: 10/30/2019] [Indexed: 12/15/2022]
Abstract
The ocular lens is a unique tissue that contains an age gradient of cells and proteins ranging from newly differentiated cells containing newly synthesized proteins to cells and proteins that are as old as the organism. Thus, the ocular lens is an excellent model for studying long-lived proteins (LLPs) and the effects of aging and post-translational modifications on protein structure and function. Given the architecture of the lens, with young fiber cells in the outer cortex and the oldest cells in the lens nucleus, spatially-resolved studies provide information on age-specific protein changes. In this review, experimental strategies and proteomic methods that have been used to examine age-related and cataract-specific changes to the human lens proteome are described. Measured spatio-temporal changes in the human lens proteome are summarized and reveal a highly consistent, time-dependent set of modifications observed in transparent human lenses. Such measurements have led to the discovery of cataract-specific modifications and the realization that many animal systems are unsuitable to study many of these modifications. Mechanisms of protein modifications such as deamidation, racemization, truncation, and protein-protein crosslinking are presented and the implications of such mechanisms for other long-lived proteins in other tissues are discussed in the context of age-related neurological diseases. A comprehensive understanding of LLP modifications will enhance our ability to develop new therapies for the delay, prevention or reversal of age-related diseases.
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Affiliation(s)
- Kevin L Schey
- Department of Biochemistry, Vanderbilt University, USA.
| | - Zhen Wang
- Department of Biochemistry, Vanderbilt University, USA
| | - Michael G Friedrich
- Illawarra Health and Medical Research Institute, University of Wollongong, Australia
| | | | - Roger J W Truscott
- Illawarra Health and Medical Research Institute, University of Wollongong, Australia
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10
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Wang Z, Friedrich MG, Truscott RJW, Schey KL. Cleavage C-terminal to Asp leads to covalent crosslinking of long-lived human proteins. BIOCHIMICA ET BIOPHYSICA ACTA-PROTEINS AND PROTEOMICS 2019; 1867:831-839. [PMID: 31226490 DOI: 10.1016/j.bbapap.2019.06.009] [Citation(s) in RCA: 21] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/18/2019] [Revised: 05/29/2019] [Accepted: 06/16/2019] [Indexed: 01/27/2023]
Abstract
With age, long-lived proteins in the human body deteriorate, which can have consequences both for aging and disease. The aging process is often associated with the formation of covalently crosslinked proteins. Currently our knowledge of the mechanism of formation of these crosslinks is limited. In this study, proteomics was used to characterize sites of covalent protein-protein crosslinking and identify a novel mechanism of protein-protein crosslinking in the adult human lens. In this mechanism, Lys residues are crosslinked to C-terminal Asp residues that are formed by non-enzymatic protein truncation. Ten different crosslinks were identified in major lens proteins such as αA-crystallin, αB-crystallin and AQP0. Crosslinking in AQP0 increased significantly with age and also increased significantly in cataract lenses compared with normal lenses. Using model peptides, a mechanism of formation of the Lys-Asp crosslink was elucidated. The mechanism involves spontaneous peptide cleavage on the C-terminal side of Asp residues which can take place in the pH range 5-7.4. Cleavage appears to involve attack by the side chain carboxyl group on the adjacent peptide bond, resulting in the formation of a C-terminal Asp anhydride. This anhydride intermediate can then either react with water to form Asp, or with a nucleophile, such as a free amine group to form a crosslink. If an ε-amino group of Lys or an N-terminal amine group attacks the anhydride, a covalent protein-protein crosslink will be formed. This bi-phasic mechanism represents the first report to link two spontaneous events: protein cleavage and crosslinking that are characteristic of long-lived proteins.
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Affiliation(s)
- Zhen Wang
- Department of Biochemistry and Mass Spectrometry Research Center, Vanderbilt University School of Medicine, Nashville, TN, USA
| | - Michael G Friedrich
- Illawarra Health and Medical Research Institute, University of Wollongong, Wollongong, NSW 2522, Australia
| | - Roger J W Truscott
- Illawarra Health and Medical Research Institute, University of Wollongong, Wollongong, NSW 2522, Australia.
| | - Kevin L Schey
- Department of Biochemistry and Mass Spectrometry Research Center, Vanderbilt University School of Medicine, Nashville, TN, USA.
