Hyperoxia Causes Maturation-Dependent Cell Death in the Developing White Matter

Abstract

Periventricular leukomalacia is the predominant injury in the preterm infant leading to cerebral palsy. Oxygen exposure may be an additional cause of brain injury in these infants. In this study, we investigated pathways of maturation-dependent oligodendrocyte (OL) death induced by hyperoxia in vitro and in vivo. Developing and mature OLs were subjected to 80% oxygen (0 -24 h). Lactate dehydrogenase (LDH) assay was used to assess cell viability. Furthermore, 3-, 6-, and 10-d-old rat pups were subjected to 80% oxygen (24 h), and their brains were processed for myelin basic protein staining. Significant cell death was detected after 6 -24 h incubation in 80% oxygen in pre-OLs (O4ϩ,O1Ϫ), but not in mature OLs (MBPϩ). Cell death was executed by a caspase-dependent apoptotic pathway and could be blocked by the pan-caspase inhibitor zVAD-fmk. Overexpression of BCL2 (Homo sapiens B-cell chronic lymphocytic leukemia/lymphoma 2) significantly reduced apoptosis. Accumulation of superoxide and generation of reactive oxygen species (ROS) were detected after 2 h of oxygen exposure. Lipoxygenase inhibitors 2,3,5-trimethyl-6-(12-hydroxy-5-10-dodecadiynyl-1,4-benzoquinone and N-benzyl-N-hydroxy-5-phenylpentamide fully protected the cells from oxidative injury. Overexpression of superoxide dismutase (SOD1) dramatically increased injury to pre-OLs but not to mature OLs. We extended these studies by testing the effects of hyperoxia on neonatal white matter. Postnatal day 3 (P3) and P6 rats, but not P10 pups, showed bilateral reduction in MBP (myelin basic protein) expression with 24 h exposure to 80% oxygen. Hyperoxia causes oxidative stress and triggers maturation-dependent apoptosis in pre-OLs, which involves the generation of ROS and caspase activation, and leads to white matter injury in the neonatal rat brain. These observations may be relevant to white matter injury observed in premature infants.

Longitudinal diffusion tensor and manganese-enhanced MRI detect delayed cerebral gray and white matter injury after hypoxia–ischemia and hyperoxia

“…In contrast, this normalization was not seen among HI+hyperoxia, possibly indicating an irreversible effect of hyperoxia on immature white matter. This is in agreement with emerging evidence of selective vulnerability of white matter to prolonged hyperoxia exposure during the first postnatal week in rats (29), leading to long-term reduction in FA of corpus callosum (32). The observation of activated microglia in white matter supports the hypothesis that these cells, abundant in developing white matter, are key effectors in the pathogenesis of injury to perinatal white matter (4).…”

“…White matter deviations are often seen in preterm infants (28), and both hypoxia and ischemia, as well as hyperoxia, are thought to play an important role in the pathogenesis (4,29). During normal maturational development of white matter in rats, increasing FA and decreasing radial diffusivity observed during the first postnatal weeks are thought to be related to increasing oligodendrocyte coverage and myelination of white matter tracts (30,31).…”

Aberrant Rab11-Dependent Trafficking of the Neuronal Glutamate Transporter EAAC1 Causes Oxidative Stress and Cell Death in Huntington's Disease

“…Carboxy-DCFDA is a cellpermeable nonfluorescent dye that is oxidized into highly green fluorescent DCF in the presence of oxidants, including ROS. The intensity of fluorescence of DCF generated from carboxy-DCFDA is proportional to the amount of ROS in cells (Pérez-Severiano et al, 2004;Kirkland et al, 2007;Gerstner et al, 2008;Vaughn and Deshmukh, 2008). We found that both WT and HD 140Q/140Q neurons exhibited DCF signal in the somata and neurites.…”

Effect of oxygen inhalation on cerebral blood flow velocity in premature neonates

“…It has been observed in experimental animals that hyperoxemia increases apoptotic cell death and white matter damage (14,15). The vulnerability to oxygen-induced cell death is age dependent and the maximal incidence is observed during the first week of life (16).…”