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

Functional analyses of human DNA repair proteins important for aging and genomic stability using yeast genetics

Model systems have been extremely useful for studying various theories of aging. Studies of yeast have been particularly helpful to explore the molecular mechanisms and pathways that affect aging at the cellular level in the simple eukaryote. Although genetic analysis has been useful to interrogate the aging process, there has been both interest and debate over how functionally conserved the mechanisms of aging are between yeast and higher eukaryotes, especially mammalian cells. One area of interest has been the importance of genomic stability for age-related processes, and the potential conservation of proteins and pathways between yeast and human. Translational genetics have been employed to examine the functional roles of mammalian proteins using yeast as a pliable model system. In the current review recent advancements made in this area are discussed, highlighting work which shows that the cellular functions of human proteins in DNA repair and maintenance of genomic stability can be elucidated by genetic rescue experiments performed in yeast.

Circadian rhythms, aging, and life span in mammals

Resetting the circadian clock leads to well being and increased life span, whereas clock disruption is associated with aging and morbidity. Increased longevity and improved health can be achieved by different feeding regimens that reset circadian rhythms and may lead to better synchrony in metabolism and physiology. This review focuses on recent findings concerning the relationships between circadian rhythms, aging attenuation, and life-span extension in mammals.

Height and survival at older ages among men born in an inland village in Sardinia (Italy), 1866-2006

This study investigated the relationship between individual height and survival at older ages among conscripts born between 1866 and 1915 in an inland village of Sardinia, Italy. Individual age at death was related to military height measurement at age 20. Differential longevity of conscripts at older ages was investigated through the comparison of age-specific mortality rates and life expectancy estimates. Results indicated that short conscripts (<161.1 cm) generally had higher survival rates than their tall peers (≥ 161.1 cm). At 70 years of age, tall peers were expected to live two years less than short conscripts. Biological mechanisms were examined in relation to the greater longevity of shorter people.

Low-dose-rate, low-dose irradiation delays neurodegeneration in a model of retinitis pigmentosa

The existence of radiation hormesis is controversial. Several stimulatory effects of low-dose (LD) radiation have been reported to date; however, the effects on neural tissue or neurodegeneration remain unknown. Here, we show that LD radiation has a neuroprotective effect in mouse models of retinitis pigmentosa, a hereditary, progressive neurodegenerative disease that leads to blindness. Various LD radiation doses were administered to the eyes in a retinal degeneration mouse model, and their pathological and physiological effects were analyzed. LD gamma radiation in a low-dose-rate (LDR) condition rescues photoreceptor cell apoptosis both morphologically and functionally. The greatest effect was observed in a condition using 650 mGy irradiation and a 26 mGy/minute dose rate. Multiple rounds of irradiation strengthened this neuroprotective effect. A characteristic up-regulation (563%) of antioxidative gene peroxiredoxin-2 (Prdx2) in the LDR-LD-irradiated retina was observed compared to the sham-treated control retina. Silencing the Prdx2 using small-interfering RNA administration reduced the LDR-LD rescue effect on the photoreceptors. Our results demonstrate for the first time that LDR-LD irradiation has a biological effect in neural cells of living animals. The results support that radiation exhibits hormesis, and this effect may be applied as a novel therapeutic concept for retinitis pigmentosa and for other progressive neurodegenerative diseases regardless of the mechanism of degeneration involved.

Calorie restriction and prevention of age-associated chronic disease

Life expectancy in the world has increased dramatically during the last century; the number of older adults is expected to rise while the number of youths will decline in the near future. This demographic shift has considerable public health and economic implications since aging is associated with the development of serious chronic diseases. Calorie restriction (CR) is the most effective nutritional intervention for slowing aging and preventing chronic disease in rodents. In non-human and human primates, CR with adequate nutrition protects against abdominal obesity, diabetes, hypertension and cardiovascular diseases. Cancer morbidity and mortality are also diminished in CR monkeys, and data obtained from individuals practicing long-term CR show a reduction of metabolic and hormonal factors associated with increased cancer risk.

Extended longevity of reproductives appears to be common in Fukomys mole-rats (Rodentia, Bathyergidae)

African mole-rats (Bathyergidae, Rodentia) contain several social, cooperatively breeding species with low extrinsic mortality and unusually high longevity. All social bathyergids live in multigenerational families where reproduction is skewed towards a few breeding individuals. Most of their offspring remain as reproductively inactive “helpers” in their natal families, often for several years. This “reproductive subdivision” of mole-rat societies might be of interest for ageing research, as in at least one social bathyergid (Ansell's mole-rats Fukomys anselli), breeders have been shown to age significantly slower than non-breeders. These animals thus provide excellent conditions for studying the epigenetics of senescence by comparing divergent longevities within the same genotypes without the inescapable short-comings of inter-species comparisons. It has been claimed that many if not all social mole-rat species may have evolved similar ageing patterns, too. However, this remains unclear on account of the scarcity of reliable datasets on the subject. We therefore analyzed a 20-year breeding record of Giant mole-rats Fukomys mechowii, another social bathyergid species. We found that breeders indeed lived significantly longer than helpers (ca. 1.5–2.2fold depending on the sex), irrespective of social rank or other potentially confounding factors. Considering the phylogenetic positions of F. mechowii and F. anselli and unpublished data on a third Fukomys-species (F. damarensis) showing essentially the same pattern, it seems probable that the reversal of the classic trade-off between somatic maintenance and sexual reproduction is characteristic of the whole genus and hence of the vast majority of social mole-rats.

