Reduced neurotrophic factor level is the early event before the functional neuronal deficiency in high-fat diet induced obese mice

Hypothalamic TrkB.FL overexpression improves metabolic outcomes in the BTBR mouse model of autism

BTBR T+ Itpr3tf/J (BTBR) mice are used as a model of autism spectrum disorder (ASD), displaying similar behavioral and physiological deficits observed in patients with ASD. Our recent study found that implementation of an enriched environment (EE) in BTBR mice improved metabolic and behavioral outcomes. Brain-derived neurotrophic factor (Bdnf) and its receptor tropomyosin kinase receptor B (Ntrk2) were upregulated in the hypothalamus, hippocampus, and amygdala by implementing EE in BTBR mice, suggesting that BDNF-TrkB signaling plays a role in the EE-BTBR phenotype. Here, we used an adeno-associated virus (AAV) vector to overexpress the TrkB full-length (TrkB.FL) BDNF receptor in the BTBR mouse hypothalamus in order to assess whether hypothalamic BDNF-TrkB signaling is responsible for the improved metabolic and behavioral phenotypes associated with EE. Normal chow diet (NCD)-fed and high fat diet (HFD)-fed BTBR mice were randomized to receive either bilateral injections of AAV-TrkB.FL or AAV-YFP as control, and were subjected to metabolic and behavioral assessments up to 24 weeks post-injection. Both NCD and HFD TrkB.FL overexpressing mice displayed improved metabolic outcomes, characterized as reduced percent weight gain and increased energy expenditure. NCD TrkB.FL mice showed improved glycemic control, reduced adiposity, and increased lean mass. In NCD mice, TrkB.FL overexpression altered the ratio of TrkB.FL/TrkB.T1 protein expression and increased phosphorylation of PLCγ in the hypothalamus. TrkB.FL overexpression also upregulated expression of hypothalamic genes involved in energy regulation and altered expression of genes involved in thermogenesis, lipolysis, and energy expenditure in white adipose tissue and brown adipose tissue. In HFD mice, TrkB.FL overexpression increased phosphorylation of PLCγ. TrkB.FL overexpression in the hypothalamus did not improve behavioral deficits in either NCD or HFD mice. Together, these results suggest that enhancing hypothalamic TrkB.FL signaling improves metabolic health in BTBR mice.

Amelioration of Age-Related Multiple Neuronal Impairments and Inflammation in High-Fat Diet-Fed Rats: The Prospective Multitargets of Geraniol

Neuroinflammation is documented to alter brain function as a consequence of metabolic changes linked with a high-fat diet (HFD). The primary target of this study is to see how geraniol is effective in manipulating age- and diet-associated multiple toxicity and neuroinflammation in HFD-fed rats. Sixty-four adult male Wistar rats were partitioned into two groups: Group 1 (untreated normal young and aged rats) and Group 2 (HFD-fed young and aged rats) that received HFD for 16 weeks before being orally treated with geraniol or chromax for eight weeks. The results revealed a dropping in proinflammatory cytokines (TNF-α and IL-6) and leptin while boosting adiponectin in geraniol-supplemented rats. The liver, kidney, and lipid profiles were improved in geraniol-HFD-treated groups. HFD-induced brain insulin resistance decreased insulin clearance and insulin-degrading enzyme (IDE) levels significantly after geraniol supplementation. Geraniol suppressed acetylcholinesterase (AChE) activity and alleviated oxidative stress by boosting neuronal reduced glutathione (GSH), catalase (CAT), glutathione-S-transferase (GST), and superoxide dismutase (SOD) activities. It lowered malondialdehyde concentration (TBARS), nitric oxide (NO), and xanthine oxidase (XO) and restored the structural damage to the brain tissue caused by HFD. Compared with model rats, geraniol boosted learning and memory function and ameliorated the inflammation status in the brain by lowering the protein levels of IL-1β, iNOS, NF-κBp65, and COX-2. In addition, the expression levels of inflammation-related genes (MCP-1, TNF-α, IL-6, IL-1β, and IDO-1) were lessened significantly. Remarkably, the supplementation of geraniol reversed the oxidative and inflammation changes associated with aging. It affected the redox status of young rats. In conclusion, our results exhibit the effectiveness of dietary geraniol supplementation in modifying age-related neuroinflammation and oxidative stress in rats and triggering off the use of geraniol as a noninvasive natural compound for controlling age- and diet-associated neuronal impairments and toxicity.

