Calorie restriction modulates age-dependent changes in the retinas of Brown Norway rats

Multifaceted mitochondrial as a novel therapeutic target in dry eye: insights and interventions

Dry eye, recognized as the most prevalent ocular surface disorder, has risen to prominence as a significant public health issue, adversely impacting the quality of life for individuals across the globe. Despite decades of extensive research into the chronic inflammation that characterizes dry eye, the intricate mechanisms fueling this persistent inflammatory state remain incompletely understood. Among the various cellular components under investigation, mitochondria-essential for cellular energy production and homeostasis-have attracted increasing attention for their role in dry eye pathogenesis. This involvement points to mechanisms such as oxidative stress, apoptosis, and sustained inflammation, which are central to the progression of the disease. This review aims to provide a thorough exploration of mitochondrial dysfunction in dry eye, shedding light on the critical roles played by mitochondrial oxidative stress, apoptosis, and mitochondrial DNA damage. It delves into the mechanisms through which diverse pathogenic factors may trigger mitochondrial dysfunction, thereby contributing to the onset and exacerbation of dry eye. Furthermore, it lays the groundwork for an overview of current therapeutic strategies that specifically target mitochondrial dysfunction, underscoring their potential in managing this complex condition. By spotlighting this burgeoning area of research, our review seeks to catalyze the development of innovative drug discovery and therapeutic approaches. The ultimate goal is to unlock promising avenues for the future management of dry eye, potentially revolutionizing treatment paradigms and improving patient outcomes. Through this comprehensive examination, we endeavor to enrich the scientific community's understanding of dry eye and inspire novel interventions that address the underlying mitochondrial dysfunctions contributing to this widespread disorder.

Evaluating the impact of caloric restriction, body mass index and exercise on primary open-angle glaucoma: A review

This literature review evaluates any possible links between primary open-angle glaucoma (POAG) and caloric restriction (CR), body mass index (BMI), and exercise, aiming to map the extent of the literature. Its primary objective is to recognise the nature and breadth of research evidence, identify possible gaps in these topics and develop future studies. The databases searched were MEDLINE (PudMed), Scopus and ScienceDirect, in April 2023 for articles published in English, with no date restriction. A total of 447 search results were retrieved. Of these, 73 were related to CR, 249 to BMI, and 125 to exercise. Records identified included systematic reviews, meta-analyses, randomised controlled trials, cohort studies and animal studies. CR has been shown to halt the degeneration of retinal ganglion cells and protect against various glaucomatous processes in animal models. Low BMI has been shown to be associated with an increased risk of POAG and a faster rate of visual field deterioration in POAG. However, the association between high BMI and POAG is not consistent. Exercise has been shown to cause mechanical, vascular, and neurobiological changes affecting the pathophysiology of POAG. The present review helps identify key characteristics and factors relating to the impacts of CR, BMI, or exercise on POAG.

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.

A narrative review on dietary components and patterns and age-related macular degeneration

Age-related macular degeneration (AMD) is one of the most prevalent eye diseases among the ageing population worldwide. It is a leading cause of blindness in individuals over 55, particularly in industrialised Western countries. The prevalence of AMD increases with age, and genetic factors and environmental influences are believed to contribute to its development. Among the environmental factors, diet plays a significant role in AMD. This review explores the association between dietary components, dietary patterns and AMD. Various nutrients, non-nutrient substances and dietary models that have the potential to counteract oxidative stress and inflammation, which are underlying mechanisms of AMD, are discussed. Consuming fruits, vegetables, fish and seafood, whole grains, olive oil, nuts and low-glycaemic-index foods has been highlighted as beneficial for reducing the risk of AMD. Adhering to the Mediterranean diet, which encompasses these elements, can be recommended as a dietary pattern for AMD. Furthermore, the modulation of the gut microbiota through dietary interventions and probiotics has shown promise in managing AMD.

The promise of neuroprotection by dietary restriction in glaucoma

Glaucoma, a progressive age-related optic neuropathy characterized by the death of retinal ganglion cells, is the most common neurodegenerative cause of irreversible blindness worldwide. The therapeutic management of glaucoma, which is limited to lowering intraocular pressure, is still a challenge since visual loss progresses in a significant percentage of treated patients. Restricted dietary regimens have received considerable attention as adjuvant strategy for attenuating or delaying the progression of neurodegenerative diseases. Here we discuss the literature exploring the effects of modified eating patterns on retinal aging and resistance to stressor stimuli.

