Ling-Qiang Zhu

Activation of Glycogen Synthase Kinase-3 Inhibits Long-Term Potentiation with Synapse-Associated Impairments

Activation of glycogen synthase kinase-3 (GSK-3) can cause memory deficits as seen in Alzheimers disease, the most common age-associated dementia, but the mechanism is not understood. Here, we found that activation of GSK-3 by wortmannin or transient overexpression of wild-type GSK-3β could suppress the induction of long-term potentiation (LTP) in rat hippocampus, whereas simultaneous inhibition of GSK-3 by lithium or SB216763 or transient expression of a dominant-negative GSK-3β mutant (dnGSK-3β) preserved the LTP. After high-frequency stimulation (HFS), the presynaptic release of glutamate and the expression/clustering of synapsin I, a synaptic vesicle protein playing an important role in neurotransmitter release, decreased markedly after upregulation of GSK-3. In vitro studies further demonstrated that GSK-3 inhibited the expression of SynI independent of HFS. In postsynaptic level, the expression of PSD93 and NR2A/B proteins decreased significantly when GSK-3 was activated. The LTP-associated synapse impairments including less presynaptic active zone, thinner postsynaptic density, and broader synaptic cleft were also prominent in the hippocampal slices after HFS with activation of GSK-3. These synaptic impairments were attenuated when GSK-3 was simultaneously inhibited by LiCl or SB216763 or transient expression of dnGSK-3. We conclude that upregulation of GSK-3 impairs the synaptic plasticity both functionally and structurally, which may underlie the GSK-3-involved memory deficits.

Role of Dopamine Receptors in ADHD: A Systematic Meta-analysis

The dopaminergic system plays a pivotal role in the central nervous system via its five diverse receptors (D1–D5). Dysfunction of dopaminergic system is implicated in many neuropsychological diseases, including attention deficit hyperactivity disorder (ADHD), a common mental disorder that prevalent in childhood. Understanding the relationship of five different dopamine (DA) receptors with ADHD will help us to elucidate different roles of these receptors and to develop therapeutic approaches of ADHD. This review summarized the ongoing research of DA receptor genes in ADHD pathogenesis and gathered the past published data with meta-analysis and revealed the high risk of DRD5, DRD2, and DRD4 polymorphisms in ADHD.

EPAC null mutation impairs learning and social interactions via aberrant regulation of miR-124 and Zif268 translation.

EPAC proteins are the guanine nucleotide exchange factors that act as the intracellular receptors for cyclic AMP. Two variants of EPAC genes including EPAC1 and EPAC2 are cloned and are widely expressed throughout the brain. But, their functions in the brain remain unknown. Here, we genetically delete EPAC1 (EPAC1(-/-)), EPAC2 (EPAC2(-/-)), or both EPAC1 and EPAC2 genes (EPAC(-/-)) in the forebrain of mice. We show that EPAC null mutation impairs long-term potentiation (LTP) and that this impairment is paralleled with the severe deficits in spatial learning and social interactions and is mediated in a direct manner by miR-124 transcription and Zif268 translation. Knockdown of miR-124 restores Zif268 and hence reverses all aspects of the EPAC(-/-) phenotypes, whereas expression of miR-124 or knockdown of Zif268 reproduces the effects of EPAC null mutation. Thus, EPAC proteins control miR-124 transcription in the brain for processing spatial learning and social interactions.

