Glucose metabolism and insulin receptor signal transduction in Alzheimer disease

Potential role of tanycyte-derived neurogenesis in Alzheimer's disease

Tanycytes, specialized ependymal cells located in the hypothalamus, play a crucial role in the generation of new neurons that contribute to the neural circuits responsible for regulating the systemic energy balance. The precise coordination of the gene networks controlling neurogenesis in naive and mature tanycytes is essential for maintaining homeostasis in adulthood. However, our understanding of the molecular mechanisms and signaling pathways that govern the proliferation and differentiation of tanycytes into neurons remains limited. This article aims to review the recent advancements in research into the mechanisms and functions of tanycyte-derived neurogenesis. Studies employing lineage-tracing techniques have revealed that the neurogenesis specifically originating from tanycytes in the hypothalamus has a compensatory role in neuronal loss and helps maintain energy homeostasis during metabolic diseases. Intriguingly, metabolic disorders are considered early biomarkers of Alzheimer's disease. Furthermore, the neurogenic potential of tanycytes and the state of newborn neurons derived from tanycytes heavily depend on the maintenance of mild microenvironments, which may be disrupted in Alzheimer's disease due to the impaired blood-brain barrier function. However, the specific alterations and regulatory mechanisms governing tanycyte-derived neurogenesis in Alzheimer's disease remain unclear. Accumulating evidence suggests that tanycyte-derived neurogenesis might be impaired in Alzheimer's disease, exacerbating neurodegeneration. Confirming this hypothesis, however, poses a challenge because of the lack of long-term tracing and nucleus-specific analyses of newborn neurons in the hypothalamus of patients with Alzheimer's disease. Further research into the molecular mechanisms underlying tanycyte-derived neurogenesis holds promise for identifying small molecules capable of restoring tanycyte proliferation in neurodegenerative diseases. This line of investigation could provide valuable insights into potential therapeutic strategies for Alzheimer's disease and related conditions.

Navigating the intersection: Diabetes and Alzheimer's intertwined relationship

Alzheimer's disease (AD) and Diabetes mellitus (DM) exhibit comparable pathophysiological pathways. Genetic abnormalities in APP, PS-1, and PS-2 are linked to AD, with diagnostic aid from CSF and blood biomarkers. Insulin dysfunction, termed "type 3 diabetes mellitus" in AD, involves altered insulin signalling and neuronal shrinkage. Insulin influences beta-amyloid metabolism, exacerbating neurotoxicity in AD and amyloid production in DM. Both disorders display impaired glucose transporter expression, hastening cognitive decline. Mitochondrial dysfunction and Toll-like receptor 4-mediated inflammation worsen neurodegeneration in both diseases. ApoE4 raises disease risk, especially when coupled with dyslipidemia common in DM. Targeting shared pathways like insulin-degrading enzyme activation and HSP60 holds promise for therapeutic intervention. Recognizing these interconnected mechanisms underscores the imperative for developing tailored treatments addressing the overlapping pathophysiology of AD and DM, offering potential avenues for more effective management of both conditions.

Effects of chronic treatment with metformin on brain glucose hypometabolism and central insulin actions in transgenic mice with tauopathy

Brain glucose hypometabolism and insulin alterations are common features of many neurological diseases. Herein we sought to corroborate the brain glucose hypometabolism that develops with ageing in 12-months old Tau-VLW transgenic mice, a model of tauopathy, as well as to determine whether this model showed signs of altered peripheral glucose metabolism. Our results demonstrated that 12-old months Tau mice exhibited brain glucose hypometabolism as well as basal hyperglycemia, impaired glucose tolerance, hyperinsulinemia, and signs of insulin resistance. Then, we further studied the effect of chronic metformin treatment (9 months) in Tau-VLW mice from 9 to 18 months of age. Longitudinal PET neuroimaging studies revealed that chronic metformin altered the temporal profile in the progression of brain glucose hypometabolism associated with ageing. Besides, metformin altered the content and/or phosphorylation of key components of the insulin signal transduction pathway in the frontal cortex leading to significant changes in the content of the active forms. Thus, metformin increased the expression of pAKT-Y474 while reducing pmTOR-S2448 and pGSK3β. These changes might be related, at least partially, to a slow progression of ageing, neurological damage, and cognitive decline. Metformin also improved the peripheral glucose tolerance and the ability of the Tau-VLW mice to maintain their body weight through ageing. Altogether our study shows that the tau-VLW mice could be a useful model to study the potential interrelationship between tauopathy and central and peripheral glucose metabolism alterations. More importantly our results suggest that chronic metformin treatment may have direct beneficial central effects by post-transcriptional modulation of key components of the insulin signal transduction pathway.

Osteoporosis and Alzheimer´s disease (or Alzheimer´s disease and Osteoporosis)

Alzheimer's disease (AD) and osteoporosis are two diseases that mainly affect elderly people, with increases in the occurrence of cases due to a longer life expectancy. Several epidemiological studies have shown a reciprocal association between both diseases, finding an increase in incidence of osteoporosis in patients with AD, and a higher burden of AD in osteoporotic patients. This epidemiological relationship has motivated the search for molecules, genes, signaling pathways and mechanisms that are related to both pathologies. The mechanisms found in these studies can serve to improve treatments and establish better patient care protocols.

Intranasal insulin treatment ameliorates spatial memory, muscular strength, and frailty deficits in 5xFAD mice

The 5xFAD mouse model shows age-related weight loss as well as cognitive and motor deficits. Metabolic dysregulation, especially impaired insulin signaling, is also present in AD. This study examined whether intranasal delivery of insulin (INI) at low (0.875 U) or high (1.750 U) doses would ameliorate these deficits compared to saline in 10-month-old female 5xFAD and B6SJL wildtype (WT) mice. INI increased forelimb grip strength in the wire hang test in 5xFAD mice in a dose-dependent manner but did not improve the performance of 5xFAD mice on the balance beam. High INI doses reduced frailty scores in 5xFAD mice and improved spatial memory in both acquisition and reversal probe trials in the Morris water maze. INI increased swim speed in 5xFAD mice but had no effect on object recognition memory or working memory in the spontaneous alternation task, nor did it improve memory in the contextual or cued fear memory tasks. High doses of insulin increased the liver, spleen, and kidney weights and reduced brown adipose tissue weights. P-Akt signaling in the hippocampus was increased by insulin in a dose-dependent manner. Altogether, INI increased strength, reduced frailty scores, and improved visual spatial memory. Hypoglycemia was not present after INI, however alterations in tissue and organ weights were present. These results are novel and important as they indicate that intra-nasal insulin can reverse cognitive, motor and frailty deficits found in this mouse model of AD.

RGS10 mitigates high glucose-induced microglial inflammation via the reactive oxidative stress pathway and enhances synuclein clearance in microglia

Microglia play a critical role in maintaining brain homeostasis but become dysregulated in neurodegenerative diseases. Regulator of G-protein Signaling 10 (RGS10), one of the most abundant homeostasis proteins in microglia, decreases with aging and functions as a negative regulator of microglia activation. RGS10-deficient mice exhibit impaired glucose tolerance, and high-fat diet induces insulin resistance in these mice. In this study, we investigated whether RGS10 modulates microglia activation in response to hyperglycemic conditions, complementing our previous findings of its role in inflammatory stimuli. In RGS10 knockdown (KD) BV2 cells, TNF production increased significantly in response to high glucose, particularly under proinflammatory conditions. Additionally, glucose uptake and GLUT1 mRNA levels were significantly elevated in RGS10 KD BV2 cells. These cells produced higher ROS and displayed reduced sensitivity to the antioxidant N-Acetyl Cysteine (NAC) when exposed to high glucose. Notably, both BV2 cells and primary microglia that lack RGS10 exhibited impaired uptake of alpha-synuclein aggregates. These findings suggest that RGS10 acts as a negative regulator of microglia activation not only in response to inflammation but also under hyperglycemic conditions.