Metabolic syndrome and the aging retina

PURPOSE OF REVIEW

This review explores metabolic syndrome (MetS) as a risk factor that accelerates aging in retinal neurons and may contribute to the neurodegeneration seen in glaucomatous optic neuropathy (GON) and age-related macular degeneration (AMD).

RECENT FINDINGS

Both animal model experiments and epidemiologic studies suggest that metabolic stress may lead to aberrant regulation of a number of cellular pathways that ultimately lead to premature aging of the cell, including those of a neuronal lineage.

SUMMARY

GON and AMD are each leading causes of irreversible blindness worldwide. Aging is a significant risk factor in the specific retinal neuron loss that is seen with each condition. Though aging at a cellular level is difficult to define, there are many mechanistic modifiers of aging. Metabolic-related stresses induce inflammation, oxidative stress, mitochondrial dysfunction, endoplasmic reticulum stress, alterations to the unfolded protein response, defects in autophagy, alterations to the microbiome, and deposition of advanced glycation end products that can all hasten the aging process. Due to the number of variables related to metabolic health, defining criteria to enable the study of risk factors at a population level is challenging. MetS is a definable constellation of related metabolic risk factors that includes enlarged waist circumference, dyslipidemia, systemic hypertension, and hyperglycemia. MetS has been associated with both GON and AMD and may contribute to disease onset and/or progression in each disease.

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.

Effects of caloric restriction on retinal aging and neurodegeneration

Glaucoma is the most common neurodegenerative cause of irreversible blindness worldwide. Restricted caloric regimens are an attractive approach for delaying the progression of neurodegenerative diseases. Here we review the current literature on the effects of caloric restriction on retinal neurons, under physiological and pathological conditions. We focused on autophagy as one of the mechanisms modulated by restricted caloric regimens and involved in the death of retinal ganglion cells (RGCs) over the course of glaucoma.

Null Mutation of the Fascin2 Gene by TALEN Leading to Progressive Hearing Loss and Retinal Degeneration in C57BL/6J Mice

Fascin2 (FSCN2) is an actin cross-linking protein that is mainly localized in retinas and in the stereocilia of hair cells. Earlier studies showed that a deletion mutation in human FASCIN2 (FSCN2) gene could cause autosomal dominant retinitis pigmentosa. Recent studies have indicated that a missense mutation in mouse Fscn2 gene (R109H) can contribute to the early onset of hearing loss in DBA/2J mice. To explore the function of the gene, Fscn2 was knocked out using TALEN (transcription activator-like effector nucleases) on the C57BL/6J background. Four mouse strains with deletions of 1, 4, 5, and 41 nucleotides in the target region of Fscn2 were developed. F1 heterozygous (Fscn2^+/- ) mice carrying the same deletion of 41 nucleotides were mated to generate the Fscn2^-/- mice. As a result, the Fscn2^-/- mice showed progressive hearing loss, as measured in the elevation of auditory brainstem-response thresholds. The hearing impairment began at age 3 weeks at high-stimulus frequencies and became most severe at age 24 weeks. Moreover, degeneration of hair cells and loss of stereocilia were remarkable in Fscn2^-/- mice, as revealed by F-actin staining and scanning electron microscopy. Furthermore, compared to the controls, the Fscn2^-/- mice displayed significantly lower electroretinogram amplitudes and thinner retinas at 8, 16, and 24 weeks. These results demonstrate that, in C57BL/6Jmice, Fscn2 is essential for maintaining ear and eye function and that a null mutation of Fscn2 leads to progressive hearing loss and retinal degeneration.

Effect of Resveratrol as Caloric Restriction Mimetic and Environmental Enrichment on Neurobehavioural Responses in Young Healthy Mice

Caloric restriction and environmental enrichment have been separately reported to possess health benefits such as improvement in motor and cognitive functions. Resveratrol, a natural polyphenolic compound, has been reported to be caloric restriction mimetic. This study therefore aims to investigate the potential benefit of the combination of resveratrol as CR and EE on learning and memory, motor coordination, and motor endurance in young healthy mice. Fifty mice of both sexes were randomly divided into five groups of 10 animals each: group I animals received carboxymethylcellulose (CMC) orally per kg/day (control), group II animals were maintained on every other day feeding, group III animals received resveratrol 50 mg/kg, suspended in 10 g/L of (CMC) orally per kg/day, group IV animals received CMC and were kept in an enriched environment, and group V animals received resveratrol 50 mg/kg and were kept in EE. The treatment lasted for four weeks. On days 26, 27, and 28 of the study period, the animals were subjected to neurobehavioural evaluation. The results obtained showed that there was no significant change (P>0.05) in neurobehavioural responses in all the groups when compared to the control which indicates that 50 mg/kg of resveratrol administration and EE have no significant effects on neurobehavioural responses in young healthy mice over a period of four weeks.

