Molecular effects of advanced glycation end products on cell signalling pathways, ageing and pathophysiology

Preferential sites for intramolecular glucosepane cross-link formation in type I collagen: A thermodynamic study

The extracellular matrix (ECM) undergoes progressive age-related stiffening and loss of proteolytic digestibility due to an increase in concentration of advanced glycation end products (AGEs). The most abundant AGE, glucosepane, accumulates in collagen with concentrations over 100 times greater than all other AGEs. Detrimental collagen stiffening properties are believed to play a significant role in several age-related diseases such as osteoporosis and cardiovascular disease. Currently little is known of the potential location of covalently cross-linked glucosepane formation within collagen molecules; neither are there reports on how the respective cross-link sites affect the physical and biochemical properties of collagen. Using fully atomistic molecular dynamics simulations (MD) we have identified six sites where the formation of a covalent intra-molecular glucosepane cross-link within a single collagen molecule in a fibrillar environment is energetically favourable. Identification of these favourable sites enables us to align collagen cross-linking with experimentally observed changes to the ECM. For example, formation of glucosepane was found to be energetically favourable within close proximity of the Matrix Metalloproteinase-1 (MMP1) binding site, which could potentially disrupt collagen degradation.

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We conduct fully atomistic molecular dynamics simulation of fibrillar collagen.

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Glucosepane cross-link formation is energetically favourable at six positions.

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Positions identified are within key collagen biomolecule sites.

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Positioning of sites may have a significant effect on tissue function and integrity.

Rifampicin reduces advanced glycation end products and activates DAF-16 to increase lifespan in Caenorhabditis elegans

Advanced glycation end products (AGEs) are formed when glucose reacts nonenzymatically with proteins; these modifications are implicated in aging and pathogenesis of many age-related diseases including type II diabetes, atherosclerosis, and neurodegenerative disorders. Thus, pharmaceutical interventions that can reduce AGEs may delay age-onset diseases and extend lifespan. Using LC-MS(E), we show that rifampicin (RIF) reduces glycation of important cellular proteins in vivo and consequently increases lifespan in Caenorhabditis elegans by up to 60%. RIF analog rifamycin SV (RSV) possesses similar properties, while rifaximin (RMN) lacks antiglycation activity and therefore fails to affect lifespan positively. The efficacy of RIF and RSV as potent antiglycating agents may be attributed to the presence of a p-dihydroxyl moiety that can potentially undergo spontaneous oxidation to yield highly reactive p-quinone structures, a feature absent in RMN. We also show that supplementing rifampicin late in adulthood is sufficient to increase lifespan. For its effect on longevity, rifampicin requires DAF-18 (nematode PTEN) as well as JNK-1 and activates DAF-16, the FOXO homolog. Interestingly, the drug treatment modulates transcription of a different subset of DAF-16 target genes, those not controlled by the conserved Insulin-IGF-1-like signaling pathway. RIF failed to increase the lifespan of daf-16 null mutant despite reducing glycation, showing thereby that DAF-16 may not directly affect AGE formation. Together, our data suggest that the dual ability to reduce glycation in vivo and activate prolongevity processes through DAF-16 makes RIF and RSV effective lifespan-extending interventions.

Standardization and quality control in quantifying non-enzymatic oxidative protein modifications in relation to ageing and disease: Why is it important and why is it hard?

Post-translational modifications (PTM) of proteins determine the activity, stability, specificity, transportability and lifespan of a protein. Some PTM are highly specific and regulated involving various enzymatic pathways, but there are other non-enzymatic PTM (nePTM), which occur stochastically, depend on the ternary structure of proteins and can be damaging. It is often observed that inactive and abnormal proteins accumulate in old cells and tissues. The nature, site and extent of nePTM give rise to a population of that specific protein with alterations in structure and function ranging from being fully active to totally inactive molecules. Determination of the type and the amount (abundance) of nePTM is essential for establishing connection between specific protein structure and specific biological role. This article summarizes analytical demands for reliable quantification of nePTM, including requirements for the assay performance, standardization and quality control, and points to the difficulties, uncertainties and un-resolved issues.

