Normal mouse and rat strains as models for age-related cataract and the effect of caloric restriction on its development

Glycative stress as a cause of macular degeneration

People are living longer and rates of age-related diseases such as age-related macular degeneration (AMD) are accelerating, placing enormous burdens on patients and health care systems. The quality of carbohydrate foods consumed by an individual impacts health. The glycemic index (GI) is a kinetic measure of the rate at which glucose arrives in the blood stream after consuming various carbohydrates. Consuming diets that favor slowly digested carbohydrates releases sugar into the bloodstream gradually after consuming a meal (low glycemic index). This is associated with reduced risk for major age-related diseases including AMD, cardiovascular disease, and diabetes. In comparison, consuming the same amounts of different carbohydrates in higher GI diets, releases glucose into the blood rapidly, causing glycative stress as well as accumulation of advanced glycation end products (AGEs). Such AGEs are cytotoxic by virtue of their forming abnormal proteins and protein aggregates, as well as inhibiting proteolytic and other protective pathways that might otherwise selectively recognize and remove toxic species. Using in vitro and animal models of glycative stress, we observed that consuming higher GI diets perturbs metabolism and the microbiome, resulting in a shift to more lipid-rich metabolomic profiles. Interactions between aging, diet, eye phenotypes and physiology were observed. A large body of laboratory animal and human clinical epidemiologic data indicates that consuming lower GI diets, or lower glycemia diets, is protective against features of early AMD (AMDf) in mice and AMD prevalence or AMD progression in humans. Drugs may be optimized to diminish the ravages of higher glycemic diets. Human trials are indicated to determine if AMD progression can be retarded using lower GI diets. Here we summarized the current knowledge regarding the pathological role of glycative stress in retinal dysfunction and how dietary strategies might diminish retinal disease.

Roles of transmembrane protein 135 in mitochondrial and peroxisomal functions - implications for age-related retinal disease

Aging is the most significant risk factor for age-related diseases in general, which is true for age-related diseases in the eye including age-related macular degeneration (AMD). Therefore, in order to identify potential therapeutic targets for these diseases, it is crucial to understand the normal aging process and how its mis-regulation could cause age-related diseases at the molecular level. Recently, abnormal lipid metabolism has emerged as one major aspect of age-related symptoms in the retina. Animal models provide excellent means to identify and study factors that regulate lipid metabolism in relation to age-related symptoms. Central to this review is the role of transmembrane protein 135 (TMEM135) in the retina. TMEM135 was identified through the characterization of a mutant mouse strain exhibiting accelerated retinal aging and positional cloning of the responsible mutation within the gene, indicating the crucial role of TMEM135 in regulating the normal aging process in the retina. Over the past decade, the molecular functions of TMEM135 have been explored in various models and tissues, providing insights into the regulation of metabolism, particularly lipid metabolism, through its action in multiple organelles. Studies indicated that TMEM135 is a significant regulator of peroxisomes, mitochondria, and their interaction. Here, we provide an overview of the molecular functions of TMEM135 which is crucial for regulating mitochondria, peroxisomes, and lipids. The review also discusses the age-dependent phenotypes in mice with TMEM135 perturbations, emphasizing the importance of a balanced TMEM135 function for the health of the retina and other tissues including the heart, liver, and adipose tissue. Finally, we explore the potential roles of TMEM135 in human age-related retinal diseases, connecting its functions to the pathobiology of AMD.

Loss of epigenetic information as a cause of mammalian aging

All living things experience an increase in entropy, manifested as a loss of genetic and epigenetic information. In yeast, epigenetic information is lost over time due to the relocalization of chromatin-modifying proteins to DNA breaks, causing cells to lose their identity, a hallmark of yeast aging. Using a system called "ICE" (inducible changes to the epigenome), we find that the act of faithful DNA repair advances aging at physiological, cognitive, and molecular levels, including erosion of the epigenetic landscape, cellular exdifferentiation, senescence, and advancement of the DNA methylation clock, which can be reversed by OSK-mediated rejuvenation. These data are consistent with the information theory of aging, which states that a loss of epigenetic information is a reversible cause of aging.

Innate immunity dysregulation in aging eye and therapeutic interventions

The prevalence of eye diseases increases considerably with age, resulting in significant vision impairment. Although the pathobiology of age-related eye diseases has been studied extensively, the contribution of immune-related changes due to aging remains elusive. In the eye, tissue-resident cells and infiltrating immune cells regulate innate responses during injury or infection. But due to aging, these cells lose their protective functions and acquire pathological phenotypes. Thus, dysregulated ocular innate immunity in the elderly increases the susceptibility and severity of eye diseases. Herein, we emphasize the impact of aging on the ocular innate immune system in the pathogenesis of infectious and non-infectious eye diseases. We discuss the role of age-related alterations in cellular metabolism, epigenetics, and cellular senescence as mechanisms underlying altered innate immune functions. Finally, we describe approaches to restore protective innate immune functions in the aging eye. Overall, the review summarizes our current understanding of innate immune functions in eye diseases and their dysregulation during aging.

Differences reported in the lifespan and aging of male Wistar rats maintained on diets containing fat with different fatty acid profiles (virgin olive, sunflower or fish oils) are not reflected by histopathological lesions found at death in central nervous and endocrine systems

The present study was designed to examine if dietary fat sources that have shown differences in lifespan and if some aging-related aspects can modulate the range of histopathologic changes in central nervous and endocrine systems that occur during the lifespan of Wistar rats. Moreover, it was attempted to gain insight into the relationship between longevity and the development of the different pathological changes, as well as possible interaction with diet. In order to achieve this, male Wistar rats were randomly assigned to three experimental groups fed semisynthetic and isoenergetic diets from weaning until death with different dietary fat sources, namely virgin olive, sunflower, or fish oil. An individual follow-up until death of each animal was performed. Incidence, severity, and burden of specific or group (i.e., neoplastic or non-neoplastic proliferative and non-proliferative) of lesions was calculated along with individual's disease and individual organ lesion burden. Most of the histopathological lesions found have been described in previous studies. Neoplasms, and in particular pituitary adenomas followed by brain tumors, were the most prevalent lesions found in the rats and the main cause of death involving both systems. Incidence of brain lesions was associated with age-at-death. Assayed dietary fats did not present differential effects on pathological changes occurring in endocrine and central nervous systems throughout rat lifespan.

Diabetic mice have retinal and choroidal blood flow deficits and electroretinogram deficits with impaired responses to hypercapnia

Purpose

The purpose of this study was to investigate neuronal and vascular functional deficits in the retina and their association in a diabetic mouse model. We measured electroretinography (ERG) responses and choroidal and retinal blood flow (ChBF, RBF) with magnetic resonance imaging (MRI) in healthy and diabetic mice under basal conditions and under hypercapnic challenge.

Methods

Ins2^Akita diabetic (Diab, n = 8) and age-matched, wild-type C57BL/6J mice (Ctrl, n = 8) were studied under room air and moderate hypercapnia (5% CO₂). Dark-adapted ERG a-wave, b-wave, and oscillatory potentials (OPs) were measured for a series of flashes. Regional ChBF and RBF under air and hypercapnia were measured using MRI in the same mice.

