Immunohistochemical analysis of tau phosphorylation and astroglial activation with enhanced leptin receptor expression in diet-induced obesity mouse hippocampus

Astrocytes of the hippocampus and responses to periprandial neuroendocrine hormones

Astrocytes have risen as stars in the field of energy homeostasis and neurocognitive function, acting as a bridge of communication between the periphery and the brain, providing metabolic support, signaling via gliotransmitters, and altering synaptic communication. Dietary factors and energy state have a profound influence on hippocampal function, and the hippocampus is critical for appropriate behavioral responses associated with feeding and internal hunger cues (being in the fasted or full state), but how the hippocampus senses periprandial status and is impacted by diet is largely unknown. Periprandial hormones act within the hippocampus to modulate processes involved in hippocampal-dependent learning and memory function and astrocytes likely play an important role in modulating this signaling. In addition to periprandial hormones, astrocytes are positioned to respond to changes in circulating nutrients like glucose. Here, we review literature investigating how astrocytes mediate changes in hippocampal function, highlighting astrocyte location, morphology, and function in the context of integrating glucose metabolism, neuroendocrine hormone action, and/or cognitive function in the hippocampus. Specifically, we discuss research findings on the effects of insulin, ghrelin, leptin, and GLP-1 on glucose homeostasis, neural activity, astrocyte function, and behavior in the hippocampus. Because obesogenic diets impact neuroendocrine hormones, astrocytes, and cognitive function, we also discuss the effects of diet and diet-induced obesity on these parameters.

SUMO2 rescues neuronal and glial cells from the toxicity of P301L Tau mutant

Introduction

Abnormal intracellular accumulation of Tau aggregates is a hallmark of Alzheimer's disease (AD) and other Tauopathies, such as Frontotemporal dementia (FTD). Tau deposits primarily affect neurons, but evidence indicates that glial cells may also be affected and contribute distinctively to disease progression. Cells can respond to toxic insults by orchestrating global changes in posttranslational modifications of their proteome. Previous studies suggest that SUMOylation, a posttranslational modification consisting of conjugation of SUMO (Small ubiquitin-like modifier) to target proteins, was decreased in the hippocampus of AD patients and in animal model of AD compared with controls. This decrease in SUMOylation was correlated with increased Tau pathology and cognitive decline. Other studies have reported increased levels of SUMO in AD brains. The goal of our study was to evaluate whether SUMO conjugation modifies the neurodegenerative disease pathology associated with the aggregation-prone mutant TauP301L, in neurons and in glial cells.

Methods

We used viral approaches to express mutant TauP301L and SUMO2 in the hippocampus of wild-type mice. We assessed Tau distribution by immunostaining and Tau aggregation by insolubility assays followed by western blotting. We assessed neuronal toxicity and performed cell count and shape descriptor analyses on astrocytes and microglial cells.

Results

We found that mutant TauP301L, when expressed exclusively in neurons, is toxic not only to neurons but also to glial cells, and that SUMO2 counteracts TauP301L toxicity in neurons as well as in glia.

Discussion

Our results uncover an endogenous neuroprotective mechanism, whereby SUMO2 conjugation reduces Tau neuropathology and protects against toxic effects of Tau in glial cells.

Human TRPV1 is an efficient thermogenetic actuator for chronic neuromodulation

Thermogenetics is a promising neuromodulation technique based on the use of heat-sensitive ion channels. However, on the way to its clinical application, a number of questions have to be addressed. First, to avoid immune response in future human applications, human ion channels should be studied as thermogenetic actuators. Second, heating levels necessary to activate these channels in vivo in brain tissue should be studied and cytotoxicity of these temperatures addressed. Third, the possibility and safety of chronic neuromodulation has to be demonstrated. In this study, we present a comprehensive framework for thermogenetic neuromodulation in vivo using the thermosensitive human ion channel hTRPV1. By targeting hTRPV1 expression to excitatory neurons of the mouse brain and activating them within a non-harmful temperature range with a fiber-coupled infrared laser, we not only induced neuronal firing and stimulated locomotion in mice, but also demonstrated that thermogenetics can be employed for repeated neuromodulation without causing evident brain tissue injury. Our results lay the foundation for the use of thermogenetic neuromodulation in brain research and therapy of neuropathologies.

High-fat diet negatively affects brain markers, cognitive behaviors, and noncognitive behaviors in the rTg4510 tau mouse model

Alzheimer's disease (AD) drastically impacts cognitive and noncognitive behaviors in both humans and animal models. Two hallmark proteins in AD, amyloid-β plaques and tau neurofibrillary tangles, accumulate in regions of the brain critical for learning and memory, including the hippocampus. Poor dietary choices have been shown to exacerbate cognitive deficits seen in AD. In this study, we assessed the effects of a high-fat diet (HFD - 60 kcal% fat) on cognitive & noncognitive behaviors as well as on brain markers in the rTg4510 tau mouse model. While all mice learned the Morris Water Maze (MWM) task, it was noted that on the last day of acquisition female tau mice had a significantly higher latency to find the platform than male tau mice (p < 0.01). Mice given the HFD spent significantly less time in the target quadrant than those given a control diet (CD) (p < 0.05). Tau mice showed impaired burrowing (p < 0.05) and nesting behaviors (p < 0.001) compared to WT mice and HFD administration worsened burrowing in tau mice. Tau mice exhibited greater levels of glial fibrillary acidic protein (GFAP) (p < 0.05) and significantly less hippocampal cell density than WT mice (p < 0.001). We observed trends of HFD mice having greater levels of GFAP and greater average tangle size than CD mice. These results highlight the importance of dietary choices, especially in older populations more susceptible to AD and its effects.