Intermittent fasting improves functional recovery after rat thoracic contusion spinal cord injury

Spinal cord injury (SCI) often results in a loss of motor and sensory function. Currently there are no validated effective clinical treatments. Previously we found in rats that dietary restriction, in the form of every-other-day fasting (EODF), started prior to (pre-EODF), or after (post-EODF) an incomplete cervical SCI was neuroprotective, increased plasticity, and promoted motor recovery. Here we examined if EODF initiated prior to, or after, a T10 thoracic contusion injury would similarly lead to enhanced functional recovery compared to ad libitum feeding. Additionally, we tested if a group fed every day (pair-fed), but with the same degree of restriction as the EODF animals (∼25% calorie restricted), would also promote functional recovery, to examine if EODF's effect is due to overall calorie restriction, or is specific to alternating sequences of 24-h fasts and ad libitum eating periods. Behaviorally, both pre- and post-EODF groups exhibited better functional recovery in the regularity indexed BBB ambulatory assessment, along with several parameters of their walking pattern measured with the CatWalk device, compared to both the ad-libitium-fed group as well as the pair-fed group. Several histological parameters (intensity and symmetry of serotonin immunostaining caudal to the injury and gray matter sparing) correlated with functional outcome; however, no group differences were observed. Thus besides the beneficial effects of EODF after a partial cervical SCI, we now report that alternating periods of fasting (but not pair-fed) also promotes improved hindlimb locomotion after thoracic spinal cord contusion, demonstrating its robust effect in two different injury models.

Effect of feeding regimens on circadian rhythms: implications for aging and longevity

Increased longevity and improved health can be achieved in mammals by two feeding regimens, caloric restriction (CR), which limits the amount of daily calorie intake, and intermittent fasting (IF), which allows the food to be available ad libitum every other day. The precise mechanisms mediating these beneficial effects are still unresolved. Resetting the circadian clock is another intervention that can lead to increased life span and well being, while clock disruption is associated with aging and morbidity. Currently, a large body of evidence links circadian rhythms with metabolism and feeding regimens. In particular, CR, and possibly also IF, can entrain the master clock located in the suprachiasmatic nuclei (SCN) of the brain hypothalamus. These findings raise the hypothesis that the beneficial effects exerted by these feeding regimens could be mediated, at least in part, through resetting of the circadian clock, thus leading to synchrony in metabolism and physiology. This hypothesis is reinforced by a transgenic mouse model showing spontaneously reduced eating alongside robust circadian rhythms and increased life span. This review will summarize recent findings concerning the relationships between feeding regimens, circadian rhythms, and metabolism with implications for ageing attenuation and life span extension.

Caloric restriction and heart function: is there a sensible link?

Calorie restriction (CR) is defined as a reduction in calorie intake below the usual ad libitum intake without malnutrition. Ample of clinical and experimental evidence has demonstrated that CR is capable of retarding aging process and development of cardiovascular disease. Although suppression of reactive oxygen species production and inflammation plays a central role in the favorable cardiovascular effects of CR, the health benefit of CR is believed to be ultimately mediated through a cadre of biochemical and cellular adaptations including redox homeostasis, mitochondrial function, inflammation, apoptosis and autophagy. Despite the apparent beneficial cardiovascular effects of CR, implementation of CR in the health care management is still hampered by apparent applicability issues and health concerns. Here we briefly review the cardiac consequence of CR and discuss whether CR may represent a safe and effective strategy in the management of cardiovascular health.

High fat diet increases hippocampal oxidative stress and cognitive impairment in aged mice: implications for decreased Nrf2 signaling

Long term consumption of a high fat diet (HFD) contributes to increased morbidity and mortality. Yet the specific effects of HFD consumption on brain aging are poorly understood. In the present study 20-month old male C57Bl/6 mice were fed either 'western diet' (41% fat), very high fat lard diet (60% fat), or corresponding control diets for 16 weeks and then assessed for changes in metabolism and brain homeostasis. Although both HFDs increased adiposity and fasting blood glucose, only the high fat lard diet increased age-related oxidative damage (protein carbonyls) and impaired retention in the behavioral test. This selective increase in oxidative damage and cognitive decline was also associated with a decline in NF-E2-related factor 2 (Nrf2) levels and Nrf2 activity, suggesting a potential role for decreased antioxidant response. Taken together, these data suggest that while adiposity and insulin resistance following HFD consumption are linked to increased morbidity, the relationship between these factors and brain homeostasis during aging is not a linear relationship. More specifically, these data implicate impaired Nrf2 signaling and increased cerebral oxidative stress as mechanisms underlying HFD-induced declines in cognitive performance in the aged brain.

Prolonged fasting as a method of mood enhancement in chronic pain syndromes: a review of clinical evidence and mechanisms

Periods of deliberate fasting with restriction to intake of solid food are practiced worldwide, mostly based on a traditional, cultural, or religious background. Recent evidence from clinical trials shows that medically supervised modified fasting (200-500 kcal nutritional intake/day) with periods from 7 to 21 days is efficacious in the treatment of rheumatic diseases and chronic pain syndromes. Here, fasting is frequently accompanied by increased alertness and mood enhancement. The beneficial claims of fasting are supported by experimental research, which has found fasting to be associated with increased brain availability of serotonin, endogenous opioids, and endocannabinoids. Fasting-induced neuroendocrine activation and mild cellular stress response with increased production of neurotrophic factors may also contribute to the mood enhancement of fasting. Fasting treatments may be useful as an adjunctive therapeutic approach in chronic pain patients. The mood-enhancing and pain-relieving effect of therapeutic fasting should be further evaluated in randomized clinical trials.

