Xiaofei Wei

Enhancement of long-term depression by soluble amyloid β protein in rat hippocampus is mediated by metabotropic glutamate receptor and involves activation of p38MAPK, STEP and caspase-3

It is reported that the amyloid-β protein (Aβ)-induced impairments in synaptic plasticity coincide with memory decline and dementia. Although Aβ-induced inhibition of hippocampal long-term potentiation has been intensively investigated, the underlying mechanism of Aβ-enhanced long-term depression (LTD) is not clear. Here, we report that acute exposure of rat hippocampal slices to soluble Aβ-enhanced LTD induced by weak low-frequency stimulation (wLFS; 1Hz for 3 min, 180 pulses) in granule cells of the dentate gyrus. Application of LY341495 (a non-selective Group I/II metrabotropic glumate receptor (mGluR) antagonist) completely blocked Aβ-enhanced LTD, whereas D-AP5 (a not selective N-methyl-d-aspartate receptor (NMDAR) antagonist) had no effect on Aβ-enhanced LTD compared with controls. In addition, Aβ-enhanced LTD was occluded by pre-application of 3,5-dihydroxyphenylglycine, a Group1 mGluR (mGluR1/5) agonist, suggesting Aβ-enhanced LTD depends on mGluR1/5 but not NMDAR. We also report here that p38 mitogen-activated protein kinase (p38MAPK) inhibitor SB203580 and postsynaptic protein tyrosine phosphatase inhibitors phenylarsine oxide and sodium orthovanadate prevented the facilitatory effect of Aβ on LTD. Application of striatal-enriched protein tyrosine phosphatase (STEP) activator MG132 facilitated induction of LTD by wLFS, but did not block following Aβ-enhanced LTD induced by another wLFS. On the other hand, Aβ-enhanced LTD blocked following MG132-LTD by wLFS, suggesting Aβ-enhanced hippocampal LTD involves STEP activation. Application of either non-selective caspase inhibitor Z-VAD-FMK or caspase-3 selective inhibitor Z-DEVD-FMK prevented Aβ-enhanced LTD. However, neither the tumor necrosis factor-α converting enzyme inhibitor TAPI-2 nor the mammalian target of rapamycin inhibitor rapamycin prevented the enhancement of Aβ on LTD. Therefore, we conclude that soluble Aβ enhances LTD in the hippocampal dentate gyrus region, and the facilitatory effect of Aβ on LTD involves mGluR1/5, p38MAPK, STEP and caspase-3 activation.

Etazolate abrogates the lipopolysaccharide (LPS)-induced downregulation of the cAMP/pCREB/BDNF signaling, neuroinflammatory response and depressive-like behavior in mice

Increasing evidence has indicated that immune challenge by bacterial lipopolysaccharide (LPS) induces depressive-like behavior, neuroinflammatory response and upregulates phosphodiesterase-4 (PDE4), an enzyme that specifically hydrolyzes cyclic adenosine monophosphate (cAMP). However, whether the potential PDE4 inhibitor etazolate prevents the LPS-induced depressive-like behavior remains unclear. Here using a model of depression induced by the repeated administration of LPS during 16days, and then investigated the influence of LPS on the expression of PDE4, interleukin-1β (IL-1β) and antidepressant action of etazolate in mice through forced swimming, novelty suppressed feeding, sucrose preference and open-field tests. Our results showed that etazolate pretreatment facilitated the recovery from weight loss and prevented the depressive-like behavior induced by repeated LPS administration. Moreover, the antidepressant action of etazolate was paralleled by significantly reducing the expression levels of PDE4A, PDE4B, PDE4D and IL-1β and up-regulating the cAMP/phosphorylated cAMP response-element binding protein (pCREB)/brain-derived neurotrophic factor (BDNF) signaling in the hippocampus and prefrontal cortex of mice. These results indicate that the effects of etazolate on the depressive-like behavior induced by repeated LPS treatment may partially depend on the inhibition of PDE4 subtypes, the activation of the cAMP/pCREB/BDNF signaling and the anti-inflammatory responses in the hippocampus and prefrontal cortex.

Brilliant Blue G improves cognition in an animal model of Alzheimer’s disease and inhibits amyloid-β-induced loss of filopodia and dendrite spines in hippocampal neurons

Deposits of amyloid-β (Aβ) protein are one of the hallmarks of Alzheimers disease (AD). Numerous studies report that the Aβ peptide, especially in the oligomeric form, causes memory decline and other cognitive deficits. However, there have been very few effective interventions for termination or even delay of AD progression. Brilliant Blue G (BBG), a safe triphenylmethane dye and P2X7 antagonist, has been reported to have protective effects on neuroinflammation, ischemia, spinal injury and neurodegenerative disorders. Here we report that systematic administration of BBG diminishes spatial memory impairment and cognitive deficits in a mouse AD model produced by injecting soluble Aβ peptide into the hippocampal CA1 region. In addition, we show that Aβ-induced loss of filopodia and spine density in cultured hippocampal neurons was prevented by administration of BBG. We conclude that BBG prevents the learning and memory impairment and cognitive deficits induced by the toxicity of soluble Aβ, and improves the development of dendritic spines in hippocampal neurons in an AD model mouse. Considering the safety and blood-brain-barrier (BBB)-permeability of BBG, our data suggest a potential for BBG as a new therapy for AD.

