An improved gas distribution system for anaerobic screening of multiple microbial cultures

Regulation of autophagy of the heart in ischemia and reperfusion

Ischemia/reperfusion (I/R) of the heart leads to increased autophagic flux. Preconditioning stimulates autophagic flux by AMPK and PI3-kinase activation and mTOR inhibition. The cardioprotective effect of postconditioning is associated with activation of autophagy and increased activity of NO-synthase and AMPK. Oxidative stress stimulates autophagy in the heart during I/R. Superoxide radicals generated by NADPH-oxidase acts as a trigger for autophagy, possibly due to AMPK activation. There is reason to believe that AMPK, GSK-3β, PINK1, JNK, hexokinase II, MEK, PKCα, and ERK kinases stimulate autophagy, while mTOR, PKCδ, Akt, and PI3-kinase can inhibit autophagy in the heart during I/R. However, there is evidence that PI3-kinase could stimulate autophagy in ischemic preconditioning of the heart. It was found that transcription factors FoxO1, FoxO3, NF-κB, HIF-1α, TFEB, and Nrf-2 enhance autophagy in the heart in I/R. Transcriptional factors STAT1, STAT3, and p53 inhibit autophagy in I/R. MicroRNAs could stimulate and inhibit autophagy in the heart in I/R. Long noncoding RNAs regulate the viability and autophagy of cardiomyocytes in hypoxia/reoxygenation (H/R). Nitric oxide (NO) donors and endogenous NO could activate autophagy of cardiomyocytes. Activation of heme oxygenase-1 promotes cardiomyocyte tolerance to H/R and enhances autophagy. Hydrogen sulfide increases cardiac tolerance to I/R and inhibits apoptosis and autophagy via mTOR and PI3-kinase activation.

A Review of Humoral Factors in Remote Preconditioning of the Heart

A humoral mechanism of cardioprotection by remote ischemic preconditioning (RIP) has been clearly demonstrated in various models of ischemia-reperfusion including upper and lower extremities, liver, and the mesenteric and renal arteries. A wide range of humoral factors for RIP have been proposed including hydrophobic peptides, opioid peptides, adenosine, prostanoids, endovanilloids, endocannabinoids, calcitonin gene-related peptide, leukotrienes, noradrenaline, adrenomedullin, erythropoietin, apolipoprotein, A-I glucagon-like peptide-1, interleukin 10, stromal cell-derived factor 1, and microRNAs. Virtually, all of the components of ischemic preconditioning's signaling pathway such as nitric oxide synthase, protein kinase C, redox signaling, PI3-kinase/Akt, glycogen synthase kinase β, ERK1/2, mitoK_ATP channels, Connexin 43, and STAT were all found to play a role. The signaling pattern also depends on which remote vascular bed was subjected to ischemia and on the time between applying the rip and myocardial ischemia occurs. Because there is convincing evidence for many seemingly diverse humoral components in RIP, the most likely explanation is that the overall mechanism is complex like that seen in ischemic preconditioning where multiple components are both in series and in parallel and interact with each other. Inhibition of any single component in the right circumstance may block the resulting protective effect, and selectively activating that component may trigger the protection. Identifying the humoral factors responsible for RIP might be useful in developing drugs that confer RIP's protection in a more comfortable and reliable manner.

Decline in ribosomal fidelity contributes to the accumulation and stabilization of the master stress response regulator sigmaS upon carbon starvation

The sigma(S) subunit of RNA polymerase is a master regulator of Escherichia coli that retards cellular senescence and bestows cells with general stress protective functions during growth arrest. We show that mutations and drugs triggering translational errors elevate sigma(S) levels and stability. Furthermore, mutations enhancing translational fidelity attenuate induction of the rpoS regulon and prevent stabilization of sigma(S) upon carbon starvation. Destabilization of sigma(S) by increased proofreading requires the presence of the sigma(S) recognition factor SprE (RssB) and the ClpXP protease. The data further suggest that sigma(S) becomes stabilized upon starvation as a result of ClpP sequestration and this sequestration is enhanced by oxidative modifications of aberrant proteins produced by erroneous translation. ClpP overproduction counteracted starvation-induced stabilization of sigma(S), whereas overproduction of a ClpXP substrate (ssrA-tagged GFP) stabilized sigma(S) in exponentially growing cells. We present a model for the sequence of events leading to the accumulation and activation of sigma(S) upon carbon starvation, which are linked to alterations in both ribosomal fidelity and efficiency.

