Biomedical subjects

Gabor Szabo

Publications and source records attributed to Gabor Szabo.

8 recordsLinked to original sources

PubMed2026

The transcription factor BACH1 couples chromatin priming and repression to enable macrophage plasticity and adaptation.

Macrophage activation and tissue adaptation involve precise transcriptional control by lineage-determining transcription factors (LDTFs) and stimulus-dependent TFs. The heme-regulated transcriptional repressor BACH1 clusters with myeloid LDTFs in unstimulated macrophages, suggesting a role in shaping macrophage identity and function. We found that BACH1 bound to both inactive and active regulatory regions, including latent enhancers. BACH1 recruited the NuRD complex and had dual functions, establishing early chromatin accessibility while actively repressing transcription. Upon inflammatory stimulation, BACH1 rapidly redistributed in cis to nearby promoters, reshaping chromatin occupancy, motif specificity, and enhancer-promoter interactions. BACH1 constrained 3D chromatin architecture, limiting enhancer mobility and TF complex dynamics. In vivo, Bach1 deletion impaired macrophage polarization and tissue adaptation and limited resilience during systemic and regenerative inflammation. Thus, BACH1 acts as an early chromatin accessibility-priming factor while actively repressing transcription-a regulatory activity that can be defined as pioneer repression-thereby shaping the macrophage epigenome in response to inflammatory and tissue contexts.

Basic-Leucine Zipper Transcription Factors↗

PubMed2003

Receptor activation regulates cortical, but not vesicular localization of NDP kinase.

We used immunofluorescence techniques to determine the localization of nucleoside diphosphate (NDP) kinase in NIH-3T3 fibroblasts. We found that cytoplasmic NDP kinase can be separated into two populations according to subcellular localization and response to extracellular stimuli. Specifically, within minutes of stimulation of resting fibroblasts with serum, growth factors or bombesin, a portion of NDP kinase becomes associated with membrane ruffles and lamellipodia. Another pool of NDP kinase accumulates independently of stimulation around intracellular vesicles. Transfection of cells with activated Rac mimics, whereas expression of dominant negative Rac inhibits, the effects of extracellular stimulation on the translocation of NDP kinase to the cell cortex. Neither Rac mutant affects the vesicle-associated pool. Association of NDP kinase with vesicles depends on microtubule integrity and is disrupted by nocodazole. In cell-free assays NDP kinase binds tightly to membrane vesicles associated with taxol-stabilized microtubules. Binding of NDP kinase to this fraction is reduced by ATP and abolished by GTP, as well as guanine nucleotides that are NDP kinase substrates. Thus, the localization of the two NDP kinase pools identified here is regulated independently by distinct cellular components: the appearance of cortical NDP kinase is a consequence of Rac activation, whereas vesicular NDP kinase is responsive to microtubule dynamics and nucleotides, in particular GTP. These results suggest that in fibroblasts NDP kinase participates in Rac-related cortical events and in GTP-dependent processes linked to intracellular vesicle trafficking.

Animals↗

PubMed2003

Essential role of a GXXXG motif for membrane channel formation by Helicobacter pylori vacuolating toxin.

Helicobacter pylori secretes a toxin, VacA, that can form anion-selective membrane channels. Within a unique amino-terminal hydrophobic region of VacA, there are three tandem GXXXG motifs (defined by glycines at positions 14, 18, 22, and 26), which are characteristic of transmembrane dimerization sequences. The goals of the current study were to investigate whether these GXXXG motifs are required for membrane channel formation and cytotoxicity and to clarify the role of membrane channel formation in the biological activity of VacA. Six different alanine substitution mutations (P9A, G13A, G14A, G18A, G22A, and G26A) were introduced into the unique hydrophobic region located near the amino terminus of VacA. The effects of these mutations were first analyzed using the TOXCAT system, which permits the study of transmembrane oligomerization of proteins in a natural membrane environment. None of the mutations altered the capacity of ToxR-VacA-maltose-binding protein fusion proteins to insert into a membrane, but G14A and G18A mutations markedly diminished the capacity of the fusion proteins to oligomerize. We then introduced the six alanine substitution mutations into the vacA chromosomal gene of H. pylori and analyzed the properties of purified mutant VacA proteins. VacA-G13A, VacA-G22A, and VacA-G26A induced vacuolation of HeLa cells, whereas VacA-P9A, VacA-G14A, and VacA-G18A did not. Subsequent experiments examined the capacity of each mutant toxin to form membrane channels. In a planar lipid bilayer assay, VacA proteins containing G13A, G22A, and G26A mutations formed anion-selective membrane channels, whereas VacA proteins containing P9A, G14A, and G18A mutations did not. Similarly, VacA-G13A, VacA-G22A, and VacA-G26A induced depolarization of HeLa cells, whereas VacA-P9A, VacA-G14A, and VacA-G18A did not. These data indicate that an intact proline residue and an intact G(14)XXXG(18) motif within the amino-terminal hydrophobic region of VacA are essential for membrane channel formation, and they also provide strong evidence that membrane channel formation is essential for VacA cytotoxicity.

