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Biomedical subjects

J F Martin

Publications and source records attributed to J F Martin.

At least 91 records · Page 5Linked to original sources
PubMed1995

Cooperative activation of muscle gene expression by MEF2 and myogenic bHLH proteins.

Members of the myocyte enhancer factor-2 (MEF2) family of MADS domain transcription factors cannot induce myogenesis in transfected fibroblasts, but when coexpressed with the myogenic basic-helix-loop-helix (bHLH) proteins MyoD or myogenin they dramatically increase the extent of myogenic conversion above that seen with either myogenic bHLH factor alone. This cooperativity required direct interactions between the DNA-binding domains of MEF2 and the myogenic bHLH factors, but only one of the factors needed a transactivation domain, and only one of the factors needed to be bound to DNA. These interactions allow either factor to activate transcription through the other's binding site and reveal a novel mechanism for indirect activation of gene expression via protein-protein interactions between the DNA-binding domains of heterologous classes of transcription factors.

Amino Acid Sequence↗
PubMed1995

Basic fibroblast growth factor upregulates the expression of vascular endothelial growth factor in vascular smooth muscle cells. Synergistic interaction with hypoxia.

BACKGROUND: Vascular endothelial growth factor (VEGF) is a hypoxia-inducible direct angiogenic factor. Upregulation of VEGF is thought to mediate many of the angiogenic effects of growth factors that are not direct endothelial cell mitogens. Like VEGF, basic fibroblast growth factor (bFGF) is considered to induce angiogenesis by a direct effect on endothelial cells. This study investigated the possibility that bFGF may also act indirectly by regulating VEGF expression in vascular smooth muscle cells (VSMCs). METHODS AND RESULTS: Incubation of confluent and quiescent cultures of rabbit VSMCs with bFGF caused a time- and concentration-dependent increase in steady-state levels of VEGF mRNA, as analyzed by Northern blot hybridization. Exposure of VSMCs to a threshold hypoxic stimulus (2.5% O2) caused a modest increase in VEGF mRNA levels. However, the combination of 2.5% O2 with bFGF had a marked synergistic effect. This effect was specific for VEGF as hypoxia did not enhance bFGF-induced expression of the proto-oncogene c-myc. Synergistic upregulation of VEGF mRNA expression also was observed between hypoxia and TGF-beta 1. CONCLUSIONS: These results suggest that bFGF may promote angiogenesis both by a direct effect on endothelial cells and also indirectly by the upregulation of VEGF in VSMCs. The synergy demonstrated between hypoxia and either bFGF or TGF-beta 1 suggests that multiple diverse stimuli may interact via the upregulation of VEGF expression in VSMCs to amplify the angiogenic response.

Animals↗
PubMed1995

The paired-like homeo box gene MHox is required for early events of skeletogenesis in multiple lineages.

Formation of cartilage and bone involves sequential processes in which undifferentiated mesenchyme aggregates into primordial condensations that subsequently grow and differentiate, eventually forming the adult skeleton. Although much has been learned about the structural molecules that compose cartilage and bone, little is known about the nuclear factors that regulate chondrogenesis and osteogenesis. MHox is a homeo box-containing gene that is expressed in the mesenchyme of facial, limb, and vertebral skeletal precursors during mouse embryogenesis. MHox expression has been shown to require epithelial-derived signals, suggesting that MHox may regulate the epithelial-mesenchymal interactions required for skeletal organogenesis. To determine the functions of MHox, we generated a loss-of-function mutation in the MHox gene. Mice homozygous for a mutant MHox allele die soon after birth and exhibit defects of skeletogenesis, involving the loss or malformation of craniofacial, limb, and vertebral skeletal structures. The affected skeletal elements are derived from the cranial neural crest, as well as somitic and lateral mesoderm. Analysis of the mutant phenotype during ontogeny demonstrated a defect in the formation and growth of chondrogenic and osteogenic precursors. These findings provide evidence that MHox regulates the formation of preskeletal condensations from undifferentiated mesenchyme.

