Genetic associations of in vivo pathology influence Alzheimer's disease susceptibility.

INTRODUCTION: Although the heritability of sporadic Alzheimer's disease (AD) is estimated to be 60-80%, addressing the genetic contribution to AD risk still remains elusive. More specifically, it remains unclear whether genetic variants are able to affect neurodegenerative brain features that can be addressed by in vivo imaging techniques. METHODS: Targeted sequencing analysis of the coding and UTR regions of 132 AD susceptibility genes was performed. Neuroimaging data using 11C-Pittsburgh Compound B positron emission tomography (PET), 18F-fluorodeoxyglucose PET, and MRI that are available from the KBASE (Korean Brain Aging Study for Early Diagnosis and Prediction of Alzheimer's disease) cohort were acquired. A total of 557 participants consisted of 336 cognitively normal (CN) adults, 137 mild cognitive impairment (MCI), and 84 AD dementia (ADD) groups. RESULTS: We called 5391 high-quality single nucleotide variants (SNVs) on AD susceptibility genes and selected significant associations between variants and five in vivo AD pathologies: (1) amyloid ß (Aß) deposition, (2) AD-signature region cerebral glucose metabolism (AD-Cm), (3) posterior cingulate cortex (PCC) cerebral glucose metabolism (PCC-Cm), (4) AD-signature region cortical thickness (AD-Ct), and (5) hippocampal volume (Hv). The association analysis for common variants (allele frequency (AF) > 0.05) yielded several novel loci associated with Aß deposition (PIWIL1-rs10848087), AD-Cm (NME8-rs2722372 and PSEN2-rs75733498), AD-Ct (PSEN1-rs7523) and, Hv (CASS4-rs3746625). Meanwhile, in a gene-based analysis for rare variants (AF < 0.05), cases carrying rare variants in LPL, FERMT2, NFAT5, DSG2, and ITPR1 displayed associations with the neuroimaging features. Exploratory voxel-based brain morphometry between the variant carriers and non-carriers was performed subsequently. Finally, we document a strong association of previously reported APOE variants with the in vivo AD pathologies and demonstrate that the variants exert a causal effect on AD susceptibility via neuroimaging features. CONCLUSIONS: This study provides novel associations of genetic factors to Aß accumulation and AD-related neurodegeneration to influence AD susceptibility.

Thrombospondin-1 protects against Aß-induced mitochondrial fragmentation and dysfunction in hippocampal cells.

Alzheimer's disease (AD) is often characterized by the impairment of mitochondrial function caused by excessive mitochondrial fragmentation. Thrombospondin-1 (TSP-1), which is primarily secreted from astrocytes in the central nervous system (CNS), has been suggested to play a role in synaptogenesis, spine morphology, and synaptic density of neurons. In this study, we investigate the protective role of TSP-1 in the recovery of mitochondrial morphology and function in amyloid ß (Aß)-treated mouse hippocampal neuroblastoma cells (HT22). We observe that TSP-1 inhibits Aß-induced mitochondrial fission by maintaining phosphorylated-Drp1 (p-Drp1) levels, which results in reduced Drp1 translocation to the mitochondria. By using gabapentin, a drug that antagonizes the interaction between TSP-1 and its neuronal receptor α2δ1, we observe that α2δ1 acts as one of the target receptors for TSP-1, and blocks the reduction of the p-Drp1 to Drp1 ratio, in the presence of Aß. Taken together, TSP-1 appears to contribute to maintaining the balance in mitochondrial dynamics and mitochondrial functions, which is crucial for neuronal cell viability. These data suggest that TSP-1 may be a potential therapeutic target for AD.

Mitochondrial abnormalities related to the dysfunction of circulating endothelial colony-forming cells in moyamoya disease.

The authors performed morphological and functional studies of the mitochondria in particular blood cells, i.e., endothelial colony-forming cells (ECFCs), from patients with moyamoya disease. The results indicated that the mitochondria of these ECFCs exhibit morphological and functional abnormalities, which may present new insights into the pathogenesis of moyamoya disease.

Metformin Facilitates Amyloid-ß Generation by ß- and γ-Secretases via Autophagy Activation.

