Neuronal SIRT1 Activation as a Novel Mechanism Underlying the Prevention of Alzheimer Disease Amyloid Neuropathology by Calorie Restriction

Active Turnover of Heme in Hibernation Period in Mammals

Heme oxygenase (HO)-1 plays an important role during hibernation by catalyzing the degradation of heme to biliverdin/bilirubin, ferrous iron, and carbon monoxide, which activates the protective mechanisms against stress. In this context, it was important to analyze the metabolic processes of heme. Nevertheless, to date, no study has approached on biosynthesis of heme. Therefore, our study aims to understand the process of heme biosynthesis, which regulates cell survival in conditions of hypothermia and calorie restriction (CR). During hibernation, the mRNA levels of enzymes responsible for de novo heme biosynthesis were increased in the liver tissue of a Syrian hamster model of hibernation. Moreover, heme trafficking and iron metabolism were found to be more active, as assessed based on the changes in the levels of heme transporter and ferroportin mRNA. The levels of HO-1, a powerful antioxidant, were also upregulated during hibernation. Additionally, increased levels of Sirt-1 mRNA were also observed. These enzymes are known to act as cellular metabolic sensors that activate the cytoprotective mechanisms. These results indicate that HO-1 induction, brought about by the upregulation of heme during the pre-hibernation period, may protect against external stress. Here, we describe heme catabolism during hibernation by analyzing the regulation of the key molecular players involved in heme metabolism. Therefore, this study offers a new strategy for the better regulation of intracellular heme concentrations during hypothermia and other stresses.

Acute sources of mitochondrial NAD+ during respiratory chain dysfunction

It is a textbook definition that in the absence of oxygen or inhibition of the mitochondrial respiratory chain by pharmacologic or genetic means, hyper-reduction of the matrix pyridine nucleotide pool ensues due to impairment of complex I oxidizing NADH, leading to reductive stress. However, even under these conditions, the ketoglutarate dehydrogenase complex (KGDHC) is known to provide succinyl-CoA to succinyl-CoA ligase, thus supporting mitochondrial substrate-level phosphorylation (mSLP). Mindful that KGDHC is dependent on provision of NAD⁺, hereby sources of acute NADH oxidation are reviewed, namely i) mitochondrial diaphorases, ii) reversal of mitochondrial malate dehydrogenase, iii) reversal of the mitochondrial isocitrate dehydrogenase as it occurs under acidic conditions, iv) residual complex I activity and v) reverse operation of the malate-aspartate shuttle. The concept of NAD⁺ import through the inner mitochondrial membrane as well as artificial means of manipulating matrix NAD⁺/NADH are also discussed. Understanding the above mechanisms providing NAD⁺ to KGDHC thus supporting mSLP may assist in dampening mitochondrial dysfunction underlying neurological disorders encompassing impairment of the electron transport chain.

Quercetin protects against diabetic encephalopathy via SIRT1/NLRP3 pathway in db/db mice

Epidemiological studies have found that diabetes and cognitive dysfunction are closely related. Quercetin has been certified with the effect on improving diabetes mellitus (DM) and cognitive impairment. However, the effect and related mechanism of quercetin on diabetic encephalopathy (DE) are still ambiguous. In this study, we used the db/db mice (diabetic model) to discover whether quercetin could improve DE through the Sirtuin1/NLRP3 (NOD‐, LRR‐ and pyrin domain‐containing 3) pathway. Behavioural results (Morris water maze and new object recognition tests) showed that quercetin (70 mg/kg) improved the learning and memory. Furthermore, quercetin alleviated insulin resistance and the level of fasting blood glucose. Besides, Western blot analysis also showed that quercetin increased the protein expressions of nerve‐ and synapse‐related protein, including postsynapticdensity 93 (PSD93), postsynapticdensity 95 (PSD95), brain‐derived neurotrophic factor (BDNF) and nerve growth factor (NGF) in the brain of db/db mice. Quercetin also increased the protein expression of SIRT1 and decreased the expression of NLRP3 inflammation‐related proteins, including NLRP3, the adaptor protein ASC and cleaved Caspase‐1, the pro‐inflammatory cytokines IL‐1β and IL‐18. In conclusion, the present results indicate that the SIRT1/NLRP3 pathway may be a crucial mechanism for the neuroprotective effect of quercetin against DE.

Environmental Enrichment: Disentangling the Influence of Novelty, Social, and Physical Activity on Cerebral Amyloid Angiopathy in a Transgenic Mouse Model

Cerebral amyloid angiopathy (CAA) is the deposition of amyloid protein in the cerebral vasculature, a common feature in both aging and Alzheimer's disease (AD). However, the effects of environmental factors, particularly cognitive stimulation, social stimulation, and physical activity, on CAA pathology are poorly understood. These factors, delivered in the form of the environmental enrichment (EE) paradigm in rodents, have been shown to have beneficial effects on the brain and behavior in healthy aging and AD models. However, the relative importance of these subcomponents on CAA pathology has not been investigated. Therefore, we assessed the effects of EE, social enrichment (SOC), and cognitive enrichment (COG) compared to a control group that was single housed without enrichment (SIN) from 4 to 8 months of age in wild-type mice (WT) and Tg-SwDI mice, a transgenic mouse model of CAA that exhibits cognitive/behavioral deficits. The results show that individual facets of enrichment can affect an animal model of CAA, though the SOC and combined EE conditions are generally the most effective at producing physiological, cognitive/behavioral, and neuropathological changes, adding to a growing literature supporting the benefits of lifestyle interventions.

Neuroinflammation and Neurogenesis in Alzheimer's Disease and Potential Therapeutic Approaches

In adult brain, new neurons are generated throughout adulthood in the subventricular zone and the dentate gyrus; this process is commonly known as adult neurogenesis. The regulation or modulation of adult neurogenesis includes various intrinsic pathways (signal transduction pathway and epigenetic or genetic modulation pathways) or extrinsic pathways (metabolic growth factor modulation, vascular, and immune system pathways). Altered neurogenesis has been identified in Alzheimer's disease (AD), in both human AD brains and AD rodent models. The exact mechanism of the dysregulation of adult neurogenesis in AD has not been completely elucidated. However, neuroinflammation has been demonstrated to alter adult neurogenesis. The presence of various inflammatory components, such as immune cells, cytokines, or chemokines, plays a role in regulating the survival, proliferation, and maturation of neural stem cells. Neuroinflammation has also been considered as a hallmark neuropathological feature of AD. In this review, we summarize current, state-of-the art perspectives on adult neurogenesis, neuroinflammation, and the relationship between these two phenomena in AD. Furthermore, we discuss the potential therapeutic approaches, focusing on the anti-inflammatory and proneurogenic interventions that have been reported in this field.

Alzheimer's Disease and Diabetes: Insulin Signaling as the Bridge Linking Two Pathologies

Alzheimer's (or Alzheimer) disease (AD) is the most prevalent subset of dementia, affecting elderly populations worldwide. The cumulative costs of the AD care are rapidly accelerating as the average lifespan increases. Onset and risk factors for AD and AD-like dementias have been largely unknown until recently. Studies show that chronic type II diabetes mellitus (DM) is closely associated with neurodegeneration, especially AD. Type II DM is characterized by the cells' inability to take up insulin, as well as chronic hyperglycemia. In the central nervous system, insulin has crucial regulatory roles, while chronic hyperglycemia leads to formation and accumulation of advanced glycation end products (AGEs). AGEs are the major contributor to insulin resistance in diabetic cells, due to their regulatory role on sirtuin expression. Insulin activity in the central nervous system is known to interact with key proteins affected in neurodegenerative conditions, such as amyloid-β precursor protein (AβPP or APP), huntingtin-associated protein-1 (HAP1), Abelson helper integration site-1 (AHI1 or Jouberin), kinesin, and tau. Sirtuins have been theorized to be the mechanism for insulin resistance, and have been found to be affected in neurodegenerative conditions as well. There are hints that all these neuronal proteins may be closely related, although the mechanisms remain unclear. This review will gather existing research on these proteins and highlight the link between neurodegenerative conditions and diabetes mellitus.