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11
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Can the Fact That Myelin Proteins Are Old and Break down Explain the Origin of Multiple Sclerosis in Some People? J Clin Med 2018; 7:jcm7090281. [PMID: 30223497 PMCID: PMC6162792 DOI: 10.3390/jcm7090281] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/11/2018] [Revised: 09/11/2018] [Accepted: 09/12/2018] [Indexed: 01/01/2023] Open
Abstract
Recent discoveries may change the way that multiple sclerosis (MS) is viewed, particularly with regard to the reasons for the untoward immune response. The fact that myelin proteins are long-lived, and that by the time we are adults, they are extensively degraded, alters our perspective on the reasons for the onset of autoimmunity and the origin of MS. For example, myelin basic protein (MBP) from every human brain past the age of 20 years, is so greatly modified, that it is effectively a different protein from the one that was laid down in childhood. Since only a subset of people with such degraded MBP develop MS, a focus on understanding the mechanism of immune responses to central nervous system (CNS) antigens and cerebral immune tolerance appear to be worthwhile avenues to explore. In accord with this, it will be productive to examine why all people, whose brains contain large quantities of a "foreign antigen", do not develop MS. Importantly for the potential causation of MS, MBP from MS patients breaks down differently from the MBP in aged controls. If the novel structures formed in these MS-specific regions are particularly antigenic, it could help explain the origin of MS. If verified, these findings could provide an avenue for the rational synthesis of drugs to prevent and treat MS.
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Old Proteins in Man: A Field in its Infancy. Trends Biochem Sci 2016; 41:654-664. [PMID: 27426990 DOI: 10.1016/j.tibs.2016.06.004] [Citation(s) in RCA: 70] [Impact Index Per Article: 8.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/06/2016] [Revised: 06/03/2016] [Accepted: 06/08/2016] [Indexed: 12/12/2022]
Abstract
It has only recently been appreciated that the human body contains many long-lived proteins (LLPs). Their gradual degradation over time contributes to human aging and probably also to a range of age-related disorders. Indeed, the role of progressive damage of proteins in aging may be indicated by the fact that many neurological diseases do not appear until after middle age. A major factor responsible for the deterioration of old proteins is the spontaneous breakdown of susceptible amino acid residues resulting in racemization, truncation, deamidation, and crosslinking. When proteins decompose in this way, their structures and functions may be altered and novel epitopes can be formed that can induce an autoimmune response.
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Lyons B, Kwan AH, Truscott RJ. Spontaneous cleavage of proteins at serine and threonine is facilitated by zinc. Aging Cell 2016; 15:237-44. [PMID: 26751411 PMCID: PMC4783340 DOI: 10.1111/acel.12428] [Citation(s) in RCA: 18] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 10/25/2015] [Indexed: 11/29/2022] Open
Abstract
Old proteins are widely distributed in the body. Over time, they deteriorate and many spontaneous reactions, for example isomerisation of Asp and Asn, can be replicated by incubation of peptides under physiological conditions. One of the signatures of long‐lived proteins that has proven to be difficult to replicate in vitro is cleavage on the N‐terminal side of Ser residues, and this is important since cleavage at Ser, and also Thr, has been observed in a number of human proteins. In this study, the autolysis of Ser‐ and Thr‐containing peptides was investigated with particular reference to discovering factors that promote cleavage adjacent to Ser/Thr at neutral pH. It was found that zinc catalyses cleavage of the peptide bond on the N‐terminal side of Ser residues and further that this process is markedly accelerated if a His residue is adjacent to the Ser. NMR analysis indicated that the imidazole group co‐ordinates zinc and that once zinc is co‐ordinated, it can polarize the carbonyl group of the peptide bond in a manner analogous to that observed in the active site of the metalloexopeptidase, carboxypeptidase A. The hydroxyl side chain of Ser/Thr is then able to cleave the adjacent peptide bond. These observations enable an understanding of the origin of common truncations observed in long‐lived proteins, for example truncation on the N‐terminal side of Ser 8 in Abeta, Ser 19 in alpha B crystallin and Ser 66 in alpha A crystallin. The presence of zinc may therefore significantly affect the long‐term stability of cellular proteins.