Leptin Signaling Could Mediate Hippocampal Decumulation of Beta-Amyloid and Tau Induced by High-Intensity Interval Training in Rats with Type 2 Diabetes

Leptin (LEP) can cross the blood-brain barrier and facilitate cross-talk between the adipose tissue and central nerve system (CNS). This study aimed to investigate the effect of 8-week high-intensity interval training (HIIT) on the LEP signaling in the hippocampus of rats with type 2 diabetes. 20 rats were randomly divided into four groups: (i) control (Con), (ii) type 2 diabetes (T2D), (iii) exercise (EX), and (iv) type 2 diabetes + exercise (T2D + EX). The rats in the T2D and T2D + EX were fed a high-fat diet for two months, then a single dose of STZ (35 mg/kg) was injected to induce diabetes. The EX and T2D + EX groups performed 4-10 intervals of treadmill running at 80-100% of Vmax. Serum and hippocampal levels of LEP as well as hippocampal levels of LEP receptors (LEP-R), Janus kinase 2 (JAK-2), signal transducer and activator of transcription 3 (STAT-3), activated protein kinase (AMP-K), proxy zoster receptor α (PGC-1α), beta-secretase 1 (BACE1), Beta-Amyloid (Aβ), Phosphoinositide 3-kinases (PI3K), protein kinase B (AKT), mammalian target of rapamycin (mTOR), Glycogen Synthase Kinase 3 Beta (GSK3β), and hyperphosphorylated tau proteins (TAU) were measured. One-way ONOVA and Tukey post-hoc tests were used to analyze the data. Serum and hippocampal levels of LEP as well as hippocampal levels of LEP-R, JAK-2, STAT-3, AMP-K, PGC1α, PI3K, AKT, and mTOR were increased while hippocampal levels of BACE1, GSK3B, TAU, and Aβ were decreased in T2D + EX compared with T2D group. Serum LEP and hippocampal levels of LEP, LEP-R, JAK-2, STAT-3, AMP-K, PGC1α, PI3K, AKT, and mTOR were decreased. Conversely hippocampal levels of BACE1, GSK3B, TAU, and Aβ were increased in T2D group compared with CON group. HIIT could improve LEP signaling in the hippocampus of rats with type 2 diabetes and decrease the accumulation of Tau and Aβ, which may reduce the risk of memory impairments.

Ldlr-/-.Leiden mice develop neurodegeneration, age-dependent astrogliosis and obesity-induced changes in microglia immunophenotype which are partly reversed by complement component 5 neutralizing antibody

Introduction

Obesity has been linked to vascular dysfunction, cognitive impairment and neurodegenerative diseases. However, experimental models that recapitulate brain pathology in relation to obesity and vascular dysfunction are still lacking.

Methods

In this study we performed the histological and histochemical characterization of brains from Ldlr-/-.Leiden mice, an established model for obesity and associated vascular disease. First, HFD-fed 18 week-old and 50 week-old Ldlr-/-.Leiden male mice were compared with age-matched C57BL/6J mice. We then assessed the effect of high-fat diet (HFD)-induced obesity on brain pathology in Ldlr-/-.Leiden mice and tested whether a treatment with an anti-complement component 5 antibody, a terminal complement pathway inhibitor recently shown to reduce vascular disease, can attenuate neurodegeneration and neuroinflammation. Histological analyses were complemented with Next Generation Sequencing (NGS) analyses of the hippocampus to unravel molecular pathways underlying brain histopathology.

Results

We show that chow-fed Ldlr-/-.Leiden mice have more severe neurodegeneration and show an age-dependent astrogliosis that is not observed in age-matched C57BL/6J controls. This was substantiated by pathway enrichment analysis using the NGS data which showed that oxidative phosphorylation, EIF2 signaling and mitochondrial dysfunction pathways, all associated with neurodegeneration, were significantly altered in the hippocampus of Ldlr-/-.Leiden mice compared with C57BL/6J controls. Obesity-inducing HFD-feeding did not aggravate neurodegeneration and astrogliosis in Ldlr-/-.Leiden mice. However, brains from HFD-fed Ldlr-/-.Leiden mice showed reduced IBA-1 immunoreactivity and increased CD68 immunoreactivity compared with chow-fed Ldlr-/-.Leiden mice, indicating alteration of microglial immunophenotype by HFD feeding. The systemic administration of an anti-C5 treatment partially restored the HFD effect on microglial immunophenotype. In addition, NGS data of hippocampi from Ldlr-/-.Leiden mice showed that HFD feeding affected multiple molecular pathways relative to chow-fed controls: HFD notably inactivated synaptogenesis and activated neuroinflammation pathways. The anti-C5 treatment restored the HFD-induced effect on molecular pathways to a large extent.

Conclusion

This study shows that the Ldlr-/-.Leiden mouse model is suitable to study brain histopathology and associated biological processes in a context of obesity and provides evidence of the potential therapeutic value of anti-complement therapy against obesity-induced neuroinflammation.

