DIFFERENTIAL EXPRESSION OF CHOLESTEROL HYDROXYLASES IN ALZHEIMER'S DISEASE

本子项目是利用由NIH/NCRR资助的中心赠款提供的资源的众多研究子项目之一。子项目和研究者（PI）可能已经从另一个NIH来源获得了主要资金，因此可以在其他CRISP条目中表示。列出的机构是中心的，不一定是研究者的机构。胆固醇通过氧化从神经元中清除，氧化过程产生氧化甾醇。胆固醇氧化是由胆固醇24-羟化酶（CYP46A1）和胆固醇27-羟化酶（CYP27A1）介导的。免疫细胞化学研究表明，CYP46A1和CYP27A1在正常大脑的神经元和部分星形胶质细胞中表达，CYP27A1存在于少突胶质细胞中。在阿尔茨海默病（AD）中，CYP46A1在星形胶质细胞和淀粉样斑块周围显著表达，而CYP27A1在神经元中表达减少，在淀粉样斑块周围不明显，但在少突胶质细胞中表达增加。虽然以前的研究已经检测了合成的氧甾醇对淀粉样前体蛋白（APP）加工的影响，但天然存在的氧甾醇的作用尚未得到检验。为了了解胆固醇氧化在AD中的作用，我们比较了24(S)-和27-羟基胆固醇对APP加工的影响，并分析了这两种胆固醇羟化酶在人脑中的细胞特异性表达模式。两种氧甾醇均抑制神经元中A的生成，但24(S)-羟胆固醇的抑制作用是27-羟胆固醇的1000倍。24(S)-羟基胆固醇抑制A分泌的IC50为1 nM。两种氧甾醇诱导ABCA1表达的IC50值与抑制A分泌的IC50值相似，提示与肝脏X受体有关。在刺激蛋白激酶C后，氧甾醇还会抑制蛋白激酶C的活性和APP的分泌。CYP46A1在神经斑块周围的选择性表达以及24(S)-羟基胆固醇对神经元中APP加工的有效抑制表明，CYP46A1影响AD的病理生理，并为CYP46A1基因多态性如何影响这种流行疾病的病理生理提供了新的见解。

This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. Cholesterol is eliminated from neurons by oxidization, which generates oxysterols. Cholesterol oxidation is mediated by the enzymes cholesterol 24-hydroxylase (CYP46A1) and cholesterol 27-hydroxylase (CYP27A1). Immunocytochemical studies show that CYP46A1 and CYP27A1 are expressed in neurons and some astrocytes in the normal brain, and CYP27A1 is present in oligodendrocytes. In Alzheimer's disease (AD), CYP46A1 shows prominent expression in astrocytes and around amyloid plaques, whereas CYP27A1 expression decreases in neurons and is not apparent around amyloid plaques but increases in oligodendrocytes. Although previous studies have examined the effects of synthetic oxysterols on the processing of amyloid precursor protein (APP), the actions of the naturally occurring oxysterols have yet to be examined. To understand the role of cholesterol oxidation in AD, we compared the effects of 24(S)- and 27-hydroxycholesterol on the processing of APP and analyzed the cell-specific expression patterns of the two cholesterol hydroxylases in the human brain. Both oxysterols inhibited production of A in neurons, but 24(S)-hydroxycholesterol was 1000-fold more potent than 27-hydroxycholesterol. The IC50 of 24(S)-hydroxycholesterol for inhibiting A secretion was 1 nM. Both oxysterols induced ABCA1 expression with IC50 values similar to that for inhibition of A secretion, suggesting the involvement of liver X receptor. Oxysterols also inhibited protein kinase C activity and APP secretion following stimulation of protein kinase C. The selective expression of CYP46A1 around neuritic plaques and the potent inhibition of APP processing in neurons by 24(S)-hydroxycholesterol suggests that CYP46A1 affects the pathophysiology of AD and provides insight into how polymorphisms in the CYP46A1 gene might influence the pathophysiology of this prevalent disease.