Activation of PKA/SIRT1 signaling pathway by photobiomodulation therapy reduces Aβ levels in Alzheimer's disease models

A hallmark of Alzheimer's disease (AD) is the accumulation of amyloid-β (Aβ), which correlates significantly with progressive cognitive deficits. Although photobiomodulation therapy (PBMT), as a novel noninvasive physiotherapy strategy, has been proposed to improve neuronal survival, decrease neuron loss, ameliorate dendritic atrophy, and provide overall AD improvement, it remains unknown whether and how this neuroprotective process affects Aβ levels. Here, we report that PBMT reduced Aβ production and plaque formation by shifting amyloid precursor protein (APP) processing toward the nonamyloidogenic pathway, thereby improving memory and cognitive ability in a mouse model of AD. More importantly, a pivotal protein, SIRT1, was involved in this process by specifically up-regulating ADAM10 and down-regulating BACE1, which is dependent on the cAMP/PKA pathway in APP/PS1 primary neurons and SH-SY5Y cells stably expressing human APP Swedish mutation (APPswe). We further found that the activity of the mitochondrial photoacceptor cytochrome c oxidase (CcO) was responsible for PBMT-induced activation of PKA and SIRT1. Together, our research suggests that PBMT as a viable therapeutic strategy has great potential value in improving cognitive ability and combatting AD.

Molecular Mechanism of Autophagy: Its Role in the Therapy of Alzheimer's Disease

Alzheimer's disease (AD) is a neurodegenerative disorder of progressive dementia that is characterized by the accumulation of beta-amyloid (Aβ)-containing neuritic plaques and intracellular Tau protein tangles. This distinctive pathology indicates that the protein quality control is compromised in AD. Autophagy functions as a "neuronal housekeeper" that eliminates aberrant protein aggregates by wrapping then into autophagosomes and delivering them to lysosomes for degradation. Several studies have suggested that autophagy deficits in autophagy participate in the accumulation and propagation of misfolded proteins (including Aβ and Tau). In this review, we summarize current knowledge of autophagy in the pathogenesis of AD, as well as some pathways targeting the restoration of autophagy. Moreover, we discuss how these aspects can contribute to the development of disease-modifying therapies in AD.

NAD+ homeostasis in health and disease

The conceptual evolution of nicotinamide adenine dinucleotide (NAD⁺) from being seen as a simple metabolic cofactor to a pivotal cosubstrate for proteins regulating metabolism and longevity, including the sirtuin family of protein deacylases, has led to a new wave of scientific interest in NAD⁺. NAD⁺ levels decline during ageing, and alterations in NAD⁺ homeostasis can be found in virtually all age-related diseases, including neurodegeneration, diabetes and cancer. In preclinical settings, various strategies to increase NAD⁺ levels have shown beneficial effects, thus starting a competitive race to discover marketable NAD⁺ boosters to improve healthspan and lifespan. Here, we review the basics of NAD⁺ biochemistry and metabolism, and its roles in health and disease, and we discuss current challenges and the future translational potential of NAD⁺ research.

Supplementation ofBacillus amyloliquefaciensAS385 culture broth powder containing 1-deoxynojirimycin in a high-fat diet altered the gene expressions related to lipid metabolism and insulin signaling in mice epididymal white adipose tissue

Supplementation ofBacillus amyloliquefaciensAS385 culture broth powder in high-fat diet restored adiposity, glucose tolerance and insulin sensitivity in mice.

GSK3β Regulates Brain Energy Metabolism

GSK3β is a serine threonine kinase implicated in the progression of Alzheimer’s disease. Although the role of GSK3β in growth and pathology has been extensively studied, little is known about the metabolic consequences of GSK3β manipulation, particularly in the brain. Here, we show that GSK3β regulates mitochondrial energy metabolism in human H4 neuroglioma cells and rat PC12-derived neuronal cells and that inhibition of GSK3β in mice in vivo alters metabolism in the hippocampus in a region-specific manner. We demonstrate that GSK3β inhibition increases mitochondrial respiration and membrane potential and alters NAD(P)H metabolism. These metabolic effects are associated with increased PGC-1α protein stabilization, enhanced nuclear localization, and increased transcriptional co-activation. In mice treated with the GSK3β inhibitor lithium carbonate, changes in hippocampal energy metabolism are linked to increased PGC-1α. These data highlight a metabolic role for brain GSK3β and suggest that the GSK3β/PGC-1α axis may be important in neuronal metabolic integrity.

Current and emerging therapeutic targets of alzheimer's disease for the design of multi-target directed ligands

Alzheimer's disease (AD) is the most prevalent neurodegenerative disease, and a major cause of death worldwide. The number of people suffering from this debilitating disorder is rising at an unprecedented rate, with a subsequent surge in healthcare costs. Only four drugs are clinically available for the treatment of AD symptoms, but they are not disease-modifying. Consequently, there is an urgent need for a cure. Although the cause of this debilitating condition remains poorly understood, it is believed that several factors may be involved in combination - including, health and lifestyle, environmental, and genetic factors. In recent years, a number of hallmarks of the disease have also been discovered, and it is believed that these factors may play an important role in the development of AD. Amyloid aggregation is one such factor which has been highly investigated, in addition to cholinesterase enzymes and tau aggregation. In the last decade, multi-target drugs have been increasingly investigated for their application to AD treatment. By combining two or more pharmacophores in a single compound, it is possible to synthesise a drug which can target several factors that are involved in AD development. This is a particularly attractive approach as it would avoid the use of combination therapies. As a result, it could reduce the burden on carers and families, and decrease healthcare and social care costs. Many active pharmacophores have been employed for the development of hybrid drugs, due to their abilities to inhibit the factors currently widely recognised to be involved in AD. These compounds have demonstrated promising results; however, research is still required to optimise the pharmacological profiles of the drugs, in addition to their potencies. Meanwhile, extensive research is continuously being performed into other potential targets for the treatment of AD. Based on the results obtained thus far, it is likely that multi-target compounds will continue to be increasingly studied in the future as potential treatments for AD.

NAD+ homeostasis in renal health and disease

The mammalian kidney relies on abundant mitochondria in the renal tubule to generate sufficient ATP to provide the energy required for constant reclamation of solutes from crude blood filtrate. The highly metabolically active cells of the renal tubule also pair their energetic needs to the regulation of diverse cellular processes, including energy generation, antioxidant responses, autophagy and mitochondrial quality control. Nicotinamide adenine dinucleotide (NAD⁺) is essential not only for the harvesting of energy from substrates but also for an array of regulatory reactions that determine cellular health. In acute kidney injury (AKI), substantial decreases in the levels of NAD⁺ impair energy generation and, ultimately, the core kidney function of selective solute transport. Conversely, augmentation of NAD⁺ may protect the kidney tubule against diverse acute stressors. For example, NAD⁺ augmentation can ameliorate experimental AKI triggered by ischaemia–reperfusion, toxic injury and systemic inflammation. NAD⁺-dependent maintenance of renal tubular metabolic health may also attenuate long-term profibrotic responses that could lead to chronic kidney disease. Further understanding of the genetic, environmental and nutritional factors that influence NAD⁺ biosynthesis and renal resilience may lead to novel approaches for the prevention and treatment of kidney disease.

