Knockdown of astrocytic Grin2a exacerbated sleep deprivation-induced cognitive impairments and elevation of amyloid-beta.

Sleep disorders are associated with cognitive impairments, greater amyloid-ß (Aß) burden and increased risk of developing Alzheimer's disease, while the underlying mechanism is unclear. N-methyl-d-aspartate receptors (NMDARs), as vital modulators of cognition, are sensitive to sleep disturbance. Sleep deprivation (SD) could induce the alterations of neuronal NMDAR subunits expression, however the alterations of astrocytic NMDARs in SD have not been reported. Our previous study has demonstrated knockdown of astrocytic Grin2a (gene encoding NMDAR subunit GluN2A) could aggravate Aß-induced cognitive impairments, but what role astrocytic GluN2A may play in SD is unknown. Here we focused on the changes and roles of hippocampal astrocytic GluN2A in SD. Our results showed SD increased the expression of astrocytic GluN2A. Specific knockdown of hippocampal astrocytic Grin2a aggravated SD-induced cognitive decline, elevated Aß, and attenuated the SD-induced increase in autophagy flux. Our finding, for the first time, revealed a novel neuroprotective role for astrocytic GluN2A in SD, which may be helpful for developing new preventive and therapeutic targets to sleep disorders.

Astrocytic N-Methyl-D-Aspartate Receptors Protect the Hippocampal Neurons Against Amyloid-ß142-Induced Synaptotoxicity by Regulating Nerve Growth Factor.

BACKGROUND: Soluble oligomeric amyloid-ß (Aß)-induced synaptic dysfunction is an early event in Alzheimer's disease (AD) pathogenesis. Mounting evidence has suggested N-methyl-D-aspartate receptors (NMDARs) play an important role in Aß-induced synaptotoxicity. Originally NMDARs were believed to be expressed exclusively in neurons; however, recent two decades studies have demonstrated functional NMDARs present on astrocytes. Neuronal NMDARs are modulators of neurodegeneration, while our previous initial study found that astrocytic NMDARs mediated synaptoprotection and identified nerve growth factor (NGF) secreted by astrocytes, as a likely mediator, but how astrocytic NMDARs protect neurons against Aß-induced synaptotoxicity through regulating NGF remains unclear. OBJECTIVE: To achieve further insight into the mechanism of astrocytic NMDARs oppose Aß-induced synaptotoxicity through regulating NGF. METHODS: With the primary hippocampal neuronal and astrocytic co-cultures, astrocytes were pretreated with agonist or antagonist of NMDARs before Aß142 oligomers application to neuron-astrocyte co-cultures. Western blot, RT-PCR, etc., were used for the related proteins evaluation. RESULTS: Activation of astrocytic NMDARs can significantly mitigate Aß142-induced loss of PSD-95 and synaptophysin through increasing NGF release. Blockade of astrocytic NMDARs inhibited Aß-induced compensatory protective NGF increase in protein and mRNA levels through modulating NF-κB of astrocytes. Astrocytic NMDARs activation can enhance Aß-induced Furin increase, and blockade of astrocytic NMDARs inhibited Aß-induced immunofluorescent intensity elevation of vesicle trafficking protein VAMP3 and NGF double-staining. CONCLUSION: Astrocytic NMDARs oppose Aß-induced synaptotoxicity through modulating the synthesis, maturation, and secretion of NGF in astrocytes. This new information may contribute to the quest for specific targeted strategy of intervention to delay the onset of AD.

Knockdown of astrocytic Grin2a aggravates ß-amyloid-induced memory and cognitive deficits through regulating nerve growth factor.

