Huaqi Xiong

ABCG2 Is Upregulated in Alzheimer's Brain with Cerebral Amyloid Angiopathy and May Act as a Gatekeeper at the Blood–Brain Barrier for Aβ1–40 Peptides

Alzheimers disease (AD) is characterized by accumulation and deposition of Aβ peptides in the brain. Aβ deposition in cerebrovessels occurs in many AD patients and results in cerebral amyloid angiopathy (AD/CAA). Since Aβ can be transported across blood–brain barrier (BBB), aberrant Aβ trafficking across BBB may contribute to Aβ accumulation in the brain and CAA development. Expression analyses of 273 BBB-related genes performed in this study showed that the drug transporter, ABCG2, was significantly upregulated in the brains of AD/CAA compared with age-matched controls. Increased ABCG2 expression was confirmed by Q-PCR, Western blot, and immunohistochemistry. Abcg2 was also increased in mouse AD models, Tg-SwDI and 3XTg. Aβ alone or in combination with hypoxia/ischemia failed to stimulate ABCG2 expression in BBB endothelial cells; however, conditioned media from Aβ-activated microglia strongly induced ABCG2 expression. ABCG2 protein in AD/CAA brains interacted and coimmunoprecipitated with Aβ. Overexpression of hABCG2 reduced drug uptake in cells; however, interaction of Aβ1–40 with ABCG2 impaired ABCG2-mediated drug efflux. The role of Abcg2 in Aβ transport at the BBB was investigated in Abcg2-null and wild-type mice after intravenous injection of Cy5.5-labeled Aβ1–40 or scrambled Aβ40–1. Optical imaging analyses of live animals and their brains showed that Abcg2-null mice accumulated significantly more Aβ in their brains than wild-type mice. The finding was confirmed by immunohistochemistry. These results suggest that ABCG2 may act as a gatekeeper at the BBB to prevent blood Aβ from entering into brain. ABCG2 upregulation may serve as a biomarker of CAA vascular pathology in AD patients.

Biochemical and behavioral characterization of the double transgenic mouse model (APPswe/PS1dE9) of Alzheimer’s disease