Here, the authors discuss evidence for a role of NAD⁺ imbalance in the pathogenesis of acute kidney injury (AKI) and chronic kidney disease (CKD). They suggest that disruption of NAD⁺ metabolism may contribute to mechanistic links among AKI, CKD and ageing.

NAD⁺ has critical roles in the generation of ATP from fuel substrates and as a substrate for important enzymes that regulate cellular health and stress responses.

The renal tubule is highly metabolically active and requires a constant supply of ATP to provide the energy required to pump solutes across unfavourable gradients.

Experimental acute kidney injury (AKI) induced by various insults rapidly leads to a decrease in NAD⁺ levels that probably results from a combination of reduced NAD⁺ biosynthesis and increased NAD⁺ consumption.

Renal NAD⁺ levels can be augmented using vitamin B₃ analogues and related nutritional precursors.

NAD⁺ augmentation can prevent and/or treat various aetiologies of experimental AKI and might also attenuate long-term profibrotic responses following AKI, suggesting a potential role in the treatment of chronic kidney disease.

Liraglutide Treatment Ameliorates Neurotoxicity Induced by Stable Silencing of Pin1

Post-translational modulation of peptidylprolyl isomerase Pin1 might link impaired glucose metabolism and neurodegeneration, being Pin1 effectors target for the glucagon-Like-Peptide1 analog liraglutide. We tested the hypotheses in Pin1 silenced cells (SH-SY5Y) treated with 2-deoxy-d-glucose (2DG) and methylglyoxal (MG), stressors causing altered glucose trafficking, glucotoxicity and protein glycation. Rescue by liraglutide was investigated. Pin1 silencing caused increased levels of reactive oxygen species, upregulated energy metabolism as suggested by raised levels of total ATP content and mRNA of SIRT1, PGC1α, NRF1; enhanced mitochondrial fission events as supported by raised protein expression of FIS1 and DRP1. 2DG and MG reduced significantly cell viability in all the cell lines. In Pin1 KD clones, 2DG exacerbated altered mitochondrial dynamics causing higher rate of fission events. Liraglutide influenced insulin signaling pathway (GSK3b/Akt); improved cell viability also in cells treated with 2DG; but it did not revert mitochondrial dysfunction in Pin1 KD model. In cells treated with MG, liraglutide enhanced cell viability, reduced ROS levels and cell death (AnnexinV/PI); and trended to reduce anti-apoptotic signals (BAX, BCL2, CASP3). Pin1 silencing mimics neuronal metabolic impairment of patients with impaired glucose metabolism and neurodegeneration. Liraglutide rescues to some extent cellular dysfunctions induced by Pin1 silencing.

Stimulation of SIRT1 Attenuates the Level of Oxidative Stress in the Brains of APP/PS1 Double Transgenic Mice and in Primary Neurons Exposed to Oligomers of the Amyloid-β Peptide

In the study, we examined whether the silent information regulator 1 (SIRT1) can attenuate oxidative stress in the brains of mice carrying the APP/PS1 double mutation and/or in primary neonatal rat neurons exposed to oligomers of amyloid-β peptide (AβOs). Starting at 4 or 8 months of age, the transgenic mice were treated with resveratrol (RSV, a stimulator of SIRT1) or suramin (an inhibitor) (each 20 mg/kg BW/day) for two months. The primary neurons were exposed to AβOs (0.5 μM) for 48 h and thereafter RSV (20 μM) or suramin (300 mg/ml) for 24 h. Cell viability was assessed by the CCK-8 assay; SIRT1 protein and mRNA determined by western blotting and real-time PCR, respectively; senile plaques examined immunohistochemically; ROS monitored by flow cytometry; and the contents of OH-, H2O2, O2·-, and MDA, and the activities of SOD and GSH-Px measured by standard biochemical procedures. In comparison to wild-type mice or untreated primary neurons, the expression of SIRT1 was significantly lower in the brains of APP/PS1 mice or neurons exposed to AβOs. In these same systems, increased numbers of senile plaques and a high level of oxidative stress were apparent. Interestingly, these two latter changes were attenuated by treatment with RSV, but enhanced by suramin. These findings indicate that SIRT1 may be neuroprotective.

Significant association of 3-hydroxy-3-methylglutaryl-CoA reductase (HMGCR) rs3846662 and sirtuin 1 (SIRT1) rs7895833 and apolipoprotein E (APOE) hypermethylation with mild cognitive impairment (MCI)

Our study investigated the association of five genes with MCI in the Xinjiang Uygur population in China. In addition, we also analyzed the association between APOE methylation and MCI.Forty-three MCI and 125 controls were included in the present study. Genotyping was done by Sanger sequencing. DNA methylation assay was done using quantitative methylation-specific polymerase chain reaction (qMSP).The distribution of HMGCR rs3846662 allele frequencies was significantly different between the MCI group and the control group (P = .04), especially in women (P = .032). Subgroup analysis showed that there was a statistically significant association of HMGCR rs3846662 with MCI in the non-APOE ε4 group (P = .024), especially in the females with non-APOE ε4. Similarly, HMGCR rs3846662 genotype and allele frequency in the ApoE E2 protein group were significantly different in the MCI group and the control group (genotype P = .021; allele P = .007). In addition, SIRT1 rs7895833 genotype frequency in the APOE ε4 group was found to be significantly different between the MCI and the control group (P = .005). We also observed a significant association of SIRT1 rs7895833 with MCI in the ApoE E4 protein subgroup (P = .005). In addition, APOE methylation levels were significantly different between the MCI group and the control group (P = .021), especially in men (P = .006). Subgroup analysis showed that APOE methylation levels were significantly associated with MCI in the non-APOE ε4 group (P = .009), especially in men (P = .015).This study found a significant association of HMGCR rs3846662 with MCI in females independent of APOE ε4. In contrast, we revealed that the association of SIRT1 rs7895833 with MCI was dependent on with APOE ε4. We also showed that hypermethylation of APOE in MCI was independent of APOE ε4.

miR-146a and miR-181a are involved in the progression of mild cognitive impairment to Alzheimer's disease

The identification of mechanisms associated with Alzheimer's disease (AD) development in mild cognitive impairment (MCI) would be of great usefulness to clarify AD pathogenesis and to develop preventive and therapeutic strategies. In this study, blood levels of the candidate microRNAs (small noncoding RNAs that play a pivotal role in gene expression) miR-146a, miR-181a, miR-181b, miR-24-3p, miR-186a, miR-101, miR-339, miR-590, and miR-22 have been investigated for association to AD conversion within 2 years in a group of 45 patients with MCI. Baseline miR-146a (p = 0.036) and miR-181a (p = 0.026) showed a significant upregulation in patients with MCI who later converted to AD. These alterations were related to AD hallmarks: a significant negative correlation was found with amyloid beta cerebrospinal fluid concentration for miR-146a (p = 0.006) and miR-181a (p = 0.001). Moreover, higher levels of miR-146a were associated to apolipoprotein E ε4 allele presence, smaller volume of the hippocampus (p = 0.045) and of the CA1 (p = 0.013) and the subiculum (p = 0.027) subfields. Increased levels of miR-146a (p = 0.031) and miR-181a (p = 0.002) were also linked with diffusivity alterations in the cingulum. These data support a role for miR-146a and miR-181a in the mechanisms of AD progression.

