Glutathione Reductase Promotes Fungal Clearance and Suppresses Inflammation during Systemic Candida albicans Infection in Mice.

Glutathione reductase (Gsr) catalyzes the reduction of glutathione disulfide to glutathione, which plays an important role in redox regulation. We have previously shown that Gsr facilitates neutrophil bactericidal activities and is pivotal for host defense against bacterial pathogens. However, it is unclear whether Gsr is required for immune defense against fungal pathogens. It is also unclear whether Gsr plays a role in immunological functions outside of neutrophils during immune defense. In this study, we report that Gsr-/- mice exhibited markedly increased susceptibility to Candida albicans challenge. Upon C. albicans infection, Gsr-/- mice exhibited dramatically increased fungal burden in the kidneys, cytokine and chemokine storm, striking neutrophil infiltration, histological abnormalities in both the kidneys and heart, and substantially elevated mortality. Large fungal foci surrounded by massive numbers of neutrophils were detected outside of the glomeruli in the kidneys of Gsr -/- mice but were not found in wild-type mice. Examination of the neutrophils and macrophages of Gsr-/- mice revealed several defects. Gsr -/- neutrophils exhibited compromised phagocytosis, attenuated respiratory burst, and impaired fungicidal activity in vitro. Moreover, upon C. albicans stimulation, Gsr -/- macrophages produced increased levels of inflammatory cytokines and exhibited elevated p38 and JNK activities, at least in part, because of lower MAPK phosphatase (Mkp)-1 activity and greater Syk activity. Thus, Gsr-mediated redox regulation is crucial for fungal clearance by neutrophils and the proper control of the inflammatory response by macrophages during host defense against fungal challenge.

In-air hearing of a diving duck: A comparison of psychoacoustic and auditory brainstem response thresholds.

Auditory sensitivity was measured in a species of diving duck that is not often kept in captivity, the lesser scaup. Behavioral (psychoacoustics) and electrophysiological [the auditory brainstem response (ABR)] methods were used to measure in-air auditory sensitivity, and the resulting audiograms were compared. Both approaches yielded audiograms with similar U-shapes and regions of greatest sensitivity (2000-3000 Hz). However, ABR thresholds were higher than psychoacoustic thresholds at all frequencies. This difference was least at the highest frequency tested using both methods (5700 Hz) and greatest at 1000 Hz, where the ABR threshold was 26.8 dB higher than the behavioral measure of threshold. This difference is commonly reported in studies involving many different species. These results highlight the usefulness of each method, depending on the testing conditions and availability of the animals.

KatG and KatE confer Acinetobacter resistance to hydrogen peroxide but sensitize bacteria to killing by phagocytic respiratory burst.

AIMS: Catalase catalyzes the degradation of H2O2. Acinetobacter species have four predicted catalase genes, katA, katE, katG, and katX. The aims of the present study seek to determine which catalase(s) plays a predominant role in determining the resistance to H2O2, and to assess the role of catalase in Acinetobacter virulence. MAIN METHODS: Mutants of Acinetobacter baumannii and Acinetobacter nosocomialis with deficiencies in katA, katE, katG, and katX were tested for sensitivity to H2O2, either by halo assays or by liquid culture assays. Respiratory burst of neutrophils, in response to A. nosocomialis, was assessed by chemiluminescence to examine the effects of catalase on the production of reactive oxygen species (ROS) in neutrophils. Bacterial virulence was assessed using a Galleria mellonella larva infection model. KEY FINDINGS: The capacities of A. baumannii and A. nosocomialis to degrade H2O2 are largely dependent on katE. The resistance of both A. baumannii and A. nosocomialis to H2O2 is primarily determined by the katG gene, although katE also plays a minor role in H2O2 resistance. Bacteria lacking both the katG and katE genes exhibit the highest sensitivity to H2O2. While A. nosocomialis bacteria with katE and/or katG were able to decrease ROS production by neutrophils, these cells also induced a more robust respiratory burst in neutrophils than did cells deficient in both katE and katG. We also found that A. nosocomialis deficient in both katE and katG was more virulent than the wildtype A. nosocomialis strain. SIGNIFICANCE: Our findings suggest that inhibition of Acinetobacter catalase may help to overcome the resistance of Acinetobacter species to microbicidal H2O2 and facilitate bacterial disinfection.

Measuring In-Air and Underwater Hearing in Seabirds.