[Nutritional problems in multiple system atrophy--necessity of early tube feeding and caloric restriction at the advanced stage]

We investigated nutritional states of 28 patients with multiple system atrophy (MSA) by measuring body mass index (BMI), arm muscle circumference (% AMC) and triceps skin fold thickness (% TSF). We also analyzed retrospectively chronological changes of nutritional status in 13 MSA patients surviving more than 10 years. BMI and % AMC were significantly reduced in patients having tube feeding compared with patients who had oral intake, whereas % TSF was increased in some patients with tube feeding. From the chronological study, patients at the stage of respiratory or swallowing deterioration showed marked malnutrition, whereas patients during the advanced, but stable stages with tracheostomy and gastrostomy showed much fat accumulation even under low calorie intake less than 1,000 kcal/day. Daily amount of calorie intake should be sufficient during respiratory or swallowing deterioration, but it should be restricted at the advanced stable stage to avoid fat accumulation.

Mild calorie restriction induces fat accumulation in female C57BL/6J mice

This study investigated the effects of mild calorie restriction (CR) (5%) on body weight, body composition, energy expenditure, feeding behavior, and locomotor activity in female C57BL/6J mice. Mice were subjected to a 5% reduction of food intake relative to baseline intake of ad libitum (AL) mice for 3 or 4 weeks. In experiment 1, body weight was monitored weekly and body composition (fat and lean mass) was determined at weeks 0, 2, and 4 by dual energy X-ray absorptiometry. In experiment 2, body weight was measured every 3 days and body composition was determined by quantitative magnetic resonance weekly, and energy expenditure, feeding behavior, and locomotor activity were determined over 3 weeks in a metabolic chamber. At the end of both experiments, CR mice had greater fat mass (P < 0.01) and less lean mass (P < 0.01) compared with AL mice. Total energy expenditure (P < 0.05) and resting energy expenditure (P < 0.05) were significantly decreased in CR mice compared with AL mice over 3 weeks. CR mice ate significantly more food than AL mice immediately following daily food provisioning at 1600 hours (P < 0.01). These findings showed that mild CR caused increased fat mass, decreased lean mass and energy expenditure, and altered feeding behavior in female C57BL/6J mice. Locomotor activity or brown adipose tissue (BAT) thermogenic capacity did not appear to contribute to the decrease in energy expenditure. The increase in fat mass and decrease in lean mass may be a stress response to the uncertainty of food availability.

Leptin modulates cell morphology and cytokine release in microglia

The appetite suppressing hormone, leptin is now established as an important component of the immune response to pathogens partly via the induction of brain IL-1beta. We have previously demonstrated that this hormone acts on microglia to induce the release of IL-1beta through actions on its functional receptors. In the present study, we extended these findings by demonstrating that leptin's action on microglia is that of a modulator rather than a direct trigger of inflammation. Using primary microglia cultures prepared from rat brain we show that pre-incubation of these cells with leptin for 24h prior to treatment with LPS increased the IL-1beta output 2-fold. This effect was not limited to IL-1beta but was also true for another cytokine, TNF-alpha and chemokines such as CINC-1 and MIP-2. The role of leptin in potentiating the microglial response to LPS appeared to be linked to morphological changes rendering the microglia more reactive. These results suggest that leptin has an important role in microglial function in inflammation and given that its circulating levels fluctuate across a number of conditions, these findings can have important implications for an individual's ability to mount an efficient and complete response to invading pathogens.

Metabolism and circadian rhythms--implications for obesity

Obesity has become a serious public health problem and a major risk factor for the development of illnesses, such as insulin resistance and hypertension. Human homeostatic systems have adapted to daily changes in light and dark in a way that the body anticipates the sleep and activity periods. Mammals have developed an endogenous circadian clock located in the suprachiasmatic nuclei of the anterior hypothalamus that responds to the environmental light-dark cycle. Similar clocks have been found in peripheral tissues, such as the liver, intestine, and adipose tissue, regulating cellular and physiological functions. The circadian clock has been reported to regulate metabolism and energy homeostasis in the liver and other peripheral tissues. This is achieved by mediating the expression and/or activity of certain metabolic enzymes and transport systems. In return, key metabolic enzymes and transcription activators interact with and affect the core clock mechanism. In addition, the core clock mechanism has been shown to be linked with lipogenic and adipogenic pathways. Animals with mutations in clock genes that disrupt cellular rhythmicity have provided evidence for the relationship between the circadian clock and metabolic homeostasis. In addition, clinical studies in shift workers and obese patients accentuate the link between the circadian clock and metabolism. This review will focus on the interconnection between the circadian clock and metabolism, with implications for obesity and how the circadian clock is influenced by hormones, nutrients, and timed meals.

Longevity: potential life span and health span enhancement through practice of the basic yoga meditation regimen

This chapter briefly reviews recent psychological, physiological, molecular biological, and anthropological research which has important implications, both direct and indirect, for the recognition and understanding of the potential life span and health span enhancing effects of the basic yoga meditational regimen. This regimen consists of meditation, yogic breath control practices, physical exercises (of both a postural- and movement-based, including aerobic nature), and dietary practices. While each of these component categories exhibit variations in different schools, lineages, traditions, and cultures, the focus of this chapter is primarily on basic forms of relaxation meditation and breath control, as well as postural and aerobic physical exercises (e.g., yogic prostration regimens, see below), and a standard form of yogic or ascetic diet, all of which constitute a basic form of regimen found in many if not most cultures, though with variations.

