A sequential view of neurotransmitter release

Alzheimer’s Disease-related Biomarkers in Aging Adults with Down Syndrome: Systematic Review

Background:

Down syndrome (DS) is associated with a high prevalence of cognitive impairment and dementia in middle age and older adults. Given the presence of common neuropathological findings and similar pathogenic mechanisms, dementia in DS is regarded as a form of genetically determined, early-onset AD. The clinical characterization of cognitive decline in persons with DS is a difficult task, due to the presence intellectual disability and pre-existing cognitive impairment. Subtle changes that occur at early stages of the dementing process may not be perceived clinically, given that most cognitive screening tests are not sensitive enough to detect them. Therefore, biological markers will provide support to the diagnosis of DS-related cognitive impairment and dementia, particularly at early stages of this process.

Objective:

To perform a systematic review of the literature on AD-related biomarkers in DS.

Method:

We searched PubMed, Web of Science and Cochrane Library for scientific papers published between 2008 and 2018 using as primary mesh terms ‘Down’, ‘Alzheimer’, ‘biomarker’.

Results:

79 studies were retrieved, and 39 were considered eligible for inclusion in the systematic review: 14 post-mortem studies, 10 neuroimaging, 4 addressing cerebrospinal fluid biomarkers, and 11 on peripheral markers.

Conclusion:

There is consistent growth in the number of publication in this field over the past years. Studies in DS-related dementia tend to incorporate many of the diagnostic technologies that have been more extensively studied and validated in AD. In many instances, the study of CNS and peripheral biomarkers reinforces the presence of AD pathology in DS.

Ginsenoside Rg1 Ameliorates Behavioral Abnormalities and Modulates the Hippocampal Proteomic Change in Triple Transgenic Mice of Alzheimer's Disease

Alzheimer's disease (AD) is one of the most common neurodegenerative diseases, so far, there are no effective measures to prevent and cure this deadly condition. Ginsenoside Rg1 (Rg1) was shown to improve behavioral abnormalities in AD; however, the potential mechanisms remain unclear. In this study, we pretreated 7-month-old 3xTg-AD mice for 6 weeks with Rg1 and evaluated the effects of Rg1 on the behaviors and the protein expression of hippocampal tissues. The behavioral tests showed that Rg1 could improve the memory impairment and ameliorate the depression-like behaviors of 3xTg-AD mice. Proteomic results revealed a total of 28 differentially expressed hippocampal proteins between Rg1-treated and nontreated 3xTg-AD mice. Among these proteins, complexin-2 (CPLX2), synapsin-2 (SYN2), and synaptosomal-associated protein 25 (SNP25) were significantly downregulated in the hippocampus of 3xTg-AD mice compared with the WT mice, and the treatment of Rg1 modulated the expression of CPLX2 and SNP25 in the hippocampus of 3xTg-AD mice. The expression of CPLX2, SYN2, and SNP25 was further validated by Western blot analysis. Taken together, we concluded that Rg1 could be a potential candidate drug to improve the behavioral deficits in AD via modulating the expression of the proteins (i.e., CPLX2, SYN2, and SNP25).

Differential effects of antipsychotics on hippocampal presynaptic protein expressions and recognition memory in a schizophrenia model in mice

We compared the effects of subchronic clozapine and haloperidol administration on the expression of SNAP-25 and synaptophysin in an animal model of schizophrenia based on the glutamatergic hypothesis. Mice were first treated with a non-competitive NMDA antagonist MK-801 (0.3 mg/kg/day) or saline for 5 days, and then clozapine (5 mg/kg/day), haloperidol (1 mg/kg/day) or saline was administered for two weeks. The locomotion test, as a behavioral model of the positive symptoms of schizophrenia, was applied after MK-801/saline administration on day 6 for acute effects and after antipsychotic/saline administration on day 19 for enduring effects on mice activity. Memory function was assessed by the Novel Object Recognition (NOR) test, one day after the last day of antipsychotic/saline administration (day 20). Western Blotting technique was used to determine SNAP-25 and synaptophysin expressions in the hippocampus and frontal cortex. Both antipsychotics reversed the enhanced locomotion effects of MK-801. MK-801 and haloperidol decreased recognition memory performance. On the other hand, clozapine did not compromise memory. It also did not reverse the negative effects of MK-801 on memory performance. MK-801 did not change SNAP-25 and synaptophysin expressions in the hippocampus and frontal cortex. Clozapine increased hippocampal SNAP-25, decreased hippocampal synaptophysin expression, whereas frontal SNAP-25 and synaptophysin expressions remained unchanged. Haloperidol had no effects on levels of SNAP-25 and synaptophysin in the frontal cortex and hippocampus. These findings support the idea that the differential effects of clozapine might be related to its plastic effects and synaptic reorganization of the hippocampus.

