Host inflammatory response governs fitness in an avian ectoparasite, the northern fowl mite (Ornithonyssus sylviarum)

Vertebrate immune responses to ectoparasites influence pathogen transmission and host fitness costs. Few studies have characterized natural immune responses to ectoparasites and resultant fitness effects on the ectoparasite. These are critical gaps in understanding vertebrate-ectoparasite interaction, disease ecology and host-parasite co-adaptation. This study focused on an ectoparasite of birds—the northern fowl mite (NFM) (Ornithonyssus sylviarum). Based on prior evidence that chickens develop resistance to NFM, these experiments tested two hypotheses: (i) skin inflammation blocks mite access to blood, impairing development, reproduction and survival; and (ii) host immunogenetic variation influences the inflammatory response and subsequent effects on the ectoparasite. On infested hosts, histology of skin inflammation revealed increased epidermal cell number and size, immigration of leukocytes and deposition of serous exudates on the skin surface. Survival of adult mites and their offspring decreased as the area of skin inflammation increased during an infestation. Inflammation increased the distance to blood vessels beyond the length of mite mouthparts (100-160 μm) and prevented protonymphs and adults from reaching a blood source. Consequently, protonymphs could not complete development, evidenced by a significant inverse relationship between inflammation and protonymph feeding success, as well as an increasing protonymph/adult ratio. Adult females were unable to feed and reproduce, indicated by an inverse relationship between inflammation and egg production, and decreasing female/juvenile ratio. These combined impacts of host inflammation reversed NFM population growth. Intensity of inflammation was influenced by the genotype of the major histocompatibility complex (MHC), supporting previous research that linked these immunological loci with NFM resistance. Overall, these data provide a model for a mechanism of avian resistance to an ectoparasitic arthropod and the fitness costs to the parasite of that host defense.     

A Mutation in Transmembrane Domain 7 (TM7) of Excitatory Amino Acid Transporters Disrupts the Substrate-dependent Gating of the Intrinsic Anion Conductance and Drives the Channel into a Constitutively Open State

In the mammalian central nervous system, excitatory amino acid transporters (EAATs) are responsible for the clearance of glutamate after synaptic release. This energetically demanding activity is crucial for precise neuronal communication and for maintaining extracellular glutamate concentrations below neurotoxic levels. In addition to their ability to recapture glutamate from the extracellular space, EAATs exhibit a sodium- and glutamate-gated anion conductance. Here we show that substitution of a conserved positively charged residue (Arg-388, hEAAT1) in transmembrane domain 7 with a negatively charged amino acid eliminates the ability of glutamate to further activate the anion conductance. When expressed in oocytes, R388D or R388E mutants show large anion currents that display no further increase in amplitude after application of saturating concentrations of Na⁺ and glutamate. They also show a substantially reduced transport activity. The mutant transporters appear to exist preferentially in a sodium- and glutamate-independent constitutive open channel state that rarely transitions to complete the transport cycle. In addition, the accessibility of cytoplasmic residues to membrane-permeant modifying reagents supports the idea that this substrate-independent open state correlates with an intermediate outward facing conformation of the transporter. Our data provide additional insights into the mechanism by which substrates gate the anion conductance in EAATs and suggest that in EAAT1, Arg-388 is a critical element for the structural coupling between the substrate translocation and the gating mechanisms of the EAAT-associated anion channel.     

Metapopulation structure,population trends,and status of Florida Grasshopper Sparrows

ABSTRACT The federally Endangered Florida Grasshopper Sparrow (FGSP, Ammodramus savannarum floridanus) is endemic to dry prairie habitat in central Florida and is currently only found at three public management areas (Avon Park Air Force Range, APAFR; Kissimmee Prairie Preserve State Park, KPPSP; and Three Lakes Wildlife Management Area, TLWMA). We analyzed long‐term (1991–2008) point‐count data to compare population trends of FGSPs at these management areas to determine if they function as independent populations by using Spearman's rank correlation to test for independence between annual trends. We also examined banding and resighting data to infer metapopulation structure. Populations fluctuated across years at all three sites, declining significantly at APAFR (r_s=?0.89, P < 0.001, N= 13) and KPPSP (r_s=?0.78, P= 0.004, N= 11) and remaining stable at TLWMA (r_s= 0.19, P= 0.46, N= 17). Population trends among the three management areas appeared independent (absolute value of r_s≤ 0.50, P≥ 0.12). Previous studies indicated that sparrows in the three areas were not genetically differentiated, and two cases of dispersal between APAFR and KPPSP have been documented. However, dispersal rates among areas appear to be too low to influence demographic dynamics within individual areas. Within APAFR, FGSPs are aggregated into three spatially distinct habitat patches previously considered separate populations, but dispersal among these patches is more frequent than previously reported and population trends among these patches are correlated (r_s≥ 0.91, P < 0.001). These patterns suggest that a single metapopulation of FGSPs exists consisting of three distinct populations (APAFR, KPPSP, and TLWMA), and the spatially distinct aggregations at APAFR constitute a single population using several habitat patches. The population at APAFR is at risk of extirpation, and immediate action is needed if that population is to recover. Taking broader metapopulation dynamics into account will be useful for guiding management efforts aimed at conserving the FGSP in the broader central Florida landscape.     

