Exercise prevents obesity-induced cognitive decline and white matter damage in mice

Determination of no observable effect level of nanoplastics on intestinal flora

The risk of human exposure to nanoplastics (NPs) is increasing due to the incomplete decomposition and accumulation of plastic debris in the environment. Dietary intake is the most common way for human body to ingest NPs. NPs cannot degrade in vivo and will accumulate in multiple tissues, which result in various tissue damages. Although numerous studies have focused on evaluating the influences of exposure to NPs, the exposure amounts investigated were much higher than the actual exposure level in human daily life. Therefore, it is necessary to evaluate the hazards of exposure to low-dose NPs. Intestinal flora is a generally recognized sensitive indicator for NPs exposure, so determining a safe threshold to intestinal flora can represent the maximal no-effective dose for the human body of NPs exposure. Based on these information, mice were exposed to NPs at concentrations of 0, 0.001, 0.005, 0.01 and 0.1 mg kg-1·BW, respectively. The composition changes of the intestinal flora were investigated after exposing 28 days. The obtained consequences indicated that 0.01 mg kg-1·BW was the maximal no-effective dose to intestinal flora. This study provided a clear safe threshold for investigating the potential adverse effects of low-dose NPs exposures on human health.

Exercise Reshapes the Brain: Molecular, Cellular, and Structural Changes Associated with Cognitive Improvements

Physical exercise is well known as a non-pharmacological and holistic therapy believed to prevent and mitigate numerous neurological conditions and alleviate ageing-related cognitive decline. To do so, exercise affects the central nervous system (CNS) at different levels. It changes brain physiology and structure, promoting cognitive improvements, which ultimately improves quality of life. Most of these effects are mediated by neurotrophins release, enhanced adult hippocampal neurogenesis, attenuation of neuroinflammation, modulation of cerebral blood flow, and structural reorganisation, besides to promote social interaction with beneficial cognitive outcomes. In this review, we discuss, based on experimental and human research, how exercise impacts the brain structure and function and how these changes contribute to cognitive improvements. Understanding the mechanisms by which exercise affects the brain is essential to understand the brain plasticity following exercise, guiding therapeutic approaches to improve the quality of life, especially in obesity, ageing, neurodegenerative disorders, and following traumatic brain injury.

The Preventive Effect of Exercise and Oral Branched-Chain Amino Acid Supplementation on Obesity-Induced Brain Changes in Ldlr−/−.Leiden Mice

Exercise and dietary interventions are promising approaches to tackle obesity and its obesogenic effects on the brain. We investigated the impact of exercise and possible synergistic effects of exercise and branched-chain amino acids (BCAA) supplementation on the brain and behavior in high-fat-diet (HFD)-induced obese Ldlr−/−.Leiden mice. Baseline measurements were performed in chow-fed Ldlr−/−.Leiden mice to assess metabolic risk factors, cognition, and brain structure using magnetic resonance imaging. Thereafter, a subgroup was sacrificed, serving as a healthy reference. The remaining mice were fed an HFD and divided into three groups: (i) no exercise, (ii) exercise, or (iii) exercise and dietary BCAA. Mice were followed for 6 months and aforementioned tests were repeated. We found that exercise alone changed cerebral blood flow, attenuated white matter loss, and reduced neuroinflammation compared to non-exercising HFD-fed mice. Contrarily, no favorable effects of exercise on the brain were found in combination with BCAA, and neuroinflammation was increased. However, cognition was slightly improved in exercising mice on BCAA. Moreover, BCAA and exercise increased the percentage of epididymal white adipose tissue and muscle weight, decreased body weight and fasting insulin levels, improved the circadian rhythm, and transiently improved grip strength. In conclusion, BCAA should be supplemented with caution, although beneficial effects on metabolism, behavior, and cognition were observed.

Physical exercise mediates a cortical FMRP-mTOR pathway to improve resilience against chronic stress in adolescent mice

Aerobic exercise effectively relieves anxiety disorders via modulating neurogenesis and neural activity. The molecular mechanism of exercise-mediated anxiolysis, however, remains incomplete. On a chronic restrain stress (CRS) model in adolescent mice, we showed that 14-day treadmill exercise profoundly maintained normal neural activity and axonal myelination in the medial prefrontal cortex (mPFC), in association with the prevention of anxiety-like behaviors. Further interrogation of molecular mechanisms revealed the activation of the mechanistic target of the rapamycin (mTOR) pathway within mPFC under exercise training. At the upstream of mTOR, exercise-mediated brain RNA methylation inhibited the expression of Fragile X mental retardation protein (FMRP) to activate the mTOR pathway. In summary, treadmill exercise modulates an FMRP-mTOR pathway to maintain cortical neural activity and axonal myelination, contributing to improved stress resilience. These results extended our understanding of the molecular substrate of exercise-mediated anxiolytic effect during adolescent period.

Nutrition Strategies Promoting Healthy Aging: From Improvement of Cardiovascular and Brain Health to Prevention of Age-Associated Diseases

BACKGROUND

An increasing number of studies suggest that diet plays an important role in regulating aging processes and modulates the development of the most important age-related diseases.