GIT2 Acts as a Systems-Level Coordinator of Neurometabolic Activity and Pathophysiological Aging

Aging represents one of the most complicated and highly integrated somatic processes. Healthy aging is suggested to rely upon the coherent regulation of hormonal and neuronal communication between the central nervous system and peripheral tissues. The hypothalamus is one of the main structures in the body responsible for sustaining an efficient interaction between energy balance and neurological activity and therefore likely coordinates multiple systems in the aging process. We previously identified, in hypothalamic and peripheral tissues, the G protein-coupled receptor kinase interacting protein 2 (GIT2) as a stress response and aging regulator. As metabolic status profoundly affects aging trajectories, we investigated the role of GIT2 in regulating metabolic activity. We found that genomic deletion of GIT2 alters hypothalamic transcriptomic signatures related to diabetes and metabolic pathways. Deletion of GIT2 reduced whole animal respiratory exchange ratios away from those related to primary glucose usage for energy homeostasis. GIT2 knockout (GIT2KO) mice demonstrated lower insulin secretion levels, disruption of pancreatic islet beta cell mass, elevated plasma glucose, and insulin resistance. High-dimensionality transcriptomic signatures from islets isolated from GIT2KO mice indicated a disruption of beta cell development. Additionally, GIT2 expression was prematurely elevated in pancreatic and hypothalamic tissues from diabetic-state mice (db/db), compared to age-matched wild type (WT) controls, further supporting the role of GIT2 in metabolic regulation and aging. We also found that the physical interaction of pancreatic GIT2 with the insulin receptor and insulin receptor substrate 2 was diminished in db/db mice compared to WT mice. Therefore, GIT2 appears to exert a multidimensional "keystone" role in regulating the aging process by coordinating somatic responses to energy deficits.

AGE-modified basement membrane cooperates with Endo180 to promote epithelial cell invasiveness and decrease prostate cancer survival

Biomechanical strain imposed by age-related thickening of the basal lamina and augmented tissue stiffness in the prostate gland coincides with increased cancer risk. Here we hypothesized that the structural alterations in the basal lamina associated with age can induce mechanotransduction pathways in prostate epithelial cells (PECs) to promote invasiveness and cancer progression. To demonstrate this, we developed a 3D model of PEC acini in which thickening and stiffening of basal lamina matrix was induced by advanced glycation end-product (AGE)-dependent non-enzymatic crosslinking of its major components, collagen IV and laminin. We used this model to demonstrate that antibody targeted blockade of CTLD2, the second of eight C-type lectin-like domains in Endo180 (CD280, CLEC13E, KIAA0709, MRC2, TEM9, uPARAP) that can recognize glycosylated collagens, reversed actinomyosin-based contractility [myosin-light chain-2 (MLC2) phosphorylation], loss of cell polarity, loss of cell-cell junctions, luminal infiltration and basal invasion induced by AGE-modified basal lamina matrix in PEC acini. Our in vitro results were concordant with luminal occlusion of acini in the prostate glands of adult Endo180(Δ) (Ex2-6/) (Δ) (Ex2-6) mice, with constitutively exposed CTLD2 and decreased survival of men with early (non-invasive) prostate cancer with high epithelial Endo180 expression and levels of AGE. These findings indicate that AGE-dependent modification of the basal lamina induces invasive behaviour in non-transformed PECs via a molecular mechanism linked to cancer progression. This study provides a rationale for targeting CTLD2 in Endo180 in prostate cancer and other pathologies in which increased basal lamina thickness and tissue stiffness are driving factors. © 2014 The Authors. The Journal of Pathology published by John Wiley & Sons Ltd on behalf of Pathological Society of Great Britain and Ireland.

