Susceptibility to diet-induced obesity and glucose intolerance in the APP (SWE)/PSEN1 (A246E) mouse model of Alzheimer's disease is associated with increased brain levels of protein tyrosine phosphatase 1B (PTP1B) and retinol-binding protein 4 (RBP4), and basal phosphorylation of S6 ribosomal protein

Molecular mechanisms linking type 2 diabetes mellitus and late-onset Alzheimer's disease: A systematic review and qualitative meta-analysis

Research evidence indicating common metabolic mechanisms through which type 2 diabetes mellitus (T2DM) increases risk of late-onset Alzheimer's dementia (LOAD) has accumulated over recent decades. The aim of this systematic review is to provide a comprehensive review of common mechanisms, which have hitherto been discussed in separate perspectives, and to assemble and evaluate candidate loci and epigenetic modifications contributing to polygenic risk linkages between T2DM and LOAD. For the systematic review on pathophysiological mechanisms, both human and animal studies up to December 2023 are included. For the qualitative meta-analysis of genomic bases, human association studies were examined; for epigenetic mechanisms, data from human studies and animal models were accepted. Papers describing pathophysiological studies were identified in databases, and further literature gathered from cited work. For genomic and epigenomic studies, literature mining was conducted by formalised search codes using Boolean operators in search engines, and augmented by GeneRif citations in Entrez Gene, and other sources (WikiGenes, etc.). For the systematic review of pathophysiological mechanisms, 923 publications were evaluated, and 138 gene loci extracted for testing candidate risk linkages. 3 57 publications were evaluated for genomic association and descriptions of epigenomic modifications. Overall accumulated results highlight insulin signalling, inflammation and inflammasome pathways, proteolysis, gluconeogenesis and glycolysis, glycosylation, lipoprotein metabolism and oxidation, cell cycle regulation or survival, autophagic-lysosomal pathways, and energy. Documented findings suggest interplay between brain insulin resistance, neuroinflammation, insult compensatory mechanisms, and peripheral metabolic dysregulation in T2DM and LOAD linkage. The results allow for more streamlined longitudinal studies of T2DM-LOAD risk linkages.

Overexpression of forebrain PTP1B leads to synaptic and cognitive impairments in obesity

Obesity has reached pandemic proportions and is a risk factor for neurodegenerative diseases, including Alzheimer's disease. Chronic inflammation is common in obese patients, but the mechanism between inflammation and cognitive impairment in obesity remains unclear. Accumulative evidence shows that protein-tyrosine phosphatase 1B (PTP1B), a neuroinflammatory and negative synaptic regulator, is involved in the pathogenesis of neurodegenerative processes. We investigated the causal role of PTP1B in obesity-induced cognitive impairment and the beneficial effect of PTP1B inhibitors in counteracting impairments of cognition, neural morphology, and signaling. We showed that obese individuals had negative relationship between serum PTP1B levels and cognitive function. Furthermore, the PTP1B level in the forebrain increased in patients with neurodegenerative diseases and obese cognitive impairment mice with the expansion of white matter, neuroinflammation and brain atrophy. PTP1B globally or forebrain-specific knockout mice on an obesogenic high-fat diet showed enhanced cognition and improved synaptic ultrastructure and proteins in the forebrain. Specifically, deleting PTP1B in leptin receptor-expressing cells improved leptin synaptic signaling and increased BDNF expression in the forebrain of obese mice. Importantly, we found that various PTP1B allosteric inhibitors (e.g., MSI-1436, well-tolerated in Phase 1 and 1b clinical trials for obesity and type II diabetes) prevented these alterations, including improving cognition, neurite outgrowth, leptin synaptic signaling and BDNF in both obese cognitive impairment mice and a neural cell model of PTP1B overexpression. These findings suggest that increased forebrain PTP1B is associated with cognitive decline in obesity, whereas inhibition of PTP1B could be a promising strategy for preventing neurodegeneration induced by obesity.

Eicosapentaenoic Acid Protects against Metabolic Impairments in the APPswe/PS1dE9 Alzheimer's Disease Mouse Model

BACKGROUND

Alzheimer's disease (AD) is an age-related neurodegenerative disease characterized by amyloid-β (Aβ) plaques. Systemic inflammation and obesity may exacerbate AD pathogenesis. We previously reported anti-inflammatory and anti-obesity effects of EPA in mice.

OBJECTIVES

We aimed to determine whether EPA reduces obesity-associated metabolic dysfunctions and Aβ accumulation in AD amyloidogenic mice.

METHODS

Two-mo-old APPswe/PS1dE9 transgenic (TG) mice and non-TG littermates were randomly assigned to low fat (LF; 10% kcal fat), high fat (HF; 45% kcal fat), or EPA (36 g/kg)-supplemented HF diets. Body composition, glucose tolerance, and energy expenditure were measured, and serum and brain metabolic markers were tested 38 wk postintervention. Outcomes were statistically analyzed via 3-factor ANOVA, modeling genotype, sex, and diet interactions.

