Therapeutic hypothermia has emerged as an effective neuroprotective
therapy for
cardiac arrest survivors. There are a number of purported mechanisms for
therapeutic hypothermia, but the exact mechanism still remains to be elucidated. Although
hypothermia generally down-regulates
protein synthesis and metabolism in mammalian cells, a small subset of homologous (>70%)
cold-shock proteins (RNA-binding motif
protein 3, RBM3 and cold-inducible
RNA-binding protein, CIRP) are induced under these conditions. In addition, RBM3 up-regulation in neuronal cells has recently been implicated in
hypothermia-induced neuroprotection. Therefore, we compared the effects of moderate (33.5°C) and deep (17°C)
hypothermia with normothermia (37°C) on the regulation of RBM3 and CIRP expressions in murine organotypic hippocampal slice cultures (OHSC), hippocampal neuronal cells (HT-22), and microglia cells (BV-2). Moderate
hypothermia resulted in significant up-regulation of both RBM3 and CIRP
mRNA in murine OHSC, but deep hyporthermia did not. RBM3
protein regulation was also significantly up-regulated by 33.5°C, but no significant up-regulation of CIRP
protein was observed in the OHSC. Additionally, OHSC exposed to 17°C for 24h were positive for
Propidium Iodide (PI) immunostaining, indicating the onset of cell death. Similarly, RBM3 gene expression in a HT-22 neuronal cells mono-culture and direct co-culture of HT-22 neuronal cells with BV-2 microglia cells were also up-regulated at 33.5°C but only in the co-culture at 17°C. No significant up-regulation of RBM3 nor CIRP gene expression were observed in a BV-2 mono-culture at either temperature. We observed that RBM3
mRNA and
protein expressions in murine OHSC, as well as in mono-culture of HT-22 neuronal cells and direct co-culture of HT-22 neuronal cells with BV-2 microglia cells were significantly up-regulated by exposure to moderate
hypothermia. These findings further support the implication of RBM3 as a potential effector for
hypothermia-induced neuroprotection.