Common risk factors for changes in body weight and psychological well-being in Japanese male middle-aged workers

OBJECTIVES

Overweight and poor psychological well-being are becoming serious health issues in the Japanese workplace. Concurrence of those physical and mental conditions has been pointed out, especially in middle-aged workers. Therefore, we tried to determine common risk factors for body weight gain and the deterioration of psychological well-being in male middle-aged office workers using a five-year follow-up study.

METHODS

We administered General Health Questionnaire-12 (GHQ-12) as an indicator of psychological well-being to 110 male workers with ages ranging from 40-59 years, and analyzed the influence of several psychological factors, namely sense of coherence (SOC), health locus of control (HLC), and lifestyle variables such as exercise frequency, alcohol intake, smoking status, and dietary intake on changes of body mass index and GHQ-12 score.

RESULTS

McNemar's chi-squared test showed significant concurrence of weight gain and deterioration of psychological well-being after five-year follow-up. Low-SOC score, low frequency of exercise, and high-dietary intake at supper were significantly associated with both weight gain and poorer psychological well-being in workers, results which were supported by multiple regression analysis.

CONCLUSIONS

These results suggest that exercise and calorie restriction seem to prevent weight gain and promote psychological well-being in workers. Low SOC, which implies difficulty in coping with stress, may be an important risk factor not only for deterioration of psychological well-being but also for becoming overweight. These assumptions must be confirmed by conducting future intervention studies on SOC and lifestyle including exercise and eating behavior.

Caloric restriction increases hippocampal glutamate uptake and glutamine synthetase activity in Wistar rats

Recent studies indicate that caloric restriction (CR) protects the central nervous system from several pathological conditions. The impairment of astroglial cell function, including glutamate uptake, glutamine synthetase (GS) activity and S100B secretion, may contribute to the progression of neurological disorders. The present study aimed to evaluate hippocampal astrocytic changes in response to CR diet, measuring astroglial parameters, such as glutamate uptake, GS activity and the immunocontent of GFAP and S100B. Blood biochemical parameters were also analyzed. Rats (60-day old) were fed ad libitum or on CR diets for 12 weeks. CR-fed rats showed approximately 16% less body weight gain than control rats. The CR diet was able to induce a significant increase in glutamate uptake (23%) and in GS activity (26%). There were no statistically significant differences in the immunocontent of either GFAP or S100B. In summary, the present study indicates that CR also modulates astrocyte functions by increasing glutamate uptake and GS activity, suggesting that CR might exert its neuroprotective effects against brain illness by modulation of astrocytic functions.

Effect of intermittent fasting on circadian rhythms in mice depends on feeding time

Calorie restriction (CR) resets circadian rhythms and extends life span. Intermittent fasting (IF) also extends life span, but its affect on circadian rhythms has not been studied. To study the effect of IF alongside CR, we imposed IF in FVB/N mice or IF combined with CR using the transgenic FVB/N alphaMUPA mice that, when fed ad libitum, exhibit spontaneously reduced eating and extended life span. Our results show that when food was introduced during the light period, body temperature peak was not disrupted. In contrast, IF caused almost arrhythmicity in clock gene expression in the liver and advanced mPer2 and mClock expression. However, IF restored the amplitudes of clock gene expression under disruptive light condition regardless whether the animals were calorically restricted or not. Unlike daytime feeding, nighttime feeding yielded rhythms similar to those generated during ad libitum feeding. Taken together, our results show that IF can affect circadian rhythms differently depending on the timing of food availability, and suggest that this regimen induces a metabolic state that affects the suprachiasmatic nuclei (SCN) clock.

Promoting cognitive health and vitality: a review of clinical implications

To maintain cognitive health and vitality, multidimensional cognitive structures must be developed and preserved. With a focus on patient education and health promotion, nurses in general, and geriatric nurses in particular, can proactively address concerns and fears that their patients have about dementia-related illnesses through strategies geared at promoting cognitive health and sustaining abilities. A clinical review of the research literature on the topic of cognitive health revealed the transdisciplinary nature of research on this topic. Effective strategies identified for promoting cognitive health and vitality are categorized as follows: prevention and management of chronic conditions, nutrition, physical activity, mental activity, and social engagement. Current research findings on the promotion of cognitive health and vitality are explored, and research-based implications for geriatric nursing practice are discussed.

Role of secretory phospholipase a(2) in CNS inflammation: implications in traumatic spinal cord injury

Secretory phospholipases A(2) (sPLA(2)s) are a subfamily of lipolytic enzymes which hydrolyze the acyl bond at the sn-2 position of glycerophospholipids to produce free fatty acids and lysophospholipids. These products are precursors of bioactive eicosanoids and platelet-activating factor (PAF). The hydrolysis of membrane phospholipids by PLA(2) is a rate-limiting step for generation of eicosanoids and PAF. To date, more than 10 isozymes of sPLA(2) have been found in the mammalian central nervous system (CNS). Under physiological conditions, sPLA(2)s are involved in diverse cellular responses, including host defense, phospholipid digestion and metabolism. However, under pathological situations, increased sPLA(2) activity and excessive production of free fatty acids and their metabolites may lead to inflammation, loss of membrane integrity, oxidative stress, and subsequent tissue injury. Emerging evidence suggests that sPLA(2) plays a role in the secondary injury process after traumatic or ischemic injuries in the brain and spinal cord. Importantly, sPLA(2) may act as a convergence molecule that mediates multiple key mechanisms involved in the secondary injury since it can be induced by multiple toxic factors such as inflammatory cytokines, free radicals, and excitatory amino acids, and its activation and metabolites can exacerbate the secondary injury. Blocking sPLA(2) action may represent a novel and efficient strategy to block multiple injury pathways associated with the CNS secondary injury. This review outlines the current knowledge of sPLA(2) in the CNS with emphasis placed on the possible roles of sPLA(2) in mediating CNS injuries, particularly the traumatic and ischemic injuries in the brain and spinal cord.