RESULTS

HF-fed males gained more weight than females (Δ = 61 mg; P < 0.001). Compared with LF, HF increased body weights of wild-type (WT) males (Δ = 31 mg; P < 0.001). EPA reduced HF-induced weight gain in WT males (Δ = 24 mg; P = 0.054) but not in females. HF mice showed decreased glucose clearance and respiratory energy compared with LF-fed groups (Δ = -1.31 g/dL; P < 0.001), with no significant effects of EPA. However, EPA conferred metabolic improvements by decreasing serum leptin and insulin (Δ = -2.51 g/mL and Δ = -0.694 ng/mL, respectively compared with HF, P ≤ 0.05) and increasing adiponectin (Δ = 21.6 ng/mL; P < 0.001). As we expected, TG mice expressed higher serum and brain Aβ than WT mice (Δ = 0.131 ng/mL; P < 0.001 and Δ = 0.56%; P < 0.01, respectively), and EPA reduced serum Aβ1-40 in TG males compared with HF (Δ = 0.053 ng/mL; P ≤ 0.05).

CONCLUSIONS

To our knowledge, this is the first report that EPA reduces serum Aβ1-40 in obese AD male mice, warranting further investigations into tissue-specific mechanisms of EPA in AD.

Emerging Links between Nonalcoholic Fatty Liver Disease and Neurodegeneration

The association between liver and brain health has gained attention as biomarkers of liver function have been revealed to predict neurodegeneration. The liver is a central regulator in metabolic homeostasis. However, in nonalcoholic fatty liver disease (NAFLD), homeostasis is disrupted which can result in extrahepatic organ pathologies. Emerging literature provides insight into the mechanisms behind the liver-brain health axis. These include the increased production of liver-derived factors that promote insulin resistance and loss of neuroprotective factors under conditions of NAFLD that increase insulin resistance in the central nervous system. In addition, elevated proinflammatory cytokines linked to NAFLD negatively impact the blood-brain barrier and increase neuroinflammation. Furthermore, exacerbated dyslipidemia associated with NAFLD and hepatic dysfunction can promote altered brain bioenergetics and oxidative stress. In this review, we summarize the current knowledge of the crosstalk between liver and brain as it relates to the pathophysiology between NAFLD and neurodegeneration, with an emphasis on Alzheimer's disease. We also highlight knowledge gaps and future areas for investigation to strengthen the potential link between NAFLD and neurodegeneration.

Prodromal Glutamatergic Modulation with Riluzole Impacts Glucose Homeostasis and Spatial Cognition in Alzheimer's Disease Mice

BACKGROUND

Prior research supports a strong link between Alzheimer's disease (AD) and metabolic dysfunction that involves a multi-directional interaction between glucose, glutamatergic homeostasis, and amyloid pathology. Elevated soluble amyloid-β (Aβ) is an early biomarker for AD-associated cognitive decline that contributes to concurrent glutamatergic and metabolic dyshomeostasis in humans and male transgenic AD mice. Yet, it remains unclear how primary time-sensitive targeting of hippocampal glutamatergic activity may impact glucose regulation in an amyloidogenic mouse model. Previous studies have illustrated increased glucose uptake and metabolism using a neuroprotective glutamate modulator (riluzole), supporting the link between glucose and glutamatergic homeostasis.

OBJECTIVE

We hypothesized that targeting early glutamatergic hyperexcitation through riluzole treatment could aid in attenuating co-occurring metabolic and amyloidogenic pathologies with the intent of ameliorating cognitive decline.

METHODS

We conducted an early intervention study in male and female transgenic (AβPP/PS1) and knock-in (APPNL - F/NL - F) AD mice to assess the on- and off-treatment effects of prodromal glutamatergic modulation (2-6 months of age) on glucose homeostasis and spatial cognition through riluzole treatment.

RESULTS

Results indicated a sex- and genotype-specific effect on glucose homeostasis and spatial cognition with riluzole intervention that evolved with disease progression and time since treatment.

CONCLUSION

These findings support the interconnected nature of glucose and glutamatergic homeostasis with amyloid pathology and petition for further investigation into the targeting of this relationship to improve cognitive performance.