Recent Development in the Understanding of Molecular and Cellular Mechanisms Underlying the Etiopathogenesis of Alzheimer's Disease

Alzheimer's disease (AD) is a progressive neurodegenerative disorder that leads to dementia and patient death. AD is characterized by intracellular neurofibrillary tangles, extracellular amyloid beta (Aβ) plaque deposition, and neurodegeneration. Diverse alterations have been associated with AD progression, including genetic mutations, neuroinflammation, blood-brain barrier (BBB) impairment, mitochondrial dysfunction, oxidative stress, and metal ion imbalance.Additionally, recent studies have shown an association between altered heme metabolism and AD. Unfortunately, decades of research and drug development have not produced any effective treatments for AD. Therefore, understanding the cellular and molecular mechanisms underlying AD pathology and identifying potential therapeutic targets are crucial for AD drug development. This review discusses the most common alterations associated with AD and promising therapeutic targets for AD drug discovery. Furthermore, it highlights the role of heme in AD development and summarizes mathematical models of AD, including a stochastic mathematical model of AD and mathematical models of the effect of Aβ on AD. We also summarize the potential treatment strategies that these models can offer in clinical trials.

Pleiotrophin deficiency protects against high-fat diet-induced neuroinflammation: Implications for brain mitochondrial dysfunction and aberrant protein aggregation

Metabolic Syndrome (MetS) is a risk factor for the development of neurodegenerative diseases. Neuroinflammation associated with MetS may contribute significantly to neurodegeneration. Pleiotrophin (PTN) is a neurotrophic factor that modulates neuroinflammation and is a key player in regulating energy metabolism and thermogenesis, suggesting that PTN could be important in the connection between MetS and neuroinflammation. We have now used a high-fat diet (HFD)-induced obesity model in Ptn^-/- mice. HFD and Ptn deletion caused alterations in circulating hormones including GIP, leptin and resistin. HFD produced in Ptn^+/+ mice a neuroinflammatory state as observed in cerebral quantifications of proinflammatory markers, including Il1β, Tnfα and Ccl2. The upregulation of neuroinflammatory markers was prevented in Ptn^-/- mice. Changes induced by HFD in genes related to mitochondrial biogenesis and dynamics were less pronounced in the brain of Ptn^-/- mice and were accompanied by significant increases in the protein expression of mitochondrial oxidative phosphorylation (OXPHOS) complexes I and IV. HFD-induced changes in genes related to the elimination of protein aggregates were also less pronounced in the brain of Ptn^-/- mice. This study provides substantial evidence that Ptn deletion protects against HFD-induced neuroinflammation, mitochondrial dysfunction, and aberrant protein aggregation, prominent features in neurodegenerative diseases.

The Role of Glia in Addiction: Dopamine as a Modulator of Glial Responses in Addiction

Addiction is a chronic and potentially deadly disease considered a global health problem. Nevertheless, there is still no ideal treatment for its management. The alterations in the reward system are the most known pathophysiological mechanisms. Dopamine is the pivotal neurotransmitter involved in neuronal drug reward mechanisms and its neuronal mechanisms have been intensely investigated in recent years. However, neuroglial interactions and their relation to drug addiction development and maintenance of drug addiction have been understudied. Many reports have found that most neuroglial cells express dopamine receptors and that dopamine activity may induce neuroimmunomodulatory effects. Furthermore, current research has also shown that pro- and anti-inflammatory molecules modulate dopaminergic neuron activity. Thus, studying the immune mechanisms of dopamine associated with drug abuse is vital in researching new pathophysiological mechanisms and new therapeutic targets for addiction management.

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.

Food for Thought: Leptin and Hippocampal Synaptic Function

It is well documented that the endocrine hormone, leptin controls energy homeostasis by providing key signals to specific hypothalamic nuclei. However, our knowledge of leptin’s central actions has advanced considerably over the last 20 years, with the hippocampus now established as an important brain target for this hormone. Leptin receptors are highly localised to hippocampal synapses, and increasing evidence reveals that activation of synaptically located leptin receptors markedly impacts cognitive processes, and specifically hippocampal-dependent learning and memory. Here, we review the recent actions of leptin at hippocampal synapses and explore the consequences for brain health and disease.

β-Glucan-Rich Extract of Gray Oyster Mushroom, Pleurotus pulmonarius, Improves Object Recognition Memory and Hippocampus Morphology in Mice Fed a High-Fat Diet

Obesity may cause behavioral alterations, while maternal obesity can contribute to metabolic disorders in subsequent generations. The effect of β-glucan-rich Pleurotus pulmonarius (βgPp) was investigated on mouse neurobehavior and hippocampus and its offspring's hippocampus development. Female ICR mice were fed with normal diet (ND), ND with βgPp, high-fat diet (HFD), or HFD with βgPp for 3 months followed by behavioral test and mating. Immunohistochemistry for the expression of neuronal nuclear protein (NeuN) and ionized calcium binding adaptor molecule-1 (Iba-1) in the hippocampus was carried out. βgPp significantly enhanced short-term object recognition memory in HFD-fed mice. βgPp also ameliorated the histological alterations and neuronal loss and increased Iba-1-positive microglia in the hippocampus regions of HFD-fed mice and their male offspring. These findings demonstrated that βgPp supplementation attenuated the effects of HFD on object recognition memory and the alterations on the hippocampal regions of maternal mice and their male offspring.

