Amyloid-β induces hepatic insulin resistance in vivo via JAK2

Modulation of oxidative stress and apoptosis by alteration of bioactive lipids in the pancreas, and effect of zinc chelation in a rat model of Alzheimer's disease

INTRODUCTION

Increasing epidemiological evidence highlights the association between systemic insulin resistance and Alzheimer's disease (AD). It is known that peripheral insulin resistance in the early stages of AD precedes and is a precursor to amyloid-β (Aβ) deposition. Although it is known that improving the CNS insulin sensitivity of AD patients is an important therapeutic goal and that the majority of insulin in the brain comes from the periphery, there has been little attention to the changes that occur in the pancreatic tissue of AD patients. Therefore, it is crucial to elucidate the mechanisms affecting insulin resistance in pancreatic tissue in AD. It is known that zinc (Zn2+) chelation is effective in reducing peripheral insulin resistance, cell apoptosis, cell death, and oxidative stress.

OBJECTIVE

It was aimed to determine the changes in bioactive lipids, amylin (AIPP), oxidative stress and apoptosis in pancreatic cells in the early stages of Alzheimer's disease. The main aim is to reveal the therapeutic effect of the Cyclo-Z agent on these changes seen in the pancreas due to AD disease.

METHODS

AD and ADC rats were intracerebroventricular (i.c.v.) Aβ1-42 oligomers. Cyclo-Z gavage was applied to ADC and SHC rats for 21 days. First of all, the effects of AIPP, bioactive ceramides, apoptosis and oxidative stress on the pancreatic tissue of AD group rats were evaluated. Then, the effect of Cyclo-Z treatment on these was examined. ELISA kit was used in biochemical analyses.

RESULTS

AIPP and ceramide (CER) levels and CER/ sphingosine-1 phosphate (S1P) ratio were increased in the pancreatic tissue of AD rats. It also increased the level of CER kinase (CERK), which is known to increase the concentration of CER 1-phosphate (C1P), which is known to be toxic to cells in the presence of excessive CER concentration. Due to the increase in CER level, it was observed that apoptosis and oxidative stress increased in the pancreatic cells of AD group rats.

CONCLUSION

Cyclo-Z, which has Zn2+ chelating properties, reduced AD model rats' AIPP level and oxidative stress and could prevent pancreatic apoptosis. Similar therapeutic effects were not observed in the pancreatic tissue of Cyclo-Z administered to the SH group. For this reason, it is thought that Cyclo-Z agent may have a therapeutic effect on the peripheral hyperinsulinemia observed in the early stages of AD disease and the resulting low amount of insulin transported to the brain, by protecting pancreatic cells from apoptosis and oxidative stress by regulating their bioactive metabolites.

The interaction between insulin resistance and Alzheimer's disease: a review article

Insulin serves multiple functions as a growth-promoting hormone in peripheral tissues. It manages glucose metabolism by promoting glucose uptake into cells and curbing the production of glucose in the liver. Beyond this, insulin fosters cell growth, drives differentiation, aids protein synthesis, and deters degradative processes like glycolysis, lipolysis, and proteolysis. Receptors for insulin and insulin-like growth factor-1 are widely expressed in the central nervous system. Their widespread presence in the brain underscores the varied and critical functions of insulin signaling there. Insulin aids in bolstering cognition, promoting neuron extension, adjusting the release and absorption of catecholamines, and controlling the expression and positioning of gamma-aminobutyric acid (GABA). Importantly, insulin can effortlessly traverse the blood-brain barrier. Furthermore, insulin resistance (IR)-induced alterations in insulin signaling might hasten brain aging, impacting its plasticity and potentially leading to neurodegeneration. Two primary pathways are responsible for insulin signal transmission: the phosphoinositide 3-kinase (PI3K)/protein kinase B (AKT) pathway, which oversees metabolic responses, and the mitogen-activated protein kinase (MAPK) pathway, which guides cell growth, survival, and gene transcription. This review aimed to explore the potential shared metabolic traits between Alzheimer's disease (AD) and IR disorders. It delves into the relationship between AD and IR disorders, their overlapping genetic markers, and shared metabolic indicators. Additionally, it addresses existing therapeutic interventions targeting these intersecting pathways.

Comorbidity Genes of Alzheimer's Disease and Type 2 Diabetes Associated with Memory and Cognitive Function

Alzheimer's disease (AD) and type 2 diabetes mellitus (T2DM) are comorbidities that result from the sharing of common genes. The molecular background of comorbidities can provide clues for the development of treatment and management strategies. Here, the common genes involved in the development of the two diseases and in memory and cognitive function are reviewed. Network clustering based on protein-protein interaction network identified tightly connected gene clusters that have an impact on memory and cognition among the comorbidity genes of AD and T2DM. Genes with functional implications were intensively reviewed and relevant evidence summarized. Gene information will be useful in the discovery of biomarkers and the identification of tentative therapeutic targets for AD and T2DM.

Association of overexpressed carboxyl-terminal amyloid precursor protein in brains with altered glucose metabolism and liver toxicity

Alzheimer’s disease (AD) is the most prevalent neurodegenerative disease. The deposition of amyloid plaques mainly composed of amyloid beta (Aβ) is observed in brain regions in AD patients. AD presents with similar pathophysiology to that of metabolic syndrome, including glucose and insulin resistance. In addition, epidemiological studies indicate diabetes, impaired glucose metabolism, and obesity increase the prevalence of AD. The liver is considered a key organ in the reciprocal relationship between AD and metabolic syndrome and is the major organ for the clearance of Aβ in the periphery. Furthermore, liver dysfunction aggravates Aβ-induced pathophysiology. Aβ is produced in the brain and peripheral tissues and penetrates the blood–brain barrier. However, in vivo evidence showing the effect of Aβ on the crosstalk between the brain and liver has not been reported yet. In the present study, we investigated the toxicity of brain-derived Aβ on glucose metabolism and the liver using transgenic mice overexpressing the carboxyl-terminal of amyloid precursor protein in the brain. The transgenic mice were overweight, which was associated with impaired glucose metabolism and insulin resistance, but not due to increased food intake. In addition, transgenic mice had enlarged livers and reduced gene expressions associated with glucose and lipid metabolism. Thus, overexpressed amyloid precursor protein in the brain may promote being overweight and glucose resistance, possibly through liver toxicity.

The role of peripheral β-amyloid in insulin resistance, insulin secretion, and prediabetes: in vitro and population-based studies

Background

Previous experimental studies have shown that mice overexpressing amyloid precursor protein, in which β-amyloid (Aβ) is overproduced, exhibit peripheral insulin resistance, pancreatic impairment, and hyperglycemia. We aimed to explore the effects of Aβ on insulin action and insulin secretion in vitro and the association of plasma Aβ with prediabetes in human.

Methods

We examined the effects of Aβ40 and Aβ42 on insulin-inhibited glucose production in HepG2 cells, insulin-promoted glucose uptake in C2C12 myotubes, and insulin secretion in INS-1 cells. Furthermore, we conducted a case-control study (N = 1142) and a nested case-control study (N = 300) within the prospective Tongji-Ezhou cohort. Odds ratios (ORs) and 95% confidence intervals (CIs) for prediabetes were estimated by using conditional logistic regression analyses.

Results

In the in vitro studies, Aβ40 and Aβ42 dose-dependently attenuated insulin-inhibited glucose production in HepG2 cells, insulin-promoted glucose uptake in C2C12 myotubes, and basal and glucose-stimulated insulin secretion in INS-1 cells. In the case-control study, plasma Aβ40 (adjusted OR: 2.00; 95% CI: 1.34, 3.01) and Aβ42 (adjusted OR: 1.94; 95% CI: 1.33, 2.83) were positively associated with prediabetes risk when comparing the extreme quartiles. In the nested case-control study, compared to the lowest quartile, the highest quartile of plasma Aβ40 and Aβ42 were associated with 3.51-fold (95% CI: 1.61, 7.62) and 2.75-fold (95% CI: 1.21, 6.22) greater odds of prediabetes, respectively.

Conclusion

Elevated plasma Aβ40 and Aβ42 levels were associated with increased risk of prediabetes in human subjects, which may be through impairing insulin sensitivity in hepatocytes and myotubes and insulin secretion in pancreatic β-cells.