Effects of Long-term Vitamin K (Phylloquinone) Intake on Retina Aging

Emerging evidence suggests neuroprotective functions of vitamin K and/or vitamin K-dependent proteins. We investigated the effect of dietary vitamin K on retina aging (thinning). Female Sprague-Dawley rats were maintained from weaning on low (80 microg kg(-1) diet), adequate (500 microg kg(-1) diet) or high (2000 microg kg(-1) diet) levels of vitamin K1 (phylloquinone). Relative concentrations of brain vitamin K associated with these diets were 1: 3.3: 25 (K1) and 1: 2.7: 9.0 (menaquinone-4). Histomorphometry of old (21 month) rats revealed positive associations between vitamin K and thickness of retina layers, especially in the equatorial/peripheral retina. No association of diet and retina thickness was detected among young (6 month) animals. The sparing effect of vitamin K in the retina was most evident in the inner plexiform layer and in the photoreceptor inner and outer segments. Surprisingly, we observed no effect of vitamin K on the age-dependent loss of photoreceptor cells, interneurons or ganglion cells. These data suggest a role for vitamin K in maintaining the aging retina and suggest that the sparing effect of vitamin K does not reflect the survival-promoting (anti-apoptotic) activities of vitamin K-dependent proteins.

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.

The eye of the laboratory mouse remains anatomically adapted for natural conditions

Evolutionary effects of domestication have been demonstrated for several body systems, including the eye, and for several vertebrate species, including the mouse. Given the importance of the laboratory mouse to vision science, we wished to determine whether the anatomical and histological features of the eyes of laboratory mice are distinct from those of their naturally adapted, wild counterparts. We measured dimensions and masses of whole eyes and lenses from a wild population plus three inbred strains (C57BL/6J, NZB/BINJ, and DBA/1J) of the house house, Mus musculus, as well as wild and outbred laboratory-domesticated stock of the deer mouse, Peromyscus maniculatus. Histological preparations from these eyes were used to determine outer nuclear layer thickness, linear density of the ganglion cell layer, and for indirect immunofluorescence evaluation of cone opsin expression. For all of these traits, no statistically significant differences were found between any laboratory strain and its wild counterpart. The evolutionary effects of domestication of mice therefore do not include changes to the eye in any variable measured, supporting the continued use of this animal as a model for a naturally adapted visual system.

Accommodative function in rhesus monkeys: effects of aging and calorie restriction

Numerous degenerative changes in the visual system occur with age, including a loss of accommodative function possibly related to hardening of the lens or loss of ciliary muscle mobility. The rhesus monkey is a reliable animal model for studying age-related changes in ocular function, including loss of accommodation. Calorie restriction (CR) is the only consistent intervention to slow aging and extend lifespan in rodents, and more recently the beneficial effects of CR have been reported in nonhuman primates. The goal of the present study was to evaluate age-related changes in ocular accommodation and the potential effect of long-term (>8 years) CR on accommodation in male and female rhesus monkeys. Refraction, accommodation (Hartinger coincidence refractometer), and lens thickness (A-scan ultrasound) were measured in 97 male and female rhesus monkeys age 8-36 years under Telazol/acepromazine anesthesia. Refraction and accommodation measurements were taken before and after 40% carbachol corneal iontophoresis to induce maximum accommodation. Half the animals were in the control (CON) group and were fed ad libitum. The CR group received 30% fewer calories than age- and weight-matched controls. Males were on CR for 12 years and females for eight years. With increasing age, accommodative ability declined in both CON and CR monkeys by 1.03 ± 0.12 (P = 0.001) and 1.18 ± 0.12 (P = 0.001) diopters/year, respectively. The age-related decline did not differ significantly between the groups (P = 0.374). Baseline lens thickness increased with age in both groups by 0.03 ± 0.005 mm/year (P = 0.001) and 0.02 ± 0.005 mm/year (P = 0.001) for the CON and CR groups, respectively. The tendency for the for the lens to thicken with age occurred at a slower rate in the CR group vs. the CON group but the difference was not statistically significant (P = 0.086). Baseline refraction was -2.8 ± 0.55 and -3.0 ± 0.62 diopters for CON and CR, respectively. Baseline refraction tended to become slightly more negative with age (P = 0.070), but this trend did not differ significantly between the groups (P = 0.587). In summary, there was no difference in the slope of the age-related changes in accommodation, lens thickness, or refraction in the carbachol-treated eyes due to diet. These data are consistent with previous findings of decreased accommodative ability in aging rhesus monkeys, comparable to the age-dependent decrease in accommodative ability in humans. This study is the first to indicate that the accommodative system may not benefit from calorie restriction.