ObjectiveThe double transgenic mouse model (APPswe/PS1dE9) of Alzheimer’s disease (AD) has been widely used in experimental studies. β-Amyloid (Aβ) peptide is excessively produced in AD mouse brain, which affects synaptic function and the development of central nervous system. However, little has been reported on characterization of this model. The present study aimed to characterize this mouse AD model and its wild-type counterparts by biochemical and functional approaches.MethodsBlood samples were collected from the transgenic and the wild-type mice, and radial arm water maze behavioral test was conducted at the ages of 6 and 12 months. The mice were sacrificed at 12-month age. One hemisphere of the brain was frozen-sectioned for immunohistochemistry and the other hemisphere was dissected into 7 regions. The levels of Aβ1–40, Aβ1–42 and 8-hydroxydeoxyguanosine (8-OHdG) in blood or/and brain samples were analyzed by ELISA. Secretase activities in brain regions were analyzed by in vitro assays.ResultsThe pre-mature death rate of transgenic mice was approximately 35% before 6-month age, and high levels of Aβ1–40 and Aβ1–42 were detected in these dead mice brains with a ratio of 1:10. The level of blood-borne Aβ at 6-month age was similar with that at 12-month age. Besides, Aβ1–40 level in the blood was significantly higher than Aβ1–42 level at the ages of 6 and 12 months (ratio 2.37:1). In contrast, the level of Aβ1–42 in the brain (160.6 ng/mg protein) was higher than that of Aβ1–40 (74 ng/mg protein) (ratio 2.17:1). In addition, the levels of Aβ1–40 and Aβ1–42 varied markedly among different brain regions. Aβ1–42 level was significantly higher than Aβ1–40 level in cerebellum, frontal and posterior cortex, and hippocampus. Secretase activity assays did not reveal major differences among different brain regions or between wild-type and transgenic mice, suggesting that the transgene PS1 did not lead to higher γ-secretase activity but was more efficient in producing Aβ1–42 peptides. 8-OHdG, the biomarker of DNA oxidative damage, showed a trend of increase in the blood of transgenic mice, but with no significant difference, as compared with the wild-type mice. Behavioral tests showed that transgenic mice had significant memory deficits at 6-month age compared to wild-type controls, and the deficits were exacerbated at 12-month age with more errors.ConclusionThese results suggest that this mouse model mimics the early-onset human AD and may represent full-blown disease at as early as 6-month age for experimental studies.摘要目的阿尔茨海默病(Alzheimer’s disease, AD) APPswe/PS1dE9双转基因小鼠已被广泛运用于各种实验研究。 AD小鼠脑内产生过量的β淀粉样蛋白(Aβ), 后者会影响突触功能和中枢神经系统的发育。 然而, 该转基因小鼠模型的生化和行为学特征却未见报道。 本研究旨在对该小鼠模型的病理从生化和行为学角度进行检测。方法对6月和12月龄转基因和野生型小鼠取血约100 μL, 1 200 g离心后, 分离血清。 在小鼠6月和12月龄时, 进行为期15天的辐射状六臂水迷宫实验。 ELISA法检测血清和大脑中Aβ1–40和Aβ1–42的含量, 以及血清中8-羟基脱氧鸟苷的含量。 比较转基因和野生型小鼠大脑不同部位中α-, β- 和 γ-分泌酶活性的差异。结果在6月龄之前, APPswe/PS1dE9双转基因小鼠的死亡率约为35%, 这些死亡的小鼠脑内Aβ1–40和Aβ1–42水平较高, 两者比例约为1:10。 在6月和12月龄时, 转基因小鼠血清中Aβ1–40水平均显著高于Aβ1–42水平, Aβ1–40与Aβ1–42比例为 2.37:1。 在12月龄时, 转基因小鼠大脑中Aβ1–42水平显著高于Aβ1–40水平, 两者比例约为2.17: 1, 并且在不同脑区中, Aβ1–42和Aβ1–40含量变化较大。 在小脑、 前、 后部皮质层以及海马中, Aβ1–42水平显著高于Aβ1–40。 分泌酶活性在转基因和野生型小鼠之间以及在不同脑部位之间没有很大的差异, 这提示PS1转基因并没有导致高γ-分泌酶活性, 该基因可能使 γ-分泌酶更有效的切割和产生Aβ1–42。 此外, 转基因小鼠血清中8-羟基脱氧鸟苷含量较野生型小鼠升高, 但没有显著性差异。 行为学结果显示, 在6月龄时, 转基因小鼠与野生型相比呈现出显著的记忆障碍, 到12月龄时, 这种障碍变得更为严重, 表现为水迷宫实验中产生更多的错误。结论APPswe/PS1dE9双转基因小鼠最早在6月龄时就能很好地模拟早发性AD, 可用于实验研究。

ABCG2 reduces ROS-mediated toxicity and inflammation: a potential role in Alzheimer's disease.

J. Neurochem. (2010) 114, 1590–1604.

Abcg2 deficiency augments oxidative stress and cognitive deficits in Tg‐SwDI transgenic mice

J. Neurochem. (2012) 122, 456–469.

Rapid transmission of exogenous beta-amyloid peptides from blood to the brain

of inhibition is indicated by the lack of similar inhibition of OGG1. Furthermore, Fe(II) inhibits NEIL1’s interaction 4to 6-fold with the downstream repair enzymes DNA polymerase b (Polb) and flap endonuclease-1 (FEN1), a prerequisite for efficient repair of 5-hydroxy uracil (5-OHU), a common base lesion product of cytidine. As expected, Fe(II/III) and Cu(II) inhibited NEIL-initiated complete repair. Further, we also found inhibition of mitochondrial BER in SH-SY5Y cells treated with MPTP and/or Fe and correlated with accumulation of mitochondrial DNA damage in Parkinson’s cell culture model. Specific metal chelators and the natural chemopreventive compound curcumin reversed NEILs’ inhibition both in vitro and in cells. Conclusions: Excess accumulation of transition metals in PD brain can act as a ‘double edged sword’ by inducing DNA damage (by ROS formation) and also by blocking DNA repair. The study provides evidence to inhibiton of repair of oxidative DNA damage by etiological factors of PD and correlation to accumulation of oxidized DNA bases in human brain dopaminergic neurons, and importantly develop potential strategies to reverse this inhibition using natural compounds (e.g. curcumin) for improved therapeutic intervention of PD.