The Integrated Stress Response in Hypoxia-Induced Diffuse White Matter Injury

Abstract

Currently no treatments exist for preterm infants with diffuse white matter injury (DWMI) caused by hypoxia. Due to the improved care of preterm neonates and increased recognition by advanced imaging techniques, the prevalence of DWMI is increasing. A better understanding of the pathophysiology of DWMI is therefore of critical importance. The integrated stress response (ISR), a conserved eukaryotic response to myriad stressors including hypoxia, may play a role in hypoxia-induced DWMI and may represent a novel target for much needed therapies. In this study, we use in vitro and in vivo hypoxic models of DWMI to investigate whether the ISR is involved in DWMI. We demonstrate that hypoxia activates the ISR in primary mouse oligodendrocyte precursor cells (OPCs) in vitro and that genetically inhibiting the ISR in differentiating OPCs increases their susceptibility to in vitro hypoxia. We also show that a well established in vivo mild chronic hypoxia (MCH) mouse model and a new severe acute hypoxia (SAH) mouse model of DWMI activates the initial step of the ISR. Nonetheless, genetic inhibition of the ISR has no detectable effect on either MCH-or SAH-induced DWMI. In addition, we demonstrate that genetic enhancement of the ISR does not ameliorate MCH-or SAH-induced DWMI. These studies suggest that, while the ISR protects OPCs from hypoxia in vitro, it does not appear to play a major role in either MCH-or SAH-induced DWMI and is therefore not a likely target for therapies aimed at improving neurological outcome in preterm neonates with hypoxia-induced DWMI.

Non-Canonical Targets of HIF1a Drive Cell-Type-Specific Dysfunction

“…MCH is a well described model of Diffuse White Matter Injury (DWMI) (Clayton et al, 2017a; Clayton et al, 2017b; Fancy et al, 2011; Scafidi et al, 2014; Yuen et al, 2014) and protein samples were generously provided by Brian Popko. In brief, postnatal day 3 (P3) C57Bl6 pups were placed into a BioSpherix chamber maintained at 10+/- 0.5% O2 by displacement of nitrogen until P11.…”

“…In brief, postnatal day 3 (P3) C57Bl6 pups were placed into a BioSpherix chamber maintained at 10+/- 0.5% O2 by displacement of nitrogen until P11. Animals were then quickly sacrificed by CO 2 asphyxiation followed by decapitation and the frontal cortex was isolated as this region has been shown to contain subcortical white matter that is susceptible to hypoxia-induced DWMI (Clayton et al, 2017b; Jablonska et al, 2012; Sanjana et al, 2014; Yuen et al, 2014).…”

Non-canonical Targets of HIF1a Impair Oligodendrocyte Progenitor Cell Function

“…Tissue from mild chronic hypoxia (MCH) mice MCH is a well described model of Diffuse White Matter Injury (DWMI) (Clayton et al, 2017a(Clayton et al, , 2017bFancy et al, 2011;Scafidi et al, 2014;Yuen et al, 2014) and protein samples were generously provided by Brian Popko. In brief, postnatal day 3 (P3) C57Bl6 pups were placed into a BioSpherix chamber maintained at 10+/À 0.5% O2 by displacement of nitrogen until P11.…”

Intranasal IL-4 Administration Alleviates Functional Deficits of Periventricular Leukomalacia in Neonatal Mice

“…We established the preterm PVL model by placing mice in severe acute hypoxia or room air conditions, according to the methods described by Clayton et al with brief modification ( 33 ). It was observed that reduced myelination due to a disrupted oligodendrocyte progenitor (preOL) pool contributes to PVL.…”

“…All the male pups were randomly divided into three groups: the normoxia group (Control), the hypoxia-induced saline-treated group (Hypoxia), and the hypoxia-induced IL-4-treated group (Hypoxia + IL-4 group). The PVL animal model was established according to Clayton et al and Shen et al with modification ( 33 , 34 ). Given the unstable state of C57BL/6 mice under hypoxic environments, all the male pups were fostered to gestational age-matched lactating CD1 (ICR) dams at postnatal day 1 (P1).…”