The associations between type 2 diabetes and plasma biomarkers of Alzheimer's disease in the Health and Aging Brain Study: Health Disparities (HABS-HD)

Alzheimer's disease (AD) affects Latinos disproportionately. One of the reasons underlying this disparity may be type 2 diabetes (T2D) that is a risk factor for AD. The purpose of this study was to examine the associations of T2D and AD blood biomarkers and the differences in these associations between Mexican Americans and non-Hispanic Whites. This study was a secondary analysis of baseline data from the observational Health and Aging Brain Study: Health Disparities (HABS-HD) that investigated factors underlying health disparities in AD in Mexican Americans in comparison to non-Hispanic Whites. HABS-HD participants were excluded if they had missing data or were large outliers (z-scores >|4|) on a given AD biomarker. Fasting blood glucose and glycosylated hemoglobin (HbA1c) levels were measured from clinical labs. T2D was diagnosed by licensed clinicians. Plasma amyloid-beta 42 and 40 (Aβ42/42) ratio, total tau (t-tau), and neurofilament light (NfL) were measured via ultra-sensitive Simoa assays. The sample sizes were 1,552 for Aβ42/40 ratio, 1,570 for t-tau, and 1,553 for NfL. Mexican Americans were younger (66.6±8.7 vs. 69.5±8.6) and had more female (64.9% female vs. 55.1%) and fewer years of schooling (9.5±4.6 vs. 15.6±2.5) than non-Hispanic Whites. Mexican Americans differed significantly from non-Hispanic Whites in blood glucose (113.5±36.6 vs. 99.2±17.0) and HbA1c (6.33±1.4 vs. 5.51±0.6) levels, T2D diagnosis (35.3% vs. 11.1%), as well as blood Aβ42/40 ratio (.051±.012 vs. .047±.011), t-tau (2.56±.95 vs. 2.33±.90), and NfL levels (16.3±9.5 vs. 20.3±10.3). Blood glucose, blood HbA1c, and T2D diagnosis were not related to Aβ42/40 ratio and t-tau but explained 3.7% of the variation in NfL (p < .001). Blood glucose and T2D diagnosis were not, while HbA1c was positively (b = 2.31, p < .001, β = 0.26), associated with NfL among Mexican Americans. In contrast, blood glucose, HbA1c, and T2D diagnosis were negatively (b = -0.09, p < .01, β = -0.26), not (b = 0.34, p = .71, β = 0.04), and positively (b = 3.32, p < .01, β = 0.33) associated with NfL, respectively in non-Hispanic Whites. To conclude, blood glucose and HbA1c levels and T2D diagnosis are associated with plasma NfL levels, but not plasma Aβ and t-tau levels. These associations differ in an ethnicity-specific manner and need to be further studied as a potential mechanism underlying AD disparities.

Mechanisms and structure-activity relationships of polysaccharides in the intervention of Alzheimer's disease: A review

Alzheimer's disease (AD) is a complex neurodegenerative disease. Despite several decades of research, the development of effective treatments and responses for Alzheimer's disease remains elusive. The utilization of polysaccharides for Alzheimer's disease became more popular due to their beneficial characteristics, notably their multi-target activity and low toxicity. This review mainly focuses on the researches of recent 5 years in the regulation of AD by naturally derived polysaccharides, systematically lists the possible intervention pathways of polysaccharides from different mechanisms, and explores the structure-activity relationship between polysaccharide structural activities, so as to provide references for the intervention and treatment of AD by polysaccharides.

Semaglutide ameliorates cognition and glucose metabolism dysfunction in the 3xTg mouse model of Alzheimer's disease via the GLP-1R/SIRT1/GLUT4 pathway

Disorders of brain glucose metabolism is known to affect brain activity in neurodegenerative diseases including Alzheimer's disease (AD). Furthermore, recent evidence has shown an association between AD and type 2 diabetes. Numerous reports have found that glucagon-like peptide-1 (GLP-1) receptor agonists improve the cognitive behavior and pathological features in AD patients and animals, which may be related to the improvement of glucose metabolism in the brain. However, the mechanism by which GLP-1 agonists improve the brain glucose metabolism in AD patients remains unclear. In this study, we found that SIRT1 is closely related to expression of GLP-1R in hippocampus of 3xTg mice. Therefore, we used semaglutide, a novel GLP-1R agonist currently undergoing two phase 3 clinical trials in AD patients, to observe the effect of SIRT1 after semaglutide treatment in 3XTg mice and HT22 cells, and to explore the mechanism of SIRT1 in the glucose metabolism disorders of AD. The mice were injected with semaglutide on alternate days for 30 days, followed by behavioral experiments including open field test, new object recognition test, and Y-maze. The content of glucose in the brain was also measured by using 18FDG-PET-CT scans. We measured the expression of Aβ and tau in the hippocampus, observed the expression of GLUT4 which is downstream of SIRT1, and tested the Glucose oxidase assay (GOD-POD) and Hexokinase (HK) in HT22 cells. Here, we found in the 3xTg mouse model of AD and in cultured HT22 mouse neurons that SIRT1 signaling is involved in the impairment of glucose metabolism in AD. Semaglutide can increased the expression levels of SIRT1 and GLUT4 in the hippocampus of 3xTg mice, accompanied by an improvement in learning and memory, decreased in Aβ plaques and neurofibrillary tangles. In addition, we further demonstrated that semaglutide improved glucose metabolism in the brain of 3xTg mice in vitro, semaglutide promoted glycolysis and improved glycolytic disorders, and increased the membrane translocation of GLUT4 in cultured HT22 cells. These effects were blocked by the SIRT1 inhibitor (EX527). These findings indicate that semaglutide can regulate the expression of GLUT4 to mediate glucose transport through SIRT1, thereby improving glucose metabolism dysfunction in AD mice and cells. The present study suggests that SIRT1/GLUT4 signaling pathway may be an important mechanism for GLP-1R to promote glucose metabolism in the brain, providing a reliable strategy for effective therapy of AD.

NOX-induced oxidative stress is a primary trigger of major neurodegenerative disorders

Neurodegenerative diseases (NDDs) causing cognitive impairment and dementia are difficult to treat due to the lack of understanding of primary initiating factors. Meanwhile, major sporadic NDDs share many risk factors and exhibit similar pathologies in their early stages, indicating the existence of common initiation pathways. Glucose hypometabolism associated with oxidative stress is one such primary, early and shared pathology, and a likely major cause of detrimental disease-associated cascades; targeting this common pathology may therefore be an effective preventative strategy for most sporadic NDDs. However, its exact cause and trigger remain unclear. Recent research suggests that early oxidative stress caused by NADPH oxidase (NOX) activation is a shared initiating mechanism among major sporadic NDDs and could prove to be the long-sought ubiquitous NDD trigger. We focus on two major NDDs - Alzheimer's disease (AD) and Parkinson's disease (PD), as well as on acquired epilepsy which is an increasingly recognized comorbidity in NDDs. We also discuss available data suggesting the relevance of the proposed mechanisms to other NDDs. We delve into the commonalities among these NDDs in neuroinflammation and NOX involvement to identify potential therapeutic targets and gain a deeper understanding of the underlying causes of NDDs.

Antidiabetic agents as a novel treatment for Alzheimer's and Parkinson's disease

Therapeutic strategies for neurodegenerative disorders have commonly targeted individual aspects of the disease pathogenesis to little success. Neurodegenerative diseases, including Alzheimer's disease (AD) and Parkinson's disease (PD), are characterized by several pathological features. In AD and PD, there is an abnormal accumulation of toxic proteins, increased inflammation, decreased synaptic function, neuronal loss, increased astrocyte activation, and perhaps a state of insulin resistance. Epidemiological evidence has revealed a link between AD/PD and type 2 diabetes mellitus, with these disorders sharing some pathological commonalities. Such a link has opened up a promising avenue for repurposing antidiabetic agents in the treatment of neurodegenerative disorders. A successful therapeutic strategy for AD/PD would likely require a single or several agents which target the separate pathological processes in the disease. Targeting cerebral insulin signalling produces numerous neuroprotective effects in preclinical AD/PD brain models. Clinical trials have shown the promise of approved diabetic compounds in improving motor symptoms of PD and preventing neurodegenerative decline, with numerous further phase II trials and phase III trials underway in AD and PD populations. Alongside insulin signalling, targeting incretin receptors in the brain represents one of the most promising strategies for repurposing currently available agents for the treatment of AD/PD. Most notably, glucagon-like-peptide-1 (GLP-1) receptor agonists have displayed impressive clinical potential in preclinical and early clinical studies. In AD the GLP-1 receptor agonist, liraglutide, has been demonstrated to improve cerebral glucose metabolism and functional connectivity in small-scale pilot trials. Whilst in PD, the GLP-1 receptor agonist exenatide is effective in restoring motor function and cognition. Targeting brain incretin receptors reduces inflammation, inhibits apoptosis, prevents toxic protein aggregation, enhances long-term potentiation and autophagy as well as restores dysfunctional insulin signalling. Support is also increasing for the use of additional approved diabetic treatments, including intranasal insulin, metformin hydrochloride, peroxisome proliferator-activated nuclear receptor γ agonists, amylin analogs, and protein tyrosine phosphatase 1B inhibitors which are in the investigation for deployment in PD and AD treatment. As such, we provide a comprehensive review of several promising anti-diabetic agents for the treatment of AD and PD.

