Nicotinamide adenine dinucleotide (NAD)؉ -dependent sirtuins have been identified to be key regulators in the lifespan extending effects of calorie restriction (CR) in a number of species. In this study we report for the first time that promotion of the NAD ؉ -dependent sirtuin, SIRT1-mediated deacetylase activity, may be a mechanism by which CR influences Alzheimer disease (AD)-type amyloid neuropathology. Most importantly, we report that the predicted attenuation of ␤-amyloid content in the brain during CR can be reproduced in mouse neurons in vitro by manipulating cellular SIRT1 expression/activity through mechanisms involving the regulation of the serine/threonine Rho kinase ROCK1, known in part for its role in the inhibition of the non-amyloidogenic ␣-secretase processing of the amyloid precursor protein. Conversely, we found that the expression of constitutively active ROCK1 in vitro cultures significantly prevented SIRT1-mediated response, suggesting that ␣-secretase activity is required for SIRT1-mediated prevention of AD-type amyloid neuropathology. Consistently we found that the expression of exogenous human (h) SIRT1 in the brain of hSIRT1 transgenics also resulted in decreased ROCK1 expression and elevated ␣-secretase activity in vivo. These results demonstrate for the first time a role for SIRT1 activation in the brain as a novel mechanism through which CR may influence AD amyloid neuropathology. The study provides a potentially novel pharmacological strategy for AD prevention and/or treatment.Sirtuins are a family of NAD ϩ -dependent histone/protein deacetylases that are highly conserved in their catalytic domains and are distributed across all kingdoms of life (1-4). These enzymes utilize NAD ϩ as a substrate to catalyze deacetylation of specific acetylated-protein substrates (1, 5). Sirtuins can deacetylate a variety of substrates and are, therefore, involved in a broad range of physiological functions, including control of gene expression, metabolism, and aging (6). Accumulating evidence implicates sirtuins in calorie restriction (CR)-mediated health effects including increased organism longevity in yeast, worms, flies, and mammals (1-4, 6). Mammalian genomes encode seven distinct sirtuins (SIRT1-SIRT7). SIRT1 is induced by CR 4 in several tissues and has been implicated in various effects such as stress resistance, reduced apoptosis, and metabolic changes associated with CR (1). SIRT1 is also expressed in the developing and the adult mammalian brain (7). Based on these considerations and on the evidence that CR prevents AD-type amyloid neuropathology in animal models (8, 9), we sought to test the hypothesis that CR may reduce AD-type amyloid neuropathology through mechanisms involving promotion of SIRT1. The relevance of CR treatment in experimental models of AD to human pathology is supported by recent epidemiological evidence suggesting that humans who maintain a low calorie diet have a reduced risk of developing AD (10 -12).Abnormal A␤ deposition within the brain is a hallmark of AD neuropat...

Glial fibrillary acidic protein (GFAP), an astrocytic cytoskeletal protein, can be measured in blood samples, and has been associated with Alzheimer’s disease (AD). However, plasma GFAP has not been investigated in cognitively normal older adults at risk of AD, based on brain amyloid-β (Aβ) load. Cross-sectional analyses were carried out for plasma GFAP and plasma Aβ1–42/Aβ1–40 ratio, a blood-based marker associated with brain Aβ load, in participants (65–90 years) categorised into low (Aβ−, n = 63) and high (Aβ+, n = 33) brain Aβ load groups via Aβ positron emission tomography. Plasma GFAP, Aβ1–42, and Aβ1–40 were measured using the Single molecule array (Simoa) platform. Plasma GFAP levels were significantly higher (p < 0.00001), and plasma Aβ1–42/Aβ1–40 ratios were significantly lower (p < 0.005), in Aβ+ participants compared to Aβ− participants, adjusted for covariates age, sex, and apolipoprotein E-ε4 carriage. A receiver operating characteristic curve based on a logistic regression of the same covariates, the base model, distinguished Aβ+ from Aβ− (area under the curve, AUC = 0.78), but was outperformed when plasma GFAP was added to the base model (AUC = 0.91) and further improved with plasma Aβ1–42/Aβ1–40 ratio (AUC = 0.92). The current findings demonstrate that plasma GFAP levels are elevated in cognitively normal older adults at risk of AD. These observations suggest that astrocytic damage or activation begins from the pre-symptomatic stage of AD and is associated with brain Aβ load. Observations from the present study highlight the potential of plasma GFAP to contribute to a diagnostic blood biomarker panel (along with plasma Aβ1–42/Aβ1–40 ratios) for cognitively normal older adults at risk of AD.

