Biomedical subjects

G Chen

Publications and source records attributed to G Chen.

At least 271 records · Page 15Linked to original sources

PubMed2000

Lesion or muscimol in the rostral ventral medulla reduces ventilatory output and the CO(2) response in decerebrate piglets.

Developmental abnormalities have been described in the arcuate nucleus of sudden infant death syndrome (SIDS) victims. The arcuate nucleus has putative homologues in chemosensitive areas of the ventral medulla in animals. We refer to some of these areas collectively as the rostral ventral medulla (RVM). In the RVM of decerebrate piglets 2-15 days of age, we studied the effects of electrolytic lesions (n=7) or microdialysis of muscimol (n=15), a GABAA receptor agonist, on ventilatory output and the response to hypercapnia. Lesions caused a 66.7+/-17.3% reduction in eupneic phrenic minute activity (MA) and abolished the response to hypercapnia. Muscimol dialysis caused a 32.4+/-10.4% reduction in MA with a significant downward displacement of the response to hypercapnia with no significant effect on the slope. We conclude that the piglet RVM contains neurons of vital importance in the maintenance of normal breathing and the response to systemic CO(2). We hypothesize that dysfunction of homologous regions in the human infant could lead to impaired ability to respond to hypercapnia and could potentially be involved in the pathogenesis of SIDS.

Animals↗

PubMed2000

Role of T lymphocytes in renal disease in HIV-transgenic mice.

The pathogenesis of human immunodeficiency virus (HIV)-associated focal segmental glomerulosclerosis (FSGS) has remained obscure. It has been proposed that renal parenchymal cells may be infected with HIV-1. If such infection occurs, the target cells would be expected to express viral proteins and thus could be targets for cytotoxic T lymphocytes. We previously described mice transgenic for a gag-pol-deleted HIV-1 genome that developed FSGS. In the present study, we tested the requirement for functional T cells in the evolution of renal disease in this model. We bred the HIV-transgenic mice (T26) with athymic nude mice to produce athymic T26 mice. We confirmed by flow cytometry of peripheral blood, thymus, lymph node, and spleen that the athymic T26 mice lacked mature T cells. The athymic T26 mice developed renal disease characterized by FSGS, tubular atrophy and dilatation, and interstitial infiltrate that was qualitatively identical to that seen in the parental T26 mice. Quantitative assessment of the athymic T26 mouse kidneys showed that glomerulosclerosis, tubular injury, and interstitial infiltrate were less severe compared with the parental T26 mouse kidneys. Although T26 mouse kidneys had a mixed cellular infiltrate composed of CD4 cells, CD8 cells, and macrophages, interstitial infiltrates within the athymic T26 mouse kidneys included macrophages but lacked both CD4 and CD8 cells. The renal expression of the HIV transgene was 1. 7-fold greater in T26 mice compared with athymic T26 mice. We conclude that mature T cells are not absolutely required for the development of HIV-associated nephropathy in transgenic mice but that, in their absence, renal disease is significantly milder. These data suggest that T-cell-mediated cytotoxicity directed against renal cells expressing virally encoded proteins is not an essential feature of renal pathogenesis in this model.

Animals↗

PubMed2000

Role of climbing fibers in determining the spatial patterns of activation in the cerebellar cortex to peripheral stimulation: an optical imaging study.