Amyloid Precursor Protein (APP) and GABAergic Neurotransmission

The amyloid precursor protein (APP) is the parent polypeptide from which amyloid-beta (Aβ) peptides, key etiological agents of Alzheimer's disease (AD), are generated by sequential proteolytic processing involving β- and γ-secretases. APP mutations underlie familial, early-onset AD, and the involvement of APP in AD pathology has been extensively studied. However, APP has important physiological roles in the mammalian brain, particularly its modulation of synaptic functions and neuronal survival. Recent works have now shown that APP could directly modulate γ-aminobutyric acid (GABA) neurotransmission in two broad ways. Firstly, APP is shown to interact with and modulate the levels and activity of the neuron-specific Potassium-Chloride (K+-Cl-) cotransporter KCC2/SLC12A5. The latter is key to the maintenance of neuronal chloride (Cl-) levels and the GABA reversal potential (EGABA), and is therefore important for postsynaptic GABAergic inhibition through the ionotropic GABAA receptors. Secondly, APP binds to the sushi domain of metabotropic GABAB receptor 1a (GABABR1a). In this regard, APP complexes and is co-transported with GABAB receptor dimers bearing GABABR1a to the axonal presynaptic plasma membrane. On the other hand, secreted (s)APP generated by secretase cleavages could act as a GABABR1a-binding ligand that modulates presynaptic vesicle release. The discovery of these novel roles and activities of APP in GABAergic neurotransmission underlies the physiological importance of APP in postnatal brain function.

Catalytic-independent neuroprotection by SIRT1 is mediated through interaction with HDAC1

SIRT1, a NAD+-dependent deacetylase, protects neurons in a variety of in vitro and in vivo models of neurodegenerative disease. We have previously described a neuroprotective effect by SIRT1 independent of its catalytic activity. To confirm this conclusion we tested a panel of SIRT1 deletion mutant constructs, designated Δ1–Δ10, in cerebellar granule neurons induced to undergo apoptosis by low potassium treatment. We find that deletions of its N-terminal, those lacking portions of the catalytic domain, as well as one that lacks the ESA (Essential for SIRT1 Activity) motif, are as protective as wild-type SIRT1. In contrast, deletion of the region spanning residues 542–609, construct Δ8, substantially reduced the neuroprotective activity of SIRT1. As observed with LK-induced apoptosis, all SIRT1 constructs except Δ8 protect neurons against mutant huntingtin toxicity. Although its own catalytic activity is not required, neuroprotection by SIRT1 is abolished by inhibitors of Class I HDACs as well as by knockdown of endogenous HDAC1. We find that SIRT1 interacts with HDAC1 and this interaction is greatly increased by deleting regions of SIRT1 necessary for its catalytic activity. However, SIRT1-mediated protection is not dependent on HDAC1 deacetylase activity. Although other studies have described that catalytic activity of SIRT1 mediates is neuroprotective effect, our study suggests that in cerebellar granule neurons its deacetylase activity is not important and that HDAC1 contributes to the neuroprotective effect of SIRT1.

Dihydronicotinamide riboside is a potent NAD+ concentration enhancer in vitro and in vivo

Interest in pharmacological agents capable of increasing cellular NAD⁺ concentrations has stimulated investigations of nicotinamide riboside (NR) and nicotinamide mononucleotide (NMN). NR and NMN require large dosages for effect. Herein, we describe synthesis of dihydronicotinamide riboside (NRH) and the discovery that NRH is a potent NAD⁺ concentration-enhancing agent, which acts within as little as 1 h after administration to mammalian cells to increase NAD⁺ concentrations by 2.5-10-fold over control values. Comparisons with NR and NMN show that in every instance, NRH provides greater NAD⁺ increases at equivalent concentrations. NRH also provides substantial NAD⁺ increases in tissues when administered by intraperitoneal injection to C57BL/6J mice. NRH substantially increases NAD⁺/NADH ratio in cultured cells and in liver and no induction of apoptotic markers or significant increases in lactate levels in cells. Cells treated with NRH are resistant to cell death caused by NAD⁺-depleting genotoxins such as hydrogen peroxide and methylmethane sulfonate. Studies to identify its biochemical mechanism of action showed that it does not inhibit NAD⁺ consumption, suggesting that it acts as a biochemical precursor to NAD⁺ Cell lysates possess an ATP-dependent kinase activity that efficiently converts NRH to the compound NMNH, but independent of Nrk1 or Nrk2. These studies identify a putative new metabolic pathway to NAD⁺ and a potent pharmacologic agent for NAD⁺ concentration enhancement in cells and tissues.

Sirtuins in Alzheimer's Disease: SIRT2-Related GenoPhenotypes and Implications for PharmacoEpiGenetics

Sirtuins (SIRT1-7) are NAD⁺-dependent protein deacetylases/ADP ribosyltransferases with important roles in chromatin silencing, cell cycle regulation, cellular differentiation, cellular stress response, metabolism and aging. Sirtuins are components of the epigenetic machinery, which is disturbed in Alzheimer’s disease (AD), contributing to AD pathogenesis. There is an association between the SIRT2-C/T genotype (rs10410544) (50.92%) and AD susceptibility in the APOEε4-negative population (SIRT2-C/C, 34.72%; SIRT2-T/T 14.36%). The integration of SIRT2 and APOE variants in bigenic clusters yields 18 haplotypes. The 5 most frequent bigenic genotypes in AD are 33CT (27.81%), 33CC (21.36%), 34CT (15.29%), 34CC (9.76%) and 33TT (7.18%). There is an accumulation of APOE-3/4 and APOE-4/4 carriers in SIRT2-T/T > SIRT2-C/T > SIRT2-C/C carriers, and also of SIRT2-T/T and SIRT2-C/T carriers in patients who harbor the APOE-4/4 genotype. SIRT2 variants influence biochemical, hematological, metabolic and cardiovascular phenotypes, and modestly affect the pharmacoepigenetic outcome in AD. SIRT2-C/T carriers are the best responders, SIRT2-T/T carriers show an intermediate pattern, and SIRT2-C/C carriers are the worst responders to a multifactorial treatment. In APOE-SIRT2 bigenic clusters, 33CC carriers respond better than 33TT and 34CT carriers, whereas 24CC and 44CC carriers behave as the worst responders. CYP2D6 extensive metabolizers (EM) are the best responders, poor metabolizers (PM) are the worst responders, and ultra-rapid metabolizers (UM) tend to be better responders that intermediate metabolizers (IM). In association with CYP2D6 genophenotypes, SIRT2-C/T-EMs are the best responders. Some Sirtuin modulators might be potential candidates for AD treatment.

Resveratrol Promotes Mitochondrial Biogenesis and Protects against Seizure-Induced Neuronal Cell Damage in the Hippocampus Following Status Epilepticus by Activation of the PGC-1α Signaling Pathway

Peroxisome proliferator-activated receptor gamma coactivator 1-alpha (PGC-1α) is known to regulate mitochondrial biogenesis. Resveratrol is present in a variety of plants, including the skin of grapes, blueberries, raspberries, mulberries, and peanuts. It has been shown to offer protective effects against a number of cardiovascular and neurodegenerative diseases, stroke, and epilepsy. This study examined the neuroprotective effect of resveratrol on mitochondrial biogenesis in the hippocampus following experimental status epilepticus. Kainic acid was microinjected into left hippocampal CA3 in Sprague Dawley rats to induce bilateral prolonged seizure activity. PGC-1α expression and related mitochondrial biogenesis were investigated. Amounts of nuclear respiratory factor 1 (NRF1), mitochondrial transcription factor A (Tfam), cytochrome c oxidase 1 (COX1), and mitochondrial DNA (mtDNA) were measured to evaluate the extent of mitochondrial biogenesis. Increased PGC-1α and mitochondrial biogenesis machinery after prolonged seizure were found in CA3. Resveratrol increased expression of PGC-1α, NRF1, and Tfam, NRF1 binding activity, COX1 level, and mtDNA amount. In addition, resveratrol reduced activated caspase-3 activity and attenuated neuronal cell damage in the hippocampus following status epilepticus. These results suggest that resveratrol plays a pivotal role in the mitochondrial biogenesis machinery that may provide a protective mechanism counteracting seizure-induced neuronal damage by activation of the PGC-1α signaling pathway.

