Novel role for the δ-opioid receptor in hypoxic preconditioning in rat retinas

δ-Opioid receptor (DOR) is an oxygen-sensitive protein whose function in the rat retina is unknown. We examined whether DOR is involved in hypoxic preconditioning (HPC)-mediated retinoprotection following intraocular pressure (IOP) elevation. Rats were exposed to intermittent hypoxia (10% oxygen) to induce HPC. Unilateral retinal ischemia/reperfusion injury was induced by elevating IOP to 100 mmHg for 1 h. HPC attenuated the loss of neuronal marker expression and increased pro-apoptotic caspase 3 activity in the IOP retina. Excess superoxide production and 8-iso-prostaglandin F2α accumulation caused by enhanced oxidant protein expression and reduced antioxidant enzyme level after IOP elevation were largely abrogated by HPC. HPC markedly increased the expression of hypoxia-inducible factor-1α (HIF-1α) and DOR, but intravitreal administration of HIF-1α-specific small interfering RNA abrogated the up-regulation of DOR. This suggested that DOR functions downstream of HIF-1α. However, the endogenous content of leucine enkephalin in retinas was not affected by HPC or IOP. Treatment of retinas with the DOR antagonist naltrindole attenuated the HPC-induced protection and activation of extracellular signal-regulated kinase. These results suggest a novel mechanism of HPC-mediated retinoprotection whereby HIF-1α induces the expression of DOR, and DOR-mediated activation of extracellular signal-regulated kinase triggers cellular events that correct the redox imbalance in the post-ischemic retina.     

p75NTR-dependent modulation of cellular handling of reactive oxygen species

Our previous studies demonstrated that p75NTR confers protection against oxidative stress-induced apoptosis upon PC12 cells; however, the mechanisms responsible for this effect are not known. The present studies reveal decreased mitochondrion membrane potential and increased generation of reactive oxygen species (ROS) in p75NTR-deficient PC12 cells as well as diminution of ROS generation after transfection of a full-length p75NTR construct into these cells. They also show that p75NTR deficiency attenuates activation of the phosphatidylinositol 3-kinase → phospho-Akt/protein kinase B pathway in PC12 cells by oxidative stress or neurotrophic ligands and inhibition of Akt phosphorylation decreases the glutathione (GSH) content in PC12 cells. In addition, decreased de novo GSH synthesis and increased GSH consumption are observed in p75NTR-deficient cells. These findings indicate that p75NTR regulates cellular handling of ROS to effect a survival response to oxidative stress.     

Validation of Fecal Glucocorticoid Metabolite Assays for South African Herbivores

ABSTRACT Fecal glucocorticoid metabolite (FGM) assays are a popular means of monitoring adrenocortical activity (i.e., physiological stress response) in wildlife. Species-specific differences in glucocorticoid metabolism and excretion require assay validation, including both laboratory and biological components, before assay use in new species. We validated a commercially available radioimmunoassay (MP ¹²⁵I corticosterone RIA kit [MP Biomedicals, Solon, OH]) for measuring FGMs of several South African herbivores, including giraffe (Giraffa camelopardalis), impala (Aepyceros melampus), nyala (Tragelaphus buxtoni), kudu (Tragelaphus strepsiceros), wildebeest (Connochaetes taurinus), and zebra (Equus burchelli). These herbivores are important in South African parks and reserves for ecotourism and as a prey base for predators and serve an integral role in ecosystem processes. Standard biochemical validations (e.g., recovery of exogenous corticosterone, intra- and interassay variation, and parallelism) demonstrated that the assay accurately and precisely measured FGMs of all 6 herbivore species. Our biological validations demonstrated that the assay was sensitive enough to detect changes in FGM production associated with season. Samples collected during the dry season (Jun-Aug) contained higher FGM concentrations than those from the wet season (Dec-Feb) in all species. We established optimal sample dilutions and reference FGM levels for these 6 herbivores, which can now be used to monitor the effects of management and ecotourism activities on the stress responses of these herbivores.     

Physiological Stress Response of Captive White-Tailed Deer to Video Collars

ABSTRACT Animal-borne video and environmental data collection systems (AVEDs) are an advanced form of biotelemetry that combines video with other sensors. As a proxy for physiological stress, we assessed fecal glucocorticoid metabolite (FGM) excretion in 7 white-tailed deer (Odocoileus virginianus) fitted with AVED dummy collars; 9 additional deer served as controls. We collected fecal samples over 3 2-week periods: pretreatment, treatment, and posttreatment periods. There were no differences in FGMs across time periods (F_2,218 = 1.94, P = 0.147) and no difference between FGMs of control and treatment individuals (F_1,14 = 0.72, P = 0.411). Fecal glucocorticoid metabolite excretion in AVED-collared deer was indistinguishable from uncollared animals and within the normal, baseline range for this species. Absence of an adrenal response to collaring suggested that AVED collaring does not induce physiological stress in deer.     

Biotic and abiotic stress down-regulate miR398 expression in Arabidopsis

MicroRNA398 targets two Cu/Zn superoxide dismutases (CSD1 and CSD2) in higher plants. Previous investigations revealed both decreased miR398 expression during high Cu²⁺ or paraquat stress and increased expression under low Cu²⁺ or high sucrose in the growth medium. Here, we show that additional abiotic stresses such as ozone and salinity also affect miR398 levels. Ozone fumigation decreased miR398 levels that were gradually restored to normal levels after relieved from the stress. Furthermore, miR398 levels decreased in Arabidopsis leaves infiltrated with avirulent strains of Pseudomonas syringae pv. tomato, Pst DC3000 (avrRpm1 or avrRpt2) but not the virulent strain Pst DC3000. To our knowledge, miR398 is the first miRNA shown to be down-regulated in response to biotic stress (P. syringae). CSD1, but not CSD2, mRNA levels were negatively correlated with miR398 levels during ozone, salinity and biotic stress, suggesting that CSD2 regulation is not strictly under miR398 control during diverse stresses. Overall, this study further establishes a link between oxidative stress and miR398 in Arabidopsis.