OBJECTIVE

The aim of this review is to provide an overview of the relationship between nutrition and critical age-associated diseases.

METHODS

A literature review was conducted to survey recent pre-clinical and clinical findings related to the role of nutritional factors in modulation of fundamental cellular and molecular mechanisms of aging and their role in prevention of the genesis of the diseases of aging.

RESULTS

Studies show that the development of cardiovascular and cerebrovascular diseases, neurodegenerative diseases, cognitive impairment and dementia can be slowed down or prevented by certain diets with anti-aging action. The protective effects of diets, at least in part, may be mediated by their beneficial macro- (protein, fat, carbohydrate) and micronutrient (vitamins, minerals) composition.

CONCLUSIONS

Certain diets, such as the Mediterranean diet, may play a significant role in healthy aging by preventing the onset of certain diseases and by improving the aging process itself. This latter can be strengthened by incorporating fasting elements into the diet. As dietary recommendations change with age, this should be taken into consideration as well, when developing a diet tailored to the needs of elderly individuals. Future and ongoing clinical studies on complex anti-aging dietary interventions translating the results of preclinical investigations are expected to lead to novel nutritional guidelines for older adults in the near future.

Sexual dimorphism in spatial learning and brain metabolism after exposure to a western diet and early life stress in rats

Prolonged daily intake of Western-type diet rich in saturated fats and sugars, and exposure to early life stress have been independently linked to impaired neurodevelopment and behaviour in animal models. However, sex-specific effects of both environmental factors combined on spatial learning and memory, behavioural flexibility, and brain oxidative capacity have still not been addressed. The current study aimed to evaluate the impact of maternal and postnatal exposure to a high-fat and high-sugar diet (HFS), and exposure to early life stress by maternal separation in adult male and female Wistar rats. For this purpose, spatial learning and memory and behavioural flexibility were evaluated in the Morris water maze, and regional brain oxidative capacity and oxidative stress levels were measured in the hippocampus and medial prefrontal cortex. Spatial memory, regional brain oxidative metabolism, and levels of oxidative stress differed between females and males, suggesting sexual dimorphism in the effects of a HFS diet and early life stress. Males fed the HFS diet performed better than all other experimental groups independently of early life stress exposure. However, behavioural flexibility evaluated in the spatial reversal leaning task was impaired in males fed the HFS diet. In addition, exposure to maternal separation or the HFS diet increased the metabolic capacity of the prefrontal cortex and dorsal hippocampus in males and females. Levels of oxidative stress measured in the latter brain regions were also increased in groups fed the HFS diet, but maternal separation seemed to dampen regional brain oxidative stress levels. Therefore, these results suggest a compensatory effect resulting from the interaction between prolonged exposure to a HFS diet and early life stress.

Voluntary physical activity improves spatial and recognition memory deficits induced by post-weaning chronic exposure to a high-fat diet

Childhood and adolescent exposure to obesogenic environments has contributed to the development of several health disorders, including neurocognitive impairment. Adolescence is a critical neurodevelopmental window highly influenced by environmental factors that affect brain function until adulthood. Post-weaning chronic exposure to a high-fat diet (HFD) adversely affects memory performance; physical activity is one approach to coping with these dysfunctions. Previous studies indicate that voluntary exercise prevents HFD's detrimental effects on memory; however, it remains to evaluate whether it has a remedial/therapeutical effect when introduced after a long-term HFD exposure. This study was conducted on a diet-induced obesity mice model over six months. After three months of HFD exposure (without interrupting the diet) access to voluntary physical activity was provided. HFD produced weight gain, increased adiposity, and impaired glucose tolerance. Voluntary physical exercise ameliorated glucose tolerance and halted weight gain and fat accumulation. Additionally, physical activity mitigated HFD-induced spatial and recognition memory impairments. Our data indicate that voluntary physical exercise starting after several months of periadolescent HFD exposure reverses metabolic and cognitive alterations demonstrating that voluntary exercise, in addition to its known preventive effect, also has a restorative impact on metabolism and cognition dysfunctions associated with obesity.

Long-term exercise training down-regulates m6A RNA demethylase FTO expression in the hippocampus and hypothalamus: an effective intervention for epigenetic modification

Background

Exercise boosts the health of some brain parts, such as the hippocampus and hypothalamus. Several studies show that long-term exercise improves spatial learning and memory, enhances hypothalamic leptin sensitivity, and regulates energy balance. However, the effect of exercise on the hippocampus and hypothalamus is not fully understood. The study aimed to find epigenetic modifications or changes in gene expression of the hippocampus and hypothalamus due to exercise.

Methods

Male C57BL/6 mice were randomly divided into sedentary and exercise groups. All mice in the exercise group were subjected to treadmill exercise 5 days per week for 1 h each day. After the 12-week exercise intervention, the hippocampus and hypothalamus tissue were used for RNA-sequencing or molecular biology experiments.