Emotional and Spontaneous Locomotor Behaviors Related to cerebellar Daidzein-dependent TrkB Expression Changes in Obese Hamsters

Current evidence supports the beneficial role of phytoestrogens in metabolic diseases, but their influences on spontaneous motor and anxiety behaviors plus neuroprotective effects have still not been completely elucidated. With the present study, neuro-behavioral activities were correlated to daidzein (DZ)-dependent expression changes of a high affinity catalytic receptor for several neurotrophins, and namely tropomyosin-related kinase B receptor (TrkB) in the cerebellar cortex of high-fat diet (HFD) hamsters (Mesocricetus auratus). Indeed, these changes appear to be tightly linked to altered plasma lipid profiles as shown by reduced low-density lipoproteins plus total cholesterol levels in DZ-treated obesity hamsters accounting for increased spontaneous locomotor together with diminished anxiety activities in novel cage (NCT) and light/dark box (LDT) tests. For this latter case, the anxiolytic-like hamsters spent more time in the light compartment, which was retained the aversive area of the LDT box. As for the evaluation of the neurotrophin receptor site, significantly elevated TrkB levels were also detected, for the first time, in the cerebellum of obese hamsters treated with DZ. In this condition, such a treatment widely led to an overall improvement of HFD-induced neurodegeneration damages, above all in the Purkinje and granular layers of the cerebellum. In this context, the notably active TrkB signaling events occurring in a DZ-dependent manner may turn out to be a key neuroprotective element capable of restoring normal emotional and spontaneously linked locomotor behaviors regulated by cerebellar cortical areas especially in obesity-related conditions.

Methylcobalamin Alleviates Neuronal Apoptosis and Cognitive Decline Induced by PM2.5 Exposure in Mice

Background: Fine particulate matter (particulate matter 2.5, PM2.5) is considered one of the harmful factors to neuronal functions. Apoptosis is one of the mechanisms of neuronal injury induced by PM2.5. Methylcobalamine (MeCbl) has been shown to have anti-apoptotic and neuroprotective effects. Objective: The current work tried to explore the neuroprotective effects and mechanisms that MeCbl protects mice against cognitive impairment and neuronal apoptosis induced by chronic real-time PM2.5 exposure. Methods: Twenty-four 6-week-old male C57BL/6 mice were exposed to ambient PM2.5 and fed with MeCbl for 6 months. Morris water maze was used to evaluate the changes of spatial learning and memory ability in mice. PC12 cells and primary hippocampal neurons were applied as the in vitro model. Cell viability, cellular reactive oxygen species (ROS) and the expressions of apoptosis-related proteins were examined. And cells were stained with JC-1 and mitochondrial membrane potential was evaluated. Results: In C57BL/6 mice, MeCbl supplementation alleviated cognitive impairment and apoptosis-related protein expression induced by PM2.5 exposure. In in vitro cell model, MeCbl supplementation could effectively rescued the downregulation of cell viability induced by PM2.5, and inhibited the increased levels of ROS, cellular apoptosis, and the expressions of apoptosis related proteins related to PM2.5 treatment, which may be associated with modulation of mitochondrial function. Conclusion: MeCbl treatment alleviated cognitive impairment and neuronal apoptosis induced by PM2.5 both in vivo and in vitro. The mechanism for the neuroprotective effects of MeCbl may at least partially dependent on the regulation of mitochondrial apoptosis.

S-adenosylmethionine decarboxylase 1 and its related spermidine synthesis mediate PM2.5 exposure-induced neuronal apoptosis

PM2.5 exposure is considered harmful to central nerve system, while the specific biochemical mechanism underlying is still unrevealed. Neuronal apoptosis is believed the crucial event in pathogenesis of neurodegenerative diseases, but evidence supporting neuronal apoptosis as the mechanism for PM2.5 exposure induced neuronal injury is insufficient. S-adenosylmethionine decarboxylase 1 (AMD1) and its related spermidine synthesis have been shown to associate with cellular apoptosis, but its role in PM2.5 exposure induced neuronal apoptosis was rarely reported. The current study was aimed to better understand contribution of AMD1 activity and spermidine in PM2.5 exposure induced neuronal apoptosis. Sixteen C57BL/6 male mice were randomly divided and kept into ambient PM2.5 chamber or filtered air chamber for 6 months to establish the mouse model of whole-body ambient PM2.5 chronic exposure. In parallel, PC12 cells and primary hippocampal neurons were applied for various concentrations of PM2.5 treatment (0, 25, 50, 100, 200, and 400 μg/mL) to explore the possible cellular and molecular mechanism which may be critically involved in the process. Results showed that PM2.5 exposure triggered neuronal apoptosis with increased expression of Bax/Bcl-2 and cleaved caspase-3. PM2.5 exposure reduced AMD1 expression and spermidine synthesis. AMD1 inhibition could mimic PM2.5 exposure induced neuronal apoptosis. Spermidine supplementation rescued against neurotoxicity and inhibited PM2.5 induced apoptosis via impaired depolarization of mitochondrial membrane potential and reduced mitochondrial apoptosis related proteins. In summary, our work demonstrated that exposure to PM2.5 led to neuronal apoptosis, which may be the key event in the process of air pollution induced neurodegenerative diseases. AMD1 and spermidine associated with neuronal apoptosis induced by PM2.5 exposure, which was at least partially dependent on mitochondria mediated pathway.