Anion Transport Proteins↗

PubMed2003

Inhaled nitric oxide inhibits platelet-leukocyte interactions in patients with acute respiratory distress syndrome.

INTRODUCTION: In addition to its effects on platelet function, recent studies suggest that inhaled nitric oxide (NO) also influences the function of circulating leukocytes. Therefore, the aim of this work was to investigate the formation of platelet-leukocyte aggregates (PLAs) and platelet and leukocyte cell surface receptor expression during NO therapy in patients with acute respiratory distress syndrome. METHODS: In 16 patients responding to NO therapy with an improvement in oxygenation (NO group) and in four nonresponders (control), platelet P-selectin expression, platelet fibrinogen binding, the expression CD11a on leukocytes, and the formation of PLAs were investigated at 0, 60, 120, and 180 mins of therapy or at corresponding time points by means of flow cytometry. In addition, PLA was investigated in 30 healthy volunteers during NO inhalation, in five mechanically ventilated patients without acute respiratory distress syndrome and without NO inhalation, and during NO incubation in platelet-rich plasma of ten healthy volunteers in vitro. RESULTS: NO therapy inhibited PLA formation at 60 (13% +/- 4% in the NO group vs. 19% +/- 7% in the control group, p <.01) and 120 mins (14% +/- 4% vs. 18% +/- 7%, p <.05) and slightly decreased CD11a expression at 60 mins (152 +/- 22 arbitrary units vs. 187 +/- 36 arbitrary units, p <.05). Furthermore, besides inhibiting platelet fibrinogen binding, NO also led to a significant inhibition of P-selectin expression at 120 (38% +/- 4% vs. 43% +/- 5%, p <.05) and 180 mins (34% +/- 5% vs. 43% +/- 6%, p <.01), demonstrating a significant correlation between changes in P-selectin expression and PLA formation. In contrast, PLA formation was not influenced by mechanical ventilation in patients without acute respiratory distress syndrome. These results were further supported by additional studies showing inhibition of PLA formation in healthy volunteers as well. CONCLUSIONS: NO-dependent inhibition of PLA formation in patients with acute respiratory distress syndrome can be explained by the inhibition in platelet P-selectin expression. Thus, this study provides rational evidence of systemic antileukocytic and antiplatelet properties of NO therapy in the clinical setting.

Administration, Inhalation↗

PubMed2002

Brain death impairs coronary endothelial function.

BACKGROUND: To characterize the impact of brain death (BD) on endothelial dysfunction after cardiac transplantation we investigated coronary circulation and vasomotor function in a canine model. METHODS: Left ventricular pressure-volume data (conductance catheter) and coronary blood flow (CBF) were monitored continuously. Endothelium-dependent vasodilatation after acetylcholine and endothelium-independent vasodilation after sodium nitroprusside were assessed before and 3 hr after BD induction (inflation of a subdural balloon). RESULTS: BD led to an initial hyperdynamic reaction with significant (P<0.05) increase of CBF. After 3 hr, CBF decreased significantly (P<0.05). Although before BD, application of acetylcholine led to a monophasic vasodilatative response, after BD a short mild vasodilatation was followed by a longer vasoconstriction. Endothelium-independent vasodilatation remained unchanged. CONCLUSIONS: BD affects coronary circulation by two means: (1) impairment of CBF to decrease in parallel in afterload with consecutive hemodynamic deterioration and (2) severe endothelial dysfunction that may be a contributing factor to posttransplant outcome.

