A Ca(2+)-activated NADPH oxidase in testis, spleen, and lymph nodes

Superoxide and its derivatives are increasingly implicated in the regulation of physiological functions from oxygen sensing and blood pressure regulation to lymphocyte activation and sperm-oocyte fusion. Here we describe a novel superoxide-generating NADPH oxidase referred to as NADPH oxidase 5 (NOX5). NOX5 is distantly related to the gp91(phox) subunit of the phagocyte NADPH oxidase with conserved regions crucial for the electron transport (NADPH, FAD and heme binding sites). However, NOX5 has a unique N-terminal extension that contains three EF hand motifs. The mRNA of NOX5 is expressed in pachytene spermatocytes of testis and in B- and T-lymphocyte-rich areas of spleen and lymph nodes. When heterologously expressed, NOX5 was quiescent in unstimulated cells. However, in response to elevations of the cytosolic Ca(2+) concentration it generated large amounts of superoxide. Upon Ca(2+) activation, NOX5 also displayed a second function: it became a proton channel, presumably to compensate charge and pH alterations due to electron export. In summary, we have identified a novel NADPH oxidase that generates superoxide and functions as a H(+) channel in a Ca(2+)-dependent manner. NOX5 is likely to be involved in Ca(2+)-activated, redox-dependent processes of spermatozoa and lymphocytes such as sperm-oocyte fusion, cell proliferation, and cytokine secretion.     

Heme histidine ligands within gp91(phox) modulate proton conduction by the phagocyte NADPH oxidase

The membrane subunit of the phagocyte NADPH oxidase, gp91(phox), possesses a H(+) channel motif formed by membrane-spanning histidines postulated to coordinate the two heme groups forming the redox center of the flavocytochrome. To study the role of heme-binding histidines on proton conduction, we stably expressed the gp91(phox) cytochrome in human embryonic kidney 293 cells and measured proton currents with the patch clamp technique. Similar to its shorter homologue, NADPH oxidase homologue 1, which is predicted not to bind heme, gp91(phox) generated voltage-activated, pH-dependent, H(+)-selective currents that were reversibly blocked by Zn(2+). The gp91(phox) currents, however, activated faster, deactivated more slowly, and were markedly affected by the inhibition of heme synthesis. Upon heme removal, the currents had larger amplitude, activated faster and at lower voltages, and became sensitive to the histidine reagent diethylpyrocarbonate. Mutation of the His-115 residue to leucine abolished both the gp91(phox) characteristic 558-nm absorbance peak and voltage-activated currents, indicating that His-115 is involved in both heme ligation and proton conduction. These results indicate that the gp91(phox) proton channel is activated upon release of heme from its His-115 ligand. During activation of the oxidase complex, changes in heme coordination within the cytochrome might increase the mobility of histidine ligands, thereby coupling electron and proton transport.     

Natural ceramide reverses Fas resistance of acid sphingomyelinase(-/-) hepatocytes

The role of the second messenger ceramide in Fas-mediated death requires clarification. To address this issue, we generated hepatocytes from paired acid sphingomyelinase (ASMase; asmase)(+/+) and asmase(-/-) mice. asmase(-/-) hepatocytes, derived from 8-week-old mice, manifested normal sphingomyelin content and normal morphological, biochemical, and biologic features. Nonetheless, ASMase-deficient hepatocytes did not display rapid ceramide elevation or apoptosis in response to Jo2 anti-Fas antibody. asmase(-/-) hepatocytes were not inherently resistant to apoptosis because staurosporine, which did not induce early ceramide elevation, stimulated a normal apoptotic response. The addition of low nanomolar quantities of natural C16-ceramide, which by itself did not induce apoptosis, completely restored the apoptotic response to anti-Fas in asmase(-/-) hepatocytes. Other sphingolipids did not replace natural ceramide and restore Fas sensitivity. Overcoming resistance to Fas in asmase(-/-) hepatocytes by natural ceramide is evidence that it is the lack of ceramide and not ASMase which determines the apoptotic phenotype. The ability of natural ceramide to rescue the phenotype without reversing the genotype provides evidence that ceramide is obligate for Fas induction of apoptosis in hepatocytes.     

Species-specific and conserved epitopes on mouse and human E-selectin important for leukocyte adhesion

The cdk5 and its activator p35 constitute one of the main tau-phosphorylating systems in neuronal cells. Under normal conditions for neurons, its activity is required for modulating tau involvement in neuronal polarity and in development of the mammalian central nervous system. Recently, we reported that the treatment of rat hippocampal cells in culture with fibrillary beta-amyloid (Abeta) results in deregulation of the protein kinase cdk5. The neurotoxic effects of Abeta fibrils were prevented by inhibition of cdk5 activity by butyrolactone I or by using antisense oligonucleotides that control the expression of this kinase. Here, we show that the Abeta-promoted increase of cdk5 activity is associated with changes in tau phosphorylation patterns and in the intraneuronal distribution of tau. In addition to hippocampal cells, deregulation of cdk5 was observed in other cell types. However, butyrolactone I prevented Abeta-induced cell death only in neuronal cells in which cdk5 activation was sensitive to Abeta fibrils. This lost of cdk5 regulation in hippocampal cells exposed to Abeta fibrils appears to be associated with an increase in the cdk5-p35 complex stability. Complex stabilization was sensitive to phosphorylation of cdk5. However, no changes in cdk5 and p35 mRNAs were observed, suggesting that the main effects on cdk5 occur at the posttranslational level. These studies indicate that cdk5 phosphorylation and the formation of an abnormally active cdk5-p35 complex are directly involved in the molecular paths leading to the neurodegenerative process of rat hippocampal neurons triggered by Abeta fibrils.     