Abnormalities, Multiple↗
PubMed1995

The mouse MRF4 promoter is trans-activated directly and indirectly by muscle-specific transcription factors.

MRF4 is a member of the basic helix-loop-helix (bHLH) family of muscle-specific transcription factors, which also includes MyoD, myogenin, and myf5. The myocyte enhancer binding factor 2 (MEF2) proteins also serve as important muscle-specific transcription factors. In addition to activating the expression of many muscle-specific structural genes, various members of these two classes of proteins activate their own expression and the expression of each other in a complex transcriptional network that results in the establishment and maintenance of the muscle phenotype. To begin to determine how the expression of MRF4 is regulated by other muscle-specific transcription factors, we have isolated a region of the MRF4 gene that confers muscle-specific expression and have analyzed this promoter region for cis-acting elements involved in trans-activation by the myogenic bHLH and MEF2 transcription factors. Here, we show that in 10T1/2 fibroblasts the MRF4 promoter is trans-activated by myogenin, MyoD, myf5, and by the MEF2 factors, but that MRF4 does not activate expression of its own promoter. Myogenin activated the MRF4 promoter directly by an E box-dependent mechanism, while MEF2 factors activated the promoter through an indirect pathway. The E box-dependent regulation of the MRF4 promoter is in contrast to the regulation of the myogenin and MyoD promoters and may represent a mechanism for the differential expression of these factors during myogenesis.

Animals↗
PubMed1995

Hypoxia and platelet-derived growth factor-BB synergistically upregulate the expression of vascular endothelial growth factor in vascular smooth muscle cells.

Vascular endothelial growth factor (VEGF) mRNA expression was analysed in rabbit vascular smooth muscle cells following exposure to hypoxia and platelet-derived growth factor-BB (PDGF-BB). Hypoxia potently upregulated VEGF mRNA steady-state levels in a time- and concentration-dependent manner reaching a maximum level (approximately 30-fold increase) after 12-24 h at 0% 0(2). In contrast, PDGF-BB caused a modest increase in VEGF expression. However, the combination of PDGF-BB and a threshold hypoxic stimulus (2.5% O2 for 4 h) had a marked synergistic effect. Synergy between hypoxia and PDGF-BB was selective for VEGF expression as hypoxia had no effect on the PDGF-induced upregulation of the proto-oncogene c-myc. These results raise the possibility that hypoxia and PDGF-BB may act in concert to induce VEGF expression in the arterial wall during the development of atherosclerosis.

Base Sequence↗
PubMed1995

The influence of the adventitia on the presence of smooth muscle cells and macrophages in the arterial intima.

OBJECTIVE: To test the hypothesis that atherosclerosis may be initiated by hypoperfusion or thrombotic occlusion of the adventitial vasa vasonum. DESIGN: In a new model of atherogenesis, an early atherosclerotic lesion may be initiated by removal of the adventitia from the carotid artery of the New Zealand White rabbit, wherein lie the vasa vasorum. SETTING: Animal laboratory, University Department of Surgery and Medicine. CHIEF OUTCOME MEASURES: Immunocytochemistry was undertaken to demonstrate the presence of smooth muscle cells and macrophages within the intimal lesions. Smooth muscle cells were labelled with a monoclonal antibody designated HHF35 and macrophages were labelled with a rabbit specific, macrophage specific antibody, RAM11. CHIEF RESULTS: In rabbits fed a normal diet, at day 14, the intimal lesion was composed exclusively of smooth muscle cells. By day 28, such lesions had regressed. In rabbits fed a high cholesterol diet, at day 14, the intimal lesion was composed of a mixture of macrophages and smooth muscle cells. By day 42, the pattern of cellular distribution was such that macrophages (present as foam cells) were predominant. In the presence of persistent hypercholesterolaemia these lesions did not regress. CONCLUSIONS: This new model can produce two different cellular responses that may mimic the intimal lesions seen with re-stenosis after angioplasty or in hypercholesterolaemic man and as such, might be useful in separating out these two different pathophysiologies.