Western diet as a trigger of Alzheimer's disease: From metabolic syndrome and systemic inflammation to neuroinflammation and neurodegeneration

An excess of saturated fatty acids and simple sugars in the diet is a known environmental risk factor of Alzheimer's disease (AD) but the holistic view of the interacting processes through which such diet may contribute to AD pathogenesis is missing. We addressed this need through extensive analysis of published studies investigating the effects of western diet (WD) on AD development in humans and laboratory animals. We reviewed WD-induced systemic alterations comprising metabolic changes, induction of obesity and adipose tissue inflammation, gut microbiota dysbiosis and acceleration of systemic low-grade inflammation. Next we provide an overview of the evidence demonstrating that WD-associated systemic alterations drive impairment of the blood-brain barrier (BBB) and development of neuroinflammation paralleled by accumulation of toxic amyloid. Later these changes are followed by dysfunction of synaptic transmission, neurodegeneration and finally memory and cognitive impairment. We conclude that WD can trigger AD by acceleration of inflammaging, and that BBB impairment induced by metabolic and systemic inflammation play the central role in this process. Moreover, the concurrence of neuroinflammation and Aβ dyshomeostasis, which by reciprocal interactions drive the vicious cycle of neurodegeneration, contradicts Aβ as the primary trigger of AD. Given that in 2019 the World Health Organization recommended focusing on modifiable risk factors in AD prevention, this overview of the sequential, complex pathomechanisms initiated by WD, which can lead from peripheral disturbances to neurodegeneration, can support future prevention strategies.

High-fat diet-induced activation of SGK1 promotes Alzheimer's disease-associated tau pathology

Type 2 diabetes mellitus (T2DM) has long been considered a risk factor for Alzheimer’s disease (AD). However, the molecular links between T2DM and AD remain obscure. Here, we reported that serum-/glucocorticoid-regulated kinase 1 (SGK1) is activated by administering a chronic high-fat diet (HFD), which increases the risk of T2DM, and thus promotes Tau pathology via the phosphorylation of tau at Ser214 and the activation of a key tau kinase, namely, GSK-3ß, forming SGK1-GSK-3ß-tau complex. SGK1 was activated under conditions of elevated glucocorticoid and hyperglycemia associated with HFD, but not of fatty acid–mediated insulin resistance. Elevated expression of SGK1 in the mouse hippocampus led to neurodegeneration and impairments in learning and memory. Upregulation and activation of SGK1, SGK1-GSK-3ß-tau complex were also observed in the hippocampi of AD cases. Our results suggest that SGK1 is a key modifier of tau pathology in AD, linking AD to corticosteroid effects and T2DM.

The Complex Interactions Between Obesity, Metabolism and the Brain

Obesity is increasing at unprecedented levels globally, and the overall impact of obesity on the various organ systems of the body is only beginning to be fully appreciated. Because of the myriad of direct and indirect effects of obesity causing dysfunction of multiple tissues and organs, it is likely that there will be heterogeneity in the presentation of obesity effects in any given population. Taken together, these realities make it increasingly difficult to understand the complex interplay between obesity effects on different organs, including the brain. The focus of this review is to provide a comprehensive view of metabolic disturbances present in obesity, their direct and indirect effects on the different organ systems of the body, and to discuss the interaction of these effects in the context of brain aging and the development of neurodegenerative diseases.

The Synergistic Effects of APOE Genotype and Obesity on Alzheimer's Disease Risk

The APOE gene has three common alleles—E2, E3, and E4, with APOE4 being the strongest genetic risk factor for developing Alzheimer’s Disease (AD). Obesity is a global epidemic and contributes to multiple metabolic problems. Obesity is also a risk factor for cognitive decline. Here, we review the effects of APOE4 and obesity on cognition and AD development, independently and together. We describe studies that have associated APOE4 with cognitive deficits and AD, as well as studies that have associated obesity to cognitive deficits and AD. We then describe studies that have examined the effects of obesity and APOE genotypes together, with a focus on APOE4 and high fat diets. Both human studies and rodent models have contributed to understanding the effects of obesity on the different APOE genotypes, and we outline possible underlying mechanisms associated with these effects. Data across approaches support a model in which APOE4 and obesity combine for greater detrimental effects on metabolism and cognition, in ways that are influenced by both age and sex.

TLR4 inhibitor TAK-242 attenuates the adverse neural effects of diet-induced obesity

BACKGROUND

Obesity exerts negative effects on brain health, including decreased neurogenesis, impaired learning and memory, and increased risk for Alzheimer's disease and related dementias. Because obesity promotes glial activation, chronic neuroinflammation, and neural injury, microglia are implicated in the deleterious effects of obesity. One pathway that is particularly important in mediating the effects of obesity in peripheral tissues is toll-like receptor 4 (TLR4) signaling. The potential contribution of TLR4 pathways in mediating adverse neural outcomes of obesity has not been well addressed. To investigate this possibility, we examined how pharmacological inhibition of TLR4 affects the peripheral and neural outcomes of diet-induced obesity.

METHODS

Male C57BL6/J mice were maintained on either a control or high-fat diet for 12 weeks in the presence or absence of the specific TLR4 signaling inhibitor TAK-242. Outcomes examined included metabolic indices, a range of behavioral assessments, microglial activation, systemic and neuroinflammation, and neural health endpoints.

RESULTS

Peripherally, TAK-242 treatment was associated with partial inhibition of inflammation in the adipose tissue but exerted no significant effects on body weight, adiposity, and a range of metabolic measures. In the brain, obese mice treated with TAK-242 exhibited a significant reduction in microglial activation, improved levels of neurogenesis, and inhibition of Alzheimer-related amyloidogenic pathways. High-fat diet and TAK-242 were associated with only very modest effects on a range of behavioral measures.

CONCLUSIONS

These results demonstrate a significant protective effect of TLR4 inhibition on neural consequences of obesity, findings that further define the role of microglia in obesity-mediated outcomes and identify a strategy for improving brain health in obese individuals.

