The Hypothermic Influence on CHOP and Ero1-α in an Endoplasmic Reticulum Stress Model of Cerebral Ischemia

Abstract

Hypoxia induced endoplasmic reticulum stress causes accumulation of unfolded proteins in the endoplasmic reticulum and activates the unfolded protein response, resulting in apoptosis through CCAAT-enhancer-binding protein homologous protein (CHOP) activation. In an in vitro and in vivo model of ischemic stroke, we investigated whether hypothermia regulates the unfolded protein response of CHOP and Endoplasmic reticulum oxidoreductin-α (Ero1-α), because Ero1-α is suggested to be a downstream CHOP target. The gene expression of CHOP and Ero1-α was measured using Quantitative-PCR (Q-PCR) in rat hippocampi following global cerebral ischemia, and in hypoxic pheochromocytoma cells during normothermic (37 °C) and hypothermic (31 °C) conditions. As a result of ischemia, a significant increase in expression of CHOP and Ero1-α was observed after three, six and twelve hours of reperfusion following global ischemia. A stable increase in CHOP expression was observed throughout the time course (p < 0.01, p < 0.0001), whereas Ero1-α expression peaked at three to six hours (p < 0.0001). Induced hypothermia in hypoxia stressed PC12 cells resulted in a decreased expression of CHOP after three, six and twelve hours (p < 0.0001). On the contrary, the gene expression of Ero1-α increased as a result of hypothermia and peaked at twelve hours (p < 0.0001). Hypothermia attenuated the expression of CHOP, supporting that hypothermia suppress endoplasmic reticulum stress induced apoptosis in stroke. As hypothermia further induced up-regulation of Ero1-α, and since CHOP and Ero1-α showed differential regulation as a consequence of both disease (hypoxia) and treatment (hypothermia), we conclude that they are regulated independently.

Cold-inducible proteins CIRP and RBM3, a unique couple with activities far beyond the cold

“…Notably, although RBM3 is induced by hypothermia, hypothermia itself can activate UPR without inducing apoptosis [ 42 ]. Upon ischemia-induced prolonged ER stress, hypothermia has a protective effect by suppressing UPR to prevent apoptosis [ 174 ], in accordance with Zhu et al’s report [ 47 ].…”

CAAT/enhancer binding protein–homologous protein deficiency attenuates liver ischemia/reperfusion injury in mice

“…(33) The relationship between CHOP and IRI of other organs has also been reported. In the kidney and cerebellum, elevation of CHOP expression induced by IRI continues until after 24 hours, (22,34) whereas CHOP expression peaks at 0.5 hours after reperfusion in myocardial reperfusion injury. (21) In our liver IRI model, CHOP expression peaked at 3 hours after reperfusion at mRNA and protein levels.…”

Cold‐inducible RBM3 inhibits PERK phosphorylation through cooperation with NF90 to protect cells from endoplasmic reticulum stress

“…A hallmark of hypothermia in mammalian cells is the general inhibition of protein synthesis, which is regulated through an increase in phosphorylated eIF2α (33) and by a pathway involving eukaryotic elongation factor 2 (34, 35). Furthermore, hypothermia attenuates ER stress‐induced apoptosis through CHOP in rat models of cerebral ischemia (4, 36). This finding was confirmed by our data, which indicate that moderate hypothermia attenuates PERK and eIF2α phosphorylation and subsequent apoptosis in the presence of ER stress (Figs.…”