Animals↗
PubMed1995

Systemic effects of S-nitroso-glutathione in the human following intravenous infusion.

Nitric oxide (NO) is a potent vasodilator and inhibitor of platelet aggregation. At present the clinical use of NO donors as inhibitors of platelet activation is limited by their concomitant hypotensive effect. The new NO donor S-nitroso-glutathione (GSNO) has a significant antiplatelet effect at doses that cause only a small decrease in blood pressure in rats. We have examined the antiplatelet and vasodilator properties of this nitrosothiol following systemic intravenous infusion in the human. GSNO was administered intravenously to 10 normal females of reproductive age noting changes in blood pressure, pulse and reported side effects. Ex vivo platelet aggregation to ADP was then performed in a platelet-ionized calcium lumiaggregometer on blood samples taken both before and after the infusions. Side effects such as headache or palpitations occurred only in two subjects at the highest infusion rate of 250 micrograms min-1. Blood pressure and pulse did not vary significantly during the study. Ex vivo platelet aggregation in response to ADP was significantly reduced by the infusion. These results suggest that GSNO is a more potent inhibitor of platelet activation than it is a vasodilator and therefore potentially represents a more clinically useful NO donor than has so far been available where an anti-thrombotic effect is required.

Adolescent↗
PubMed1995

The expression of mRNA for fibrinogen in megakaryocytes isolated from patients with T-cell lymphoma.

The expression of fibrinogen mRNA was studied by in situ hybridization in freshly isolated megakaryocytes in 14 newly-diagnosed patients: seven with non-Hodgkin's lymphoma (NHL), three with immune thrombocytopenic purpura (ITP) and four haematologically normal patients prior to coronary artery bypass surgery. Fibrinogen mRNA in megakaryocytes was not detected in ITP, B-cell lymphomas or in healthy donors. However, it was present in all patients with the high-grade T-cell lymphomas, both with and without thrombocytopenia.

Adult↗
PubMed1995

Response of digital arteries to endothelium dependent and independent vasodilators in patients with Raynaud's phenomenon.

The cause of the digital artery spasm seen in Raynaud's phenomenon (RP) is unclear. A dysfunction of endothelium-dependent vasodilation might contribute to the development of this spasm. We studied the digital artery responses to endothelium-dependent and independent vasodilators in eight Raynaud's phenomenon patients and eight sex-matched controls. A sequential series of infusions alternating with physiological saline were administered at a rate of 1 mL min-1 via the radial artery. The infusions contained acetylcholine chloride (ACh) 110 nm mL-1 and 550 nm mL-1, L-arginine 50 mumol mL-1, prostacyclin (PGI2) 2.5 ng mL-1 and glyceryl trinitrate (GTN) 4.5 nm mL-1. Digital artery diameter (DAD) and cutaneous temperature were measured. DAD was measured using a high frequency A-mode ultrasound scanner. There was no significant difference in mean brachial artery pressure, digital cutaneous temperature and DAD between the two groups at the start of the study. Comparing responses in the groups, there was a significantly greater increase in DAD and cutaneous temperature to Ach (endothelium-dependent vasodilator) at both concentrations in controls. A significantly greater increase in DAD was obtained in response to GTN (endothelium-independent vasodilator) in the RP subjects. There was no significant difference in response to L-arginine and PGI2 between the groups. These results suggest that a dysfunction of endothelium-dependent vasodilation is present in RP patients.

Acetylcholine↗
PubMed1995

Myocardial calcium-independent nitric oxide synthase activity is present in dilated cardiomyopathy, myocarditis, and postpartum cardiomyopathy but not in ischaemic or valvar heart disease.

