AMPK γ2 subunit gene PRKAG2 polymorphism associated with cognitive impairment as well as diabetes in old age

Longitudinal genome-wide DNA methylation changes in response to kidney failure replacement therapy

Chronic kidney disease (CKD) is an emerging public health priority associated with high mortality rates and demanding treatment regimens, including life-style changes, medications or even dialysis or renal transplantation. Unavoidably, the uremic milieu disturbs homeostatic processes such as DNA methylation and other vital gene regulatory mechanisms. Here, we aimed to investigate how dialysis or kidney transplantation modifies the epigenome-wide methylation signature over 12 months of treatment. We used the Infinium HumanMethylation450 BeadChip on whole blood samples from CKD-patients undergoing either dialysis (n = 11) or kidney transplantation (n = 12) and 24 age- and sex-matched population-based controls. At baseline, comparison between patients and controls identified several significant (P_FDR < 0.01) CpG methylation differences in genes with functions relevant to inflammation, cellular ageing and vascular calcification. Following 12 months, the global DNA methylation pattern of patients approached that seen in the control group. Notably, 413 CpG sites remained differentially methylated at follow-up in both treatment groups compared to controls. Together, these data indicate that the uremic milieu drives genome-wide methylation changes that are partially reversed with kidney failure replacement therapy. Differentially methylated CpG sites unaffected by treatment may be of particular interest as they could highlight candidate genes for kidney disease per se.

CARS senses cysteine deprivation to activate AMPK for cell survival

Adenosine 5'-monophosphate (AMP)-activated protein kinase (AMPK) is an important cellular metabolite-sensing enzyme that can directly sense changes not only in ATP but also in metabolites associated with carbohydrates and fatty acids. However, less is known about whether and how AMPK senses variations in cellular amino acids. Here, we show that cysteine deficiency significantly triggers calcium/calmodulin-dependent protein kinase kinase 2 (CaMKK2)-mediated activation of AMPK. In addition, we found that CaMKK2 directly associates with cysteinyl-tRNA synthetase (CARS), which then binds to AMPKγ2 under cysteine deficiency to activate AMPK. Interestingly, we discovered that cysteine inhibits the binding of CARS to AMPKγ2, and thus, under cysteine deficiency conditions wherein the inhibitory effect of cysteine is abrogated, CARS mediates the binding of AMPK to CaMKK2, resulting in the phosphorylation and activation of AMPK by CaMKK2. Importantly, we demonstrate that blocking AMPK activation leads to cell death under cysteine-deficient conditions. In summary, our study is the first to show that CARS senses the absence of cysteine and activates AMPK through the cysteine-CARS-CaMKK2-AMPKγ2 axis, a novel adaptation strategy for cell survival under nutrient deprivation conditions.

PRKAG2 Gene Expression Is Elevated and its Protein Levels Are Associated with Increased Amyloid-β Accumulation in the Alzheimer's Disease Brain

Increased amyloid-β (Aβ) accumulation associated with abnormal autophagy-lysosomal activity and nutrient kinase dysregulation are common features in Alzheimer’s disease (AD) brain. Recent studies have identified PRKAG2 and TIPRL genes that control nutrient kinase regulated autophagy, and here we determined if their expression is altered in postmortem AD brains. Gene and protein expression of TIPRL were unchanged. However, gene expression of PRKAG2 was increased 3-fold and its protein levels positively correlated with Aβ accumulation in the AD brain. In summary, our findings suggest that increased PRKAG2 is an important contributing factor to Aβ accumulation in the AD brain.

Decrease in Serum Levels of Adiponectin and Increase in 8-OHdG: a Culprit for Cognitive Impairment in the Elderly Patients with Type 2 Diabetes

BACKGROUND

Adiponectin and 8-Hydroxy-2'-deoxyguanosine (8-OHdG) are identified as important biomarkers in the pathogenesis process of type 2 diabetes mellitus (T2DM). Whether adiponectin and 8-OHdG have a relation to cognitive decline in the elderly T2DM patients has been poorly understood. The aim of this study was to evaluate the effects of adiponectin and 8-OHdG in the elderly patients with T2DM and to determine the role of adiponectin and 8-OHdG in the cognitive impairment of the elderly patients with T2DM.

