Activation of hypoxia-inducible factor-1α in rat brain after perinatal anoxia: role of body temperature

Abstract

Transcriptional hypoxia-inducible factor-1α (HIF-1α) plays the fundamental role in adaptive processes in response to hypoxia. Specific HIF-1α target genes are involved in glycolysis, erythropoiesis and angiogenesis to promote survival. In our previous study we have demonstrated that naturally low body temperature of newborn rats protects them against damage due to perinatal hypoxia. Therefore, our experiments aimed at checking the effects of body temperature during simulated perinatal anoxia on subsequent changes of expression of HIF-1α and its specific target genes such as vascular endothelial growth factor (VEGF) and erythropoietin (EPO) in the rat brain. Two-day old Wistar rats were divided into three temperature groups: normothermic −33 °C, hyperthermic −37 °C and extremely hyperthermic −39 °C. The temperature was controlled 15 min before start and continued during 10 min of anoxia as well as for 2 h post-anoxia. HIF-1α was analysed by Western blot and immunofluorescence and mRNA levels of HIF-1α and its downstream genes (VEGF, EPO) were quantified by qRT-PCR. Thermal conditions during neonatal anoxia affected the hippocampal and neocortical level of HIF-1α protein. Physiological body temperature of newborn rats led to prominent accumulation of cerebral HIF-1α protein and significant upregulation of VEGF and EPO mRNA. In contrast, anoxia-induced HIF-1α activation at elevated body temperatures was less pronounced. Since HIF-1α and EPO have recently been regarded as promising therapeutical targets against brain lesions due to hypoxia/ischemia, presented data imply that in order to achieve a full effect of neuroprotection, the thermal conditions during and after the insult should be taken into consideration.