Dietary glucosinolates derived isothiocyanates: chemical properties, metabolism and their potential in prevention of Alzheimer's disease

Alzheimer's disease (AD) is the most prevalent form of dementia affecting millions of people worldwide. It is a progressive, irreversible, and incurable neurodegenerative disorder that disrupts the synaptic communication between millions of neurons, resulting in neuronal death and functional loss due to the abnormal accumulation of two naturally occurring proteins, amyloid β (Aβ) and tau. According to the 2018 World Alzheimer's Report, there is no single case of an Alzheimer's survivor; even 1 in 3 people die from Alzheimer's disease, and it is a growing epidemic across the globe fruits and vegetables rich in glucosinolates (GLCs), the precursors of isothiocyanates (ITCs), have long been known for their pharmacological properties and recently attracted increased interest for the possible prevention and treatment of neurodegenerative diseases. Epidemiological evidence from systematic research findings and clinical trials suggests that nutritional and functional dietary isothiocyanates interfere with the molecular cascades of Alzheimer's disease pathogenesis and prevent neurons from functional loss. The aim of this review is to explore the role of glucosinolates derived isothiocyanates in various molecular mechanisms involved in the progression of Alzheimer's disease and their potential in the prevention and treatment of Alzheimer's disease. It also covers the chemical diversity of isothiocyanates and their detailed mechanisms of action as reported by various in vitro and in vivo studies. Further clinical studies are necessary to evaluate their pharmacokinetic parameters and effectiveness in humans.

Systemic Metabolism and Mitochondria in the Mechanism of Alzheimer's Disease: Finding Potential Therapeutic Targets

Elderly people over the age of 65 are those most likely to experience Alzheimer's disease (AD), and aging and AD are associated with apparent metabolic alterations. Currently, there is no curative medication against AD and only several drugs have been approved by the FDA, but these drugs can only improve the symptoms of AD. Many preclinical and clinical trials have explored the impact of adjusting the whole-body and intracellular metabolism on the pathogenesis of AD. The most recent evidence suggests that mitochondria initiate an integrated stress response to environmental stress, which is beneficial for healthy aging and neuroprotection. There is also an increasing awareness of the differential risk and potential targeting strategies related to the metabolic level and microbiome. As the main participants in intracellular metabolism, mitochondrial bioenergetics, mitochondrial quality-control mechanisms, and mitochondria-linked inflammatory responses have been regarded as potential therapeutic targets for AD. This review summarizes and highlights these advances.

Role of Hydroxytyrosol and Oleuropein in the Prevention of Aging and Related Disorders: Focus on Neurodegeneration, Skeletal Muscle Dysfunction and Gut Microbiota

Aging is a multi-faceted process caused by the accumulation of cellular damage over time, associated with a gradual reduction of physiological activities in cells and organs. This degeneration results in a reduced ability to adapt to homeostasis perturbations and an increased incidence of illnesses such as cognitive decline, neurodegenerative and cardiovascular diseases, cancer, diabetes, and skeletal muscle pathologies. Key features of aging include a chronic low-grade inflammation state and a decrease of the autophagic process. The Mediterranean diet has been associated with longevity and ability to counteract the onset of age-related disorders. Extra virgin olive oil, a fundamental component of this diet, contains bioactive polyphenolic compounds as hydroxytyrosol (HTyr) and oleuropein (OLE), known for their antioxidant, anti-inflammatory, and neuroprotective properties. This review is focused on brain, skeletal muscle, and gut microbiota, as these systems are known to interact at several levels. After the description of the chemistry and pharmacokinetics of HTyr and OLE, we summarize studies reporting their effects in in vivo and in vitro models of neurodegenerative diseases of the central/peripheral nervous system, adult neurogenesis and depression, senescence and lifespan, and age-related skeletal muscle disorders, as well as their impact on the composition of the gut microbiota.

Dysfunctional gene splicing in glucose metabolism may contribute to Alzheimer's disease

ABSTRACT

The glucose metabolism is crucial for sustained brain activity as it provides energy and is a carbon source for multiple biomacromolecules; glucose metabolism decreases dramatically in Alzheimer's disease (AD) and may be a fundamental cause for its development. Recent studies reveal that the alternative splicing events of certain genes effectively regulate several processes in glucose metabolism including insulin receptor, insulin-degrading enzyme, pyruvate kinase M, receptor for advanced glycation endproducts, and others, thereby, influencing glucose uptake, glycolysis, and advanced glycation end-products-mediated signaling pathways. Indeed, the discovery of aberrant alternative splicing that changes the proteomic diversity and protein activity in glucose metabolism has been pivotal in our understanding of AD development. In this review, we summarize the alternative splicing events of the glucose metabolism-related genes in AD pathology and highlight the crucial regulatory roles of splicing factors in the alternative splicing process. We also discuss the emerging therapeutic approaches for targeting splicing factors for AD treatment.

A PDK-1 allosteric agonist improves spatial learning and memory in a βAPP/PS-1 transgenic mouse-high fat diet intervention model of Alzheimer's disease

Diabetes mellitus (DM), peripheral insulin resistance (IR) and obesity are clear risk factors for Alzheimer's disease. Several anti-diabetic drugs and insulin have been tested in rodents and humans with MCI or AD, yielding promising but inconclusive results. The PDK-1/Akt axis, essential to the action of insulin, has not however been pharmacologically interrogated to a similar degree. Our previous cell culture and in vitro studies point to such an approach. Double transgenic APPsw/PSENdE9 mice, a model for Alzheimer's disease, were used to test the oral administration of PS48, a PDK-1 agonist, on preventing the expected decline in learning and memory in the Morris Water Maze (MWM). Mice were raised on either standard (SD) or high fat (HFD) diets, dosed beginning 10 months age and tested at an advanced age of 14 months. PS48 had positive effects on learning the spatial location of a hidden platform in the TG animals, on either SD or HFD, compared to vehicle diet and WT animals. On several measures of spatial memory following successful acquisition (probe trials), the drug also proved significantly beneficial to animals on either diet. The PS48 treatment-effect size was more pronounced in the TG animals on HFD compared to on SD in several of the probe measures. HFD produced some of the intended metabolic effects of weight gain and hyperglycemia, as well as accelerating cognitive impairment in the TG animals. PS48 was found to have added value in modestly reducing body weights and improving OGTT responses in TG groups although results were not definitive. PS48 was well tolerated without obvious clinical signs or symptoms and did not itself affect longevity. These results recommend a larger preclinical study before human trial.

PP2Cα aggravates neuronal insulin resistance leading to AD-like phenotype in vitro

Neuronal insulin resistance is a major risk for development of Alzheimer's Disease (AD). Studies already reported few kinases participating in neuronal insulin signaling connected with progression of AD pathogenesis, yet complete information is missing. α isoform of Protein Phosphatase-2C (PP2C) is a Ser/Thr phosphatase, only known in 3T3-L1 adipocytes as a positive regulator of insulin signaling. However, many aspects of its function in neuronal insulin signaling and insulin resistance are unidentified. Recently, we reported that PP2Cα positively regulates neuronal glucose uptake possibly by a mechanism of dephosphorylation of IRS-1 at Ser522 and by inactivating AMPK, exacerbating hyperinsulinemia mediated neuronal insulin resistance. Since PP2Cα affected neuronal insulin signaling and AD is connected to neuronal insulin resistance, in the present study, we studied the role of PP2Cα in regulating activities of both isoforms of GSK3α and GSK3β (one of the leading kinases for AD progression). The results led us to test the role of PP2Cα on AD hallmarks. Silencing of PP2Cα caused hyperphosphorylation of a potential kinase Tau, leading to NFT formation and increased Aβ deposition. Our study thereby demonstrates escalation of hyperinsulinemia mediated neuronal insulin resistance leading to AD-like pathogenesis by PP2Cα in vitro and hints a novel molecule, PP2Cα, linking AD pathogenesis.

Effect of Various Intermittent Fasting Protocols on Hyperglycemia-Induced Cognitive Dysfunction in Rats

Diabetes mellitus is a highly prevalent metabolic disorder that causes cognitive decline. Here, we investigated the impact of various intermittent fasting protocols on type 2 diabetes mellitus (T2DM)-induced cognitive dysfunction in a rodent model. Male Sprague-Dawley rats (aged 3 months) were randomly assigned to five groups (n = 6 per group) and T2DM was induced by streptozotocin (60 mg/kg, IM). The control group was untreated. Cognitive function was tested (Y-maze, novel object recognition, and elevated plus maze tests) and glucose was assessed. The T2DM rats exhibited significantly higher blood glucose, which is associated with cognitive dysfunction. Compared to the validated animal model of T2DM in rats, various intermittent fasting protocols decreased blood glucose and improved cognitive function. These results indicate that various intermittent fasting protocols may be a potential strategy for managing the hyperglycemia-associated cognitive dysfunction.