SOCS7-Derived BC-Box Motif Peptide Mediated Cholinergic Differentiation of Human Adipose-Derived Mesenchymal Stem Cells

Adipose-derived mesenchymal stem cells (ADMSCs) are a type of pluripotent somatic stem cells that differentiate into various cell types such as osteoblast, chondrocyte, and neuronal cells. ADMSCs as donor cells are used to produce regenerative medicines at hospitals and clinics. However, it has not been reported that ADMSCs were differentiated to a specific type of neuron with a peptide. Here, we report that ADMSCs differentiate to the cholinergic phenotype of neurons by the SOCS7-derived BC-box motif peptide. At operations for patients with neurological disorders, a small amount of subcutaneous fat was obtained. Two weeks later, adipose-derived mesenchymal stem cells (ADMSCs) were isolated and cultured for a further 1 to 2 weeks. Flow cytometry analysis for characterization of ADMSCs was performed with CD73, CD90, and CD105 as positive markers, and CD14, CD31, and CD56 as negative markers. The results showed that cultured cells were compatible with ADMSCs. Immunocytochemical studies showed naïve ADMSCs immunopositive for p75NTR, RET, nestin, keratin, neurofilament-M, and smooth muscle actin. ADMSCs were suggested to be pluripotent stem cells. A peptide corresponding to the amino-acid sequence of BC-box motif derived from SOCS7 protein was added to the medium at a concentration of 2 μM. Three days later, immunocytochemistry analysis, Western blot analysis, ubiquitination assay, and electrophysiological analysis with patch cramp were performed. Immunostaining revealed the expression of neurofilament H (NFH), choline acetyltransferase (ChAT), and tyrosine hydroxylase (TH). In addition, Western blot analysis showed an increase in the expression of NFH, ChAT, and TH, and the expression of ChAT was more distinct than TH. Immunoprecipitation with JAK2 showed an increase in the expression of ubiquitin. Electrophysiological analysis showed a large holding potential at the recorded cells through path electrodes. The BC-box motif peptide derived from SOCS7 promoted the cholinergic differentiation of ADMSCs. This novel method will contribute to research as well as regenerative medicine for cholinergic neuron diseases.

Based on molecular structures: Amyloid-β generation, clearance, toxicity and therapeutic strategies

Amyloid-β (Aβ) has long been considered as one of the most important pathogenic factors in Alzheimer’s disease (AD), but the specific pathogenic mechanism of Aβ is still not completely understood. In recent years, the development of structural biology technology has led to new understandings about Aβ molecular structures, Aβ generation and clearance from the brain and peripheral tissues, and its pathological toxicity. The purpose of the review is to discuss Aβ metabolism and toxicity, and the therapeutic strategy of AD based on the latest progress in molecular structures of Aβ. The Aβ structure at the atomic level has been analyzed, which provides a new and refined perspective to comprehend the role of Aβ in AD and to formulate therapeutic strategies of AD.

Aerobic Exercise Improves Type 2 Diabetes Mellitus-Related Cognitive Impairment by Inhibiting JAK2/STAT3 and Enhancing AMPK/SIRT1 Pathways in Mice

Type 2 diabetes mellitus (T2DM) is a prevalent risk factor for cognitive impairment. Aerobic exercise can improve T2DM-related cognitive impairment; however, the possible mechanisms remain elusive. Thus, we assessed db/m mice and leptin receptor-deficient (db/db) mice that did or did not perform aerobic exercise (8 m/min, 60 min/day, and 5 days/week for 12 weeks). In this study, cognitive function was significantly impaired in the T2DM mice; aerobic exercise improved cognitive impairment through activating the AMPK/SIRT1 signalling pathway and inhibiting the JAK2/STAT3 signalling pathway in T2DM mice. However, after the application of RO8191 (JAK2 activator) or Compound C (AMPK inhibitor), the positive improvement of the exercise was evidently suppressed. Taken together, our data indicated that long-term aerobic exercise improves type 2 diabetes mellitus-related cognitive impairment by inhibiting JAK2/STAT3 and enhancing AMPK/SIRT1 pathways in mice.

Association analysis of SOCS3, JAK2 and STAT3 gene polymorphisms and genetic susceptibility to type 2 diabetes mellitus in Chinese population

AIM

The association of polymorphisms in the three genes of SOCS3, JAK2 and STAT3 with genetic susceptibility to type 2 diabetes mellitus (T2DM) was explored, and its interaction with environmental factors such as hypertension and triglycerides was analyzed.

METHODS

The Hardy-Weinberg balance test was used to analyze the random balance of genes in the population. The analysis of the association of SNPs with T2DM was performed using Pearson's chi-square test. Haplotype frequency distribution, SNPs-SNPs interaction and environmental factors were analyzed by chi-square test and logistic regression.

RESULTS

The genotype distribution of SNPs rs2280148 of the SOCS3 gene was statistically significant. The allele frequency distribution of SNPs (rs4969168/rs2280148) was statistically different. After covariate correction, the SOCS3 gene locus (rs4969168) showed an association with T2DM in additive model, while the rs2280148 locus showed an association with T2DM in all three models. The locus (rs10974914/rs10815157) allele and genotype frequency distribution of JAK2 were statistically significant. After covariate correction, two SNPs in the gene showed association with T2DM in both additive and recessive models. The distribution of genotype frequencies of SNPs rs1053005 locus in gene STAT3 was statistically significant between the two groups. In recessive genetic models, rs1053005 locus polymorphisms was associated with T2DM. Haplotype S3 (G G)/S 4 (G T) of the SOCS3 gene as well as haplotype J2 (A G)/J 3 (G C) of the JAK2 gene were closely associated with T2DM. There was an interaction between SNPs rs4969168 and SNPs rs2280148 in the SOCS3 gene. There was an interaction between the SOCS3, JAK2 and STAT3 genes and hypertension/triglycerides.

CONCLUSION

The SOCS3 and JAK2 genes may be associated with T2DM in the Chinese population, in which SNPs carrying the A allele (rs4969168)/G allele (rs2280148)/C allele (rs10815157) have a reduced risk of T2DM. Haplotype S3 (G G)/S 4 (G T) of the SOCS3 gene and haplotype J2 (A G)/J 3 (G C) of the JAK2 gene may be influencing factor for T2DM. The interaction between SNPs rs4969168 and SNPs rs2280148 increases the risk of T2DM. Hypertension and triglycerides may interact with SNPs of T2DM susceptibility genes.

Insulin and Insulin Resistance in Alzheimer's Disease

Insulin plays a range of roles as an anabolic hormone in peripheral tissues. It regulates glucose metabolism, stimulates glucose transport into cells and suppresses hepatic glucose production. Insulin influences cell growth, differentiation and protein synthesis, and inhibits catabolic processes such as glycolysis, lipolysis and proteolysis. Insulin and insulin-like growth factor-1 receptors are expressed on all cell types in the central nervous system. Widespread distribution in the brain confirms that insulin signaling plays important and diverse roles in this organ. Insulin is known to regulate glucose metabolism, support cognition, enhance the outgrowth of neurons, modulate the release and uptake of catecholamine, and regulate the expression and localization of gamma-aminobutyric acid (GABA). Insulin is also able to freely cross the blood–brain barrier from the circulation. In addition, changes in insulin signaling, caused inter alia insulin resistance, may accelerate brain aging, and affect plasticity and possibly neurodegeneration. There are two significant insulin signal transduction pathways: the PBK/AKT pathway which is responsible for metabolic effects, and the MAPK pathway which influences cell growth, survival and gene expression. The aim of this study is to describe the role played by insulin in the CNS, in both healthy people and those with pathologies such as insulin resistance and Alzheimer’s disease.

Metformin a Potential Pharmacological Strategy in Late Onset Alzheimer's Disease Treatment

Alzheimer's disease (AD) is one of the most devastating brain disorders. Currently, there are no effective treatments to stop the disease progression and it is becoming a major public health concern. Several risk factors are involved in the progression of AD, modifying neuronal circuits and brain cognition, and eventually leading to neuronal death. Among them, obesity and type 2 diabetes mellitus (T2DM) have attracted increasing attention, since brain insulin resistance can contribute to neurodegeneration. Consequently, AD has been referred to "type 3 diabetes" and antidiabetic medications such as intranasal insulin, glitazones, metformin or liraglutide are being tested as possible alternatives. Metformin, a first line antihyperglycemic medication, is a 5'-adenosine monophosphate (AMP)-activated protein kinase (AMPK) activator hypothesized to act as a geroprotective agent. However, studies on its association with age-related cognitive decline have shown controversial results with positive and negative findings. In spite of this, metformin shows positive benefits such as anti-inflammatory effects, accelerated neurogenesis, strengthened memory, and prolonged life expectancy. Moreover, it has been recently demonstrated that metformin enhances synaptophysin, sirtuin-1, AMPK, and brain-derived neuronal factor (BDNF) immunoreactivity, which are essential markers of plasticity. The present review discusses the numerous studies which have explored (1) the neuropathological hallmarks of AD, (2) association of type 2 diabetes with AD, and (3) the potential therapeutic effects of metformin on AD and preclinical models.