Effects of insulin combined with idebenone on blood-brain barrier permeability in diabetic rats

This study investigates the effect of insulin combined with idebenone on blood-brain barrier (BBB) permeability in experimental streptozotocin-induced diabetic rats as well as the underlying mechanisms. With a diabetic rat model, we show that insulin and idebenone normalize body weight and water intake and restore BBB permeability and that their combination displays a synergistic effect. The results from transmission electron microscopy show that the combination of insulin and idebenone significantly closed the tight junction (TJ) in diabetic rats. The results from Western blotting in diabetic rats show that the upregulation of TJ-associated proteins occludin, and zonula occludens (ZO)-1 caused by the combination of insulin and idebenone is more remarkable than that with either agent alone. In addition, the activations of reactive oxygen species (ROS) and advanced glycation end products (AGEs) and the expression levels of receptors for advanced glycation end-products (RAGE) and nuclear factor-κB (NF-κB) were significantly decreased after treatment with insulin and idebenone in diabetic rats. These results suggest that the combination of insulin and idebenone could decrease the BBB permeability in diabetic rats by upregulating the expression of occludin, claudin-5, and ZO-1 and that the ROS/AGE/RAGE/NF-κB signal pathway might be involved in the process.

The amazing ubiquitin-proteasome system: structural components and implication in aging

Proteome quality control (PQC) is critical for the maintenance of cellular functionality and it is assured by the curating activity of the proteostasis network (PN). PN is constituted of several complex protein machines that under conditions of proteome instability aim to, firstly identify, and then, either rescue or degrade nonnative polypeptides. Central to the PN functionality is the ubiquitin-proteasome system (UPS) which is composed from the ubiquitin-conjugating enzymes and the proteasome; the latter is a sophisticated multi-subunit molecular machine that functions in a bimodal way as it degrades both short-lived ubiquitinated normal proteins and nonfunctional polypeptides. UPS is also involved in PQC of the nucleus, the endoplasmic reticulum and the mitochondria and it also interacts with the other main cellular degradation axis, namely the autophagy-lysosome system. UPS functionality is optimum in the young organism but it is gradually compromised during aging resulting in increasing proteotoxic stress; these effects correlate not only with aging but also with most age-related diseases. Herein, we present a synopsis of the UPS components and of their functional alterations during cellular senescence or in vivo aging. We propose that mild UPS activation in the young organism will, likely, promote antiaging effects and/or suppress age-related diseases.

Advanced glycation end products increase expression of S100A8 and A9 via RAGE-MAPK in rat dental pulp cells

OBJECTIVE

Advanced glycation end products (AGE) are involved in the progression of diabetic complications. Although our previous reports show that AGE increased dental pulp calcification, AGE accumulation is also associated with inflammation. This study examined AGE effect on the expression of inflammation factors using rat dental pulp tissues and cell cultures.

MATERIALS AND METHODS

Receptor for AGE (RAGE), S100A8, S100A9, and interleukin (IL)-1β were selected as inflammation parameters. Rat dental pulp cells were cultured and treated with AGE, and the effects were determined by real-time PCR. An anti-RAGE antibody or MAPK pathway inhibitors (PD98059, SB203580, and SP60012) were used to investigate AGE signaling pathway.

RESULTS

The mRNA levels of RAGE, S100A8, S100A9, and IL-1β were higher in diabetic pulp tissues. AGE increased mRNA expressions of S100A8, S100A9, and IL-1β in cultured dental pulp cells. In the presence of anti-RAGE antibody, AGE did not increase in S100A8 or S100A9 expressions. The AGE-induced increases in S100A8 and S100A9 were inhibited by PD98059 and SB203580, respectively.

CONCLUSIONS

Advanced glycation end products increased mRNA expression of S100A8, S100A9, and IL-1β under diabetic pulp conditions, and AGE-induced increases in S100A8 and S100A9 expressions may be associated with the RAGE-MAPK signaling pathway.

Chronic spontaneous urticaria is characterized by lower serum advanced glycation end-products

Background. Chronic spontaneous urticaria (CSU) is associated with activation of acute phase response. On the other hand, it is known that systemic inflammation may lead to increased formation of advanced glycation end-products (AGEs), associated with pathogenesis of various diseases. Aim. We aim to test whether chronic inflammation manifested by activated acute phase response may provide a mechanism for increased serum AGEs concentration in CSU. Methods. Concentrations of AGEs were measured spectrofluorimetrically in serum of CSU patients and the healthy subjects. Results. Serum AGEs and albumin concentrations in CSU patients were significantly lower as compared with the healthy subjects. Serum CRP concentration was significantly higher in patients with CSU than in the controls. Significant positive correlation was observed between AGEs and albumin concentrations in the subjects. Conclusions. CSU is not associated with increased circulating AGEs concentrations, despite the enhanced systemic inflammatory response. Paradoxical decrease of serum AGEs concentrations is probably a reflection of lower concentration of “negative acute phase proteins” such as albumin.