The spatial patterns of activation in the rat cerebellar cortex evoked by ipsilateral face stimulation were mapped using optical imaging based on the pH sensitive dye, Neutral Red. The aims of the study were to characterize the optical responses evoked by peripheral stimulation and test the hypothesis that the resultant parasagittal banding is due to climbing fiber activation. In the anesthetized rat Crus I and II of the cerebellar cortex were stained with Neutral Red. Epi-fluorescent changes produced by a train of stimuli (5-10s and 4-20 Hz) to the ipsilateral face were monitored in time using a fast, high resolution charge-coupled device camera. The patterns of activation were quantified using a two-dimensional fast Fourier transform analysis that removed signals with high spatial frequencies and minimized the contribution of horizontal structural elements (i.e. blood vessels). The dominant spatial pattern of activation evoked by face stimulation was that of parasagittal bands. The bands were highly frequency-dependent and were elicited most strongly by stimulus frequencies in the range of 6-8 Hz. There was a large fall-off in the response for frequencies above and below. The optical signal evoked by face stimulation built up over a period of 10s and then gradually decayed. Within a folium the individual parasagittal bands exhibited some frequency and temporal specificity. Stimulation of the contralateral inferior olive also resulted in the activation of parasagittal bands with characteristics similar to the bands evoked by face stimulation, including a preferred stimulus frequency which peaked at 10 Hz. Injection of lidocaine into the contralateral inferior olive blocked the parasagittal bands evoked by ipsilateral face stimulation, while control injections of saline had no effect. The results confirm that a parasagittal banding pattern is a dominant feature of the functional architecture of the cerebellar cortex. The parasagittal banding pattern observed with Neutral Red is due primarily to the activation of climbing fiber afferents. The frequency tuning of the responses, with the preference for peripheral stimuli of 6-8 Hz, is in agreement with previous findings that the inferior olive is inherently rhythmic. These observations support the hypothesis that inferior olivary neurons are dynamically coupled into groups that activate parasagittal bands of Purkinje cells in the cerebellar cortex. The frequency tuning also supports the hypothesis that the climbing fiber system is involved with timing. Activation of this afferent system may require stimuli with appropriate frequency content and stimuli synchronized to the rhythmicity of the inferior olive.

Action Potentials↗

PubMed2000

On impulsive autoassociative neural networks.

Many systems existing in physics, chemistry, biology, engineering, and information science can be characterized by impulsive dynamics caused by abrupt jumps at certain instants during the process. These complex dynamical behaviors can be modeled by impulsive differential systems or impulsive neural networks. This paper formulates and studies a new model of impulsive autoassociative neural networks. Several fundamental issues, such as global exponential stability and existence and uniqueness of equilibria of such neural networks, are established.

Models, Neurological↗

PubMed2000

Extraction and characterization of adenovirus proteins from sodium dodecylsulfate polyacrylamide gel electrophoresis by matrix-assisted laser desorption/ionization mass spectrometry.

A new methodology for the extraction and characterization of proteins from Coomassie-stained sodium dodecylsulfate polyacrylamide gel electrophoresis using matrix-assisted laser desorption/ionization mass spectrometry (MALDI-MS) has been described. The utility of this methodology was demonstrated in the characterization of adenovirus proteins. The key steps in the extraction and destaining process involve washing the excised band with a combination of solvents that include 10% acetic acid, acetonitrile, methanol, and formic acid:water:isopropanol mixture. By using this procedure, we determined adenovirus proteins with molecular weights ranging from 10,000 to 110,000 Da by MALDI-MS, obtaining a detection limit of approximately 6 pmol. Parallel experiments were successfully carried out to analyze adenovirus proteins from Cu-stained gels. It was observed that increase in laser intensity resulted in significant improvements in the quality of MALDI mass spectra for the analysis of inefficiently destained proteins from Cu-stained gels.

Adenoviridae↗

PubMed2000

Gene repression by coactivator repulsion.

We show that the IRF-2 oncoprotein represses virus-induced IFN-beta gene transcription via a novel mechanism. Virus infection induces recruitment of IRF-2 to some of the endogenous IFN-beta enhancers as part of the enhanceosome. Enhanceosomes bearing IRF-2 cannot activate transcription, due to the presence of a domain in IRF-2 that prevents enhanceosome-dependent recruitment of the CBP-Pol II holoenzyme complex. As a consequence, IRF-2 incorporation into enhanceosomes restricts the number of IFN-beta promoters directing transcription. Remarkably, deletion of the IRF-2 gene increases IFN-beta expression by expanding the number of cells capable of inducing IFN-beta gene transcription in response to virus infection.

Animals↗

PubMed2000

Lithium regulates PKC-mediated intracellular cross-talk and gene expression in the CNS in vivo.