Metabolic Syndrome: Is It Time to Add the Central Nervous System?

Metabolic syndrome (MS) is a set of cardio-metabolic risk factors that includes central obesity, hyperglycemia, hypertension, and dyslipidemias. The syndrome affects 25% of adults worldwide. The definition of MS has evolved over the last 80 years, with various classification systems and criteria, whose limitations and benefits are currently the subject of some controversy. Likewise, hypotheses regarding the etiology of MS add more confusion from clinical and epidemiological points of view. The leading suggestion for the pathophysiology of MS is insulin resistance (IR). IR can affect multiple tissues and organs, from the classic “triumvirate” (myocyte, adipocyte, and hepatocyte) to possible effects on organs considered more recently, such as the central nervous system (CNS). Mild cognitive impairment (MCI) and Alzheimer’s disease (AD) may be clinical expressions of CNS involvement. However, the association between MCI and MS is not understood. The bidirectional relationship that seems to exist between these factors raises the questions of which phenomenon occurs first and whether MCI can be a precursor of MS. This review explores shared pathophysiological mechanisms between MCI and MS and establishes a hypothesis of a possible MCI role in the development of IR and the appearance of MS.

Network Pharmacology-Based Investigation of the Therapeutic Mechanisms of Action of Danning Tablets in Nonalcoholic Fatty Liver Disease

Nonalcoholic fatty liver disease (NAFLD) is a rising global public health concern due to its prevalence. Danning Tablets (DNt), a composite prescription of Chinese herbal medicine, shows significant curative effects on NAFLD in clinical application. This study aimed to decipher the bioactive substances and potential mechanisms of action of DNt in the treatment of NAFLD, applying an integrated network pharmacology approach. First, the bioactive compounds of DNt were screened based on their pharmacokinetic properties, and the corresponding drug targets were predicted. Then, the NAFLD-related targets were collected. The overlapping targets between the putative targets of DNt and NAFLD-related targets were identified as the potential therapeutic targets of DNt against NAFLD. Subsequently, the networks were constructed and analyzed, and the key bioactive compounds and targets were screened out depending on their importance in the networks. Functional enrichment analysis was carried out to elucidate the potential mechanisms of DNt acting on NAFLD. Finally, a molecular docking simulation was implemented to assess the potential binding affinity between the key targets and the bioactive compounds. As a result, 43 bioactive compounds of DNt and 69 putative targets were identified. Based on the network analysis, we found seven key bioactive compounds (quercetin, ß-sitosterol, luteolin, kaempferol, supraene, curcumenolactone C, and stigmasterol) of DNt might treat NAFLD via intervening IL6, MAPK8, VEGFA, CASP3, ALB, APP, MYC, PPARG, and RELA. The functional enrichment analysis revealed that DNt might affect NAFLD by modulating the signaling pathways involved in lipid metabolism, inflammation, oxidation, insulin resistance (IR), atherosclerosis, and apoptosis. Furthermore, most key bioactive compounds might bind firmly with the key targets. This study predicted the multicomponent, multitarget, and multipathway mechanisms of DNt in the treatment of NAFLD from a holistic perspective. DNt could be a promising agent for NAFLD, but further experimental verifications are still needed.

An activity-dependent determinant of synapse elimination in the mammalian brain

To establish functional neural circuits in the brain, synaptic connections are refined by neural activity during development, where active connections are maintained and inactive ones are eliminated. However, the molecular signals that regulate synapse refinement remain to be elucidated. When we inactivate a subset of neurons in the mouse cingulate cortex, their callosal connections are eliminated through activity-dependent competition. Using this system, we identify JAK2 tyrosine kinase as a key regulator of inactive synapse elimination. We show that JAK2 is necessary and sufficient for elimination of inactive connections; JAK2 is activated at inactive synapses in response to signals from other active synapses; STAT1, a substrate of JAK2, mediates inactive synapse elimination; JAK2 signaling is critical for physiological refinement of synapses during normal development; and JAK2 regulates synapse refinement in multiple brain regions. We propose that JAK2 is an activity-dependent switch that serves as a determinant of inactive synapse elimination.

Functions of amyloid precursor protein in metabolic diseases

Amyloid precursor protein (APP) is a transmembrane precursor protein that is widely expressed in the central nervous system and peripheral tissues in the liver and pancreas, adipose tissue, and myotubes. APP can be cleaved by proteases in two different ways to produce a variety of short peptides, each with different physiological properties and functions. APP peptides generated by non-amyloidogenic processing can positively influence metabolism, while the peptides produced by amyloidogenic processing have the opposite effects. Here, we summarize the regulatory effects of APP and its cleavage peptides on metabolism in the central nervous system and peripheral tissues. In addition, abnormal expression and function of APP and APP-derived peptides are associated with metabolic diseases, such as type 2 diabetes, obesity, non-alcoholic fatty liver disease, and cardiovascular disease, and cancers. Pharmacological intervention of APP function or reduction of the production of peptides derived from amyloidogenic processing may be effective strategies for the prevention and treatment of Alzheimer's disease, and they may also provide new guidance for the treatment of metabolic diseases.

δ-Secretase-cleaved Tau stimulates Aβ production via upregulating STAT1-BACE1 signaling in Alzheimer's disease

δ-Secretase, an age-dependent asparagine protease, cleaves both amyloid precursor protein (APP) and Tau and is required for amyloid plaque and neurofibrillary tangle pathologies in Alzheimer's disease (AD). However, whether δ-secretase activation is sufficient to trigger AD pathogenesis remains unknown. Here we show that the fragments of δ-secretase-cleavage, APP (586-695) and Tau(1-368), additively drive AD pathogenesis and cognitive dysfunctions. Tau(1-368) strongly augments BACE1 expression and Aβ generation in the presence of APP. The Tau(1-368) fragment is more robust than full-length Tau in binding active STAT1, a BACE1 transcription factor, and promotes its nuclear translocation, upregulating BACE1 and Aβ production. Notably, Aβ-activated SGK1 or JAK2 kinase phosphorylates STAT1 and induces its association with Tau(1-368). Inhibition of these kinases diminishes stimulatory effect of Tau(1-368). Knockout of STAT1 abolishes AD pathologies induced by δ-secretase-generated APP and Tau fragments. Thus, we show that Tau may not only be a downstream effector of Aβ in the amyloid hypothesis, but also act as a driving force for Aβ, when cleaved by δ-secretase.

Targeting Insulin Resistance to Treat Cognitive Dysfunction

Dementia is a devastating disease associated with aging. Alzheimer's disease is the most common form of dementia, followed by vascular dementia. In addition to clinically diagnosed dementia, cognitive dysfunction has been reported in diabetic patients. Recent studies are now beginning to recognize type 2 diabetes mellitus, characterized by chronic hyperglycemia and insulin resistance, as a risk factor for Alzheimer's disease and other cognitive disorders. While studies on insulin action have remained traditionally in the domain of peripheral tissues, the detrimental effects of insulin resistance in the central nervous system on cognitive dysfunction are increasingly being reported by recent clinical and preclinical studies. The findings from these studies suggest that antidiabetic drugs have the potential to be used to treat dementia. In this review, we discuss the physiological functions of insulin in the brain, studies on the evaluation of cognitive function under conditions of insulin resistance, and reports on the beneficial actions of antidiabetic drugs in the brain. This review covers clinical studies as well as investigations in animal models and will further highlight the emerging link between insulin resistance and neurodegenerative disorders.

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.

Are Heat Shock Proteins an Important Link between Type 2 Diabetes and Alzheimer Disease?

