PPARγ Dysfunction in the Medial Prefrontal Cortex Mediates High-Fat Diet-Induced Depression.

Epidemiological studies suggest a bidirectional association between depression and obesity; however, the biological mechanisms that link the development of depression to a metabolic disorder remain unclear. Even though nuclear receptor peroxisome proliferator-activated receptor γ (PPARγ) agonists show anti-depressive effect, and high-fat diet-(HFD)-induced PPARγ dysfunction is involved in the pathogenesis of metabolic disorders, the neuronal PPARγ has never been studied in HFD-induced depression. Thus, we aimed to investigate the effect of neuronal PPARγ on depressive-like behaviors in HFD-induced obese mice.We fed male C57BL/6 J mice with HFD to generate obese mice and conducted a series of behavioral tests to assess the effects of HFD feeding on depression. We generated neuron-specific PPARγ knockout mice (NKO) to determine whether neuronal PPARγ deficiency was correlated with depressive-like behaviors. To further prove whether PPARγ in the medial prefrontal cortex (mPFC) neurons is involved in depressive-like behaviors, we applied AAV- CaMKIIα-Cre approach to specifically knockout PPARγ in the mPFC neurons of LoxP mice and used AAV-syn-PPARγ vectors to overexpress PPARγ in the mPFC neurons of NKO mice.We observed a low mPFC PPARγ level and an increase in depressive-like behaviors in the HFD-fed mice. Moreover, neuronal-specific PPARγ deficiency in mice induced depressive-like behaviors, which could be abolished by imipramine. Furthermore, overexpressing PPARγ in the mPFC reversed the depressive-like behaviors in HFD-fed mice as well as in neuronal-specific PPARγ knockout mice.These results implicate that dysregulation of neuronal PPARγ in the mPFC may contribute to an increased risk for depression in obese populations.

The Effect of Chronic Cerebral Hypoperfusion on Blood-Brain Barrier Permeability in a Transgenic Alzheimer's Disease Mouse Model (PS1V97L).

The blood-brain barrier (BBB) can restrict the therapeutic effects of Alzheimer's disease (AD) medications. While a large number of AD drug treatment trials targeting BBB dynamics have emerged, most have failed due to insufficient permeability. Furthermore, a subset of AD cases, which also feature chronic hypoperfusion are complicated by BBB deficits. We used a mouse model of AD with chronic hypoperfusion-transgenic mice (PS1V97L) with right common carotid artery ligation. In this model, we assessed how chronic cerebral hypoperfusion changed the pathophysiological processes that increase BBB permeability. Compared with control mice, AD mice with chronic hypoperfusion revealed significantly upregulated expression of the receptor for advanced glycation end products (RAGE) on the BBB. Upregulated RAGE caused increased accumulation of amyloid-ß (Aß) in the brain in these mice. Upregulation of RAGE (or binding to Aß) can promote activation of the NF-κB pathway and enhance oxidative stress and increase the release of pro-inflammatory factors. These factors promoted the reduction of tight junction proteins between the endothelial cells in the BBB and increased its permeability. These findings suggest that the transporter RAGE dysregulation on the BBB initiates a series of pathophysiological processes which lead to increased BBB permeability. Taken together, we have shown that chronic hypoperfusion can serve to enhance and aggravate the BBB impairment in AD.

Toxic amyloid-ß oligomers induced self-replication in astrocytes triggering neuronal injury.

BACKGROUND: Soluble amyloid-ß oligomer (AßO) induced deleterious cascades have recently been considered to be the initiating pathologic agents of Alzheimer's disease (AD). However, little is known about the neurotoxicity and production of different AßOs. Understanding the production and spread of toxic AßOs within the brain is important to improving understanding of AD pathogenesis and treatment. METHODS: Here, PS1V97L transgenic mice, a useful tool for studying the role of AßOs in AD, were used to identify the specific AßO assembly that contributes to neuronal injury and cognitive deficits. Then, we investigated the production and spread of toxic Aß assemblies in astrocyte and neuron cultures, and further tested the results following intracerebroventricular injection of AßOs in animal model. FINDINGS: The results showed that cognitive deficits were mainly caused by the accumulation of nonameric and dodecameric Aß assemblies in the brains. In addition, we found that the toxic AßOs were duplicated in a time-dependent manner when BACE1 and apolipoprotein E were overexpressed, which were responsible for producing redundant Aß and forming nonameric and dodecameric assemblies in astrocytes, but not in neurons. INTERPRETATION: Our results suggest that astrocytes may play a central role in the progression of AD by duplicating and spreading toxic AßOs, thus triggering neuronal injury. FUND: This study was supported by the Key Project of the National Natural Science Foundation of China; the National Key Scientific Instrument and Equipment Development Project; Beijing Scholars Program, and Beijing Brain Initiative from Beijing Municipal Science & Technology Commission.