Hormesis and medicine

Evidence is presented which supports the conclusion that the hormetic dose-response model is the most common and fundamental in the biological and biomedical sciences, being highly generalizable across biological model, endpoint measured and chemical class and physical agent. The paper provides a broad spectrum of applications of the hormesis concept for clinical medicine including anxiety, seizure, memory, stroke, cancer chemotherapy, dermatological processes such as hair growth, osteoporosis, ocular diseases, including retinal detachment, statin effects on cardiovascular function and tumour development, benign prostate enlargement, male sexual behaviours/dysfunctions, and prion diseases.

The neuroprotective properties of calorie restriction, the ketogenic diet, and ketone bodies

Both calorie restriction and the ketogenic diet possess broad therapeutic potential in various clinical settings and in various animal models of neurological disease. Following calorie restriction or consumption of a ketogenic diet, there is notable improvement in mitochondrial function, a decrease in the expression of apoptotic and inflammatory mediators and an increase in the activity of neurotrophic factors. However, despite these intriguing observations, it is not yet clear which of these mechanisms account for the observed neuroprotective effects. Furthermore, limited compliance and concern for adverse effects hamper efforts at broader clinical application. Recent research aimed at identifying compounds that can reproduce, at least partially, the neuroprotective effects of the diets with less demanding changes to food intake suggests that ketone bodies might represent an appropriate candidate. Ketone bodies protect neurons against multiple types of neuronal injury and are associated with mitochondrial effects similar to those described during calorie restriction or ketogenic diet treatment. The present review summarizes the neuroprotective effects of calorie restriction, of the ketogenic diet and of ketone bodies, and compares their putative mechanisms of action.

Driving GDNF expression: the green and the red traffic lights

Glial cell line-derived neurotrophic factor (GDNF) is widely recognized as a potent survival factor for dopaminergic neurons of the nigrostriatal pathway that degenerate in Parkinson's disease (PD). In animal models of PD, GDNF delivery to the striatum or the substantia nigra protects dopaminergic neurons against subsequent toxin-induced injury and rescues previously damaged neurons, promoting recovery of the motor function. Thus, GDNF was proposed as a potential therapy to PD aimed at slowing down, halting or reversing neurodegeneration, an issue addressed in previous reviews. However, the use of GDNF as a therapeutic agent for PD is hampered by the difficulty in delivering it to the brain. Another potential strategy is to stimulate the endogenous expression of GDNF, but in order to do that we need to understand how GDNF expression is regulated. The aim of this review is to do a comprehensive analysis of the state of the art on the control of endogenous GDNF expression in the nervous system, focusing mainly on the nigrostriatal pathway. We address the control of GDNF expression during development, in the adult brain and after injury, and how damaged neurons signal glial cells to up-regulate GDNF. Pharmacological agents or natural molecules that increase GDNF expression and show neuroprotective activity in animal models of PD are reviewed. We also provide an integrated overview of the signalling pathways linking receptors for these molecules to the induction of GDNF gene, which might also become targets for neuroprotective therapies in PD.

Gene expression atlas of the mouse central nervous system: impact and interactions of age, energy intake and gender

The transcriptional profiles of five regions of the central nervous system (CNS) of mice varying in age, gender and dietary intake were measured by microarray. The resulting data provide insights into the mechanisms of age-, diet- and gender-related CNS plasticity and vulnerability in mammals.

Background

The structural and functional complexity of the mammalian central nervous system (CNS) is organized and modified by complicated molecular signaling processes that are poorly understood.

Results

We measured transcripts of 16,896 genes in 5 CNS regions from cohorts of young, middle-aged and old male and female mice that had been maintained on either a control diet or a low energy diet known to retard aging. Each CNS region (cerebral cortex, hippocampus, striatum, cerebellum and spinal cord) possessed its own unique transcriptome fingerprint that was independent of age, gender and energy intake. Less than 10% of genes were significantly affected by age, diet or gender, with most of these changes occurring between middle and old age. The transcriptome of the spinal cord was the most responsive to age, diet and gender, while the striatal transcriptome was the least responsive. Gender and energy restriction had particularly robust influences on the hippocampal transcriptome of middle-aged mice. Prominent functional groups of age- and energy-sensitive genes were those encoding proteins involved in DNA damage responses (Werner and telomere-associated proteins), mitochondrial and proteasome functions, cell fate determination (Wnt and Notch signaling) and synaptic vesicle trafficking.

Conclusion

Mouse CNS transcriptomes responded to age, energy intake and gender in a regionally distinctive manner. The systematic transcriptome dataset also provides a window into mechanisms of age-, diet- and sex-related CNS plasticity and vulnerability.

Brain foods: the effects of nutrients on brain function

It has long been suspected that the relative abundance of specific nutrients can affect cognitive processes and emotions. Newly described influences of dietary factors on neuronal function and synaptic plasticity have revealed some of the vital mechanisms that are responsible for the action of diet on brain health and mental function. Several gut hormones that can enter the brain, or that are produced in the brain itself, influence cognitive ability. In addition, well-established regulators of synaptic plasticity, such as brain-derived neurotrophic factor, can function as metabolic modulators, responding to peripheral signals such as food intake. Understanding the molecular basis of the effects of food on cognition will help us to determine how best to manipulate diet in order to increase the resistance of neurons to insults and promote mental fitness.