Tau Loss of Function, by Deletion or Aggregation, Contributes to Peripheral Insulin Resistance

BACKGROUND

Several epidemiological data revealed an association between Alzheimer's disease (AD) and type 2 diabetes. Researchers concentrated on brain insulin resistance with little emphasis on the link between systemic insulin resistance and AD, despite the fact that the incidence of type 2 diabetes is higher in AD patients and that impairment in insulin signaling is a risk factor for AD.

OBJECTIVE

The goal of this study is to determine the role of systemic insulin resistance in the pathogenesis of Alzheimer's disease by evaluating the consequences of tau loss-of-function on peripheral insulin sensitivity.

METHODS

Primary hepatocytes isolated from transgenic mouse models (Tau KO, P301 L) and wild type mice (C57BL/6) were evaluated for their insulin sensitivity using glucose uptake assays as well as biochemical analysis of insulin signaling markers.

RESULTS

Our data show that tau deletion or loss of function promotes peripheral insulin resistance as seen in primary hepatocytes isolated from Tau KO and P301 L mice, respectively. Furthermore, exposure of wild-type primary hepatocytes to sub-toxic concentrations of tau oligomers results in a dose-dependent inhibition of glucose uptake, associated with downregulation of insulin signaling. Tau oligomers-induced inactivation of insulin signaling proteins was rescued by inhibition of p38 MAPK, suggesting the involvement of p38 MAPK.

CONCLUSIONS

This is the first study testing tau role in peripheral insulin resistance at the cellular level using multiple transgenic mouse models. Moreover, this study suggests that tau should be functional for insulin sensitivity, therefore, any loss of function by deletion or aggregation would result in insulin resistance.

Neuroprotective effects of insulin-like growth factor-2 in 6-hydroxydopamine-induced cellular and mouse models of Parkinson's disease

Skin-derived precursor Schwann cells have been reported to play a protective role in the central nervous system. The neuroprotective effects of skin-derived precursor Schwann cells may be attributable to the release of growth factors that nourish host cells. In this study, we first established a cellular model of Parkinson's disease using 6-hydroxydopamine. When SH-SY5Y cells were pretreated with conditioned medium from skin-derived precursor Schwann cells, their activity was greatly increased. The addition of insulin-like growth factor-2 neutralizing antibody markedly attenuated the neuroprotective effects of skin-derived precursor Schwann cells. We also found that insulin-like growth factor-2 levels in the peripheral blood were greatly increased in patients with Parkinson's disease and in a mouse model of Parkinson's disease. Next, we pretreated cell models of Parkinson's disease with insulin-like growth factor-2 and administered insulin-like growth factor-2 intranasally to a mouse model of Parkinson's disease induced by 6-hydroxydopamine and found that the level of tyrosine hydroxylase, a marker of dopamine neurons, was markedly restored, α-synuclein aggregation decreased, and insulin-like growth factor-2 receptor down-regulation was alleviated. Finally, in vitro experiments showed that insulin-like growth factor-2 activated the phosphatidylinositol 3 kinase (PI3K)/AKT pathway. These findings suggest that the neuroprotective effects of skin-derived precursor Schwann cells on the central nervous system were achieved through insulin-like growth factor-2, and that insulin-like growth factor-2 may play a neuroprotective role through the insulin-like growth factor-2 receptor/PI3K/AKT pathway. Therefore, insulin-like growth factor-2 may be an useful target for Parkinson's disease treatment.

Ser/Thr phosphatases: One of the key regulators of insulin signaling

Protein phosphorylation is an important post-translational modification that regulates several cellular processes including insulin signaling. The evidences so far have already portrayed the importance of balanced actions of kinases and phosphatases in regulating the insulin signaling cascade. Therefore, elucidating the role of both kinases and phosphatases are equally important. Unfortunately, the role of phosphatases is less studied as compared to kinases. Since brain responds to insulin and insulin signaling is reported to be crucial for many neuronal processes, it is important to understand the role of neuronal insulin signaling regulators. Ser/Thr phosphatases seem to play significant roles in regulating neuronal insulin signaling. Therefore, in this review, we discussed the involvement of Ser/Thr phosphatases in regulating insulin signaling and insulin resistance in neuronal system at the backdrop of the same phosphatases in peripheral insulin sensitive tissues.

Protein tyrosine phosphatase 1B (PTP1B) as a potential therapeutic target for neurological disorders

Protein tyrosine phosphatase 1B (PTP1B) is a typical member of the PTP family, considered a direct negative regulator of several receptor and receptor-associated tyrosine kinases. This widely localized enzyme has been involved in the pathophysiology of several diseases. More recently, PTP1B has attracted attention in the field of neuroscience, since its activation in brain cells can lead to schizophrenia-like behaviour deficits, anxiety-like effects, neurodegeneration, neuroinflammation and depression. Conversely, PTP1B inhibition has been shown to prevent microglial activation, thus exerting a potent anti-inflammatory effect and has also shown potential to increase the cognitive process through the stimulation of hippocampal insulin, leptin and BDNF/TrkB receptors. Notwithstanding, most research on the clinical efficacy of targeting PTP1B has been developed in the field of obesity and type 2 diabetes mellitus (TD2M). However, despite the link existing between these metabolic alterations and neurodegeneration, no clinical trials assessing the neurological advantages of PTP1B inhibition have been performed yet. Preclinical studies, though, have provided strong evidence that targeting PTP1B could allow to reach different pathophysiological mechanisms at once. herefore, specific interventions or trials should be designed to modulate PTP1B activity in brain, since it is a promising strategy to decelerate or prevent neurodegeneration in aged individuals, among other neurological diseases. The present paper fails to include all neurological conditions in which PTP1B could have a role; instead, it focuses on those which have been related to metabolic alterations and neurodegenerative processes. Moreover, only preclinical data is discussed, since clinical studies on the potential of PTP1B inhibition for treating neurological diseases are still required.

Prediction value of the genetic risk of type 2 diabetes on the amnestic mild cognitive impairment conversion to Alzheimer’s disease

Amnestic mild cognitive impairment (aMCI) and Type 2 diabetes mellitus (T2DM) are both important risk factors for Alzheimer’s disease (AD). We aimed to investigate whether a T2DM-specific polygenic risk score (PRS_sT2DM) can predict the conversion of aMCI to AD and further explore the underlying neurological mechanism. All aMCI patients were from the Alzheimer’s disease Neuroimaging Initiative (ADNI) database and were divided into conversion (aMCI-C, n = 164) and stable (aMCI-S, n = 222) groups. PRS_sT2DM was calculated by PRSice-2 software to explore the predictive efficacy of the aMCI conversion to AD. We found that PRS_sT2DM could independently predict the aMCI conversion to AD after removing the common variants of these two diseases. PRS_sT2DM was significantly negatively correlated with gray matter volume (GMV) of the right superior frontal gyrus in the aMCI-C group. In all aMCI patients, PRS_sT2DM was significantly negatively correlated with the cortical volume of the right superior occipital gyrus. The cortical volume of the right superior occipital gyrus could significantly mediate the association between PRS_sT2DM and aMCI conversion. Gene-based analysis showed that T2DM-specific genes are highly expressed in cortical neurons and involved in ion and protein binding, neural development and generation, cell junction and projection, and PI3K-Akt and MAPK signaling pathway, which might increase the aMCI conversion by affecting the Tau phosphorylation and amyloid-beta (Aβ) accumulation. Therefore, the PRS_sT2DM could be used as a measure to predict the conversion of aMCI to AD.

Knockdown of CLC-3 may improve cognitive impairment caused by diabetic encephalopathy

BACKGROUND

Diabetic encephalopathy(DE) is a neurological complication of diabetes, and its pathogenesis is unclear. Current studies indicate that insulin receptors and downstream signaling pathways play a key role in the occurrence and development of DE. Additionally, CLC-3, a member of the CLC family of anion channels and transporters, is closely related to the secretion and processing of insulin. Here, we investigated the changes and putative roles of CLC-3 in diabetic encephalopathy.

