Overactivation of glycogen synthase kinase-3 by inhibition of phosphoinositol-3 kinase and protein kinase C leads to hyperphosphorylation of tau and impairment of spatial memory

Neurofibrillary tangles (NFTs) consisting of the hyperphosphorylated microtubule-associated protein tau are a defining pathological characteristic of Alzheimer's disease (AD). Hyperphosphorylation of tau is hypothesized to impair the microtubule stabilizing function of tau, leading to the formation of paired helical filaments and neuronal death. Glycogen synthase kinase-3 (GSK-3) has been shown to be one of several kinases that mediate tau hyperphosphorylation in vitro. However, molecular mechanisms underlying overactivation of GSK-3 and its potential linkage to AD-like pathologies in vivo remain unclear. Here, we demonstrate that injection of wortmannin (a specific inhibitor of phosphoinositol-3 kinase) or GF-109203X (a specific inhibitor of protein kinase C) into the left ventricle of rat brains leads to overactivation of GSK-3, hyperphosphorylation of tau at Ser 396/404/199/202 and, most significantly, impaired spatial memory. The effects of wortmannin and GF-109203X are additive. Significantly, specific inhibition of GSK-3 activity by LiCl prevents hyperphosphorylation of tau, and spatial memory impairment resulting from PI3K and PKC inhibition. These results indicate that in vivo inhibition of phosphoinositol-3 kinase and protein kinase C results in overactivation of GSK-3 and tau hyperphosphorylation and support a direct role of GSK-3 in the formation of AD-like cognitive deficits.     

6-(4-Pyridyl)pyrimidin-4(3H)-ones as CNS penetrant glycogen synthase kinase-3β inhibitors

The discovery of a series of 6-(4-pyridyl)pyrimidin-4(3H)-ones derived from a hit compound with low molecular weight and sufficient chemical space is reported. Transformation of substituents led to subnanomolar potent inhibitors with in vivo tau phoshorylation lowering activity.     

阿尔茨海默病患者红细胞膜蛋白表达的变化

目的:探讨早发性和迟发性阿尔茨海默病(AD)患者红细胞(RBC)膜蛋白表达的变化。方法:选取2016年1月至2018年1月经青海省人民医院确诊为AD的患者40例,根据年龄将AD患者分为迟发性AD患者(年龄≥65岁)23例和早发性AD患者(年龄65岁)17例。选取同期同医院19名年龄≥65岁的健康体检者为迟发性AD对照组,16名年龄65岁的健康体检者为早发性AD对照组。采用流式细胞术检测全血样本中葡萄糖转运蛋白1 (glucose transporter1, Glut1)、三磷酸腺苷结合盒转运蛋白A1(ATP-binding cassette transporter A1, ABCA1)、三磷酸腺苷结合盒超家族G成员2(ATP-binding cassette super-family G member 2,ABCG2)和三磷酸腺苷结合盒超家族B成员6 (ATP-binding cassette sub-family B member 6, ABCB6)等转运蛋白以及胰岛素受体(insulin receptor, INSR)、质膜钙泵(plasma membrane Ca2+ATPase, PMCA)等这些RBC膜蛋白的表达。结果:与同年龄段健康体检者对比,早发性AD患者RBC膜Glut1和INSR的表达水平显著增加(P均0.05),而ABCA1、ABCG2、PMCA和ABCB6表达无显著差异。与同年龄段健康体检者对比,迟发性AD患者RBC膜Glut1、INSR、ABCA1和ABCG2的表达显著增加(P均0.05),而PMCA和ABCB6表达无显著差异。结论:RBC膜Glut1、INSR、ABCA1和ABCG2蛋白表达的检测可能可作为AD病程诊断的新的参考标记物。     

miR-219-5p inhibits tau phosphorylation by targeting TTBK1 and GSK-3β in Alzheimer's disease

As the most common neurodegenerative disease, Alzheimer's disease (AD) is characterized by memory, perception, and behavioral damage, which may ultimately lead to emotional fluctuation and even lethal delirium. Increasing studies indicate that microRNAs (miRNAs) are associated with pathological features of AD. However, the role of miR-219-5p in AD progression is still unclear. In this study, the functions of miR-219-5p were analyzed in vitro and in vivo. miR-219-5p was notably overexpressed in brain tissues of patients with AD. The overexpression of miR-219-5p activated the phosphorylation of Tau-Ser198, Tau-Ser199, Tau-Ser201, and Tau-Ser422. We further showed that miR-219-5p could mediate a decrease in the protein levels of tau-tubulin kinase 1 (TTBK1) and glycogen synthase kinase 3β (GSK-3β) by directly binding to their 3′-untranslated region, thereby promoting the phosphorylation of tau in SH-SY5Y Cells. Rescue experiments further revealed that the phosphorylation of tau-mediated by miR-219-5p was dependent on the inhibition of TTBK1 and GSK-3β. Moreover, suppressing the expression of both TTBK1 and GSK-3β using miR-219-5p remarkably rescued AD-like symptoms in amyloid precursor protein/presenilin 1 mice. Our findings indicate that the upregulation of TTBK1 and GSK-3β mediated by the loss of miR-219-5p is a possible mechanism that contributes to tau phosphorylation and AD progression.     