Rapid-acting antidepressant-like effects of acetyl-l-carnitine mediated by PI3K/AKT/BDNF/VGF signaling pathway in mice

The possible involvement of the PI3K/AKT/BDNF/VGF signaling in rapid-acting antidepressant-like effects of antidepressants has been explored progressively by more studies. However, whether this signaling participates in the antidepressant-like effects of acetyl-l-carnitine (ALC) has not been examined. Herein, we assessed the antidepressant-like effects of ALC using the forced swimming test (FST). Our results demonstrated the dose-effect relationship of acute administration of ALC (5, 25, 50 and 100mg/kg, i.p.) and showed that it dose-dependently decreased the immobility time on FST of mice. In addition, ALC (100 mg/kg, i.p.) also reversed depressive-like behavior and the down-regulation of phosphorylated AKT (pAKT), brain-derived neurotrophic factor (BDNF) and neuropeptide VGF in the hippocampus and prefrontal cortex of mice induced by chronic unpredictable mild stress (CUMS) paradigm. Further, intra-cerebroventricular (i.c.v.) infusions of LY294002 (10 nmol/side), a specific phosphatidylinositol 3-kinase (PI3K) inhibitor, significantly prevented the antidepressant-like effect of ALC (100mg/kg, i.p.). In conclusion, our results demonstrated that ALC exerts rapid-acting antidepressant-like effects that might be mediated by the PI3K/AKT/BDNF/VGF signaling pathway.

Rosiglitazone prevents the memory deficits induced by amyloid-beta oligomers via inhibition of inflammatory responses

Rosiglitazone has been known to attenuate neurodegeneration in Alzheimers disease (AD), but the underlying mechanisms remain unclear. In this study, Morris water maze test, ELISA and electrophysiological methods were used to examine the role and underling mechanisms of rosiglitazone on Aβ42 oligomer-induced memory impairments. We found that rosiglitazone attenuated Aβ42 oligomer-induced memory impairments in rats in a dose-dependent manner. The levels of inflammatory cytokines interleukin-1 beta (IL-1β) and interferon gamma (IFNγ) were significantly increased 7 days after injection of Aβ42 oligomers into the rat hippocampus. Inhibition of microglia activation prevented Aβ42 oligomer-induced increases in IL-1β and IFNγ levels. Rosiglitazone completely prevented the increase in the levels of IL-1β and IFNγ induced by Aβ42 oligomers. Treatment of hippocampal slices with the inflammatory cytokine IL-1β or IFNγ significantly inhibited the production of long-term potentiation (LTP) in the dentate gyrus. Rosiglitazone prevented the inhibitory effects of inflammatory cytokines on LTP. Thus, inhibition of inflammatory responses may be part of the mechanisms of action of rosiglitazone on preventing memory deficits induced by Aβ42 oligmers.

Sunitinib, a Clinically Used Anticancer Drug, Is a Potent AChE Inhibitor and Attenuates Cognitive Impairments in Mice

Sunitinib, a tyrosine kinase inhibitor, is clinically used for the treatment of cancer. In this study, we found for the first time that sunitinib inhibits acetylcholinesterase (AChE) at submicromolar concentrations in vitro. In addition, sunitinib dramatically decreased the hippocampal and cortical activity of AChE in a time-dependent manner in mice. Molecular docking analysis further demonstrates that sunitinib might interact with both the catalytic anion and peripheral anionic sites within AChE, which is in accordance with enzymatic activity results showing that sunitinib inhibits AChE in a mixed pattern. Most importantly, we evaluated the effects of sunitinib on scopolamine-induced cognitive impairments in mice by using novel object recognition and Morris water maze tests. Surprisingly, sunitinib could attenuate cognitive impairments to a similar extent as donepezil, a marketed AChE inhibitor used for the treatment of Alzheimers disease. In summary, our results have shown that sunitinib could potently inhibit AChE and attenuate cognitive impairments in mice.