RESULTS

To this aim, we combined lentivirus and adeno-associated virus gene transfer to change the expression level of CLC-3 in the HT-22 hippocampal cell line and hippocampal CA1. We studied the role of CLC-3 in DE through the Morris water maze test.CLC-3 expression increased significantly in HT-22 cells cultured with high glucose and STZ-induced DE model hippocampus. Moreover, Insulin receptor(IR) and downstream PI3K/AKT/GSK3β signaling pathways were also dysfunctional. After knocking down CLC-3, impaired cell proliferation, apoptosis, IR and the downstream PI3K/AKT/GSK3β signaling pathways were significantly improved. However, when CLC-3 was overexpressed, the neurotoxicity induced by high glucose was further aggravated. Rescue experiments found that through the use of inhibitors such as GSK3β, the PI3K/AKT/GSK3β signaling pathways pathway changes with the use of inhibition, and the expression of related downstream signaling molecules such as Tau and p-Tau also changes accordingly. Using adeno-associated virus gene transfer to knock down CLC-3 in the hippocampal CA1 of the DE model, the IR caused by DE and the dysfunction of the downstream PI3K/AKT/GSK3β signaling pathway were significantly improved. In addition, the impaired spatial recognition of DE was partially restored.

CONCLUSION

Our study proposes that CLC-3, as a key molecule, may regulate insulin receptor signaling and downstream PI3K/AKT/GSK3β signaling pathways and affect the pathogenesis of diabetic encephalopathy.

GLP-1 Receptor Agonists in Neurodegeneration: Neurovascular Unit in the Spotlight

Defects in brain energy metabolism and proteopathic stress are implicated in age-related degenerative neuronopathies, exemplified by Alzheimer’s disease (AD) and Parkinson’s disease (PD). As the currently available drug regimens largely aim to mitigate cognitive decline and/or motor symptoms, there is a dire need for mechanism-based therapies that can be used to improve neuronal function and potentially slow down the underlying disease processes. In this context, a new class of pharmacological agents that achieve improved glycaemic control via the glucagon-like peptide 1 (GLP-1) receptor has attracted significant attention as putative neuroprotective agents. The experimental evidence supporting their potential therapeutic value, mainly derived from cellular and animal models of AD and PD, has been discussed in several research reports and review opinions recently. In this review article, we discuss the pathological relevance of derangements in the neurovascular unit and the significance of neuron–glia metabolic coupling in AD and PD. With this context, we also discuss some unresolved questions with regard to the potential benefits of GLP-1 agonists on the neurovascular unit (NVU), and provide examples of novel experimental paradigms that could be useful in improving our understanding regarding the neuroprotective mode of action associated with these agents.

Association of β-cell function and cognitive impairment in patients with abnormal glucose metabolism

Background

Insulin has been demonstrated to play an important role in the occurrence and development of Alzheimer’s disease, especially in those with diabetes. β cells are important insulin-producing cells in human pancreas. This study aimed to investigate the association between β-cell dysfunction and cognitive impairment among patients over 40-year-old with abnormal glucose metabolism in Chinese rural communities.

Methods

A sample of 592 participants aged 40 years or older from the China National Stroke Prevention Project (CSPP) between 2015 and 2017 were enrolled in this study. Abnormal glucose metabolism was defined when hemoglobin Alc ≥ 5.7%. Cognitive function was assessed by the Beijing edition of the Montreal Cognitive Assessment scale. Homeostasis assessment of β-cell function was performed and classified into 4 groups according to the quartiles. A lower value of HOMA-β indicated a worse condition of β-cell function. Multivariate logistic regression was used to analyze the association between β-cell function and cognitive impairment.

Results

In a total of 592 patients with abnormal glucose metabolism, the average age was 60.20 ± 7.63 years and 60.1% patients had cognitive impairment. After adjusting for all potential risk factors, we found the first quartile of β-cell function was significantly associated with cognitive impairment (OR: 2.27, 95%CI: 1.32–3.92), especially at the domains of language (OR: 1.64, 95%CI: 1.01–2.65) and abstraction (OR: 2.29, 95%CI: 1.46–3.58).

Conclusions

Our study showed that worse β-cell function is associated with cognitive impairment of people over 40-year-old with abnormal glucose metabolism in Chinese rural communities, especially in the cognitive domains of abstraction and language.

Metformin and the risk of neurodegenerative diseases in patients with diabetes: A meta-analysis of population-based cohort studies

AIMS

The association between metformin use and neurodegenerative disease (ND) onset remains controversial. In this systematic review and meta-analysis, we aimed to determine the relationship between metformin use and ND risk based on data from population-based cohort studies.

METHODS

Articles were systematically searched in PubMed, EMBASE and Cochrane Library databases. Pooled relative risks (RRs) with 95% CIs were obtained using a random-effects model. Subgroup analyses, sensitivity analyses and meta-regression were performed to identify the sources of heterogeneity and strengthen the results.

RESULTS

Twelve population-based cohort studies involving 194,792 participants (94,462 metformin users and 100,330 metformin non-users) were eligible for inclusion in this meta-analysis. The pooled RR of NDs reached 0.77 (95% CI 0.67-0.88) when comparing metformin users with non-users. The effects were more prominent in long-term metformin users (≥4 years) (RR 0.29, 95% CI 0.13-0.44) and studies from Asian countries (RR 0.69, 95% CI 0.64-0.74). The effect estimates were stable when stratified by subtypes of NDs, study designs, and control definitions (p for interaction >0.05). Meta-regression did not identify the coefficients as the sources of heterogeneity (all p > 0.05).

CONCLUSIONS

This systematic review and meta-analysis found that metformin use, especially long-term use, was associated with lower ND risk. However, because there was substantial heterogeneity among studies, high-quality randomized controlled trials are still needed to confirm this finding.

Protective effects of Aster yomena (Kitam.) Honda from cognitive dysfunction induced by high-fat diet

In our study, we investigated whether Aster yomena (Kitam.) Honda (AY) improved cognitive impairment which results from consumption of high-fat diet (HFD). When ethyl acetate fraction from AY (EFAY) was administered to C57BL/6J mice fed with 60% HFD, EFAY significantly enhanced cognitive ability that was impaired by HFD in T-maze test and novel object recognition test. Furthermore, EFAY increased memory and learning functions that were proven during Morris water maze test. We further elucidated protective mechanisms of EFAY against cognitive decline that resulted from obesity by western blotting. In the brain, HFD increased neuronal inflammation and disturbed insulin receptor substrate-1 (IRS-1)/Akt pathway. However, EFAY significantly downregulated inflammation-related protein expressions such as nuclear factor-κB interleukin-1β, inducible nitric oxide synthase and cyclooxygenase-2, compared with the HFD-fed control group. Furthermore, the IRS-1/Akt pathway was regulated by EFAY, indicating that EFAY ameliorated insulin resistance in the brain. PRACTICAL APPLICATIONS: Obesity and its complications increase the risk for developing cognitive dysfunction such as dementia. Administration of ethyl acetate fraction from AY (EFAY)-attenuated cognitive and memory impairment by inhibitions of neuronal oxidative stress and low-grade chronic inflammation in high-fat diet (HFD)-induced cognitive impairment mouse model. In addition, EFAY-administered mice disturbed cerebral insulin receptor substrate-1 (IRS-1)/Akt pathway. These data suggest that EFAY-improved cognitive impairment induced by HFD through modulation of insulin resistance and inflammation. Therefore, we proposed that AY could be a potential agent to prevent cognitive dysfunction induced by obesity and insulin resistance.

Targeting whole body metabolism and mitochondrial bioenergetics in the drug development for Alzheimer's disease

Aging is by far the most prominent risk factor for Alzheimer's disease (AD), and both aging and AD are associated with apparent metabolic alterations. As developing effective therapeutic interventions to treat AD is clearly in urgent need, the impact of modulating whole-body and intracellular metabolism in preclinical models and in human patients, on disease pathogenesis, have been explored. There is also an increasing awareness of differential risk and potential targeting strategies related to biological sex, microbiome, and circadian regulation. As a major part of intracellular metabolism, mitochondrial bioenergetics, mitochondrial quality-control mechanisms, and mitochondria-linked inflammatory responses have been considered for AD therapeutic interventions. This review summarizes and highlights these efforts.

Protective properties of GLP-1 and associated peptide hormones in neurodegenerative disorders

Type 2 diabetes mellitus and the associated desensitisation of insulin signalling has been identified as a risk factor for progressive neurodegenerative disorders such as Alzheimer's disease, Parkinson's disease and others. Glucagon-like peptide 1 (GLP-1) is a hormone that has growth factor-like and neuroprotective properties. Several clinical trials have been conducted, testing GLP-1 receptor agonists in patients with Alzheimer's disease, Parkinson's disease or diabetes-induced memory impairments. The trials showed clear improvements in Alzheimer's disease, Parkinson's disease and diabetic patients. Glucose-dependent insulinotropic polypeptide/gastric inhibitory peptide (GIP) is the 'sister' incretin hormone of GLP-1. GIP analogues have shown neuroprotective effects in animal models of disease and can improve on the effects of GLP-1. Novel dual GLP-1/GIP receptor agonists have been developed that can enter the brain at an enhanced rate. The improved neuroprotective effects of these drugs suggest that they are superior to single GLP-1 receptor agonists and could provide disease-modifying care for Alzheimer's disease and Parkinson's disease patients. LINKED ARTICLES: This article is part of a themed issue on GLP1 receptor ligands (BJP 75th Anniversary). To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v179.4/issuetoc.