Effect of prenatal tramadol on postnatal cerebellar development: Role of oxidative stress

BACKGROUND AND AIM

The adverse neurological effects of tramadol have recently raised attention. The literature pertaining to studying postnatal cerebellar changes induced by prenatal tramadol is very scanty, thus the current study has been designed to improve understanding of the cerebellar oxidative stress-related alterations associated with tramadol administration during pregnancy in this critical period of neuronal differentiation and synaptic development, thereby highlighting the importance of controlling prenatal prescription of opioids and optimizing care for opioid-dependent pregnant women and their infants.

MATERIAL AND METHODS

Twenty pregnant female rats of Sprague Dawley strains were used in the study. Their offspring were divided into two groups: group I (control group) offspring of mothers given saline; group II offspring of mothers given tramadol from the 10th day (D10) of gestation till D21. The pups were sacrificed on the 7^th, 14^th and 21^st postnatal days. Cerebellar specimens were processed for histomorphometric, immunohistochemical and electron microscopic assessment and were evaluated for various oxidative stress parameters.

RESULTS

Tramadol administration during pregnancy caused profound structural abnormalities on the post-natal cerebellar cortex and was associated with oxidative stress evidenced by elevation of lipid peroxidation products and inhibition of antioxidant enzyme activities.

Leptin Receptor Expression in Mouse Intracranial Perivascular Cells

Past studies have suggested that non-neuronal brain cells express the leptin receptor. However, the identity and distribution of these leptin receptor-expressing non-neuronal brain cells remain debated. This study assessed the distribution of the long form of the leptin receptor (LepRb) in non-neuronal brain cells using a reporter mouse model in which LepRb-expressing cells are permanently marked by tdTomato fluorescent protein (LepRb-Cre^tdTomato). Double immunohistochemistry revealed that, in agreement with the literature, the vast majority of tdTomato-tagged cells across the mouse brain were neurons (i.e., based on immunoreactivity for NeuN). Non-neuronal structures also contained tdTomato-positive cells, including the choroid plexus and the perivascular space of the meninges and, to a lesser extent, the brain. Based on morphological criteria and immunohistochemistry, perivascular cells were deduced to be mainly pericytes. Notably, tdTomato-positive cells were immunoreactive for vitronectin and platelet derived growth factor receptor beta (PDGFBR). In situ hybridization studies confirmed that most tdTomato-tagged perivascular cells were enriched in leptin receptor mRNA (all isoforms). Using qPCR studies, we confirmed that the mouse meninges were enriched in Leprb and, to a greater extent, the short isoforms of the leptin receptor. Interestingly, qPCR studies further demonstrated significantly altered expression for Vtn and Pdgfrb in the meninges and hypothalamus of LepRb-deficient mice. Collectively, our data demonstrate that the only intracranial non-neuronal cells that express LepRb in the adult mouse are cells that form the blood-brain barrier, including, most notably, meningeal perivascular cells. Our data suggest that pericytic leptin signaling plays a role in the integrity of the intracranial perivascular space and, consequently, may provide a link between obesity and numerous brain diseases.

Association of body mass index with amnestic and non-amnestic mild cognitive impairment risk in elderly

BACKGROUND

Previous studies focused on the relationship between body mass index and cognitive disorder and obtained many conflicting results. This study explored the potential effects of body mass index on the risk of mild cognitive impairment (amnestic and non-amnestic) in the elderly.

METHODS

The study enrolled 240 amnestic mild cognitive impairment patients, 240 non-amnestic mild cognitive impairment patients and 480 normal cognitive function controls. Data on admission and retrospective data at baseline (6 years ago) were collected from their medical records. Cognitive function was evaluated using Mini-Mental State Examination and Montreal Cognitive Assessment.

RESULTS

Being underweight, overweight or obese at baseline was associated with an increased risk of amnestic mild cognitive impairment (OR: 2.30, 95%CI: 1.50 ~ 3.52; OR: 1.74, 95%CI: 1.36 ~ 2.20; OR: 1.71, 95%CI: 1.32 ~ 2.22, respectively). Being overweight or obese at baseline was also associated with an increased risk of non-amnestic mild cognitive impairment (OR: 1.51, 95%CI: 1.20 ~ 1.92; OR: 1.52, 95%CI: 1.21 ~ 1.97, respectively). In subjects with normal weights at baseline, an increased or decreased body mass index at follow-up was associated with an elevated risk of amnestic mild cognitive impairment (OR: 1.80, 95%CI: 1.10 ~ 3.05; OR: 3.96, 95%CI: 2.88 ~ 5.49, respectively), but only an increased body mass index was associated with an elevated risk of non-amnestic mild cognitive impairment (OR: 1.71, 95%CI: 1.16 ~ 2.59).

CONCLUSIONS

Unhealthy body mass index levels at baseline and follow-up might impact the risk of both types of mild cognitive impairment (amnestic and non-amnestic).