High-fat diet exacerbates cognitive and metabolic abnormalities in neuronal BACE1 knock-in mice - partial prevention by Fenretinide

Objective: The β-site APP-cleaving enzyme 1 (BACE1) is a rate-limiting step in β-amyloid (Aβ) production in Alzheimer's disease (AD) brains, but recent evidence suggests that BACE1 is also involved in metabolic regulation. Here, we aimed to assess the effects of highfat diet (HFD) on metabolic and cognitive phenotypes in the diabetic BACE1 knock-in mice (PLB4) and WT controls; we additionally examined whether these phenotypes can be normalized with a synthetic retinoid (Fenretinide, Fen) targeting weight loss.Methods: Five-month old male WT and PLB4 mice were fed either (1) control chow diet, (2) 45%-saturated fat diet (HFD), (3) HFD with 0.04% Fen (HFD + Fen) or (4) control chow diet with 0.04% Fen (Fen) for 10 weeks. We assessed basic metabolic parameters, circadian rhythmicity, spatial habituation (Phenotyper) and working memory (Y-maze). Hypothalami, forebrain and liver tissues were assessed using Western blots, qPCR and ELISAs.Results: HFD feeding drastically worsened metabolism and induced early mortality (-40%) in otherwise viable PLB4 mice. This was ameliorated by Fen, despite no effects on glucose intolerance. In HFD-fed WT mice, Fen reduced weight gain, glucose intolerance and hepatic steatosis. The physiological changes induced in WT and PLB4 mice by HFD (+/-Fen) were accompanied by enhanced cerebral astrogliosis, elevated PTP1B, phopsho-eIF2α and altered hypothalamic transcription of Bace1, Pomc and Mc4r. Behaviourally, HFD feeding exacerbated spatial memory deficits in PLB4 mice, which was prevented by Fen and linked with increased full-length APP, normalized brain Aβ*56 oligomerization and astrogliosis.Conclusions: HFD induces early mortality and worsened cognition in the Alzheimer's-like BACE1 mice- partial prevention was achieved with Fenretinide, without improvements in glucose homeostasis.

Impaired Glucose Homeostasis in a Tau Knock-In Mouse Model

Alzheimer’s disease (AD) is the leading cause of dementia. While impaired glucose homeostasis has been shown to increase AD risk and pathological loss of tau function, the latter has been suggested to contribute to the emergence of the glucose homeostasis alterations observed in AD patients. However, the links between tau impairments and glucose homeostasis, remain unclear. In this context, the present study aimed at investigating the metabolic phenotype of a new tau knock-in (KI) mouse model, expressing, at a physiological level, a human tau protein bearing the P301L mutation under the control of the endogenous mouse Mapt promoter. Metabolic investigations revealed that, while under chow diet tau KI mice do not exhibit significant metabolic impairments, male but not female tau KI animals under High-Fat Diet (HFD) exhibited higher insulinemia as well as glucose intolerance as compared to control littermates. Using immunofluorescence, tau protein was found colocalized with insulin in the β cells of pancreatic islets in both mouse (WT, KI) and human pancreas. Isolated islets from tau KI and tau knock-out mice exhibited impaired glucose-stimulated insulin secretion (GSIS), an effect recapitulated in the mouse pancreatic β-cell line (MIN6) following tau knock-down. Altogether, our data indicate that loss of tau function in tau KI mice and, particularly, dysfunction of pancreatic β cells might promote glucose homeostasis impairments and contribute to metabolic changes observed in AD.

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.

Discovery of Novel PTP1B Inhibitors Derived from the BH3 Domain of Proapoptotic Bcl-2 Proteins with Antidiabetic Potency

BH3 peptide analogues are generally believed to exhibit great potency as cancer therapeutics via targeting antiapoptotic Bcl-2 proteins. Here, we describe the synthesis and identification of a new class of palmitoylated peptide BH3 analogues derived from the core region (h1-h4) of BH3 domains of proapoptotic Bcl-2 proteins and as alternative PTP1B inhibitors with antidiabetic potency in vitro and in vivo. PTP1B inhibitors are attractive for treatment of type 2 diabetes. We design the analogues using a simple lipidation approach and discovered novel lead analogues with promising antidiabetic potency in vitro and in vivo. The results presented here expanded the alternative target and function for the BH3 peptide analogues from one member Bim to other members of the proapoptotic Bcl-2 proteins and emphasize their therapeutic potential in T2DM. Furthermore, our findings may provide new proof of the regulatory function of Bcl-2 family proteins in mitochondrial nutrient and energy metabolism.

Expression of Microtubule Associated Protein Tau in Mouse Pancreatic Islets Is Restricted to Autonomic Nerve Fibers

BACKGROUND

Evidence from clinical studies and basic research has shown a strong correlation between Alzheimer's disease (AD) and type 2 diabetes. Tau, a neuronal microtubule-associated protein, is hyperphosphorylated and aggregated into neurofibrillary tangles in the AD brain. However, the expression of tau in pancreas is under debate.

OBJECTIVE

We determined the expression of tau in mouse pancreas.

METHODS

We used western blots, immunoprecipitation, and immunohistochemical staining to analyze pancreatic expression of tau in mice.