Neuronal susceptibility to damage: comparison of the retinas of young, old and old/caloric restricted rats before and after transient ischemia

Compared to young rats, old age increases susceptibility and caloric restriction decreases susceptibility for the loss of retinal ganglion cells and displaced amacrine cells following retinal ischemia/reperfusion. In retinas of old animals before ischemia, reactive gliosis, including activation of Muller cells, microglia and astrocytes, is increased compared to retinas from young and old/caloric restricted animals. Post-ischemia, the existing reactive gliosis in retinas of old animals is not neuroprotective and the reactive gliosis is even further increased in old animals compared to young or old/caloric restricted animals. In retinas from old/caloric restricted animals, inducible heat shock protein-70 and brain-derived neurotrophic factor increased more markedly after ischemia/reperfusion compared to retinas from young and old animals. Thus, compared to retinas in young animals, neurons of old animals may be more susceptible to cell death by secondary glial mechanisms after retinal ischemia/reperfusion. Caloric restriction in old animals is neuroprotective against damage in the retina following ischemia, perhaps by suppressing glial activity and by the neuroprotective effects of inducible heat shock protein-70 and brain-derived neurotrophic factor.

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.

2-Deoxy-D-glucose protects retinal ganglion cells against excitotoxicity

Caloric restriction mimicked by administration of 2-deoxy-D-glucose (2DG) has been shown to protect cerebral neurons against ischemia and excitotoxicity. This study examined the protective effects of pretreatment with 2DG on retinal neurons in N-methyl-D-aspartate (NMDA) excitotoxicity in rats. There was a significantly reduced number of TUNEL-labeled cells in the retinal ganglion cell layer 18 h after intravitreal injection of NMDA with 2DG pretreatment. At 7 days after NMDA, 2DG pretreatment significantly preserved neurons in the retinal ganglion cell layer and reduced immunoreactivity of glial fibrillary acidic proteins in retinas. Our findings demonstrate that caloric restriction mimicked by 2DG protects retinas from NMDA excitotoxicity.

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.

Evidence for two apoptotic pathways in light-induced retinal degeneration

Excessive phototransduction signaling is thought to be involved in light-induced and inherited retinal degeneration. Using knockout mice with defects in rhodopsin shut-off and transducin signaling, we show that two different pathways of photoreceptor-cell apoptosis are induced by light. Bright light induces apoptosis that is independent of transducin and accompanied by induction of the transcription factor AP-1. By contrast, low light induces an apoptotic pathway that requires transducin. We also provide evidence that additional genetic factors regulate sensitivity to light-induced damage. Our use of defined mouse mutants resolves some of the complexity underlying the mechanisms that regulate susceptibility to retinal degeneration.

Augmented rod bipolar cell function in partial receptor loss: an ERG study in P23H rhodopsin transgenic and aging normal rats

Physiological consequences of early stages of photoreceptor degeneration were examined in heterozygous P23H rhodopsin transgenic (Tg) and in aging normal Sprague-Dawley rats. Rod photoreceptor and rod bipolar (RB) cell function were estimated with maximum value and sensitivity parameters of P3 and P2 components of the electroretinogram. In both Tg and aging normal rats, the age-related rate of decline of P3 amplitude was steeper than that of the P2 amplitude. Tg rats showed greater than normal sensitivity of the rods. A new model of distal RB pathway connectivity suggested photoreceptor loss could not be the sole cause of physiological abnormalities; there was an additional increase of post-receptoral sensitivity. We propose that changes at rod-RB synapses compensate for the partial loss of rod photoreceptors in senescence and in early stages of retinal degeneration.