The evidence of strong pathological associations between type 2 diabetes and Alzheimer's disease (AD) has increased in recent years. Contrary to suggestions that anti-diabetes drugs may have potential for treating AD, we demonstrate here that the insulin sensitizing anti-diabetes drug metformin (Glucophage®) increased the generation of amyloid-ß (Aß), one of the major pathological hallmarks of AD, by promoting ß- and γ-secretase-mediated cleavage of amyloid-ß protein precursor (AßPP) in SH-SY5Y cells. In addition, we show that metformin caused autophagosome accumulation in Tg6799 AD model mice. Extremely high γ-secretase activity was also detected in autophagic vacuoles, apparently a novel site of Aß peptide generation. Together, these data suggest that metformin-induced accumulation of autophagosomes resulted in increased γ-secretase activity and Aß generation. Additional experiments indicated that metformin increased phosphorylation of AMP-activated protein kinase, which activates autophagy by suppressing mammalian target of rapamycin (mTOR). The suppression of mTOR then induces the abnormal accumulation of autophagosomes. We conclude that metformin, an anti-diabetes drug, may exacerbate AD pathogenesis by promoting amyloidogenic AßPP processing in autophagosomes.

Thrombospondin-1 prevents amyloid beta-mediated synaptic pathology in Alzheimer's disease.

Alzheimer's disease (AD) is characterized by impaired cognitive function and memory loss, which are often the result of synaptic pathology. Thrombospondin (TSP) is an astrocyte-secreted protein, well known for its function as a modulator of synaptogenesis and neurogenesis. Here, we investigated the effects of TSP-1 on AD pathogenesis. We found that the level of TSP-1 expression was decreased in AD brains. When we treated astrocytes with amyloid beta (Aß), secreted TSP-1 was decreased in autophagy-dependent manner. In addition, treatment with Aß induced synaptic pathology, such as decreased dendritic spine density and reduced synaptic activity. These effects were prevented by coincubation of TSP-1 with Aß, which acts through the TSP-1 receptor alpha-2-delta-1 in neurons. Finally, intrasubicular injection with TSP-1 into AD model mouse brains mitigated the Aß-mediated reduction of synaptic proteins and related signaling pathways. These results indicate that TSP-1 is a potential therapeutic target in AD pathogenesis.

The effect of ladder-climbing exercise on atrophy/hypertrophy-related myokine expression in middle-aged male Wistar rats.

We investigated the change in myokine expression related to hypertrophy (IL-4, IL-6, IL-10) and atrophy (TNF-α, NFκB, IL-1ß) in middle-aged rats after resistance exercise with ladder climbing. 50- and 10-week-old male Wistar rats were randomly assigned to two groups: the sedentary and exercise groups. The exercise groups underwent a ladder-climbing exercise for 8 weeks. While the tibialis anterior muscle mass in the young group significantly increased after the ladder-climbing exercise, the middle-aged group did not show any changes after undergoing the same exercise. To understand the molecular mechanism causing this difference, we analyzed the change in hypertrophy- and atrophy-related myokine levels from the tibialis anterior muscle. After 8 weeks of ladder-climbing exercise, the IL-4 and IL-10 protein levels did not change. However, the IL-6 level significantly increased after exercise training, but the amount of increase in the young training group was higher than in the middle-aged training group. IL-1ß and TNF-α as well as NFκB protein levels were significantly higher in the middle-aged group than in the young group. Except for TNF-α, exercise training did not affect IL-1ß and NFκB protein levels. The TNF-α level significantly decreased in the middle-aged exercise training group. AMPK and PGC-1α levels also significantly increased after exercise training, but there was no difference between age-related groups. Therefore, 8-week high-intensity exercise training using ladder climbing downregulates the skeletal muscle production of myokine involved in atrophy and upregulates hypertrophic myokine. However, the extent of these responses was lower in the middle-aged than young group.

Association of Angiotensin Converting Enzyme I/D and α-actinin-3 R577X Genotypes with Growth Factors and Physical Fitness in Korean Children.