Alagebrium (ALT-711) improves the anti-hypertensive efficacy of nifedipine in diabetic-hypertensive rats

Combining drugs with complementary mechanisms of action may contribute to improved hypertension control in diabetic patients. Advanced glycation end-product (AGE) breakers, a new class of candidate drugs targeting aging-related cardiovascular dysfunction, may be useful as novel adjuvant agents to improve the efficacy of diabetic hypertension (DH) treatment. This study evaluated the effects of alagebrium (ALT-711), an AGE breaker, combined with nifedipine, a Ca(2+) channel blocker, in a rat model of streptozotocin-induced DH. Compared with monotherapy, combination treatment significantly decreased systolic and diastolic blood pressure values, increased the pulse pressure, and decreased the coefficient of variation of the systolic blood pressure. Plasma biochemistry indicated that the concentrations of prostacyclin and nitric oxide were increased. Gene expression analysis showed significantly decreased prepro-endothelin-1expression in the aorta. These results reveal that alagebrium significantly improves the anti-hypertensive actions of nifedipine in a rat model of DH and suggest its potential use in the successful control of clinical DH.

Effect of therapeutic plasma exchange on plasma levels of oxidative biomarkers in a patient with thrombotic thrombocytopenic purpura

BACKGROUND

The role of oxidative stress in the initiation and progression of endothelial damage in thrombotic thrombocytopenic purpura (TTP) syndrome has been the subject of much speculation in the recent past.

OBJECTIVES

The aim of this study was to measure the concentration of plasma advanced oxidation protein products (AOPPs), advanced glycation end products (AGEs), and carbonyl groups (CG) as markers of oxidative stress in plasma of a patient with TTP during the course of the disease until recovery and to evaluate the effect of plasmapheresis (PE) on these biomarkers.

MATERIALS AND METHODS

The study consisted of plasma analysis of the patient, and 23 healthy subjects served as controls. In the patient with TTP, AOPP, AGE, and CG analysis was performed before and after each PE at the days +1 (Tα), +2, +4, +6, +10, +9, and +17 after the last plasmapheresis (Tω).

RESULTS

Plasma concentrations of AOPPs were increased in the acute phase of TTP, and at Tα, the patient had AOPPs levels higher than 99°‰ of controls. AOPPs decreased in the recovery phase, and at Tω, their values were between 84° and 85°‰ of controls. No significant difference was found in AOPP levels before and after each PE. No significant differences for AGEs or CG concentrations were found at Tα with respect to the control group, while only a trend was observed for reduction of plasma AGEs after each plasmapheresis.

CONCLUSION

Our data seem to confirm the hypothesis that oxidative stress is a critical component of the pathogenesis of TTP.

Oxidation scrutiny in persuaded aging and chronological aging at systemic redox homeostasis level

BACKGROUND

The effect of the natural aging process on systemic redox homeostasis is previously documented. However, none of the studies specify the effect of experimental aging on systemic redox homeostasis. The purpose of this study is to clarify the ambiguity raised in preliminary reports as to mimetic aging dependency of the type and magnitude of oxidative damage on constituents of plasma.

METHODS

In the current study, we investigated the interrelationship among various groups of the systemic oxidative damage markers such as protein oxidation products (protein carbonyl groups, protein hydroperoxides, advanced oxidation protein products, protein thiol groups), lipid peroxidation products (malondialdehyde, lipid hydroperoxides, conjugated dienes), glycoxidation adducts (advanced glycation end products), and antioxidant capacity (ferric reducing/antioxidant power, Cu,Zn-superoxide dismutase, total thiol, non-protein thiol). All these markers were measured in plasma of mimetically aged (MA) rats (5-month-old rats subjected to d-galactose-induced experimental aging), naturally aged (NA) rats (24-month-old), and their corresponding young controls (YC) (5months old).