A Non-Invasive Determination of Ketosis-Induced Elimination of Chronic Daytime Somnolence in a Patient with Late-Stage Dementia (Assessed with Type 3 Diabetes): A Potential Role of Neurogenesis

Background

The study involved a female patient diagnosed with late-stage dementia, with chronic daytime somnolence (CDS) as a prominent symptom.

Objective

To explore whether her dementia resulted from Type 3 diabetes, and whether it could be reversed through ketosis therapy.

Methods

A ketogenic diet (KD) generating low-dose 100 μM Blood Ketone Levels (BKL) enhanced by a brief Ketone Mono Ester (KME) regimen with high-dose 2-4 mM BKLs was used.

Results

Three sets of data describe relief (assessed by % days awake) from CDS: 1) incremental, slow, time-dependent KD plus KME-induced sigmoid curve responses which resulted in partial wakefulness (0-40% in 255 days) and complete wakefulness (40-85% in 50 days); 2) both levels of wakefulness were shown to be permanent; 3) initial permanent relief from CDS with low-dose ketosis from 6.7% to 40% took 87 days. Subsequent low-dose recovery from illness-induced CDS (6.9% to 40%) took 10 days. We deduce that the first restoration involved permanent repair, and the second energized the repaired circuits.

Conclusion

The results suggest a role for ketosis in the elimination of CDS with the permanent functional restoration of the awake neural circuits of the Sleep-Wake cycle. We discuss whether available evidence supports ketosis-induced bioenergetics alone or whether other mechanisms of functional renewal were the basis for the elimination of CDS. Given evidence for permanent repair, two direct links between ketosis and neurogenesis in the adult mammalian brain are discussed: Ketosis-induced 1) brain-derived neurotrophic factor, resulting in neural progenitor/stem cell proliferation, and 2) mitochondrial bioenergetics-induced stem cell biogenesis.

Challenges of repurposing tetracyclines for the treatment of Alzheimer's and Parkinson's disease

The novel antibiotic-exploiting strategy in the treatment of Alzheimer's (AD) and Parkinson's (PD) disease has emerged as a potential breakthrough in the field. The research in animal AD/PD models provided evidence on the antiamyloidogenic, anti-inflammatory, antioxidant and antiapoptotic activity of tetracyclines, associated with cognitive improvement. The neuroprotective effects of minocycline and doxycycline in animals initiated investigation of their clinical efficacy in AD and PD patients which led to inconclusive results and additionally to insufficient safety data on a long-standing doxycycline and minocycline therapy in these patient populations. The safety issues should be considered in two levels; in AD/PD patients (particularly antibiotic-induced alteration of gut microbiota and its consequences), and as a world-wide threat of development of bacterial resistance to these antibiotics posed by a fact that AD and PD are widespread incurable diseases which require daily administered long-lasting antibiotic therapy. Recently proposed subantimicrobial doxycycline doses should be thoroughly explored for their effectiveness and long-term safety especially in AD/PD populations. Keeping in mind the antibacterial activity-related far-reaching undesirable effects both for the patients and globally, further work on repurposing these drugs for a long-standing therapy of AD/PD should consider the chemically modified tetracycline compounds tailored to lack antimicrobial but retain (or introduce) other activities effective against the AD/PD pathology. This strategy might reduce the risk of long-term therapy-related adverse effects (particularly gut-related ones) and development of bacterial resistance toward the tetracycline antibiotic agents but the therapeutic potential and desirable safety profile of such compounds in AD/PD patients need to be confirmed.

CDK5 inhibition improves glucose uptake in insulin-resistant neuronal cells via ERK1/2 pathway

Role of CDK5 and its inhibition in various neuronal processes and functions are well established. However, role of CDK5 and its inhibition in neuronal insulin-signaling and-resistance is not yet explored. In the present study, we investigated the effect of CDK5 inhibition in neuronal insulin signaling, specifically insulin-stimulated glucose uptake. CDK5 expression in neuro-2a cells was increased under insulin-resistant state, developed by chronic treatment of insulin, confirming the crucial role of CDK5 in insulin resistance in neuronal cells. However, whether increased expression of CDK5 in hyperinsulinemia-mediated insulin-resistant conditions is a cause or a consequence, is still an unanswered question. We showed that CDK5 inhibition did not affect basal insulin signaling; however, insulin-stimulated glucose uptake enhanced in insulin-resistant cells. Moreover, CDK5 inhibition could improve glucose uptake, the ultimate outcome of insulin signaling, in insulin-resistant neuro-2a cells. We first time showed that CDK5 inhibition by roscovitine could ameliorate insulin resistance and increase glucose uptake in neuronal cells via ERK1/2 pathway. Our study provides intriguing insights about the effect of CDK5 inhibition on neuronal insulin resistance and opens up a new paradigm to develop new therapeutic strategies for neuronal insulin resistance and associated pathophysiological conditions.

Nutrients, Cognitive Function, and Brain Aging: What We Have Learned from Dogs

Due to a difference in genetics, environmental factors, and nutrition, just like in people, dogs age at different rates. Brain aging in people and dogs share similar morphological changes including irreversible cortical atrophy, cerebral amyloid angiopathy, and ventricular enlargement. Due to severe and irreversible brain atrophy, some aging dogs develop cognitive dysfunction syndrome (CDS), which is equivalent to dementia or Alzheimer’s disease (AD) in people. The risk factors and causes of CDS in dogs have not been fully investigated, but age, gender, oxidative stress, and deficiency of sex hormones appears to be associated with increased risk of accelerated brain aging and CDS in dogs. Both AD and CDS are incurable diseases at this moment, therefore more efforts should be focused on preventing or reducing brain atrophy and minimizing the risk of AD in people and CDS in dogs. Since brain atrophy leads to irreversible cognitive decline and dementia, an optimal nutritional solution should be able to not only enhance cognitive function during aging but also reduce irreversible brain atrophy. Up to now, only one nutritional intervention has demonstrated both cognition-enhancing benefits and atrophy-reducing benefits.

Tau Cleavage Contributes to Cognitive Dysfunction in Strepto-Zotocin-Induced Sporadic Alzheimer's Disease (sAD) Mouse Model

Tau cleavage plays a crucial role in the onset and progression of Alzheimer’s Disease (AD), a widespread neurodegenerative disease whose incidence is expected to increase in the next years. While genetic and familial forms of AD (fAD) occurring early in life represent less than 1%, the sporadic and late-onset ones (sAD) are the most common, with ageing being an important risk factor. Intracerebroventricular (ICV) infusion of streptozotocin (STZ)—a compound used in the systemic induction of diabetes due to its ability to damage the pancreatic β cells and to induce insulin resistance—mimics in rodents several behavioral, molecular and histopathological hallmarks of sAD, including memory/learning disturbance, amyloid-β (Aβ) accumulation, tau hyperphosphorylation, oxidative stress and brain glucose hypometabolism. We have demonstrated that pathological truncation of tau at its N-terminal domain occurs into hippocampi from two well-established transgenic lines of fAD animal models, such as Tg2576 and 3xTg mice, and that it’s in vivo neutralization via intravenous (i.v.) administration of the cleavage-specific anti-tau 12A12 monoclonal antibody (mAb) is strongly neuroprotective. Here, we report the therapeutic efficacy of 12A12mAb in STZ-infused mice after 14 days (short-term immunization, STIR) and 21 days (long-term immunization regimen, LTIR) of i.v. delivery. A virtually complete recovery was detected after three weeks of 12A12mAb immunization in both novel object recognition test (NORT) and object place recognition task (OPRT). Consistently, three weeks of this immunization regimen relieved in hippocampi from ICV-STZ mice the AD-like up-regulation of amyloid precursor protein (APP), the tau hyperphosphorylation and neuroinflammation, likely due to modulation of the PI3K/AKT/GSK3-β axis and the AMP-activated protein kinase (AMPK) activities. Cerebral oxidative stress, mitochondrial impairment, synaptic and histological alterations occurring in STZ-infused mice were also strongly attenuated by 12A12mAb delivery. These results further strengthen the causal role of N-terminal tau cleavage in AD pathogenesis and indicate that its specific neutralization by non-invasive administration of 12A12mAb can be a therapeutic option for both fAD and sAD patients, as well as for those showing type 2 diabetes as a comorbidity.