METHODS

57 individuals were recruited and analyzed , with 26 cases of T2DM without cognitive impairment and 31 cases of T2DM with cognitive impairment. All of them underwent an examination of diabetes scales and blood glucose at different times. A primary diagnosis of diabetes was in line with the diagnosis criteria set by the American Diabetes Association (ADA). Statistical significance was defined as a P-value of less than 0.05.

RESULTS

The variables of sex, age, body mass index (BMI), hypertension, diabetes, metabolic syndrome, lacunar cerebral infarction, smoking and drinking in T2DM patients without cognitive impairment and with cognitive impairment showed no difference according to the univariate analysis exploring each variable separately (p>0.05). A significant difference was observed in the serum levels of adiponectin and 8-OHdG and the scales of MMSE and MoCA (p<0.05). Therefore, it was inferred that there is no correlation between glucose metabolic value and cognitive outcome of T2DM patients. Serum levels of adiponectin and 8-OHdG could act as biomarkers of cognitive impairment degree in the elderly T2DM patients.

CONCLUSION

Serum levels of adiponectin and 8-OHdG could act as specific and sensitive biomarkers for the early diagnosis and treatment of cognitive impairment in elderly T2DM patients. Serum levels of adiponectin and 8-OHdG have a close relation to the neurological cognitive outcome of the elderly T2DM patients.

Aggression based genome-wide, glutamatergic, dopaminergic and neuroendocrine polygenic risk scores predict callous-unemotional traits

Aggression and callous, uncaring, and unemotional (CU) traits are clinically related behavioral constructs caused by genetic and environmental factors. We performed polygenic risk score (PRS) analyses to investigate shared genetic etiology between aggression and these three CU-traits. Furthermore, we studied interactions of PRS with smoking during pregnancy and childhood life events in relation to CU-traits. Summary statistics for the base phenotype were derived from the EAGLE-consortium genome-wide association study of children's aggressive behavior and were used to calculate individual-level genome-wide and gene-set PRS in the NeuroIMAGE target-sample. Target phenotypes were 'callousness', 'uncaring', and 'unemotional' sumscores of the Inventory of Callous-Unemotional traits. A total of 779 subjects and 1,192,414 single-nucleotide polymorphisms were available for PRS-analyses. Gene-sets comprised serotonergic, dopaminergic, glutamatergic, and neuroendocrine signaling pathways. Genome-wide PRS showed evidence of association with uncaring scores (explaining up to 1.59% of variance; self-contained Q = 0.0306, competitive-P = 0.0015). Dopaminergic, glutamatergic, and neuroendocrine PRS showed evidence of association with unemotional scores (explaining up to 1.33, 2.00, and 1.20% of variance respectively; self-contained Q-values 0.037, 0.0115, and 0.0473 respectively, competitive-P-values 0.0029, 0.0002, and 0.0045 respectively). Smoking during pregnancy related to callousness scores while childhood life events related to both callousness and unemotionality. Moreover, dopaminergic PRS appeared to interact with childhood life events in relation to unemotional scores. Our study provides evidence suggesting shared genetic etiology between aggressive behavior and uncaring, and unemotional CU-traits in children. Gene-set PRS confirmed involvement of shared glutamatergic, dopaminergic, and neuroendocrine genetic variation in aggression and CU-traits. Replication of current findings is needed.

AMPK Subunits Harbor Largely Nonoverlapping Genetic Determinants for Body Fat Mass, Glucose Metabolism, and Cholesterol Metabolism

CONTEXT

Adenosine monophosphate (AMP)-activated protein kinase (AMPK) is a heterotrimeric enzyme and central regulator of cellular energy metabolism. The impact of single nucleotide polymorphisms (SNPs) in all 7 AMPK subunit genes on adiposity, glucose metabolism, and lipid metabolism has not yet been systematically studied.