Results

Under room air, Diab mice had compromised ERG b-wave and OPs (e.g., b-wave amplitude was 422.2±10.7 μV in Diab vs. 600.1±13.9 μV in Ctrl, p < 0.001). Under hypercapnia, OPs and b-wave amplitudes were significantly reduced in Diab (OPs by 30.3±3.0% in Diab vs. -3.0±3.6% in Ctrl, b-wave by 17.9±1.4% in Diab vs. 1.3±0.5% in Ctrl). Both ChBF and RBF had significant differences in regional blood flow, with Diab mice having substantially lower blood flow in the nasal region (ChBF was 5.4±1.0 ml/g/min in Diab vs. 8.6±1.0 ml/g/min in Ctrl, RBF was 0.91±0.10 ml/g/min in Diab vs. 1.52±0.24 ml/g/min in Ctrl). Under hypercapnia, ChBF increased in both Ctrl and Diab without significant group difference (31±7% in Diab vs. 17±7% in Ctrl, p > 0.05), but an increase in RBF was not detected for either group.

Conclusions

Inner retinal neuronal function and both retinal and choroidal blood flow were impaired in Diab mice. Hypercapnia further compromised inner retinal neuronal function in diabetes, while the blood flow response was not affected, suggesting that the diabetic retina has difficulty adapting to metabolic challenges due to factors other than impaired blood flow regulation.

Aged Nrf2-Null Mice Develop All Major Types of Age-Related Cataracts

Purpose

Age-related cataracts affect the majority of older adults and are a leading cause of blindness worldwide. Treatments that delay cataract onset or severity have the potential to delay cataract surgery, but require relevant animal models that recapitulate the major types of cataracts for their development. Unfortunately, few such models are available. Here, we report the lens phenotypes of aged mice lacking the critical antioxidant transcription factor Nfe2l2 (designated as Nrf2 −/−).

Methods

Three independent cohorts of Nrf2 −/− and wild-type C57BL/6J mice were evaluated for cataracts using combinations of slit lamp imaging, photography of freshly dissected lenses, and histology. Mice were fed high glycemic diets, low glycemic diets, regular chow ad libitum, or regular chow with 30% caloric restriction.

Results

Nrf2 −/− mice developed significant opacities between 11 and 15 months and developed advanced cortical, posterior subcapsular, anterior subcapsular, and nuclear cataracts. Cataracts occurred similarly in male mice fed high or low glycemic diets, and were also observed in 21-month male and female Nrf2 −/− mice fed ad libitum or 30% caloric restriction. Histological observation of 18-month cataractous lenses revealed significant disruption to fiber cell architecture and the retention of nuclei throughout the cortical region of the lens. However, fiber cell denucleation and initiation of lens differentiation was normal at birth, with the first abnormalities observed at 3 months.

Conclusions

Nrf2 −/− mice offer a tool to understand how defective antioxidant signaling causes multiple forms of cataract and may be useful for screening drugs to prevent or delay cataractogenesis in susceptible adults.

Targeting Lipid Metabolism for the Treatment of Age-Related Macular Degeneration: Insights from Preclinical Mouse Models

Age-related macular degeneration (AMD) is a major leading cause of irreversible visual impairment in the world with limited therapeutic interventions. Histological, biochemical, genetic, and epidemiological studies strongly implicate dysregulated lipid metabolism in the retinal pigmented epithelium (RPE) in AMD pathobiology. However, effective therapies targeting lipid metabolism still need to be identified and developed for this blinding disease. To test lipid metabolism-targeting therapies, preclinical AMD mouse models are needed to establish therapeutic efficacy and the role of lipid metabolism in the development of AMD-like pathology. In this review, we provide a comprehensive overview of current AMD mouse models available to researchers that could be used to provide preclinical evidence supporting therapies targeting lipid metabolism for AMD. Based on previous studies of AMD mouse models, we discuss strategies to modulate lipid metabolism as well as examples of studies evaluating lipid-targeting therapeutics to restore lipid processing in the RPE. The use of AMD mouse models may lead to worthy lipid-targeting candidate therapies for clinical trials to prevent the blindness caused by AMD.

The tumor suppression theory of aging

Despite continued increases in human life expectancy, the factors determining the rate of human biological aging remain unknown. Without understanding the molecular mechanisms underlying aging, efforts to prevent aging are unlikely to succeed. The tumor suppression theory of aging introduced here proposes somatic mutation as the proximal cause of aging, but postulates that oncogenic transformation and clonal expansion, not functional impairment, are the relevant consequences of somatic mutation. Obesity and caloric restriction accelerate and decelerate aging due to their effect on cell proliferation, during which most mutations arise. Most phenotypes of aging are merely tumor-suppressive mechanisms that evolved to limit malignant growth, the dominant age-related cause of death in early and middle life. Cancer limits life span for most long-lived mammals, a phenomenon known as Peto's paradox. Its conservation across species demonstrates that mutation is a fundamental but hard limit on mammalian longevity. Cell senescence and apoptosis and differentiation induced by oncogenes, telomere shortening or DNA damage evolved as a second line of defense to limit the tumorigenic potential of clonally expanding cells, but accumulating senescent cells, senescence-associated secretory phenotypes and stem cell exhaustion eventually cause tissue dysfunction and the majority, if not most, phenotypes of aging.

The aging mouse lens transcriptome

Age is a major risk factor for cataract (ARC). However, the influence of aging on the lens transcriptome is under studied. Lens epithelial (LEC) and fiber cells (LFC) were isolated from young (3 month old) and aged (24 month old) C57BL/6J mice, and the transcriptome elucidated via RNAseq. EdgeR estimated differential gene expression in pairwise contrasts, and Advaita's Ipathway guide and custom R scripts were used to evaluate the potential biological significance of differentially expressed genes (DEGs). This analysis revealed age-dependent decreases in lens differentiation marker expression in both LECs and LFCs, with gamma crystallin transcripts downregulating nearly 50 fold in aged LFCs. The expression of the transcription factors Hsf4 and Maf, which are known to activate lens fiber cell preferred genes, are downregulated, while FoxE3, which represses gamma crystallin expression, is upregulated in aged fibers. Aged LECs upregulate genes controlling the immune response, complement pathways, and cellular stress responses, including glutathione peroxidase 3 (Gpx3). Aged LFCs exhibit broad changes in the expression of genes regulating cell communication, and upregulate genes involved in antigen processing/presentation and cholesterol metabolism, while changes in the expression of mitochondrial respiratory chain genes are consistent with mitochondrial stress, including upregulation of NDufa4l2, which encodes an alternate electron transport chain protein. However, age did not profoundly affect the response of LECs to injury as both young and aged LECs upregulate inflammatory gene signatures at 24 h post injury to similar extents. These RNAseq profiles provide a rich data set that can be mined to understand the genetic regulation of lens aging and how this impinges on the pathophysiology of age related cataract.