OBJECTIVE: To determine the activity of the calcium-dependent constitutive (cNOS) and calcium-independent inducible nitric oxide (iNOS) synthases in heart tissue from patients with different cardiac diseases. PATIENTS AND DESIGN: Endomyocardial biopsy specimens were obtained from patients with dilated hearts (by echocardiography and ventriculography) and normal coronary arteries (by selective angiography). Recognised clinical, radiological, and histopathological criteria were used to diagnose non-inflammatory dilated cardiomyopathy (DCM) (n = 6), inflammatory cardiomyopathy (ICM) (n = 5), and peripartum cardiomyopathy (PPCM) (n = 3). Comparative groups were chosen with similarly dilated hearts caused by ischaemic (n = 5) or valvar disease (n = 4), and, in addition, non-dilated hearts with ischaemic (n = 5) and valvar (n = 3) disease. Venous blood was taken at the time of myocardial biopsy for assay of plasma tumour necrosis factor alpha (TNF alpha). RESULTS: Myocardial tissue from patients with DCM, ICM, and PPCM showed considerable iNOS activity (16.8 (2.7) pmol citrulline/mg protein/min) with little or no cNOS activity (1.3 (0.9) pmol citrulline/mg protein/min). In contrast, myocardial tissue from patients with both dilated and non-dilated hearts of ischaemic or valvar aetiology showed cNOS and little, if any, iNOS activity (dilated--cNOS 11.7 (2.4) and iNOS 0.8 (0.6) pmol citrulline/mg protein/min; non-dilated--cNOS 12.1 (1.8) and iNOS 1.4 (0.8) pmol citrulline/mg protein/min). Plasma TNF alpha was detectable only in patients with inflammatory DCM. CONCLUSIONS: These results support the hypothesis the generation of nitric oxide by iNOS accounts for some of the dilatation and impaired contractility associated with inflammatory and non-inflammatory dilated cardiomyopathy and peripartum cardiomyopathy.

Adult↗
PubMed1995

Cloning and characterization of an alpha-amylase gene from Streptomyces sp WL6.

An alpha-amylase gene from Streptomyces sp WL6 was cloned on a 3.1kb DNA fragment, which was completely sequenced. The 3088 nucleotide sequence obtained contains three putative coding regions in the same orientation. The one corresponding to the structural region of the alpha-amylase gene has a deduced amino acid sequence of 459 residues, showing up to 71% identity to other alpha-amylases. An incomplete ORF was identified upstream the alpha-amylase gene, and the deduced product presents some homology to proteins involved in catabolic regulation.

Amino Acid Sequence↗
PubMed1995

Expression of mef2 genes in the mouse central nervous system suggests a role in neuronal maturation.

Members of the myocyte enhancer factor 2 (MEF2) gene family are expressed in a dynamic pattern during development of the CNS of pre- and postnatal mice. The four MEF2 genes, Mef2A, -B, -C, -D, encode transcription factors belonging to the MADS (MCM1-agamous-deficiens-serum response factor) superfamily of DNA binding proteins. MEF2 factors have previously been shown to be positive regulators of gene expression in terminally differentiated muscle cells. To begin to determine the role of MEF2 factors in CNS development, we used in situ hybridization with gene-specific cRNA probes to define the expression patterns of each of the four Mef2 mRNAs in the developing and mature mouse CNS. Mef2C mRNA was first detected in a ventral portion of the telencephalon at 11.5 d postcoitum (p.c.). By 13.5 d p.c., each of the four Mef2 genes were expressed in overlapping yet distinct patterns in regions of the frontal cortex, midbrain, thalamus, hippocampus, and hindbrain. Temporal and spatial patterns of embryonic Mef2 gene expression appeared to follow gradients of neuron maturation and suggested that the onset of Mef2 gene expression coincides with withdrawal from the cell cycle and initiation of neuronal differentiation. This correlation is particularly striking for Purkinje cells in the cerebellum. Since the molecular mechanisms that regulate neuron differentiation are unknown, we propose that the MEF2 factors are likely to play an important role in this process.

Animals↗
PubMed1995

Cigarette smoking sensitizes and desensitizes impedance-measured ADP-induced platelet aggregation in whole blood.