Results

In both groups, numerous differentially expressed genes of the hippocampus (up-regulated: 53, down-regulated: 49) and hypothalamus (up-regulated: 24, down-regulated: 40) were observed. In the exercise group, increased level of N6-methyladenosine (m⁶A) was observed in the hippocampus and hypothalamus (p < 0.05). Furthermore, the fat mass and obesity-associated gene (FTO) of the hippocampus and hypothalamus were down-regulated in the exercise group (p < 0.001). In addition, the Fto co-expression genes of the mouse brain were studied and analyzed using database to determine the potential roles of exercise-downregulated FTO in the brain.

Conclusion

The findings demonstrate that long-term exercise might elevates the levels of m⁶A-tagged transcripts in the hippocampus and hypothalamus via down-regulation of FTO. Hence, exercise might be an effective intervention for epigenetic modification.

Glial-neuron crosstalk in health and disease: A focus on metabolism, obesity, and cognitive impairment

Dementia is a complex set of disorders affecting normal cognitive function. Recently, several clinical studies have shown that diabetes, obesity, and components of the metabolic syndrome (MetS) are associated with cognitive impairment, including dementias such as Alzheimer's disease. Maintaining normal cognitive function is an intricate process involving coordination of neuron function with multiple brain glia. Well-orchestrated bioenergetics is a central requirement of neurons, which need large amounts of energy but lack significant energy storage capacity. Thus, one of the most important glial functions is to provide metabolic support and ensure an adequate energy supply for neurons. Obesity and metabolic disease dysregulate glial function, leading to a failure to respond to neuron energy demands, which results in neuronal damage. In this review, we outline evidence for links between diabetes, obesity, and MetS components to cognitive impairment. Next, we focus on the metabolic crosstalk between the three major glial cell types, oligodendrocytes, astrocytes, and microglia, with neurons under physiological conditions. Finally, we outline how diabetes, obesity, and MetS components can disrupt glial function, and how this disruption might impair glia-neuron metabolic crosstalk and ultimately promote cognitive impairment.

The Obese Brain: Mechanisms of Systemic and Local Inflammation, and Interventions to Reverse the Cognitive Deficit

Overweight and obesity are now considered a worldwide pandemic and a growing public health problem with severe economic and social consequences. Adipose tissue is an organ with neuroimmune-endocrine functions, which participates in homeostasis. So, adipocyte hypertrophy and hyperplasia induce a state of chronic inflammation that causes changes in the brain and induce neuroinflammation. Studies with obese animal models and obese patients have shown a relationship between diet and cognitive decline, especially working memory and learning deficiencies. Here we analyze how obesity-related peripheral inflammation can affect central nervous system physiology, generating neuroinflammation. Given that the blood-brain barrier is an interface between the periphery and the central nervous system, its altered physiology in obesity may mediate the consequences on various cognitive processes. Finally, several interventions, and the use of natural compounds and exercise to prevent the adverse effects of obesity in the brain are also discussed.

Milk fat globule membrane attenuates high fat diet-induced neuropathological changes in obese Ldlr-/-.Leiden mice

BACKGROUND

Milk-fat globule membrane (MFGM) is a complex structure secreted by the mammary gland and present in mammalian milk. MFGM contains lipids and glycoproteins as well as gangliosides, which may be involved in myelination processes. Notably, myelination and thereby white matter integrity are often altered in obesity. Furthermore, MFGM interventions showed beneficial effects in obesity by affecting inflammatory processes and the microbiome. In this study, we investigated the impact of a dietary MFGM intervention on fat storage, neuroinflammatory processes and myelination in a rodent model of high fat diet (HFD)-induced obesity.

METHODS

12-week-old male low density lipoprotein receptor-deficient Leiden mice were exposed to a HFD, a HFD enriched with 3% whey protein lipid concentrate (WPC) high in MFGM components, or a low fat diet. The impact of MFGM supplementation during 24-weeks of HFD-feeding was examined over time by analyzing body weight and fat storage, assessing cognitive tasks and MRI scanning, analyzing myelinization with polarized light imaging and examining neuroinflammation using immunohistochemistry.

RESULTS

We found in this study that 24 weeks of HFD-feeding induced excessive fat storage, increased systolic blood pressure, altered white matter integrity, decreased functional connectivity, induced neuroinflammation and impaired spatial memory. Notably, supplementation with 3% WPC high in MFGM components restored HFD-induced neuroinflammation and attenuated the reduction in hippocampal-dependent spatial memory and hippocampal functional connectivity.

CONCLUSIONS

We showed that supplementation with WPC high in MFGM components beneficially contributed to hippocampal-dependent spatial memory, functional connectivity in the hippocampus and anti-inflammatory processes in HFD-induced obesity in rodents. Current knowledge regarding exact biological mechanisms underlying these effects should be addressed in future studies.