It has become increasingly appreciated that the long-term treatment of complex neuropsychiatric disorders like bipolar disorder (BD) involves the strategic regulation of signaling pathways and gene expression in critical neuronal circuits. Accumulating evidence from our laboratories and others has identified the family of protein kinase C (PKC) isozymes as a shared target in the brain for the long-term action of both lithium and valproate (VPA) in the treatment of BD. In rats chronically treated with lithium at therapeutic levels, there is a reduction in the levels of frontal cortical and hippocampal membrane-associated PKC alpha and PKC epsilon. Using in vivO microdialysis, we have investigated the effects of chronic lithium on the intracellular cross-talk between PKC and the cyclic AMP (cAMP) generating system in vivo. We have found that activation of PKC produces an increase in dialysate cAMP levels in both prefrontal cortex and hippocampus, effects which are attenuated by chronic lithium administration. Lithium also regulates the activity of another major signaling pathway the c-Jun N-terminal kinase pathway--in a PKC-dependent manner. Both Li and VPA, at therapeutically relevant concentrations, increase the DNA binding of activator protein 1 (AP-1) family of transcription factors in cultured cells in vitro, and in rat brain ex vivo. Furthermore, both agents increase the expression of an AP-1 driven reporter gene, as well as the expression of several endogenous genes known to be regulated by AP-1. Together, these results suggest that the PKC signaling pathway and PKC-mediated gene expression may be important mediators of lithium's long-term therapeutic effects in a disorder as complex as BD.

Adaptor Protein Complex alpha Subunits↗

PubMed2000

Examination of relationships among trait-like individual differences, state-like individual differences, and learning performance.

Several authors (e.g., J.T. Austin & H.J. Klein, 1996; R. Kanfer, 1990b, 1992) have urged researchers to examine comprehensive models of distal individual differences as predictors of proximal motivational processes and performance. Two field studies in an academic setting tested a model of relationships among trait-like individual differences (cognitive ability, general self-efficacy, and goal orientation), state-like individual differences (state anxiety, task-specific self-efficacy, and goals), and learning performance. Most hypothesized relationships among these constructs received support when tested on 2 samples, when examining different performance episodes, and when using different goal orientation and state-anxiety measures. In general, state-like individual differences were found to mediate the relationships between trait-like individual differences and learning performance. Implications of these results are discussed and suggestions for future research are provided.

Adolescent↗

PubMed2000

Induction of potent antitumor response by vaccination with tumor lysate-pulsed macrophages engineered to secrete macrophage colony-stimulating factor and interferon-gamma.

Adoptive transfer of activated macrophages, being both effector cells and antigen-presenting cells, represents a promising approach to immunotherapy of cancer. In order to get activated macrophages with increased antitumor potential, in the present study, murine peritoneal macrophages were transduced with human macrophage colony-stimulating factor (M-CSF) and murine interferon-gamma (IFNgamma) by recombinant adenovirus infection. The results demonstrate that M-CSF and IFNgamma gene-modified macrophages exhibited higher expression of MHC-II, B7.1 and ICAM-1, increased antigen-presenting activity and cytotoxicity. It was also shown that they secreted more tumor necrosis factor, interleukin-1 and nitric oxide. In vivo experiments showed that in previously initiated murine pulmonary metastatic melanoma, tumor lysate-pulsed, M-CSF and IFNgamma gene-modified macrophages elicited more potent antitumor effects than tumor lysate pulsed M-CSF or IFNgamma gene-modified macrophages. Cytotoxic T lymphocyte (CTL) activity, IFNgamma and tumor-necrosis factor production of the splenocytes increased significantly in mice after intravenous injection of the gene-modified macrophages. M-CSF and IFNgamma gene-modified macrophages may act as activated effector and antigen-presenting cells, thus eliciting a more potent antitumor response.

Animals↗

PubMed2000

Interleukin-18 gene transfer increases antitumor effects of suicide gene therapy through efficient induction of antitumor immunity.