Chemo-enzymatic synthesis of isotopically labeled nicotinamide riboside

As a cofactor for numerous reactions, NAD+ is found widely dispersed across many maps of cellular metabolism. This core redox role alone makes the biosynthesis of NAD+ of great interest. Recent studies have revealed new biological roles for NAD+ as a substrate for diverse enzymes that regulate a broad spectrum of key cellular tasks. These NAD+-consuming enzymes further highlight the importance of understanding NAD+ biosynthetic pathways. In this study, we developed a chemo-enzymatic synthesis of isotopically labeled NAD+ precursor, nicotinamide riboside (NR). The synthesis of NR isotopomers allowed us to unambiguously determine that NR is efficiently converted to NAD+ in the cellular environment independent of degradation to nicotinamide, and it is incorporated into NAD+ in its intact form. The versatile synthetic method along with the isotopically labeled NRs will provide powerful tools to further decipher the important yet complicated NAD+ metabolism.

Emerging Role of microRNAs in Dementia

MicroRNAs are small non-coding RNAs regulating mRNA translation. They play a crucial role in regulating homeostasis in neurons, especially in regulating local and stimulation dependent protein synthesis. Since activity-mediated protein synthesis in neurons is critical for memory and cognition, microRNAs have become key players in modulating these processes. Dementia is a broad term used for symptoms involving decline of memory and cognition. Several studies have implicated the dysregulation of microRNAs in many brain diseases like neurodegenerative diseases, neurodevelopmental disorders, brain injuries and dementia. In this review, we give an overview of microRNA-mediated regulation of proteins and cellular processes affected in dementia pathology, hence illustrating the importance of microRNAs in normal functioning. We also focus on a relatively less explored area in dementia pathology-the importance of activity-mediated protein synthesis at the synapse and the role of microRNAs in modulating this. Overall, this review will be helpful in looking at the significance of microRNAs in dementia from the perspective of defective regulation of protein synthesis and synaptic dysfunction.

Age- and AD-related redox state of NADH in subcellular compartments by fluorescence lifetime imaging microscopy

Nicotinamide adenine dinucleotide (reduced form: NADH) serves as a vital redox-energy currency for reduction-oxidation homeostasis and fulfilling energetic demands. While NADH exists as free and bound forms, only free NADH is utilized for complex I to power oxidative phosphorylation, especially important in neurons. Here, we studied how much free NADH remains available for energy production in mitochondria of old living neurons. We hypothesize that free NADH in neurons from old mice is lower than the levels in young mice and even lower in neurons from the 3xTg-AD Alzheimer's disease (AD) mouse model. To assess free NADH, we used lifetime imaging of NADH autofluorescence with 2-photon excitation to be able to resolve the pool of NADH in mitochondria, cytoplasm, and nuclei. Primary neurons from old mice were characterized by a lower free/bound NADH ratio than young neurons from both non-transgenic (NTg) and more so in 3xTg-AD mice. Mitochondrial compartments maintained 26 to 41% more reducing NADH redox state than cytoplasm for each age, genotype, and sex. Aging diminished the mitochondrial free NADH concentration in NTg neurons by 43% and in 3xTg-AD by 50%. The lower free NADH with age suggests a decline in capacity to regenerate free NADH for energetic supply to power oxidative phosphorylation which further worsens in AD. Applying this non-invasive approach, we showed the most explicit measures yet of bioenergetic deficits in free NADH with aging at the subcellular level in live neurons from in-bred mice and an AD model.

The protective effects of the native flavanone flavanomarein on neuronal cells damaged by 6-OHDA

BACKGROUND

Flavanomarein is the main component of Coreopsis tinctoria Nutt. (C. tinctoria), which is a globally well-known flower tea that has a distinct flavor and many beneficial health effects, such as antioxidant activities. We aimed to explore the effect of flavanomarein on a 6-hydroxydopamine (6-OHDA)-lesioned cell model of oxidative stress.

METHODS

In this study, we used 6-OHDA-lesioned PC12 cells and primary cortical neurons to investigate the protective effects of flavanomarein and its potential mechanism.

RESULTS

The results indicated that pretreatment with flavanomarein (25, 50, or 100 µM for 24 h) significantly increased the cell viability, reduced the lactate dehydrogenase (LDH) release and improved the mitochondrial membrane potential (∆Ψm) and mitochondrial impairment. Additionally, flavanomarein markedly reduced the gene expression of tumor necrosis factor (TNF)-α and protein kinase C ζ (PKC-ζ), the nuclear translocation of p65, and the levels of p-AMPK-α and acetyl-p53. Flavanomarein also elevated the gene expression of P85α, PKC-β1, and Bcl-2, the protein expression of Sirt1 and ICAD, and the phosphorylation level of AKT.

CONCLUSIONS

Together, these results suggest that flavanomarein protects PC12 cells and primary cortical neurons from 6-OHDA-induced neurotoxicity by upregulating the PI3K/AKT signaling pathway and attenuating the nuclear factor kappa B (NF-κB) signaling pathway. Therefore, our study provides evidence that may aid in the development of a potential compound against 6-OHDA toxicity.

Role of Nicotinamide Adenine Dinucleotide and Related Precursors as Therapeutic Targets for Age-Related Degenerative Diseases: Rationale, Biochemistry, Pharmacokinetics, and Outcomes

Significance: Nicotinamide adenine dinucleotide (NAD+) is an essential pyridine nucleotide that serves as an essential cofactor and substrate for a number of critical cellular processes involved in oxidative phosphorylation and ATP production, DNA repair, epigenetically modulated gene expression, intracellular calcium signaling, and immunological functions. NAD+ depletion may occur in response to either excessive DNA damage due to free radical or ultraviolet attack, resulting in significant poly(ADP-ribose) polymerase (PARP) activation and a high turnover and subsequent depletion of NAD+, and/or chronic immune activation and inflammatory cytokine production resulting in accelerated CD38 activity and decline in NAD+ levels. Recent studies have shown that enhancing NAD+ levels can profoundly reduce oxidative cell damage in catabolic tissue, including the brain. Therefore, promotion of intracellular NAD+ anabolism represents a promising therapeutic strategy for age-associated degenerative diseases in general, and is essential to the effective realization of multiple benefits of healthy sirtuin activity. The kynurenine pathway represents the de novo NAD+ synthesis pathway in mammalian cells. NAD+ can also be produced by the NAD+ salvage pathway. Recent Advances: In this review, we describe and discuss recent insights regarding the efficacy and benefits of the NAD+ precursors, nicotinamide (NAM), nicotinic acid (NA), nicotinamide riboside (NR), and nicotinamide mononucleotide (NMN), in attenuating NAD+ decline in degenerative disease states and physiological aging. Critical Issues: Results obtained in recent years have shown that NAD+ precursors can play important protective roles in several diseases. However, in some cases, these precursors may vary in their ability to enhance NAD+ synthesis via their location in the NAD+ anabolic pathway. Increased synthesis of NAD+ promotes protective cell responses, further demonstrating that NAD+ is a regulatory molecule associated with several biochemical pathways. Future Directions: In the next few years, the refinement of personalized therapy for the use of NAD+ precursors and improved detection methodologies allowing the administration of specific NAD+ precursors in the context of patients' NAD+ levels will lead to a better understanding of the therapeutic role of NAD+ precursors in human diseases.