RESULTS AND CONCLUSIONS

Our current results show that systemic oxidation markers of the MA group share significant similarities in terms of impaired redox homeostasis with the NA rats and may be considered as a reliable experimental aging model for intravascular aging. Additional methodological studies including d-galactose dosage and application time are warranted to clarify the potential involvement of all these systemic redox variations as mechanistic factors in the development of mimetic aging related intravascular deterioration. Reversing or preventing systemic oxidative damage in experimental and natural aging should therefore be considered the primary target for the development of effective therapeutic strategies to prevent or treat age-related vascular disorders.

Glycation: the angiogenic paradox in aging and age-related disorders and diseases

Angiogenesis is generally a quiescent process which, however, may be modified by different physiological and pathological conditions. The "angiogenic paradox" has been described in diabetes because this disease impairs the angiogenic response in a manner that differs depending on the organs involved and disease evolution. Aging is also associated with pro- and antiangiogenic processes. Glycation, the post-translational modification of proteins, increases with aging and the progression of diabetes. The effect of glycation on angiogenesis depends on the type of glycated proteins and cells involved. This complex link could be responsible for the "angiogenic paradox" in aging and age-related disorders and diseases. Using diabetes as a model, the present work has attempted to review the age-related angiogenic paradox, in particular the effects of glycation on angiogenesis during aging.

Soft-tissue wound healing by anti-advanced glycation end-products agents

The blocking of advanced glycation end-products (AGE) has been shown to reduce diabetic complications and control periodontitis. This study investigated the pattern of palatal wound-healing after graft harvesting under the administration of aminoguanidine (AG), an AGE inhibitor, or N-phenacylthiazolium bromide (PTB), a glycated cross-link breaker. Full-thickness palatal excisional wounds (5.0 x 1.5 mm(2)) were created in 72 Sprague-Dawley rats. The rats received daily intraperitoneal injections of normal saline (control), AG, or PTB and were euthanized after 4 to 28 days. The wound-healing pattern was assessed by histology, histochemistry for collagen matrix deposition, immunohistochemistry for AGE and the AGE receptor (RAGE), and the expression of RAGE, as well as inflammation- and recovery-associated genes. In the first 14 days following AG or PTB treatments, wound closure, re-epithelialization, and collagen matrix deposition were accelerated, whereas AGE deposition, RAGE-positive cells, and inflammation were reduced. RAGE and tumor necrosis factor-alpha were significantly down-regulated at day 7, and heme oxygenase-1 was persistently down-regulated until day 14. The levels of vascular endothelial growth factor, periostin, type I collagen, and fibronectin were all increased at day 14. In conclusion, anti-AGE agents appeared to facilitate palatal wound-healing by reducing AGE-associated inflammation and promoting the recovery process.

Molecular chaperones and proteostasis regulation during redox imbalance

Free radicals originate from both exogenous environmental sources and as by-products of the respiratory chain and cellular oxygen metabolism. Sustained accumulation of free radicals, beyond a physiological level, induces oxidative stress that is harmful for the cellular homeodynamics as it promotes the oxidative damage and stochastic modification of all cellular biomolecules including proteins. In relation to proteome stability and maintenance, the increased concentration of oxidants disrupts the functionality of cellular protein machines resulting eventually in proteotoxic stress and the deregulation of the proteostasis (homeostasis of the proteome) network (PN). PN curates the proteome in the various cellular compartments and the extracellular milieu by modulating protein synthesis and protein machines assembly, protein recycling and stress responses, as well as refolding or degradation of damaged proteins. Molecular chaperones are key players of the PN since they facilitate folding of nascent polypeptides, as well as holding, folding, and/or degradation of unfolded, misfolded, or non-native proteins. Therefore, the expression and the activity of the molecular chaperones are tightly regulated at both the transcriptional and post-translational level at organismal states of increased oxidative and, consequently, proteotoxic stress, including ageing and various age-related diseases (e.g. degenerative diseases and cancer). In the current review we present a synopsis of the various classes of intra- and extracellular chaperones, the effects of oxidants on cellular homeodynamics and diseases and the redox regulation of chaperones.

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Free radicals originate from various sources and at physiological concentrations are essential for the modulation of cell signalling pathways.

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Abnormally high levels of free radicals induce oxidative stress and damage all cellular biomolecules, including proteins.

