Amyloid precursor protein cytoplasmic domain with phospho-Thr668 accumulates in Alzheimer’s disease and its transgenic models: a role to mediate interaction of Aβ and tau

Abnormal accumulation of Aβ and tau in senile plaques (SP) and neurofibrillary tangles (NFTs) is a key event in Alzheimer’s disease (AD). Here, we show that T668-phosphorylated cytoplasmic domain of APP (pT668-ACD) accumulates Aβ and tau in AD and its transgenic models. Anti-pT668 immunostaining of AD brain sections with hydrated autoclave enhancement identified SP neurites and NFTs in which pT668-ACD colocalizes with tau. We produced and examined transgenic (Tg) mice that overexpress human APP695, harboring the double Swedish/London mutation, and develop age-dependently Aβ plaques in the brain. All Aβ plaques contain co-accumulations of pT668-ACD, but co-accumulation of tau appears in only a fraction of Aβ plaques in older animals. We also examined the established tau Tg mice that overexpress the smallest human brain tau isoform and develop neuronal accumulations of tau in older animals. Examination of the old tau Tg mice showed that neuronal cells affected by tau accumulation induce co-accumulation of pT668-ACD. We speculate that in AD brains, extracellular Aβ deposition is accompanied by intracellular accumulation of pT668-ACD, followed by tau accumulation in the SP with dystrophic neurites and that neuronal cells affected by tau accumulation induce co-accumulation of pT668-ACD in NFTs. Thus, pT668-ACD is likely to mediate pathological interaction between Aβ and tau.     

Intracellular pH regulates amyloid precursor protein intracellular domain accumulation

The amyloid precursor protein (APP) metabolism is central to pathogenesis of Alzheimer's disease (AD). Parenchymal amyloid deposits, a neuropathological hallmark of AD, are composed of amyloid-beta peptides (Abeta). Abeta derives from the amyloid precursor protein (APP) by sequential cleavages by beta- and gamma-secretases. Gamma-secretase cleavage releases the APP intracellular domain (AICD), suggested to mediate a nuclear signaling. Physiologically, AICD is seldom detected and thus supposed to be rapidly degraded. The mechanisms responsible of its degradation remain unknown. We used a pharmacological approach and showed that several alkalizing drugs induce the accumulation of AICD in neuroblastoma SY5Y cell lines stably expressing APP constructs. Moreover, alkalizing drugs induce AICD accumulation in naive SY5Y, HEK and COS cells. This accumulation is not mediated by the proteasome or metallopeptidases and is not the result of an increased gamma-secretase activity since the gamma-secretase cleavage of Notch1 and N-Cadherin is not affected by alkalizing drug treatments. Altogether, our data demonstrate for the first time that alkalizing drugs induce the accumulation of AICD, a mechanism likely mediated by the endosome/lysosome pathway.     

Drebrin和SYP在APP/PS1转基因AD小鼠海马内的表达与认知障碍的关系

已知Alzheimer病(AD)患者脑内的主要病理变化之一是树突棘与突触的退化,而树突棘与突触的正常发育及病理改变均与树突棘肌动蛋白结合蛋白drebrin和突触前成分内突触素(synaptophysin,SYP)的表达水平密切相关。为探讨drebrin和SYP的表达与AD认知障碍之间的关系,本实验先采用Morris水迷宫法观测了6、9、12月龄APP/PS1转基因小鼠和同种野生型小鼠的学习记忆能力;再用Western blot法检测了其海马内drebrin和SYP蛋白表达水平。结果显示:9月龄APP/PS1转基因小鼠海马内drebrin蛋白的表达水平已有下降,其学习记忆能力也相应地降低,12月龄时二者下降明显;但作为突触前成分中的SYP蛋白表达水平的下降则较前二者的出现为迟。本结果提示,drebrin的表达下降在AD早期行为学改变的分子机制中发挥重要的作用,而SYP的表达下降则在drebrin下降之后参与AD的进一步发展。     

