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Biomedical subjects

N Nelson

Publications and source records attributed to N Nelson.

At least 37 records · Page 2Linked to original sources
PubMed1999

The identification of seven metalloproteinase-disintegrin (ADAM) genes from genomic libraries.

Metalloproteinase-disintegrins (ADAMs) are membrane-spanning multi-domain proteins containing a zinc metalloproteinase domain and a disintegrin domain which may serve as an integrin ligand. Based on a conserved sequence within the disintegrin domain, GE(E/Q)CDCG, seven genes were isolated from a human genomic library. Two of these genes lack introns and show testis-specific expression (ADAM20 and ADAM21), while the other two genes contain introns (ADAM22 and ADAM23) and are expressed predominantly in the brain. In addition, three pseudogenes were isolated; one of which evolved from ADAM21. Human chromosomal mapping indicated that ADAM22 and ADAM23 mapped to chromosome 7q21 and 2q33, respectively, while the three pseudogenes 1-2, 3-3, and 1-32 mapped to chromosome 14q24.1, 8p23, and 14q24.1, respectively. An ancestral analysis of all known ADAMs indicates that the zinc-binding motif in the catalytic domain arose once in a common ancestor and was lost by those members lacking this motif.

ADAM Proteins↗
PubMed1999

Metal ion transporters and homeostasis.

Transition metals are essential for many metabolic processes and their homeostasis is crucial for life. Aberrations in the cellular metal ion concentrations may lead to cell death and severe diseases. Metal ion transporters play a major role in maintaining the correct concentrations of the various metal ions in the different cellular compartments. Recent studies of yeast mutants revealed key elements in metal ion homeostasis, including novel transport systems. Several of the proteins discovered in yeast are highly conserved, and defects in some of the yeast mutants could be complemented by their human homologs. The studies of yeast metal ion transporters helped to unravel the molecular mechanism of macrophage defense against bacterial infection and hereditary diseases.

Animals↗
PubMed1999

Action of bicyclic isoxazole GABA analogues on GABA transporters and its relation to anticonvulsant activity.

The inhibitory action of bicyclic isoxazole gamma-aminobutyric acid (GABA) analogues and their 4,4-diphenyl-3-butenyl (DPB) substituted derivatives has been investigated in cortical neurones and astrocytes as well as in human embryonic kidney (HEK 293) cells transiently expressing either mouse GABA transporter-1 (GAT-1), GAT-2, -3 or -4. It was found that 4,5,6,7-tetrahydroisoxazolo(4,5-c)pyridin-3-ol (THPO) and 5,6,7,8-tetrahydro-4H-isoxazolo[4,5-c]azepin-3-ol (THAO) displayed some inhibitory activity on GAT-1 and GAT-2, where the compounds exhibited a slightly lower potency on GAT-2 compared to GAT-1. DPB substituted THPO displayed higher inhibitory potency than the parent compound regarding the ability to inhibit GABA uptake via GAT-1 and GAT-2. Concerning the inhibitory mechanism, THPO, THAO and DPB-THPO were competitive inhibitors on GAT-1 transfected HEK 293 cells and the same mechanism was observed for THPO in GAT-3 transfected cells. Regarding GABA uptake into neurones and astroglia cells THAO and DPB-THAO both displayed competitive inhibitory action. The observations that THPO, THAO as well as their DPB derivatives act as competitive inhibitors together with earlier findings such as potent anticonvulsant activity, lack of proconvulsant activity and the ability of THPO to increase extracellular GABA concentration, indicate that these bicyclic isoxazole GABA analogues and their DPB derivatives may be useful lead structures in future search for new antiepileptic drugs.

Animals↗
PubMed1999

Developmental expression of the neurotransmitter transporter GAT3.

Neurotransmitter transporters are involved in termination of the synaptic neurotransmission and they also play a key role in neuroregulation and brain development. In this report, we describe the developmental distribution of the y-aminobutyric acid transporter GAT3 which transports gamma-aminobutyric acid (GABA) and beta-alanine in a sodium chloride-dependent manner. GAT3 was localized to the meninges in developmental stages where two other GABA transporters, GAT1 and GAT4, were adjacently expressed. In later developmental stages, only GAT3 remained in this area. The expression of GAT3 in the peripheral embryonic tissues was confined to the liver, to a layer of cells under the skin, to the mouse kidney, and to hipoccampal blood vessels only in late developmental stages. The developmental distribution of GAT3 suggests involvement in central nervous system (CNS) maturation.