Saponins from stems and leaves of Panax ginseng prevent obesity via regulating thermogenesis, lipogenesis and lipolysis in high-fat diet-induced obese C57BL/6 mice

In this study, high-fat diet (HFD)-induced obesity in mouse model was used to evaluate the dietary effect of saponins from stems and leaves of Panax ginseng (SLG), and to explore its mechanism of action in producing anti-obesity effects. The results indicate that SLG showed significant anti-obesity effects in diet-induced obese mice, represented by decreased serum levels of free fatty acids (FFA), total cholesterol (TC), triglycerides (TG), low-density lipoprotein (LDL)-cholesterol, glucose, leptin and insulin, as well as a reduction in overall body and liver weight, epididymal adipose tissue weight, and food efficiency, and inhibition of abnormal increases in acyl carnitine levels normally caused by an HFD. Additionally, the down-regulated expression of PPARγ, FAS, CD36, FATP2 and up-regulated expression of CPT-1, UCP-2, PPARα, HSL, and ATGL in liver tissue was induced by SLG. In addition, the SLG groups showed decreased PPARγ, aP2 and leptin mRNA levels and increased expression of PPARα, PGC-1α, UCP-1 and UCP-3 genes in adipose tissues, compared with the HFD group. In short, SLG may play a key role in producing anti-obesity effects in mice fed an HFD, and its mechanism may be related to regulation of thermogenesis, lipogenesis and lipolysis.

Obesity Accelerates Alzheimer-Related Pathology in APOE4 but not APOE3 Mice

Alzheimer's disease (AD) risk is modified by both genetic and environmental risk factors, which are believed to interact to cooperatively modify pathogenesis. Although numerous genetic and environmental risk factors for AD have been identified, relatively little is known about potential gene-environment interactions in regulating disease risk. The strongest genetic risk factor for late-onset AD is the ε4 allele of apolipoprotein E (APOE4). An important modifiable risk factor for AD is obesity, which has been shown to increase AD risk in humans and accelerate development of AD-related pathology in rodent models. Potential interactions between APOE4 and obesity are suggested by the literature but have not been thoroughly investigated. In the current study, we evaluated this relationship by studying the effects of diet-induced obesity (DIO) in the EFAD mouse model, which combines familial AD transgenes with human APOE3 or APOE4. Male E3FAD and E4FAD mice were maintained for 12 weeks on either a control diet or a Western diet high in saturated fat and sugars. We observed that metabolic outcomes of DIO were similar in E3FAD and E4FAD mice. Importantly, our data showed a significant interaction between diet and APOE genotype on AD-related outcomes in which Western diet was associated with robust increases in amyloid deposits, β-amyloid burden, and glial activation in E4FAD but not in E3FAD mice. These findings demonstrate an important gene-environment interaction in an AD mouse model that suggests that AD risk associated with obesity is strongly influenced by APOE genotype.

Decline in Weight and Incident Mild Cognitive Impairment: Mayo Clinic Study of Aging

IMPORTANCE

Unintentional weight loss has been associated with risk of dementia. Because mild cognitive impairment (MCI) is a prodromal stage for dementia, we sought to evaluate whether changes in weight and body mass index (BMI) may predict incident MCI.

OBJECTIVE

To investigate the association of change in weight and BMI with risk of MCI.

DESIGN, SETTING, AND PARTICIPANTS

A population-based, prospective study of participants 70 years of age or older from the Mayo Clinic Study of Aging, which was initiated on October 1, 2004. Maximum weight and height in midlife (40-65 years of age) were retrospectively ascertained from the medical records of participants using a medical records-linkage system. The statistical analyses were performed between January and November 2015.

MAIN OUTCOMES AND MEASURES

Participants were evaluated for cognitive outcomes of normal cognition, MCI, or dementia at baseline and prospectively assessed for incident events at each 15-month evaluation. The association of rate of change in weight and BMI with risk of MCI was investigated using proportional hazards models.

RESULTS

Over a mean follow-up of 4.4 years, 524 of 1895 cognitively normal participants developed incident MCI (50.3% were men; mean age, 78.5 years). The mean (SD) rate of weight change per decade from midlife to study entry was greater for participants who developed incident MCI vs those who remained cognitively normal (-2.0 [5.1] vs -1.2 [4.9] kg; P = .006). A greater decline in weight per decade was associated with an increased risk of incident MCI (hazard ratio [HR], 1.04 [95% CI, 1.02-1.06]; P < .001) after adjusting for sex, education, and apolipoprotein E (APOE) ε4 allele. A weight loss of 5 kg per decade corresponds to a 24% increase in risk of MCI (HR, 1.24). A higher decrease in BMI per decade was also associated with incident MCI (HR, 1.08 [95% CI, 1.03-1.13]; P = .003).

CONCLUSIONS AND RELEVANCE

These findings suggest that increasing weight loss per decade from midlife to late life is a marker for MCI and may help identify persons at increased risk for MCI.

Assessment of neuroinflammation in a mouse model of obesity and β-amyloidosis using PET

BACKGROUND

Obesity has been identified as a risk factor for cognitive decline and Alzheimer's disease (AD). The aim of this study was to investigate the effect of obesity on neuroinflammation and cerebral glucose metabolism using PET in a mouse model of β-amyloidosis and determine the relationship between these PET imaging biomarkers, pathogenic changes, and functional outcomes.

METHODS

Three-month-old C57BL/J6 mice were fed either a standard (control group) or high-fat diet (obese group) for 3 months and intracerebroventricularly infused with vehicle or human beta amyloid 1-42 (Aβ42). We assessed obesity-induced abnormalities in peripheral metabolic indices including adiposity, fasting glucose, and glucose tolerance. Brain glucose metabolism was assessed by (18)F-FDG PET, and glial activation was assessed using the translocator protein (TSPO) ligand (11)C-PBR-28. TSPO expression was confirmed by immunohistochemistry of brain sections obtained from scanned mice. The association between inflammatory state and (11)C-PBR-28 PET signals was characterized by examination of the cytokine expression profile in both the serum and hippocampus by antibody array. Learning and memory performance was assessed in the object recognition task, and anxiety-related behavior was assessed in the elevated plus maze.