OBJECTIVE

To analyze the associations of common SNPs in all AMPK genes, and of different scores thereof, with adiposity, insulin sensitivity, insulin secretion, blood glucose, low-density lipoprotein (LDL) cholesterol, high-density lipoprotein (HDL) cholesterol, total cholesterol, and triglycerides.

STUDY DESIGN AND METHODS

A cohort of 2789 nondiabetic participants from the Tübingen Family study of type 2 diabetes, metabolically characterized by oral glucose tolerance test and genotyped by genome-wide SNP array, was analyzed.

RESULTS

We identified 6 largely nonoverlapping SNP sets across 4 AMPK genes (PRKAA1, PRKAA2, PRKAG2, PRKAG3) associated with adiposity, insulin sensitivity, insulin secretion, blood glucose, total/LDL cholesterol, or HDL cholesterol, respectively. A genetic score of body-fat-increasing alleles revealed per-allele effect sizes on body mass index (BMI) of +0.22 kg/m2 (P = 2.3 × 10-7), insulin sensitivity of -0.12 × 1019 L2/mol2 (P = 9.9 × 10-6) and 2-hour blood glucose of +0.02 mmol/L (P = 0.0048). Similar effects on blood glucose were observed with scores of insulin-sensitivity-reducing, insulin-secretion-reducing and glucose-raising alleles, respectively. A genetic cholesterol score increased total and LDL cholesterol by 1.17 mg/dL per allele (P = 0.0002 and P = 3.2 × 10-5, respectively), and a genetic HDL score decreased HDL cholesterol by 0.32 mg/dL per allele (P = 9.1 × 10-6).

CONCLUSIONS

We describe largely nonoverlapping genetic determinants in AMPK genes for diabetes-/atherosclerosis-related traits, which reflect the metabolic pathways controlled by the enzyme. Formation of trait-specific genetic scores revealed additivity of allele effects, with body-fat-raising alleles reaching a marked effect size. (J Clin Endocrinol Metab XX: 0-0, 2019).

Functional Prediction of Chronic Kidney Disease Susceptibility Gene PRKAG2 by Comprehensively Bioinformatics Analysis

The genetic predisposition to chronic kidney disease (CKD) has been widely evaluated especially using the genome-wide association studies, which highlighted some novel genetic susceptibility variants in many genes, and estimated glomerular filtration rate to diagnose and stage CKD. Of these variants, rs7805747 in PRKAG2 was identified to be significantly associated with both serum creatinine and CKD with genome wide significance level. Until now, the potential mechanism by which rs7805747 affects CKD risk is still unclear. Here, we performed a functional analysis of rs7805747 variant using multiple bioinformatics software and databases. Using RegulomeDB and HaploReg (version 4.1), rs7805747 was predicated to locate in enhancer histone marks (Liver, Duodenum Mucosa, Fetal Intestine Large, Fetal Intestine Small, and Right Ventricle tissues). Using GWAS analysis in PhenoScanner, we showed that rs7805747 is not only associated with CKD, but also is significantly associated with other diseases or phenotypes. Using metabolite analysis in PhenoScanner, rs7805747 is identified to be significantly associated with not only the serum creatinine, but also with other 16 metabolites. Using eQTL analysis in PhenoScanner, rs7805747 is identified to be significantly associated with gene expression in multiple human tissues and multiple genes including PRKAG2. The gene expression analysis of PRKAG2 using 53 tissues from GTEx RNA-Seq of 8555 samples (570 donors) in GTEx showed that PRKAG2 had the highest median expression in Heart-Atrial Appendage. Using the gene expression profiles in human CKD, we further identified different expression of PRKAG2 gene in CKD cases compared with control samples. In summary, our findings provide new insight into the underlying susceptibility of PRKAG2 gene to CKD.