Animals↗
PubMed1999

Developmental expression of the neurotransmitter transporter NTT4.

Neurotransmitter transporters are involved in termination of the synaptic neurotransmission and are implicated as the sites of action of antidepressant medicines and illicit drugs. In addition to their function in neurotransmission, neurotransmitter transporters play a key role in neuroregulation and brain development. In this report, the developmental distribution of the "orphan" transporter NTT4, whose substrate has not yet been shown, is described. Immunohistochemical studies have previously shown NTT4 to be specifically and widely localized to the central nervous system. In this report, the distribution of NTT4 in brain areas enriched in glutamatergic and gamma-aminobutyric acid-ergic innervations is further substantiated. NTT4 is detected beginning at E18 in various parts of the rat brain, including the cerebral cortex, fimbria hippocampi, fornix, lateral lemniscus, anterior commissure, and spinal cord. At E18, strong immunoreactivity of NTT4 is observed in the cortical subplate and marginal layers that later develops into the fimbria hippocampi, and at P22, the expression of NTT4 in the hippocampal formation reaches the mature form. The expression of NTT4 in the spinal cord begins at E18 in the ventral white matter. Heavy staining for NTT4 is observed in the substantia nigra since birth and through all time points examined. Transient immunoreactivity is observed in the inferior colliculus, reaching maximal expression at P10, whereas the superior colliculus commences to express NTT4 only after this time point. The globus pallidus is highly stained after birth, and the caudate putamen shows strong staining for NTT4 only at P22. In the adult rat brain, NTT4 is strongly expressed in the olfactory bulb, cerebral cortex, striatum, hippocampus, thalamus, substantia nigra, pontine nucleus, cerebellum, and spinal cord. The developmental distribution of NTT4 suggests involvement in central nervous system maturation.

Animals↗
PubMed1999

Characterization of the cDNA and gene for mouse tumour necrosis factor alpha converting enzyme (TACE/ADAM17) and its location to mouse chromosome 12 and human chromosome 2p25.

Numerous proteins are cleaved or "shed" from their membrane-bound form. One such protein, tumour necrosis factor alpha (TNF-alpha), is synthesized as a type 2 transmembrane protein. Recently, a human protease responsible for this shedding, the TNF-alpha converting enzyme (TACE/ADAM17), was isolated. TACE/ADAM17 is a member of the adamalysin class of zinc-binding metalloproteases or ADAM (a disintegrin and metalloprotease). We report the isolation and characterization of the mouse TACE/ADAM17 cDNA and gene. Mouse TACE/ADAM17 has a 92% amino-acid identity with the human protein and was ubiquitously expressed. A recombinant form of the protease is found to cleave a peptide representing the cleavage site of precursor mouse TNF-alpha. An alternatively spliced form of mouse TACE/ADAM17 was found that would produce a soluble protein. The gene for TACE/ADAM17 is approximately 50 kb and contains 19 exons. Chromosomal mapping places TACE/ADAM17 on mouse chromosome 12 and human chromosome 2p25.

ADAM Proteins↗
PubMed1999

Rapid transbilayer movement of fluorescent phospholipid analogues in the plasma membrane of endocytosis-deficient yeast cells does not require the Drs2 protein.