Overexpression of wild-type human APP in mice causes cognitive deficits and pathological features unrelated to Aβ levels

Transgenic mice expressing mutant human amyloid precursor protein (APP) develop an age-dependent amyloid pathology and memory deficits, but no overt neuronal loss. Here, in mice overexpressing wild-type human APP (hAPP_wt) we found an early memory impairment, particularly in the water maze and to a lesser extent in the object recognition task, but β-amyloid peptide (Aβ₄₂) was barely detectable in the hippocampus. In these mice, hAPP processing was basically non-amyloidogenic, with high levels of APP carboxy-terminal fragments, C83 and APP intracellular domain. A tau pathology with an early increase in the levels of phosphorylated tau in the hippocampus, a likely consequence of enhanced ERK1/2 activation, was also observed. Furthermore, these mice presented a loss of synapse-associated proteins: PSD95, AMPA and NMDA receptor subunits and phosphorylated CaMKII. Importantly, signs of neurodegeneration were found in the hippocampal CA1 subfield and in the entorhinal cortex that were associated to a marked loss of MAP2 immunoreactivity. Conversely, in mice expressing mutant hAPP, high levels of Aβ₄₂ were found in the hippocampus, but no signs of neurodegeneration were apparent. The results support the notion of Aβ-independent pathogenic pathways in Alzheimer's disease.     

锌离子与锌转运体6在APP/PS1转基因小鼠小脑内的分布

 目的 研究游离锌离子和锌转运体6（zinc transporter 6,ZnT6）在APP/PS1转基因小鼠小脑内的分布。方法 应用浸入式金属自显影技术（AMG）和免疫组织化学染色标记游离锌离子、ZnT6和淀粉样前体蛋白（amyloid precursor protein,AYY）,通过免疫荧光染色和共聚焦激光扫描显微镜观察ZnT6和β-淀粉样蛋白（β-amyloid,Aβ）在老年斑内的定位,并分析锌离子、ZnT6与APP和Aβ分布的相关性。结果 游离锌离子、ZnT6和APP免疫阳性反应产物均定位于老年斑内,老年斑主要分布于小脑分子层,浦肯野细胞层和颗粒层分布较少;ZnT6和Aβ荧光双标的结果进一步证实两者共存于老年斑内。结论 APP/PS1转基因小鼠小脑Aβ老年斑内有大量的ZnT6蛋白表达,并聚集着大量的锌离子,提示锌离子可能参与小脑Aβ老年斑的形成,而ZnT6在老年斑内锌离子的聚集过程中起着重要的调节作用。     

白藜芦醇通过SIRT1激活ADAM10促进APPα代谢

目的：探讨白藜芦醇可否通过SIRT1激活解整合素金属蛋白酶10（ADAM10）促进APPα代谢抑制Aβ分泌。方法：选取过表达人瑞典突变淀粉样前体蛋白APP695sw的细胞模型,分别设立DMSO空白对照组、SIRT1激活剂白藜芦醇组和SIRT1抑制剂EX527组。给药后,ELISA法分别检测细胞培养上清中sAPPα和Aβ的含量,免疫印记Western Blot法检测细胞SIRT1和ADAM10的蛋白水平。结果：与对照组比较,白藜芦醇组细胞培养上清sAPPα的含量增高,Aβ含量下降,sAPPα/Aβ比值增大,细胞SIRT1和ADAM10蛋白水平增高;而抑制剂EX527组与对照相比,细胞培养上清sAPPα的含量降低,Aβ含量升高,sAPPα/Aβ比值减小,细胞SIRT1和ADAM10蛋白水平降低;抑制剂下调SIRT1后各项指标与激动剂组呈现相反的趋势（P<0.05）。结论：白藜芦醇可通过SIRT1激活ADAM10,促进APP进行α非淀粉样代谢途径,增强sAPPα分泌并抑制Aβ产生。     

