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Biomedical subjects

G Kendall

Publications and source records attributed to G Kendall.

At least 19 recordsLinked to original sources
PubMed2004

Acute fetal hypoxia: the modulating effect of infection.

The fetal brain is protected from the effects of acute hypoxia by a range of haemodynamic and metabolic compensations. Hypoxia alone is therefore an unusual cause of perinatal brain injury in either preterm or term infants. More recently, materno-fetal infection has been implicated as a causative factor in cases of cerebral palsy associated with preterm and term birth. This paper explores the concept that exposure to infection, and in particular pro-inflammatory cytokines, may reduce the threshold at which hypoxia becomes neurotoxic, so making the brain much more vulnerable to even mild hypoxic insults. The hypothesis is supported by an increasing body of evidence from animal studies that also demonstrate the importance of duration between exposure to infection and subsequent hypoxia. There are a number of clinical and research implications that centre around the role of antibiotics, mode and timing of delivery, maternal cooling during labour and the role of immune-modulating drugs.

Anti-Bacterial Agents↗
PubMed2003

Association between antenatal cytokine production and the development of atopy and asthma at age 6 years.

BACKGROUND: Various lines of evidence suggest that antenatal factors are important in determining susceptibility to atopy and asthma. One possible mechanism is cytokines, production of which in the placenta is high throughout gestation and which protect placental integrity via control of local immunological homoeostasis. We investigated antenatal cytokine concentrations in a prospective birth cohort, intensively monitored for atopy and asthma outcomes at age 6 years. METHODS: Cryopreserved cord-blood serum samples from 407 children were assayed for interleukins 4, 5, 6, 10, 12, and 13, interferon gamma, and tumour necrosis factor alpha (TNFalpha). Associations between family, antenatal, and perinatal factors, cord-blood cytokine concentrations, and atopy or asthma outcomes were analysed by logistic regression. Causal effects of cytokines on outcomes were estimated by propensity scores based on family, antenatal, and perinatal factors. FINDINGS: Detectable cord-blood concentrations of interleukin 4 and interferon gamma were each associated with lower risk of physician-diagnosed asthma (adjusted odds ratios 0.60 [95% CI 0.37-0.99] and 0.60 [0.37-0.97] respectively), current asthma (0.59 [0.33-1.00] and 0.39 [0.22-0.71]), and current wheeze (0.55 [0.32-0.93] and 0.52 [0.31-0.90]) and atopy (sensitisation to some inhalant allergens) outcomes at 6 years. High concentrations of TNFalpha were associated with lower risk of atopy but not with asthma risk. These associations were broadly unaltered by propensity-score adjustment. Maternal smoking was associated with higher risk of both wheeze at 6 years and lower concentrations of interleukin 4 and interferon gamma in cord blood. INTERPRETATION: The mechanism underlying attenuated T-helper-1/T-helper-2 cytokine production in high-risk children also apparently operates in control of cytokine production in the fetoplacental unit. The finding that this mechanism is dysregulated by maternal smoking suggests it is a target for antenatal environmental factors relevant to asthma aetiology.

Asthma↗
PubMed2001

Specific electrochemical nitration of horse heart myoglobin.

Earlier findings on electronitration of hen egg-white lysozyme demonstrated a product which was mononitrated at Tyr23, by ion-exchange chromatography, absorbance at 430 nm, dithionite reduction, and Edman sequencing of a nitrated proteolytic peptide. However, the whole protein was not sequenced; therefore, although the enzyme remained active upon nitration, reaction at other residues could not be completely eliminated. This study has now been extended to the redox protein myoglobin. We demonstrate the novel electronitration (electrooxidation in the presence of nitrite) of a specific tyrosine residue in horse heart myoglobin and also in apomyoglobin. Production of the yellow chromophore, 3-nitrotyrosine (3-NT), was apparent in apomyoglobin from A430 but was masked in holomyoglobin by the Soret band. In both cases, the presence of 3-NT in the electronitrated samples was further indicated by the binding of antibody to 3-NT in Western blots. High-resolution electrospray ionization (ESI) Fourier transform ion cyclotron resonance (FTICR) mass spectrometry revealed a reaction product at [M + 45] (consistent with substitution of NO2 for H), indicating that the nitration reaction is the only reaction occurring which gives rise to a change in mass in the electrooxidation. Fragmentation mass spectrometry identified the nitration site as Tyr103, with no nitration at Tyr146. The procedure may be useful in preparing model nitrated proteins for the study of disease mechanisms.

Amino Acid Sequence↗
PubMed2001

Evolving collective behavior in an artificial ecology.