Type 2 diabetes (T2D) and Alzheimer’s disease (AD) are growing in prevalence worldwide. The development of T2D increases the risk of AD disease, while AD patients can show glucose imbalance due to an increased insulin resistance. T2D and AD share similar pathological features and underlying mechanisms, including the deposition of amyloidogenic peptides in pancreatic islets (i.e., islet amyloid polypeptide; IAPP) and brain (β-Amyloid; Aβ). Both IAPP and Aβ can undergo misfolding and aggregation and accumulate in the extracellular space of their respective tissues of origin. As a main response to protein misfolding, there is evidence of the role of heat shock proteins (HSPs) in moderating T2D and AD. HSPs play a pivotal role in cell homeostasis by providing cytoprotection during acute and chronic metabolic stresses. In T2D and AD, intracellular HSP (iHSP) levels are reduced, potentially due to the ability of the cell to export HSPs to the extracellular space (eHSP). The increase in eHSPs can contribute to oxidative damage and is associated with various pro-inflammatory pathways in T2D and AD. Here, we review the role of HSP in moderating T2D and AD, as well as propose that these chaperone proteins are an important link in the relationship between T2D and AD.

BC-Box Motif in SOCS6 Induces Differentiation of Epidermal Stem Cells into GABAnergic Neurons

The BC-box motif in suppressor of cytokine signaling 6 (SOCS6) promotes the neuronal differentiation of somatic stem cells, including epidermal stem cells. SOCS6 protein belongs to the group of SOCS proteins and inhibits cytokine signaling. Here we showed that epidermal stem cells were induced to differentiate into GABAnergic neurons by the intracellular delivery of a peptide composed of the amino-acid sequences encoded by the BC-box motif in SOCS6 protein. The BC-box motif (SLQYLCRFVI) in SOCS6 corresponded to the binding site of elongin BC. GABAnergic differentiation mediated by the BC-box motif in SOCS6 protein was caused by ubiquitination of JAK2 and inhibition of the JAK2-STAT3 pathway. Furthermore, GABAnergic neuron-like cells generated from epidermal stem cells were transplanted into the brain of a rodent ischemic model. Then, we demonstrated that these transplanted cells were GAD positive and that the cognitive function of the ischemic model rodents with the transplanted cells was improved. This study could contribute to not only elucidating the mechanism of GABAnergic neuronal differentiation but also to neuronal regenerative medicine utilizing GABAnergic neurons.

Association of plasma β-amyloid 40 and 42 concentration with type 2 diabetes among Chinese adults

AIMS/HYPOTHESIS

There is evidence for a bidirectional association between type 2 diabetes and Alzheimer's disease. Plasma β-amyloid (Aβ) is a potential biomarker for Alzheimer's disease. We aimed to investigate the association of plasma Aβ40 and Aβ42 with risk of type 2 diabetes.

METHODS

We performed a case-control study and a nested case-control study within a prospective cohort study. In the case-control study, we included 1063 newly diagnosed individuals with type 2 diabetes and 1063 control participants matched by age (±3 years) and sex. In the nested case-control study, we included 121 individuals with incident type 2 diabetes and 242 matched control individuals. Plasma Aβ40 and Aβ42 concentrations were simultaneously measured with electrochemiluminescence immunoassay. Conditional logistic regression was used to evaluate the association of plasma Aβ40 and Aβ42 concentrations with the likelihood of type 2 diabetes.

RESULTS

In the case-control study, the multivariable-adjusted ORs for type 2 diabetes, comparing the highest with the lowest quartile of plasma Aβ concentrations, were 1.97 (95% CI 1.46, 2.66) for plasma Aβ40 and 2.01 (95% CI 1.50, 2.69) for plasma Aβ42. Each 30 ng/l increment of plasma Aβ40 was associated with 28% (95% CI 15%, 43%) higher odds of type 2 diabetes, and each 5 ng/l increment of plasma Aβ42 was associated with 37% (95% CI 21%, 55%) higher odds of type 2 diabetes. Individuals in the highest tertile for both plasma Aβ40 and Aβ42 concentrations had 2.96-fold greater odds of type 2 diabetes compared with those in the lowest tertile for both plasma Aβ40 and Aβ42 concentrations. In the nested case-control study, the multivariable-adjusted ORs for type 2 diabetes for the highest vs the lowest quartile were 3.79 (95% CI 1.81, 7.94) for plasma Aβ40 and 2.88 (95% CI 1.44, 5.75) for plasma Aβ42. The multivariable-adjusted ORs for type 2 diabetes associated with each 30 ng/l increment in plasma Aβ40 and each 5 ng/l increment in plasma Aβ42 were 1.44 (95% CI 1.18, 1.74) and 1.47 (95% CI 1.15, 1.88), respectively.

CONCLUSIONS/INTERPRETATION

Our findings suggest positive associations of plasma Aβ40 and Aβ42 concentration with risk of type 2 diabetes. Further studies are warranted to elucidate the underlying mechanisms and explore the potential roles of plasma Aβ in linking type 2 diabetes and Alzheimer's disease.

Bis(ethylmaltolato)oxidovanadium(iv) inhibited the pathogenesis of Alzheimer's disease in triple transgenic model mice

Vanadium compounds have been reported to mimic the anti-diabetes effects of insulin on rodent models, but their effects on Alzheimer's disease (AD) have rarely been explored. In this paper, 9-month-old triple transgenic AD model mice (3×Tg-AD) received bis(ethylmaltolato)oxidovanadium(iv) (BEOV) at doses of 0.2 mmol L^-1 (68.4 μg mL^-1) and 1.0 mmol L^-1 (342 μg mL^-1) for 3 months. BEOV at both doses was found to improve contextual memory and spatial learning in AD mice. It also improved glucose metabolism and protected neuronal synapses in the AD brain, as evidenced respectively by ¹⁸F-labeled fluoro-deoxyglucose positron emission tomography (¹⁸F-FDG-PET) scanning and by transmission electron microscopy. Inhibitory effects of BEOV on β-amyloid (Aβ) plaques and neuronal impairment in the cortex and hippocampus of fluorescent AD mice were visualized three-dimensionally by applying optical clearing technology to brain slices before confocal laser scanning microscopy. Western blot analysis semi-quantitatively revealed the altered levels of Aβ₄₂ in the brains of wildtype, AD, and AD treated with 0.2 and 1.0 mmol L^-1 BEOV mice (70.3%, 100%, 83.2% and 56.8% in the hippocampus; 82.4%, 100%, 66.9% and 42% in the cortex, respectively). The mechanism study showed that BEOV increased the expression of peroxisome proliferator-activated receptor γ (PPARγ) (140%, 100%, 142% and 160% in the hippocampus; 167%, 100%, 124% and 133% in the cortex) to inactivate the JAK2/STAT3/SOCS-1 pathway and to block the amyloidogenesis cascade, thus attenuating Aβ-induced insulin resistance in AD models. BEOV also reduced protein tyrosine phosphatase 1B (PTP1B) expression (74.8%, 100%, 76.5% and 53.8% in the hippocampus; 71.8%, 100%, 94.2% and 81.8% in cortex) to promote insulin sensitivity and to stimulate the PI3K/Akt/GSK3β pathway, subsequently reducing tau hyperphosphorylation (phosphorylated tau396 levels were 51.1%, 100%, 56.1% and 50.2% in the hippocampus; 22.2%, 100%, 36.1%, and 24% in the cortex). Our results suggested that BEOV reduced the pathological hallmarks of AD by targeting the pathways of PPARγ and PTP1B in 3×Tg AD mice.

Suppressors of cytokine signalling (SOCS)-1 inhibits neuroinflammation by regulating ROS and TLR4 in BV2 cells

OBJECTIVE

The suppressors of cytokine signaling (SOCS) proteins are physiological suppressors of cytokine signaling which have been identified as a negative feedback loop to weaken cytokine signaling. However, the underlying molecular mechanisms is unknown. This study was to investigate the role of SOCS1 in the oxygen-glucose deprivation and reoxygenation (OGDR) or LPS-induced inflammation in microglia cell line BV-2 cells.

MATERIALS AND METHODS

BV-2 microglial cells were used to construct inflammation model. A SOCS1 over-expression plasmid was constructed, and the SOCS1-deficient cells were generated by utilizing the CRISPR/CAS9 system. BV-2 microglial cells were pretreated with over-expression plasmid or SOCS1 CRISPR plasmid before OGDR and LPS stimulation. The effect of SOCS1 on proinflammatory cytokines, toll-like receptor 4 (TLR4), and reactive oxygen species (ROS) were evaluated.