Electrophysiological methods were used to measure the in-air hearing of 10 species of seabirds. There are currently no measures of the underwater hearing abilities of diving birds. In preparation for constructing a behavioral audiogram both in-air and underwater hearing, several species of diving ducks were raised. Because there is a considerable amount of literature on bird hearing in air, the technical setup and training methods were modeled on similar studies, with modifications to address the nature of the underwater sound field and the difficulty of the task for the birds.

A comparison of auditory brainstem responses across diving bird species.

There is little biological data available for diving birds because many live in hard-to-study, remote habitats. Only one species of diving bird, the black-footed penguin (Spheniscus demersus), has been studied in respect to auditory capabilities (Wever et al., Proc Natl Acad Sci USA 63:676-680, 1969). We, therefore, measured in-air auditory threshold in ten species of diving birds, using the auditory brainstem response (ABR). The average audiogram obtained for each species followed the U-shape typical of birds and many other animals. All species tested shared a common region of the greatest sensitivity, from 1000 to 3000 Hz, although audiograms differed significantly across species. Thresholds of all duck species tested were more similar to each other than to the two non-duck species tested. The red-throated loon (Gavia stellata) and northern gannet (Morus bassanus) exhibited the highest thresholds while the lowest thresholds belonged to the duck species, specifically the lesser scaup (Aythya affinis) and ruddy duck (Oxyura jamaicensis). Vocalization parameters were also measured for each species, and showed that with the exception of the common eider (Somateria mollisima), the peak frequency, i.e., frequency at the greatest intensity, of all species' vocalizations measured here fell between 1000 and 3000 Hz, matching the bandwidth of the most sensitive hearing range.

Post-translational regulation of mitogen-activated protein kinase phosphatase (MKP)-1 and MKP-2 in macrophages following lipopolysaccharide stimulation: the role of the C termini of the phosphatases in determining their stability.

MAPK phosphatases (MKPs) are critical modulators of the innate immune response, and yet the mechanisms regulating their accumulation remain poorly understood. In the present studies, we investigated the role of post-translational modification in the accumulation of MKP-1 and MKP-2 in macrophages following LPS stimulation. We found that upon LPS stimulation, MKP-1 and MKP-2 accumulated with different kinetics: MKP-1 level peaked at ∼1 h, while MKP-2 levels continued to rise for at least 6 h. Accumulation of both MKP-1 and MKP-2 were attenuated by inhibition of the ERK cascade. Interestingly, p38 inhibition prior to LPS stimulation had little effect on MKP-1 and MKP-2 protein levels, but hindered their detection by an M-18 MKP-1 antibody. Studies of the epitope sequence recognized by the M-18 MKP-1 antibody revealed extensive phosphorylation of two serine residues in the C terminus of both MKP-1 and MKP-2 by the ERK pathway. Remarkably, the stability of both MKP-1 and MKP-2 was markedly decreased in macrophages in the presence of an ERK pathway inhibitor. Mutation of the two C-terminal serine residues in MKP-1 and MKP-2 to alanine decreased their half-lives, while mutating these residues to aspartate dramatically increased their half-lives. Deletion of the C terminus from MKP-1 and MKP-2 also considerably increased their stabilities. Surprisingly, enhanced stabilities of the MKP-1 and MKP-2 mutants were not associated with decreased ubiquitination. Degradation of both MKP-1 and MKP-2 was attenuated by proteasomal inhibitors. Our studies suggest that MKP-1 and MKP-2 stability is regulated by ERK-mediated phosphorylation through a degradation pathway independent of polyubiquitination.

Trust in the provider and glaucoma-related blindness.

Purpose. We hypothesized that lower trust in the physician is associated with worse visual outcomes in glaucoma. Methods. Subjects completed the Trust in Provider Scale (TPS) and performed visual field tests at least two years apart. The primary outcome was glaucoma-related blindness. Results. Subjects with glaucoma-related blindness scored lower on the TPS (74.9 ± 7.4, n = 21) than subjects without blindness (78.8 ± 6.9, n = 39; P = 0.04). In white subjects, TPS scores were similar for blind (77.1 ± 7.7, n = 12) versus not blind subjects (76.4 ± 6.7, n = 10; P = 0.82). For nonwhite subjects, TPS scores were lower for blind (72.0 + 6.2, n = 9) versus not blind subjects (79.6 ± 6.9, n = 29; P = 0.005). In multiple regression models, the interaction between race and trust was significant (P = 0.007), indicating that the increase in odds for blindness with each unit decrease in TPS score was different for white versus nonwhite subjects. Discussion. Glaucoma patients' trust in the physician is associated with glaucoma-related blindness in this study. The association between lower trust in the physician with blindness in patients of nonwhite race deserves further attention as we strive to reduce disparities in visual outcomes.