3D QSAR studies on 3,4-dihydroquinazolines as T-type calcium channel blocker by comparative molecular similarity indices analysis (CoMSIA)

A comparative molecular similarity indices analysis (CoMSIA) of a set of 42 3,4-dihydroquinazolines have been performed to find out the pharmacophore elements for T-type calcium channel blocking activity. The most potent compound, 33 (KYS05090) was used to align the molecules. As a result, we obtained 3D QSAR model which provided good predictivity for the training set (q(2)=0.642, r(2)=0.874) and the test set (r(pred)(2)=0.884). This model would guide the design of new chemical entities potentially having high potency.

Synthesis and SAR study of T-type calcium channel blockers. Part II

3,4-Dihydroquinazoline derivatives have been known to be the novel and potent T-type calcium channel blockers. From a systematic variation of 3,4-dihydroquinazoline derivative 5c (KYS05043), plausible SAR results were established. It was revealed that a 5-(dimethylamino)pentylamino group at R(1), a biphenyl group at R(2), and a benzyl amido group at R(3)in the 3,4-dihydroquinazoline backbone are closely related with the channel selectivity (T/N-type) as well as the potency based on the discovery of 6k (KYS05090).

Discovery of potent T-type calcium channel blocker

The intensive SAR study of 3,4-dihydroquinazoline series led to the most potent compound 10 (KYS05090: IC(50)=41+/-1 nM) against T-type calcium channel and its potency is nearly comparable to that of Kurtoxin. As a small organic molecule, this compound showed the highest blocking activity reported to date.

FAPP2 is involved in the transport of apical cargo in polarized MDCK cells

Phosphatidylinositol-4-phosphate (PI(4)P) is the main phosphoinositide in the Golgi complex and has been reported to play a pleiotropic role in transport of cargo from the trans-Golgi network to the plasma membrane (PM) in polarized Madin–Darby canine kidney (MDCK) cells. Overexpression of the chimeric fluorescent protein encoding the pleckstrin homology domain, which is specific for PI(4)P, inhibited both apical and basolateral transport pathways. The transport of apical cargo from the Golgi was shown to be specifically decreased by adenovirus-mediated RNA interference directed against PI(4)P adaptor protein (FAPP) 2. FAPP1 depletion had no effect on transport. On the other hand, FAPP2 was not involved in the Golgi-to-PM transport of cargo that was targeted to the basolateral membrane domain. Thus, we conclude that FAPP2 plays a specific role in apical transport in MDCK cells.

The role of voltage-gated calcium channels in pain and nociception

The voltage-gated calcium channels (VGCCs) are a large and functionally diverse group of ion channels found throughout the central nervous system (CNS) and the periphery. Neuronal functions include the control of neurotransmitter release and neuronal excitability in important pain pathways. In the current review we will give an overview of the data that has been generated in support of these channels performing a pivotal role in the pain pathway.

Molecular mechanisms underlying the modulation of exocytotic noradrenaline release via presynaptic receptors

The release of noradrenaline from nerve terminals is modulated by a variety of presynaptic receptors. These receptors belong to one of the following three receptor superfamilies: transmitter-gated ion channels, G protein-coupled receptors (GPCR), and membrane receptors with intracellular enzymatic activities. For representatives of each of these three superfamilies, receptor activation has been reported to cause either an enhancement or a reduction of noradrenaline release. As these receptor classes display greatly diverging structures and functions, a multitude of different molecular mechanisms are involved in the regulation of noradrenaline release via presynaptic receptors. This review gives a short overview of the presynaptic receptors on noradrenergic nerve terminals and summarizes the events involved in vesicle exocytosis in order to finally delineate the most important signaling cascades that mediate the modulation via presynaptic receptors. In addition, the interactions between the various presynaptic receptors are described and the underlying molecular mechanisms are elucidated. Together, these presynaptic signaling mechanisms form a sophisticated network that precisely adapts the amount of noradrenaline being released to a given situation.