Collective behavior refers to coordinated group motion, common to many animals. The dynamics of a group can be seen as a distributed model, each "animal" applying the same rule set. This study investigates the use of evolved sensory controllers to produce schooling behavior. A set of artificial creatures "live" in an artificial world with hazards and food. Each creature has a simple artificial neural network brain that controls movement in different situations. A chromosome encodes the network structure and weights, which may be combined using artificial evolution with another chromosome, if a creature should choose to mate. Prey and predators coevolve without an explicit fitness function for schooling to produce sophisticated, nondeterministic, behavior. The work highlights the role of species' physiology in understanding behavior and the role of the environment in encouraging the development of sensory systems.

Animals↗
PubMed1999

Regulation of T-helper cell responses to inhalant allergen during early childhood.

BACKGROUND: Recent evidence suggests that preschool children manifest patterns of allergen-specific skin prick test (SPT) reactivity and in vitro T-cell cytokine production which are similar to that of either atopic or nonatopic adults. However, published studies on this age group involve small sample sizes and a restricted number of cytokines, usually in response to polyclonal stimuli. OBJECTIVE: To elucidate the relationship between in vivo and in vitro immune responses to a major inhalant allergen house dust mite (HDM) in preschoolers. METHODS: Peripheral blood mononuclear cells (PBMCs) from matched groups of HDM-SPT+ and SPT- 6-year-olds (n = 30 and 29, respectively) tested for PBMC responses to HDM, and cytokine production measured at both the protein and mRNA levels. Immunoglobulin (Ig) E and IgG subclass antibody titres were determined in serum. Interrelationships between in vitro and in vivo HDM responses were examined via multivariate analyses. RESULTS: SPT reactivity to HDM was associated with in vitro production by putative T cells of interleukin (IL) -4, IL-5, IL-9, IL-10, IL-13 and low level IFNgamma, and with production in vivo of IgE and (all) IgG subclass antibodies; HDM responses in the SPT- group were restricted mainly to IL-10 and IFNgamma and very low levels of IL-4; IL-6 production from non-T-cell sources was common. The cytokine most associated with positive SPT responses was IL-9; SPT weal diameter correlated positively with IL-4, IL-5 and IL-13 and negatively with IL-10. CONCLUSION: Detailed analysis of cytokine responses in this very young age group have the potential to uncover subtle relationships between in vivo and in vitro allergen reactivity which may be less clear in adults, in whom T-cell response patterns are modified via chronic stimulation. The present findings which suggest potentially important roles for IL-9 and IL-10 in the early phase of allergic disease, may be one such example.

Administration, Inhalation↗
PubMed1998

Heat shock protein 27: developmental regulation and expression after peripheral nerve injury.

The heat shock protein (HSP) 27 is constitutively expressed at low levels in medium-sized lumbar dorsal root ganglion (DRG) cells in adult rats. Transection of the sciatic nerve results in a ninefold upregulation of HSP27 mRNA and protein in axotomized neurons in the ipsilateral DRG at 48 hr, without equivalent changes in the mRNAs encoding HSP56, HSP60, HSP70, and HSP90. Dorsal rhizotomy, injuring the central axon of the DRG neuron, does not upregulate HSP27 mRNA levels. After peripheral axotomy, HSP27 mRNA and protein are present in small, medium, and large DRG neurons, and HSP27 protein is transported anterogradely, accumulating in the dorsal horn and dorsal columns of the spinal cord, where it persists for several months. Axotomized motor neurons also upregulate HSP27. Only a minority of cultured adult DRG neurons are HSP27-immunoreactive soon after dissociation, but all express HSP27 after 24 hr in culture with prominent label throughout the neuron, including the growth cone. HSP27 differs from most axonal injury-regulated and growth-associated genes, which are typically present at high levels in early development and downregulated on innervation of their targets, in that its mRNA is first detectable in the DRG late in development and only approaches adult levels by postnatal day 21. In non-neuronal cells, HSP27 has been shown to be involved both in actin filament dynamics and in protection against necrotic and apoptotic cell death. Therefore, its upregulation after adult peripheral nerve injury may both promote survival of the injured neurons and contribute to alterations in the cytoskeleton associated with axonal growth.

Animals↗
PubMed1996

Activation of the gene encoding decay accelerating factor following nerve growth factor treatment of sensory neurons is mediated by promoter sequences within 206 bases of the transcriptional start site.