H2O2-induced cataract as a model of age-related cataract: Lessons learned from overexpressing the proteasome activator PA28αβ in mouse eye lens

Cataract, the world-leading cause of blindness, is formed when crystallin aggregates cloud the eye lens. We overexpressed PA28αβ, a proteasome activator with properties protective against aggregation and oxidative stress, and examined whether they are less prone to develop cataract arisen from aging and/or hydrogen peroxide (H₂O₂) treatment. Another objective of this work was to compare the H₂O₂-induced cataracts of mouse lenses ex vivo to cataracts formed upon aging in mice. As part of an aging study of F2 hybrid C57BL/6NxBALB/c mice, ocular lenses of mature adult (7 months), middle-aged (15 months), and old (22 months of age) PA28αOE mice and their wildtype littermates (n = 22-44 lenses per group) were dissected and evaluated with regard to their cataractous state. In parallel, ocular lenses from 3 to 4 months old PA28αOE and wildtype C57BL/6 N littermates were treated with 100 μM H₂O₂ every 24 h for 7 days, with progression of cataract and physical appearance monitored daily. Lenses from both studies were also subjected to analysis of oxidative protein damage (carbonylation) and protein solubility. We found that overexpression of PA28αβ had no effect on neither age-related nor H₂O₂-induced cataract and conclude that overexpression of PA28αβ does not protect mice from developing cataract. The inefficiency of PA28αβ against cataract could be due to its anti-aggregation activity being already excessively present in the eye lens, exerted by crystallins. Crystallins are likely also constituting the 20-25 kDa proteins that were the dominant carbonyl targets in the eye lens irrespective of cataractous state. Assessment of H₂O₂-induced cataract in relation to age-related cataract demonstrated that high molecular weight protein carbonylation correlates to cataract both in vivo and ex vivo, while reduced protein solubility is more pronounced in age-related cataract. Furthermore, this work highlights vast dissimilarities in the physical manifestations of cataract upon aging and H₂O₂ ex vivo treatment. Age-related cataract initiation can take various forms, as a vague general blurriness or as a barely visible demarcated opacity, while H₂O₂-induced cataractogenesis seems to follow a specific scheme. In mice, this scheme begins with relatively opaque peripheral areas emerging that clear up later on as the lenses start to display a hat-like appearance. This transformation takes place synchronous to swelling of the eye lens, and is likely a result of osmotic disturbances causing a phase separation between the viscous lens cortex and the more solid fibers of the lens nucleus.

Dietary Patterns, Carbohydrates, and Age-Related Eye Diseases

Over a third of older adults in the U.S. experience significant vision loss, which decreases independence and is a biomarker of decreased health span. As the global aging population is expanding, it is imperative to uncover strategies to increase health span and reduce the economic burden of this age-related disease. While there are some treatments available for age-related vision loss, such as surgical removal of cataracts, many causes of vision loss, such as dry age-related macular degeneration (AMD), remain poorly understood and no treatments are currently available. Therefore, it is necessary to better understand the factors that contribute to disease progression for age-related vision loss and to uncover methods for disease prevention. One such factor is the effect of diet on ocular diseases. There are many reviews regarding micronutrients and their effect on eye health. Here, we discuss the impact of dietary patterns on the incidence and progression of age-related eye diseases, namely AMD, cataracts, diabetic retinopathy, and glaucoma. Then, we focus on the specific role of dietary carbohydrates, first by outlining the physiological effects of carbohydrates on the body and then how these changes translate into eye and age-related ocular diseases. Finally, we discuss future directions of nutrition research as it relates to aging and vision loss, with a discussion of caloric restriction, intermittent fasting, drug interventions, and emerging randomized clinical trials. This is a rich field with the capacity to improve life quality for millions of people so they may live with clear vision for longer and avoid the high cost of vision-saving surgeries.

Esculetin and idebenone ameliorate galactose-induced cataract in a rat model

Cataract is the principal cause of blindness. The enzyme, aldose reductase (AR) is a key player in polyol pathway. Buildup of polyols and oxidative stress are the main causes of cataractogenesis. This study investigated the cytoprotective properties of esculetin and idebenone in galactose-induced cataract. Rats were partitioned into four groups each of ten rats. Control group was fed with normal diet; group 2 rats were fed with galactose diet (50%); groups 3, 4 rats were fed with galactose diet concurrently with either esculetin (50 mg/kg BW) or idebenone (100 mg/kg BW), for 20 days. The study revealed that esculetin and idebenone significantly reduced the elevated levels of Bax/Bcl-2 ratio, malondialdehyde, and DNA fragmentation and increased total antioxidant capacity level in lenses compared to the cataract-induced group. Only esculetin decreased AR, galactitol, and advanced glycated end products levels in lenses. Histopathological examinations supported the biochemical findings. Esculetin and idebenone may have chemopreventive effects for sugar cataract. PRACTICAL APPLICATIONS: Cataract is an age-related disease that might cause blindness in older adult people. Presently, no absolute pharmacological treatment is accessible for cataract. The use of natural products or their derivatives attract particular attention in modern medicines as they are believed to be safer with few or no side effects. Esculetin is a polyphenolic compound found in many medicinal plants. Idebenone is a synthetic analogue of coenzyme Q10. The current study is an approach to explore the anticataract effects of esculetin and idebenone in galactose-induced cataract in rats. Our study proved that both agents have anticataractogenic potentials due to their antioxidant and antiapoptotic properties.

Retinal analysis of a mouse model of Alzheimer's disease with multicontrast optical coherence tomography

Significance. Recent Alzheimer's disease (AD) patient studies have focused on retinal analysis, as the retina is the only part of the central nervous system that can be imaged noninvasively by optical methods. However, as this is a relatively new approach, the occurrence and role of retinal pathological features are still debated. Aim. The retina of an APP/PS1 mouse model was investigated using multicontrast optical coherence tomography (OCT) in order to provide a documentation of what was observed in both transgenic and wild-type mice. Approach. Both eyes of 24 APP/PS1 transgenic mice (age: 45 to 104 weeks) and 15 age-matched wild-type littermates were imaged by the custom-built OCT system. At the end of the experiment, retinas and brains were harvested from a subset of the mice (14 transgenic, 7 age-matched control) in order to compare the in vivo results to histological analysis and to quantify the cortical amyloid beta plaque load. Results. The system provided a combination of standard reflectivity data, polarization-sensitive data, and OCT angiograms. Qualitative and quantitative information from the resultant OCT images was extracted on retinal layer thickness and structure, presence of hyper-reflective foci, phase retardation abnormalities, and retinal vasculature. Conclusions. Although multicontrast OCT revealed abnormal structural properties and phase retardation signals in the retina of this APP/PS1 mouse model, the observations were very similar in transgenic and control mice.

Age-related changes in eye lens biomechanics, morphology, refractive index and transparency

Life-long eye lens function requires an appropriate gradient refractive index, biomechanical integrity and transparency. We conducted an extensive study of wild-type mouse lenses 1-30 months of age to define common age-related changes. Biomechanical testing and morphometrics revealed an increase in lens volume and stiffness with age. Lens capsule thickness and peripheral fiber cell widths increased between 2 to 4 months of age but not further, and thus, cannot account for significant age-dependent increases in lens stiffness after 4 months. In lenses from mice older than 12 months, we routinely observed cataracts due to changes in cell structure, with anterior cataracts due to incomplete suture closure and a cortical ring cataract corresponding to a zone of compaction in cortical lens fiber cells. Refractive index measurements showed a rapid growth in peak refractive index between 1 to 6 months of age, and the area of highest refractive index is correlated with increases in lens nucleus size with age. These data provide a comprehensive overview of age-related changes in murine lenses, including lens size, stiffness, nuclear fraction, refractive index, transparency, capsule thickness and cell structure. Our results suggest similarities between murine and primate lenses and provide a baseline for future lens aging studies.

