The Effect Of Tamoxifen On The Expression Of ER-α36 In Hippocampal CA1 Region In Cerebral Ischemia Reperfusion

Stroke is the most common and important vascular disease of the cerebral nervous system.Accumulating evidences suggested that estrogen,as trophic factors for neurons,was involved in the prevention of stroke.ER-α36,a novel variant of ER-α,which was firstly identified by Dr Wang in 2005.Previous studies reported the expression and function of ER-α36 in several normal tissue such as breast,liver and bone,which respond to the membrane-initiated estrogenic signaling pathways.We have found that ER-α36 was expressed in primary cultured hippocampal and cortical astrocytes and neurons.In nervous system,ER-α36 may involved in the estrogenic signaling pathway.But the expression pattern of ER-α36 in the brain of adult rat and the fuction of ER-α36 in nervous system diseases such as stroke remains unclear.Tamoxifen(TAM)is one of the selective estrogen receptor modulators(SERMs)which was mainly applied in the treatment of breast cancer.Several studies have shown that TAM may function as neuroprotective agents inhibited neuron apoptosis in focal ischemic area of rat with middle cerabral artery acclusion(MCAO).But the role TAM played in MCAO following ovariectomy in female rats was unknown.In this study,we firstly conducted bioinformatic analysis to explore the subcellular localization and protein characteristics of ER-α36.Then the expression pattern of ER-α36 in adult rats’ hippocampus was detected by immunofluorescence histochemistry.Subsequently,the modified suture-occluded method was performed combined with ovariectomy to develop the focal cerebral ischemia/reperfusion model of rats to indicate the effects of ER-α36 signaling pathway on stroke.The neuroprotective effect of endogenous estrogen was detected by HE staining,Nissl staining and Western Blot assay.We also explore the function of ER-α36 in the neuroprotective effects of TAM in ovariectomized rat on stroke.Results are as follows:1)Bioinformatic analysis of ER-α36 protein showed that ER-α36 mainly located in the cytoplasmic and possessed two fuctional domains.ER-α36 didn’t have transmembrane structure and alpha helix was the mainly type secondary structure of ER-α36.As a hydrophobic protein,ER-α36 contains ligand binding domain and C4 Zinc finger domain but lacks transmembrane domain.2)ER-α36 was widely expressed in the neurons of hippocampal CA1,CA3 and DG regions.Strong fluorescence intensity of ER-α36 was detected in CA3 area of hippocampus compared to other area.The expression pattern of ER-α36 was higher in the hippocampus of female rat.3)ER-α36 involed in the neuroprotection of estrogen in MCAO under low level endogenous estrogen.Hippocampal CA1 region was sensitive to MCAO.Compared with the sham group,declining endogenous estrogen strengthened the damage degree of cerebral ischemia injury and reduced the expression of both ER-α66 and ER-α36 in CA1 of hippocampus.After ovariectomy,it was mainly ER-α36,but not ER-α66,induced the neuroprotection effect of estrogen.4)The neuroprotective effect of TAM in MCAO in ovariectomized rat was remarkable.ER-α36 was involved in the progress of the neuroprotection of TAM in a concentration dependent manner.Conclusion: Our findings suggested that ER-α36 was widely expressed in hippocampus.TAM had the neuroprotective effect in MCAO and the actions may mediated by promoting the expression of ER-α36 under low level endogenous estrogen.