Disruption of Glucose Metabolism in Aged Octodon degus: A Sporadic Model of Alzheimer's Disease

Alzheimer's disease is a progressive neurodegenerative disorder and the most common cause of dementia. Although transgenic Alzheimer's disease (AD) animal models have greatly contributed to our understanding of the disease, therapies tested in these animals have resulted in a high rate of failure in preclinical trials for AD. A promising model is Octodon degus (degu), a Chilean rodent that spontaneously develops AD-like neuropathology. Previous studies have reported that, during aging, degus exhibit a progressive decline in cognitive function, reduced neuroinflammation, and concomitant increases in the number and size of amyloid β (Aβ) plaques in several brain regions. Importantly, in humans and several AD models, a correlation has been shown between brain dysfunction and neuronal glucose utilization impairment, a critical aspect considering the high-energy demand of the brain. However, whether degus develop alterations in glucose metabolism remains unknown. In the present work, we measured several markers of glucose metabolism, namely, glucose uptake, ATP production, and glycolysis and pentose phosphate pathway (PPP) flux, in hippocampal slices from degus of different ages. We found a significant decrease in hippocampal glucose metabolism in aged degus, caused mainly by a drop in glucose uptake, which in turn, reduced ATP synthesis. Moreover, we observed a negative correlation between age and PPP flux. Together, our data further support the use of degus as a model for studying the neuropathology involved in sporadic AD-like pathology and as a potentially valuable tool in the search for effective treatments against the disease.

Aβ initiates brain hypometabolism, network dysfunction and behavioral abnormalities via NOX2-induced oxidative stress in mice

A predominant trigger and driver of sporadic Alzheimer’s disease (AD) is the synergy of brain oxidative stress and glucose hypometabolism starting at early preclinical stages. Oxidative stress damages macromolecules, while glucose hypometabolism impairs cellular energy supply and antioxidant defense. However, the exact cause of AD-associated glucose hypometabolism and its network consequences have remained unknown. Here we report NADPH oxidase 2 (NOX2) activation as the main initiating mechanism behind Aβ_1-42-related glucose hypometabolism and network dysfunction. We utilize a combination of electrophysiology with real-time recordings of metabolic transients both ex- and in-vivo to show that Aβ_1-42 induces oxidative stress and acutely reduces cellular glucose consumption followed by long-lasting network hyperactivity and abnormalities in the animal behavioral profile. Critically, all of these pathological changes were prevented by the novel bioavailable NOX2 antagonist GSK2795039. Our data provide direct experimental evidence for causes and consequences of AD-related brain glucose hypometabolism, and suggest that targeting NOX2-mediated oxidative stress is a promising approach to both the prevention and treatment of AD.

Anton Malkov, Irina Popova et al. demonstrate that beta-amyloid application induces oxidative stress and reduces glucose consumption in the mouse brain, leading to network hyperactivity and behavioral changes—pathologies similar to those observed early on in Alzheimer’s disease patients. Inhibition of NADPH oxidase 2 (NOX2) rescued these phenotypes, suggesting that NOX2 may represent an important therapeutic target for Alzheimer’s disease.

Cerebrospinal fluid lipidomics for biomarkers of Alzheimer's disease

Alzheimer's disease (AD) is the most common cause of dementia and is associated with serious neurologic sequelae resulting from neurodegenerative changes. Identification of markers of early-stage AD could be important for designing strategies to arrest the progression of the disease. The brain is rich in lipids because they are crucial for signal transduction and anchoring of membrane proteins. Cerebrospinal fluid (CSF) is an excellent specimen for studying the metabolism of lipids in AD because it can reflect changes occurring in the brain. We aimed to identify CSF lipidomic alterations associated with AD, using untargeted lipidomics, carried out in positive and negative ion modes. We found CSF lipids that were significantly altered in AD cases. In addition, comparison of CSF lipid profiles between persons with mild cognitive impairment (MCI) and AD showed a strong positive correlation between the lipidomes of the MCI and AD groups. The novel lipid biomarkers identified in this study are excellent candidates for validation in a larger set of patient samples and as predictive biomarkers of AD through future longitudinal studies. Once validated, the lipid biomarkers could lead to early detection, disease monitoring and the ability to measure the efficacy of potential therapeutic interventions in AD.

O-GlcNAcylation of TDP-43 suppresses proteinopathies and promotes TDP-43's mRNA splicing activity

Pathological TDP-43 aggregation is characteristic of several neurodegenerative diseases, including amyotrophic lateral sclerosis (ALS) and frontotemporal lobar degeneration (FTLD-TDP); however, how TDP-43 aggregation and function are regulated remain poorly understood. Here, we show that O-GlcNAc transferase OGT-mediated O-GlcNAcylation of TDP-43 suppresses ALS-associated proteinopathies and promotes TDP-43's splicing function. Biochemical and cell-based assays indicate that OGT's catalytic activity suppresses TDP-43 aggregation and hyperphosphorylation, whereas abolishment of TDP-43 O-GlcNAcylation impairs its RNA splicing activity. We further show that TDP-43 mutations in the O-GlcNAcylation sites improve locomotion defects of larvae and adult flies and extend adult life spans, following TDP-43 overexpression in Drosophila motor neurons. We finally demonstrate that O-GlcNAcylation of TDP-43 promotes proper splicing of many mRNAs, including STMN2, which is required for normal axonal outgrowth and regeneration. Our findings suggest that O-GlcNAcylation might be a target for the treatment of TDP-43-linked pathogenesis.

A New Approach to Model Sporadic Alzheimer's Disease by Intracerebroventricular Streptozotocin Injection in APP/PS1 Mice

Alzheimer's disease (AD) is the most common cause of dementia among elderly people. Majority of AD cases are sporadic (SAD) with unknown cause. Transgenic animal models closely reflect the familial (genetic) aspect of the disease but not the sporadic type. However, most new drug candidates which are tested positive in transgenic animal models failed in clinical studies so far. Herein, we aim to develop an AD animal model that combines most of the neuropathological features seen in sporadic AD in humans with amyloid plaques observed in transgenic mice. Four-month-old wild-type and APP/PS1 AD mice were given a single intracerebroventricular (ICV) injection of 3 mg/kg streptozotocin (STZ), a diabetogenic agent. Three weeks later, their cognitive behavior was assessed, and their brain tissues were collected for biochemical and histological analysis. STZ produced cognitive deficits in both non-transgenic mice and AD mice. Biochemical analysis showed a severe decline in synaptic proteins, increase in tau phosphorylation, oxidative stress, disturbed brain insulin signaling with extensive neuroinflammation, and cell death. Significant increase was also observed in the level of the soluble beta amyloid precursor protein (APP) fragments and robust accumulation of amyloid plaques in AD mice compared to the control. These results suggest that STZ ICV treatment causes disturbance in multiple metabolic and cell signaling pathways in the brain that facilitated amyloid plaque accumulation and tau phosphorylation. Therefore, this animal model can be used to evaluate new AD therapeutic agents for clinical translation.

Neuroprotective mechanisms of chronic physical exercise via reduction of β-amyloid protein in experimental models of Alzheimer's disease: A systematic review

AIMS

Alzheimer's disease (AD) is the most common irreversible chronic neurodegenerative disease. It is characterized by the abnormal accumulation of β-amyloid protein (Aβ), which triggers homeostatic breakage in several physiological systems. However, the effect of chronic exercise on the formation of Aβ as an alternative therapy has been investigated. This systematic review examines the antiamyloid effect of different types and intensities of exercise, seeking to elucidate its neuroprotective mechanisms.

MAIN METHODS

The research was conducted in the electronic databases Pubmed, Embase, Scopus and Web of Science, using the following descriptors: "amyloid beta" (OR senile plaque OR amyloid plaque) and "exercise" (OR physical activity OR training). The risk of bias was evaluated through SYRCLE's Risk of Bias for experimental studies.

KEY FINDINGS

2268 articles were found, being 36 included in the study. A higher frequency of use of mice with genetic alterations was identified for the Alzheimer's disease (AD) model (n = 29). It was used as chronic training: treadmill running (n = 24), voluntary running wheel (n = 7), swimming (n = 4) and climbing (n = 2). The hippocampus and the cortex were the most investigated regions. However, physiological changes accompanied by the reduction of Aβ and associated with AD progression were verified. It is concluded that exercise reduces the production of Aβ in models of animals with AD.

SIGNIFICANCE

Nevertheless, this effect contributes to the improvement of several physiological aspects related to Aβ and that contribute to neurological impairment in AD.

Does insulin resistance influence neurodegeneration in non-diabetic Alzheimer's subjects?