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Affiliation(s)
- Brian Lyons
- Illawarra Health and Medical Research Institute University of Wollongong Northfields Ave Wollongong NSW 2522 Australia
- Save Sight Institute University of Sydney Sydney Eye Hospital 8 Macquarie St Sydney NSW 2000 Australia
| | - Ann H. Kwan
- School of Molecular Bioscience University of Sydney Sydney NSW 2006 Australia
| | - Roger J.W. Truscott
- Illawarra Health and Medical Research Institute University of Wollongong Northfields Ave Wollongong NSW 2522 Australia
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14
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Truscott RJW, Friedrich MG. The etiology of human age-related cataract. Proteins don't last forever. Biochim Biophys Acta Gen Subj 2015; 1860:192-8. [PMID: 26318017 DOI: 10.1016/j.bbagen.2015.08.016] [Citation(s) in RCA: 85] [Impact Index Per Article: 9.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/24/2015] [Revised: 08/19/2015] [Accepted: 08/24/2015] [Indexed: 11/17/2022]
Abstract
BACKGROUND It is probable that the great majority of human cataract results from the spontaneous decomposition of long-lived macromolecules in the human lens. Breakdown/reaction of long-lived proteins is of primary importance and recent proteomic analysis has enabled the identification of the particular crystallins, and their exact sites of amino acid modification. SCOPE OF REVIEW Analysis of proteins from cataractous lenses revealed that there are sites on some structural proteins that show a consistently greater degree of deterioration than age-matched normal lenses. MAJOR CONCLUSIONS The most abundant posttranslational modification of aged lens proteins is racemization. Deamidation, truncation and crosslinking, each arising from the spontaneous breakdown of susceptible amino acids within proteins, are also present. Fundamental to an understanding of nuclear cataract etiology, it is proposed that once a certain degree of modification at key sites occurs, that protein-protein interactions are disrupted and lens opacification ensues. GENERAL SIGNIFICANCE Since long-lived proteins are now recognized to be present in many other sites of the body, such as the brain, the information gleaned from detailed analyses of degraded proteins from aged lenses will apply more widely to other age-related human diseases. This article is part of a Special Issue entitled Crystallin Biochemistry in Health and Disease.
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Affiliation(s)
- Roger J W Truscott
- Illawarra Health and Medical Research Institute, University of Wollongong, Wollongong, NSW, 2522, Australia.
| | - Michael G Friedrich
- Illawarra Health and Medical Research Institute, University of Wollongong, Wollongong, NSW, 2522, Australia
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15
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Su SP, Song X, Xavier D, Aquilina JA. Age-related cleavages of crystallins in human lens cortical fiber cells generate a plethora of endogenous peptides and high molecular weight complexes. Proteins 2015; 83:1878-86. [PMID: 26238763 DOI: 10.1002/prot.24872] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/12/2015] [Revised: 07/16/2015] [Accepted: 07/29/2015] [Indexed: 11/07/2022]
Abstract
Low molecular weight peptides derived from the breakdown of crystallins have been reported in adult human lenses. The proliferation of these LMW peptides coincides with the earliest stages of cataract formation, suggesting that the protein cleavages involved may contribute to the aggregation and insolubilization of crystallins. This study reports the identification of 238 endogenous LMW crystallin peptides from the cortical extracts of four human lenses representing young, middle and old-age human lenses. Analysis of the peptide terminal amino acids showed that Lys and Arg were situated at the C-terminus with significantly higher frequency compared to other residues, suggesting that trypsin-like proteolysis may be active in the lens cortical fiber cells. Selected reaction monitoring analysis of an endogenous αA-crystallin peptide (αA(57-65)) showed that the concentration of this peptide in the human lens increased gradually to middle age, after which the rate of αA(57-65) formation escalated significantly. Using 2D gel electrophoresis/nanoLC-ESI-MS/MS, 12 protein complexes of 40-150 kDa consisting of multiple crystallin components were characterized from the water soluble cortical extracts of an adult human lens. The detection of these protein complexes suggested the possibility of crystallin cross-linking, with these complexes potentially acting to stabilize degraded crystallins by sequestration into water soluble complexes.