Dietary restriction started after spinal cord injury improves functional recovery

Spinal cord injury typically results in limited functional recovery. Here we investigated whether therapeutic dietary restriction, a multi-faceted, safe, and clinically-feasible treatment, can improve outcome from cervical spinal cord injury. The well-established notion that dietary restriction increases longevity has kindled interest in its potential benefits in injury and disease. When followed for several months prior to insult, prophylactic dietary restriction triggers multiple molecular responses and improves outcome in animal models of stroke and myocardial infarction. However, the efficacy of the clinically-relevant treatment of post-injury dietary restriction is unknown. Here we report that "every-other-day fasting" (EODF), a form of dietary restriction, implemented after rat cervical spinal cord injury was neuroprotective, promoted plasticity, and improved behavioral recovery. Without causing weight loss, EODF improved gait-pattern, forelimb function during ladder-crossing, and vertical exploration. In agreement, EODF preserved neuronal integrity, dramatically reduced lesion volume by >50%, and increased sprouting of corticospinal axons. As expected, blood beta-hydroxybutyrate levels, a ketone known to be neuroprotective, were increased by 2-3 fold on the fasting days. In addition, we found increased ratios of full-length to truncated trkB (receptor for brain-derived neurotrophic factor) in the spinal cord by 2-6 folds at both 5 days (lesion site) and 3 weeks after injury (caudal to lesion site) which may further enhance neuroprotection and plasticity. Because EODF is a safe, non-invasive, and low-cost treatment, it could be readily translated into the clinical setting of spinal cord injury and possibly other insults.

Exercise, oxidative stress and hormesis

Physical inactivity leads to increased incidence of a variety of diseases and it can be regarded as one of the end points of the exercise-associated hormesis curve. On the other hand, regular exercise, with moderate intensity and duration, has a wide range of beneficial effects on the body including the fact that it improves cardio-vascular function, partly by a nitric oxide-mediated adaptation, and may reduce the incidence of Alzheimer's disease by enhanced concentration of neurotrophins and by the modulation of redox homeostasis. Mechanical damage-mediated adaptation results in increased muscle mass and increased resistance to stressors. Physical inactivity or strenuous exercise bouts increase the risk of infection, while moderate exercise up-regulates the immune system. Single bouts of exercise increases, and regular exercise decreases the oxidative challenge to the body, whereas excessive exercise and overtraining lead to damaging oxidative stress and thus are an indication of the other end point of the hormetic response. Based upon the genetic setup, regular moderate physical exercise/activity provides systemic beneficial effects, including improved physiological function, decreased incidence of disease and a higher quality of life.

Motor skill training, but not voluntary exercise, improves skilled reaching after unilateral ischemic lesions of the sensorimotor cortex in rats

BACKGROUND AND PURPOSE

Exercise and rehabilitative training each have been implicated in the promotion of restorative neural plasticity after cerebral injury. Because motor skill training induces synaptic plasticity and exercise increases plasticity-related proteins, we asked if exercise could improve the efficacy of training on a skilled motor task after focal cortical lesions.

METHODS

Female young and middle-aged rats were trained on the single-pellet retrieval task and received unilateral ischemic sensorimotor cortex lesions contralateral to the trained limb. Rats then received both, either, or neither voluntary running and/or rehabilitative training for 5 weeks beginning 5 days postlesion. Motor skill training consisted of daily practice of the impaired forelimb in a tray-reaching task. Exercised rats had free access to running wheels for 6 h/day. Reaching function was periodically probed using the single-pellet retrieval task.

RESULTS

In young adults, motor skill training significantly enhanced skilled reaching recovery compared to controls. However, exercise did not significantly enhance performance when administered alone or in combination with skill training. There was also no major benefit of exercise in older rats. Additionally, there were no effects of exercise in a measure of coordinated forelimb placement (the foot-fault test) or in immunocytochemical measures of several plasticity-related proteins in the motor cortex.

CONCLUSIONS

In young and middle-aged animals, exercise did not improve motor skill training efficacy following ischemic lesions. Practicing motor skills more effectively improved recovery of these skills than did exercise. It remains possible that an alternative manner of administering exercise would be more effective.

The gene cluster hypothesis of aging and longevity

The maximum longevity of different species can vary by 100-fold in mammals and by 1,000-fold or more from invertebrates to mammals. However, the life extension effect of single gene mutations or dietary restriction converges on a comparatively minute 1.3- to 1.6-fold difference with controls. It is proposed that this can be due to organization of genes affecting maximum life span in large clusters functionally linked by complex interactions analogously to homeotic genes during development. A relatively small number of master genes would control the activity of the structural target genes of the whole cluster, strongly facilitating changes in longevity during species evolution. Experimentally manipulating the expression of those master genes would have the potential to increase maximum longevity to a much higher extent than the options available nowadays. The present availability of the full genome sequence of various organisms including rats, mice and men can greatly help to discover such clustering and to identify those master genes. Fortunately for gerontology, the first highly reliable completed genomes were those of the laboratory rodents and humans, mammals with strongly different maximum longevities, 3-4 years and 122 years, respectively. Comparing them focusing on longevity will help to discover the longevity gene cluster and many other relevant aspects concerning aging rate, and should be encouraged. The gene cluster hypothesis of aging can be tested at least: (a) using bioinformatics tools allowing to look for common sequences in known genes that, based on the evidence available, are expected to be part of the longevity gene cluster; (b) looking for spatial clustering of some of these genes in particular chromosome regions. The huge benefits that could be obtained discovering the longevity gene cluster will amply outweigh the comparatively small research effort involved.