AMPK: Potential Therapeutic Target for Ischemic Stroke

5'-AMP-activated protein kinase (AMPK), a member of the serine/threonine (Ser/Thr) kinase group, is universally distributed in various cells and organs. It is a significant endogenous defensive molecule that responds to harmful stimuli, such as cerebral ischemia, cerebral hemorrhage, and, neurodegenerative diseases (NDD). Cerebral ischemia, which results from insufficient blood flow or the blockage of blood vessels, is a major cause of ischemic stroke. Ischemic stroke has received increased attention due to its '3H' effects, namely high mortality, high morbidity, and high disability. Numerous studies have revealed that activation of AMPK plays a protective role in the brain, whereas its action in ischemic stroke remains elusive and poorly understood. Based on existing evidence, we introduce the basic structure, upstream regulators, and biological roles of AMPK. Second, we analyze the relationship between AMPK and the neurovascular unit (NVU). Third, the actions of AMPK in different phases of ischemia and current therapeutic methods are discussed. Finally, we evaluate existing controversy and provide a detailed analysis, followed by ethical issues, potential directions, and further prospects of AMPK. The information complied here may aid in clinical and basic research of AMPK, which may be a potent drug candidate for ischemic stroke treatment in the future.

Cholinesterase Inhibitor Donepezil Increases Mitochondrial Biogenesis through AMP-Activated Protein Kinase in the Hippocampus

OBJECTIVE

Donepezil, a widely prescribed drug for Alzheimer's disease (AD), is now considered to have multimodal actions beyond cholinesterase inhibition. We aimed to see whether donepezil enhances mitochondrial biogenesis and relevant signaling pathways since mitochondrial dysfunction is a key feature of the hypometabolic AD brain.

METHODS

As a metabolic gauge, AMP-activated protein kinase (AMPK) was investigated as a tentative mediator of neurometabolic action of donepezil. Changes in phospho-AMPK levels, mitochondrial biogenesis, and ATP levels were measured upon donepezil treatment using neuroblastoma cells, primary cultured neurons and ex vivo hippocampal tissue of adult mice.

RESULTS

Donepezil dose-dependently increased mitochondrial biogenesis and ATP levels as well as expression of PGC-1α and NRF-1 in neuroblastoma cells. Donepezil dose-dependently activated AMPK; however, inhibition of AMPK abolished the observed effects of donepezil, indicating that AMPK is a key mediator of donepezil's action. Notably, mitochondrial biogenesis upon donepezil treatment was mainly observed within dendritic regions of primary cultured hippocampal neurons. Levels of synaptic markers were also increased by donepezil. Finally, AMPK- dependent mitochondrial biogenesis by donepezil was confirmed in organotypic hippocampal tissue.

CONCLUSIONS

Our findings indicate that AMPK/PGC-1α signaling is involved in beneficial actions of donepezil on neurometabolism. Pharmacological activation of AMPK might be a promising approach to counteract AD pathogenesis associated with brain hypometabolism.

Blunted response of hippocampal AMPK associated with reduced neurogenesis in older versus younger mice

The rate of hippocampal neurogenesis declines with aging. This is partly explained by decreased neural responsiveness to various cues stimulating metabolism. AMP-activated protein kinase (AMPK), a pivotal enzyme regulating energy homeostasis in response to metabolic demands, showed the diminished sensitivity in peripheral tissues during aging. AMPK is also known to be involved in neurogenesis. We aimed to see whether AMPK reactivity is also blunted in the aged hippocampus, and thus is associated with aging-related change in neurogenesis. Following subchronic (7days) intraperitoneal and acute intracerebroventricular (i.c.v.) administration of either 5-aminoimidazole-4-carboxamide ribonucleoside (AICAR; AMPK activator) or saline (sham) to young (16-week-old) and old (72-week-old) mice, we measured changes in AMPK activity, brain-derived neurotrophic factor (BDNF) expression or neurogenesis in the hippocampus. AICAR-induced changes in AMPK activity were observed in the hippocampus of young mice after acute i.c.v. injection. However, neither subchronic nor acute treatment induced significant changes in AMPK activity in old mice. Intriguingly, directions of AICAR-induced changes in AMPK activity were opposite between the hippocampus (decrease) and skeletal muscle (increase). ATP levels were inversely correlated with hippocampal AMPK activity, suggesting that the higher energy levels achieved by AICAR treatment might deactivate neuronal AMPK in young mice. The blunted response of AMPK to AICAR in old age was also indicated by the observations that the levels of neurogenesis and BDNF expression were significantly changed only in young mice upon AICAR treatment. Our findings suggest that the blunted response of neuronal AMPK in old age might be responsible for aging-associated decline in neurogenesis. Therefore, in addition to activation of AMPK, recovering its sensitivity may be necessary to enhance hippocampal neurogenesis in old age.