This study analyzed the differences in aerobic and anaerobic exercise ability and growth-related indicators, depending on the polymorphism of the ACE and the ACTN3 genes, to understand the genetic influence of exercise ability in the growth process of children. The subjects of the study consisted of elementary school students (n=856, age 10.32±0.07 yr). The anthropometric parameters, physical fitness and growth factors were compared among groups of the ACE I/D or the ACTN3 R577X polymorphisms. There were no significant differences between the anthropometric parameters, physical fitness and growth factors for the ACE gene ID or the ACTN3 gene R577X polymorphism. However, the DD type of ACE gene was highest in the side step test (p<0.05), and the DD type was significantly higher than the II+ID type (p<0.05) in the early bone age. The combined group of the ACE gene II+ID and the ACTN3 gene XX type significantly showed lower early bone age (p< 0.05). This study did not find any individual or compounding effects of the polymorphism in the ACE I/D or the ACTN3 R577X polymorphisms on the anthropometric parameters, physical fitness and growth factors of Korean children. However, the exercise experience and the DD type of the ACE gene may affect the early maturity of the bones.

Accumulation of autophagosomes contributes to enhanced amyloidogenic APP processing under insulin-resistant conditions.

Alzheimer disease (AD) is sometimes referred to as type III diabetes because of the shared risk factors for the two disorders. Insulin resistance, one of the major components of type II diabetes mellitus (T2DM), is a known risk factor for AD. Insulin resistance increases amyloid-ß peptide (Aß) generation, but the exact mechanism underlying the linkage of insulin resistance to increased Aß generation in the brain is unknown. In this study, we investigated the effect of insulin resistance on amyloid ß (A4) precursor protein (APP) processing in mice fed a high-fat diet (HFD), and diabetic db/db mice. We found that insulin resistance promotes Aß generation in the brain via altered insulin signal transduction, increased BACE1/ß-secretase and γ-secretase activities, and accumulation of autophagosomes. Using an in vitro model of insulin resistance, we found that defects in insulin signal transduction affect autophagic flux by inhibiting the mechanistic target of rapamycin (MTOR) pathway. The insulin resistance-induced autophagosome accumulation resulted in alteration of APP processing through enrichment of secretase proteins in autophagosomes. We speculate that the insulin resistance that underlies the pathogenesis of T2DM might alter APP processing through autophagy activation, which might be involved in the pathogenesis of AD. Therefore, we propose that insulin resistance-induced autophagosome accumulation becomes a potential linker between AD and T2DM.

Altered APP processing in insulin-resistant conditions is mediated by autophagosome accumulation via the inhibition of mammalian target of rapamycin pathway.

Insulin resistance, one of the major components of type 2 diabetes mellitus (T2DM), is a known risk factor for Alzheimer's disease (AD), which is characterized by an abnormal accumulation of intra- and extracellular amyloid ß peptide (Aß). Insulin resistance is known to increase Aß generation, but the underlying mechanism that links insulin resistance to increased Aß generation is unknown. In this study, we examined the effect of high-fat diet-induced insulin resistance on amyloid precursor protein (APP) processing in mouse brains. We found that the induced insulin resistance promoted Aß generation in the brain via altered insulin signal transduction, increased ß- and γ-secretase activities, and accumulation of autophagosomes. These findings were confirmed in diabetic db/db mice brains. Furthermore, in vitro experiments in insulin-resistant SH-SY5Y cells and primary cortical neurons confirmed the alteration of APP processing by insulin resistance-induced autophagosome accumulation. Defects in insulin signal transduction affect autophagic flux by inhibiting the mammalian target of rapamycin pathway, resulting in altered APP processing in these cell culture systems. Thus, the insulin resistance that underlies the pathogenesis of T2DM might also trigger accumulation of autophagosomes, leading to increased Aß generation, which might be involved in the pathogenesis of AD.

Mitochondria-specific accumulation of amyloid ß induces mitochondrial dysfunction leading to apoptotic cell death.

