Defective innate cell response and lymph node infiltration specify Yersinia pestis infection

Since its recent emergence from the enteropathogen Yersinia pseudotuberculosis, Y. pestis, the plague agent, has acquired an intradermal (id) route of entry and an extreme virulence. To identify pathophysiological events associated with the Y. pestis high degree of pathogenicity, we compared disease progression and evolution in mice after id inoculation of the two Yersinia species. Mortality studies showed that the id portal was not in itself sufficient to provide Y. pseudotuberculosis with the high virulence power of its descendant. Surprisingly, Y. pseudotuberculosis multiplied even more efficiently than Y. pestis in the dermis, and generated comparable histological lesions. Likewise, Y. pseudotuberculosis translocated to the draining lymph node (DLN) and similar numbers of the two bacterial species were found at 24 h post infection (pi) in this organ. However, on day 2 pi, bacterial loads were higher in Y. pestis-infected than in Y. pseudotuberculosis-infected DLNs. Clustering and multiple correspondence analyses showed that the DLN pathologies induced by the two species were statistically significantly different and identified the most discriminating elementary lesions. Y. pseudotuberculosis infection was accompanied by abscess-type polymorphonuclear cell infiltrates containing the infection, while Y. pestis-infected DLNs exhibited an altered tissue density and a vascular congestion, and were typified by an invasion of the tissue by free floating bacteria. Therefore, Y. pestis exceptional virulence is not due to its recently acquired portal of entry into the host, but is associated with a distinct ability to massively infiltrate the DLN, without inducing in this organ an organized polymorphonuclear cell reaction. These results shed light on pathophysiological processes that draw the line between a virulent and a hypervirulent pathogen.     

Positive potentials ot the human brain in the latent presaccadic period under conditions of stimulation of the leading and nonleading eye

We used backward averaging method to study fast positive presaccadic EEG-potentials under conditions of the monocular stimulation of the leading and nonleading eye. Two schemes of the visual stimulus presentation ("no gap" and "overlap") were used. In the "no gap" condition, potential P1 dominated in the hemispere ipsilateral to a saccade direction. In the "overlap" condition, when the gaze was fixed at the central point, foci of this potential were localized in the sagittal derivations or in the same sites as in the "no gap" conditions. Irrespective on the stimulation scheme, the P2 foci were localized in the hemisphere contralateral to a saccade direction. We assume that the fast positive potentials involve both activation and inhibition processes in visuomotor structures and can be also associated with cognitive presaccadic processes (such as fixation disengage, attention lateralization and a preliminary extraction of motor programs from memory).     

The yeast cAMP protein kinase Tpk3p is involved in the regulation of mitochondrial enzymatic content during growth

During aerobic cell growth, mitochondria must meet energy demand either by adjusting cellular mitochondrial content or by adjusting ATP production flux, allowing a constant growth yield. On respiratory substrate, the Ras/cAMP pathway has been shown to be involved in this process in the yeast Saccharomyces cerevisiae. We show that of the three cAMP protein kinase catalytic subunits, Tpk3p is the one specifically involved in the regulation of cellular mitochondrial content when energy demand decreases. In decreased energy demand, the Deltatpk3 mitochondrial enzymatic content decreases leading to a subsequent decrease in the cellular growth rate. Moreover, enzymatic content decreases in the Deltatpk3 isolated mitochondria, suggesting that the amount of cellular mitochondria is not affected, but rather that the mitochondria are modified. Our study points to an important decrease in the cytochrome c content in the Deltatpk3 mitochondria, which leads to a decrease in the slipping process at the level of cytochrome-c-oxidase.     

Organization and regulation of the cytosolic NADH metabolism in the yeast Saccharomyces cerevisiae

Keeping a cytosolic redox balance is a prerequisite for living cells in order to maintain a metabolic activity and enable growth. During growth of Saccharomyces cerevisiae, an excess of NADH is generated in the cytosol. Aerobically, it has been shown that the external NADH dehydrogenase, Nde1p and Nde2p, as well as the glycerol-3-phosphate dehydrogenase shuttle, comprising the cytoplasmic glycerol-3-phosphate dehydrogenase, Gpdlp, and the mitochondrial glycerol-3-phosphate dehydrogenase, Gut2p, are the most important mechanisms for mitochondrial oxidation of cytosolic NADH. In this review we summarize the recent results showing (i) the contribution of each of the mechanisms involved in mitochondrial oxidation of the cytosolic NADH, under different physiological situations; (ii) the kinetic and structural properties of these metabolic pathways in order to channel NADH from cytosolic dehydrogenases to the inner mitochondrial membrane and (iii) the organization in supramolecular complexes and, the peculiar ensuing kinetic regulation of some of the enzymes (i.e. Gut2p inhibition by external NADH dehydrogenase activity) leading to a highly integrated functioning of enzymes having a similar physiological function. The cell physiological consequences of such an organized and regulated network are discussed.     