Pharmacologic inhibition of S-nitrosoglutathione reductase protects against experimental asthma in BALB/c mice through attenuation of both bronchoconstriction and inflammation

Background

S-nitrosoglutathione (GSNO) serves as a reservoir for nitric oxide (NO) and thus is a key homeostatic regulator of airway smooth muscle tone and inflammation. Decreased levels of GSNO in the lungs of asthmatics have been attributed to increased GSNO catabolism via GSNO reductase (GSNOR) leading to loss of GSNO- and NO- mediated bronchodilatory and anti-inflammatory actions. GSNOR inhibition with the novel small molecule, N6022, was explored as a therapeutic approach in an experimental model of asthma.

Methods

Female BALB/c mice were sensitized and subsequently challenged with ovalbumin (OVA). Efficacy was determined by measuring both airway hyper-responsiveness (AHR) upon methacholine (MCh) challenge using whole body plethysmography and pulmonary eosinophilia by quantifying the numbers of these cells in the bronchoalveolar lavage fluid (BALF). Several other potential biomarkers of GSNOR inhibition were measured including levels of nitrite, cyclic guanosine monophosphate (cGMP), and inflammatory cytokines, as well as DNA binding activity of nuclear factor kappa B (NFκB). The dose response, onset of action, and duration of action of a single intravenous dose of N6022 given from 30 min to 48 h prior to MCh challenge were determined and compared to effects in mice not sensitized to OVA. The direct effect of N6022 on airway smooth muscle tone also was assessed in isolated rat tracheal rings.

Results

N6022 attenuated AHR (ED₅₀ of 0.015?±?0.002 mg/kg; Mean?±?SEM) and eosinophilia. Effects were observed from 30 min to 48 h after treatment and were comparable to those achieved with three inhaled doses of ipratropium plus albuterol used as the positive control. N6022 increased BALF nitrite and plasma cGMP, while restoring BALF and plasma inflammatory markers toward baseline values. N6022 treatment also attenuated the OVA-induced increase in NFκB activation. In rat tracheal rings, N6022 decreased contractile responses to MCh.

Conclusions

The significant bronchodilatory and anti-inflammatory actions of N6022 in the airways are consistent with restoration of GSNO levels through GSNOR inhibition. GSNOR inhibition may offer a therapeutic approach for the treatment of asthma and other inflammatory lung diseases. N6022 is currently being evaluated in clinical trials for the treatment of inflammatory lung disease.     

Chromosomal mapping and candidate gene discovery of chicken developmental mutants and genome-wide variation analysis of MHC congenics

The chicken has been widely used in experimental research given its importance to agriculture and its utility as a model for vertebrate biology and biomedical pursuits for over 100 years. Herein we used advanced technologies to investigate the genomic characteristics of specialized chicken congenic genetic resources developed on a highly inbred background. An Illumina 3K chicken single nucleotide polymorphism (SNP) array was utilized to study variation within and among major histocompatibility complex (MHC)-congenic lines as well as investigate line-specific genomic diversity, inbreeding coefficients, and MHC B haplotype-specific GGA 16 SNP profiles. We also investigated developmental mutant-congenic lines to map a number of single-gene mutations using both the Illumina 3K array and a recently developed Illumina 60K chicken SNP array. In addition to identifying the chromosomes and specific subregions, the mapping results affirmed prior analyses indicating recessive or dominant and autosomal or sex chromosome modes of inheritance. Priority candidate genes are described for each mutation based on association with similar phenotypes in other vertebrates. These single-gene mutations provide a means of studying amniote development and in particular serve as invaluable biomedical models for similar malformations found in human.