RESULTS

We found that SOCS1 increased in OGDR or LPS-treated BV-2 microglial cells in vitro. SOCS1 over-expression significantly reduced the production of proinflammatory cytokines including tumor necrosis factor α (TNF-α), interleukin 1β (IL-1β), and IL-6, and CRISPR/CAS9-mediated SOCS1 knockout reversed this effect. Also we determined that SOCS1 over-expression reduced the level of reactive oxygen species (ROS) while the absence of SOCS1 increased the production of ROS after OGDR or LPS-stimulated inflammation. Furthermore, we found that OGDR and LPS induced the expression of toll-like receptor 4 (TLR4) in BV2 cells. Nevertheless, SOCS1 over-expression attenuated the expression of TLR4, while knockdown of SOCS1 upregulated TLR4.

CONCLUSIONS

Our study indicated that SOCS1 played a protective role under inflammatory conditions in OGDR or LPS treated BV-2 cells through regulating ROS and TLR4. These data demonstrated that SOCS1 served as a potential therapeutic target to alleviate inflammation after ischemic stroke.

A high-sucrose diet aggravates Alzheimer's disease pathology, attenuates hypothalamic leptin signaling, and impairs food-anticipatory activity in APPswe/PS1dE9 mice

High-fat and high-sugar diets contribute to the prevalence of type 2 diabetes and Alzheimer's disease (AD). Although the impact of high-fat diets on AD pathogenesis has been established, the effect of high-sucrose diets (HSDs) on AD pathogenesis remains unclear. This study sought to determine the impact of HSDs on AD-related pathologies. Male APPswe/PS1dE9 (APP/PS1) transgenic and wild-type mice were provided with HSD and their cognitive and hypothalamus-related noncognitive parameters, including feeding behaviors and glycemic regulation, were compared. HSD-fed APP/PS1 mice showed increased neuroinflammation, as well as increased cortical and serum levels of amyloid-β. HSD-fed APP/PS1 mice showed aggravated obesity, hyperinsulinemia, insulin resistance, and leptin resistance, but there was no induction of hyperphagia or hyperleptinemia. Leptin-induced phosphorylation of signal transducer and activator of transcription 3 in the dorsomedial and ventromedial hypothalamus was reduced in HSD-fed APP/PS1 mice, which might be associated with attenuated food-anticipatory activity, glycemic dysregulation, and AD-related noncognitive symptoms. Our study demonstrates that HSD aggravates metabolic stresses, increases AD-related pathologies, and attenuates hypothalamic leptin signaling in APP/PS1 mice.

The Involvement of Peripheral and Brain Insulin Resistance in Late Onset Alzheimer's Dementia

Nowadays, Alzheimer's disease (AD) is a severe sociological and clinical problem. Since it was first described, there has been a constant increase in its incidence and, for now, there are no effective treatments since current approved medications have only shown short-term symptomatic benefits. Therefore, it is imperative to increase efforts in the search for molecules and non-pharmacological strategies that are capable of slowing or stopping the progress of the disease and, ideally, to reverse it. The amyloid cascade hypothesis based on the fundamental role of amyloid has been the central hypothesis in the last 30 years. However, since amyloid-directed treatments have shown no relevant beneficial results other theories have been postulated to explain the origin of the pathology. The brain is a highly metabolically active energy-consuming tissue in the human body. It has an almost complete dependence on the metabolism of glucose and uses most of its energy for synaptic transmission. Thus, alterations on the utilization or availability of glucose may be cause for the appearance of neurodegenerative pathologies like AD. In this review article, the hypothesis known as Type 3 Diabetes (T3D) will be evaluated by summarizing some of the data that has been reported in recent years. According to published research, the adherence over time to low saturated fatty acids diets in the context of the Mediterranean diet would reduce the inflammatory levels in brain, with a decrease in the pro-inflammatory glial activation and mitochondrial oxidative stress. In this situation, the insulin receptor pathway would be able to fine tune the mitochondrial biogenesis in neuronal cells, regulation the adenosine triphosphate/adenosine diphosphate intracellular balance, and becoming a key factor involved in the preservation of the synaptic connexions and neuronal plasticity. In addition, new targets and strategies for the treatment of AD will be considered in this review for their potential as new pharmacological or non-pharmacological approaches.

A metabolic perspective of late onset Alzheimer's disease

After decades of research, the molecular neuropathology of Alzheimer's disease (AD) is still one of the hot topics in biomedical sciences. Some studies suggest that soluble amyloid β (Aβ) oligomers act as causative agents in the development of AD and could be initiators of its complex neurodegenerative cascade. On the other hand, there is also evidence pointing to Aβ oligomers as mere aggravators, with an arguable role in the origin of the disease. In this line of research, the relative contribution of soluble Aβ oligomers to neuronal damage associated with metabolic disorders such as Type 2 Diabetes Mellitus (T2DM) and obesity is being actively investigated. Some authors have proposed the endoplasmic reticulum (ER) stress and the induction of the unfolded protein response (UPR) as important mechanisms leading to an increase in Aβ production and the activation of neuroinflammatory processes. Following this line of thought, these mechanisms could also cause cognitive impairment. The present review summarizes the current understanding on the neuropathological role of Aβ associated with metabolic alterations induced by an obesogenic high fat diet (HFD) intake. It is believed that the combination of these two elements has a synergic effect, leading to the impairement of ER and mitochondrial functions, glial reactivity status alteration and inhibition of insulin receptor (IR) signalling. All these metabolic alterations would favour neuronal malfunction and, eventually, neuronal death by apoptosis, hence causing cognitive impairment and laying the foundations for late-onset AD (LOAD). Moreover, since drugs enhancing the activation of cerebral insulin pathway can constitute a suitable strategy for the prevention of AD, we also discuss the scope of therapeutic approaches such as intranasal administration of insulin in clinical trials with AD patients.

The BACE1 product sAPPβ induces ER stress and inflammation and impairs insulin signaling

OBJECTIVE

β-secretase/β-site amyloid precursor protein (APP)-cleaving enzyme 1 (BACE1) is a key enzyme involved in Alzheimer's disease that has recently been implicated in insulin-independent glucose uptake in myotubes. However, it is presently unknown whether BACE1 and the product of its activity, soluble APPβ (sAPPβ), contribute to lipid-induced inflammation and insulin resistance in skeletal muscle cells.

MATERIALS/METHODS

Studies were conducted in mouse C2C12 myotubes, skeletal muscle from Bace1^-/-mice and mice treated with sAPPβ and adipose tissue and plasma from obese and type 2 diabetic patients.

RESULTS

We show that BACE1 inhibition or knockdown attenuates palmitate-induced endoplasmic reticulum (ER) stress, inflammation, and insulin resistance and prevents the reduction in Peroxisome Proliferator-Activated Receptor γ Co-activator 1α (PGC-1α) and fatty acid oxidation caused by palmitate in myotubes. The effects of palmitate on ER stress, inflammation, insulin resistance, PGC-1α down-regulation, and fatty acid oxidation were mimicked by soluble APPβ in vitro. BACE1 expression was increased in subcutaneous adipose tissue of obese and type 2 diabetic patients and this was accompanied by a decrease in PGC-1α mRNA levels and by an increase in sAPPβ plasma levels of obese type 2 diabetic patients compared to obese non-diabetic subjects. Acute sAPPβ administration to mice reduced PGC-1α levels and increased inflammation in skeletal muscle and decreased insulin sensitivity.

CONCLUSIONS

Collectively, these findings indicate that the BACE1 product sAPPβ is a key determinant in ER stress, inflammation and insulin resistance in skeletal muscle and gluconeogenesis in liver.

The Therapeutic Potential of Metformin in Neurodegenerative Diseases

The search for treatments for neurodegenerative diseases is a major concern in light of today's aging population and an increasing burden on individuals, families, and society. Although great advances have been made in the last decades to understand the underlying genetic and biological cause of these diseases, only some symptomatic treatments are available. Metformin has long since been used to treat Type 2 Diabetes and has been shown to be beneficial in several other conditions. Metformin is well-tested in vitro and in vivo and an approved compound that targets diverse pathways including mitochondrial energy production and insulin signaling. There is growing evidence for the benefits of metformin to counteract age-related diseases such as cancer, cardiovascular disease, and neurodegenerative diseases. We will discuss evidence showing that certain neurodegenerative diseases and diabetes are explicitly linked and that metformin along with other diabetes drugs can reduce neurological symptoms in some patients and reduce disease phenotypes in animal and cell models. An interesting therapeutic factor might be how metformin is able to balance survival and death signaling in cells through pathways that are commonly associated with neurodegenerative diseases. In healthy neurons, these overarching signals keep energy metabolism, oxidative stress, and proteostasis in check, avoiding the dysfunction and neuronal death that defines neurodegenerative disease. We will discuss the biological mechanisms involved and the relevance of neuronal vulnerability and potential difficulties for future trials and development of therapies.