Production of phthiocerol dimycocerosates protects Mycobacterium tuberculosis from the cidal activity of reactive nitrogen intermediates produced by macrophages and modulates the early immune response to infection

The growth of Mycobacterium tuberculosis mutants unable to synthesize phthiocerol dimycocerosates (DIMs) was recently shown to be impaired in mouse lungs. However, the precise role of these molecules in the course of infection remained to be determined. Here, we provide evidence that the attenuation of a DIM-deficient strain takes place during the acute phase of infection in both lungs and spleen of mice, and that this attenuation results in part from the increased sensitivity of the mutant to the cidal activity of reactive nitrogen intermediates released by activated macrophages. We also show that the DIM-deficient mutant, the growth and survival of which were not impaired within resting macrophages and dendritic cells, induced these cells to secrete more tumour necrosis factor (TNF)-alpha and interleukin (IL)-6 than the wild-type strain. Although purified DIM molecules by themselves had no effect on the activation of macrophages and dendritic cells in vitro, we found that the proper localization of DIMs in the cell envelope of M. tuberculosis is critical to their biological effects. Thus, our findings suggest that DIM production contributes to the initial growth of M. tuberculosis by protecting it from the nitric oxide-dependent killing of macrophages and modulating the early immune response to infection.     

Effect of chronic administration of aminoguanidine on the reactivity of pulmonary vessels in rats with monocrotaline-induced pulmonary hypertension

Monocrotaline (MCT)-induced pulmonary hepertension (PH) is associated with impaired endothelium-dependent relaxation and increased activity of inducible NO-synthase (iNOS). To examine the role of iNOS in MCT-induced PH, we used iNOS inhibitor: aminoguanidine (AG). The PH was simulated with a subcutaneous injection of 60 mg/kg MCT to Wistar rats; control rats were injected with saline. Then each group was separated into 2 subgroups: the 1st one was given drinking water (MCT-C and C-C groups) whereas the 2nd one was given AG in drinking water (15 mg/(kg(-1) x day(-1)) (MCT-AG and C-AG groups). In 4 weeks, the perfusion pressure (PP) responses of isolated pulmonary arteries to acetylcholine (Ach) and activator of soluble guanylate cyclase (sGC), FPTO, were examined. In the MCT-C group, a decrease of relative PP to perfusion of 1 x 10(-8) M and 5 x 10(-8) M Ach and 1 x 10(-8) M FPTO was diminished. This reduction of relaxant responses in MCT-treated rats was prevented by AG treatment. The findings suggest that AG administration restores the impaired endothelium-dependent and sGC-dependent relaxation of the pulmonary artery at MCT-induced PH.     

Latent period of antisaccades in various conditions of visual stimulation in man

The latent periods (LP) of normal saccades and antisaccades were studied in 10 right-handed healthy subjects in two series of experiments. Peripheral visual stimuli were located at an angle of 10 degrees with respect to the central fixation stimulus in the left and right visual semifields. Two standard schemes of visual stimulation: 1) SS (single step), i.e., switching the peripheral stimulus on immediately after switching the central stimulus of; 2) GAP, i.e., the same with the interstimulus interval in 200 ms. It was shown that in the GAP stimulation condition, the LP of both saccades and antisaccades was 30-50 shorter than in the SS condition. The LP of antisaccades was longer than that of saccades by 145-300 ms. The LP of the leftward antisaccades was by 10-100 ms shorter than that of the rightward ones. Probably, this phenomenon reflects the dominance of the right hemisphere in spatial attention.     

Dimethylbiguanide inhibits cell respiration via an indirect effect targeted on the respiratory chain complex I

We report here a new mitochondrial regulation occurring only in intact cells. We have investigated the effects of dimethylbiguanide on isolated rat hepatocytes, permeabilized hepatocytes, and isolated liver mitochondria. Addition of dimethylbiguanide decreased oxygen consumption and mitochondrial membrane potential only in intact cells but not in permeabilized hepatocytes or isolated mitochondria. Permeabilized hepatocytes after dimethylbiguanide exposure and mitochondria isolated from dimethylbiguanide pretreated livers or animals were characterized by a significant inhibition of oxygen consumption with complex I substrates (glutamate and malate) but not with complex II (succinate) or complex IV (N,N,N',N'-tetramethyl-1, 4-phenylenediamine dihydrochloride (TMPD)/ascorbate) substrates. Studies using functionally isolated complex I obtained from mitochondria isolated from dimethylbiguanide-pretreated livers or rats further confirmed that dimethylbiguanide action was located on the respiratory chain complex I. The dimethylbiguanide effect was temperature-dependent, oxygen consumption decreasing by 50, 20, and 0% at 37, 25, and 15 degrees C, respectively. This effect was not affected by insulin-signaling pathway inhibitors, nitric oxide precursor or inhibitors, oxygen radical scavengers, ceramide synthesis inhibitors, or chelation of intra- or extracellular Ca(2+). Because it is established that dimethylbiguanide is not metabolized, these results suggest the existence of a new cell-signaling pathway targeted to the respiratory chain complex I with a persistent effect after cessation of the signaling process.