Activation of Nrf2/ARE pathway alleviates the cognitive deficits in PS1V97L-Tg mouse model of Alzheimer's disease through modulation of oxidative stress.

Oxidative stress refers to an imbalance between oxidative and antioxidative systems due to environmental factors. Although oxidative stress is implicated in the pathogenesis of Alzheimer's disease (AD), its precise role is not yet understood. We aimed to investigate the pathogenic mechanisms of the oxidative stress by using in vitro cultured neurons and in vivo AD models of PS1V97L-transgenic (Tg) mice. Our results showed that when oxidative stress became increasingly evident, the endogenous protective pathway of nuclear factor E2-related factor 2 (Nrf2)/antioxidant response element (ARE) decreased in 10-month-old PS1V97L-Tg mice. Activating the Nrf2/ARE pathway suppressed oxidative stress, decreased amyloid-ß (Aß), and improved the cognitive function of the PS1V97L-Tg mice. In contrast, blocking the Nrf2/ARE pathway augmented oxidative injury and decreased the cell viability of PS1V97L-Tg neurons. Our results highlight the role of the Nrf2/ARE pathway in regulating oxidative stress of the PS1V97L-Tg mice and may indicate a potential therapeutic avenue for AD treatment.

Honokiol Alleviates Cognitive Deficits of Alzheimer's Disease (PS1V97L) Transgenic Mice by Activating Mitochondrial SIRT3.

Accumulating evidence has demonstrated that mitochondrial dysfunction is a prominent early event in the progression of Alzheimer's disease (AD). Whether protecting mitochondrial function can reduce amyloid-ß oligomer (AßO)-induced neurotoxicity in PS1V97L transgenic mice remains unknown. In this study, we examined the possible protective effects of honokiol (HKL) on mitochondrial dysfunction induced by AßOs in neurons, and cognitive function in AD PS1V97Ltransgenic mice. We determined that HKL increased mitochondrial sirtuin 3 (SIRT3) expression levels and activity, which in turn markedly improved ATP production and weakened mitochondrial reactive oxygen species production. We demonstrated that the enhanced energy metabolism and attenuated oxidative stress of HKL restores AßO-mediated mitochondrial dysfunction in vitro and in vivo. Consequently, memory deficits in the PS1V97L transgenic mice were rescued by HKL in the early stages. These results suggest that HKL has therapeutic potential for delaying the onset of AD symptoms by alleviating mitochondrial impairment and increasing hyperactivation of SIRT3 in the pathogenesis of preclinical AD.

Sulforaphane Inhibits the Generation of Amyloid-ß Oligomer and Promotes Spatial Learning and Memory in Alzheimer's Disease (PS1V97L) Transgenic Mice.

Abnormal amyloid-ß (Aß) aggregates are a striking feature of Alzheimer's disease (AD), and Aß oligomers have been proven to be crucial in the pathology of AD. Any intervention targeting the generation or aggregation of Aß can be expected to be useful in AD treatment. Oxidative stress and inflammation are common pathological changes in AD that are involved in the generation and aggregation of Aß. In the present study, 6-month-old PS1V97L transgenic (Tg) mice were treated with sulforaphane, an antioxidant, for 4 months, and this treatment significantly inhibited the generation and aggregation of Aß. Sulforaphane also alleviated several downstream pathological changes that including tau hyperphosphorylation, oxidative stress, and neuroinflammation. Most importantly, the cognition of the sulforaphane-treated PS1V97L Tg mice remained normal compared to that of wild-type mice at 10 months of age, when dementia typically emerges in PS1V97L Tg mice. Pretreating cultured cortical neurons with sulforaphane also protected against neuronal injury caused by Aß oligomers in vitro. These findings suggest that sulforaphane may be a potential compound that can inhibit Aß oligomer production in AD.

CBX2 Inhibits Neurite Development by Regulating Neuron-Specific Genes Expression.