Critical Role of Astrocyte NAD+ Glycohydrolase in Myelin Injury and Regeneration

Western-style diets cause disruptions in myelinating cells and astrocytes within the mouse CNS. Increased CD38 expression is present in the cuprizone and experimental autoimmune encephalomyelitis models of demyelination and CD38 is the main nicotinamide adenine dinucleotide (NAD⁺)-depleting enzyme in the CNS. Altered NAD⁺ metabolism is linked to both high fat consumption and multiple sclerosis (MS). Here, we identify increased CD38 expression in the male mouse spinal cord following chronic high fat consumption, after focal toxin [lysolecithin (LL)]-mediated demyelinating injury, and in reactive astrocytes within active MS lesions. We demonstrate that CD38 catalytically inactive mice are substantially protected from high fat-induced NAD⁺ depletion, oligodendrocyte loss, oxidative damage, and astrogliosis. A CD38 inhibitor, 78c, increased NAD⁺ and attenuated neuroinflammatory changes induced by saturated fat applied to astrocyte cultures. Conditioned media from saturated fat-exposed astrocytes applied to oligodendrocyte cultures impaired myelin protein production, suggesting astrocyte-driven indirect mechanisms of oligodendrogliopathy. In cerebellar organotypic slice cultures subject to LL-demyelination, saturated fat impaired signs of remyelination effects that were mitigated by concomitant 78c treatment. Significantly, oral 78c increased counts of oligodendrocytes and remyelinated axons after focal LL-induced spinal cord demyelination. Using a RiboTag approach, we identified a unique in vivo brain astrocyte translatome profile induced by 78c-mediated CD38 inhibition in mice, including decreased expression of proinflammatory astrocyte markers and increased growth factors. Our findings suggest that a high-fat diet impairs oligodendrocyte survival and differentiation through astrocyte-linked mechanisms mediated by the NAD⁺ase CD38 and highlights CD38 inhibitors as potential therapeutic candidates to improve myelin regeneration.SIGNIFICANCE STATEMENT Myelin disturbances and oligodendrocyte loss can leave axons vulnerable, leading to permanent neurologic deficits. The results of this study suggest that metabolic disturbances, triggered by consumption of a diet high in fat, promote oligodendrogliopathy and impair myelin regeneration through astrocyte-linked indirect nicotinamide adenine dinucleotide (NAD⁺)-dependent mechanisms. We demonstrate that restoring NAD⁺ levels via genetic inactivation of CD38 can overcome these effects. Moreover, we show that therapeutic inactivation of CD38 can enhance myelin regeneration. Together, these findings point to a new metabolic targeting strategy positioned to improve disease course in multiple sclerosis and other conditions in which the integrity of myelin is a key concern.

A Review of miRNAs as Biomarkers and Effect of Dietary Modulation in Obesity Associated Cognitive Decline and Neurodegenerative Disorders

There has been a progressive increase in the prevalence of obesity and its comorbidities such as type 2 diabetes and cardiovascular diseases worldwide. Recent studies have suggested that the crosstalk between adipose tissue and central nervous system (CNS), through cellular mediators and signaling pathways, may causally link obesity with cognitive decline and give rise to neurodegenerative disorders. Several mechanisms have been proposed in obesity, including inflammation, oxidative stress, insulin resistance, altered lipid and cholesterol homeostasis, which may result in neuroinflammation, altered brain insulin signaling, amyloid-beta (Aβ) deposition and neuronal cell death. Since obesity is associated with functional and morphological alterations in the adipose tissues, the resulting peripheral immune response augments the development and progression of cognitive decline and increases susceptibility of neurodegenerative disorders, such as Alzheimer's Disease (AD) and Parkinson's Disease (PD). Studies have also elucidated an important role of high fat diet in the exacerbation of these clinical conditions. However, the underlying factors that propel and sustain this obesity associated cognitive decline and neurodegeneration, remains highly elusive. Moreover, the mechanisms linking these phenomena are not well-understood. The cumulative line of evidence have demonstrated an important role of microRNAs (miRNAs), a class of small non-coding RNAs that regulate gene expression and transcriptional changes, as biomarkers of pathophysiological conditions. Despite the lack of utility in current clinical practices, miRNAs have been shown to be highly specific and sensitive to the clinical condition being studied. Based on these observations, this review aims to assess the role of several miRNAs and aim to elucidate underlying mechanisms that link obesity with cognitive decline and neurodegenerative disorders. Furthermore, this review will also provide evidence for the effect of dietary modulation which can potentially ameliorate cognitive decline and neurodegenerative diseases associated with obesity.

The Association between Body Mass Index and Intra-Cortical Myelin: Findings from the Human Connectome Project

Intra-cortical myelin is a myelinated part of the cerebral cortex that is responsible for the spread and synchronization of neuronal activity in the cortex. Recent animal studies have established a link between obesity and impaired oligodendrocyte maturation vis-à-vis cells that produce and maintain myelin; however, the association between obesity and intra-cortical myelination remains to be established. To investigate the effects of obesity on intra-cortical myelin in living humans, we employed a large, demographically well-characterized sample of healthy young adults drawn from the Human Connectome Project (n = 1066). Intra-cortical myelin was assessed using a novel T1-w/T2-w ratio method. Linear regression analysis was used to investigate the association between body mass index (BMI), an indicator of obesity, and intra-cortical myelination, adjusting for covariates of no interest. We observed BMI was related to lower intra-cortical myelination in regions previously identified to be involved in reward processing (i.e., medial orbitofrontal cortex, rostral anterior cingulate cortex), attention (i.e., visual cortex, inferior/middle temporal gyrus), and salience detection (i.e., insula, supramarginal gyrus) in response to viewing food cues (corrected p < 0.05). In addition, higher BMIs were associated with more intra-cortical myelination in regions associated with somatosensory processing (i.e., the somatosensory network) and inhibitory control (i.e., lateral inferior frontal gyrus, frontal pole). These findings were also replicated after controlling for key potential confounding factors including total intracranial volume, substance use, and fluid intelligence. Findings suggested that altered intra-cortical myelination may represent a novel microstructure-level substrate underlying prior abnormal obesity-related brain neural activity, and lays a foundation for future investigations designed to evaluate how living habits, such as dietary habit and physical activity, affect intra-cortical myelination.