Acetylcholine↗

PubMed2002

NO donors potentiate the beta-adrenergic stimulation of I(Ca,L) and the muscarinic activation of I(K,ACh) in rat cardiac myocytes.

The effects of nitric oxide (NO) donors on the L-type Ca(2+) current (I(Ca,L)) and the muscarinic activated K(+) current (I(K,ACh)) were studied in isolated rat cardiac myocytes. The nitrosothiol S-nitroso-N-acetyl-D,L-penicillamine (SNAP, 1 pM-1 microM) strongly potentiated the stimulation of the I(Ca,L) elicited by subthreshold concentrations of isoprenaline (Iso, 0.1-0.5 nM) in ventricular myocytes. The effect of SNAP was mimicked by 2-(N,N-diethylamino)-diazenolate-2-oxide (DEANO, 1 pM-1 nM), a NONOate that spontaneously releases NO in a pH-controlled manner, and was blunted by 2-(4-carboxyphenyl)-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide (100 microM), a NO trap. 1H-[1,2,4]Oxadiazolo[4,3-a]quinoxaline-1-one (10 microM), a guanylyl cyclase inhibitor, did not alter the effect of SNAP. SNAP (1 pM-1 microM) did not modify the effect of L858051 (0.1-0.3 microM), a forskolin analogue that activates adenylyl cyclase, on I(Ca,L) and did not enhance the basal I(Ca,L) in the presence of rolipram (1 microM), a phosphodiesterase type 4 inhibitor. Superfusion with Rp-CPT-cAMPS (500 microM), or internal dialysis with cAMP-dependent protein kinase (cA-PK) inhibitory peptide (PKI; 20 microM), inhibitors of the cA-PK, blunted the effect of SNAP (1 nM and 1 microM) on the Iso-stimulated (1-100 pM) I(Ca,L). SNAP (1 nM and 1 microM) potentiated the threshold stimulation of I(Ca,L) elicited by internal GTP-gammaS (10 microM), a non-hydrolysable analogue of GTP. SNAP (1 pM-1 microM) and DEANO (1 microM) potentiated the stimulation of I(K,ACh) elicited by low concentrations of ACh (1-2 nM) in rat atrial myocytes. The threshold stimulation of I(K,ACh) elicited by internal 5'-guanylylimidodiphosphate (10 microM) was also potentiated by NO donors. SNAP (1 microM) did not modify I(K,ACh) reconstituted in human embryonic kidney 293 cells, in the absence or in the presence of ACh (1 or 10 nM). Taken together, these data suggest that NO is a cGMP-independent modulator of G-protein-coupled muscarinic and beta-adrenergic receptor actions on cardiac ion channels. Although this action of NO seemed to occur at the level of G proteins, it appeared to require a component distinct from receptors, G proteins or their effectors.

3',5'-Cyclic-AMP Phosphodiesterases↗

PubMed2002

Near-infrared diode laser based spectroscopic detection of ammonia: a comparative study of photoacoustic and direct optical absorption methods.

A photoacoustic spectroscopic (PAS) and a direct optical absorption spectroscopic (OAS) gas sensor, both using continuous-wave room-temperature diode lasers operating at 1531.8 nm, were compared on the basis of ammonia detection. Excellent linear correlation between the detector signals of the two systems was found. Although the physical properties and the mode of operation of both sensors were significantly different, their performances were found to be remarkably similar, with a sub-ppm level minimum detectable concentration of ammonia and a fast response time in the range of a few minutes.

Acoustics↗

PubMed2002

A variable valve area, lumped parameter model of left ventricular filling.

A variable valve lumped parameter model was developed and validated in porcine trials. The model was used to simulate ventricular and atrial pressures and flows during diastolic filling. The variable valve area model simulations provide reasonable results and take into account other considerations like venous inflow and initial valve aperture. Comparisons between model outputs and in-vivo porcine experiments suggest that the model may be used in the future to assess compliance and effective orifice area based on parameters derived from non-invasive Doppler waveforms.

Animals↗