Presynaptic impairment in Niemann–Pick C1-deficient neurons: Not dependent on presence of glial cells

Niemann-Pick disease type C (NPC) is a progressive neurodegenerative disorder characterized by accumulation of free cholesterol in late endosomes/lysosomes. The pathological basis for the disease has been poorly understood yet. In our previous study, we have demonstrated that synaptic function is impaired in this disease. In the current study, electrophysiological and fluorescent dyes studies were used to determine whether the synaptic defects result from presynaptic or postsynaptic contributions. Furthermore, we would like to ascertain whether such defects are caused by direct effect of NPC1 deficiency in neurons or indirect effect of NPC1 deficiency in glial cells. Both mean inter-event interval of miniature excitatory postsynaptic currents (mEPSCs) and miniature inhibitory postsynaptic currents (mIPSCs) were significantly larger in NPC1(-/-) neurons than those in the wild-type neurons, while the amplitudes and the receptor kinetics were not different compared with those in wild-type controls. Synaptic vesicle exocytosis was also slower in the NPC1(-/-) neurons. The mean time constant of destaining was larger in NPC1(-/-) neurons than in wild-type controls both in the presence and absence of glial cells. All these results indicated a general presynaptic functional impairment in the NPC1(-/-) neurons and such defects were not dependent of glial cells. Therefore, neuropathology characteristics of NPC diseases may be a more possible consequence of neuronal presynaptic dysfunction than indirect defects in glial cells.

Chronic inflammatory pain upregulates expression of P2Y2 receptor in small-diameter sensory neurons

Roles of ionotropic purinergic (P2X) receptors in chronic pain have been intensively investigated. However, the contribution of metabotropic purinergic (P2Y) receptors to pathological pain is controversial. In the present study, using single cell RT-PCR (reverse transcription-polymerase chain reaction) and single cell nested-PCR techniques, we examined the expression of P2X2, P2X3, P2Y1 and P2Y2 mRNA transcripts in retrogradely labeled cutaneous sensory neurons from mouse lumber dorsal root ganglia (DRGs) following peripheral inflammation. The percentage of cutaneous sensory neurons expressing P2Y2 mRNA transcripts increased after complete Freund’s adjuvant (CFA) treatment. Particularly, the P2Y2 mRNA transcripts were more frequently detected in small-diameter cutaneous neurons from CFA-treated mice than those from control mice. Coexpression of P2Y2 and P2X (P2X2 or P2X3) mRNAs was more frequently observed in cutaneous sensory neurons from CFA-treated mice relative to controls. Pain behavioral tests showed that the blockade of P2Y receptors by suramin attenuated mechanical allodynia evoked either by CFA or uridine triphosphate (UTP), an endogenous P2Y2 and P2Y4 agonist. These results suggest that chronic inflammatory pain enhances expression of P2Y2 receptor in peripheral sensory neurons that innervate the injured tissue and the activation of P2Y receptors contributes to mechanical allodynia following inflammation.

The Rapid Effect of Bisphenol-A on Long-Term Potentiation in Hippocampus Involves Estrogen Receptors and ERK Activation

Bisphenol-A (BPA), a widely used synthetic compound in plastics, disrupts endocrine function and interferes with physiological actions of endogenous gonadal hormones. Chronic effects of BPA on reproductive function, learning and memory, brain structure, and social behavior have been intensively investigated. However, less is known about the influence of BPA on long-term potentiation (LTP), one of the major cellular mechanisms that underlie learning and memory. In the present study, for the first time we investigated the effect of different doses of BPA on hippocampal LTP in rat brain slices. We found a biphasic effect of BPA on LTP in the dentate gyrus: exposure to BPA at a low dose (100 nM) enhanced LTP and exposure to BPA at a high dose (1000 nM) inhibited LTP compared with vehicle controls. The rapid facilitatory effect of low-dose BPA on hippocampal LTP required membrane-associated estrogen receptor (ER) and involved activation of the extracellular signal-regulated kinase (ERK) signaling pathway. Coadministration of 17β-estradiol (E2, the primary estrogen hormone) and BPA (100 nM) abolished both the BPA-induced enhancement of LTP and the E2-induced enhancement of baseline fEPSP, suggesting a complex interaction between BPA- and E2-mediated signaling pathways. Our investigation implies that even nanomolar levels of endocrine disrupters (e.g., BPA) can induce significant effects on hippocampal LTP.

CCK-8S increased the filopodia and spines density in cultured hippocampal neurons of APP/PS1 and wild-type mice

Cholecystokinin (CCK), a neuropeptide, is widely distributed in the brain. The function of CCK is involved in many brain functions including learning and memory, but the cellular mechanism is poorly understood. In the present study, we investigated the effect of CCK on dendritic filopodia and spines of cultured hippocampal neurons from wild-type and APP/PS1 mice. The cultured hippocampal neurons were infected with CMV-GFP (CMV promoter with green fluorescent protein) adenovirus 24h before image acquisition to display the subtle structure of dendrites. Cholecystokinin octapeptide sulfated (CCK-8S, 0.2μM) was added into the cultured solution from divided in vitro day 2 (DIV 2). A decrease of filopodia and spines density was observed in APP/PS1 mice compared with that of wild type mice. CCK-8S increased the density of filopodia and spines at DIV 7, DIV 14 and DIV 21 in hippocampal neurons of both wild-type and APP/PS1 mice. In addition, this effect was inhibited by CI988, an antagonist of CCK-2 receptor. Those results indicate that CCK-8S can influence the dendritic development and spine genesis of cultured hippocampal neurons derived from both wild-type and APP/PS1 mice. These data suggest that CCK may play an important role in learning and memory.