The Therapeutic Potential of Metformin in Neurodegenerative Diseases

The search for treatments for neurodegenerative diseases is a major concern in light of today's aging population and an increasing burden on individuals, families, and society. Although great advances have been made in the last decades to understand the underlying genetic and biological cause of these diseases, only some symptomatic treatments are available. Metformin has long since been used to treat Type 2 Diabetes and has been shown to be beneficial in several other conditions. Metformin is well-tested in vitro and in vivo and an approved compound that targets diverse pathways including mitochondrial energy production and insulin signaling. There is growing evidence for the benefits of metformin to counteract age-related diseases such as cancer, cardiovascular disease, and neurodegenerative diseases. We will discuss evidence showing that certain neurodegenerative diseases and diabetes are explicitly linked and that metformin along with other diabetes drugs can reduce neurological symptoms in some patients and reduce disease phenotypes in animal and cell models. An interesting therapeutic factor might be how metformin is able to balance survival and death signaling in cells through pathways that are commonly associated with neurodegenerative diseases. In healthy neurons, these overarching signals keep energy metabolism, oxidative stress, and proteostasis in check, avoiding the dysfunction and neuronal death that defines neurodegenerative disease. We will discuss the biological mechanisms involved and the relevance of neuronal vulnerability and potential difficulties for future trials and development of therapies.

APP deficiency results in resistance to obesity but impairs glucose tolerance upon high fat feeding

The amyloid precursor protein (APP) generates a number of peptides when processed through different cleavage mechanisms, including the amyloid beta peptide that is implicated in the development of Alzheimer's disease. It is well established that APP via its cleaved peptides regulates aspects of neuronal metabolism. Emerging evidence suggests that amyloidogenic processing of APP can lead to altered systemic metabolism, similar to that observed in metabolic disease states. In the present study, we investigated the effect of APP deficiency on obesity-induced alterations in systemic metabolism. Compared with WT littermates, APP-deficient mice were resistant to diet-induced obesity, which was linked to higher energy expenditure and lipid oxidation throughout the dark phase and was associated with increased spontaneous physical activity. Consistent with this lean phenotype, APP-deficient mice fed a high-fat diet (HFD) had normal insulin tolerance. However, despite normal insulin action, these mice were glucose intolerant, similar to WT mice fed a HFD. This was associated with reduced plasma insulin in the early phase of the glucose tolerance test. Analysis of the pancreas showed that APP was required to maintain normal islet and β-cell mass under high fat feeding conditions. These studies show that, in addition to regulating aspects of neuronal metabolism, APP is an important regulator of whole body energy expenditure and glucose homeostasis under high fat feeding conditions.

The Interleukin-20 Cytokine Family in Liver Disease

The three main causes of inflammation and chronic injury in the liver are viral hepatitis, alcohol consumption, and non-alcoholic steatohepatitis, all of which can lead to liver fibrosis, cirrhosis, and hepatocellular carcinoma, which in turn may prompt the need for liver transplant. The interleukin (IL)-20 is a subfamily part of the IL-10 family of cytokines that helps the liver respond to damage and disease, they participate in the control of tissue homeostasis, and in the immunological responses developed in this organ. The best-studied member of the family in inflammatory balance of the liver is the IL-22 cytokine, which on the one hand may have a protective role in fibrosis progression but on the other may induce liver tissue susceptibility in hepatocellular carcinoma development. Other members of the family might also carry out this dual function, as some of them share IL receptor subunits and signal through common intracellular pathways. Investigators are starting to consider the potential for targeting IL-20 subfamily members in liver disease. The recently explored role of miRNA in the transcriptional regulation of IL-22 and IL-24 opens the door to promising new approaches for controlling the local immune response and limiting organ injury. The IL-20RA cytokine receptor has also been classified as being under miRNA control in non-alcoholic steatohepatitis. Moreover, researchers have proposed combining anti-inflammatory drugs with IL-22 as a hepatoprotective IL for alcoholic liver disease (ALD) treatment, and clinical trials of ILs for managing severe alcoholic-derived liver degeneration are ongoing. In this review, we focus on exploring the role of the IL-20 subfamily of cytokines in viral hepatitis, ALD, non-alcoholic steatohepatitis, and hepatocellular carcinoma, as well as delineating the main strategies explored so far in terms of therapeutic possibilities of the IL-20 subfamily of cytokines in liver disease.

Insulin differentially affects the distribution kinetics of amyloid beta 40 and 42 in plasma and brain

Impaired brain clearance of amyloid-beta peptides (Aβ) 40 and 42 across the blood-brain barrier (BBB) is believed to be one of the pathways responsible for Alzheimer's disease (AD) pathogenesis. Hyperinsulinemia prevalent in type II diabetes was shown to damage cerebral vasculature and increase Aβ accumulation in AD brain. However, there is no clarity on how aberrations in peripheral insulin levels affect Aβ accumulation in the brain. This study describes, for the first time, an intricate relation between plasma insulin and Aβ transport at the BBB. Upon peripheral insulin administration in wild-type mice: the plasma clearance of Aβ40 increased, but Aβ42 clearance reduced; the plasma-to-brain influx of Aβ40 increased, and that of Aβ42 reduced; and the clearance of intracerebrally injected Aβ40 decreased, whereas Aβ42 clearance increased. In hCMEC/D3 monolayers (in vitro BBB model) exposed to insulin, the luminal uptake and luminal-to-abluminal permeability of Aβ40 increased and that of Aβ42 reduced; the abluminal-to-luminal permeability of Aβ40 decreased, whereas Aβ42 permeability increased. Moreover, Aβ cellular trafficking machinery was altered. In summary, Aβ40 and Aβ42 demonstrated distinct distribution kinetics in plasma and brain compartments, and insulin differentially modulated their distribution. Cerebrovascular disease and metabolic disorders may disrupt this intricate homeostasis and aggravate AD pathology.

The Link between Type 2 Diabetes and Neurodegeneration: Roles for Amyloid-β, Amylin, and Tau Proteins

A wealth of evidence indicates a strong link between type 2 diabetes (T2D) and neurodegenerative diseases such as Alzheimer's disease (AD). Although the precise mechanism remains unclear, T2D can exacerbate neurodegenerative processes. Brain atrophy, reduced cerebral glucose metabolism, and central nervous system insulin resistance are features of both AD and T2D. The T2D phenotype (glucose dyshomeostasis, insulin resistance, impaired insulin signaling) also promotes AD pathology, namely accumulation of amyloid-β (Aβ) and hyperphosphorylated tau and can induce other aspects of neuronal degeneration including inflammatory and oxidative processes. Aβ and hyperphosphorylated tau may also have roles in pancreatic β-cell dysfunction and in reducing insulin sensitivity and glucose uptake by peripheral tissues such as liver, skeletal muscle, and adipose tissue. This suggests a role for these AD-related proteins in promoting T2D. The accumulation of the islet amyloid polypeptide (IAPP, or amylin) within islet β-cells is a major pathological feature of the pancreas in patients with chronic T2D. Co-secreted with insulin, amylin accumulates over time and contributes to β-cell toxicity, ultimately leading to reduced insulin secretion and onset of overt (insulin dependent) diabetes. Recent evidence also suggests that this protein accumulates in the brain of AD patients and may interact with Aβ to exacerbate the neurodegenerative process. In this review, we highlight evidence indicating T2D in promoting Aβ and tau mediated neurodegeneration and the potential contributions of Aβ and tau in promoting a diabetic phenotype that could further exacerbate neurodegeneration. We also discuss underlying mechanisms by which amylin can contribute to the neurodegenerative processes.