To increase the antitumor effects of cytosine deaminase (AdCD) gene therapy and induce more potent antitumor immunity, Th1 cytokine interleukin-18 encoded adenovirus (AdIL18) was combined with adenovirus encoding CD (AdCD) for the therapy of established murine B16 melanoma. Combination therapy of the tumor-bearing mice with AdIL 18 and AdCD/5FC inhibited the growth of the subcutaneous B16 tumors more significantly, compared with AdIL 18 or AdCD/5FC alone. In vivo depletion analysis with anti-CD4, anti-CD8 or anti-NK 1.1 McAb illustrated that both CD8+ T cells and CD4+ T cells played key roles in the augmented antitumor response of the combined therapy. Peptide/MHC tetramer represents a powerful and general tool for rapid, highly sensitive, and direct analysis of antigen-specific T cells. In this study, we prepared H-2Kb/TRP-2180-188 tetramer, which was demonstrated to bind H-2Kb-restricted, B16 melanoma-specific CD8+ T cells. B16 specific H-2Kb/TRP2180-188 tetramer was used to stain the tumor-specific CD8+ T cells and the results showed that CD8+ tetramer+ T cells were about 3-5% of the splenic CD8+ T cells derived from tumor-bearing mice after combined therapy. The CTL cytotoxicity was markedly induced in mice after combined therapy, suggesting efficient induction of tumor-specific CD8+ T cells after combined gene therapy with AdCD/5FC/AdIL18. IL-18 gene transfer could significantly augment the cytotoxicity of NK cells and macrophages, and increase the production of interleukin-2 and interferon-gamma, as compared with treatments with AdCD/5FC, AdlacZ/5FC or PBS. These data suggested that in vivo IL-18 gene transfer could augment the antitumor effects of CD suicide gene therapy through efficient induction of antitumor immunity.

Adenoviridae↗

PubMed2000

Neuroplasticity and cellular resilience in mood disorders.

Although mood disorders have traditionally been regarded as good prognosis diseases, a growing body of data suggests that the long-term outcome for many patients is often much less favorable than previously thought. Recent morphometric studies have been investigating potential structural brain changes in mood disorders, and there is now evidence from a variety of sources demonstrating significant reductions in regional CNS volume, as well as regional reductions in the numbers and/or sizes of glia and neurons. Furthermore, results from recent clinical and preclinical studies investigating the molecular and cellular targets of mood stabilizers and antidepressants suggest that a reconceptualization about the pathophysiology and optimal long-term treatment of recurrent mood disorders may be warranted. It is proposed that impairments of neuroplasticity and cellular resilience may underlie the pathophysiology of mood disorders, and further that optimal long-term treatment for these severe illnesses may only be achieved by the early and aggressive use of agents with neurotrophic/neuroprotective effects. It is noteworthy that lithium, valproate and antidepressants indirectly regulate a number of factors involved in cell survival pathways including CREB, BDNF, bcl-2 and MAP kinases, and may thus bring about some of their delayed long-term beneficial effects via underappreciated neurotrophic effects. The development of novel treatments which more directly target molecules involved in critical CNS cell survival and cell death pathways have the potential to enhance neuroplasticity and cellular resilience, and thereby modulate the long-term course and trajectory of these devastating illnesses.

Animals↗

PubMed2000

Enhancement of hippocampal neurogenesis by lithium.

Increasing evidence suggests that mood disorders are associated with a reduction in regional CNS volume and neuronal and glial cell atrophy or loss. Lithium, a mainstay in the treatment of mood disorders, has recently been demonstrated to robustly increase the levels of the cytoprotective B-cell lymphoma protein-2 (bcl-2) in areas of rodent brain and in cultured cells. In view of bcl-2's antiapoptotic and neurotrophic effects, the present study was undertaken to determine if lithium affects neurogenesis in the adult rodent hippocampus. Mice were chronically treated with lithium, and 5-bromo-2-deoxyuridine (BrdU) labeling of dividing cells was conducted over 12 days. Immunohistochemical analysis was undertaken 1 day after the last injection, and three-dimensional stereological cell counting revealed that lithium produced a significant 25% increase in the BrdU-labeled cells in the dentate gyrus. Double-labeling immunofluorescence studies were undertaken to co-localize BrdU-positive cells with neuron-specific nuclear protein and showed that approximately 65% of the cells were double-labeled. These results add to the growing body of evidence suggesting that mood stabilizers and antidepressants exert neurotrophic effects and may therefore be of use in the long-term treatment of other neuropsychiatric disorders.