From proteomics to biomarker discovery in Alzheimer's disease

Alzheimer's disease (AD) is the most common form of dementia in the elderly. AD is an invariably fatal neurodegenerative disorder with no effective treatment or definitive antemortem diagnostic test. Little is known about the changes in the brain preceding or accompanying initiation of the disease. Understanding the biological processes, which occur during AD onset and/or progression, will improve the diagnosis and treatment of the disease. As we will discuss in this review article, using high-throughput cDNA microarray we identified candidate genes whose expression is altered in the brain of cases at risk for AD dementia. However, it is possible that the use of the cDNA microarray technology alone may underestimate post-transcriptional modifications and therefore provides only a partial view of the biological problem of interest. As such, the combination of cDNA and protein arrays may provide a more global picture of the biological processes being studied. Based on this hypothesis, we initiated a series of high-throughput proteomic studies and found that the expressions of proteins involved in synaptic plasticity are selectively altered in the brain of cases at high risk to develop AD dementia (mild cognitive impairment; MCI). This is consistent with our cDNA microarray evidence showing that the expression of a-type synapsins is selectively altered in the brain of MCI cases. Collectively, these studies support the feasibility and usefulness of high-throughput cDNA microarray and proteomics techniques to study the sequential changes of distinctive gene expression patterns in the brain as a function of the progression of AD dementia.

Adenosine triphosphate levels in steelhead (Oncorhynchus mykiss) eggs: an examination of turnover, localization and role

The dynamics of energy production and utilization in fish eggs before and shortly after fertilization may be critical for embryo survival. Therefore, the current study examined the turnover of adenosine triphosphate (ATP) as well as examined the possible role and localization of ATP in unfertilized steelhead (Oncorhynchus mykiss) eggs and early embryos. The mean ATP level in unfertilized steelhead eggs was 1.92+/-0.10 (mean+/-S.E.M., n=17) nmol ATP per egg. Exposure of the unfertilized egg to 10 degrees C water (water activation) and fertilization resulted in comparable and substantial decreases (approx. 20-50%) in egg ATP levels within 3 min. This suggests that the energy expended at fertilization is used in response to water activation rather than fertilization per se. Unfertilized eggs maintained in ovarian fluid for 9 days at 10 degrees C under air showed a progressive decline of fertility that reached zero after 6 days. In contrast, no significant changes were seen in ATP levels throughout this 9 days period. Thus, fertility does not positively correlate with egg ATP levels in stored eggs. In the unfertilized egg, the ATP stored in the yolk accounted for approximately 1.5% of the total egg ATP. After fertilization, the concentration of ATP in the yolk increased approximately seven-fold, with the yolk and blastoderm each now accounting for approximately 20% of the total remaining ATP. Finally, to estimate the changes in oxidative metabolism following fertilization, the cyanide (KCN)-sensitive decline in total ATP was determined for unfertilized eggs and 1 day embryos. In the presence of KCN, ATP levels declined to approximately 50% within 24 h in both unfertilized eggs as well as embryos; the rates of ATP decline were not different. Therefore, there was not a discernible increase in ATP generation by oxidative phosphorylation at the time of fertilization.

Ca(2+) and Mg(2+)/ATP independently trigger homotypic membrane fusion in gastric secretory membranes