Opacification of lentoid bodies derived from human induced pluripotent stem cells is accelerated by hydrogen peroxide and involves protein aggregation

Despite the recent breakthrough in cataract drug development, further improvements have been limited by the lack of human in vitro cataract disease models. This study, therefore, aims to generate a qualified cataract disease model. Mature lentoid bodies (LBs) on Day 25 (D25), which were differentiated from human induced pluripotent stem cells (iPSCs) using the "fried egg" method, were continually culturing (control) or extra treated with either ultraviolet (UV) radiation or hydrogen peroxide (H₂ O₂ ). The LBs' shape alteration and opacity were examined using light microscopy and mean gray value evaluation. Their structure and crystallin expression were examined using immunofluorescence and transmission electron microscopy (TEM). Real-time polymerase chain reaction and western blot were used to investigate the potential role of autophagy in cloudy LBs. Mature LBs became cloudy with time which was accelerated by H₂ O₂ . Immunofluorescence examinations and TEM showed that the H₂ O₂ -treated and control LBs had similar shapes, lens capsule, and monolayer lens epithelial cell (LEC) structures. However, we were unable to do further assessment of the UV-treated LBs as the structures of LBs were easily damaged when treated with UV radiation. Cells containing aggregated protein (αA-crystallin and αB-crystallin) puncta were more abundant in the H₂ O₂ -treated LBs as compared with control LBs. Moreover, LC3B expression decreased with age in anterior lens capsules obtained from age-related cataracts (ARCs) patients as compared with LC3B levels in primary LECs, which is consistent with that LC3B expression in LBs was lower on D45 than on D25. Our study found that human iPSCs-derived LBs became cloudy with time which was accompanied by protein aggregation, and this phenomenon was accelerated by H₂ O₂ , suggesting that LBs with extending culture may serve as a human model for in vitro ARCs.

Advancing the pathologic phenotype of giant axonal neuropathy: early involvement of the ocular lens

Giant axonal neuropathy (GAN; ORPHA: 643; OMIM# 256850) is a rare, hereditary, pediatric neurodegenerative disorder associated with intracellular accumulations of intermediate filaments (IFs). GAN knockout (KO) mouse models mirror the IF dysregulation and widespread nervous system pathology seen in human GAN. Validation of therapeutic efficacy and viral vector delivery systems with these GAN KO models has provided the springboard for the development of a viral vector being delivered intrathecally in an ongoing Phase I gene therapy clinical trial for the treatment of children with GAN (https://clinicaltrials.gov/ct2/show/NCT02362438). During the course of a comprehensive pathologic characterization of the GAN KO mouse, we discovered the very early and unexpected involvement of the ocular lens. Light microscopy revealed the presence of intracytoplasmic inclusion bodies within lens epithelial cells. The inclusion bodies showed strong immunohistochemical positivity for glial fibrillary acidic protein (GFAP). We confirmed that intracytoplasmic inclusion bodies are also present within lens epithelial cells in human GAN. These IF inclusion bodies in lens epithelial cells are unique to GAN. Similar IF inclusion bodies in lens epithelial cells have not been reported previously in experimental animal models or human diseases. Since current paradigms in drug discovery and drug repurposing for IF-associated disorders are often hindered by lack of validated targets, our findings suggest that lens epithelial cells in the GAN KO mouse may provide a potential target, in vivo and in vitro, for evaluating drug efficacy and alternative therapeutic approaches in promoting the clearance of IF inclusions in GAN and other diseases characterized by intracellular IF accumulations.

Polarization-sensitive optical coherence tomography imaging of the anterior mouse eye

Polarization-sensitive optical coherence tomography (PS-OCT) enables noninvasive, high-resolution imaging of tissue polarization properties. In the anterior segments of human eyes, PS-OCT allows the visualization of birefringent and depolarizing structures. We present the use of PS-OCT for imaging the murine anterior eye. Using a spectral domain PS-OCT setup operating in the 840-nm regime, we performed in vivo volumetric imaging in anesthetized C57BL/6 mice. The polarization properties of murine anterior eye structures largely replicated those known from human PS-OCT imagery, suggesting that the mouse eye may also serve as a model system under polarization contrast. However, dissimilarities were found in the depolarizing structure of the iris which, as we confirmed in postmortem histological sections, were caused by anatomical differences between both species. In addition to the imaging of tissues in the anterior chamber and the iridocorneal angle, we demonstrate longitudinal PS-OCT imaging of the murine anterior segment during mydriasis as well as birefringence imaging of corneal pathology in an aged mouse.

Eye and Associated Glands

The eye is susceptible to adverse toxic effects by direct application, inadvertent ocular contact, or systemic exposure to chemicals or their metabolites. Although the albino rat is a less than ideal model for ocular toxicity studies, it has gained popularity for specific applications and may be the first species in which the ocular toxicity of a systemically administered xenobiotic becomes evident. This chapter reviews the embryology, anatomy, and physiology of the eye and associated glands and describes common nonneoplastic and neoplastic lesions encountered in laboratory rats.

Voluntary running exercise protects against sepsis-induced early inflammatory and pro-coagulant responses in aged mice

Background

Despite many animal studies and clinical trials, mortality in sepsis remains high. This may be due to the fact that most experimental studies of sepsis employ young animals, whereas the majority of septic patients are elderly (60 − 70 years). The objective of the present study was to examine the sepsis-induced inflammatory and pro-coagulant responses in aged mice. Since running exercise protects against a variety of diseases, we also examined the effect of voluntary running on septic responses in aged mice.

Methods

Male C57BL/6 mice were housed in our institute from 2–3 to 22 months (an age mimicking that of the elderly). Mice were prevented from becoming obese by food restriction (given 70–90% of ad libitum consumption amount). Between 20 and 22 months, a subgroup of mice ran voluntarily on wheels, alternating 1–3 days of running with 1–2 days of rest. At 22 months, mice were intraperitoneally injected with sterile saline (control) or 3.75 g/kg fecal slurry (septic). At 7 h post injection, we examined (1) neutrophil influx in the lung and liver by measuring myeloperoxidase and/or neutrophil elastase in the tissue homogenates by spectrophotometry, (2) interleukin 6 (IL6) and KC in the lung lavage by ELISA, (3) pulmonary surfactant function by measuring percentage of large aggregates, (4) capillary plugging (pro-coagulant response) in skeletal muscle by intravital microscopy, (5) endothelial nitric oxide synthase (eNOS) protein in skeletal muscle (eNOS-derived NO is putative inhibitor of capillary plugging) by immunoblotting, and (6) systemic blood platelet counts by hemocytometry.

Results

Sepsis caused high levels of pulmonary myeloperoxidase, elastase, IL6, KC, liver myeloperoxidase, and capillary plugging. Sepsis also caused low levels of surfactant function and platelet counts. Running exercise increased eNOS protein and attenuated the septic responses.

Conclusions

Voluntary running protects against exacerbated sepsis-induced inflammatory and pro-coagulant responses in aged mice. Protection against pro-coagulant responses may involve eNOS upregulation. The present discovery in aged mice calls for clinical investigation into potential beneficial effects of exercise on septic outcomes in the elderly.

Electronic supplementary material

The online version of this article (doi:10.1186/s13054-017-1783-1) contains supplementary material, which is available to authorized users.

Genetic background influences age-related decline in visual and nonvisual retinal responses, circadian rhythms, and sleep

The circadian system is entrained to the environmental light/dark cycle via retinal photoreceptors and regulates numerous aspects of physiology and behavior, including sleep. These processes are all key factors in healthy aging showing a gradual decline with age. Despite their importance, the exact mechanisms underlying this decline are yet to be fully understood. One of the most effective tools we have to understand the genetic factors underlying these processes are genetically inbred mouse strains. The most commonly used reference mouse strain is C57BL/6J, but recently, resources such as the International Knockout Mouse Consortium have started producing large numbers of mouse mutant lines on a pure genetic background, C57BL/6N. Considering the substantial genetic diversity between mouse strains we expect there to be phenotypic differences, including differential effects of aging, in these and other strains. Such differences need to be characterized not only to establish how different mouse strains may model the aging process but also to understand how genetic background might modify age-related phenotypes. To ascertain the effects of aging on sleep/wake behavior, circadian rhythms, and light input and whether these effects are mouse strain-dependent, we have screened C57BL/6J, C57BL/6N, C3H-HeH, and C3H-Pde6b+ mouse strains at 5 ages throughout their life span. Our data show that sleep, circadian, and light input parameters are all disrupted by the aging process. Moreover, we have cataloged a number of strain-specific aging effects, including the rate of cataract development, decline in the pupillary light response, and changes in sleep fragmentation and the proportion of time spent asleep.

