Hypothermia and Rewarming Activate a Macroglial Unfolded Protein Response Independent of Hypoxic-Ischemic Brain Injury in Neonatal Piglets

Abstract

Therapeutic hypothermia provides incomplete neuroprotection after hypoxia-ischemia (HI)-induced brain injury in neonates. We previously showed that cortical neuron and white matter apoptosis are promoted by hypothermia and early rewarming in a piglet model of HI. The unfolded protein response (UPR) may be one of the potential mediators of this cell death. Here, neonatal piglets underwent HI or sham surgery followed by 29 h of normothermia, 2 h of normothermia + 27 h of hypothermia or 18 h of hypothermia + rewarming. Piglets recovered for 29 h. Immunohistochemistry for endoplasmic reticulum to nucleus signaling-1 protein (ERN1), a marker of UPR activation, was used to determine the ratios of ERN1+ macroglia and neurons in the motor subcortical white matter and cerebral cortex. The ERN1+ macroglia were immunophenotyped as oligodendrocytes and astrocytes by immunofluorescent colabeling. Temperature (p = 0.046) and HI (p < 0.001) independently affected the ratio of ERN1+ macroglia. In sham piglets, sustained hypothermia (p = 0.011) and rewarming (p = 0.004) increased the ERN1+ macroglia ratio above that in normothermia. HI prior to hypothermia diminished the UPR. Ratios of ERN1+ macroglia correlated with white matter apoptotic profile counts in shams (r = 0.472; p = 0.026), thereby associating UPR activation with white matter apoptosis during hypothermia and rewarming. Accordingly, macroglial cell counts decreased in shams that received sustained hypothermia (p = 0.009) or rewarming (p = 0.007) compared to those in normothermic shams. HI prior to hypothermia neutralized the macroglial cell loss. Neither HI nor temperature affected ERN1+ neuron ratios. In summary, delayed hypothermia and rewarming activate the macroglial UPR, which is associated with white matter apoptosis. HI may decrease the macroglial endoplasmic reticulum stress response after hypothermia and rewarming.

Cerebral Autoregulation and Conventional and Diffusion Tensor Imaging Magnetic Resonance Imaging in Neonatal Hypoxic-Ischemic Encephalopathy

“…Preclinical and clinical studies of neonatal brain hypoxia suggest that rewarming may cause cytotoxic injury or otherwise may be detrimental to the brain. 16–19 The longer duration of low blood pressure and greater blood pressure variability during rewarming may have improved sensitivity for detecting these relationships (Fig 2). These observations may also reflect the withdrawal of hypothermia and highlight a potential role for autoregulation monitoring in determining the need for continued therapy.…”

Optimizing Cerebral Autoregulation May Decrease Neonatal Regional Hypoxic-Ischemic Brain Injury

“…Larger studies are needed to define the interactions between temperature and autoregulation in specific regions. Hypothermia and rewarming do not fully protect cortical grey matter and white matter from apoptotic cell death, [33–35] and blood pressure below the optimal autoregulatory level may render these regions more vulnerable to cell death. By contrast, the neuroprotection afforded by hypothermia in the putamen [36] may delay vulnerability to sub-optimal autoregulatory function until normothermia.…”

Transient temperature fluctuations severely decrease P. falciparum susceptibility to artemisinin in vitro

“…Given a recent study which indicated that the cell stress response underlies ring-stage artemisinin resistance (Zhang et al, 2017), and evidence that temperature modulations induce a similar stress response in higher eukaryotes (Lee et al, 2016; Rzechorzek et al, 2015a; Liu et al, 2013; Kim et al, 2013; Xu et al, 2011), we sought to clarify the impact of temperature variation on P. falciparum susceptibility to artemisinin in the ring stage survival assay (RSA). Unlike the methods used in previous studies, the in vitro readouts from this assay correlate well with clinical treatment outcomes (Witkowski et al, 2013).…”