GSK-3β Inhibits Presynaptic Vesicle Exocytosis by Phosphorylating P/Q-Type Calcium Channel and Interrupting SNARE Complex Formation

Glycogen synthase kinase-3 (GSK-3), a Ser/Thr protein kinase abundantly expressed in neurons, plays diverse functions in physiological and neurodegenerative conditions. Our recent study shows that upregulation of GSK-3 suppresses long-term potentiation and presynaptic release of glutamate; however, the underlying mechanism is elusive. Here, we show that activation of GSK-3β retards the synaptic vesicle exocytosis in response to membrane depolarization. Using calcium imaging, whole-cell patch-clamp, as well as specific Ca2+ channel inhibitors, we demonstrate that GSK-3β phosphorylates the intracellular loop-connecting domains II and III (LII-III) of P/Q-type Ca2+ channels, which leads to a decrease of intracellular Ca2+ rise through the P/Q-type voltage-dependent calcium channel. To further illustrate the mechanisms of GSK-3βs action, we show that activation of GSK-3β interferes with the formation of the soluble N-ethylmaleimide-sensitive factor attachment protein (SNAP) receptor (SNARE) complex through: (1) weakening the association of synaptobrevin with SNAP25 and syntaxin; (2) reducing the interactions among the phosphorylated LII-III and synaptotagmin, SNAP25, and syntaxin; and (3) inhibiting dissociation of synaptobrevin from synaptophysin I. These results indicate that GSK-3β negatively regulates synaptic vesicle fusion events via interfering with Ca2+-dependent SNARE complex formation.

Protein Phosphatase 2A Facilitates Axonogenesis by Dephosphorylating CRMP2

Protein phosphatase 2A (PP2A) is indispensable in development, and deficits of PP2A and deterioration of neuronal axons have been observed in several neurodegenerative disorders, but the direct link between PP2A and the neuronal axon development is still missing. Here, we show that PP2A is essential for axon development in transfected rat brain and the dissociated hippocampal neurons. Upregulation of PP2A catalytic subunit (PP2Ac) not only promotes formation and elongation of the functional axons but also rescues axon retardation induced by PP2A inhibition. PP2A can dephosphorylate collapsin response mediator protein-2 (CRMP2) that implements the axon polarization, whereas constitutive expression of phosphomimic-CRMP2 abrogates the effect of PP2A upregulation. We also demonstrate that PP2Ac is enriched in the distal axon of the hippocampal neurons. Our results reveal a mechanistic link between PP2A and axonogenesis/axonopathy, suggesting that upregulation of PP2A may be a promising therapeutic for some neurodegenerative disorders.

Melatonin attenuates isoproterenol‐induced protein kinase A overactivation and tau hyperphosphorylation in rat brain

Abstract:  Hyperphosphorylation of microtubule‐associated protein tau at specific sites is a recognized pathological process in Alzheimers disease (AD), and protein kinase A (PKA) is a crucial kinase in AD‐like tau hyperphosphorylation. In the present study, isoproterenol (ISO) was injected bilaterally into hippocampus of rat brain; ISO is a specific PKA activator and it induces tau hyperphosphorylation. With this system, melatonin (MT) was shown to protect against ISO‐induced tau hyperphosphorylation. We found that hippocampal injection of ISO (0.02 μm) induced PKA overactivation and tau hyperphosphorylation at both paired helical filament (PHF)‐1 and tau‐1 sites. ISO injection also resulted in activation of superoxide dismutase (SOD) and elevation of malondialdehyde (MDA), parameters suggesting elevated oxidative stress. Preinfusion of MT intraperitoneally partially reversed ISO‐induced tau hyperphosphorylation at the PHF‐1 epitope (1 and 10 mg/kg continuously for 4 wk or 10 mg/kg for 1, 2 or 3 wk) and tau‐1 epitope (10 mg/kg for 2 wk). Furthermore, MT (10 mg/kg for 2 wk) obviously antagonized ISO‐induced PKA overactivation, as well as enhanced SOD activity and decreased the level of MDA. It is suggested from these data that ISO may induce abnormal hyperphosphorylation of tau through not only the activation of PKA but also because of the fact that it increases oxidative stress; MT may protect against ISO‐induced tau hyperphosphorylation through suppression of both PKA overactivation and oxidative stress.

Effect of inhibiting melatonin biosynthesis on spatial memory retention and tau phosphorylation in rat.