Motor and memory testing of long-lived pregnancy-associated plasma protein--a knock-out mice

Mice deficient in pregnancy-associated plasma protein-A (PAPP-A), an IGF binding protein protease, have been shown to be resistant to experimentally induced atherosclerosis and diabetic nephropathy, and, in the laboratory environment, live 30-40% longer than wild-type littermates in association with delayed incidence and occurrence of age-related neoplasms and degenerative diseases.

OBJECTIVE

PAPP-A is highly expressed in the cerebellum and hippocampus of the mouse brain. Therefore, the studies presented here were aimed at determining motor behavior, learning and retention in PAPP-A knock-out (KO) mice compared to wild-type (WT) littermates with age.

DESIGN

Balance and coordination were assessed using an accelerating rotarod; learning and memory were assessed in a Stone T-maze.

RESULTS

Time on the rotarod decreased with age but there was no significant difference between PAPP-A KO and WT mice at any of the testing ages. Latency to reach the goal box and number of errors committed in the Stone T-maze did not change with age and there were no significant differences between PAPP-A KO and WT mice.

CONCLUSION

Lack of PAPP-A in mice did not impact central regulation of coordination, learning or memory.

Alive and well? Exploring disease by studying lifespan

A common concept in aging research is that chronological age is the most important risk factor for the development of diverse diseases, including degenerative diseases and cancers. The mechanistic link between the aging process and disease pathogenesis, however, is still enigmatic. Nevertheless, measurement of lifespan, as a surrogate for biological aging, remains among the most frequently used assays in aging research. In this review, we examine the connection between 'normal aging' and age-related disease from the point of view that they form a continuum of aging phenotypes. This notion of common mechanisms gives rise to the converse postulate that diseases may be risk factors for accelerated aging. We explore the advantages and caveats associated with using lifespan as a metric to understand cell and tissue aging, focusing on the elucidation of molecular mechanisms and potential therapies for age-related diseases.

Reductions in serum IGF-1 during aging impair health span

In lower or simple species, such as worms and flies, disruption of the insulin-like growth factor (IGF)-1 and the insulin signaling pathways has been shown to increase lifespan. In rodents, however, growth hormone (GH) regulates IGF-1 levels in serum and tissues and can modulate lifespan via/or independent of IGF-1. Rodent models, where the GH/IGF-1 axis was ablated congenitally, show increased lifespan. However, in contrast to rodents where serum IGF-1 levels are high throughout life, in humans, serum IGF-1 peaks during puberty and declines thereafter during aging. Thus, animal models with congenital disruption of the GH/IGF-1 axis are unable to clearly distinguish between developmental and age-related effects of GH/IGF-1 on health. To overcome this caveat, we developed an inducible liver IGF-1-deficient (iLID) mouse that allows temporal control of serum IGF-1. Deletion of liver Igf -1 gene at one year of age reduced serum IGF-1 by 70% and dramatically impaired health span of the iLID mice. Reductions in serum IGF-1 were coupled with increased GH levels and increased basal STAT5B phosphorylation in livers of iLID mice. These changes were associated with increased liver weight, increased liver inflammation, increased oxidative stress in liver and muscle, and increased incidence of hepatic tumors. Lastly, despite elevations in serum GH, low levels of serum IGF-1 from 1 year of age compromised skeletal integrity and accelerated bone loss. We conclude that an intact GH/IGF-1 axis is essential to maintain health span and that elevated GH, even late in life, associates with increased pathology.

Aging related changes in determinants of muscle force generating capacity: a comparison of muscle aging in men and male rodents

Human aging is associated with a progressive decline in skeletal muscle mass and force generating capacity, however the exact mechanisms underlying these changes are not fully understood. Rodents models have often been used to enhance our understanding of mechanisms of age-related changes in human skeletal muscle. However, to what extent age-related alterations in determinants of muscle force generating capacity observed in rodents resemble those in humans has not been considered thoroughly. This review compares the effect of aging on muscle force generating determinants (muscle mass, fiber size, fiber number, fiber type distribution and muscle specific tension), in men and male rodents at similar relative age. It appears that muscle aging in male F344*BN rat resembles that in men most; 32-35-month-old rats exhibit similar signs of muscle weakness to those of 70-80-yr-old men, and the decline in 36-38-month-old rats is similar to that in men aged over 80 yrs. For male C57BL/6 mice, age-related decline in muscle force generating capacity seems to occur only at higher relative age than in men. We conclude that the effects on determinants of muscle force differ between species as well as within species, but qualitatively show the same pattern as that observed in men.

A clinical frailty index in aging mice: comparisons with frailty index data in humans

We previously quantified frailty in aged mice with frailty index (FI) that used specialized equipment to measure health parameters. Here we developed a simplified, noninvasive method to quantify frailty through clinical assessment of C57BL/6J mice (5-28 months) and compared the relationship between FI scores and age in mice and humans. FIs calculated with the original performance-based eight-item FI increased from 0.06 ± 0.01 at 5 months to 0.36 ± 0.06 at 19 months and 0.38 ± 0.04 at 28 months (n = 14). By contrast, the increase was graded with a 31-item clinical FI (0.02 ± 0.005 at 5 months; 0.12 ± 0.008 at 19 months; 0.33 ± 0.02 at 28 months; n = 14). FI scores calculated from 70 self-report items from the first wave of the Survey of Health, Ageing and Retirement in Europe were plotted as function of age (n = 30,025 people). The exponential relationship between FI scores and age (normalized to 90% mortality) was similar in mice and humans for the clinical FI but not the eight-item FI. This noninvasive FI based on clinical measures can be used in longitudinal studies to quantify frailty in mice. Unlike the performance-based eight-item mouse FI, the clinical FI exhibits key features of the FI established for use in humans.

Time-dependent beneficial effect of chronic polyphenol treatment with catechin on endothelial dysfunction in aging mice

A controlled redox environment is essential for vascular cell maturation and function. During aging, an imbalance occurs, leading to endothelial dysfunction. We hypothesized that, according to the concept of hormesis, exposure to physiologic oxidative stress during the maturation phase of the endothelium will activate protective pathways involved in stress resistance. C57Bl/6 mice were treated with the polyphenol catechin for the last 3 (post-maturation) or 9 months prior study at 12 months of age. Endothelial dysfunction, assessed by acetylcholine-induced dilations of isolated renal arteries, was present at 12 months (P<0.05). Only the 3-month treatment with catechin fully prevented the decline in efficacy and sensitivity to acetylcholine (P<0.05). Splenocytes adhesion to the native endothelium, expression of CD18 and shedding of CD62L and PSGL-1 augmented in 12 months old mice (P<0.05): only 3-month catechin fully normalized adhesion and prevented the expression of adhesion molecules on splenocytes (P<0.05). Aging was associated with vascular gene alterations, which were prevented by 3-month catechin treatment (P<0.05). In contrast, 9-month catechin further increased COX-2, p22(phox) and reduced MnSOD (P<0.05). In conclusion, we demonstrate a pivotal role of cellular redox equilibrium: exposure to physiologic oxidative stress during the maturation phase of the endothelium is essential for its function.

Resveratrol prevention of oxidative stress damage to lens epithelial cell cultures is mediated by forkhead box O activity

PURPOSE

To evaluate the potential role that FoxO transcription factors play in modulating resveratrol's protective effects against oxidative stress in lens epithelial cells.