Plasma concentrations of interleukin-1beta (IL-1beta), interleukin-6 (IL-6), C reactive protein (CRP) and alpha-1-antichymotrypsin (ACT) in 145 patients with probable Alzheimer's disease (AD) and 51 non-demented controls were measured. To investigate the cellular activation of peripheral immune system, plasma levels of neopterin were also investigated. Plasma levels of IL-1 were detectable in 17 patients with AD (13%) and only in one control (2%) and average levels of IL-1 were higher in AD patients than in controls (p < 0.001). IL-6 plasma levels were detectable in a higher proportion of AD and controls (53% and 27%, respectively), and were increased in patients with AD (p < 0.001). Plasma levels of ACT were increased in patients with AD (p < 0.001) and CRP levels were in the normal range. Plasma levels of neopterin were slightly lower in AD patients than in controls, but differences were not statistically significant. No significant correlation was observed between IL-1 and IL-6 levels or neopterin and cytokine levels in plasma from AD patients. Plasma levels of ACT negatively correlated with cognitive performances, as assessed by the mini mental state examination (MMSE; R = -0.26, p < 0.02) and positively correlated with the global deterioration state (GDS) of AD patients (R = 0.30, p < 0.007). Present findings suggested that detectable levels of circulating cytokines and increased ACT might not be derived by activation of peripheral immune system of AD patients. Detection of these molecules might be used for monitoring the progression of brain inflammation associated with AD.

Genetic association studies have identified 44 common genome-wide significant risk loci for late-onset Alzheimer’s disease (LOAD). However, LOAD genetic architecture and prediction are unclear. Here we estimate the optimal P-threshold (Poptimal) of a genetic risk score (GRS) for prediction of LOAD in three independent datasets comprising 676 cases and 35,675 family history proxy cases. We show that the discriminative ability of GRS in LOAD prediction is maximised when selecting a small number of SNPs. Both simulation results and direct estimation indicate that the number of causal common SNPs for LOAD may be less than 100, suggesting LOAD is more oligogenic than polygenic. The best GRS explains approximately 75% of SNP-heritability, and individuals in the top decile of GRS have ten-fold increased odds when compared to those in the bottom decile. In addition, 14 variants are identified that contribute to both LOAD risk and age at onset of LOAD.

BackgroundStatins are widely used cholesterol-lowering drugs that act by inhibiting HMGCoA reductase, the rate-limiting enzyme in cholesterol biosynthesis. Recent evidence suggests that statin use may be associated with a decreased risk for Alzheimer disease, although the mechanisms underlying this apparent risk reduction are poorly understood. One popular hypothesis for statin action is related to the drugs' ability to activate α-secretase-type shedding of the α-secretase-cleaved soluble Alzheimer amyloid precursor protein ectodomain (sAPPα). Statins also inhibit the isoprenoid pathway, thereby modulating the activities of the Rho family of small GTPases—Rho A, B, and C—as well as the activities of Rac and cdc42. Rho proteins, in turn, exert many of their effects via Rho-associated protein kinases (ROCKs). Several cell-surface molecules are substrates for activated α-secretase-type ectodomain shedding, and regulation of shedding typically occurs via activation of protein kinase C or extracellular-signal-regulated protein kinases, or via inactivation of protein phosphatase 1 or 2A. However, the possibility that these enzymes play a role in statin-stimulated shedding has been excluded, leading us to investigate whether the Rho/ROCK1 protein phosphorylation pathway might be involved.Methods and FindingsWe found that both atorvastatin and simvastatin stimulated sAPPα shedding from a neuroblastoma cell line via a subcellular mechanism apparently located upstream of endocytosis. A farnesyl transferase inhibitor also increased sAPPα shedding, as did a dominant negative form of ROCK1. Most conclusively, a constitutively active ROCK1 molecule inhibited statin-stimulated sAPPα shedding.ConclusionTogether, these data suggest that statins exert their effects on shedding of sAPPα from cultured cells, at least in part, by modulation of the isoprenoid pathway and ROCK1.