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Affiliation(s)
- Shih-Ping Su
- Illawarra Health and Medical Research Institute, School of Biological Sciences, Faculty of Science, Medicine and Health, University of Wollongong, Wollongong, New South Wales, 2522, Australia
| | - Xiaomin Song
- Australian Proteome Analysis Facility, Macquarie University, Sydney, New South Wales, 2109, Australia
| | - Dylan Xavier
- Australian Proteome Analysis Facility, Macquarie University, Sydney, New South Wales, 2109, Australia
| | - J Andrew Aquilina
- Illawarra Health and Medical Research Institute, School of Biological Sciences, Faculty of Science, Medicine and Health, University of Wollongong, Wollongong, New South Wales, 2522, Australia
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16
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Fujii N, Takata T, Fujii N, Aki K. Isomerization of aspartyl residues in crystallins and its influence upon cataract. Biochim Biophys Acta Gen Subj 2015; 1860:183-91. [PMID: 26275494 DOI: 10.1016/j.bbagen.2015.08.001] [Citation(s) in RCA: 42] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/03/2015] [Revised: 07/25/2015] [Accepted: 08/03/2015] [Indexed: 12/26/2022]
Abstract
BACKGROUND Age-related cataracts, which probably form due to insolubilization of lens proteins, can lead to loss of vision. Although the exact reason is unknown, lens protein aggregation may be triggered by increases in PTMs such as D-β-, L-β- and D-α-Asp isomers. These isomers have been observed in aged lens; however, there have been few quantitative and site-specific studies owing to the lack of a quick and precise method for distinguishing between D- and L-Asp in a peptide or protein. SCOPE OF REVIEW We describe a new method for detecting peptides containing Asp isomers at individual sites in any protein by using an LC-MS/MS system combined with commercial enzymes that specifically react with different isomers. We also summarize current data on the effect of Asp isomerization on lens crystallins. MAJOR CONCLUSIONS The new technique enabled the analysis of isomers of Asp residues in lens proteins precisely and quickly. An extensive proportion of Asp isomerization was observed at all Asp sites of crystallins in the insoluble fraction of aged lens. In addition, d-amino acid substitutions in crystallin-mimic peptides showed altered structural formation and function. These results indicate that isomerization of Asp residues affects the stability, structure and inter-subunit interaction of lens crystallins, which will induce crystallin aggregation and insolubilization, disrupt the associated functions, and ultimately contribute to the onset of senile cataract formation. GENERAL SIGNIFICANCE The mechanism underlying the onset of age-related diseases may involve isomerization, whereby D-amino acids are incorporated in the L-amino acid world of life. This article is part of a Special Issue entitled Crystallin Biochemistry in Health and Disease.
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Affiliation(s)
- Noriko Fujii
- Research Reactor Institute, Kyoto University, Kumatori, Osaka 590-0494, Japan.
| | - Takumi Takata
- Research Reactor Institute, Kyoto University, Kumatori, Osaka 590-0494, Japan
| | - Norihiko Fujii
- Radioisotope Research Center, Teikyo University, Kaga Itabashi-ku, Tokyo 173-8605, Japan
| | - Kenzo Aki
- Faculty of Pharmaceutical Sciences, Himeji Dokkyo University, Kamiohno, Himeji 670-8524, Japan
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Raju M, Mooney BP, Thakkar KM, Giblin FJ, Schey KL, Sharma KK. Role of αA-crystallin-derived αA66-80 peptide in guinea pig lens crystallin aggregation and insolubilization. Exp Eye Res 2015; 132:151-60. [PMID: 25639202 DOI: 10.1016/j.exer.2015.01.024] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/24/2014] [Revised: 01/26/2015] [Accepted: 01/28/2015] [Indexed: 11/29/2022]
Abstract
Earlier we reported that low molecular weight (LMW) peptides accumulate in aging human lens tissue and that among the LMW peptides, the chaperone inhibitor peptide αA66-80, derived from α-crystallin protein, is one of the predominant peptides. We showed that in vitro αA66-80 induces protein aggregation. The current study was undertaken to determine whether LMW peptides are also present in guinea pig lens tissue subjected to hyperbaric oxygen (HBO) in vivo. The nuclear opacity induced by HBO in guinea pig lens is the closest animal model for studying age-related cataract formation in humans. A LMW peptide profile by mass spectrometry showed the presence of an increased amount of LMW peptides in HBO-treated guinea pig lenses compared to age-matched controls. Interestingly, the mass spectrometric data also showed that the chaperone inhibitor peptide αA66-80 accumulates in HBO-treated guinea pig lens. Following incubation of synthetic chaperone inhibitor peptide αA66-80 with α-crystallin from guinea pig lens extracts, we observed a decreased ability of α-crystallin to inhibit the amorphous aggregation of the target protein alcohol dehydrogenase and the formation of large light scattering aggregates, similar to those we have observed with human α-crystallin and αA66-80 peptide. Further, time-lapse recordings showed that a preformed complex of α-crystallin and αA66-80 attracted additional crystallin molecules to form even larger aggregates. These results demonstrate that LMW peptide-mediated cataract development in aged human lens and in HBO-induced lens opacity in the guinea pig may have common molecular pathways.