Exocytic activation of gastric parietal cells represents a massive transformation. We studied a step in this process, homotypic fusion of H,K-ATPase-containing tubulovesicles, using R18 dequenching. Ca(2+) and Mg(2+)/ATP each caused dramatic dequenching, reflecting a change in R18 distribution from 5% to 65-90% of the assay's membranes in 2.5 min. These stimuli also triggered fusion between tubulovesicles and liposomes. Independent confirmation that dequenching represented membrane fusion was established by separating tubulovesicle-liposome fusion products on density gradients. Only agents that trigger fusion allowed the transmembrane H,K-ATPase to move to low-density fractions along with R18. EC(50) for Ca(2+)-triggered fusion was 150 nm and for Mg(2+)/ATP-triggered fusion 1 mm, the latter having a Hill coefficient of 2.5. ATP-triggered fusion was specific for Mg(2+)/ATP, required ATP hydrolysis, and was insensitive to inhibition of NSF and/or H,K-ATPase. Fusion initiated by either trigger caused tubulovesicles to become resistant to subsequent challenge by either trigger. Ca(2+) and Mg(2+)/ATP-triggered fusion required protein component(s) in tubulovesicles, though this was required in only one of the fusing membranes since tubulovesicles fused well with liposomes containing no proteins. Our data suggest that exocytosis in parietal cells is triggered by separate but interacting pathways and is regulated by self-inhibition.

Obligatory role of protein kinase Cbeta and MARCKS in vesicular trafficking in living neurons

Neurotransmitter release from neurons involves both vesicular trafficking and subsequent fusion of synaptic vesicles with the plasma membrane. The mechanisms involving the formation and fusion of vesicles that allow the exocytotic release of transmitters are understood well. Little is known, however, about the signaling mechanism involved in the trafficking of vesicles along the neurites. In this study, we used real-time confocal microscopy to search for evidence that vesicular trafficking in neurons requires the activation of protein kinase Cbeta (PKCbeta) and the myristoylated alanine-rich C kinase substrate (MARCKS) signaling pathway. Dopamine-beta-hydroxylase fused to green fluorescent protein has been used to trace vesicular movement. Angiotensin II, an established neuromodulatory hormone, stimulates translocation of green fluorescent protein-dopamine-beta-hydroxylase vesicles from the cell body to neurites. This translocation was blocked by an antisense oligonucleotide to PKCbeta and MARCKS. Stimulation of PKC by other means, such as phorbol-12-myristate-13-acetate or carbachol, also resulted in the redistribution of fluorescence in a manner similar to that observed for angiotensin II. These observations demonstrate that PKCbeta-MARCKS signaling may be a general mechanism for the stimulation of vesicular trafficking in brain neurons.

Use of cDNA microarray in the search for molecular markers involved in the onset of Alzheimer's disease dementia

Alzheimer's disease (AD) is the most common form of dementia, affecting as many as 4 million older persons and results from abnormal changes in the brain that most likely begin long before cognitive impairment and other clinical symptoms become apparent. Thus, efforts aimed at identifying methods of early detection and diagnosis for improving AD care might be the most appropriate strategy to initiate promising new treatments and/or prevention. We used cDNA microarray technology to investigate the sequence of changes in gene expression in brain that may take place during the transition from normal cognitive functioning through the early stages of impairment to frank AD. We examined the expression of approximately 7,000 genes in the brains of cases at the early stage of AD dementia using reference sample cases characterized by normal cognitive status. Genes that are differentially regulated in early AD cases were identified and were categorized into gene clusters based on similarities in biological functions. This analysis revealed that selected biological processes, including protein and amino acid metabolism, cytoskeleton integrity, and fatty acid metabolism, are involved in early phases of AD dementia. Most notable is the observation that selected genes involved in neurotransmitter release are differentially regulated in the brains of cases at high risk for dementia. This evidence supports the feasibility and usefulness of cDNA microarray techniques to study sequential changes of distinctive gene-expression patterns in the brain as a function of the progression of AD dementia. The study suggests new means to dissect and classify stages of AD dementia, or neuropathology, at the molecular level.

Neurotransmitter release mechanisms in sympathetic neurons: past, present, and future perspectives

In 1969, Paton and Vizi described the inhibitory actions of noradrenaline on acetylcholine release from the innervation of the guinea-pig ileum longitudinal muscle. They concluded "that acetylcholine output by the nervous networks of the longitudinal strip is under the normal control of the sympathetic by a species of presynaptic inhibition mediated by <==> receptors". This work was carried out in the Pharmacology Department at Oxford University. Clearly, a period in the 'Dreaming Spires' of Oxford sufficiently inspired Sylvester to take up a life long career in scientific research. He has published more than 300 papers on a wide range of topics but clearly has a strong interest in neurotransmitter release mechanisms and recently, non-synaptic interactions between neurons. It seems fitting therefore to write a brief review on the continuing studies on neurotransmitter release mechanisms in sympathetic neurons in a volume honoring the now distinguished Professor Vizi.