Synapse degeneration correlates strongly with cognitive impairments in Alzheimer's disease (AD) patients. Soluble Amyloid-beta (Aß) oligomers are thought as the major trigger of synaptic malfunctions. Our earlier studies have demonstrated that Aß oligomers interfere with synaptic function through N-methyl-D-aspartate receptors (NMDARs). Our recent in vitro study found the neuroprotective role of astrocytic GluN2A in the promotion of synapse survival and identified nerve growth factor (NGF) derived from astrocytes, as a likely mediator of astrocytic GluN2A buffering against Aß synaptotoxicity. Our present in vivo study focused on exploring the precise mechanism of astrocytic GluN2A influencing Aß synaptotoxicity through regulating NGF. We generated an adeno-associated virus (AAV) expressing an astrocytic promoter (GfaABC1D) shRNA targeted to Grin2a (the gene encoding GluN2A) to perform astrocyte-specific Grin2a knockdown in the hippocampal dentate gyrus, after 3 weeks of virus vector expression, Aß were bilaterally injected into the intracerebral ventricle. Our results showed that astrocyte-specific knockdown of Grin2a and Aß application both significantly impaired spatial memory and cognition, which associated with the reduced synaptic proteins PSD95, synaptophysin and compensatory increased NGF. The reduced astrocytic GluN2A can counteract Aß-induced compensatory protective increase of NGF through regulating pNF-κB, Furin and VAMP3, which modulating the synthesis, mature and secretion of NGF respectively. Our present data reveal, for the first time, a novel mechanism of astrocytic GluN2A in exerting protective effects on synapses at the early stage of Aß exposure, which may contribute to establish new targets for AD prevention and early therapy.

Influence of three different anesthesia protocols on aged rat brain: a resting-state functional magnetic resonance imaging study.

BACKGROUND: Resting-state functional magnetic resonance imaging (rs-fMRI) is a promising method for the study of brain function. Typically, rs-fMRI is performed on anesthetized animals. Although different functional connectivity (FC) in various anesthetics on whole brain have been studied, few studies have focused on different FC in the aged brain. Here, we measured FC under three commonly used anesthesia methods and analyzed data to determine if the FC in whole brain analysis were similar among groups. METHODS: Twenty-four male aged Wistar rats were randomly divided into three groups (n = 8 in each group). Anesthesia was performed under either isoflurane (ISO), combined ISO + dexmedetomidine (DEX) or α-chloralose (AC) according to the groups. Data of rs-fMRI was analyzed by FC in a voxel-wise way. Differences in the FC maps between the groups were analyzed by one-way analysis of variance and post hoc two-sample t tests. RESULTS: Compared with ISO + DEX anesthesia, ISO anesthesia caused increased FC in posterior brain and decreased FC in the middle brain of the aged rat. AC anesthesia caused global suppression as no increase in FC was observed. CONCLUSION: ISO could be used as a substitute for ISO + DEX in rat default mode network studies if the left temporal association cortex is not considered important.

Signal transducer and activator of transcription 3 promotes the Warburg effect possibly by inducing pyruvate kinase M2 phosphorylation in liver precancerous lesions.

BACKGROUND: Study shows that signal transducer and activator of transcription 3 (STAT3) can increase the Warburg effect by stimulating hexokinase 2 in breast cancer and upregulate lactate dehydrogenase A and pyruvate dehydrogenase kinase 1 in myeloma. STAT3 and pyruvate kinase M2 (PKM2) can also be activated and enhance the Warburg effect in hepatocellular carcinoma. Precancerous lesions are critical to human and rodent hepatocarcinogenesis. However, the underlying molecular mechanism for the development of liver precancerous lesions remains unknown. We hypothesized that STAT3 promotes the Warburg effect possibly by upregulating p-PKM2 in liver precancerous lesions in rats. AIM: To investigate the mechanism of the Warburg effect in liver precancerous lesions in rats. METHODS: A model of liver precancerous lesions was established by a modified Solt-Farber method. The liver pathological changes were observed by HE staining and immunohistochemistry. The transformation of WB-F344 cells induced with N-methyl-N'-nitro-N-nitrosoguanidine and hydrogen peroxide was evaluated by the soft agar assay and aneuploidy. The levels of glucose and lactate in the tissue and culture medium were detected with a spectrophotometer. The protein levels of glutathione S-transferase-π, proliferating cell nuclear antigen (PCNA), STAT3, and PKM2 were examined by Western blot and immunofluorescence. RESULTS: We found that the Warburg effect was increased in liver precancerous lesions in rats. PKM2 and p-STAT3 were upregulated in activated oval cells in liver precancerous lesions in rats. The Warburg effect, p-PKM2, and p-STAT3 expression were also increased in transformed WB-F344 cells. STAT3 activation promoted the clonal formation rate, aneuploidy, alpha-fetoprotein expression, PCNA expression, G1/S phase transition, the Warburg effect, PKM2 phosphorylation, and nuclear translocation in transformed WB-F344 cells. Moreover, the Warburg effect was inhibited by stattic, a specific inhibitor of STAT3, and further reduced in transformed WB-F344 cells after the intervention for PKM2. CONCLUSION: The Warburg effect is initiated in liver precancerous lesions in rats. STAT3 activation promotes the Warburg effect by enhancing the phosphorylation of PKM2 in transformed WB-F344 cells.