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Affiliation(s)
- Murugesan Raju
- Department of Ophthalmology, University of Missouri-Columbia, School of Medicine, Columbia 65212, MO, USA
| | - Brian P Mooney
- Department of Biochemistry, University of Missouri-Columbia, School of Medicine, Columbia 65212, MO, USA
| | - Kavi M Thakkar
- Department of Ophthalmology, University of Missouri-Columbia, School of Medicine, Columbia 65212, MO, USA
| | - Frank J Giblin
- Eye Research Institute, Oakland University, Rochester 48309, MI, USA
| | - Kevin L Schey
- Department of Biochemistry, Vanderbilt University School of Medicine, Nashville 37232, USA
| | - K Krishna Sharma
- Department of Ophthalmology, University of Missouri-Columbia, School of Medicine, Columbia 65212, MO, USA; Department of Biochemistry, University of Missouri-Columbia, School of Medicine, Columbia 65212, MO, USA.
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Holm T, Raghavan CT, Nahomi R, Nagaraj RH, Kessel L. Effects of photobleaching on selected advanced glycation end products in the human lens. BMC Res Notes 2015; 8:5. [PMID: 25592966 PMCID: PMC4302587 DOI: 10.1186/s13104-015-0977-3] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/30/2014] [Accepted: 01/06/2015] [Indexed: 11/17/2022] Open
Abstract
Background Cataract is the leading cause of blindness, especially in the developing world. To ease access to treatment, we have proposed that cataract could be treated non-invasively by photobleaching of the chemically modified proteins responsible for cataract formation. The present study was aimed at examining the optical and biochemical effects of the proposed treatment. Methods Human donor lenses were photobleaced using a 445 nm cw laser. Lens optical quality was assessed before and after photobleaching by light transmission and scattering. The concentration of the advanced glycation end products (AGEs) pentosidine, argpyrimidine, carboxymethyllysine, hydroimidazolone was measured. Results Transmission increased and AGE-related fluorescence decreased significantly after photobleaching but no changes were observed in the concentration of the measured AGEs. Conclusions We found a significant effect of the photobleaching treatment on lens optical parameters but we could not associate the optical findings to a change in the concentration of the AGEs we measured. This finding suggests that other AGEs were responsible for the observed photobleaching of the human lens after laser treatment. The biochemical nature of the photochemical reactions associated with photobleaching remains to be elucidated.
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Affiliation(s)
- Thomas Holm
- Department of Ophthalmology, Glostrup Hospital, Ringvej 57, 2600, Glostrup, Denmark.
| | - Cibin T Raghavan
- Department of Ophthalmology & Visual Sciences, Case Western Reserve University School of Medicine, Cleveland, Ohio, USA. .,Present address: Department of Ophthalmology, University of Colorado School of Medicine, 12800 East 19th Avenue, RC-1 North 5102, Aurora, CO, 80045, USA.
| | - Rooban Nahomi
- Department of Ophthalmology & Visual Sciences, Case Western Reserve University School of Medicine, Cleveland, Ohio, USA. .,Present address: Department of Ophthalmology, University of Colorado School of Medicine, 12800 East 19th Avenue, RC-1 North 5102, Aurora, CO, 80045, USA.
| | - Ram H Nagaraj
- Department of Ophthalmology & Visual Sciences, Case Western Reserve University School of Medicine, Cleveland, Ohio, USA. .,Present address: Department of Ophthalmology, University of Colorado School of Medicine, 12800 East 19th Avenue, RC-1 North 5102, Aurora, CO, 80045, USA.
| | - Line Kessel
- Department of Ophthalmology, Glostrup Hospital, Ringvej 57, 2600, Glostrup, Denmark.