SNAP-25-associated Hrs-2 protein colocalizes with AQP2 in rat kidney collecting duct principal cells

The vasopressin-induced trafficking of aquaporin-2 (AQP2) water channels in kidney collecting duct is likely mediated by vesicle-targeting proteins (N-ethylmaleimide-sensitive factor attachment protein receptors). Hrs-2 is an ATPase believed to have a modulatory role in regulated exocytosis. To examine whether Hrs-2 is expressed in rat kidney, we carried out RT-PCR combined with DNA sequence analysis and Northern blotting using a digoxigenin-labeled Hrs-2 RNA probe. RT-PCR and Northern blotting revealed that Hrs-2 mRNA is localized in all zones of rat kidney. The presence of Hrs-2 protein in rat kidney was confirmed by immunoblotting, revealing a 115-kDa protein in kidney and brain membrane fractions corresponding to the expected molecular size of Hrs-2. Immunostaining and confocal laser scanning microscopy of LLC-PK(1) cells (a porcine proximal tubule cell line) transfected with Hrs-2 DNA confirmed the specificity of the antibody and revealed that Hrs-2 is mainly localized in intracellular compartments, including cathepsin D-containing lysosomal/endosomal compartments. The cellular and subcellular localization of Hrs-2 in rat kidney was examined by immunocytochemistry and confocal laser scanning microscopy. Hrs-2 immunoreactivity was observed in collecting duct principal cells, and weaker labeling was detected in other nephron segments. The labeling was predominantly present in intracellular vesicles, but labeling was also observed in the apical plasma membrane domains of some cells. Colabeling with AQP2 revealed colocalization in vesicles and apical plasma membrane domains, suggesting a role for Hrs-2 in regulated AQP2 trafficking.

Yeast homotypic vacuole fusion: a window on organelle trafficking mechanisms

Homotypic (self) fusion of yeast vacuoles, which is essential for the low copy number of this organelle, uses catalytic elements similar to those used in heterotypic vesicular trafficking reactions between different organelles throughout nature. The study of vacuole inheritance has benefited from the ease of vacuole isolation, the availability of the yeast genome sequence and numerous mutants, and from a rapid, quantitative in vitro assay of fusion. The soluble proteins and small molecules that support fusion are being defined, conserved membrane proteins that catalyze the reaction have been identified, and the vacuole membrane has been solubilized and reconstituted into fusion-competent proteoliposomes, allowing the eventual purification of all needed factors. Studies of homotypic vacuole fusion have suggested a modified paradigm of membrane fusion in which integral membrane proteins termed "SNAREs" can form stable complexes in cis (when on the same membrane) as well as in trans (when anchored to opposing membranes). Chaperones (NSF/Sec18p, LMA1, and -SNAP/Sec17p) disassemble cis-SNARE complexes to prepare for the docking of organelles rather than to drive fusion. The specificity of organelle docking resides in a cascade of trans-interactions (involving Rab-like GTPases), "tethering factors," and trans-SNARE pairing. Fusion itself, the mixing of the membrane bilayers and the organelle contents, is triggered by calcium signaling.

The use of permeabilized cells to assay protein phosphorylation and catecholamine release

A number of approaches can be used to determine the protein kinases and protein phosphatases acting on particular phosphoproteins in vivo. Cell permeabilization represents one such approach. In this overview we discuss the different permeabilization procedures used in bovine adrenal chromaffin cells and in particular the use of digitonin. The effect of various factors on the extent of digitonin-permeabilization, protein phosphorylation and catecholamine release are also discussed. The factors include the permeabilization medium, the ions such as calcium, and the second messengers, such as cAMP, IP3, cADPR and calmodulin. The effect of specific peptide inhibitors of protein kinases on tyrosine hydroxylase phosphorylation is illustrated. Advantages and disadvantages of cell permeabilization procedures are discussed throughout the text.