Neuropharmacological Actions of Metformin in Stroke

Increasing epidemiologic evidence suggests that metformin, a well-established AMPK activator and the most favorable first-line anti-diabetic drug, reduces stroke incidence and severity. However, the mechanism for this remains unclear. Moreover, previous experimental studies have reported controversial results about the effects of metformin on stroke outcomes during the acute phase. However, recent studies have consistently suggested that AMPK-mediated microglia/macrophage polarization and angioneurogenesis may play essential roles in metformin-promoted, long-term functional recovery following stroke. The present review summarizes the neuropharmacological actions of metformin in experimental stroke with an emphasis on the recent findings that the cell-specific effects and duration of AMPK activation are critical to the effects of metformin on stroke outcomes.

Analysis of risk factors for vascular cognitive impairment in patients with cerebral infarction

This study aimed to identify risk factors for vascular cognitive impairment (VCI) in cerebral infarction patients. Associations between VCI and age, gender, blood pressure, lipid levels, glycosylated hemoglobin, atrial fibrillation, tobacco smoking, alcohol consumption, homocysteine (Hcy), and High-Sensitivity C-Reactive Protein (HS-CRP) were evaluated in patients with cerebral infarction (n = 300) using single factor analysis and multivariate logistic regression analysis. By single factor analysis, the age, glycosylated hemoglobin, atrial fibrillation, blood pressure, Hcy, HS-CRP, tobacco smoking, and alcohol consumption were significantly associated with VCI in these patients. By multivariate logistic regression analysis, the age, glycosylated hemoglobin, blood pressure, Hcy, and HS-CRP were revealed as independent risk factors. The age, glycosylated hemoglobin, blood pressure, Hcy, and HS-CRP can serve as predictive factors for VCI in patients with cerebral infarction.

Hippocampal transcriptome-guided genetic analysis of correlated episodic memory phenotypes in Alzheimer's disease

As the most common type of dementia, Alzheimer's disease (AD) is a neurodegenerative disorder initially manifested by impaired memory performances. While the diagnosis information indicates a dichotomous status of a patient, memory scores have the potential to capture the continuous nature of the disease progression and may provide more insights into the underlying mechanism. In this work, we performed a targeted genetic study of memory scores on an AD cohort to identify the associations between a set of genes highly expressed in the hippocampal region and seven cognitive scores related to episodic memory. Both main effects and interaction effects of the targeted genetic markers on these correlated memory scores were examined. In addition to well-known AD genetic markers APOE and TOMM40, our analysis identified a new risk gene NAV2 through the gene-level main effect analysis. NAV2 was found to be significantly and consistently associated with all seven episodic memory scores. Genetic interaction analysis also yielded a few promising hits warranting further investigation, especially for the RAVLT list B Score.

Increased plasma levels of heat shock protein 70 associated with subsequent clinical conversion to mild cognitive impairment in cognitively healthy elderly

Background and Aims

Heat shock proteins (HSPs) have been regarded as cytoprotectants that protect brain cells during the progression of neurodegenerative diseases and from damage resulting from cerebral ischemia. In this study, we assessed the association between plasma HSP 70/27 levels and cognitive decline.

Methods

Among participants in the community-based cohort study of dementia called the Gwangju Dementia and Mild Cognitive Impairment Study, subjects without cognitive impairment at baseline, who then either remained without impairment (non-conversion group), or suffered mild cognitive impairment (MCI) (conversion group) (non-conversion group, N = 36; conversion group, N = 30) were analyzed.