Evidence is presented that endocytosis-deficient Saccharomyces cerevisiae end4 yeast cells rapidly internalize the fluorescent phospholipid analogues 1-palmitoyl-2-{6-[7-nitro-2,1, 3-benzoxadiazol-4-yl(NBD)amino] caproyl}phosphatidylcholine (P-C6-NBD-PtdCho) and P-C6-NBD-phosphatidylserine (P-C6-NBD-PtdSer). Both analogues redistributed between the exoplasmic and cytoplasmic leaflet with a half-time of < 15 min at 0 degrees C. The plateau of internalized analogues was about 70%. Transbilayer movement is probably protein-mediated, as the flip-flop of both analogues was very slow in liposomes composed of plasma-membrane lipids. Rapid analogue internalization was not abolished on depletion of intracellular ATP by about 90%. For P-C6-NBD-PtdCho only was a moderate decrease in the plateau of internalized analogues of about 20% observed, while that of P-C6-NBD-PtdSer was not affected. The Drs2 protein plays only a minor role, if any, in the rapid transbilayer movement of analogues in S. cerevisiae end4 cells. In S. cerevisiae end4 Deltadrs2 cells harbouring both an end4 allele and a drs2 null allele, about 60% and 50% of P-C6-NBD-PtdCho and P-C6-NBD-PtdSer, respectively, became internalized within 15 min at 0 degrees C. The preferential orientation of P-C6-NBD-PtdSer to the cytoplasmic leaflet is in qualitative agreement with the sequestering of endogenous phosphatidylserine to the cytoplasmic leaflet, as assessed by binding of annexin V. Virtually no binding of annexin V to spheroplasts of the parent wild-type strain or the mutant strains was observed. Likewise, no difference in the exposure of endogenous aminophospholipids to the exoplasmic leaflet between these strains was found by labelling with trinitrobenzenesulfonic acid. Thus, lipid asymmetry, at least of aminophospholipids, was preserved in S. cerevisiae end4 cells independently of the presence of the Drs2 protein.

4-Chloro-7-nitrobenzofurazan↗
PubMed1999

Vacuolar and plasma membrane proton-adenosinetriphosphatases.

The vacuolar H+-ATPase (V-ATPase) is one of the most fundamental enzymes in nature. It functions in almost every eukaryotic cell and energizes a wide variety of organelles and membranes. V-ATPases have similar structure and mechanism of action with F-ATPase and several of their subunits evolved from common ancestors. In eukaryotic cells, F-ATPases are confined to the semi-autonomous organelles, chloroplasts, and mitochondria, which contain their own genes that encode some of the F-ATPase subunits. In contrast to F-ATPases, whose primary function in eukaryotic cells is to form ATP at the expense of the proton-motive force (pmf), V-ATPases function exclusively as ATP-dependent proton pumps. The pmf generated by V-ATPases in organelles and membranes of eukaryotic cells is utilized as a driving force for numerous secondary transport processes. The mechanistic and structural relations between the two enzymes prompted us to suggest similar functional units in V-ATPase as was proposed to F-ATPase and to assign some of the V-ATPase subunit to one of four parts of a mechanochemical machine: a catalytic unit, a shaft, a hook, and a proton turbine. It was the yeast genetics that allowed the identification of special properties of individual subunits and the discovery of factors that are involved in the enzyme biogenesis and assembly. The V-ATPases play a major role as energizers of animal plasma membranes, especially apical plasma membranes of epithelial cells. This role was first recognized in plasma membranes of lepidopteran midgut and vertebrate kidney. The list of animals with plasma membranes that are energized by V-ATPases now includes members of most, if not all, animal phyla. This includes the classical Na+ absorption by frog skin, male fertility through acidification of the sperm acrosome and the male reproductive tract, bone resorption by mammalian osteoclasts, and regulation of eye pressure. V-ATPase may function in Na+ uptake by trout gills and energizes water secretion by contractile vacuoles in Dictyostelium. V-ATPase was first detected in organelles connected with the vacuolar system. It is the main if not the only primary energy source for numerous transport systems in these organelles. The driving force for the accumulation of neurotransmitters into synaptic vesicles is pmf generated by V-ATPase. The acidification of lysosomes, which are required for the proper function of most of their enzymes, is provided by V-ATPase. The enzyme is also vital for the proper function of endosomes and the Golgi apparatus. In contrast to yeast vacuoles that maintain an internal pH of approximately 5.5, it is believed that the vacuoles of lemon fruit may have a pH as low as 2. Similarly, some brown and red alga maintain internal pH as low as 0.1 in their vacuoles. One of the outstanding questions in the field is how such a conserved enzyme as the V-ATPase can fulfill such diverse functions.

Animals↗
PubMed1999

Double-blind treatment of major depression with dehydroepiandrosterone.