The Action of Polyphenols in Diabetes Mellitus and Alzheimer's Disease: A Common Agent for Overlapping Pathologies

Diabetes Mellitus (DM) and Alzheimer's disease (AD) are two prevalent diseases in modern societies, which are caused mainly by current lifestyle, aging and genetic alterations. It has already been demonstrated that these two diseases are associated, since individuals suffering from DM are prone to develop AD. Conversely, it is also known that individuals with AD are more susceptible to DM, namely type 2 diabetes (T2DM). Therefore, these two pathologies, although completely different in terms of symptomatology, end up sharing several mechanisms at the molecular level, with the most obvious being the increase of oxidative stress and inflammation. Polyphenols are natural compounds widely spread in fruits and vegetables whose dietary intake has been considered inversely proportional to the incidence of DM and AD. So, it is believed that this group of phytochemicals may have preventive and therapeutic potential, not only by reducing the risk and delaying the development of these pathologies, but also by improving brain's metabolic profile and cognitive function. The aim of this review is to understand the extent to which DM and AD are related pathologies, the degree of similarity and the relationship between them, to detail the molecular mechanisms by which polyphenols may exert a protective effect, such as antioxidant and anti-inflammatory effects, and highlight possible advantages of their use as common preventive and therapeutic alternatives.

Current and Emerging Pharmacological Targets for the Treatment of Alzheimer's Disease

No cure or disease-modifying therapy for Alzheimer's disease (AD) has yet been realized. However, a multitude of pharmacological targets have been identified for possible engagement to enable drug discovery efforts for AD. Herein, we review these targets comprised around three main therapeutic strategies. First is an approach that targets the main pathological hallmarks of AD: amyloid-β (Aβ) oligomers and hyperphosphorylated tau tangles which primarily focuses on reducing formation and aggregation, and/or inducing their clearance. Second is a strategy that modulates neurotransmitter signaling. Comprising this strategy are the cholinesterase inhibitors and N-methyl-D-aspartate receptor blockade treatments that are clinically approved for the symptomatic treatment of AD. Additional targets that aim to stabilize neuron signaling through modulation of neurotransmitters and their receptors are also discussed. Finally, the third approach comprises a collection of 'sensitive targets' that indirectly influence Aβ or tau accumulation. These targets are proteins that upon Aβ accumulation in the brain or direct Aβ-target interaction, a modification in the target's function is induced. The process occurs early in disease progression, ultimately causing neuronal dysfunction. This strategy aims to restore normal target function to alleviate Aβ-induced toxicity in neurons. Overall, we generally limit our analysis to targets that have emerged in the last decade and targets that have been validated using small molecules in in vitro and/or in vivo models. This review is not an exhaustive list of all possible targets for AD but serves to highlight the most promising and critical targets suitable for small molecule drug intervention.

Poly(ADP-Ribose) Polymerases in Host-Pathogen Interactions, Inflammation, and Immunity

The literature review presented here details recent research involving members of the poly(ADP-ribose) polymerase (PARP) family of proteins. Among the 17 recognized members of the family, the human enzyme PARP1 is the most extensively studied, resulting in a number of known biological and metabolic roles. This review is focused on the roles played by PARP enzymes in host-pathogen interactions and in diseases with an associated inflammatory response. In mammalian cells, several PARPs have specific roles in the antiviral response; this is perhaps best illustrated by PARP13, also termed the zinc finger antiviral protein (ZAP). Plant stress responses and immunity are also regulated by poly(ADP-ribosyl)ation. PARPs promote inflammatory responses by stimulating proinflammatory signal transduction pathways that lead to the expression of cytokines and cell adhesion molecules. Hence, PARP inhibitors show promise in the treatment of inflammatory disorders and conditions with an inflammatory component, such as diabetes, arthritis, and stroke. These functions are correlated with the biophysical characteristics of PARP family enzymes. This work is important in providing a comprehensive understanding of the molecular basis of pathogenesis and host responses, as well as in the identification of inhibitors. This is important because the identification of inhibitors has been shown to be effective in arresting the progression of disease.

Prognostic value of Sirtuin1 in acute ischemic stroke and its correlation with functional outcomes

BACKGROUND

The blood-brain barrier is impaired in patients with stroke. The release of protein markers such as Sirtuin1 (SIRTl) into circulation may be useful to assess the prognosis of patients with cerebrovascular disease. In this study, we investigated the predictive value of SIRT1 levels in acute ischemic stroke (AIS) patients.

METHODS

In all, 101 AIS patients and 38 healthy controls were enrolled, and blood samples were collected within 72 hours of stroke onset. SIRT1 was analyzed using a commercially available enzyme-linked immunosorbent assay kit. On admission, neurological status was assessed by the standardized National Institutes of Health Stroke Scale (NIHSS). Functional outcomes were measured 1 year after admission using the modified Rankin scale.

RESULTS

Compared with the control group, SIRT1 was significantly increased in the AIS group (0.63 ± 0.75 vs 0.48 ± 0.80 ng/mL; P ≤ 0.05). However, there was no significant correlation between SIRT1 and NIHSS score at admission (r = -0.01, P = .920). In addition, with an unadjusted odds ratio of 0.862 (95% confidence interval 0.495-1.502), SIRT1 was not significantly correlated with functional outcomes.

CONCLUSIONS

Serum concentrations of SIRT1 have no significant predictive value for favorable functional outcome after acute stroke in our study.

Sirtuins in Neuroendocrine Regulation and Neurological Diseases

Silent information regulator 1 (SIRT1) is a mammalian homolog of the nicotinamide adenine dinucleotide (NAD)-dependent deacetylase sirtuin family. Sirtuin was originally studied as the lifespan-extending gene, silent information regulator 2 (SIRT2) in budding yeast. There are seven mammalian homologs of sirtuin (SIRT1–7), and SIRT1 is the closest homolog to SIRT2. SIRT1 modulates various key targets via deacetylation. In addition to histones, these targets include transcription factors, such as forkhead box O (FOXO), Ku70, p53, NF-κB, PPAR-gamma co-activator 1-alpha (PGC-1α), and peroxisome proliferator-activated receptor γ (PPARγ). SIRT1 has many biological functions, including aging, cell survival, differentiation, and metabolism. Genetic and physiological analyses in animal models have shown beneficial roles for SIRT1 in the brain during both development and adulthood. Evidence from in vivo and in vitro studies have revealed that SIRT1 regulates the cellular fate of neural progenitors, axon elongation, dendritic branching, synaptic plasticity, and endocrine function. In addition to its importance in physiological processes, SIRT1 has also been implicated in protection of neurons from degeneration in models of neurological diseases, such as traumatic brain injury and Alzheimer’s disease. In this review, we focus on the role of SIRT1 in the neuroendocrine system and neurodegenerative diseases. We also discuss the potential therapeutic implications of targeting the sirtuin pathway.