New Horizon: Exercise and a Focus on Tissue-Brain Crosstalk

The world population is aging, leading to increased rates of neurodegenerative disorders. Exercise has countless health benefits and has consistently been shown to improve brain health and cognitive function. The purpose of this review is to provide an overview of exercise-induced adaptations in the brain with a focus on crosstalk between peripheral tissues and the brain. We highlight recent investigations into exercise-induced circulating factors, or exerkines, including irisin, cathepsin B, GPLD1, and ketones and the mechanisms mediating their effects in the brain.

Aerobic exercise, cardiorespiratory fitness, and the human hippocampus

The hippocampus is particularly susceptible to neurodegeneration. Physical activity, specifically increasing cardiorespiratory fitness via aerobic exercise, shows promise as a potential method for mitigating hippocampal decline in humans. Numerous studies have now investigated associations between the structure and function of the hippocampus and engagement in physical activity. Still, there remains continued debate and confusion about the relationship between physical activity and the human hippocampus. In this review, we describe the current state of the physical activity and exercise literature as it pertains to the structure and function of the human hippocampus, focusing on four magnetic resonance imaging measures: volume, diffusion tensor imaging, resting-state functional connectivity, and perfusion. We conclude that, despite significant heterogeneity in study methods, populations of interest, and scope, there are consistent positive findings, suggesting a promising role for physical activity in promoting hippocampal structure and function throughout the lifespan.

Sex-dependent effects of forced exercise in the body composition of adolescent rats

Determining the body composition during adolescence can predict diseases such as obesity, diabetes, and metabolic syndromes later in life; and physical activity became an effective way to restore changes in body composition. However, current available literature assessing the body composition before, during and after adolescence in female and male rodents by in vivo techniques is scarce. Thus, by using computerized tomography, we aimed to define the baseline of the weight and body composition during the adolescence and young adulthood of female and male Sprague-Dawley rats (on P30, P60 and P90) under standard diet. Then, we determined the effect of 18 days of forced exercise on the body weight and composition during the early adolescence (P27-45). The highest percentual increments in weight, body volume and relative adipose contents occurred during the female and male adolescence. Forced running during the early adolescence decreased weight, body volume and relative adipose delta and increment values in males only. The adolescence of rats is a period of drastic body composition changes, where exercise interventions have sex-dependent effects. These results support a model that could open new research windows in the field of adolescent obesity.

Staging Alzheimer's Disease in the Brain and Retina of B6.APP/PS1 Mice by Transcriptional Profiling

Alzheimer's disease (AD) is a common form of dementia characterized by amyloid plaque deposition, tau pathology, neuroinflammation, and neurodegeneration. Mouse models recapitulate some key features of AD. For instance, the B6.APP/PS1 model (carrying human transgenes for mutant forms of APP and PSEN1) shows plaque deposition and neuroinflammation involving both astrocytes and microglia beginning around 4-6 months of age. However, significant tau pathology and neurodegeneration are not apparent in this model even when assessed at old age. Therefore, this model is ideal for studying neuroinflammatory responses to amyloid deposition. Here, RNA sequencing of brain and retinal tissue, generalized linear modeling (GLM), functional annotation followed by validation by immunofluorescence was performed in B6.APP/PS1 mice to determine the earliest molecular changes prior to and around the onset of plaque deposition (2-6 months of age). Multiple pathways were shown to be activated in response to amyloid deposition including the JAK/STAT and NALFD pathways. Putative, cell-specific targets of STAT3, a central component of the JAK/STAT pathway, were identified that we propose provide more precise options for assessing the potential for targeting activation of the JAK/STAT pathway as a treatment for human AD. In the retina, GLM predicted activation of vascular-related pathways. However, many of the gene expression changes comparing B6 with B6.APP/PS1 retina samples occurred prior to plaque onset (2 months of age). This suggests retinal changes in B6.APP/PS1 mice may be an artefact of overexpression of mutant forms of APP and PSEN1 providing limited translatability to human AD. Therefore, caution should be taken when using this mouse model to assess the potential of using the eye as a window to the brain for AD.

Evidence of association between obesity and lower cerebral myelin content in cognitively unimpaired adults

BACKGROUND

Myelin loss is a central feature of several neurodegenerative diseases, including Alzheimer's disease (AD). In animal studies, a link has been established between obesity and impairment of oligodendrocyte maturation, the cells that produce and maintain myelin. Although clinical magnetic resonance imaging (MRI) studies have revealed microstructural alterations of cerebral white matter tissue in subjects with obesity, no specific myelin vs. obesity correlation studies have been performed in humans using a direct myelin content metric.