OBJECTIVE: This study was designed to assess possible antidepressant effects of dehydroepiandrosterone (DHEA), an abundant adrenocortical hormone in humans. METHOD: Twenty-two patients with major depression, either medication-free or on stabilized antidepressant regimens, received either DHEA (maximum dose = 90 mg/day) or placebo for 6 weeks in a double-blind manner and were rated at baseline and at the end of the 6 weeks with the Hamilton Depression Rating Scale. Patients previously stabilized with antidepressants had the study medication added to that regimen; others received DHEA or placebo alone. RESULTS: DHEA was associated with a significantly greater decrease in Hamilton depression scale ratings than was placebo. Five of the 11 patients treated with DHEA, compared with none of the 11 given placebo, showed a 50% decrease or greater in depressive symptoms. CONCLUSIONS: These results suggest that DHEA treatment may have significant antidepressant effects in some patients with major depression. Further, larger-scale trials are warranted.

Adult↗
PubMed1999

Hippocampal GABA and glutamate transporter immunoreactivity in patients with temporal lobe epilepsy.

OBJECTIVE: Sodium-coupled transporters remove extracellular neurotransmitters and alterations in their function could enhance or suppress synaptic transmission and seizures. This study determined hippocampal gamma-aminobutyric acid (GABA) and glutamate transporter immunoreactivity (IR) in temporal lobe epilepsy (TLE) patients. METHODS: Hippocampal sclerosis (HS) patients (n = 25) and non-HS cases (mass lesion and cryptogenic; n = 20) were compared with nonseizure autopsies (n = 8). Hippocampal sections were studied for neuron densities along with IR for glutamate decarboxylase (GAD; presynaptic GABA terminals), GABA transporter-1 (GAT-1; presynaptic GABA transporter), GAT-3 (astrocytic GABA transporter), excitatory amino acid transporter 3 (EAAT3; postsynaptic glutamate transporter), and EAAT2-1 (glial glutamate transporters). RESULTS: Compared with autopsies, non-HS cases with similar neuron counts showed: 1) increased GAD IR gray values (GV) in the fascia dentata outer molecular layer (OML), hilus, and stratum radiatum; 2) increased GAT-1 OML GVs; 3) increased astrocytic GAT-3 GVs in the hilus and Ammon's horn; and 4) no IR differences for EAAT3-1. HS patients with decreased neuron densities demonstrated: 1) increased OML and inner molecular layer GAD puncta; 2) decreased GAT-1 puncta relative to GAD in the stratum granulosum and pyramidale; 3) increased GAT-1 OML GVs; 4) decreased GAT-3 GVs; 5) increased EAAT3 IR on remaining granule cells and pyramids; 6) decreased glial EAAT2 GVs in the hilus and CA1 stratum radiatum associated with neuron loss; and 7) increased glial EAAT1 GVs in CA2/3 stratum radiatum. CONCLUSIONS: Hippocampal GABA and glutamate transporter IR differ in TLE patients compared with autopsies. These data support the hypothesis that excitatory and inhibitory neurotransmission and seizure susceptibility could be altered by neuronal and glial transporters in TLE patients.

ATP-Binding Cassette Transporters↗
PubMed1998

An essential role for ectodomain shedding in mammalian development.

The ectodomains of numerous proteins are released from cells by proteolysis to yield soluble intercellular regulators. The responsible protease, tumor necrosis factor-alpha converting enzyme (TACE), has been identified only in the case when tumor necrosis factor-alpha (TNFalpha) is released. Analyses of cells lacking this metalloproteinase-disintegrin revealed an expanded role for TACE in the processing of other cell surface proteins, including a TNF receptor, the L-selectin adhesion molecule, and transforming growth factor-alpha (TGFalpha). The phenotype of mice lacking TACE suggests an essential role for soluble TGFalpha in normal development and emphasizes the importance of protein ectodomain shedding in vivo.

ADAM Proteins↗
PubMed1998

Characterization of the genes for mouse LERK-3/Ephrin-A3 (Epl3), mouse LERK-4/Ephrin-A4 (Epl4), and human LERK-6/Ephrin-A2 (EPLG6): conservation of intron/exon structure.