The effect of smoking on platelet aggregation appears to produce conflicting results, with some studies indicating an enhancement and others a decrease of aggregation. This epidemiological study of 120 male smokers, a subset of the Caerphilly Heart Disease Study, examined the relationship of two dimensions of smoking (time proximity of last cigarette before venepuncture and serum nicotine concentration) with threshold dose of adenosine diphosphate (ADP) necessary to induce platelet aggregation in whole blood. Means (range) of ADP threshold dose and nicotine concentration were 1.66 (0.5-2.5, censored) microM and 12.2 (0-35.2) ng/ml. Men smoking within 30 min of venepuncture demonstrated lower ADP threshold doses (-0.48 microM lower [95% C.I.: -0.95, -0.02])--reflecting increased sensitivity. Men with higher nicotine concentration had higher ADP threshold doses (Regression Coefficient: +0.032 microM per ng/ml [95% C.I.: 0.003, 0.062])--reflecting decreased sensitivity. Men smoking 30 min or more before venepuncture who also had high nicotine concentration (25-30 ng/ml) demonstrated the highest ADP threshold doses compared to never smokers and to men smoking the previous day (approximately 2.20 vs 1.86 and 1.81 microM). Relations involving nicotine concentration do not necessarily reflect a pharmacological effect although the potential for a short term nicotine mediated tolerance effect cannot be dismissed. These observations support an hypothesis suggesting a temporal sequence of platelet sensitization and desensitization during smoking.

Adenosine Diphosphate↗
PubMed1994

Inhibition of platelet activity by S-nitrosoglutathione during coronary angioplasty.

Platelet activation is associated with acute vessel occlusion and chronic restenosis after percutaneous transluminal coronary angioplasty (PTCA). Organic nitrates, which act by releasing the vasodilator and anti-platelet agent nitric oxide (NO), have a predominantly vasodilator action and cause hypotension at doses required to inhibit platelet activation. S-nitrosoglutathione (GSNO) is an NO donor with a preferential action on platelets. We investigated platelet activation in patients undergoing PTCA and the effect of GSNO. Blood was sampled from the coronary sinus to measure platelet surface expression of P-selectin and glycoprotein IIb/IIIa as indices of platelet activation. In 7 control patients, PTCA caused a rise in platelet surface expression of P-selectin and glycoprotein IIb/IIIa, which was maximal 5 minutes after PTCA, indicating increased platelet activation despite treatment with aspirin, glyceryl trinitrate, and heparin. 6 patients received an intracoronary infusion of GSNO, starting 10 min before PTCA. GSNO significantly inhibited the PTCA-induced increase in platelet surface expression of P-selectin and glycoprotein IIb/IIIa without altering blood pressure. These findings show that platelets are activated following PTCA and that GSNO can prevent this activation.

Aged↗
PubMed1994

Nitric oxide generation. A predictive parameter of acute allograft rejection.

The L-arginine:nitric oxide (NO) biosynthetic pathway has been proposed as an important mediator in host defense mechanisms and may therefore play a role in the acute allograft response. We have studied NO generation in liver allograft rejection and determined its value in immunological monitoring. Stable end products of this pathway have been determined serially in 50 primary liver recipients and compared with 2 known mediators and markers of acute allograft rejection (IL-2R positive lymphocytes and circulating TNF alpha). Plasma concentrations of acid-labile nitrosocompounds (NOx), which increased during acute allograft rejection (P < 0.0001), correlated with rejection severity and were reduced after administration of supplemental high dose glucocorticoids. Concentrations were significantly lower in nonrejection graft complications but were elevated during episodes of sepsis. Correlations between plasma NOx levels and circulating TNF-alpha (r = 0.451, P < 0.001) and IL-2R-positive lymphocytes in peripheral blood (r = 0.781, P < 0.001) were demonstrated. In a logistic analysis of these variables, plasma NOx was the most predictive parameter of an episode of acute cellular rejection. Nitric oxide generation in FK506-treated patients was lower compared with patients receiving a CsA-based immunosuppression regimen and was associated with a reduced frequency of acute rejection in the FK506 group. These data are consistent with a role for NO in the cellular alloantigen immune response and indicate that monitoring of plasma levels of NOx may be useful in the detection of acute allograft rejection.

Biomarkers↗