OBJECTIVES

To assess the association between obesity and myelin integrity in cerebral white matter using advanced MRI methodology for myelin content imaging.

METHODS

Studies were performed in the clinical unit of the National Institute on Aging on a cohort of 119 cognitively unimpaired adults. Using advanced MRI methodology, we measured whole-brain myelin water fraction (MWF), a marker of myelin content. Automated brain mapping algorithms and statistical models were used to evaluate the relationships between MWF and obesity, measured using the body mass index (BMI) or waist circumference (WC), in various white matter brain regions.

RESULTS

MWF was negatively associated with BMI or WC in all brain regions evaluated. These associations, adjusted for sex, ethnicity, and age, were statistically significant in most brain regions examined (p < 0.05), with higher BMI or WC corresponding to lower myelin content. Finally, in agreement with previous work, MWF exhibited a quadratic, inverted U-shaped, association with age; this is attributed to the process of myelination from youth through middle age, followed by demyelination afterward.

CONCLUSIONS

These findings suggest that obesity was significantly associated with white matter integrity, and in particular myelin content. We expect that this work will lay the foundation for further investigations to clarify the nature of myelin damage in neurodegeneration, including AD, and the effect of lifestyle factors such as diet and physical activity on myelination.

The Role of Hypothalamic Inflammation in Diet-Induced Obesity and Its Association with Cognitive and Mood Disorders

Obesity is often associated with cognitive and mood disorders. Recent evidence suggests that obesity may cause hypothalamic inflammation. Our aim was to investigate the hypothesis that there is a causal link between obesity-induced hypothalamic inflammation and cognitive and mood disorders. Inflammation may influence hypothalamic inter-connections with regions important for cognition and mood, while it may cause dysregulation of the Hypothalamic-Pituitary-Adrenal (HPA) axis and influence monoaminergic systems. Exercise, healthy diet, and glucagon-like peptide receptor agonists, which can reduce hypothalamic inflammation in obese models, could improve the deleterious effects on cognition and mood.

From Obesity to Hippocampal Neurodegeneration: Pathogenesis and Non-Pharmacological Interventions

High-caloric diet and physical inactivity predispose individuals to obesity and diabetes, which are risk factors of hippocampal neurodegeneration and cognitive deficits. Along with the adipose-hippocampus crosstalk, chronically inflamed adipose tissue secretes inflammatory cytokine could trigger neuroinflammatory responses in the hippocampus, and in turn, impairs hippocampal neuroplasticity under obese and diabetic conditions. Hence, caloric restriction and physical exercise are critical non-pharmacological interventions to halt the pathogenesis from obesity to hippocampal neurodegeneration. In response to physical exercise, peripheral organs, including the adipose tissue, skeletal muscles, and liver, can secret numerous exerkines, which bring beneficial effects to metabolic and brain health. In this review, we summarized how chronic inflammation in adipose tissue could trigger neuroinflammation and hippocampal impairment, which potentially contribute to cognitive deficits in obese and diabetic conditions. We also discussed the potential mechanisms underlying the neurotrophic and neuroprotective effects of caloric restriction and physical exercise by counteracting neuroinflammation, plasticity deficits, and cognitive impairments. This review provides timely insights into how chronic metabolic disorders, like obesity, could impair brain health and cognitive functions in later life.

Long-Term Running Exercise Delays Age-Related Changes in White Matter in Rats

Running exercise, one of the strategies to protect brain function, has positive effects on neurons and synapses in the cortex and hippocampus. However, white matter, as an important structure of the brain, is often overlooked, and the effects of long-term running exercise on white matter are unknown. Here, 14-month-old male Sprague–Dawley (SD) rats were divided into a middle-aged control group (18-month-old control group), an old control group (28-month-old control group), and a long-term runner group (28-month-old runner group). The rats in the runner group underwent a 14-month running exercise regime. Spatial learning ability was tested using the Morris water maze, and white matter volume, myelinated fiber parameters, total mature oligodendrocyte number, and white matter capillary parameters were investigated using stereological methods. The levels of growth factors related to nerve growth and vascular growth in peripheral blood and the level of neurite outgrowth inhibitor-A (Nogo-A) in white matter were measured using an enzyme-linked immunosorbent assay (ELISA). The present results indicated that long-term running exercise effectively delayed the age-related decline in spatial learning ability and the atrophy of white matter by protecting against age-related changes in myelinated fibers and oligodendrocytes in the white matter. Moreover, long-term running exercise prevented age-related changes in capillaries within white matter, which might be related to the protective effects of long-term exercise on aged white matter.