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Lyons B, Kwan AH, Truscott R. Spontaneous cyclization of polypeptides with a penultimate Asp, Asn or isoAsp at the N-terminus and implications for cleavage by aminopeptidase. FEBS J 2014; 281:2945-55. [DOI: 10.1111/febs.12833] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/20/2014] [Revised: 04/20/2014] [Accepted: 05/02/2014] [Indexed: 12/31/2022]
Affiliation(s)
- Brian Lyons
- Save Sight Institute; University of Sydney; Sydney Eye Hospital; Australia
| | - Ann H Kwan
- School of Molecular Bioscience; University of Sydney; Australia
| | - Roger Truscott
- Illawarra Health and Medical Research Institute; University of Wollongong; Australia
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20
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Wang Z, Lyons B, Truscott RJW, Schey KL. Human protein aging: modification and crosslinking through dehydroalanine and dehydrobutyrine intermediates. Aging Cell 2014; 13:226-34. [PMID: 24134651 PMCID: PMC4114717 DOI: 10.1111/acel.12164] [Citation(s) in RCA: 61] [Impact Index Per Article: 6.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 09/12/2013] [Indexed: 11/29/2022] Open
Abstract
Nonenzymatic post-translational modification (PTM) of proteins is a fundamental molecular process of aging. The combination of various modifications and their accumulation with age not only affects function, but leads to crosslinking and protein aggregation. In this study, aged human lens proteins were examined using HPLC–tandem mass spectrometry and a blind PTM search strategy. Multiple thioether modifications of Ser and Thr residues by glutathione (GSH) and its metabolites were unambiguously identified. Thirty-four of 36 sites identified on 15 proteins were found on known phosphorylation sites, supporting a mechanism involving dehydroalanine (DHA) and dehydrobutyrine (DHB) formation through β-elimination of phosphoric acid from phosphoserine and phosphothreonine with subsequent nucleophilic attack by GSH. In vitro incubations of phosphopeptides demonstrated that this process can occur spontaneously under physiological conditions. Evidence that this mechanism can also lead to protein–protein crosslinks within cells is provided where five crosslinked peptides were detected in a human cataractous lens. Nondisulfide crosslinks were identified for the first time in lens tissue between βB2- & βB2-, βA4- & βA3-, γS- & βB1-, and βA4- & βA4-crystallins and provide detailed structural information on in vivo crystallin complexes. These data suggest that phosphoserine and phosphothreonine residues represent susceptible sites for spontaneous breakdown in long-lived proteins and that DHA- and DHB-mediated protein crosslinking may be the source of the long-sought after nondisulfide protein aggregates believed to scatter light in cataractous lenses. Furthermore, this mechanism may be a common aging process that occurs in long-lived proteins of other tissues leading to protein aggregation diseases.
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Affiliation(s)
- Zhen Wang
- Department of Biochemistry and Mass Spectrometry Research Center Vanderbilt University School of Medicine Nashville TN 37232 USA
| | - Brian Lyons
- Save Sight Institute University of Sydney Sydney NSW 2000 Australia
| | - Roger J. W. Truscott
- Illawarra Health and Medical Research Institute University of Wollongong Wollongong NSW 2522 Australia
| | - Kevin L. Schey
- Department of Biochemistry and Mass Spectrometry Research Center Vanderbilt University School of Medicine Nashville TN 37232 USA
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21
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Lyons B, Jamie JF, Truscott RJW. Separate mechanisms for age-related truncation and racemisation of peptide-bound serine. Amino Acids 2013; 46:199-207. [PMID: 24306455 DOI: 10.1007/s00726-013-1619-5] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/28/2013] [Accepted: 11/03/2013] [Indexed: 12/23/2022]
Abstract
Some amino acids are particularly susceptible to degradation in long-lived proteins. Foremost among these are asparagine, aspartic acid and serine. In the case of serine residues, cleavage of the peptide bond on the N-terminal side, as well as racemisation, has been observed. To investigate the role of the hydroxyl group, and whether cleavage and racemisation are linked by a common mechanism, serine peptides with a free hydroxyl group were compared to analogous peptides where the serine hydroxyl group was methylated. Peptide bond cleavage adjacent to serine was increased when the hydroxyl group was present, and this was particularly noticeable when it was present as the hydroxide ion. Adjacent amino acid residues also had a pronounced affect on cleavage at basic pH, with the SerPro motif being especially susceptible to scission. Methylation of the serine hydroxyl group abolished truncation, as did insertion of a bulky amino acid on the N-terminal side of serine. By contrast, racemisation of serine occurred to a similar extent in both O-methylated and unmodified peptides. On the basis of these data, it appears that racemisation of Ser, and cleavage adjacent to serine, occur via separate mechanisms. Addition of water across the double bond of dehydroalanine was not detected, suggesting that this mechanism was unlikely to be responsible for conversion of L-serine to D-serine. Abstraction of the alpha proton may account for the majority of racemisation of serine in proteins.