Induction of the heat shock regulon in response to increased mistranslation requires oxidative modification of the malformed proteins

The Escherichia coli rpsD12 allele, which reduces translational fidelity and elevates expression of heat shock protein (Hsp) genes, only enhanced Hsp gene expression in the presence of oxygen. Similarly, the rpsL141 allele, which reduces mistranslation and Hsp gene expression, failed to affect the Hsp regulon in cells grown anaerobically. Increased production of Hsps in response to starvation is associated with increased mistranslation and was demonstrated to likewise require the presence of oxygen. Thus, mistranslation triggered by starvation or mutations in the accuracy centre of the ribosome appear to elevate Hsp gene expression via an oxidative modification of mistranslated proteins. In contrast, Hsp gene induction during temperature upshifts was independent of oxygen availability. The data further suggest that it is the oxidative modification of mistranslated DnaK substrates rather than oxidation of DnaK itself that triggers Hsp gene expression upon starvation.

NADH-reductive stress in Saccharomyces cerevisiae induces the expression of the minor isoform of glyceraldehyde-3-phosphate dehydrogenase (TDH1)

A strain of Saccharomyces cerevisiae lacking the GPD2 gene, encoding one of the glycerol-3-phosphate dehydrogenases, grows slowly under anaerobic conditions, due to reductive stress caused by the accumulation of cytoplasmic NADH. We used 2D-PAGE to study the effect on global protein expression of reductive stress in the anaerobically grown gpd2Delta strain. The most striking response was a strongly elevated expression of Tdh1p, the minor isoform of glyceraldehyde-3-phosphate dehydrogenase. This increased expression could be reversed by the addition of acetoin, a NADH-specific redox sink, which furthermore largely restored anaerobic growth of the gpd2Delta strain. Additional deletion of the TDH1 gene (but not of TDH2 or TDH3) improved anaerobic growth of the gpd2Delta strain. We therefore propose that TDH1 has properties not displayed by the other TDH isogenes and that its expression is regulated by reductive stress caused by an excess of cytoplasmic NADH.

Dihydroxyacetone kinases in Saccharomyces cerevisiae are involved in detoxification of dihydroxyacetone

The genes YML070W/DAK1 and YFL053W/DAK2 in the yeast Saccharomyces cerevisiae were characterized by a combined genetic and biochemical approach that firmly functionally classified their encoded proteins as dihydroxyacetone kinases (DAKs), an enzyme present in most organisms. The kinetic properties of the two isoforms were similar, exhibiting K(m)((DHA)) of 22 and 5 microm and K(m)((ATP)) of 0.5 and 0.1 mm for Dak1p and Dak2p, respectively. We furthermore show that their substrate, dihydroxyacetone (DHA), is toxic to yeast cells and that the detoxification is dependent on functional DAK. The importance of DAK was clearly apparent for cells where both isogenes were deleted (dak1 Delta dak2 Delta), since this strain was highly sensitive to DHA. In the opposite case, overexpression of either DAK1 or DAK2 made the dak1 Delta dak2 Delta highly resistant to DHA. In fact, overexpression of either DAK provided cells with the capacity to grow efficiently on DHA as the only carbon and energy source, with a generation time of about 5 h. The DHA toxicity was shown to be strongly dependent on the carbon and energy source utilized, since glucose efficiently suppresses the lethality, whereas galactose or ethanol did so to a much lesser extent. However, this suppression was found not to be explained by differences in DHA uptake, since uptake kinetics revealed a simple diffusion mechanism with similar capacity independent of carbon source. Salt addition strongly aggravated the DHA toxicity, independent of carbon source. Furthermore, the DHA toxicity was not linked to the presence of oxygen or to the known harmful agents methylglyoxal and formaldehyde. It is proposed that detoxification of DHA may be a vital part of the physiological response during diverse stress conditions in many species.