Animals↗

PubMed2000

Overexpression of the oncofetal Fn variant containing the EDA splice-in segment in the dermal-epidermal junction of psoriatic uninvolved skin.

The extracellular matrix protein, Fn, has critical functions in cell attachment, migration, differentiation, and proliferation. We have previously shown that fibronectin (Fn) is abnormally expressed and potentiates entry into the cell cycle of basal keratinocytes in uninvolved psoriatic skin, in combination with T cell lymphokines. It is not known what type of Fn is present in psoriatic skin, however, and how this Fn may regulate signaling. Embryonic forms of cellular Fn containing extra domains, designated EDA and EDB, are generated by alternative splicing and are seen in proliferating, developing tissue and in wound healing. Because the EDA segment enhances the integrin binding sequence Arg, Gly, Asp (RGD), which, when present, has been shown to be critical in integrin-extracellular matrix signaling, we were particularly interested in determining whether or not EDA-containing Fn (EDA+Fn) represented the aberrantly expressed Fn in psoriasis. Increased EDA+ Fn protein was demonstrated by immunostaining at the dermal-epidermal junction in clinically uninvolved skin from six of six patients with psoriasis, but not in skin from control subjects. Using reverse transcription polymerase chain reaction an increased ratio of EDA+ Fn versus EDA- Fn mRNA was present in epidermal samples from psoriatic but not control individuals. Interestingly, the EDA+Fn in the psoriatic epidermis had the IIICS region spliced out (EDA+, FDB-, IIICS-, III9+), which was shared with normal epidermis (EDA-, EDB-, IIICS-, III9+). These results suggest a selective predominance of the EDA+ Fn isoform at the dermal-epidermal junction of psoriatic skin. The consistent aberrant localization of EDA+ Fn at the dermal-epidermal junction in uninvolved skin of psoriatics may confer the hyperresponsiveness of psoriatic uninvolved basal keratinocytes for rapid cellular proliferation in response to T cell signals. Key words: immunohistochemistry/integrin/keratinocyte/RT-PCR.

Dermatitis, Atopic↗

PubMed2000

Regulation of iNOS mRNA levels in endothelial cells by glutathione, a double-edged sword.

Both inducible nitric oxide synthase (iNOS) and glutathione are important mediators in various physiological and pathological conditions in humans. In human endothelial cells the intracellular glutathione levels were modulated by N-acetyl-L-cysteine (NAC), a precursor of glutathione and 1,3-bis(chloroethyl)-1-nitrosourea (BCNU), an inhibitor of glutathione reductase. BCNU significantly decreased reduced glutathione (GSH) but increased oxidized glutathione (GSSG) whereas NAC markedly elevated GSH with a relatively small increase in GSSG. Appropriate concentrations of GSH and GSSG increase the expression of iNOS gene. However, either GSH or GSSG at a too high concentration inhibits its expression, indicating that iNOS gene is fine tuned by the metabolites of glutathione cycle. The changes of iNOS mRNA steady state levels by the glutathione metabolites were associated with a similar alteration in its gene transcription and NF-kappaB activity. BCNU at high concentrations also shortens the half-life of iNOS mRNA, suggesting a role of GSSG in the stability of the iNOS gene. Thus, the change of glutathione levels in vitro can regulate iNOS mRNA steady state levels in a bi-phasic manner in human endothelial cells.