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Affiliation(s)
- Brian Lyons
- Save Sight Institute, Sydney Eye Hospital, University of Sydney, 8 Macquarie St, Sydney, NSW, 2001, Australia,
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22
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Demarchi B, Collins M, Bergström E, Dowle A, Penkman K, Thomas-Oates J, Wilson J. New experimental evidence for in-chain amino acid racemization of serine in a model peptide. Anal Chem 2013; 85:5835-42. [PMID: 23705982 DOI: 10.1021/ac4005869] [Citation(s) in RCA: 26] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/01/2023]
Abstract
The facile racemization of protein-bound amino acids plays an important role in the aging and pathologies of living tissues, and it can be exploited for protein geochronological studies in subfossil biominerals. However, the in-chain degradation pathways of amino acids are complex and difficult to elucidate. Serine has proven to be particularly elusive, and its ability to racemize as a peptide-bound residue (like asparagine and aspartic acid) has not been demonstrated. This study investigates the patterns of degradation of a model peptide (WNSVWAW) at elevated temperatures, quantifying the extent of racemization and peptide bond hydrolysis using reverse-phase high-performance liquid chromatography (RP-HPLC) and tracking the presence of degradation products by MALDI-MS. We provide direct evidence that, under these experimental conditions, both serine and asparagine are able to undergo racemization as internally bound residues, which shows their potential for initiating protein breakdown and provides an explanation for the presence of d-enantiomers in living mammalian tissues.
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Affiliation(s)
- Beatrice Demarchi
- BioArCh, Department of Archaeology, University of York, York YO10 5DD, United Kingdom.
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Friedrich MG, Lam J, Truscott RJW. Degradation of an old human protein: age-dependent cleavage of γS-crystallin generates a peptide that binds to cell membranes. J Biol Chem 2012; 287:39012-20. [PMID: 22995907 DOI: 10.1074/jbc.m112.391565] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/13/2023] Open
Abstract
Long-lived proteins exist in a number of tissues in the human body; however, little is known about the reactions involved in their degradation over time. Lens proteins, which do not turn over, provide a useful system to examine such processes. Using a combination of Western blotting and proteomic methodology, age-related changes to a major protein, γS-crystallin, were studied. By teenage years, insoluble intact γS-crystallin was detected, indicative of protein denaturation. This was not the only change, however, because blots revealed evidence of significant cross-linking as well as cleavage of γS-crystallin in all adult lenses. Cleavage at a serine residue near the C terminus was a major reaction that caused the release of a 12-residue peptide, SPAVQSFRRIVE, which bound tightly to lens cell membranes. Several other crystallin-derived peptides with double basic residues also lodged in the cell membrane fraction. Model studies showed that once cleaved from γS-crystallin, SPAVQSFRRIVE adopts a markedly different shape from that in the intact protein. Further, the acquired helical conformation may explain why the peptide seems to affect water permeability. This observation may help explain the changes to cell membranes known to be associated with aging in human lenses. Age-related cleavage of long-lived proteins may therefore yield peptides with untoward biological activity.
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Affiliation(s)
- Michael G Friedrich
- Save Sight Institute, Macquarie Street, Sydney, New South Wales 2001, Australia
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