The effects of erythropoietin on STAT1 and STAT3 levels following cerebral ischemia-reperfusion in rats

Abstract

Objective To explore the effects of erythropoietin （EPO） on the expression of signal transducer and activator of transcription （STAT） 1, phosphorylated STAT1 （ P-STAT1 ）, STAT3, P-STAT3 and cell apoptosis in rat models of focal cerebral ischemia-reperfusion. Methods Eighty male Sprague- Dawley rats were randomly and evenly divided into four groups by completely random design method： shamoperation （group A ）, cerebral isehemia-reperfusion （group B ）, cerebral ischemia-reperfusion ＋ saline （group C） and cerebral ischemia-reperfusion ＋ EPO （group D）. The model of focal cerebral ischemiareperfusion injury was established by blocking the left middle cerebral artery. All rats underwent MRI for the detection of the changes of infarct area between 2 h post ischemia and 24 h of reperfusion. Western blot was used to observe the expression of STAT1, P-STAT1, STAT3, P-STAT3. Terminal oxynucleotidyl transferase mediated dUTP biotin nick end labeling （TUNEL） was used to evaluate the cell apoptosis including the relative area （ ROI area/whole brain area of the same layer x 100% ） of abnormal signal region, relative optical density （rOD） and apoptotic index. One-way analysis of variance and q test were used to analyze the data. Results On T2WI imaging, rats in group B and group C presented large hyperintense areas in the cortex and subcortex of left hemispheric （ （28.00±4.60） % and （29.70±4.80） % respectively）. Group D presented less hyperintense areas in the cortex and subcortex of left hemispheric compared with group B and group C （（21.10±2. 40）%; F= 11.285, P〈0.01 ）. The expression of STAT1 and STAT3 proteins was not significandy affected by ischemia-reperfusion and EPO intervention compared with normal brain tissue （ F= 0.806, 1.558, both P〉0.05）. However, the level of P-STAT1 was low in group A （rOD = 0.75±0.13） but increased after cerebral ischemia-reperfusion. Compared with group B and group C, P-STAT1 expression was lower in group D （B-D： 2. 08±0.15, 2.05±0.16, 1.92±0.05; F= 3.274, P〉0.05）. The level of P-STAT3 was also low in group A （rOD= 1.02＋0.09）. Compared with group B and group C, P-STAT3 expression in group D was significantly higher （ B- D ： 2.22 ± 0.13, 2.04 ± 0.14, 4.21± 0.21 ; F = 40.719, P 〈 0.01 ）. The apoptotic index of group B and group C was （42.00±1.30）% and （41.20±2.50）%, respectively, which was significantly higher than that of group D （ （20. 90±1.46）%; F= 378.704, P〈0.01 ）. Conclusion Intraperitoneal injection of EPO can reduce the cerebral ischemic area and the number of apoptotic cells in the ischemic penumbra in rat ischemia-reperfusion models through increasing P-STAT3 and decreasing P-STAT1 levels. Key words: Cerebral ischemia; Reperfusion; STAT transcription factors; Erythropoietin; Magnetic resonance imaging; Rats