Acetylcysteine↗

PubMed2000

Two mixed-metal carboxylate-base adducts

The crystal structures of hexa-&mgr;-propionato-1:2kappa(6)O:O';1:3kappa(6)O:O'-diquinoline-2ka ppaN,3kappaN-calcium(II)dizinc(II), [CaZn(2)(C(3)H(5)O(2))(6)(C(9)H(7)N)(2)], and hexa-&mgr;-pivalato-1:2kappa(6)O:O';1:3kappa(6)O:O'-diquinoline-2kapp aN,3kappaN-calcium(II)dicobalt(II), [CaCo(2)(C(5)H(9)O(2))(6)(C(9)H(7)N)(2)], are described. Both contain a linear array of one Ca(II) ion and two M(II) (M = Zn, Co) ions connected by two sets of three carboxylate ligands in syn-syn bridging modes. The distorted tetrahedral geometry around the M(II) ion is completed by a quinoline N atom. The central Ca(II) ion occupies a crystallographic inversion centre and is octahedrally coordinated by six carboxyl O atoms in each structure. The Zn(II). Ca(II) and Co(II).Ca(II) distances are 3.8504 (9) and 3.7929 (5) A, respectively.

Journal Article↗

PubMed2000

Crystallization and preliminary analysis of neurolysin.

Neuropeptidases inactivate or modify the activity of peptide neurotransmitters and neurohormones. The neuropeptidase neurolysin acts only on short peptides and accepts a variety of cleavage-site sequences. Structures of the enzyme and enzyme-substrate complexes will help to determine the mechanisms of substrate selectivity used by this enzyme. Crystals of recombinant neurolysin have been grown in the orthorhombic space group P2(1)2(1)2, with unit-cell parameters a = 157.8, b = 88.0, c = 58.4 A. Data have been collected to 2.3 A at 110 K with observed diffraction to 1.8 A. Circular dichroism measurements suggest that the enzyme is primarily alpha-helical, with little beta-strand secondary structure. Sequence-based secondary-structure prediction supports this conclusion.

Animals↗

PubMed2000

The use of stimulus-biased assay systems to detect agonist-specific receptor active states: implications for the trafficking of receptor stimulus by agonists.

The quantitative comparison of the relative potency of agonists is a standard method of receptor and agonist classification. If agonist potency ratios do not correspond in two given tissues, this is used as presumptive data to conclude that the receptors in those two tissues are different. This article presents data to show that a single receptor can demonstrate varying agonist potency ratios in different host cells. These data are described in terms of the production of more than one agonist-selective receptor active state and the interaction of these different active states with multiple G proteins in the membrane to produce cellular response. Stable host human embryonic kidney 293 cells with enhanced quantities of the respective Galpha-protein were created. Wild-type and Galpha-subunit enriched cells were then transiently transfected with human calcitonin receptor type 2 (hCTR2). Binding did not detect differences in the G protein-enriched cells versus wild-type cells. In contrast, functional studies did show differences between the host cell lines and Galpha-subunit enriched cell lines. The relative potency of eight calcitonin agonists was measured in studies of calcium fluorescence in transfected cells containing human calcitonin receptor type 2 by comparing pEC(50) (-log molar concentration producing half-maximal response) values. In Galphas-enriched cells, the relative order of potency of the agonists changed. The host-cell dependent differences in potency ratios ranged from 2-fold to more than 46-fold. This finding is not consistent with the idea that all of the agonists produce response in the same manner (i.e., through a common active state of the receptor). These data are consistent with the idea that these different agonists produce arrays of active states that differentially use G proteins. This idea is discussed in terms of the design of stimulus-bias assay systems to detect agonist-selective receptor active states with resulting potential for increased selectivity of agonists.

Binding, Competitive↗

PubMed2000

Two patches of amino acids on the E2 DNA binding domain define the surface for interaction with E1.

The E1 and E2 proteins from bovine papillomavirus bind cooperatively to the viral origin of DNA replication (ori), forming a complex which is essential for initiation of DNA replication. Cooperative binding has two components, in which (i) the DNA binding domains (DBDs) of the two proteins interact with each other and (ii) the E2 transactivation domain interacts with the helicase domain of E1. By generating specific point mutations in the DBD of E2, we have defined two patches of amino acids that are involved in the interaction with the E1 DBD. These same mutations, when introduced into the viral genome, result in severely reduced replication of the viral genome, as well as failure to transform mouse cells in tissue culture. Thus, the interaction between the E1 and E2 DBDs is important for the establishment of the viral genome as an episome and most likely contributes to the formation of a preinitiation complex on the viral ori.

Animals↗