Dietary restriction alters demographic but not behavioral aging in Drosophila

Dietary restriction extends lifespan substantially in numerous species including Drosophila. However, it is unclear whether dietary restriction in flies impacts age-related functional declines in conjunction with its effects on lifespan. Here, we address this issue by assessing the effect of dietary restriction on lifespan and behavioral senescence in two wild-type strains, in our standard white laboratory stock, and in short-lived flies with reduced expression of superoxide dismutase 2. As expected, dietary restriction extended lifespan in all of these strains. The effect of dietary restriction on lifespan varied with genetic background, ranging from 40 to 90% extension of median lifespan in the seven strains tested. Interestingly, despite its robust positive effects on lifespan, dietary restriction had no substantive effects on senescence of behavior in any of the strains in our studies. Our results suggest that dietary restriction does not have a global impact on aging in Drosophila and support the hypothesis that lifespan and behavioral senescence are not driven by identical mechanisms.

Effects of exercise on brain function: role of free radicals

Reactive oxygen species (ROS) are continuously generated during aerobic metabolism. Certain levels of ROS, which could be dependent on the type of cell, cell age, history of ROS exposure, etc., could facilitate specific cell functions. Indeed, ROS stimulate a number of stress responses and activate gene expression for a wide range of proteins. It is well known that increased levels of ROS are involved in the aging process and the pathogenesis of a number of neurodegenerative diseases. Because of the enhanced sensitivity of the central nervous system to ROS, it is especially important to maintain the normal redox state in different types of neuro cells. In the last decade it became clear that regular exercise beneficially affects brain function as well, and can play an important preventive and therapeutic role in stroke and in Alzheimer’s and Parkinson’s diseases. The effects of exercise appear to be very complex and could include neurogenesis via neurotrophic factors, increased capillarization, decreased oxidative damage, and increased proteolytic degradation by proteasome and neprilysin. Data from our and other laboratories indicate that exercise-induced modulation of ROS levels plays a role in the protein content and expression of brain-derived neurotrophic factor, tyrosine recepetor kinase B, and cAMP response element binding protein, resulting in better function and increased neurogenesis. The enhanced activities of proteasome and neprilysin result in decreased accumulation of carbonyls and amyloid beta-proteins, as well as improved memory. It appears that exercise-induced modulation of the redox state is an important means by which exercise benefits brain function, increases the resistance against oxidative stress, and facilitates recovery from oxidative stress.

Brain-derived neurotrophic factor and its receptor tropomyosin-related kinase B in the mechanism of action of antidepressant therapies

The focus of this review is to critically examine and review the literature on the role of brain-derived neurotrophic factor (BDNF) and its primary receptor, tropomyosin-related kinase B (TrkB), in the actions of pharmacologically diverse antidepressant treatments for depression. This will include a review of the studies on the regulation of BDNF and TrkB by different types of antidepressant drug treatments and animal in models of depression, as well as altered levels of BDNF and TrkB in the blood and postmortem brain of patients with depression. Results from clinical and basic studies have demonstrated that stress and depression decrease BDNF expression and neurogenesis and antidepressant treatment reverses or blocks these effects, leading to the neurotrophic hypothesis of depression. Clinical studies demonstrate an association between BDNF levels and several disorders, including depression, epilepsy, bipolar disorder, Parkinson's and Alzheimer's diseases. Physical activity and diet exert neurotrophic effects and positively modulate BDNF levels. A common single nucleotide polymorphism (SNP) in the BDNF gene, a methionine substitution for valine, is associated with alterations in brain anatomy and memory, but what role it has in clinical disorders is unclear. Findings suggest that early childhood events and adult stress produce neurodegenerative alterations in the brain that can eventually cause breakdown of information processing in the neuronal networks regulating mood. Antidepressant treatments elevate activity-dependent neuronal plasticity by activating BDNF, thereby gradually restoring network function and ultimately mood.

The interrelations among feeding, circadian rhythms and ageing

The master clock located in the suprachiasmatic nuclei (SCN) of the anterior hypothalamus in the brain regulates circadian rhythms in mammals. Similar circadian oscillators have been found in peripheral tissues, such as the liver, intestine and retina. Life span has been previously linked independently to both circadian rhythms and caloric restriction (CR). The mechanisms by which CR attenuates ageing and extends life span are virtually unknown. It has recently been found that the alphaMUPA mice, transgenic mice that exhibit spontaneously reduced eating and live longer compared to their FVB/N wild-type control mice, show high amplitude, appropriately reset circadian rhythms. These pronounced rhythms were found both in clock gene expression in the liver and clock-controlled output systems, such as feeding time and body temperature. Furthermore, it was previously shown that CR could reset the central biological clock in the SCN. As the circadian clock in the SCN controls many physiological and biochemical systems, we suggest that appropriately reset peripheral rhythms could constitute an important mediator of longevity in calorically restricted animals. Thus, we suggest that three parameters, i.e., caloric restriction, circadian rhythms and life span, are interconnected. This surmise is novel, and we provide evidence to support it. Furthermore, we discuss other feeding regimens and their effects on circadian rhythms and/or life span.