Peripheral and Central Effects of Memantine in a Mixed Preclinical Mice Model of Obesity and Familial Alzheimer's Disease

There is growing evidence that obesity associated with type 2 diabetes mellitus (T2DM) and aging are risk factors for the development of Alzheimer's disease (AD). However, the molecular mechanisms through which obesity interacts with β-amyloid (Aβ) to promote cognitive decline remains poorly understood. Memantine (MEM), a N-methyl-D-aspartate receptor antagonist, is currently used for the treatment of AD. Nonetheless, few studies have reported its effects on genetic preclinical models of this neurodegenerative disease exacerbated with high-fat diet (HFD)-induced obesity. Therefore, the present research aims to elucidate the effects of MEM on familial AD HFD-induced insulin resistance and learning and memory impairment. Furthermore, it aspires to determine the possible underlying mechanisms that connect AD to T2DM. Wild type and APPswe/PS1dE9 mice were used in this study. The animals were fed with either chow or HFD until 6 months of age, and they were treated with MEM-supplemented water (30 mg/kg) during the last 12 weeks. Our study demonstrates that MEM improves the metabolic consequences produced by HFD in this model of familial AD. Behavioural assessments confirmed that the treatment also improves animals learning abilities and decreases memory loss. Moreover, MEM treatment improves brain insulin signalling upregulating AKT, as well as cyclic adenosine monophosphate response element binding (CREB) expression, and modulates the amyloidogenic pathway, which, in turn, reduced the accumulation of Aβ. Moreover, this drug increases the activation of molecules involved with insulin signalling in the liver, such as insulin receptor substrate 2 (IRS2), which is a key protein regulating hepatic resistance to insulin. These results provide new insight into the role of MEM not only in the occurrence of AD treatment, but also in its potential application on peripheral metabolic disorders where Aβ plays a key role, as is the case of T2DM.

The Implication of the Brain Insulin Receptor in Late Onset Alzheimer's Disease Dementia

Alzheimer's disease (AD) is progressive neurodegenerative disorder characterized by brain accumulation of the amyloid β peptide (Aβ), which form senile plaques, neurofibrillary tangles (NFT) and, eventually, neurodegeneration and cognitive impairment. Interestingly, epidemiological studies have described a relationship between type 2 diabetes mellitus (T2DM) and this pathology, being one of the risk factors for the development of AD pathogenesis. Information as it is, it would point out that, impairment in insulin signalling and glucose metabolism, in central as well as peripheral systems, would be one of the reasons for the cognitive decline. Brain insulin resistance, also known as Type 3 diabetes, leads to the increase of Aβ production and TAU phosphorylation, mitochondrial dysfunction, oxidative stress, protein misfolding, and cognitive impairment, which are all hallmarks of AD. Moreover, given the complexity of interlocking mechanisms found in late onset AD (LOAD) pathogenesis, more data is being obtained. Recent evidence showed that Aβ42 generated in the brain would impact negatively on the hypothalamus, accelerating the "peripheral" symptomatology of AD. In this situation, Aβ42 production would induce hypothalamic dysfunction that would favour peripheral hyperglycaemia due to down regulation of the liver insulin receptor. The objective of this review is to discuss the existing evidence supporting the concept that brain insulin resistance and altered glucose metabolism play an important role in pathogenesis of LOAD. Furthermore, we discuss AD treatment approaches targeting insulin signalling using anti-diabetic drugs and mTOR inhibitors.

Memantine for the Treatment of Dementia: A Review on its Current and Future Applications

Alzheimer's disease (AD) is a neurodegenerative disorder characterized by the presence in the brain of extracellular amyloid-β protein (Aβ) and intracellular neurofibrillary tangles composed of hyperphosphorylated tau protein. The N-Methyl-D-aspartate receptors (NMDAR), ionotropic glutamate receptor, are essential for processes like learning and memory. An excessive activation of NMDARs has been associated with neuronal loss. The discovery of extrasynaptic NMDARs provided a rational and physiological explanation between physiological and excitotoxic actions of glutamate. Memantine (MEM), an antagonist of extrasynaptic NMDAR, is currently used for the treatment of AD jointly with acetylcholinesterase inhibitors. It has been demonstrated that MEM preferentially prevents the excessive continuous extrasynaptic NMDAR disease activation and therefore prevents neuronal cell death induced by excitotoxicity without disrupting physiological synaptic activity. The problem is that MEM has shown no clear positive effects in clinical applications while, in preclinical stages, had very promising results. The data in preclinical studies suggests that MEM has a positive impact on improving AD brain neuropathology, as well as in preventing Aβ production, aggregation, or downstream neurotoxic consequences, in part through the blockade of extrasynaptic NMDAR. Thus, the focus of this review is primarily to discuss the efficacy of MEM in preclinical models of AD, consider possible combinations of this drug with others, and then evaluate possible reasons for its lack of efficacy in clinical trials. Finally, applications in other pathologies are also considered.

Impaired peripheral glucose homeostasis and Alzheimer's disease

Alzheimer's disease (AD) is the most common type of dementia. Recent studies suggest that metabolic disturbances, particularly type 2 diabetes (T2D) increase the risk of cognitive decline and AD. AD is also a risk factor for T2D, and a growing body of evidence indicates that these diseases are connected both at clinical and molecular levels. In T2D, peripheral insulin resistance, hyperglycemia and eventually insulin deficiency develops, leading to an overall decline in tissue health. More recently, brain insulin resistance has been shown to be a key feature of AD that is linked to neuronal dysfunction and cognitive impairment. Furthermore, both AD and T2D are amyloidogenic diseases, with abnormal aggregation of amyloid-β peptide (Aβ) and islet amyloid polypeptide (IAPP) respectively contributing to cellular death and disease pathogenesis. Emerging data suggests that Aβ may have peripheral effects including its co-deposition in the pancreas. In this review, we discuss how peripheral effects of Aβ and metabolic disturbances may impact AD pathogenesis. This article is part of the Special Issue entitled 'Metabolic Impairment as Risk Factors for Neurodegenerative Disorders.'

Insulin Resistance and Alzheimer's Disease: Bioenergetic Linkages

Metabolic dysfunction is a well-established feature of Alzheimer's disease (AD), evidenced by brain glucose hypometabolism that can be observed potentially decades prior to the development of AD symptoms. Furthermore, there is mounting support for an association between metabolic disease and the development of AD and related dementias. Individuals with insulin resistance, type 2 diabetes mellitus (T2D), hyperlipidemia, obesity, or other metabolic disease may have increased risk for the development of AD and similar conditions, such as vascular dementia. This association may in part be due to the systemic mitochondrial dysfunction that is common to these pathologies. Accumulating evidence suggests that mitochondrial dysfunction is a significant feature of AD and may play a fundamental role in its pathogenesis. In fact, aging itself presents a unique challenge due to inherent mitochondrial dysfunction and prevalence of chronic metabolic disease. Despite the progress made in understanding the pathogenesis of AD and in the development of potential therapies, at present we remain without a disease-modifying treatment. In this review, we will discuss insulin resistance as a contributing factor to the pathogenesis of AD, as well as the metabolic and bioenergetic disruptions linking insulin resistance and AD. We will also focus on potential neuroimaging tools for the study of the metabolic dysfunction commonly seen in AD with hopes of developing therapeutic and preventative targets.

Central insulin dysregulation and energy dyshomeostasis in two mouse models of Alzheimer's disease

Alzheimer's disease (AD) is the most prevalent neurodegenerative disorder worldwide. While the causes of AD are not known, several risk factors have been identified. Among these, type two diabetes (T2D), a chronic metabolic disease, is one of the most prevalent risk factors for AD. Insulin resistance, which is associated with T2D, is defined as diminished or absent insulin signaling and is reflected by peripheral blood hyperglycemia and impaired glucose clearance. In this study, we used complementary approaches to probe for peripheral insulin resistance, central nervous system (CNS) insulin sensitivity and energy homeostasis in Tg2576 and 3xTg-AD mice, two widely used animal models of AD. We report that CNS insulin signaling abnormalities are evident months before peripheral insulin resistance. In addition, we find that brain energy metabolism is differentially altered in both mouse models, with 3xTg-AD mice showing more extensive changes. Collectively, our data suggest that early AD may reflect engagement of different signaling networks that influence CNS metabolism, which in turn may alter peripheral insulin signaling.