Results

After a five to six year follow-up period, comparison of the plasma HSP 70 and HSP 27 levels of the two groups revealed that only the plasma HSP 70 level was associated with a conversion to MCI after adjustments for age, gender, years of education, follow-up duration, APOE e4, hypertension, and diabetes (repeated measure analysis of variance: F = 7.59, p = 0.008). Furthermore, an increase in plasma HSP 70 level was associated with cognitive decline in language and executive function (linear mixed model: Korean Boston Naming Test, -0.426 [-0.781, -0.071], p = 0.019; Controlled Oral Word Association Test, -0.176 [-0.328, -0.023], p = 0.024; Stroop Test, -0.304 [-0.458, -0.150], p<0.001).

Conclusions

These findings suggest that the plasma HSP 70 level may be related to cognitive decline in the elderly.

The unfolded protein response, inflammation, oscillators, and disease: a systems biology approach

Non-communicable diseases (NCDs) such as cardiovascular disease, cancers, diabetes and obesity are responsible for about two thirds of mortality worldwide, and all of these ailments share a common low-intensity systemic chronic inflammation, endoplasmic reticulum stress (ER stress), and the ensuing Unfolded Protein Response (UPR). These adaptive mechanisms are also responsible for significant metabolic changes that feedback with the central clock of the suprachiasmatic nucleus (SCN) of the hypothalamus, as well as with oscillators of peripheral tissues. In this review we attempt to use a systems biology approach to explore such interactions as a whole; to answer two fundamental questions: (1) how dependent are these adaptive responses and subsequent events leading to NCD with their state of synchrony with the SCN and peripheral oscillators? And, (2) How could modifiers of the activity of SCN for instance, food intake, exercise, and drugs, be potentially used to modulate systemic inflammation and ER stress to ameliorate or even prevent NCDs?

Differential central pathology and cognitive impairment in pre-diabetic and diabetic mice

Although age remains the main risk factor to suffer Alzheimer's disease (AD) and vascular dementia (VD), type 2 diabetes (T2D) has turned up as a relevant risk factor for dementia. However, the ultimate underlying mechanisms for this association remain unclear. In the present study we analyzed central nervous system (CNS) morphological and functional consequences of long-term insulin resistance and T2D in db/db mice (leptin receptor KO mice). We also included C57Bl6 mice fed with high fat diet (HFD) and a third group of C57Bl6 streptozotocin (STZ) treated mice. Db/db mice exhibited pathological characteristics that mimic both AD and VD, including age dependent cognitive deterioration, brain atrophy, increased spontaneous hemorrhages and tau phosphorylation, affecting the cortex preferentially. A similar profile was observed in STZ-induced diabetic mice. Moreover metabolic parameters, such as body weight, glucose and insulin levels are good predictors of many of these alterations in db/db mice. In addition, in HFD-induced hyperinsulinemia in C57Bl6 mice, we only observed mild CNS alterations, suggesting that central nervous system dysfunction is associated with well established T2D. Altogether our results suggest that T2D may promote many of the pathological and behavioral alterations observed in dementia, supporting that interventions devoted to control glucose homeostasis could improve dementia progress and prognosis.

Overexpression of G100S mutation in PRKAG2 causes Wolff-Parkinson-White syndrome in zebrafish

The Wolff-Parkinson-White (WPW) syndrome was believed to be associated with PRKAG2 gene mutations. In this study, we verified the pathopoiesis of G100S mutation, a novel mutation only discovered in Chinese patients with WPW, in cardiac disorder. Similar to R302Q, when overexpressed PRKAG2 G100S mutant in zebrafish, we observed a thicker heart wall, detected a decreased AMPK enzymatic activity by tissue AMPK kinase activity colorimetric technique, as well as examined an increased glycogen storage in heart wall using the method for periodic acid-Schiff staining, in comparison with the zebrafish without exogenous PRKAG2 (mock) or with wild-type PRKAG2 (WT). Taken together, we concluded PRKAG2 G100S mutation might contribute to impair the AMP-activated protein kinase function, which resulted in increased cardiac glycogen storage, serving as a pathogenesis for WPW syndrome in Chinese.