Using two independent differential screening procedures designed to identify novel mRNAs induced by nerve growth factor (NGF) treatment of adult dorsal root ganglion (DRG) neurons, we have isolated cDNA clones derived from the gene encoding decay accelerating factor (DAF). Hybridization analysis and semi-quantitative polymerase chain reaction confirmed that the DAF mRNA was indeed induced in NGF-treated adult DRG neurons. Moreover, the DAF gene promoter is NGF inducible (approximately two- to threefold) when transfected into DRG neurons, and this effect is primarily dependent on sequences between -206 and -77 relative to the transcriptional start site. Hence, the DAF gene constitutes a novel NGF-inducible gene whose mRNA is elevated in response to NGF treatment of DRG neurons. The potential significance of this effect is discussed in terms of the role of NGF in modulating the transcriptional activity and function of adult DRG neurons.

Animals↗
PubMed1996

Nerve growth factor treatment of sensory neuron primary cultures causes elevated levels of the mRNA encoding the ATP synthase beta-subunit as detected by a novel PCR-based differential cloning method.

The mRNA encoding the rat ATP synthase beta-subunit was rapidly induced by nerve growth factor, within 60 min, in cultured adult rat dorsal root ganglion neurons. ATP synthase beta-subunit cDNA clones were isolated from a lambda library. The library was constructed using rat dorsal root ganglion mRNA that was differentially screened with cDNA-derived probes from untreated and nerve-growth-factor-treated primary cultures of adult rat dorsal root ganglion sensory neurons. Radiolabelled probes were made from submicrogram quantities of RNA, by a novel PCR-based technique, which allows small amounts of primary tissue to be used for library screening. The use of this technique in isolating novel differentially expressed mRNAs is discussed.

Animals↗
PubMed1996

Induction of the Oct-2 transcription factor in primary sensory neurons during inflammation is nerve growth factor-dependent.

The mRNA encoding the POU family transcription factor Oct-2 is induced in cultured adult sensory neurons following treatment with nerve growth factor (NGF) but not with a variety of other growth factors. We show here that the Oct-2 mRNA is also upregulated in vivo in sensory neurons innervating inflamed tissue following intraplantar injection of complete Freund's adjuvant. This rise is abolished by systemic administration of anti-NGF neutralizing antibodies indicating that it is an NGF-dependent effect. Hence a very specific aspect of the NGF response occurs in sensory neurons innervating inflamed tissue in vivo. In turn, the induction of Oct-2 may play a role in the other changes observed in such neurons both in gene expression and in their ability to respond to painful stimuli.

Animals↗
PubMed1996

Polymerase Chain Reaction for RNA Analysis

This paper presents two methods using the polymerase chain reaction to allow the efficient comparison of the relative amounts of particular mRNA species present in tissue or cell cultures. The methods have been used on cultures of primary dorsal root ganglion neurons that produce small yields of RNA. The mRNAs examined encode the transcription factors NGFIA and Oct-2, neither of which are present in great abundance in cellular material. Nevertheless, the polymerase chain reaction was able to amplify rare mRNAs to sufficient levels at which differences could be detected between untreated cultured neurons and cultures treated with nerve growth factor.

Journal Article↗
PubMed1996

Expression of two alternatively spliced forms of the 5' untranslated region of the GM-CSF receptor alpha chain mRNA.

The granulocyte-macrophage colony-stimulating factor receptor (GM-CSFR) is composed of at least two chains (alpha and beta). The alpha chain binds GM-CSF specifically with low affinity, and the binding is converted to high affinity when the alpha chain is associated with the beta chain. To date, there are at least six isoforms described for the GM-CSFR alpha, all involving alternative splicing at the 3' end, which alters the coding region and hence the protein produced. To detect variants at the 5' end of the GM-CSFR alpha mRNA, RNAse protection and reverse transcriptase polymerase chain reaction (RT-PCR) assays were performed using a probe spanning nucleotides 102-392 and pairs of primers covering exons 1-4. in addition to the expected full-length transcript, two mRNAs were detected, one containing a deletion of 24 nucleotides by alternative splicing at the 3' end of exon 2 (exon 2b-deleted isoform) and another in which exon 2 was completely deleted (exon 2-deleted isoform). Together, the isoforms were more highly expressed form). Together, the isoforms were more highly expressed than the full-length sequence (TF-1 cells: full-length 36 +/- 2.8% vs. exon 2-deleted isoforms 64 +/- 5.5%). These isoforms were detected in primary hematopoietic cells, blasts from patients with acute myeloid leukemia (AML), and malignant cell lines and the relative mRNA expression for the isoforms, was always similar to that of TF-1 cells. As sequences in the 5'untranslated region can be involved in the modulation of translational efficiency, translation of constructs constructs corresponding to these exon 2 deleted isoforms was assessed using an in vitro reticulocyte lysate system. Deletion of exon 2 resulted in significantly lower in vitro translation of the receptor protein relative to the full-length sequence (53, 56, and 76% in three separate batches of reticulocytes), while deletion of exon 2b resulted in higher translation of the sequence (164, 128, and 305%; p = 0.01). These data suggest a mechanism by which expression of the GM-CSFR alpha protein may be regulated by alternatively spliced transcripts with different translational efficiencies.

