Therapeutic Hypothermia Enhances Cold-Inducible RNA-Binding Protein Expression and Inhibits Mitochondrial Apoptosis in a Rat Model of Cardiac Arrest

Abstract

Therapeutic hypothermia is well known for its protective effect against brain injury after cardiac arrest, but the exact mechanism remains unclear. Cold-inducible RNA-binding protein (CIRP), a member of cold shock protein, enables mammalian cells to withstand decreased temperature by regulating gene translation. However, the role of CIRP in global cerebral ischemia after therapeutic hypothermia has not been clearly elucidated. In the present study, rats resuscitated from 4 min of cardiac arrest were separately treated with therapeutic hypothermia (immediately after return of spontaneous circulation (ROSC); targeted temperature at 33 °C) and therapeutic normothermia (targeted temperature at 36.8 °C) for 6 h. The hippocampus was harvested at 0 h (baseline), 6 h, 12 h, 1 day, 3 days, and 7 days after ROSC. The expression of CIRP messenger RNA (mRNA) was assessed by real-time PCR. CIRP and mitochondrial apoptosis-associated proteins were tested by Western blot. The histological changes and neurological function were respectively evaluated by hematoxylin-eosin staining and neurological deficit score (NDS). Compared with baseline, rats resuscitated from cardiac arrest showed increased expression of CIRP, Bax, Caspase 9, and Caspase 3 and decreased expression of Bcl-2 in hippocampus (P < 0.05). However, therapeutic hypothermia after ROSC alleviated the alterations of Bax, Caspase 9, Caspase 3, and Bcl-2, while further increased the hippocampal expression of CIRP mRNA and protein, when compared with the normothermia rats (P < 0.05). In addition, compared with the therapeutic normothermia rats, histopathological damage in CA1 zone and NDS were respectively decreased and increased in the hypothermia rats (P < 0.05). Our findings suggest that 32 °C therapeutic hypothermia exerts an important neuroprotective effects by up-regulating CIRP expression and inhibiting mitochondrial apoptosis factor production in the cardiac arrest rat model.

Recent progress in the research of cold-inducible RNA-binding protein

“…In addition, hypothermia-induced CIRP protects cell apoptosis in TNF-α-treated BALB/3T3 cells [ 64 ], contributes to the preservation of the stemness of neural stem cells [ 65 ], prevents cell apoptosis upon EGF deprivation [ 65 ], and inhibits cell apoptosis in primary rat cortical neurons in response to H 2 O 2 treatment [ 66 ] or long-term cell culture in vitro [ 67 ]. CIRP induction upon therapeutic hypothermia was also reported to improve neurological outcomes, and inhibited mitochondrial apoptosis in the cardiac arrest rat model [ 68 ] and in traumatic brain in vivo [ 69 ]. Taken together, these studies demonstrated a critical role of CIRP in regulating cell survival and protecting against cell apoptosis.…”

Extracellular CIRP (eCIRP) and inflammation

“…The precise effects of these variants in the protein structure and function remain to be adequately studied. The shortest transcript is mostly expressed at 37°C, whereas two other longer transcripts harboring an internal ribosome entry site are expressed at 32°C . During hypothermia, the core and alternate promoters and an alternative splicing tool become active for generating CIRP's transcripts .…”

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

“…Many studies have revealed that CIRP mediates, at least partially, the hypothermic protection of cells from apoptosis. Specifically, CIRP suppresses apoptosis in neural stem cells [ 95 ] and cortical neurons probably through mitochondrial pathways [ 96 ], which might mediate the protective effect of therapeutic hypothermia [ 97 ]. The inhibition of p53, Fas, and caspase-3 pathways also contributes to CIRP-mediated anti-apoptotic effects [ 57 , 98 , 99 ].…”