Alternate day calorie restriction improves clinical findings and reduces markers of oxidative stress and inflammation in overweight adults with moderate asthma

Asthma is an increasingly common disorder responsible for considerable morbidity and mortality. Although obesity is a risk factor for asthma and weight loss can improve symptoms, many patients do not adhere to low calorie diets and the impact of dietary restriction on the disease process is unknown. A study was designed to determine if overweight asthma patients would adhere to an alternate day calorie restriction (ADCR) dietary regimen, and to establish the effects of the diet on their symptoms, pulmonary function and markers of oxidative stress, and inflammation. Ten subjects with BMI>30 were maintained for 8 weeks on a dietary regimen in which they ate ad libitum every other day, while consuming less than 20% of their normal calorie intake on the intervening days. At baseline, and at designated time points during the 8-week study, asthma control, symptoms, and Quality of Life questionnaires (ACQ, ASUI, mini-AQLQ) were assessed and blood was collected for analyses of markers of general health, oxidative stress, and inflammation. Peak expiratory flow (PEF) was measured daily on awakening. Pre- and postbronchodilator spirometry was obtained at baseline and 8 weeks. Nine of the subjects adhered to the diet and lost an average of 8% of their initial weight during the study. Their asthma-related symptoms, control, and QOL improved significantly, and PEF increased significantly, within 2 weeks of diet initiation; these changes persisted for the duration of the study. Spirometry was unaffected by ADCR. Levels of serum beta-hydroxybutyrate were increased and levels of leptin were decreased on CR days, indicating a shift in energy metabolism toward utilization of fatty acids and confirming compliance with the diet. The improved clinical findings were associated with decreased levels of serum cholesterol and triglycerides, striking reductions in markers of oxidative stress (8-isoprostane, nitrotyrosine, protein carbonyls, and 4-hydroxynonenal adducts), and increased levels of the antioxidant uric acid. Indicators of inflammation, including serum tumor necrosis factor-alpha and brain-derived neurotrophic factor, were also significantly decreased by ADCR. Compliance with the ADCR diet was high, symptoms and pulmonary function improved, and oxidative stress and inflammation declined in response to the dietary intervention. These findings demonstrate rapid and sustained beneficial effects of ADCR on the underlying disease process in subjects with asthma, suggesting a novel approach for therapeutic intervention in this disorder.

Intermittent fasting and caloric restriction ameliorate age-related behavioral deficits in the triple-transgenic mouse model of Alzheimer's disease

Alzheimer's disease (AD) is a neurodegenerative disorder characterized by progressive decline in cognitive function associated with the neuropathological hallmarks amyloid beta-peptide (Abeta) plaques and neurofibrillary tangles. Because aging is the major risk factor for AD, and dietary energy restriction can retard aging processes in the brain, we tested the hypothesis that two different energy restriction regimens, 40% calorie restriction (CR) and intermittent fasting (IF) can protect against cognitive decline in the triple-transgenic mouse model of AD (3xTgAD mice). Groups of 3xTgAD mice were maintained on an ad libitum control diet, or CR or IF diets, beginning at 3 months of age. Half of the mice in each diet group were subjected to behavioral testing (Morris swim task and open field apparatus) at 10 months of age and the other half at 17 months of age. At 10 months 3xTgAD mice on the control diet exhibited reduced exploratory activity compared to non-transgenic mice and to 3xTgAD mice on CR and IF diets. Overall, there were no major differences in performance in the water maze among genotypes or diets in 10-month-old mice. In 17-month-old 3xTgAD mice the CR and IF groups exhibited higher levels of exploratory behavior, and performed better in both the goal latency and probe trials of the swim task, compared to 3xTgAD mice on the control diet. 3xTgAD mice in the CR group showed lower levels of Abeta1-40, Abeta1-42 and phospho-tau in the hippocampus compared to the control diet group, whereas Abeta and phospho-tau levels were not decreased in 3xTgAD mice in the IF group. IF may therefore protect neurons against adverse effects of Abeta and tau pathologies on synaptic function. We conclude that CR and IF dietary regimens can ameliorate age-related deficits in cognitive function by mechanisms that may or may not be related to Abeta and tau pathologies.

Effect of fasting on the pattern of urinary arsenic excretion

Millions of people in some of the poorest regions of the world are exposed to high levels of arsenic through drinking contaminated water. It has been reported that development of cancer caused by arsenic exposure in such populations is dependent on dietary and nutritional factors which can modulate arsenic metabolism. Many people in arsenic exposed regions of Bangladesh and India practice fasting for at least one month every year when they refrain from consumption of food and fluid during daylight hours. How such practices may modulate arsenic metabolism has not been previously investigated. This study investigated this issue by determining total arsenic and its species in urine samples from a group of 29 unexposed volunteers at the beginning of the fasting and at the end of approximately 12 h of fasting period. Inductively coupled plasma mass spectrometry (ICP-MS) and high performance liquid chromatography (HPLC) coupled with ICP-MS was used to measure the total arsenic and arsenic speciation in the urine samples, respectively. The mean total levels of arsenic at the beginning of fasting (18.3 microg g(-1) creatinine) and at the end of approximately 12 h of fasting (17.7 microg g(-1) creatinine) did not differ significantly (p > 0.05). However, the percentages of urinary arsenic as the methylated arsenic species methylarsonate (MA) were found to be significantly different (p < 0.05) and this species was observed more frequently at the end of fasting, although its overall concentration was similar. There were no significant differences (p > 0.05) in both the concentrations and percentages of other urinary arsenic species detected, namely arsenobetaine (AB) and dimethylarsinate (DMA). Arsenite (As(III)) and arsenate (As(V)) were also analyzed, but were not detected. We conclude that fasting for a period of 12 h results in a significant increase in the percentage of urinary arsenic as MA, and its frequency of detection in the volunteers at the end of the fasting period is almost nine fold higher. This suggests that metabolism of arsenic is altered by fasting.