Abstract:  We have found recently that melatonin protects SH‐SY5Y neuroblastoma cells from calyculin A‐induced neurofilament impairment and neurotoxicity. In the present study, we further investigated the in vivo effect of inhibiting melatonin biosynthesis on spatial memory retention and tau phosphorylation in rats and the potential underlying mechanisms by using haloperidol, a specific inhibitor of 5‐hydroxyindole‐O‐methyltransferase, and a key enzyme in melatonin biosynthesis. We have found that injection of haloperidol into the lateral ventricle and into peritoneal cavity compromises spatial memory retention of rats and induces hyperphosphorylation of microtubule‐associated protein tau at tau‐1 (Ser199/Ser202) and PHF‐1 (Ser396/Ser404) epitopes. At mean time, the activity of protein phosphatase‐2A (PP‐2A), a deficit phosphatase in the Alzheimers disease brain and superoxide dismutase decreases with an elevated level of malondialdehyde. Supplementation with melatonin by prior injection for 1 wk and reinforcement during the haloperidol administration significantly improves memory retention deficits, arrests tau hyperphosphorylation and oxidative stress, and restores PP‐2A activity. These results strongly support the involvement of decreased melatonin in Alzheimer‐like spatial memory impairment and tau hyperphosphorylation, and PP‐2A may play a role in mediating aberrant melatonin‐induced lesions.

Hsp90 Chaperone Inhibitor 17-AAG Attenuates Aβ-Induced Synaptic Toxicity and Memory Impairment

The excessive accumulation of soluble amyloid peptides (Aβ) plays a crucial role in the pathogenesis of Alzheimers disease (AD), particularly in synaptic dysfunction. The role of the two major chaperone proteins, Hsp70 and Hsp90, in clearing misfolded protein aggregates has been established. Despite their abundant presence in synapses, the role of these chaperones in synapses remains elusive. Here, we report that Hsp90 inhibition by 17-AAG elicited not only a heat shock-like response but also upregulated presynaptic and postsynaptic proteins, such as synapsin I, synaptophysin, and PSD95 in neurons. 17-AAG treatment enhanced high-frequency stimulation-evoked LTP and protected neurons from synaptic damage induced by soluble Aβ. In AD transgenic mice, the daily administration of 17-AAG over 7 d resulted in a marked increase in PSD95 expression in hippocampi. 17-AAG treatments in wild-type C57BL/6 mice challenged by soluble Aβ significantly improved contextual fear memory. Further, we demonstrate that 17-AAG activated synaptic protein expression via transcriptional mechanisms through the heat shock transcription factor HSF1. Together, our findings identify a novel function of Hsp90 inhibition in regulating synaptic plasticity, in addition to the known neuroprotective effects of the chaperones against Aβ and tau toxicity, thus further supporting the potential of Hsp90 inhibitors in treating neurodegenerative diseases.

Disease-modified glycogen synthase kinase-3β intervention by melatonin arrests the pathology and memory deficits in an Alzheimer's animal model

The current therapies for Alzheimers disease (AD) are merely palliative that cannot arrest the pathologic progression of the disease. Therefore, it is critical to develop treatments that can target the disease-modifying molecule(s). In the present study, we found that treatment of tg2576 mice with melatonin from 4-8 months of age did not improve the pathology or behavioral performance of the mice. However, remarkable attenuation of tau and β-amyloid pathologies with memory improvement were observed when melatonin was supplied from the age of 8-12 months or 4-12 months of the mice; more importantly, the improvements were still significant when the mice survived to old age. We also found that the disease stage-specific alteration of glycogen synthase kinase-3β (GSK-3β) but not protein phosphatase-2A, was correlated with the alterations of the pathology and behavior, and the timely targeting of GSK-3β was critical for the efficacy of melatonin. Our finding suggests that melatonin treatment only at proper timing could arrest AD by targeting the activated GSK-3β, which provides primary evidence for the importance and strategy in developing disease-modifying interventions of AD.

Neuroglobin attenuates Alzheimer-like tau hyperphosphorylation by activating Akt signaling

J. Neurochem. (2012) 120, 157–164.