Exenatide Reverts the High-Fat-Diet-Induced Impairment of BDNF Signaling and Inflammatory Response in an Animal Model of Alzheimer's Disease

Alzheimer's disease (AD) is a multifactorial condition in which, along with amyloid-β (Aβ) and tau-related pathology, the synergistic activity of co-morbidity factors promote the onset and progression of the disease. Epidemiological evidence indicates that glucose intolerance, deficits in insulin secretion, or type-2 diabetes mellitus (T2DM) participate in increasing cognitive impairment or dementia risk. Insulin plays a pivotal role in the process as the hormone critically regulates brain functioning. GLP-1, the glucagon-like peptide 1, facilitates insulin signaling, regulates glucose homeostasis, and modulates synaptic plasticity. Exenatide is a synthetic GLP-1 analog employed in T2DM. However, exenatide has also been shown to affect the signaling of the brain-derived neurotrophic factor (BDNF), synaptic plasticity, and cognitive performances in animal models. In this study, we tested whether exenatide exerts neuroprotection in a preclinical AD model set to mimic the clinical complexity of the human disease. We investigated the effects of exenatide treatment in 3xTg-AD mice challenged with a high-fat diet (HFD). Endpoints of the study were variations in systemic metabolism, insulin and neurotrophic signaling, neuroinflammation, Aβ and tau pathology, and cognitive performances. Results of the study indicate that exenatide reverts the adverse changes of BDNF signaling and the neuroinflammation status of 3xTg-AD mice undergoing HFD without affecting systemic metabolism or promoting changes in cognitive performances.

Ambient PM2.5 chronic exposure leads to cognitive decline in mice: From pulmonary to neuronal inflammation

Fine particulate matter 2.5 (PM_2.5), one of the main components of air pollutants, seriously threatens human health. Possible neuronal dysfunction induced by PM_2.5 has received extensive attention. However, there is little evidence for the specific biochemical mechanism of neuronal injury induced by PM_2.5. Moreover, the pathway for PM_2.5 transport from peripheral circulation to the central nervous system (CNS) is still unclear. In the current work, C57BL/6 mice were chronically exposed to ambient PM_2.5 for 3, 6, 9, and 12 months. Exposure to ambient PM_2.5 resulted in a significant reduction of cognitive ability in mice by Morris water maze test. PM_2.5 exposure induced a neuroinflammatory reaction after cognitive impairment, while inflammation in the hypothalamus and olfactory bulb tissue occurred earlier. The expression levels of integrity tight junction proteins in the blood-brain barrier (BBB) were reduced by PM_2.5 exposure. Pulmonary inflammation occurred much earlier and diminished at later stage of PM_2.5 exposure. The results indicated that chronic exposure to ambient PM_2.5 led to cognitive decline in mice; CNS dysfunction may be due to neuroinflammatory reactions; the reduced integrity of the BBB allowed the influence of pulmonary inflammation to neuronal alterations. The work may provide promising therapeutic or preventive targets for air pollution-induced neurodegenerative disease.

IL-1R-/- alleviates cognitive deficits through microglial M2 polarization in AD mice

The neuroinflammatory response is considered a crucial event in the pathology of Alzheimer's disease (AD). Neurotoxic amyloid β (Aβ) oligomers activate neuronal glial cells, leading to the elevated generation of a large variety of inflammatory factors. Therefore, the regulation of interleukin-1 receptor (IL-1R) activity is believed to be a potential target for AD therapy. However, previous evidence of the role of IL-1R in AD-related neuroinflammation is ambiguous. To reveal the exact role of IL-1R in AD and related inflammatory reactions, we generated IL-1R^-/- AD mice. Based on the Morris water maze results, 4-month-old IL-1R^-/- AD mice showed better learning and memory ability than that of AD mice. However, IL-1R^-/- had little influence on amyloid precursor protein proteolysis, while IL-1R^-/- increased ADAM17 expression level. Surprisingly, IL-1R^-/- even enhanced glial activation. IL-1R^-/- indeed attenuated inflammatory cytokine secretion, especially that of cytokins associated with M1 polarization, while it led to increased levels of some cytokins associated with M2 polarization. Finally, we found that IL-1R^-/- reduced the phagocytic ability of microglia. Taken together, these results suggest that IL-1R deficiency may alleviate cognitive deficits in AD mice in a manner that is partially dependent on ADAM17 regulation and microglia M2 repolarization.