Expression alterations of apoptosis repressor with caspase recruitment domain in Aß25-35-induced hippocampal neurotoxicity.

Many proapoptotic and antiapoptotic proteins have been involved in the pathology of Alzheimer's disease. As the first identified antiapoptotic protein, apoptosis repressor with caspase recruitment domain (ARC) is highly expressed in terminally differentiated cells, and its functions and expressions in striated muscles and cancer cells have been widely studied. However, the expression alterations of ARC in amyloid ß-induced early hippocampal neurotoxicity are less known. In this report, we not only confirm previous reports that ARC is expressed in the hippocampal neurons but also demonstrate for the first time that ARC is also expressed in the hippocampal astrocytes. Furthermore, we extend the findings to show that, contrary to the time-dependently decreased ARC levels in the hippocampal neurons, ARC in astrocytes is strikingly increased in Aß25-35-induced early neurotoxicity. Our data suggest that ARC has distinct roles based on cell type and stimuli. Our results provide valuable information for further exploring the complicated functions and related mechanisms of ARC in amyloid-related diseases.

Prenatal stress induced gender-specific alterations of N-methyl-d-aspartate receptor subunit expression and response to Aß in offspring hippocampal cells.

Prenatal stress (PS) is one of adverse life events during pregnancy, which may increase vulnerability to cognitive impairment in adult offspring. Aß synaptotoxicity is one important pathological factor for cognitive impairment, and PS-induced cognitive disorder is closely associated with N-Methyl-d-Aspartate receptor (NMDAR), which acts as a key mediator of Aß synaptotoxicity. In the present study, we tried to explore whether PS affects offspring's Aß levels and NMDAR subunit expression in a gender-specific manner in hippocampal CA and DG subregions, and whether PS affects synaptic proteins and NMDAR subunit expression in cultured offspring hippocampal cells exposed to Aß. Pregnant SD rats with restraint stress from gestation day 8-20 were used as PS model. Morris water maze, ELISA, immunofluorescence and western blot were tested on postnatal day 90 in male and female PS offspring. Our results showed that female offspring is more vulnerable to PS-induced cognitive impairment. Surprisingly, PS enhanced Aß1-40 levels in the hippocampal DG subregion of male offspring. Furthermore, WB results implied that the decreased GluN2A in CA of female may contribute to the PS-induced cognitive impairment, while in DG, the increased GluN2A and decreased GluN2B contributed to protective effects against Aß. Interestingly, we found PS could alleviate Aß synaptotoxicity in male offspring's hippocampal cells. Overall, our results provided a fundamental understanding of PS-induced gender-specific alterations of NMDAR subunit expression and the susceptibility to Aß, and paved the road for the development of timely preventive interventions on cognitive disorders of PS offspring.

Cerebral dopamine neurotrophic factor alleviates Aß25-35-induced endoplasmic reticulum stress and early synaptotoxicity in rat hippocampal cells.

Alzheimer's disease (AD) is an age-related progressive neurodegenerative disease, and early stage AD is characterized by synaptic dysfunction generally ascribed to soluble oligomers of amyloid-beta (Aß). Neurotrophic factors are promising for AD treatment and are integrally involved in neuronal growth, survival and maintenance. Cerebral dopamine neurotrophic factor (CDNF) was recently discovered to have beneficial effects on long-term memory. The present study explored the synaptoprotective effects of CDNF in Aß-treated primary hippocampal cells. Immunofluorescent analysis of synaptophysin and postsynaptic density protein 95 (PSD95) puncta densities in the group of pretreatment with CDNF before Aß exposure revealed significant improvements compared to Aß group. In addition, pretreatment with CDNF reduced the expression levels of endoplasmic reticulum (ER) stress-related proteins, including Bip (also known as GRP78), phosphorylation of eukaryotic translation initiation factor 2 subunit α (peIF2α), phosphorylation of c-Jun N-terminal kinase (pJNK), and cleaved caspase 3, which are increased by Aß treatment at early stage. Our results revealed protective effects of CDNF on Aß-induced synaptotoxicity and ER stress, implying that CDNF may protect against Aß-induced synaptotoxicity through suppression of ER stress. CDNF could be a potential drug candidate for early AD treatment.