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Molecular chaperones facilitate folding of nascent polypeptides, as well as holding, folding, and/or degradation of damaged proteins.

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The expression and the activity of chaperones during oxidative stress are regulated at both the transcriptional and post-translational level.

Natural compounds with anti-ageing activity

Ageing is a complex molecular process driven by diverse molecular pathways and biochemical events that are promoted by both environmental and genetic factors. Specifically, ageing is defined as a time-dependent decline of functional capacity and stress resistance, associated with increased chance of morbidity and mortality. These effects relate to age-related gradual accumulation of stressors that result in increasingly damaged biomolecules which eventually compromise cellular homeostasis. Nevertheless, the findings that genetic or diet interventions can increase lifespan in evolutionarily diverse organisms indicate that mortality can be postponed. Natural compounds represent an extraordinary inventory of high diversity structural scaffolds that can offer promising candidate chemical entities in the major healthcare challenge of increasing health span and/or delaying ageing. Herein, those natural compounds (either pure forms or extracts) that have been found to delay cellular senescence or in vivo ageing will be critically reviewed and summarized according to affected cellular signalling pathways. Moreover, the chemical structures of the identified natural compounds along with the profile of extracts related to their bioactive components will be presented and discussed. Finally, novel potential molecular targets for screening natural compounds for anti-ageing activity, as well as the idea that anti-ageing interventions represent a systemic approach that is also effective against age-related diseases will be discussed.

Cellular regulation of glucose uptake by glucose transporter GLUT4

GLUT4 is regulated by its intracellular localization. In the absence of insulin, GLUT4 is efficiently retained intracellularly within storage compartments in muscle and fat cells. Upon insulin stimulation (and contraction in muscle), GLUT4 translocates from these compartments to the cell surface where it transports glucose from the extracellular milieu into the cell. Its implication in insulin-regulated glucose uptake makes GLUT4 not only a key player in normal glucose homeostasis but also an important element in insulin resistance and type 2 diabetes. Nevertheless, how GLUT4 is retained intracellularly and how insulin acts on this retention mechanism is largely unclear. In this review, the current knowledge regarding the various molecular processes that govern GLUT4 physiology is discussed as well as the questions that remain.

The proteasome and the degradation of oxidized proteins: Part II - protein oxidation and proteasomal degradation

Here, we review the role of oxidative protein modification as a signal for recognition and degradation of proteins. It was clearly demonstrated that the ATP- and ubiquitin-independent 20S proteasome is playing a key role in the selective removal of oxidized proteins. Furthermore, the current knowledge of the substrate susceptibility on the degradation of oxidized proteins and the role of the immunoproteasome will be highlighted.

Diet-derived advanced glycation end products or lipofuscin disrupts proteostasis and reduces life span in Drosophila melanogaster

Advanced glycation end product (AGE)-modified proteins are formed by the nonenzymatic glycation of free amino groups of proteins and, along with lipofuscin (a highly oxidized aggregate of covalently cross-linked proteins, sugars, and lipids), have been found to accumulate during aging and in several age-related diseases. As the in vivo effects of diet-derived AGEs or lipofuscin remain elusive, we sought to study the impact of oral administration of glucose-, fructose-, or ribose-modified albumin or of artificial lipofuscin in a genetically tractable model organism. We report herein that continuous feeding of young Drosophila flies with culture medium enriched in AGEs or in lipofuscin resulted in reduced locomotor performance and in accelerated rates of AGE-modified proteins and carbonylated proteins accumulation in the somatic tissues and hemolymph of flies, as well as in a significant reduction of flies health span and life span. These phenotypic effects were accompanied by reduced proteasome peptidase activities in both the hemolymph and the somatic tissues of flies and higher levels of oxidative stress; furthermore, oral administration of AGEs or lipofuscin in flies triggered an upregulation of the lysosomal cathepsin B, L activities. Finally, RNAi-mediated cathepsin D knockdown reduced flies longevity and significantly augmented the deleterious effects of AGEs and lipofuscin, indicating that lysosomal cathepsins reduce the toxicity of diet-derived AGEs or lipofuscin. Our in vivo studies demonstrate that chronic ingestion of AGEs or lipofuscin disrupts proteostasis and accelerates the functional decline that occurs with normal aging.