MicroRNA in Alzheimer's disease revisited: implications for major neuropathological mechanisms

Pathology of Alzheimer's disease (AD) goes far beyond neurotoxicity resulting from extracellular deposition of amyloid β (Aβ) plaques. Aberrant cleavage of amyloid precursor protein and accumulation of Aβ in the form of the plaque or neurofibrillary tangles are the known primary culprits of AD pathogenesis and target for various regulatory mechanisms. Hyper-phosphorylation of tau, a major component of neurofibrillary tangles, precipitates its aggregation and prevents its clearance. Lipid particles, apolipoproteins and lipoprotein receptors can act in favor or against Aβ and tau accumulation by altering neural membrane characteristics or dynamics of transport across the blood-brain barrier. Lipids also alter the oxidative/anti-oxidative milieu of the central nervous system (CNS). Irregular cell cycle regulation, mitochondrial stress and apoptosis, which follow both, are also implicated in AD-related neuronal loss. Dysfunction in synaptic transmission and loss of neural plasticity contribute to AD. Neuroinflammation is a final trail for many of the pathologic mechanisms while playing an active role in initiation of AD pathology. Alterations in the expression of microRNAs (miRNAs) in AD and their relevance to AD pathology have long been a focus of interest. Herein we focused on the precise pathomechanisms of AD in which miRNAs were implicated. We performed literature search through PubMed and Scopus using the search term: ('Alzheimer Disease') OR ('Alzheimer's Disease') AND ('microRNAs' OR 'miRNA' OR 'MiR') to reach for relevant articles. We show how a limited number of common dysregulated pathways and abnormal mechanisms are affected by various types of miRNAs in AD brain.

Sirtuin 1 and Alzheimer's disease: An up-to-date review

Sirtuins are NAD+-dependent enzymes that regulate a large number of cellular pathways and are related to aging and age-associated diseases. In recent years, the role of sirtuins in Alzheimer's disease (AD) has become increasingly apparent. Growing evidence demonstrates that sirtuin 1 (SIRT1) regulates many processes that go amiss in AD, such as: APP processing, neuroinflammation, neurodegeneration, and mitochondrial dysfunction. Here we review how SIRT1 affects AD and cognition, the main mechanisms in which SIRT1 is related to AD pathology, and its importance for the prevention and possible diagnosis of AD.

Ketogenic diet delays spinal fusion and decreases bone mass in posterolateral lumbar spinal fusion: an in vivo rat model

BACKGROUND

Ketogenic diet (KD), a low-carbohydrate-and-high-fat diet, causes a metabolic state of ketogenesis and has been used to treat drug-resistance epilepsy. Our recent studies showed KD neuroprotective after spinal cord injury and causing bone loss. Effects of KD on spinal fusion were still unknown. This study was aimed to evaluate effects of KD on spinal fusion in rats.

METHODS

Thirty-two Sprague-Dawley rats were randomly divided into KD and standard diet (SD) groups. The KD group was fed with food of 1:4 carbohydrates to fat. All rats were subjected to L4/5 posterolateral lumbar spinal fusion. The blood ketone, and serum calcium, phosphorus, and insulin-like growth factor-1 (IGF-1) were measured, as well as the fusion rates, bone mass (BV), and bone mineral contents (BMC) of fusion sites were estimated at 4 and 8 weeks.

RESULTS

There was no significant difference in serum calcium or phosphorus levels between groups at 4 or 8 weeks. However, there was a significant increase of blood ketone (1.02 mmol/L vs 0.38 mmol/L at 4 weeks; 0.83 mmol/L vs 0.32 mmol/L, at 8 weeks) and decrease of serum IGF-1 (339.4 ng/mL vs 630.6 ng/mL at 4 weeks; 418.8 ng/mL vs 628.6 ng/mL, at 8 weeks) in the KD group compared with the SD group. The spinal fusion occurred less in the KD group (1/16 vs 6/16 at 4 weeks; 7/16 vs 10/16, at 8 weeks), particularly at 4 weeks after surgery. The BV and BMC were lower in the KD group than that in the SD group at 4 weeks, but not different between groups at 8 weeks.

CONCLUSIONS

This study demonstrated that KD delayed spinal fusion and decreased bone mass in posterolateral lumbar spinal fusion in rats.

Evaluation of Metformin on Cognitive Improvement in Patients With Non-dementia Vascular Cognitive Impairment and Abnormal Glucose Metabolism

Objective: Recent studies have suggested that metformin can penetrate the blood–brain barrier, protecting neurons via anti-inflammatory action and improvement of brain energy metabolism. In this study, we aim to investigate the effect of metformin on cognitive function in patients with abnormal glucose metabolism and non-dementia vascular cognitive impairment (NDVCI).

Methods: One hundred patients with NDVCI and abnormal glucose metabolism were randomly allocated into two groups: metformin and donepezil (n = 50) or acarbose and donepezil (n = 50). The neuropsychological status, glucose metabolism, and common carotid arteries intima–media thickness (CCA-IMT) before and after a year of treatment, were measured and compared between the groups.

Results: Ninety four patients completed all the assessment and follow-up. After a year of treatment, there was a decrease in Alzheimer’s disease Assessment Scale-Cognitive Subscale scores and the duration of the Trail Making Test in the metformin-donepezil group. Furthermore, these patients showed a significant increase in World Health Organization–University of California–Los Angeles Auditory Verbal Learning Test scores after treatment (all P < 0.05). However, there was no obvious improvement in cognitive function in the acarbose-donepezil group. We also observed a significant decrease in the level of fasting insulin and insulin resistance (IR) index in the metformin-donepezil group, with a lower CCA-IMT value than that in the acarbose-donepezil group after a year of treatment (P < 0.05).

Conclusion: We conclude that metformin can improve cognitive function in patients with NDVCI and abnormal glucose metabolism, especially in terms of performance function. Improved cognitive function may be related to improvement of IR and the attenuated progression of IMT.

Trial Registration:ChiCTR-IPR-17011855.

SIRT1, miR-132 and miR-212 link human longevity to Alzheimer's Disease

Alzheimer's Disease (AD) is the most common cause of dementia in the elderly. Centenarians - reaching the age of >100 years while maintaining good cognitive skills - seemingly have unique biological features allowing healthy aging and protection from dementia. Here, we studied the expression of SIRT1 along with miR-132 and miR-212, two microRNAs known to regulate SIRT1, in lymphoblastoid cell lines (LCLs) from 45 healthy donors aged 21 to 105 years and 24 AD patients, and in postmortem olfactory bulb and hippocampus tissues from 14 AD patients and 20 age-matched non-demented individuals. We observed 4.0-fold (P = 0.001) lower expression of SIRT1, and correspondingly higher expression of miR-132 (1.7-fold; P = 0.014) and miR-212 (2.1-fold; P = 0.036), in LCLs from AD patients compared with age-matched healthy controls. Additionally, SIRT1 expression was 2.2-fold (P = 0.001) higher in centenarian LCLs compared with LCLs from individuals aged 56-82 years; while centenarian LCLs miR-132 and miR-212 indicated 7.6-fold and 4.1-fold lower expression, respectively. Correlations of SIRT1, miR-132 and miR-212 expression with cognitive scores were observed for AD patient-derived LCLs and postmortem AD olfactory bulb and hippocampus tissues, suggesting that higher SIRT1 expression, possibly mediated by lower miR-132 and miR-212, may protect aged individuals from dementia and is reflected in their peripheral tissues.