Acute Disease↗
PubMed1995

A minimal CGRP gene promoter is inducible by nerve growth factor in adult rat dorsal root ganglion neurons but not in PC12 phaeochromocytoma cells.

The calcitonin/CGRP gene is transcribed in thyroid C cells and some neuronal cells but not in other cell types. Although the promoter sequences mediating gene activity in thyroid C cells have been extensively studied, the elements responsible for promoter activity in neuronal cells and its stimulation by nerve growth factor (NGF) have not previously been defined. We report the first use of the calcium phosphate procedure to successfully transfect adult rat dorsal root ganglion neurons, which naturally express the calcitonin/calcitonin gene-related peptide (CGRP) in an NGF-inducible manner. This method was used to characterize the elements in the calcitonin/CGRP promoter which are responsible for its basal activity and NGF inducibility in DRG neurons and in PC12 cells, a neuronally derived cell line which does not naturally express the calcitonin/CGRP gene. Although the sequences required for basal activity are similar in each cell type, we show that a minimal calcitonin/CGRP promoter is NGF-responsive in dorsal root ganglion cells, but that upstream sequences are required for such inducibility in PC12 cells.

Animals↗
PubMed1995

Nerve growth factor induces the Oct-2 transcription factor in sensory neurons with the kinetics of an immediate-early gene.

The Oct-2 transcription factor has a predominantly inhibitory effect on gene expression in neuronal cell lines. This factor and its corresponding mRNA have previously been shown to be elevated in adult rat dorsal root ganglion (DRG) neurons chronically exposed to nerve growth factor (NGF). Here we show that the Oct-2 mRNA is rapidly induced in DRG cells exposed to NGF and that such induction still occurs to a lesser extent in the presence of the protein synthesis inhibitor cycloheximide. These findings characterize Oct-2 as a novel member of the immediate-early class of NGF-induced transcription factors whose previously defined members have a predominantly stimulatory effect on the expression of other genes. Induction of the Oct-2 mRNA was also observed in DRG neurons treated with acidic fibroblast growth factor or epidermal growth factor but not with a range of other growth factors and neurotrophins. The role of the Oct-2 transcription factor in mediating the response of DRG neurons to NGF is discussed.

Animals↗
PubMed1994

Nerve growth factor induces expression of immediate-early genes NGFI-A (Egr-1) and NGFI-B (nur 77) in adult rat dorsal root ganglion neurons.

We have used primary cultures of adult rat dorsal root ganglia (DRG), enriched in sensory neurons, to investigate the induction of immediate-early genes by NGF and a variety of other growth factors. Using the polymerase chain reaction we have quantitatively amplified specific mRNA transcripts induced by NGF, in the presence and absence of the protein synthesis inhibitor cycloheximide. NGFIA (Egr-1) and NGFIB (nur 77) mRNAs were elevated in level within 60 min of NGF treatment and independently of de novo protein synthesis. This was consistent with the behaviour of immediate-early genes. These kinetics were seen at a range of NGF concentrations. NGFIA and NGFIB mRNAs were also found to be induced in DRG cultures by a variety of other growth factors. Different patterns of induction of NGFIA and NGFIB mRNA observed in DRG cultures suggested that transcript-specific pathways of signal transduction were operating within neurons, dependent upon the particular growth factor stimulus. Comparison of data reported from growth factor treatment of other cell types with data from DRG cultures also revealed patterns of NGFIA and NGFIB mRNA induction specific to DRG neurons.

Animals↗
PubMed1992

A shuttle vector which facilitates the expression of transfected genes in Trypanosoma cruzi and Leishmania.

A Trypanosoma cruzi expression vector has been constructed using sequences derived from the flanking regions of the glyceraldehyde 3-phosphate dehydrogenase (gGAPDH) genes. The neomycin phosphotransferase (neor) gene was incorporated as a selectable marker. Using electroporation we have introduced this vector into both T. cruzi and Leishmania cells and conferred G418 resistance. Transformation is mediated by large extrachromosomal circular elements composed of head-to-tail tandem repeats of the vector. The transformed phenotype is stable for at least 6 months in the absence of G418 and can be maintained during passage through the T. cruzi life-cycle. Foreign genes inserted into an expression site within the vector (pTEX) can be expressed at high levels in transformed cells. To our knowledge this paper describes the first trypanosome shuttle vector and the first vector which functions in both trypanosomes and Leishmania.

Animals↗