Polycomb group (PcG) proteins regulate the epigenetic status of transcription regulatory states during development. Progression from pluripotency to differentiation requires the sequential activation and repression of different PcG target genes, however, the relationship between early patterning signals, PcG expression, and the development of the central nervous system is still unclear. Using various models of neuronal differentiation, we provide evidence that CBX2 is a negative regulator of neuronal differentiation. Knock-down of CBX2 expression promotes neurite development, while overexpression of CBX2 inhibits neurite development. Further, we found that CBX2 is a direct target gene of miR-124. During neuronal differentiation, CBX2 was decreased while miR-124 was increased. Mechanistically, CBX2 directly interacts with the promoter region of several neuro-associated genes and regulates their expression. We found that the neuron-specific GAP-43 gene could contribute to the stimulating effect on neurite development associated with inhibition of CBX2.

miR-124 and miR-9 mediated downregulation of HDAC5 promotes neurite development through activating MEF2C-GPM6A pathway.

The class IIa histone deacetylases (HDACs) play important roles in the central nervous system during diverse biological processes such as synaptic plasticity, axon regeneration, cell apoptosis, and neural differentiation. Although it is known that HDAC5 regulates neuronal differentiation, neither the physiological function nor the regulation of HDAC5 in neuronal differentiation is clear. Here, we identify HDAC5 as an inhibitor of neurite elongation and show that HDAC5 is regulated by the brain enriched microRNA miR-124 and miR-9. We discover that HDAC5 inhibits neurite extension both in differentiated P19 cells and primary neurons. We also show that the neuronal membrane glycoprotein GPM6A (M6a) is a direct target gene of HDAC5 regulated transcriptional factor MEF2C. HDAC5 inhibits neurite elongation, acting at least partially via a MEF2C/M6a signaling pathway. We also confirmed the miR-124/miR-9 regulated HDAC5-MEF2C-M6a pathway regulates neurite development in primary neurons. Thus, HDAC5 emerges as a cellular conductor of MEF2C and M6a activity and is regulated by miR-124 and miR-9 to control neurite development.

Brain Amyloid-ß Plays an Initiating Role in the Pathophysiological Process of the PS1V97L-Tg Mouse Model of Alzheimer's Disease.

Amyloid-ß (Aß) aggregation, tau hyperphosphorylation, oxidative stress, and neuroinflammation are major pathophysiological events in Alzheimer's disease (AD). However, the relationships among these processes and which first exerts an effect are unknown. In the present study, we investigated age-dependent behavioral changes and the sequential pathological progression from the brain to the periphery in AD transgenic (PS1V97L-Tg) mice and their wild-type littermates. We discovered that the brain Aß significantly increased at 6 months old, the increased brain Aß caused memory dysfunction, and the ability of Aß to induce tau hyperphosphorylation might be due to oxidative stress and neuroinflammatory reactions. The levels of Aß42, total tau (t-tau), oxidative stress parameters, and proinflammatory cytokines in plasma can be used to differentiate between PS1V97L-Tg mice and their wild-type littermates at different time points. Collectively, our findings support the hypothesis that Aß is a trigger among these pathophysiological processions and show that plasma biomarkers can reflect the condition of the AD brain.

Soluble Epoxide Hydrolase Deficiency or Inhibition Attenuates MPTP-Induced Parkinsonism.

Soluble epoxide hydrolase (sEH) inhibition has been demonstrated to have beneficial effects on various diseases, such as hypertension, diabetes, and brain ischemia. However, whether sEH inhibition has therapeutic potential in Parkinson's disease is still unknown. In this paper, we found that sEH expression is increased in 1-methyl-4-phenyl-1,2,3,6-tetrahydro pyridine (MPTP)-treated mice, and sEH deficiency and inhibition significantly attenuated tyrosine hydroxylase (TH)-positive cell loss and improved rotarod performance. The substrate of sEH, 14,15-epoxyeicosatrienoic acid (14,15-EET), protected TH-positive cells and alleviated the rotarod performance deficits of wild-type mice but not sEH-knockout mice. Moreover, the 14,15-EET antagonist 14,15-epoxyeicosa-5(Z)-enoic acid (14,15-EEZE) abolished the neuronal protective effects of sEH deficiency. In primary cultured cortical neurons, MPP(+) induced significant Akt inactivation in neurons from sEH wild-type mice, and this effect was not observed in neurons from knockout mice. Our data indicate that sEH deficiency and inhibition increased 14,15-EET in MPTP-treated mice, which activated the Akt-mediated protection of TH-positive neurons and behavioral functioning. We also found that sEH deficiency attenuated TH-positive cell loss in a paraquat-induced mouse model of Parkinson's. Our data suggest that sEH inhibition might be a powerful tool to protect dopaminergic neurons in Parkinson's disease.