Mitochondria are best known as the essential intracellular organelles that host the homeostasis required for cellular survival, but they also have relevance in diverse disease-related conditions, including Alzheimer's disease (AD). Amyloid ß (Aß) peptide is the key molecule in AD pathogenesis, and has been highlighted in the implication of mitochondrial abnormality during the disease progress. Neuronal exposure to Aß impairs mitochondrial dynamics and function. Furthermore, mitochondrial Aß accumulation has been detected in the AD brain. However, the underlying mechanism of how Aß affects mitochondrial function remains uncertain, and it is questionable whether mitochondrial Aß accumulation followed by mitochondrial dysfunction leads directly to neuronal toxicity. This study demonstrated that an exogenous Aß(1-42) treatment, when applied to the hippocampal cell line of mice (specifically HT22 cells), caused a deleterious alteration in mitochondria in both morphology and function. A clathrin-mediated endocytosis blocker rescued the exogenous Aß(1-42)-mediated mitochondrial dysfunction. Furthermore, the mitochondria-targeted accumulation of Aß(1-42) in HT22 cells using Aß(1-42) with a mitochondria-targeting sequence induced the identical morphological alteration of mitochondria as that observed in the APP/PS AD mouse model and exogenous Aß(1-42)-treated HT22 cells. In addition, subsequent mitochondrial dysfunctions were demonstrated in the mitochondria-specific Aß(1-42) accumulation model, which proved indistinguishable from the mitochondrial impairment induced by exogenous Aß(1-42)-treated HT22 cells. Finally, cellular toxicity was directly induced by mitochondria-targeted Aß(1-42) accumulation, which mimics the apoptosis process in exogenous Aß(1-42)-treated HT22 cells. Taken together, these results indicate that mitochondria-targeted Aß(1-42) accumulation is the necessary and sufficient condition for Aß-mediated mitochondria impairments, and leads directly to cellular death rather than along with other Aß-mediated signaling alterations.

Aß-induced formation of autophagosomes is mediated by RAGE-CaMKKß-AMPK signaling.

Pathological autophagic vacuoles (AVs) accumulate in the brains of Alzheimer's disease (AD) patients, but the mechanisms by which they are induced are unknown. In this study, we found that the formation of AVs was mediated by activation of adenosine monophosphate (AMP)-activated protein kinase (AMPK) in the brains of APP/PS1 double transgenic mice, amyloid-beta peptide (Aß) pathology-bearing model mouse. Injection of sunitinib malate, AMPK inhibitor, to the mice lowered AV formation in their brains. Consistent with our in vivo observations, treatment of SH-SY5Y cells with Aß enhanced the induction of autophagosomes, which was mediated by Ca(2+)/calmodulin-dependent protein kinase kinase-beta (CaMKKß)-AMPK signaling, as shown using various inhibitors and small interfering RNA (siRNA). CaMKKß is a calcium-activated kinase, and the depletion of intracellular calcium by BAPTA-AM, a Ca(2+) chelator, also curtailed Aß-induced autophagy. Finally, the inhibition of receptor for advanced glycation end products (RAGE) attenuated autophagsome formation and AMPK signaling. Conversely, RAGE overexpression amplified the induction of autophagy. These results implicate the regulation of the Aß-induced formation of AVs by the RAGE-calcium-CaMKKß-AMPK pathway and suggest that modulation of autophagosome formation and the interaction between Aß and RAGE are beneficial in the treatment and prevention of Alzheimer's disease.

Disambiguation of similar object-place paired associations and the roles of the brain structures in the medial temporal lobe.

Amnesic patients who have damage in the hippocampus and in associated areas in the medial temporal lobe suffer from remembering specific events that may or may not share similar objects and locations. Computational models, behavioral studies, and physiological findings all suggest that neural circuits in the hippocampus are suitable for representing seemingly similar events as distinctively different individual event memories. This article offers a selective review on this particular function of the hippocampus and its associates areas such as the perirhinal cortex, mostly centering upon lesion studies and physiological studies using animals. We also present recent experimental results showing that the dentate gyrus subfield of the hippocampus and perirhinal cortex are particularly important for discriminating similar paired associates between same objects and different locations, or vice versa.

Inactivation of medial prefrontal cortex impairs time interval discrimination in rats.

Several lines of evidence suggest the involvement of prefrontal cortex in time interval estimation. The underlying neural processes are poorly understood, however, in part because of the paucity of physiological studies. The goal of this study was to establish an interval timing task for physiological recordings in rats, and test the requirement of intact medial prefrontal cortex (mPFC) for performing the task. We established a temporal bisection procedure using six different time intervals ranging from 3018 to 4784 ms that needed to be discriminated as either long or short. Bilateral infusions of muscimol (GABA(A) receptor agonist) into the mPFC significantly impaired animal's performance in this task, even when the animals were required to discriminate between only the longest and shortest time intervals. These results show the requirement of intact mPFC in rats for time interval discrimination in the range of a few seconds.