RESULTS

Obesity combined with Aβ infusion promoted neuroinflammation and cerebral hypermetabolism, and these signals were significant predictors of learning and memory performance in the object recognition task. In vivo TSPO signals were associated with inflammatory markers including CXCL1, CXCL2, CXCL12, CCL3, CCL5, TIMP-1, G-CSF, sICAM-1, and IL-1ra.

CONCLUSIONS

In vivo cerebral metabolism and TSPO signals indicate that obesity can accelerate amyloid-induced inflammation and associated cognitive decline.

Detrimental effects of a high fat/high cholesterol diet on memory and hippocampal markers in aged rats

High fat diets have detrimental effects on cognitive performance, and can increase oxidative stress and inflammation in the brain. The aging brain provides a vulnerable environment to which a high fat diet could cause more damage. We investigated the effects of a high fat/high cholesterol (HFHC) diet on cognitive performance, neuroinflammation markers, and phosphorylated Tau (p-Tau) pathological markers in the hippocampus of Young (4-month old) versus Aged (14-month old) male rats. Young and Aged male Fisher 344 rats were fed a HFHC diet or a normal control diet for 6 months. All animals underwent cognitive testing for 12days in a water radial arm maze to assess spatial and working reference memory. Hippocampal tissue was analyzed by immunohistochemistry for structural changes and inflammation, and Western blot analysis. Young and Aged rats fed the HFHC diet exhibited worse performance on a spatial working memory task. They also exhibited significant reduction of NeuN and calbindin-D28k immunoreactivity as well as an increased activation of microglial cells in the hippocampal formation. Western blot analysis of the hippocampus showed higher levels of p-Tau S202/T205 and T231 in Aged HFHC rats, suggesting abnormal phosphorylation of Tau protein following the HFHC diet exposure. This work demonstrates HFHC diet-induced cognitive impairment with aging and a link between high fat diet consumption and pathological markers of Alzheimer's disease.

Neuroprotective Effects of Endurance Exercise Against High-Fat Diet-Induced Hippocampal Neuroinflammation

Obesity contributes to systemic inflammation, which is associated with the varied pathogenesis of neurodegenerative diseases. Growing evidence has demonstrated that endurance exercise (EE) mitigates obesity-induced brain inflammation. However, exercise-mediated anti-inflammatory mechanisms remain largely unknown. We investigated how treadmill exercise (TE) reverses obesity-induced brain inflammation, mainly focusing on toll-like receptor-4 (TLR-4)-dependent neuroinflammation in the obese rat brain after 20 weeks of a high-fat diet (HFD). TE in HFD-fed rats resulted in a significant lowering in the homeostasis model assessment of insulin resistance index, the area under the curve for glucose and abdominal visceral fat, and also improved working memory ability in a passive avoidance task relative to sedentary behaviour in HFD-fed rats, with the exception of body weight. More importantly, TE revoked the increase in HFD-induced proinflammatory cytokines (tumour necrosis factor α and interleukin-1β) and cyclooxygenase-2, which is in parallel with a reduction in TLR-4 and its downstream proteins, myeloid differentiation 88 and tumour necrosis factor receptor associated factor 6, and phosphorylation of transforming growth factor β-activated kinase 1, IkBα and nuclear factor-κB. Moreover, TE reduced an indicator of microglia activation, ionised calcium-binding adapter molecule-1, and also decreased glial fibrillary acidic protein, an indicator of gliosis formed by activated astrocytes in the cerebral cortex and the hippocampal dentate gyrus, compared to HFD-fed sedentary rats. Finally, EE up-regulated the expression of anti-apoptotic protein, Bcl-2, and suppressed the expression of pro-apoptotic protein, Bax, in the hippocampus compared to HFD-fed sedentary rats. Taken together, these data suggest that TE may exert neuroprotective effects as a result of mitigating the production of proinflammatory cytokines by inhibiting the TLR4 signalling pathways. The results of the present study suggest that the unique combination of the beneficial effects of TE on the restoration of the blood profile and the anti-inflammatory and anti-apoptotic effects on cognitive function should inspire further investigations into its therapeutic potential for metabolic disorders and neurodegenerative diseases.

Insulin resistance-induced hyperglycemia decreased the activation of Akt/CREB in hippocampus neurons: Molecular evidence for mechanism of diabetes-induced cognitive dysfunction

Several previous studies have indicated that diabetic have higher risk of suffering from Alzheimer's disease, which severely induced cognitive dysfunction. However, the underlying molecular mechanism and more details on the cognitive deficits induced by hyperglycemia have not been elucidated. Here in our present study, on the basis of Goto-Kakizaki (GK) rats and streptozotocin (STZ)-induced diabetic model, we detected the variation of dendritic spine density in hippocampus as well as the differential expression of some important signal transduction molecules that were of relevance in learning and memory function. We found that the magnitude of escape latency time was significantly increased in such diabetic animals; the phosphorylated Akt/CREB; SYP and BDNF as well as other downstream molecules in hippocampus neurons were also downregulated in both diabetic groups compared to the normal groups. Thus, all of these data indicate the obstacle of neuronal pathology and the Akt/CREB signaling pathway caused by hyperglycemia that may suppress cognitive behavior, which may provide a novel way for the prevention of diabetic encephalopathy and the cognitive deficits of Alzheimer's disease.

