Dual oxidases control release of hydrogen peroxide by the gastric epithelium to prevent Helicobacter felis infection and inflammation in mice

BACKGROUND & AIMS

Dual oxidases (DUOX) are conserved reduced nicotinamide adenine dinucleotide phosphate oxidases that produce H2O2 at the epithelial cell surface. The DUOX enzyme comprises the DUOX and DUOX maturation factor (DUOXA) subunits. Mammalian genomes encode 2 DUOX isoenzymes (DUOX1/DUOXA1 and DUOX2/DUOXA2). Expression of these genes is up-regulated during bacterial infections and chronic inflammatory diseases of the luminal gastrointestinal tract. The roles of DUOX in cellular interactions with microbes have not been determined in higher vertebrates.

METHODS

Mice with disruptions of Duoxa1 and Duoxa2 genes (Duoxa(-/-) mice) and control mice were infected with Helicobacter felis to create a model of Helicobacter pylori infection--the most common human chronic infection.

RESULTS

Infection with H. felis induced expression of Duox2 and Duoxa2 in the stomachs of wild-type mice, and DUOX protein specifically localized to the apical surface of epithelial cells. H. felis colonized the mucus layer in the stomachs of Duoxa(-/-) mice to a greater extent than in control mice. The increased colonization persisted into the chronic phase of infection and correlated with an increased, yet ineffective, inflammatory response. H. felis colonization also was increased in Duoxa(+/-) mice, compared with controls. We observed reduced expression of the H2O2-inducible katA gene in H. felis that colonized Duoxa(-/-) mice, compared with that found in controls (P = .0002), indicating that Duox causes oxidative stress in these bacteria. In vitro, induction of oxidative defense by H. felis failed to prevent a direct bacteriostatic effect at sustained levels of H2O2 as low as 30 μmol/L.

CONCLUSIONS

Based on studies of Duoxa(-/-) mice, the DUOX enzyme complex prevents gastric colonization by H. felis and the inflammatory response. These findings indicate the nonredundant function of epithelial production of H2O2 in restricting microbial colonization.

Carbamazepine suppresses calpain-mediated autophagy impairment after ischemia/reperfusion in mouse livers. Toxicol Appl Pharmacol. 2013;273:600-610. [PMID: 24126417 DOI: 10.1016/j.taap.2013.10.006]

Onset of the mitochondrial permeability transition (MPT) plays a causative role in ischemia/reperfusion (I/R) injury. Current therapeutic strategies for reducing reperfusion injury remain disappointing. Autophagy is a lysosome-mediated, catabolic process that timely eliminates abnormal or damaged cellular constituents and organelles such as dysfunctional mitochondria. I/R induces calcium overloading and calpain activation, leading to degradation of key autophagy-related proteins (Atg). Carbamazepine (CBZ), an FDA-approved anticonvulsant drug, has recently been reported to increase autophagy. We investigated the effects of CBZ on hepatic I/R injury. Hepatocytes and livers from male C57BL/6 mice were subjected to simulated in vitro, as well as in vivo I/R, respectively. Cell death, intracellular calcium, calpain activity, changes in autophagy-related proteins (Atg), autophagic flux, MPT and mitochondrial membrane potential after I/R were analyzed in the presence and absence of 20 μM CBZ. CBZ significantly increased hepatocyte viability after reperfusion. Confocal microscopy revealed that CBZ prevented calcium overloading, the onset of the MPT and mitochondrial depolarization. Immunoblotting and fluorometric analysis showed that CBZ blocked calpain activation, depletion of Atg7 and Beclin-1 and loss of autophagic flux after reperfusion. Intravital multiphoton imaging of anesthetized mice demonstrated that CBZ substantially reversed autophagic defects and mitochondrial dysfunction after I/R in vivo. In conclusion, CBZ prevents calcium overloading and calpain activation, which, in turn, suppresses Atg7 and Beclin-1 depletion, defective autophagy, onset of the MPT and cell death after I/R.

Translocation of iron from lysosomes to mitochondria during ischemia predisposes to injury after reperfusion in rat hepatocytes

The mitochondrial permeability transition (MPT) initiated by reactive oxygen species (ROS) plays an essential role in ischemia-reperfusion (IR) injury. Iron is a critical catalyst for ROS formation, and intracellular chelatable iron promotes oxidative injury-induced and MPT-dependent cell death in hepatocytes. Accordingly, our aim was to investigate the role of chelatable iron in IR-induced ROS generation, MPT formation, and cell death in primary rat hepatocytes. To simulate IR, overnight-cultured hepatocytes were incubated anoxically at pH 6.2 for 4h and reoxygenated at pH 7.4. Chelatable Fe(2+), ROS, and mitochondrial membrane potential were monitored by confocal fluorescence microscopy of calcein, chloromethyldichlorofluorescein, and tetramethylrhodamine methyl ester, respectively. Cell killing was assessed by propidium iodide fluorimetry. Ischemia caused progressive quenching of cytosolic calcein by more than 90%, signifying increased chelatable Fe(2+). Desferal and starch-desferal 1h before ischemia suppressed calcein quenching. Ischemia also induced quenching and dequenching of calcein loaded into mitochondria and lysosomes, respectively. Desferal, starch-desferal, and the inhibitor of the mitochondrial Ca(2+) uniporter (MCU), Ru360, suppressed mitochondrial calcein quenching during ischemia. Desferal, starch-desferal, and Ru360 before ischemia also decreased mitochondrial ROS formation, MPT opening, and cell killing after reperfusion. These results indicate that lysosomes release chelatable Fe(2+) during ischemia, which is taken up into mitochondria by MCU. Increased mitochondrial iron then predisposes to ROS-dependent MPT opening and cell killing after reperfusion.