Discovery of novel 2-(4-aryl-2-methylpiperazin-1-yl)-pyrimidin-4-ones as glycogen synthase kinase-3β inhibitors

We herein describe the results of further evolution of glycogen synthase kinase (GSK)-3β inhibitors from our promising compounds containing a 3-methylmorpholine moiety. Transformation of the morpholine moiety into a piperazine moiety resulted in potent GSK-3β inhibitors. SAR studies focused on the nitrogen atom of the piperazine moiety revealed that a phenyl group afforded potent inhibitory activity toward GSK-3β. Docking studies indicated that the phenyl group on the piperazine nitrogen atom and the methyl group on the piperazine make cation-π and CH-π interactions with GSK-3β respectively. 4-Methoxyphenyl analogue 29 showed most potent inhibitory activity toward GSK-3β with good in vitro and in vivo pharmacokinetic profiles, and 29 demonstrated a significant decrease in tau phosphorylation after oral administration in mice.     

Abnormal cortical lysosomal β-hexosaminidase and β-galactosidase activity at post-synaptic sites during Alzheimer's disease progression

A critical role of endosomal–lysosomal system alteration in neurodegeneration is supported by several studies. Dysfunction of the lysosomal compartment is a common feature also in Alzheimer's disease. Altered expression of lysosomal glycohydrolases has been demonstrated not only in the brain and peripheral tissues of Alzheimer's disease patients, but also in presymptomatic subjects before degenerative phenomenon becomes evident. Moreover, the presence of glycohydrolases associated to the plasma membrane have been widely demonstrated and their alteration in pathological conditions has been documented. In particular, lipid microdomains-associated glycohydrolases can be functional to the maintenance of the proper glycosphingolipids pattern, especially at cell surface level, where they are crucial for the function of cell types such as neurons. In this study we investigated the localization of β-hexosaminidase and β-galactosidase glycohydrolases, both involved in step by step degradation of the GM1 to GM3 gangliosides, in lipid microdomains from the cortex of both an early and advanced TgCRND8 mouse model of Alzheimer's disease. Throughout immunoprecipitation experiments of purified cortical lipid microdomains, we demonstrated for the first time that β-hexosaminidase and β-galactosidase are associated with post-synaptic vesicles and that their activities are increased at both the early and the advanced stage of Alzheimer's disease. The early increase of lipid microdomain-associated β-hexosaminidase and β-galactosidase activities could have relevant implications for the pathophysiology of the disease since their possible pharmacological manipulation could shed light on new reliable targets and biological markers of Alzheimer's disease.     

Central angiotensin II-induced Alzheimer-like tau phosphorylation in normal rat brains

Growing evidence suggests that Alzheimer disease (AD) origins in vascular lesions. As the crucial mediator of vascular pathology, angiotensin II-induced significant amyloid production in our laboratory, although amyloid neurotoxicity depended on phosphorylated tau (p-tau) in recent studies. In the present study, p-tau levels were significantly elevated by central angiotensin II via glycogen synthase kinase 3β (GSK 3β) and other tau kinases. Moreover, angiotensin II-induced cognitive impairment and tau phosphorylation was attenuated by losartan and a GSK 3β inhibitor. These findings implicate Ang II as a crucial mediator of AD pathology and a link between cardiovascular events and AD.     

Direct binding of cholesterol to the amyloid precursor protein: An important interaction in lipid–Alzheimer's disease relationships?

It is generally believed that cholesterol homoeostasis in the brain is both linked to and impacted by Alzheimer's disease (AD). For example, elevated levels of cholesterol in neuronal plasma and endosome membranes appear to be a pro-amyloidogenic factor. The recent observation that the C-terminal transmembrane domain (C99, also known as the β-C-terminal fragment, or β-CTF) of the amyloid precursor protein (APP) specifically binds cholesterol helps to tie together previously loose ends in the web of our understanding of Alzheimer's–cholesterol relationships. In particular, binding of cholesterol to C99 appears to favor the amyloidogenic pathway in cells by promoting localization of C99 in lipid rafts. In turn, the products of this pathway—amyloid-β and the intracellular domain of the APP (AICD)—may down-regulate ApoE-mediated cholesterol uptake and cholesterol biosynthesis. If confirmed, this negative-feedback loop for membrane cholesterol levels has implications for understanding the function of the APP and for devising anti-amyloidogenic preventive strategies for AD.     

6-amino-4-(pyrimidin-4-yl)pyridones: novel glycogen synthase kinase-3β inhibitors

The synthesis and structure-activity relationships for a novel series of 6-amino-4-(pyrimidin-4-yl)pyridones derived from a high throughput screening hit are discussed. Optimization of lead matter afforded compounds with good potency, selectivity and central nervous system (CNS) exposure.