Amelioration of Huntington's disease phenotypes by Beta-Lapachone is associated with increases in Sirt1 expression, CREB phosphorylation and PGC-1α deacetylation

Huntington’s disease (HD) is one of the most devastating genetic neurodegenerative disorders with no effective medical therapy. β-Lapachone (βL) is a natural compound obtained from the bark of the Lapacho tree and has been reported to have beneficial effects on various diseases. Sirt1 is a deacetylase of the sirtuin family and deacetylates proteins including the peroxisome proliferator-activated receptor gamma coactivator-1 alpha (PGC-1α) which is associated with mitochondrial respiration and biogenesis. To examine the effectiveness of βL on HD, βL was orally applied to R6/2 HD mice and behavioral phenotypes associated with HD, such as impairment of rota-rod performance and increase of clasping behavior, as well as changes of Sirt1 expression, CREB phosphorylation and PGC-1α deacetylation were examined. Western blot results showed that Sirt1 and p-CREB levels were significantly increased in the brains of βL-treated R6/2 mice. An increase in deacetylation of PGC-1α, which is thought to increase its activity, was observed by oral administration of βL. In an in vitro HD model, βL treatment resulted in an attenuation of MitoSOX red fluorescence intensity, indicating an amelioration of mitochondrial reactive oxygen species by βL. Furthermore, improvements in the rota-rod performance and clasping score were observed in R6/2 HD mice after oral administration of βL compared to that of vehicle control-treated mice. Taken together, our data show that βL is a potential therapeutic candidate for the treatment of HD-associated phenotypes, and increases in Sirt1 level, CREB phosphorylation and PGC-103B1 deacetylation can be the possible underlying mechanism of the effects of βL.

Bushen-Yizhi formula ameliorates cognitive dysfunction through SIRT1/ER stress pathway in SAMP8 mice

The Chinese formula Bushen-Yizhi (BSYZ) has been reported to ameliorate cognitive dysfunction. However the mechanism is still unclear. In this study, we employ an aging model, SAMP8 mice, to explore whether BSYZ could protect dementia through SIRT1/endoplasmic reticulum (ER) stress pathway. Morris water maze and the fearing condition test results show that oral administration of BSYZ (1.46 g/kg/d, 2.92 g/kg/d and 5.84 g/kg/d) and donepezil (3 mg/kg/d) shorten the escape latency, increase the crossing times of the original position of the platform and the time spent in the target quadrant, and increase the freezing time. BSYZ decreases the activity of acetylcholinesterase (AChE), and increases the activity of choline acetyltransferase (ChAT) and the concentration of acetylcholine (Ach) in both hippocampus and cortex. In addition, western blot results (Bcl-2, Bax and Caspase-3) and TUNEL staining show that BSYZ prevents neuron from apoptosis, and elevates the expression of neurotrophic factors, including nerve growth factor (NGF), postsynapticdensity 95 (PSD95) and synaptophysin (SYN), in both hippocampus and cortex. BSYZ also increases the protein expression of SIRT1 and alleviates ER stress-associated proteins (PERK, IRE-1α, eIF-2α, BIP, PDI and CHOP). These results indicate that the neuroprotective mechanism of BSYZ might be related with SIRT1/ER stress pathway.

Resveratrol Intervenes Cholesterol- and Isoprenoid-Mediated Amyloidogenic Processing of AβPP in Familial Alzheimer's Disease

Deterioration of cholesterol metabolism has recently been a frontier subject of investigation in the field of Alzheimer's disease (AD). Though amyloid-β protein precursor (AβPP) primes the pathological cascade, changes in cholesterol levels and its intermediates, geranyl geranyl pyrophosphate and farnesyl pyrophosphate, is expected to have a different consequence on AβPP processing and amyloid-β (Aβ) generation. However, the use of statins (HMG-COA reductase inhibitor) has been widely implicated in slowing down the pathogenic progression of AD, while the epidemiological reports on its biological effect remains controversial. Considering this fact, the choice of drug that could maintain cholesterol homeostasis without altering its biosynthesis may yield a better therapeutic efficacy on AD. Thus, the present study focused on determining the influence of cholesterol and isoprenoids on amyloidogenic-cleavage of AβPP, in addition to resveratrol as a potent therapeutic drug in CHO-APPswe cell lines. High levels of cholesterol were found to enhance the maturation of AβPP and altered the expression and subcellular localization of ADAM10, BACE1, and PS1 thereby promoting Aβ generation, whereas high isoprenoids increased both maturation as well as amyloidogenic-cleavage of AβPP, which was evident through β-CTF production. Interestingly, the therapeutic efficacy of resveratrol maintained cholesterol homeostasis and reduced the amyloidogenic burden through its ability to enhance SIRT1 expression and thereby regulating differential expression of AD determinants.

Sirtuin activators and inhibitors: Promises, achievements, and challenges

The NAD⁺-dependent protein lysine deacylases of the Sirtuin family regulate various physiological functions, from energy metabolism to stress responses. The human Sirtuin isoforms, SIRT1-7, are considered attractive therapeutic targets for aging-related diseases, such as type 2 diabetes, inflammatory diseases and neurodegenerative disorders. We review the status of Sirtuin-targeted drug discovery and development. Potent and selective pharmacological Sirt1 activators and inhibitors are available, and initial clinical trials have been carried out. Several promising inhibitors and activators have also been described for other isoforms. Progress in understanding the mechanisms of Sirtuin modulation by such compounds provides a rational basis for further drug development.

The Role of microRNAs in Alzheimer's Disease and Their Therapeutic Potentials

MicroRNAs (miRNAs) are short, endogenous, non-coding RNAs that post-transcriptionally regulate gene expression by base pairing with mRNA targets. Altered miRNA expression profiles have been observed in several diseases, including neurodegeneration. Multiple studies have reported altered expressions of miRNAs in the brains of individuals with Alzheimer’s disease (AD) as compared to those of healthy elderly adults. Some of the miRNAs found to be dysregulated in AD have been reported to correlate with neuropathological changes, including plaque and tangle accumulation, as well as altered expressions of species that are known to be involved in AD pathology. To examine the potentially pathogenic functions of several dysregulated miRNAs in AD, we review the current literature with a focus on the activities of ten miRNAs in biological pathways involved in AD pathogenesis. Comprehensive understandings of the expression profiles and activities of these miRNAs will illuminate their roles as potential therapeutic targets in AD brain and may lead to the discovery of breakthrough treatment strategies for AD.

SIRT1 Deacetylates Tau and Reduces Pathogenic Tau Spread in a Mouse Model of Tauopathy

Hyperacetylation of tau has been implicated in neurodegeneration and cognitive decline in tauopathy brains. The nicotinamide adenosine dinucleotide-dependent class-III protein deacetylase SIRT1 is one of the major enzymes involved in removal of acetyl groups from tau in vitro However, whether SIRT1 regulates acetylation of pathogenic tau and ameliorates tau-mediated pathogenesis remains unclear. Here, we report deacetylating activity of SIRT1 for acetylated Lys174 (K174) of tau in tauP301S transgenic mice with a brain-specific SIRT1 deletion. We show that SIRT1 deficiency leads to exacerbation of premature mortality, synapse loss, and behavioral disinhibition in tauP301S transgenic mice of both sexes. By contrast, SIRT1 overexpression by stereotaxic delivery of adeno-associated virus that encodes SIRT1 into the hippocampus reduces acetylated K174 tau. Furthermore, SIRT1 overexpression significantly attenuates the spread of tau pathology into anatomically connected brain regions of tauP301S transgenic mice of both sexes. These findings suggest the functional importance of SIRT1 in regulating pathogenic tau acetylation and in suppressing the spread of tau pathology in vivoSIGNIFICANCE STATEMENT In neurodegenerative disorders with inclusions of microtubule-associated protein tau, aberrant lysine acetylation of tau plays critical roles in promoting tau accumulation and toxicity. Identifying strategies to deacetylate tau could interfere with disease progression; however, little is known about how pathogenic tau is deacetylated in vivo Here we show that the protein deacetylase SIRT1 reduces tau acetylation in a mouse model of neurodegeneration. SIRT1 deficiency in the brain aggravates synapse loss and behavioral disinhibition, and SIRT1 overexpression ameliorates propagation of tau pathology.