Ligation of microglial CD40 results in p44/42 mitogen-activated protein kinase-dependent TNF-alpha production that is opposed by TGF-beta 1 and IL-10

Recently, it has been demonstrated that the CD40 receptor is constitutively expressed on cultured microglia at low levels. Ligation of CD40 by CD40 ligand on these cells results in microglial activation, as measured by TNF-alpha production and neuronal injury. However, the intracellular events mediating this effect have yet to be investigated. We report that ligation of microglial CD40 triggers activation of p44/42 mitogen-activated protein kinase (MAPK). This effect is evident 30 min posttreatment, and progressively declines thereafter (from 30 to 240 min). Phosphorylated p38 MAPK is not observed in response to ligation of microglial CD40 across the time course examined. Inhibition of the upstream activator of p44/42 MAPK, mitogen-activated protein/extracellular signal-related kinase kinase 1/2, with PD98059, decreases phosphorylation of p44/42 MAPK and significantly reduces TNF-alpha release following ligation of microglial CD40. Furthermore, cotreatment of microglial cells with CD40 ligand and TGF-beta1 or IL-10, or both, inhibits CD40-mediated activation of p44/42 MAPK and production of TNF-alpha in a statistically interactive manner. Taken together, these data show that ligation of microglial CD40 triggers TNF-alpha release through the p44/42 MAPK pathway, an effect that can be opposed by TGF-beta1 and IL-10.     

The influence of nutritional state on shoal choice in zebrafish, Danio rerio

We investigated the mechanisms and functions of shoal choice in relation to nutritional state in the zebrafish. Single fish that had been well fed or food deprived for 2 days were presented with a choice between two stimulus shoals. Food-deprived test fish showed a significant preference for well-fed stimulus fish over food-deprived ones whereas well-fed test fish did not exhibit any significant preference. Subsequent experiments showed that food-deprived test fish had a significantly higher foraging success in shoals consisting of well-fed individuals than in ones that comprised food-deprived fish. No difference in the locomotory behaviour of food-deprived and well-fed stimulus fish was found with respect to the proportion of time spent swimming (as opposed to being motionless), the proportion of time spent in the upper part of the test tank and the number of sharp turns. However, body weight, stomach width (measured directly behind the pectoral girdle) and ventro-dorsal height significantly decreased over a 48-h food-deprivation period. The potential use of the latter factors for the recognition of food-deprived individuals is discussed. Copyright 1999 The Association for the Study of Animal Behaviour.     

Use of 16S-rRNA Based Techniques to Investigate the Ecological Succession of Microbial Populations in the Immature Lamb Rumen: Tracking of a Specific Strain of Inoculated Ruminococcus and Interactions with Other Microbial Populations in Vivo

Abstract The establishment of microorganisms in the rumen is a critical step if rumen manipulation is to be accomplished by use of microbial inoculants. Microbial populations in the maturing rumen undergo successional changes and, while in a state of flux, provide a possible opportunity for the introduction of specific strains of bacteria. While the rumen of the young lamb was maturing, we measured changes in several microbial populations with 16S-rRNA specific oligonucleotides: Rumincoccus, Fibrobacter, eukaryotes, Gram-positive bacteria, the Bacteroides–Porphromonas–Prevotella group, and anaerobic rumen fungi. In this study we repeatedly dosed 15 lambs with approximately 3.4 × 10⁸ to 0.8 × 10⁹ Ruminococcus cells dose^-1, twice a week, for 7 wk from 23 d to 63 d of age. Of the five Ruminococcus strains dosed (R. albus SY3 and AR67, and R. flavefaciens Y1, LP9155, and AR72) the most specific primers (based on 16S rDNA) were obtained for strain SY3. There was an increase in the eukaryotic population during dosing, and it was hypothesized that protozoal predation contributed to the disappearance of strain SY3. At the end of dosing PCR amplification showed that SY3 were approximately 10⁹ cells ml^-1, but decreased to below the detection limit of the PCR system (8.6 × 10⁴ ml^-1) within 28 d postdosing. These experiments showed that fibrolytic populations increased significantly (P < 0.1) above the controls during the dosing period and were elevated for several days postdosing. This suggests that dosing of highly fibrolytic bacteria makes more of the fiber available to other organisms able to degrade fiber, and in so doing increases the overall fibrolytic activity of the rumen. Examination of the succession of gram-positive bacteria and the Bacteroides–Porphromonas–Prevotella group showed a decline in relative abundance as the lambs matured. Received: 13 April 1999; Accepted: 14 July 1999; Online Publication: 15 February 2000