Possible Neuroprotective Mechanisms of Physical Exercise in Neurodegeneration

Physical exercise (PE) improves physical performance, mental status, general health, and well-being. It does so by affecting many mechanisms at the cellular and molecular level. PE is beneficial for people suffering from neuro-degenerative diseases because it improves the production of neurotrophic factors, neurotransmitters, and hormones. PE promotes neuronal survival and neuroplasticity and also optimizes neuroendocrine and physiological responses to psychosocial and physical stress. PE sensitizes the parasympathetic nervous system (PNS), Autonomic Nervous System (ANS) and central nervous system (CNS) by promoting many processes such as synaptic plasticity, neurogenesis, angiogenesis, and autophagy. Overall, it carries out many protective and preventive activities such as improvements in memory, cognition, sleep and mood; growth of new blood vessels in nervous system; and the reduction of stress, anxiety, neuro-inflammation, and insulin resistance. In the present work, the protective effects of PE were overviewed. Suitable examples from the current research work in this context are also given in the article.

A Western diet impairs CNS energy homeostasis and recovery after spinal cord injury: Link to astrocyte metabolism

A diet high in fat and sucrose (HFHS), the so-called Western diet promotes metabolic syndrome, a significant co-morbidity for individuals with spinal cord injury (SCI). Here we demonstrate that the spinal cord of mice consuming HFHS expresses reduced insulin-like growth factor 1 (IGF-1) and its receptor and shows impaired tricarboxylic acid cycle function, reductions in PLP and increases in astrogliosis, all prior to SCI. After SCI, Western diet impaired sensorimotor and bladder recovery, increased microgliosis, exacerbated oligodendrocyte loss and reduced axon sprouting. Direct and indirect neural injury mechanisms are suggested since HFHS culture conditions drove parallel injury responses directly and indirectly after culture with conditioned media from HFHS-treated astrocytes. In each case, injury mechanisms included reductions in IGF-1R, SIRT1 and PGC-1α and were prevented by metformin. Results highlight the potential for a Western diet to evoke signs of neural insulin resistance and injury and metformin as a strategy to improve mechanisms of neural neuroprotection and repair.

Deficiency of Complement Component C1Q Prevents Cerebrovascular Damage and White Matter Loss in a Mouse Model of Chronic Obesity

Age-related cognitive decline and many dementias involve complex interactions of both genetic and environmental risk factors. Recent evidence has demonstrated a strong association of obesity with the development of dementia. Furthermore, white matter damage is found in obese subjects and mouse models of obesity. Here, we found that components of the complement cascade, including complement component 1qa (C1QA) and C3 are increased in the brain of Western diet (WD)-fed obese mice, particularly in white matter regions. To functionally test the role of the complement cascade in obesity-induced brain pathology, female and male mice deficient in C1QA, an essential molecule in the activation of the classical pathway of the complement cascade, were fed a WD and compared with WD-fed wild type (WT) mice, and to C1qa knock-out (KO) and WT mice fed a control diet (CD). C1qa KO mice fed a WD became obese but did not show pericyte loss or a decrease in laminin density in the cortex and hippocampus that was observed in obese WT controls. Furthermore, obesity-induced microglia phagocytosis and breakdown of myelin in the corpus callosum were also prevented by deficiency of C1QA. Collectively, these data show that C1QA is necessary for damage to the cerebrovasculature and white matter damage in diet-induced obesity.

Effects of Long-Term Endurance Exercise and Lithium Treatment on Neuroprotective Factors in Hippocampus of Obese Rats

To investigate the effects of long-term lithium treatment and low intensity endurance exercise on brain-derived neurotrophic factor (BDNF) expression and glycogen synthase kinase 3 beta (GSK3β) activity in the hippocampus of obese rats. Fifty 10-week-old male Sprague-Dawley rats were selected. There was a control group of 10 rats (chow control group) while the other forty rats were fed on a high-fat diet for eight weeks to induce obesity. Rats were then assigned into four random groups. The rats were given 10 mg/kg lithium chloride (LiCl) dissolved in 1 mL sterile distilled water once a day, 5 times a week. The rats did 20 min of treadmill walking with an exercise intensity of 40% maximal oxygen uptake (VO₂ max) (12 m/min, slope 0%). This was performed for 20 min a day, 3 days a week. Twelve weeks of lithium treatment or endurance exercise significantly reduced body weight and body fat mass in obese rats, without showing additive effects when the treatments were given in parallel or significant toxic responses in alanine aminotransferase (ALT) and aspartate aminotransferase (AST) levels in blood and kidney and liver tissues. BDNF expression in the hippocampus was significantly increased both in exercise and lithium groups with synergistic effects found in the group where both exercise and lithium treatments were given in parallel. On the other hand, the decrease in GSK3β activity was shown only in the lithium treatment group, without showing additive effects when the treatments were given in parallel. Lithium and low-intensity endurance exercise for 12 weeks increased the expression of BDNF, a neuroprotective factor in the hippocampus of obese mice. Lithium treatment alone inhibited the activity of GSK3β. This can be interpreted as a positive indication of applicability of the two factors in the prevention of neurodegenerative diseases.