Minocycline and doxycycline, but not other tetracycline-derived compounds, protect liver cells from chemical hypoxia and ischemia/reperfusion injury by inhibition of the mitochondrial calcium uniporter

Minocycline, a tetracycline-derived compound, mitigates damage caused by ischemia/reperfusion (I/R) injury. Here, 19 tetracycline-derived compounds were screened in comparison to minocycline for their ability to protect hepatocytes against damage from chemical hypoxia and I/R injury. Cultured rat hepatocytes were incubated with 50μM of each tetracycline-derived compound 20 min prior to exposure to 500μM iodoacetic acid plus 1mM KCN (chemical hypoxia). In other experiments, hepatocytes were incubated in anoxic Krebs-Ringer-HEPES buffer at pH6.2 for 4h prior to reoxygenation at pH7.4 (simulated I/R). Tetracycline-derived compounds were added 20 min prior to reperfusion. Ca(2+) uptake was measured in isolated rat liver mitochondria incubated with Fluo-5N. Cell killing after 120 min of chemical hypoxia measured by propidium iodide (PI) fluorometry was 87%, which decreased to 28% and 42% with minocycline and doxycycline, respectively. After I/R, cell killing at 120 min decreased from 79% with vehicle to 43% and 49% with minocycline and doxycycline. No other tested compound decreased killing. Minocycline and doxycycline also inhibited mitochondrial Ca(2+) uptake and suppressed the Ca(2+)-induced mitochondrial permeability transition (MPT), the penultimate cause of cell death in reperfusion injury. Ru360, a specific inhibitor of the mitochondrial calcium uniporter (MCU), also decreased cell killing after hypoxia and I/R and blocked mitochondrial Ca(2+) uptake and the MPT. Other proposed mechanisms, including mitochondrial depolarization and matrix metalloprotease inhibition, could not account for cytoprotection. Taken together, these results indicate that minocycline and doxycycline are cytoprotective by way of inhibition of MCU.

The three α1-adrenoceptor subtypes show different spatio-temporal mechanisms of internalization and ERK1/2 phosphorylation

We analyzed the kinetic and spatial patterns characterizing activation of the MAP kinases ERK 1 and 2 (ERK1/2) by the three α1-adrenoceptor (α1-AR) subtypes in HEK293 cells and the contribution of two different pathways to ERK1/2 phosphorylation: protein kinase C (PKC)-dependent ERK1/2 activation and internalization-dependent ERK1/2 activation. The different pathways of phenylephrine induced ERK phosphorylation were determined by western blot, using the PKC inhibitor Ro 31-8425, the receptor internalization inhibitor concanavalin A and the siRNA targeting β-arrestin 2. Receptor internalization properties were studied using CypHer5 technology and VSV-G epitope-tagged receptors. Activation of α1A- and α1B-ARs by phenylephrine elicited rapid ERK1/2 phosphorylation that was directed to the nucleus and inhibited by Ro 31-8425. Concomitant with phenylephrine induced receptor internalization α1A-AR, but not α1B-AR, produced a maintained and PKC-independent ERK phosphorylation, which was restricted to the cytosol and inhibited by β-arrestin 2 knockdown or concanavalin A treatment. α1D-AR displayed constitutive ERK phosphorylation, which was reduced by incubation with prazosin or the selective α1D antagonist BMY7378. Following activation by phenylephrine, α1D-AR elicited rapid, transient ERK1/2 phosphorylation that was restricted to the cytosol and not inhibited by Ro 31-8425. Internalization of the α1D-AR subtype was not observed via CypHer5 technology. The three α1-AR subtypes present different spatio-temporal patterns of receptor internalization, and only α1A-AR stimulation translates to a late, sustained ERK1/2 phosphorylation that is restricted to the cytosol and dependent on β-arrestin 2 mediated internalization.

7,8-Dihydroxyflavone leads to survival of cultured embryonic motoneurons by activating intracellular signaling pathways

Brain-derived neurotrophic factor (BDNF), a member of the neurotrophin family and a ligand for the tropomyosin-receptor kinase B (TrkB), mediates neuronal survival, differentiation, and synaptic plasticity. However, BDNF is not used to treat neurodegenerative diseases because of its poor pharmacokinetic profile, side effects, and absence of survival properties in clinical trials. Consequently, alternative approaches such as TrkB receptor agonist application are gaining importance. 7,8-Dihydroxyflavone (7,8-DHF), a member of the flavonoid family, has been described as a robust TrkB receptor agonist in hippocampal neurons. Nevertheless, the influence of 7,8-DHF on motoneurons, one of the main targets of BDNF in vivo, is so far unknown. Therefore, we investigated the impact of 7,8-DHF treatment on primary cultured mouse motoneurons. Indeed, we found an activation of the TrkB receptor. Moreover, 7,8-DHF application promotes survival and neurite growth of cultured motoneurons and these effects appear dose-dependent. To investigate the PI3K/AKT and MAPK pathway activation in 7,8-DHF treated motoneurons, we developed a high-density culture system of primary mouse motoneurons. Analysis of both pathways demonstrated a PI3K/AKT but not MAPK pathway activation in cultured motoneurons. This is in contrast to previously published reports about BDNF-mediated activation of TrkB. The lack of MAPK pathway activation is also in contrast to what has been found for hippocampal neurons that indeed show MAPK activation after 7,8-DHF treatment. The ability of 7,8-DHF to imitate BDNF function in motoneurons by using Trk receptor signaling would provide a new approach for the treatment of motoneuron diseases, but needs a more detailed analysis of the activation profile of 7,8-DHF.