Long-lasting neurobehavioral alterations in burn-injured mice resembling post-traumatic stress disorder in humans

OBJECTIVE

To establish an animal model for posttraumatic stress disorder in burn-injured patients.

METHODS

Thermal-injured mice with 15% total body surface area were subjected to a series of neurobehavioral tests at 1 and 3 months postburn. Brains were collected for analysis of key molecules expression, spleens for T cell function analysis, and blood for biochemistry and hormones detection.

RESULTS

Comparison with sham mice, burn mice showed extremely high locomotion in homecage, open field, and forced swimming tests, indicating a hyper-arousal state. Burn mice exhibited improved spatial memory in Morris Water Maze test and heightened context fear memory in context fear conditioning, suggesting re-experiencing behavior. Although burn mice showed pronounced passive avoidance in the step-through test, their active avoidance capability in response to the conditional stimulus in the shuttle box test was relatively deteriorated. Likewise, the retention of cue-feared memory was impaired in fear conditioning test. The above negative alterations in mood were recapitulated in open-field test, in which the burn mice displayed an anxiety-like behavior with less time spent in the center. However, no sign of depression was found in the forced swimming and sucrose preference tests. The negative mood of burn mice was reinforced by a deficit in sociality and preference for social novelty in social interaction test. These neurobehavioral alterations were associated with an increased expression of brain-derived neurotrophic factor along with a remarkable microgliosis and a moderate astrocytosis in the brain of burn vs. sham mice. Moreover, a prominent Th2 switch and consequent increased nuclear NF-κB translocation were seen in the splenic T cells from burn relative to sham mice.

CONCLUSIONS

We conclude that even mild burn injury could lead to long-lasting cognitive and effective alterations in mice. These findings shed light on the interactions among neuropsychology, neurobiology, and immunology throughout the recovery period of burn injury.

Brain-derived neurotropic factor (BDNF) heterozygous mice are more susceptible to synaptic protein loss in cerebral cortex during high fat diet

In this study we aimed to investigate whether reduced BDNF levels aggravate the susceptibility of the brain to hazardous effects of high fat diet. For this purpose, we fed BDNF heterozygous mice and wild type littermates with normal and high fat diet for 16 weeks. Concentrations of two synaptic proteins (SNAP-25 and PSD-95) and oxidative stress parameters (MDA, SOD, CAT) were evaluated in the cortex after diet period. Interestingly, body weights of BDNF heterozygous groups fed with control diet were higher than their littermates and heterozygous mice fed with HFD were the heaviest in all experimental groups. MDA levels were significantly elevated in both HFD groups (wild type and BDNF(+/-)). Synaptic markers PSD-95 and SNAP-25 markedly decreased in BDNF(+/-) group fed with HFD compared to other groups. In conclusion, we suggest that endogenous BDNF has an important and possibly protective role in diet-induced changes in the cortex.

Abscisic Acid Supplementation Rescues High Fat Diet-Induced Alterations in Hippocampal Inflammation and IRSs Expression

Accumulated evidence indicates that neuroinflammation induces insulin resistance in the brain. Moreover, both processes are intimately linked to neurodegenerative disorders, including Alzheimer's disease. Potential mechanisms underlying insulin resistance include serine phosphorylation of the insulin receptor substrate (IRS) or insulin receptor (IR) misallocation. However, only a few studies have focused on IRS expression in the brain and its modulation in neuroinflammatory processes. This study used the high-fat diet (HFD) model of neuroinflammation to study the alterations of IR, an insulin-like growth factor receptor (IGF1R) and IRS expressions in the hippocampus. We observed that HFD effectively reduced mRNA and protein IRS2 expression. In contrast, a HFD induced the upregulation of the IRS1 mRNA levels, but did not alter an IR and IGF1R expression. As expected, we observed that a HFD increased hippocampal tumor necrosis factor alpha (TNFα) and amyloid precursor protein (APP) levels while reducing brain-derived neurotrophic factor (BDNF) expression and neurogenesis. Interestingly, we found that TNFα correlated positively with IRS1 and negatively with IRS2, whereas APP levels correlated positively only with IRS1 but not IRS2. These results indicate that IRS1 and IRS2 hippocampal expression can be affected differently by HFD-induced neuroinflammation. In addition, we aimed to establish whether abscisic acid (ABA) can rescue hippocampal IRS1 and IRS2 expression, as we had previously shown that ABA supplementation prevents memory impairments and improves neuroinflammation induced by a HFD. In this study, ABA restored HFD-induced hippocampal alterations, including IRS1 and IRS2 expression, TNFα, APP, and BDNF levels and neurogenesis. In conclusion, this study highlights different regulations of hippocampal IRS1 and IRS2 expression using a HFD, indicating the important differences of these scaffolding proteins, and strongly supports ABA therapeutic effects.