High fat diet consumption results in mitochondrial dysfunction, oxidative stress, and oligodendrocyte loss in the central nervous system

Metabolic syndrome is a key risk factor and co-morbidity in multiple sclerosis (MS) and other neurological conditions, such that a better understanding of how a high fat diet contributes to oligodendrocyte loss and the capacity for myelin regeneration has the potential to highlight new treatment targets. Results demonstrate that modeling metabolic dysfunction in mice with chronic high fat diet (HFD) consumption promotes loss of oligodendrocyte progenitors across the brain and spinal cord. A number of transcriptomic and metabolomic changes in ER stress, mitochondrial dysfunction, and oxidative stress pathways in HFD-fed mouse spinal cords were also identified. Moreover, deficits in TCA cycle intermediates and mitochondrial respiration were observed in the chronic HFD spinal cord tissue. Oligodendrocytes are known to be particularly vulnerable to oxidative damage, and we observed increased markers of oxidative stress in both the brain and spinal cord of HFD-fed mice. We additionally identified that increased apoptotic cell death signaling is underway in oligodendrocytes from mice chronically fed a HFD. When cultured under high saturated fat conditions, oligodendrocytes decreased both mitochondrial function and differentiation. Overall, our findings show that HFD-related changes in metabolic regulators, decreased mitochondrial function, and oxidative stress contribute to a loss of myelinating cells. These studies identify HFD consumption as a key modifiable lifestyle factor for improved myelin integrity in the adult central nervous system and in addition new tractable metabolic targets for myelin protection and repair strategies.

The orbitofrontal cortex functionally links obesity and white matter hyperintensities

Many studies have linked dysfunction in cognitive control-related brain regions with obesity and the burden of white matter hyperintensities (WMHs). This study aimed to explore how functional connectivity differences in the brain are associated with WMH burden and degree of obesity using resting-state functional magnetic resonance imaging (fMRI) in 182 participants. Functional connectivity measures were compared among four different groups: (1) low WMH burden, non-obese; (2) low WMH burden, obese; (3) high WMH burden, non-obese; and (4) high WMH burden, obese. At a large-scale network-level, no networks showed significant interaction effects, but the frontoparietal network showed a main effect of degree of obesity. At a finer node level, the orbitofrontal cortex showed interaction effects between periventricular WMH burden and degree of obesity. Higher functional connectivity was observed when the periventricular WMH burden and degree of obesity were both high. These results indicate that the functional connectivity of the orbitofrontal cortex is affected by the mutual interaction between the periventricular WMHs and degree of obesity. Our results suggest that this region links obesity with WMHs in terms of functional connectivity.

The effects of stress on cardiovascular disease and Alzheimer's disease: Physical exercise as a counteract measure

AD is a complicated multi-systemic neurological disorder that involves different biological pathways. Several risk factors have been identified, including chronic stress. Chronic stress produces an alteration in the activity of the hypothalamic pituitary adrenal (HPA) system, and the autonomic nervous system (ANS), which over time increase the risk of AD and also the incidence of cardiovascular disease (CVD) and risk factors, such as hypertension, obesity and type 2 diabetes, associated with cognitive impairment and AD. Considering the multi-factorial etiology of AD, understanding the complex interrelationships between different risk factors is of potential interest for designing adequate strategies for preventing, delaying the onset or slowing down the progression of this devastating disease. Thus, in this review we will explore the general mechanisms and evidence linking stress, cardiovascular disease and AD, and discuss the potential benefits of physical activity for AD by counteracting the negative effects of chronic stress, CVD and risk factors.

Obesity-related cognitive impairment: The role of endothelial dysfunction

Obesity is a global pandemic associated with macro- and microvascular endothelial dysfunction. Microvascular endothelial dysfunction has recently emerged as a significant risk factor for the development of cognitive impairment. In this review, we present evidence from clinical and preclinical studies supporting a role for obesity in cognitive impairment. Next, we discuss how obesity-related hyperinsulinemia/insulin resistance, systemic inflammation, and gut dysbiosis lead to cognitive impairment through induction of endothelial dysfunction and disruption of the blood brain barrier. Finally, we outline the potential clinical utility of dietary interventions, exercise, and bariatric surgery in circumventing the impacts of obesity on cognitive function.

Increased interactions and engulfment of dendrites by microglia precede Purkinje cell degeneration in a mouse model of Niemann Pick Type-C

Niemann Pick Type-C disease (NPC) is an inherited lysosomal storage disease (LSD) caused by pathogenic variants in the Npc1 or Npc2 genes that lead to the accumulation of cholesterol and lipids in lysosomes. NPC1 deficiency causes neurodegeneration, dementia and early death. Cerebellar Purkinje cells (PCs) are particularly hypersensitive to NPC1 deficiency and degenerate earlier than other neurons in the brain. Activation of microglia is an important contributor to PCs degeneration in NPC. However, the mechanisms by which activated microglia promote PCs degeneration in NPC are not completely understood. Here, we are demonstrating that in the Npc1^nmf164 mouse cerebellum, microglia in the molecular layer (ML) are activated and contacting dendrites at early stages of NPC, when no loss of PCs is detected. During the progression of PCs degeneration in Npc1^nmf164 mice, accumulation of phagosomes and autofluorescent material in microglia at the ML coincided with the degeneration of dendrites and PCs. Feeding Npc1^nmf164 mice a western diet (WD) increased microglia activation and corresponded with a more extensive degeneration of dendrites but not PC somata. Together our data suggest that microglia contribute to the degeneration of PCs by interacting, engulfing and phagocytosing their dendrites while the cell somata are still present.