Lithium: bipolar disorder and neurodegenerative diseases Possible cellular mechanisms of the therapeutic effects of lithium

Bipolar illness is a major psychiatric disorder that affects 1-3% of the worldwide population. Epidemiological studies have demonstrated that this illness is substantially heritable. However, the genetic characteristics remain unknown and a clear personality has not been identified for these patients. The clinical history of lithium began in mid-19th century when it was used to treat gout. In 1940, it was used as a substitute for sodium chloride in hypertensive patients. However, it was then banned, as it had major side effects. In 1949, Cade reported that lithium could be used as an effective treatment for bipolar disorder and subsequent studies confirmed this effect. Over the years, different authors have proposed many biochemical and biological effects of lithium in the brain. In this review, the main mechanisms of lithium action are summarised, including ion dysregulation; effects on neurotransmitter signalling; the interaction of lithium with the adenylyl cyclase system; inositol phosphate and protein kinase C signalling; and possible effects on arachidonic acid metabolism. However, none of the above mechanisms are definitive, and sometimes results have been contradictory. Recent advances in cellular and molecular biology have reported that lithium may represent an effective therapeutic strategy for treating neurodegenerative disorders like Alzheimer's disease, due to its effects on neuroprotective proteins like Bcl-2 and its actions on regulators of apoptosis and cellular resilience, such as GSK-3. However, results are contradictory and more specific studies into the use of lithium in therapeutic approaches for neurodegenerative diseases are required.     

Regulation of alpha2AR trafficking and signaling by interacting proteins

The continuing discovery of new G protein-coupled receptor (GPCR) interacting proteins and clarification of the functional consequences of these interactions has revealed multiple roles for these events. Some of these interactions serve to scaffold GPCRs to particular cellular micro-compartments or to tether them to defined signaling molecules, while other GPCR-protein interactions control GPCR trafficking and the kinetics of GPCR-mediated signaling transduction. This review provides a general overview of the variety of GPCR-protein interactions reported to date, and then focuses on one prototypical GPCR, the alpha(2)AR, and the in vitro and in vivo significance of its reciprocal interactions with arrestin and spinophilin. It seems appropriate to recognize the life and career of Arthur Hancock with a summary of studies that both affirm and surprise our preconceived notions of how nature is designed, as his career-long efforts similarly affirmed the complexity of human biology and attempted to surprise pathological changes in that biology with novel, discovery-based therapeutic interventions. Dr. Hancock's love of life, of family, and of commitment to making the world a better place are a model of the life well lived, and truly missed by those who were privileged to know, and thus love, him.     

Emerging amyloid beta (Ab) peptide modulators for the treatment of Alzheimer's disease (AD)

Background: According to the ‘amyloid cascade hypothesis’ of Alzheimer's disease (AD), abnormal processing of beta-amyloid precursor protein (βAPP) into toxic amyloid beta (Aβ)-peptides is central to the etiopathology of this uniquely human brain disorder. Objective: To review current AD drugs, pharmacological approaches and strategies aimed at modulating Aβ-peptide generation and/or aggregation in the treatment of AD. Methods: Data searches at various websites: Alzheimer Research Forum; individual drug company databases; Medline; Pharmaprojects database; unpublished research; inter-University research communications. Results/conclusion: Considerable research effort has focused on secretase-mediated mechanisms of βAPP processing, and the latest pharmacological strategies have used selective Aβ-peptide-lowering agents (SALA) to provide therapeutic benefit against Aβ-initiated neurodegenerative pathology. Currently, dedicated anticholinesterase, glutamatergic agonist and Aβ-peptide immunization have had little impact in the clinical treatment of AD. One unexpected benefit of statins (HMG-CoA inhibitors), besides their cholesterol lowering abilities, has been their ancillary effects in potentiating the enzymatic mechanisms that generate Aβ-peptides. The long-term benefits or complications of statin-based therapies for use in the clinical management of AD are not known.