METHODS

Primary human or porcine lens epithelial cells (LECs) were treated with resveratrol (RES) 25 μM and incubated under either physiologic (5%) or chronic hyperoxic (40%) oxygen conditions. Acute oxidative stress was applied using 600 μM H(2)O(2). Changes in expression of FoxO1A, FoxO3A, and FoxO4 were analyzed. The production of intracellular reactive oxygen species (iROS), SA-β-galactosidase (SA-β-gal) activity, and autofluorescence (AF) was assessed by flow cytometry. SiRNAs of FoxO1A, FoxO3A, and FoxO4 were used to study the roles that these transcription factors play in resveratrol's protective effects against cell death induced by oxidative stress.

RESULTS

RES incubation under 40% oxygen increased the expression of FoxO1A, FoxO3A, and FoxO4. RES also increases mitochondrial membrane potential under 5% and/or 40% O(2) conditions and significantly decreased iROS, SA-β-gal, and AF normally induced by hyperoxic conditions. While RES had a mild pro-apoptotic effect in nonstressed cells, it significantly prevented apoptosis induced by H(2)O(2) stress. SiRNA inhibition of FoxO1A, FoxO3A, and FoxO4 not only led to loss of the anti-apoptotic effects of RES in stressed cells but actually exhibited a mild pro-apoptotic effect.

CONCLUSIONS

RES exerts a protective effect against oxidative damage in LEC cultures. The levels of expression of FoxO1A, FoxO3A, and FoxO4 appear to play a central role in determining the pro- or anti-apoptotic effects of RES. This has implications for future studies on oxidative stress-related lenticular disorders such as cataract formation.

Dietary supplements reduce the cataractogenic potential of proton and HZE-particle radiation in mice

Abstract The present study was undertaken to investigate the ability of dietary supplements to reduce the formation and severity of cataracts in mice irradiated with high-energy protons or iron ions, which are important components of the radiation encountered by astronauts during space travel. The mice were exposed to proton or iron-ion radiation and fed with a control diet or diets supplemented with the soybean-derived protease inhibitor, Bowman-Birk inhibitor (BBI), in the form of BBI Concentrate (BBIC) or an antioxidant formulation [containing l-selenomethionine (SeM), N-acetyl cysteine (NAC), ascorbic acid, co-enzyme Q10, alpha-lipoic acid and vitamin E succinate] both before and after the radiation exposure. At approximately 2 years after the radiation exposure, the animals were killed humanely and lenses were harvested and characterized using an established classification system that assigns discrete scores based on the severity of the lens opacifications. The results showed that exposure to 1 GeV/nucleon proton (3 Gy) or iron-ion (50 cGy) radiation significantly increased the cataract prevalence and severity in CBA/J mice to levels above the baseline levels of age-induced cataract formation in this mouse strain. Treatment with BBIC or the antioxidant formulation significantly reduced the prevalence and severity of the lens opacifications in the mice exposed to iron-ion radiation. Treatment with BBIC or the antioxidant formulation also decreased the severity of the lens opacifications in the mice exposed to proton radiation; however, the decrease did not reach statistical significance. These results indicate that BBIC and the antioxidant formulation evaluated in this study could be useful for protecting astronauts against space radiation-induced cataracts during or after long-term manned space missions.

The Benefits of Calorie Restriction and Calorie Restriction Mimetics as Related to the Eye

The effects of calorie restriction without malnutrition seem to possess many beneficial effects in numerous disease states. Recently, studies related to calorie restriction mimetics that biochemically mimic the effects of calorie restriction are also becoming increasingly popular. Both calorie restriction and calorie restriction mimetics trigger an adaptive response reminiscent of mild-stress or low-dose toxic response, which is frequently referred to as hormesis in the toxicology literature. Although some benefits of calorie restriction and calorie restriction mimetics have been studied, the role of hormesis-related pathways in the eye has not been given a special attention. This review will present the current literature on calorie restriction and calorie restriction mimetics as related to most prominent eye diseases and provide insights on the therapeutic role of hormesis in eye diseases.

Aggression in cataract-bearing alpha-1,3-galactosyltransferase knockout mice

The Galalpha1-3Galbeta1-4GlcNAc epitope is the key antigen in the hyperacute rejection of pig-to-man xenotransplantation. In the alpha-1,3-galactosyltransferase knockout (alpha-1,3GT-KO) mouse - a model for xenograft donor pigs - a targeted mutation of the alpha-1,3 galactosyltransferase gene (Ggta1) has been constructed. These mice are depleted of the carbohydrate antigen and besides the mice are also known to develop cortical cataracts. The present study aimed at evaluating the morphology and the degree of the cataract in a population of alpha-GT KO mice, its age of onset, its progression and the impact the cataract may have on aggression, anxiety and perception of light. The alpha-gal epitope could be shown in the lenses with lectin GS1 B4 in all wild-type and none of the alpha-GT KO mice. Histology showed apparent cataract in all alpha-GT KO mice from six weeks of age. Apart from a single wild-type mouse with a small degree of microscopically visible cataract without epithelial involvement at the age of 30 weeks none of the wild-type mice showed signs of cataract. Behavioural testing demonstrated significantly more mounting behaviour and a longer duration of attacking in the alpha-GT KO mice. Apart from this, the agonistic behaviour was not influenced by genotype. Neither did the genotype affect anxiety or perception of light.

Cell cycle arrest by kynurenine in lens epithelial cells

PURPOSE

Indolemine 2,3-dioxygenase (IDO)-mediated oxidation of tryptophan produces kynurenines (KYNs), which may play a role in cataract formation. The molecular mechanisms by which KYNs cause cellular changes are poorly understood. The effects of KYNs on mouse lens epithelial cells by overexpression of human IDO were investigated.

METHODS

Lens epithelial cells (mLECs) derived from human IDO-overexpressing hemizygous transgenic (hemTg) and wild-type (Wt) mice were used. IDO activity was measured by quantifying kynurenine (KYN) by HPLC. KYN-mediated protein modifications were detected by immunocytochemistry and measured by ELISA. Cell proliferation and apoptosis were measured with commercially available kits. Cell distribution between cell cycle phases was examined with flow cytometric analysis. Immunoprecipitation followed by LC/MS was used to identify kynurenine-modified proteins.

RESULTS

mLECs derived from hemTg animals exhibited considerable IDO immunoreactivity and enzyme activity, which were barely detectable in Wt mLECs. KYN and KYN-mediated protein modification were detected in hemTg but not in Wt mLECs; the modified proteins were myosin II and alpha/gamma-actin. HemTg mLECs displayed reduced viability and proliferation. Cell cycle analysis of hemTg mLEC cultures showed approximately a twofold increase in cells at G(2)/M or in both phases, relative to Wt mLECs. Blocking IDO activity with 1-methyl-d,l-tryptophan in hemTg mLECs prevented KYN formation, KYN-mediated protein modification, and G(2)/M arrest.

CONCLUSIONS

Excess IDO activity in mLECs results in KYN production, KYN-mediated modification of myosin II and alpha/gamma-actin, and cell cycle perturbation. Modification of myosin II and gamma-actin by KYN may interfere with cytokinesis, leading to defective epithelial cell division and thus a decreased number of fiber cells.