Leptin in Alzheimer's disease

Alzheimer's disease (AD) is the most common cause of progressive dementia in the elderly population. AD is histologically characterized by accumulation of amyloid-β protein (Aβ) on extracellular plaques and deposition of hyperphosphorylated tau protein in intracellular neurofibrillary tangles. Several studies have shown that obesity may precede dementia and that lifestyle factors play a critical role in the onset of AD. Furthermore, accumulating evidence indicates that obesity is an independent risk factor for developing AD. In this scenario, the understanding of the role of adipose tissue in brain health is essential to clarify the establishment of demential processes. The objective of this work was to review studies regarding leptin, an anorexigenic peptide hormone synthesized in adipocytes, in the context of dementia. Some authors proposed that leptin evaluation might be a better predictor of dementia than traditional anthropometric measures. Leptin, once established as a biomarker, could enhance the understanding of late-onset AD risk over the life course, as well as the clinical progression of prodromal state to manifested AD. Other studies have proposed that leptin presents neuroprotective activities, which could be explained by inhibiting the amyloidogenic process, reducing the levels of tau protein phosphorylation and improving the cognitive function.

Genetic variability to diet-induced hippocampal dysfunction in BXD recombinant inbred (RI) mouse strains

Evidence has emerged suggesting that diet-induced obesity can have a negative effect on cognitive function. Here, we exploited a mouse genetic reference population to look for the linkage between these two processes on a genome-wide scale. The focus of this report is to determine whether the various BXD RI strains exhibited different behavioral performance and hippocampal function under high fat dietary (HFD) condition. We quantified genetic variation in body weight gain and consequent influences on behavioral tests in a cohort of 14 BXD strains of mice (8-12 mice/strain, n = 153), for which we have matched data on gene expression and neuroanatomical changes in the hippocampus. It showed that BXD66 was the most susceptible, whereas BXD77 was the least susceptible strain to dietary influences. The performance of spatial reference memory tasks was strongly correlated with body weight gain (P < 0.05). The obesity-prone strains displayed more pronounced spatial memory defects compared to the obesity-resistant strains. These abnormalities were associated with neuroinflammation, synaptic dysfunction, and neuronal loss in the hippocampus. The biological relevance of DSCAM gene polymorphism was assessed using the trait correlation analysis tool in Genenetwork. Furthermore, a significant strain-dependent gene expression difference of DSCAM was detected in the hippocampus of obese BXD strains by real-time quantitative PCR. In conclusion, a variety of across-strain hippocampal alterations and genetic predispositions to diet-induced obesity were found in a set of BXD strains. The obesity-prone and obesity-resistant lines we have identified should be highly useful to study the molecular genetics of diet-induced cognitive decline.

The role of leptin in the sporadic form of Alzheimer's disease. Interactions with the adipokines amylin, ghrelin and the pituitary hormone prolactin

Leptin (Lep) is emerging as a pivotal molecule involved in both the early events and the terminal phases of Alzheimer's disease (AD). In the canonical pathway, Lep acts as an anorexigenic factor via its effects on hypothalamic nucleus. However, additional functions of Lep in the hippocampus and cortex have been unravelled in recent years. Early events in the sporadic form of AD likely involve cellular level alterations which can have an effect on food intake and metabolism. Thus, AD can be conceivably interpreted as a multiorgan pathology that not only results in a dramatic neuronal loss in brain areas such as the hippocampus and the cortex (ultimately leading to a significant cognitive impairment) but as a disease which also affects body-weight homeostasis. According to this view, body-weight control disruptions are to be expected in both the early- and late-stage AD, concomitant with changes in serum Lep content, alterations in Lep transport across the blood-brain barrier (BBB) and Lep receptor-related signalling abnormalities. Lep is a member of the adipokine family of molecules, while the Lep receptor belongs to the class I cytokine receptors. Since cellular response to adipokine signalling can be either potentiated or diminished as a result of specific ligand-receptor interactions, Lep interactions with other members of the adipokine family including amylin, ghrelin and hormones such as prolactin require further investigation. In this review, we provide a general perspective on the functions of Lep in the brain, with a particular focus on the sporadic AD.

Obesity and cognitive decline: role of inflammation and vascular changes

The incidence of obesity in middle age is increasing markedly, and in parallel the prevalence of metabolic disorders including cardiovascular disease and type II diabetes is also rising. Numerous studies have demonstrated that both obesity and metabolic disorders are associated with poorer cognitive performance, cognitive decline, and dementia. In this review we discuss the effects of obesity on cognitive performance, including both clinical and preclinical observations, and discuss some of the potential mechanisms involved, namely inflammation and vascular and metabolic alterations.

Inflammation and insulin/IGF-1 resistance as the possible link between obesity and neurodegeneration

Obesity is a growing epidemic that contributes to several brain disorders including Alzheimer's, Parkinson's, and Huntington's diseases. Obesity could promote these diseases through several different mechanisms. Here we review evidence supporting the involvement of two recently recognized factors linking obesity with neurodegeneration: the induction of pro-inflammatory cytokines and onset of insulin and insulin-like growth factor 1 (IGF-1) resistance. Excess peripheral pro-inflammatory mediators, some of which can cross the blood brain barrier, may trigger neuroinflammation, which subsequently exacerbates neurodegeneration. Insulin and IGF-1 resistance leads to weakening of neuroprotective signaling by these molecules and can contribute to onset of neurodegenerative diseases.