ABSTRACT
BACKGROUND: Hypoxic preconditioning (HPc) protects the neonatal brain in the setting of hypoxia-ischemia (HI). The mechanisms of protection may depend on activation of hypoxia-inducible factor (HIF-1α). This study sought to clarify the role of HIF-1α after HPc and HI. METHODS: To induce HPc, HIF-1α knockout and wild-type (WT) mice were exposed to hypoxia at postnatal day 6. At day 7, the mice underwent HI. Brain injury was determined by histology. HIF-1α, downstream targets, and markers of cell death were measured by western blot. RESULTS: HPc protected the WT brain compared with WT without HPc, but did not protect the HIF-1α knockout brain. In WT, HIF-1α increased after hypoxia and after HI, but not with HPc. The HIF-1α knockout showed no change in HIF-1α after hypoxia, HI, or HPc/HI. After HI, spectrin 145/150 was higher in HIF-1α knockout, but after HPc/HI, it was higher in WT. Lysosome-associated membrane protein was higher in WT early after HI, but not later. After HPc/HI, lysosome-associated membrane protein was higher in HIF-1α knockout. CONCLUSION: These results indicate that HIF-1α is necessary for HPc protection in the neonatal brain and may affect cell death after HI. Different death and repair mechanisms depend on the timing of HPc.
Subject(s)
Brain/metabolism , Hypoxia-Inducible Factor 1, alpha Subunit/genetics , Hypoxia-Ischemia, Brain/metabolism , Hypoxia/metabolism , Animals , Animals, Newborn , Apoptosis , Brain/pathology , Brain Injuries/metabolism , Cell Death , Extracellular Signal-Regulated MAP Kinases/metabolism , Female , Genotype , Ischemic Preconditioning , Lysosomal Membrane Proteins/metabolism , Male , Mice , Mice, Knockout , Spectrin/metabolism , Time Factors , Vascular Endothelial Growth Factor A/metabolismABSTRACT
Evidence suggests that the activation of the transcription factor hypoxia-inducible factor 1 alpha (HIF-1 alpha) may promote cell survival in hypoxic or ischemic brain. To help understand the role of HIF-1 alpha in neonatal hypoxic-ischemic brain injury, mice with conditional neuron-specific inactivation of HIF-1 alpha underwent hypoxia-ischemia (HI). Mice heterozygous for Cre recombinase under the control of the calcium/calmodulin-dependent kinase II promoter were bred with homozygous 'floxed' HIF-1 alpha transgenic mice. The resulting litters produced mice with a forebrain predominant neuronal deletion of HIF-1 alpha (HIF-1 alpha(Delta)/(Delta)), as well as littermates without the deletion. In order to verify reduction of HIF-1 alpha at postnatal day 7, HIF-1 alpha(Delta)/(Delta) and wild-type mice were exposed to a hypoxic stimulus (8% oxygen) or room air for 1 h, followed by immediate collection of brain cortices for determination of HIF-1 alpha expression. Results of Western blotting of mouse cortices exposed to hypoxia stimulus or room air confirmed that HIF-1 alpha(Delta)/(Delta) cortex expressed a minimal amount of HIF-1 alpha protein compared to wild-type cortex with the same hypoxic stimulus. Subsequently, pups underwent the Vannucci procedure of HI at postnatal day 7: unilateral ligation of the right common carotid artery followed by 30 min of hypoxia (8% oxygen). Immunofluorescent staining of brains 24 h after HI confirmed a relative lack of HIF-1 alpha in the HIF-1 alpha(Delta)/(Delta) cortex compared to the wild type, and that HIF-1 alpha in the wild type is located in neurons. HIF-1 alpha expression was determined in mouse cortex 24 h after HI. Histological analysis for the degree of injury was performed 5 days after HI. HIF-1 alpha protein expression 24 h after HI showed a large increase of HIF-1 alpha in the hypoxic-ischemic cortex of the wild-type compared to the hypoxic only cortex. Histological analysis revealed that HI injury was increased in the neuronally deficient HIF-1 alpha(Delta)/(Delta) mouse brain (p < 0.05) and was more severe in the cortex. Genetic reduction of neuronal HIF-1 alpha results in a worsening of injury after neonatal HI, with a region-specific role for HIF-1 alpha in the setting of neonatal brain injury.
Subject(s)
Cerebral Cortex/pathology , Hypoxia-Inducible Factor 1, alpha Subunit/metabolism , Hypoxia-Ischemia, Brain/pathology , Neurons/pathology , Analysis of Variance , Animals , Animals, Newborn , Blotting, Western , Cerebral Cortex/metabolism , Cytoprotection , Female , Fluorescent Antibody Technique , Hypoxia/metabolism , Hypoxia/pathology , Hypoxia-Inducible Factor 1, alpha Subunit/genetics , Hypoxia-Ischemia, Brain/metabolism , Male , Mice , Mice, Transgenic , Neurons/metabolism , Statistics, Nonparametric , Up-RegulationABSTRACT
The effect of hypoxic preconditioning (PC) on hypoxic-ischemic (HI) injury was explored in glutathione peroxidase (GPx)-overexpressing mice (human GPx-transgenic [hGPx-tg]) mice. Six-day-old hGPx-tg mice and wild-type (Wt) littermates were pre-conditioned with hypoxia for 30 min and subjected to the Vannucci procedure of HI 24 h after the PC stimulus. Histopathological injury was determined 5 d later (P12). Additional animals were killed 2 h or 24 h after HI and ipsilateral cerebral cortices assayed for GPx activity, glutathione (GSH), and hydrogen peroxide (H2O2). In line with previous studies, hypoxic PC reduced injury in the Wt brain. Preconditioned Wt brain had increased GPx activity, but reduced GSH, relative to naive 24 h after HI. Hypoxic PC did not reduce injury to hGPx-tg brain and even reversed the protection previously reported in the hGPx-tg. GPx activity and GSH in hGPx-tg cortices did not change. Without PC, hGPx-tg cortex had less H2O2 accumulation than Wt at both 2 h and 24 h. With PC, H2O2 remained low in hGPx-tg compared with Wt at 2 h, but at 24 h, there was no longer a difference between hGPx-tg and Wt cortices. Accumulation of H2O2 may be a mediator of injury, but may also induce protective mechanisms.