Resveratrol delays age-related deterioration and mimics transcriptional aspects of dietary restriction without extending life span

A small molecule that safely mimics the ability of dietary restriction (DR) to delay age-related diseases in laboratory animals is greatly sought after. We and others have shown that resveratrol mimics effects of DR in lower organisms. In mice, we find that resveratrol induces gene expression patterns in multiple tissues that parallel those induced by DR and every-other-day feeding. Moreover, resveratrol-fed elderly mice show a marked reduction in signs of aging, including reduced albuminuria, decreased inflammation, and apoptosis in the vascular endothelium, increased aortic elasticity, greater motor coordination, reduced cataract formation, and preserved bone mineral density. However, mice fed a standard diet did not live longer when treated with resveratrol beginning at 12 months of age. Our findings indicate that resveratrol treatment has a range of beneficial effects in mice but does not increase the longevity of ad libitum-fed animals when started midlife.

Role of the transcriptional corepressor Bcor in embryonic stem cell differentiation and early embryonic development

Bcor (BCL6 corepressor) is a widely expressed gene that is mutated in patients with X-linked Oculofaciocardiodental (OFCD) syndrome. BCOR regulates gene expression in association with a complex of proteins capable of epigenetic modification of chromatin. These include Polycomb group (PcG) proteins, Skp-Cullin-F-box (SCF) ubiquitin ligase components and a Jumonji C (Jmjc) domain containing histone demethylase. To model OFCD in mice and dissect the role of Bcor in development we have characterized two loss of function Bcor alleles. We find that Bcor loss of function results in a strong parent-of-origin effect, most likely indicating a requirement for Bcor in extraembryonic development. Using Bcor loss of function embryonic stem (ES) cells and in vitro differentiation assays, we demonstrate that Bcor plays a role in the regulation of gene expression very early in the differentiation of ES cells into ectoderm, mesoderm and downstream hematopoietic lineages. Normal expression of affected genes (Oct3/4, Nanog, Fgf5, Bmp4, Brachyury and Flk1) is restored upon re-expression of Bcor. Consistent with these ES cell results, chimeric animals generated with the same loss of function Bcor alleles show a low contribution to B and T cells and erythrocytes and have kinked and shortened tails, consistent with reduced Brachyury expression. Together these results suggest that Bcor plays a role in differentiation of multiple tissue lineages during early embryonic development.

Reduction in glutathione peroxidase 4 increases life span through increased sensitivity to apoptosis

Glutathione peroxidase 4 (Gpx4) is an antioxidant defense enzyme that plays an important role in detoxification of oxidative damage to membrane lipids. Because oxidative stress is proposed to play a causal role in aging, we compared the life spans of Gpx4 heterozygous knockout mice (Gpx4(+/-) mice) and wild-type mice (WT mice). To our surprise, the median life span of Gpx4(+/-) mice (1029 days) was significantly longer than that of WT mice (963 days) even though the expression of Gpx4 was reduced approximately 50% in all tissues of Gpx4(+/-) mice. Pathological analysis revealed that Gpx4(+/-) mice showed a delayed occurrence of fatal tumor lymphoma and a reduced severity of glomerulonephritis. Compared to WT mice, Gpx4(+/-) mice showed significantly increased sensitivity to oxidative stress-induced apoptosis. Our data indicate that lifelong reduction in Gpx4 increased life span and reduced/retarded age-related pathology most likely through alterations in sensitivity of tissues to apoptosis.

Reduced Age-Related Cataracts Among Elderly Persons Who Reach Age 90 With Preserved Cognition: A Biomarker of Successful Aging?

Tissue damage due to oxidative stress has been implicated in aging, memory loss, and cataract formation. We hypothesized that persons who achieved exceptional longevity with preserved cognition (successful aging [SAG]) would exhibit a lower rate of age-related cataract (ARC) than the general population. The age-specific rates of ARC for a group of 100 (50 male, 50 female) elderly persons who reached at least age 90 years with preserved cognition were compared to the corresponding rates of ARC reported in five population-based studies. The principal finding of this report was that the SAG group manifested a significant reduction in the age-specific rate and lifetime cumulative incidence of ARC compared to the general population. Steroid use, alcohol consumption, gout, and skin lesions resulting from excessive sun exposure emerged as risk factors. Our findings suggest that the progressive development of lens opacities may be reflective of degenerative events occurring more generally throughout the body.

Glucose intolerance in a xenotransplantation model: studies in alpha-gal knockout mice

Xenotransplantation holds the promise of replacing failing human organs with organs of animal origin. Transplantation of pancreatic islets from pigs to humans might restore glucose homeostasis and offer diabetic patients considerable improvement in their quality of life. The alpha-gal epitope, present in all mammals except humans, apes and Old World monkeys, is a decisive obstruction to successful xenotransplantation of vascularized organs as the reaction of alpha-gal-bearing endothelia with natural alpha-gal antibodies in the human blood mediates hyperacute rejection of the xenograft. Alpha-galactosyl transferase knockout mice (alpha-GT KO) develop cataract, but no other lesions have been established in these mice. Here we report for the first time that alpha-GT KO mice have impaired glucose tolerance (p<0.001) and decreased insulin sensitivity (p<0.0001). Homeostasis model assessment shows impaired beta-cell function (p<0.05). Similar physiological changes have not been examined in the alpha-galactosyl transferase pig. However, an association between alpha-galactosyl transferase knockout and impaired beta-cell function could have critical importance for islet xenotransplantation.

Spatial learning and psychomotor performance of C57BL/6 mice: age sensitivity and reliability of individual differences

Two tests often used in aging research, the elevated path test and the Morris water maze test, were examined for their application to the study of brain aging in a large sample of C57BL/6JNia mice. Specifically, these studies assessed: (1) sensitivity to age and the degree of interrelatedness among different behavioral measures derived from these tests, (2) the effect of age on variation in the measurements, and (3) the reliability of individual differences in performance on the tests. Both tests detected age-related deficits in group performance that occurred independently of each other. However, analysis of data obtained on the Morris water maze test revealed three relatively independent components of cognitive performance. Performance in initial acquisition of spatial learning in the Morris maze was not highly correlated with performance during reversal learning (when mice were required to learn a new spatial location), whereas performance in both of those phases was independent of spatial performance assessed during a single probe trial administered at the end of acquisition training. Moreover, impaired performance during initial acquisition could be detected at an earlier age than impairments in reversal learning. There were modest but significant age-related increases in the variance of both elevated path test scores and in several measures of learning in the Morris maze test. Analysis of test scores of mice across repeated testing sessions confirmed reliability of the measurements obtained for cognitive and psychomotor function. Power calculations confirmed that there are sufficiently large age-related differences in elevated path test performance, relative to within age variability, to render this test useful for studies into the ability of an intervention to prevent or reverse age-related deficits in psychomotor performance. Power calculations indicated a need for larger sample sizes for detection of intervention effects on cognitive components of the Morris water maze test, at least when implemented at the ages tested in this study. Variability among old mice in both tests, including each of the various independent measures in the Morris maze, may be useful for elucidating the biological bases of different aspects of dysfunctional brain aging.