Background

Type 2 diabetes is a risk factor for Alzheimer’s disease (AD), and AD brain shows impaired insulin signalling. The role of peripheral insulin resistance on AD aetiopathogenesis in non-diabetic patients is still debated. Here we evaluated the influence of insulin resistance on brain glucose metabolism, grey matter volume and white matter lesions (WMLs) in non-diabetic AD subjects.

Methods

In total, 130 non-diabetic AD subjects underwent MRI and [18F]FDG PET scans with arterial cannula insertion for radioactivity measurement. T1 Volumetric and FLAIR sequences were acquired on a 3-T MRI scanner. These subjects also had measurement of glucose and insulin levels after a 4-h fast on the same day of the scan. Insulin resistance was calculated by the updated homeostatic model assessment (HOMA2). For [18F]FDG analysis, cerebral glucose metabolic rate (rCMRGlc) parametric images were generated using spectral analysis with arterial plasma input function.

Results

In this non-diabetic AD population, HOMA2 was negatively associated with hippocampal rCMRGlc, along with total grey matter volumes. No significant correlation was observed between HOMA2, hippocampal volume and WMLs.

Conclusions

In non-diabetic AD, peripheral insulin resistance is independently associated with reduced hippocampal glucose metabolism and with lower grey matter volume, suggesting that peripheral insulin resistance might influence AD pathology by its action on cerebral glucose metabolism and on neurodegeneration.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13195-021-00784-w.

The Immunopathogenesis of Alzheimer's Disease Is Related to the Composition of Gut Microbiota

The microbiota-gut-brain axis plays an important role in the development of neurodegenerative diseases. Commensal and pathogenic enteric bacteria can influence brain and immune system function by the production of lipopolysaccharides and amyloid. Dysbiosis of the intestinal microbiome induces local and consecutively systemic immune-mediated inflammation. Proinflammatory cytokines then trigger neuroinflammation and finally neurodegeneration. Immune-mediated oxidative stress can lead to a deficiency of vitamins and essential micronutrients. Furthermore, the wrong composition of gut microbiota might impair the intake and metabolization of nutrients. In patients with Alzheimer's disease (AD) significant alterations of the gut microbiota have been demonstrated. Standard Western diet, infections, decreased physical activity and chronic stress impact the composition and diversity of gut microbiota. A higher abundancy of "pro-inflammatory" gut microbiota goes along with enhanced systemic inflammation and neuroinflammatory processes. Thus, AD beginning in the gut is closely related to the imbalance of gut microbiota. Modulation of gut microbiota by Mediterranean diet, probiotics and curcumin can slow down cognitive decline and alter the gut microbiome significantly. A multi-domain intervention approach addressing underlying causes of AD (inflammation, infections, metabolic alterations like insulin resistance and nutrient deficiency, stress) appears very promising to reduce or even reverse cognitive decline by exerting positive effects on the gut microbiota.

AMPK: Potential Therapeutic Target for Alzheimer's Disease

Alzheimer's disease (AD) is the most common neurodegenerative disorder. The pathogenesis of AD is very complicated. For decades, the amyloid hypothesis has influenced and guided research in the field of AD. Meanwhile, researchers gradually realized that AD is caused by multiple concomitant factors, such as autophagy, mitochondrial quality control, insulin resistance and oxidative stress. In current clinical trials, the improvement strategies of AD, such as Aβ antibody immunotherapy and gamma secretase inhibitors, are limited. There is mounting evidence of neurodegenerative disorders indicated that activation of AMP-activated protein kinase (AMPK) may have broad neuroprotective effects. We reviewed the researches on AMPK for AD, the results demonstrated that activation of AMPK is controversial in Aβ deposition and tau phosphorylation, but is positive to promote autophagy, maintain mitochondrial quality control, reduce insulin resistance and relieve oxidative stress. It is concluded that AMPK might be a new target for AD by aggressively treating the risk factors in the future.

Deciphering Alzheimer's Disease Pathogenic Pathway: Role of Chronic Brain Hypoperfusion on p-Tau and mTOR

This review examines new biomolecular findings that lend support to the hemodynamic role played by chronic brain hypoperfusion (CBH) in driving a pathway to Alzheimer's disease (AD). CBH is a common clinical feature of AD and the current topic of intense investigation in AD models. CBH is also the basis for the vascular hypothesis of AD which we originally proposed in 1993. New biomolecular findings reveal the interplay of CBH in increasing tau phosphorylation (p-Tau) in the hippocampus and cortex of AD mice, damaging fast axonal transport, increasing signaling of mammalian target of rapamycin (mTOR), impairing learning-memory function, and promoting the formation of neurofibrillary tangles, a neuropathologic hallmark of AD. These pathologic elements have been singularly linked with neurodegeneration and AD but their abnormal, collective participation during brain aging have not been fully examined. The format for this review will provide a consolidated analysis of each pathologic phase contributing to cognitive decline and AD onset, summarized in nine chronological steps. These steps galvanize each factor's active participation and contribution in constructing a biomolecular pathway to AD onset generated by CBH.

Additional methodological considerations regarding optimization of the dose of intracerebroventricular streptozotocin A response to: "Optimization of intracerebroventricular streptozotocin dose for the induction of neuroinflammation and memory impairments in rats" by Ghosh et al., Metab Brain Dis 2020 July 21

A recent article by Ghosh et al. entitled "Optimization of intracerebroventricular streptozotocin dose for the induction of neuroinflammation and memory impairments in rats" provides an important new set of information on neuroinflammation and cognitive deficit in a rat model of sporadic Alzheimer's disease (sAD) based on intracerebroventricular administration of streptozotocin (STZ-icv) in Charles-Foster rats in the early post-treatment period of 21 days. This comment is supposed to supplement the aforementioned manuscript by providing additional perspective on important factors that should be taken into account in the process of optimization of the streptozotocin (STZ) dose for intracerebroventricular treatment, and provides a brief overview of possible sources of variation of experimental results reported by different groups working with STZ-icv rodent models.

Aging-related modifications to G protein-coupled receptor signaling diversity

Aging is a highly complex molecular process, affecting nearly all tissue systems in humans and is the highest risk factor in developing neurodegenerative disorders such as Alzheimer's and Parkinson's disease, cardiovascular disease and Type 2 diabetes mellitus. The intense complexity of the aging process creates an incentive to develop more specific drugs that attenuate or even reverse some of the features of premature aging. As our current pharmacopeia is dominated by therapeutics that target members of the G protein-coupled receptor (GPCR) superfamily it may be prudent to search for effective anti-aging therapeutics in this fertile domain. Since the first demonstration of GPCR-based β-arrestin signaling, it has become clear that an enhanced appreciation of GPCR signaling diversity may facilitate the creation of therapeutics with selective signaling activities. Such 'biased' ligand signaling profiles can be effectively investigated using both standard molecular biological techniques as well as high-dimensionality data analyses. Through a more nuanced appreciation of the quantitative nature across the multiple dimensions of signaling bias that drugs possess, researchers may be able to further refine the efficacy of GPCR modulators to impact the complex aberrations that constitute the aging process. Identifying novel effector profiles could expand the effective pharmacopeia and assist in the design of precision medicines. This review discusses potential non-G protein effectors, and specifically their potential therapeutic suitability in aging and age-related disorders.

AMPK: A bridge between diabetes mellitus and Alzheimer's disease

The pathogenesis and etiology of diabetes mellitus (DM) and Alzheimer's disease (AD) share many common cellular and molecular themes. Recently, a growing body of research has shown that AMP-activated protein kinase (AMPK), a biomolecule that regulates energy balance and glucose and lipid metabolism, plays key roles in DM and AD. In this review, we summarize the relevant research on the roles of AMPK in DM and AD, including its functions in gluconeogenesis and insulin resistance (IR) and its relationships with amyloid β-protein (Aβ), Tau and AMPK activators. In DM, AMPK is involved in the regulation of glucose metabolism and IR. AMPK is closely related to gluconeogenesis, which can not only be activated by the upstream kinases liver kinase B1 (LKB1), transforming growth factor β-activated kinase 1 (TAK1), and Ca²⁺/calmodulin-dependent protein kinase kinase β (CaMKKβ) but also regulate the downstream kinases glucose-6-phosphatase (G-6-Pase) and phosphoenolpyruvate carboxy kinase (PEPCK), thereby affecting gluconeogenesis and ameliorating DM. Moreover, AMPK can regulate glucose transporter 4 (GLUT4) and free fatty acids to improve IR. In AD, AMPK can ameliorate abnormal brain energy metabolism, not only by reduces Aβ deposition through β-secretase but also reduces tau hyperphosphorylation through sirtuin 1 (SIRT1) and protein phosphatase 2A (PP2A). Therefore, AMPK is a bridge between DM and AD.