We have isolated the genes for the eph receptor family ligands mouse LERK-3/Ephrin-A3 (Epl3), mouse LERK-4/Ephrin-A4 (Epl4), and human LERK-6/Ephrin-A2 (EPLG6). These genes show a high level of conservation in their intron/exon structures encoding the receptor-binding region. In addition, the nucleotide sequences of the genes reveal the predicted cDNA sequence of mouse LERK-3/Ephrin-A3, mouse LERK-4/Ephrin-A4, and human LERK-6/Ephrin-A2.

Amino Acid Sequence↗
PubMed1998

Reversal of ischemic-induced chronic memory dysfunction in aging rats with a free radical scavenger-glycolytic intermediate combination.

Rats were subjected to bilateral carotid artery occlusion (2-VO) or sham occlusion (No-VO) and tested 12 weeks for visuo-spatial memory (VSM) function. After 14 weeks, 2-VO rats (N = 4) showing severe visuo-spatial memory impairment were given dimethyl sulfoxide (DMSO)-fructose 1,6-diphosphate (FDP) i.p. for seven days and retested on the water maze. After DMSO-FDP, a 54% improvement in their VSM was seen which nearly reached control No-VO values. Untreated 2-VO (N = 4) and No-VO (N = 8) rats showed no significant changes in their VSM. DMSO-FDP treatment was discontinued and rats were retested on the water maze but improvement was lost and VSM function regressed to pretreatment levels. Immunohistochemical examination showed minimal neuronal damage in all 2-VO rats and slight loss of microtubule associated protein-2. Glial fibrillary acidic protein immunostaining increase was observed only in untreated 2-VO rats. The results indicate that a DMSO-FDP combination improves VSM secondary to chronic brain hypoperfusion.

Aging↗
PubMed1998

Thoracoabdominal asynchrony in small children with lung disease--methodological aspects and the relationship to lung mechanics.

Thoracoabdominal asynchrony (TAA) has been regarded as a clinical sign of lung disease. A measure of TAA is the phase angle (phi) between ribcage (RC) and abdominal (ABD) respiratory motion. The aim of this study was to assess the effect of the points chosen for phi calculation. The influence of correct respiratory timing was assessed by calculating TAA indices using a pneumotachometer (PTM) as timing reference and using the calibrated respiratory inductive plethysmograph (RIP) signal for respiratory timing. The relationship between TAA and lung mechanics was studied in 15 young children 9 months to 2.5 years of age with a wide span of restrictive and/or obstructive lung disease. phi as calculated from mid-RC points was poorly related to phi as calculated from the top RC and ABD positions, indicating non-sinusoidal respiratory motions. The estimation of the TAA indices depended on correct respiratory timing, which in the case of severe asynchrony cannot be inferred from the RIP signals alone. An external source for respiratory timing, such as the airway flow measured by a PTM, is needed. The degree of asynchronous chest wall movement was only a weak indicator of pathological lung mechanics. We conclude that the usefulness of TAA indices as indicators of impaired lung mechanics is limited by the sensitivity to the points used for their calculation (phi) and the need of an external source for respiratory timing. It was therefore not surprising that a rather weak relationship was seen between TAA indices and lung mechanics.

Abdomen↗
PubMed1998

The family of Na+/Cl- neurotransmitter transporters.

The termination of neurotransmission is achieved by rapid uptake of the released neurotransmitter by specific high-affinity neurotransmitter transporters. Most of these transporters are encoded by a family of genes (Na+/Cl- transporters) having a similar membrane topography of 12 transmembrane helices. An evolutionary tree revealed five distinct subfamilies: gamma-aminobutyric acid transporters, monoamine transporters, amino acid transporters, "orphan" transporters, and the recently discovered bacterial transporters. The bacterial transporters that belong to this family may help to develop heterologous expression systems with the aim of solving the three-dimensional structure of these membrane proteins. Some of the neurotransmitter transporters have been implicated as important sites for drug action. Monoamine transporters, for example, are targeted by major classes of antidepressants, psychostimulants, and antihypertensive drugs. Localization of individual transporters in specific cells and brain areas is pertinent to understanding their contribution to neurotransmission and their potential as targets for drugs. The most important questions in the field include resolving the mechanism of neurotransmitter transport, the structure of the transporters, and the interaction of each transporter in complex neurological activities.

Amino Acid Transport Systems↗