A Toxic Conformer of Aβ42 with a Turn at 22-23 is a Novel Therapeutic Target for Alzheimer's Disease

Immunotherapy targeting Aβ42 is drawing attention as a possible therapeutic approach for Alzheimer’s disease (AD). Considering the significance of reported oligomerized Aβ42 species, selective targeting of the oligomer will increase the therapeutic efficacy. However, what kinds of oligomers are suitable targets for immunotherapy remains unclear. We previously identified a toxic conformer of Aβ42, which has a turn structure at 22–23 (“toxic turn”), among Aβ42 conformations. This toxic conformer of Aβ42 has been reported to show rapid oligomerization and to exhibit strong neurotoxicity and synaptotoxicity. We recently developed a monoclonal antibody against the toxic conformer (24B3), which demonstrated the increase of the toxic conformer in the cerebrospinal fluid of AD patients, indicating its accumulation in AD patients’ brains. In this study, we evaluated the therapeutic efficacy of 24B3 targeting the toxic conformer in AD model mice. The intraperitoneal administration of 24B3 for 3 months improved cognitive impairment and reduced the toxic conformer levels. Notably, this treatment did not reduce the number of senile plaques. Furthermore, the single intravenous administration of 24B3 suppressed the memory deficit in AD mice. These results suggest that the toxic conformer of Aβ42 with a turn at 22–23 represents one of the promising therapeutic targets.

Type 2 diabetes mellitus in the pathophysiology of Alzheimer's disease

Both Alzheimer's disease (AD) and type 2 diabetes mellitus (DM) are two common forms of disease worldwide and many studies indicate that people with diabetes, especially DM, are at higher risk of developing AD. AD is characterized by progressive cognitive decline and accumulation of β-amyloid (Aβ) forming senile plaques. DM is a metabolic disorder characterized by hyperglycemia in the context of insulin resistance and relative lack of insulin. Both diseases also share common characteristics such as loss of cognitive function and inflammation. Inflammation resulting from Aβ further induces production of Aβ_1-42 peptides. Inflammation due to overnutrition induces insulin resistance and consequently DM. Memory deficit and a decrease in GLUT4 and hippocampal insulin signaling have been observed in animal models of insulin resistance. The objective of this review was to show the shared characteristics of AD and DM.

Ameliorating effect of anti-Alzheimer's drugs on the bidirectional association between type 2 diabetes mellitus and Alzheimer's disease

Mild to severe forms of nervous system damage were exhibited by approximately 60-70% of diabetics. It is important to understand the association between type 2 diabetes mellitus and Alzheimer's disease. The aim of the present work is to understand the bidirectional association between type 2 diabetes and Alzheimer's disease pathogenesis, that was monitored by glycaemic status, lipid profile, amyloid beta 40 and 42 (Aβ40 and Aβ42), C-reactive protein, total creatine kinase, total lactate dehydrogenase, D-dimer and magnesium measurements, to assess the association between theses biochemical markers and each other, to estimate the possibility of utilizing the amyloid beta as biochemical marker of T2D in Alzheimer's patients, and to evaluate the effect of piracetam and memantine drugs on diabetes mellitus. This study involved 120 subjects divided into 20 healthy control (group I), 20 diabetic patients (group II), 20 Alzheimer's patients (group III), 20 diabetic Alzheimer's patients with symptomatic treatment (group IV), 20 diabetic Alzheimer's patients treated with memantine (group V), and 20 diabetic Alzheimer's patients treated with piracetam (group VI). The demographic characteristics, diabetic index, and lipid profile were monitored. Plasma amyloid beta 40 and amyloid beta 42, C-reactive protein, total creatine kinase, total lactate dehydrogenase, D-dimer, and magnesium were assayed. The levels of amyloid beta 40 and amyloid beta 42 were significantly elevated in diabetic Alzheimer's patients with symptomatic treatment (group IV) compared to group II (by 50.5 and 7.5 fold, respectively) and group III (by 25.4 and 2.8 fold, respectively). In groups II, III, IV, V and VI, significant and positive associations were monitored between insulin and amyloid beta 40, amyloid beta 42, C-reactive protein, total creatine kinase, and D-dimer. Diabetic markers were significantly decreased in diabetic Alzheimer's patients treated with anti-Alzheimer's drugs (especially piracetam) compared to group IV. This study reveals the role of amyloid beta 40, amyloid beta 42, insulin, HbA1c, lipid profile disturbance, C-reactive protein, D-dimer, and magnesium in the bidirectional correlation between T2D and pathogenesis of Alzheimer's disease, that is powered by their correlations, and therefore the possibility of utilizing Aβ as a biochemical marker of T2D in Alzheimer's patients is recommended. Impact statement Several aspects associated with T2D that contribute to AD and vice versa were investigated in this study. Additionally, this work reveals the role of Aβ40, Aβ42, insulin, HbA1c, lipid profile disturbance, CRP, D-dimer, and magnesium in the bidirectional association between T2D and the pathogenesis of AD, that is powered by their correlations, and therefore the possibility of utilizing Aβ as a biochemical marker of T2D in Alzheimer's patients is recommended. Furthermore, the ameloriating effect of anti-Alzheimer's drugs on diabetes mellitus confirms this association. Hereafter, a new approach for treating insulin resistance and diabetes may be developed by new therapeutic potentials such as neutralization of Aβ by anti-Aβ antibodies.

Emerging roles for the amyloid precursor protein and derived peptides in the regulation of cellular and systemic metabolism

The amyloid precursor protein (APP) is a transmembrane protein that can be cleaved by proteases through two different pathways to yield a number of small peptides, each with distinct physiological properties and functions. It has been extensively studied in the context of Alzheimer's disease, with the APP-derived amyloid β (Aβ) peptide being a major constituent of the amyloid plaques observed in this disease. It has been known for some time that APP can regulate neuronal metabolism; however, the present review examines the evidence indicating that APP and its peptides can also regulate key metabolic processes such as insulin action, lipid synthesis and storage and mitochondrial function in peripheral tissues. This review presents the hypothesis that amyloidogenic processing of APP in peripheral tissues plays a key role in the response to nutrient excess and that this could contribute to the pathogenesis of metabolic diseases such as obesity and type 2 diabetes (T2D).

Metabolic Syndrome as a Risk Factor for Alzheimer's Disease: Is Aβ a Crucial Factor in Both Pathologies?

SIGNIFICANCE

Recently, chronic degenerative diseases have become one of the main health problems worldwide. That is the case of Alzheimer's disease (AD) and metabolic syndrome (MetS), whose expression can be influenced by different risk factors. Recent Advances: In recent decades, it has been widely described that MetS increases the risk of cognitive impairment and dementia. MetS pathogenesis involves several vascular risk factors such as diabetes, dyslipidemia, hypertension, and insulin resistance (I/R).

CRITICAL ISSUES

Reported evidence shows that vascular risk factors are associated with AD, particularly in the development of protein aggregation, inflammation, oxidative stress, neuronal dysfunction, and disturbances in signaling pathways, with insulin receptor signaling being a common alteration between MetS and AD.

FUTURE DIRECTIONS

Insulin signaling has been involved in tau phosphorylation and amyloid β (Aβ) metabolism. However, it has also been demonstrated that Aβ oligomers can bind to insulin receptors, triggering their internalization, decreasing neuron responsiveness to insulin, and promoting insulin I/R. Thus, it could be argued that Aβ could be a convergent factor in the development of both pathologies. Antioxid. Redox Signal. 26, 542-560.

Synthesis of substituted 2H-benzo[e]indazole-9-carboxylate as a potent antihyperglycemic agent that may act through IRS-1, Akt and GSK-3β pathways

Based on high throughput screening of our chemical library, we identified two 4,5-dihydro-2H-benzo[e]indazole derivatives (5d and 5g), which displayed a significant effect on glucose uptake in L6 skeletal muscle cells. Based on these lead molecules, a series of benzo[e]indazole derivatives were prepared. Among all the synthesized dihydro-2H-benzo[e]indazoles, 8-(methylthio)-2-phenyl-6-p-tolyl-4,5-dihydro-2H-benzo[e]indazole-9-carboxylate (5e) showed significant glucose uptake stimulation in L6 skeletal muscle cells, even better than lead compounds. Additionally, 5e decreased glucagon-induced glucose release in HepG2 hepatoma cells. The 2H-benzo[e]indazole 5e exerted an antihyperglycemic effect in normal, sucrose challenged streptozotocin-induced diabetic rats and type 2 diabetic db/db mice. Treatment with 5e at a dose of 30 mg kg-1 in db/db mice caused a significant decrease in triglyceride and total cholesterol levels and increased the HDL-C level in a significant manner. The mechanistic studies revealed that the 2H-benzo[e]indazole 5e significantly stimulated insulin-induced signaling at the level of IRS-1, Akt and GSK-3β in L6 skeletal muscle cells, possibly by inhibiting protein tyrosine phosphatase-1B. This new 2H-benzo[e]indazole derivative has potential for the treatment of diabetes with improved lipid profile.