Jingzhaotoxin-35, a novel gating-modifier toxin targeting both Nav1.5 and Kv2.1 channels.

Jingzhaotoxin-35 (JZTX-35), a 36-residue polypeptide, was purified from the venom of the Chinese tarantula Chilobrachys jingzhao. JZTX-35 inhibited Nav1.5 and Kv2.1 currents with the IC50 value of 1.07 µM and 3.62 µM, respectively, but showed no significant effect on either Na(+) currents or Ca(2+) currents evoked in hippocampal neurons. It shifted the activation of the Nav1.5 and Kv2.1 channels to more depolarized voltages, and markedly shifted the steady-state inactivation of Nav1.5 currents toward more hyperpolarized potentials. Moreover, JZTX-35 can bind to a close state of Nav1.5 and Kv2.1 channels. These results indicate that JZTX-35 is a new gating modifier toxin. JZTX-35 shares high sequence similarity with Jingzhaotoxins (JZTXs) targeting Nav1.5 or Kv2.1 channels, but they showed different ion channel selectivity. Structure-function analysis in this study would provide important clues for the exploration of ion channel selectivity of JZTXs.

[Neural stem cell-specific peroxisome proliferator-activated receptor γ knockout mice: breeding and genetic identification].

OBJECTIVE: To breed neual stem cell-specific peroxisome proliferator-activated receptor γ (PPARγ) knockout mice. METHODS: Two transgenic mouse models, namely B6.PPARγloxp/loxp and B6.Nestin-Cre were interbred, and the first- generation offsprings were backcrossed with B6.PPARγloxp/loxp to obtain the second-generation mice. Genomic DNA was extracted from the second-generation mice for PCR to amplify the loxp and Cre gene fragments followed by agarose gel electrophoresis to verify their sizes. The mice with the PPARγloxp/loxp.Nestin-Cre (KO) genotype were selected as the neural stem cell-specific knockout PPARγ mice, with B6.PPARγloxp/loxp (loxp) mice as the control. Tissue samples were collected from specific regions of the mouse brain and peripheral tissue for detecting the expression of PPARγ mRNA using RT-PCR and real-time quantitative PCR. RESULTS AND CONCLUSION: Genotyping results showed PPARγloxp and Cre bands in the knockout mice, which showed obviously decreased mRNA expression of PPARγ, suggesting successful establishment of neural stem cell-specific PPARγ knockout mice. The two transgenic mice we used were fertile, and their breeding pattern followed the laws of Mendelian inheritance.

[Effects of peroxisome proliferator-activated receptors γ on the expression of insulin receptor substrate-4 gene in rat cortical neurons and mouse brain].

OBJECTIVE: To investigate the effect of peroxisome proliferator-activated receptors γ (PPARγ) on insulin receptor substrate-4 (IRS-4) gene expression in the brain. METHODS: Primarily cultured cortical neurons from E17-18 Sprague Dawley rats, after 1 week of plating, were exposed to 10 µmol/L PPARγ agonist rosiglitazone for 0, 1, 4 or 24 h. Adult C57BL/6J mice or conditional brain PPARγ knock-out mice (B-PPARγ-KO, BKO) received an intraperitoneal injection of rosiglitazone in 10% DMSO at 12 mg/kg or injection of the same volume of saline containing 10% DMSO. The effect of rosiglitazone on the survival of the neurons was examined by MTT assay. The expression of IRS-4 mRNA was analyzed by real-time quantitative PCR. RESULTS: The survival of the cortical neurons showed no significant difference between the agonist groups and the control group. The expression of IRS-4 mRNA was significantly up-regulated in the cortical tissues and neurons of the agonist groups compared with the control groups (P<0.05), but in BKO mice without treatment, IRS-4 mRNA expression was significantly down-regulated (P<0.05). CONCLUSION: PPARγ can enhance the expression of IRS-4 mRNA in the brain.