Age-related cataract progression in five mouse models for anti-oxidant protection or hormonal influence

Five mouse models with known alterations of resistance to oxidative damage were compared by slit lamp examination for the presence and degree of advancement of age-related cataract in young adult and old animals along with wild type controls. A group of young and old normal C57BL/6Jax mice were examined first to constitute a standard, and they were found to exhibit age-related cataract development. Following this, four models on the C57BL/6 background with imposed genetic alterations affecting anti-oxidant enzyme presence or activity, and one outbred model in which a deletion blocked the growth hormone/IGF-1 axis, were similarly examined. There was no evidence of foetal or juvenile cataract development in any of these models, and an age-related severity for lens opacities was shown between young adult and old mice in all groups. Model 1, mice null for the anti-oxidant gene glutathione peroxidase-1 (GPX1) had significantly advanced cataracts in older mice vs. same age controls. In mouse model 2 hemizygous knockout of SOD2 (MnSOD) did not affect age-related cataract development. In model 3 combining the GPX1 and SOD2 deficiencies in the same animal did not advance cataract development beyond that of the GPX1 null alone. In model 4 the addition of anti-oxidant protection in the lens by transfection of human catalase targeted only to the mitochondria resulted in a significant delay in cataract development. The 5th model, growth hormone receptor knockout (GHR-/-) mice, also demonstrated a significant reduction in age-related cataract development, as well as dwarfism. These findings, in general, support the oxidative theory of age-related cataract development. The exception, the partial deletion of SOD2 in the hemizygous KO model, probably did not represent a sufficiently severe deprivation of anti-oxidant protection to produce pathologic changes in the lens.

Energy intake, meal frequency, and health: a neurobiological perspective

The size and frequency of meals are fundamental aspects of nutrition that can have profound effects on the health and longevity of laboratory animals. In humans, excessive energy intake is associated with increased incidence of cardiovascular disease, diabetes, and certain cancers and is a major cause of disability and death in industrialized countries. On the other hand, the influence of meal frequency on human health and longevity is unclear. Both caloric (energy) restriction (CR) and reduced meal frequency/intermittent fasting can suppress the development of various diseases and can increase life span in rodents by mechanisms involving reduced oxidative damage and increased stress resistance. Many of the beneficial effects of CR and fasting appear to be mediated by the nervous system. For example, intermittent fasting results in increased production of brain-derived neurotrophic factor (BDNF), which increases the resistance of neurons in the brain to dysfunction and degeneration in animal models of neurodegenerative disorders; BDNF signaling may also mediate beneficial effects of intermittent fasting on glucose regulation and cardiovascular function. A better understanding of the neurobiological mechanisms by which meal size and frequency affect human health may lead to novel approaches for disease prevention and treatment.

Ageing and vision: structure, stability and function of lens crystallins

The alpha-, beta- and gamma-crystallins are the major protein components of the vertebrate eye lens, alpha-crystallin as a molecular chaperone as well as a structural protein, beta- and gamma-crystallins as structural proteins. For the lens to be able to retain life-long transparency in the absence of protein turnover, the crystallins must meet not only the requirement of solubility associated with high cellular concentration but that of longevity as well. For proteins, longevity is commonly assumed to be correlated with long-term retention of native structure, which in turn can be due to inherent thermodynamic stability, efficient capture and refolding of non-native protein by chaperones, or a combination of both. Understanding how the specific interactions that confer intrinsic stability of the protein fold are combined with the stabilizing effect of protein assembly, and how the non-specific interactions and associations of the assemblies enable the generation of highly concentrated solutions, is thus of importance to understand the loss of transparency of the lens with age. Post-translational modification can have a major effect on protein stability but an emerging theme of the few studies of the effect of post-translational modification of the crystallins is one of solubility and assembly. Here we review the structure, assembly, interactions, stability and post-translational modifications of the crystallins, not only in isolation but also as part of a multi-component system. The available data are discussed in the context of the establishment, the maintenance and finally, with age, the loss of transparency of the lens. Understanding the structural basis of protein stability and interactions in the healthy eye lens is the route to solve the enormous medical and economical problem of cataract.

Protein profile of aging and its retardation by caloric restriction in neural retina

Aging is a slow, gradual deterioration process of an organism. The only experimental intervention, which can reliably retard aging and age-related degenerative diseases, is dietary caloric restriction (CR). To gain insight into the mechanism of CR intervention, we have investigated the protein profile of aging and its retardation by CR in the neural retina of Brown Norway (BN) rats using the comprehensive proteomic approach. We found that the intensities of 18 proteins decreased significantly with age. CR intervention can completely prevent seven of them, and partially protect eight of them, from such age-related declines. The major protein targets protected by CR intervention appear to be glycolytic enzymes and molecular chaperones. These data are the first to suggest that CR may retard the age-related degeneration of retina by maintaining sufficient glucose metabolism, by ensuring proper protein folding, and/or by preventing protein denaturation in the neural retina.

Dietary caloric restriction may delay the development of cataract by attenuating the oxidative stress in the lenses of Brown Norway rats

Dietary caloric restriction (CR) is the only experimental intervention that can reliably retard the development of cataract in a normal animal model. Here we have studied the possible mechanisms by which CR retards the age-related degeneration of the lens of Brown Norway rats. We have found that CR slowed protein insolubilization and blunted declines of the total soluble thiols, protein thiols, reduced glutathione and ascorbic acid levels in the lenses of old BN rats. From the lens protein point of view, the development of cataract in rat lenses has 3 stages: (1) the precipitation of gamma-crystallin, (2) the insolubilization of beta-crystallin, and (3) the final precipitation of alpha-crystallin which was saturated with other denatured lens proteins. A similar sequence is also observed when the lens proteins are subjected to oxidative stress in vitro. These data are the first to suggest that CR may retard the age-related degeneration of the lens by attenuating the oxidative stress in the lens. Since oxidative stress is likely a main cause of human cataract, CR intervention may be relevant to humans as well.

Life-long reduction in MnSOD activity results in increased DNA damage and higher incidence of cancer but does not accelerate aging

Mice heterozygous for the Sod2 gene (Sod2+/- mice) have been used to study the phenotype of life-long reduced Mn-superoxide dismutase (MnSOD) activity. The Sod2+/- mice have reduced MnSOD activity (50%) in all tissues throughout life. The Sod2+/- mice have increased oxidative damage as demonstrated by significantly elevated levels of 8-oxo-2-deoxyguanosine (8oxodG) in nuclear DNA in all tissues of Sod2+/- mice studied. The levels of 8oxodG in nuclear DNA increased with age in all tissues of Sod2+/- and wild-type (WT) mice, and at 26 mo of age, the levels of 8oxodG in nuclear DNA were significantly higher (from 15% in heart to over 60% in liver) in the Sod2+/- mice compared with WT mice. The level of 8oxodG was also higher in mitochondrial DNA isolated from liver and brain in Sod2+/- mice compared with WT mice. The increased oxidative damage to DNA in the Sod2+/- mice is associated with a 100% increase in tumor incidence (the number of mice with tumors) in old Sod2+/- mice compared with the old WT mice. However, the life spans (mean and maximum survival) of the Sod2+/- and WT mice were identical. In addition, biomarkers of aging, such as cataract formation, immune response, and formation of glycoxidation products carboxymethyl lysine and pentosidine in skin collagen changed with age to the same extent in both WT and Sod2+/- mice. Thus life-long reduction of MnSOD activity leads to increased levels of oxidative damage to DNA and increased cancer incidence but does not appear to affect aging.

Caloric restriction retards age-related changes in rat retina

The neural retina of mammals consists of light sensitive photoreceptors and connecting neural cells that receive and send visual signal to the brain. Dietary caloric restriction (CR) is the only experimental intervention that can reliably retard the age-related degeneration of the retina in a normal mammalian model. Here, we studied the effect of CR on various biochemical parameters in the retina of male Brown Norway rats at different ages. We found that CR slowed the age-dependent protein insolubilization, blunted the declines in the total soluble thiols, and reduced glutathione and ascorbic acid levels in neural retina. We also observed that CR retarded the age-related decline in the levels of taurine, a vital amino acid in neural retina. These data are the first to implicate that CR may retard the age-related degeneration of retina by attenuating the oxidative stress and/or by sustaining the pool of protective factors in the neural retina.