RESULTS

We found that neither total tau nor phosphorylated tau was detectable in the mouse pancreas by western blots. Immunostaining with pan tau antibodies R134d and Tau-5 revealed bright and dense varicosities in the pancreatic islets and the exocrine pancreas. These varicosities were immunoreactive to synapsin 1, a presynaptic marker which can outline autonomic nerve profiles in pancreas, exhibiting complete colocalization with tau. Importantly, endocrine cells in islets did not exhibit specific immunoreactivity to any of pan tau antibodies tested, nor did the exocrine cells.

CONCLUSION

In the mouse pancreas, we found that tau is exclusively expressed in autonomic nerve fibers, but there is no detectable expression in endocrine cells in the islet.

Chia seeds as a potential cognitive booster in the APP23 Alzheimer's disease model

Glucose hypometabolism potentially contributes to Alzheimer's disease (AD) and might even represent an underlying mechanism. Here, we investigate the relationship of diet-induced metabolic stress and AD as well as the therapeutic potential of chia seeds as a modulator of glucose metabolism in the APP23 mouse model. 4-6 (pre-plaque stage, PRE) and 28-32 (advanced-plaque stage, ADV) weeks old APP23 and wild type mice received pretreatment for 12 weeks with either sucrose-rich (SRD) or control diet, followed by 8 weeks of chia seed supplementation. Although ADV APP23 mice generally showed functioning glucose homeostasis, they were more prone to SRD-induced glucose intolerance. This was accompanied by elevated corticosterone levels and mild insulin insensitivity. Chia seeds improved spatial learning deficits but not impaired cognitive flexibility, potentially mediated by amelioration of glucose tolerance, attenuation of corticosterone levels and reversal of SRD-induced elevation of pro-inflammatory cytokine levels. Since cognitive symptoms and plaque load were not aggravated by SRD-induced metabolic stress, despite enhanced neuroinflammation in the PRE group, we conclude that impairments of glucose metabolism do not represent an underlying mechanism of AD in this mouse model. Nevertheless, chia seeds might provide therapeutic potential in AD as shown by the amelioration of cognitive symptoms.

Diet, Microbiota and Brain Health: Unraveling the Network Intersecting Metabolism and Neurodegeneration

Increasing evidence gives support for the idea that extra-neuronal factors may affect brain physiology and its predisposition to neurodegenerative diseases. Epidemiological and experimental studies show that nutrition and metabolic disorders such as obesity and type 2 diabetes increase the risk of Alzheimer's and Parkinson's diseases after midlife, while the relationship with amyotrophic lateral sclerosis is uncertain, but suggests a protective effect of features of metabolic syndrome. The microbiota has recently emerged as a novel factor engaging strong interactions with neurons and glia, deeply affecting their function and behavior in these diseases. In particular, recent evidence suggested that gut microbes are involved in the seeding of prion-like proteins and their spreading to the central nervous system. Here, we present a comprehensive review of the impact of metabolism, diet and microbiota in neurodegeneration, by affecting simultaneously several aspects of health regarding energy metabolism, immune system and neuronal function. Advancing technologies may allow researchers in the future to improve investigations in these fields, allowing the buildup of population-based preventive interventions and development of targeted therapeutics to halt progressive neurologic disability.

IPSC-Derived Neuronal Cultures Carrying the Alzheimer's Disease Associated TREM2 R47H Variant Enables the Construction of an Aβ-Induced Gene Regulatory Network

Genes associated with immune response and inflammation have been identified as genetic risk factors for late-onset Alzheimer´s disease (LOAD). The rare R47H variant within triggering receptor expressed on myeloid cells 2 (TREM2) has been shown to increase the risk for developing Alzheimer’s disease (AD) 2–3-fold. Here, we report the generation and characterization of a model of late-onset Alzheimer’s disease (LOAD) using lymphoblast-derived induced pluripotent stem cells (iPSCs) from patients carrying the TREM2 R47H mutation, as well as from control individuals without dementia. All iPSCs efficiently differentiated into mature neuronal cultures, however AD neuronal cultures showed a distinct gene expression profile. Furthermore, manipulation of the iPSC-derived neuronal cultures with an Aβ-S8C dimer highlighted metabolic pathways, phagosome and immune response as the most perturbed pathways in AD neuronal cultures. Through the construction of an Aβ-induced gene regulatory network, we were able to identify an Aβ signature linked to protein processing in the endoplasmic reticulum (ER), which emphasized ER-stress, as a potential causal role in LOAD. Overall, this study has shown that our AD-iPSC based model can be used for in-depth studies to better understand the molecular mechanisms underlying the etiology of LOAD and provides new opportunities for screening of potential therapeutic targets.

Central and Peripheral Metabolic Defects Contribute to the Pathogenesis of Alzheimer's Disease: Targeting Mitochondria for Diagnosis and Prevention

Significance: Epidemiological studies indicate that metabolic disorders are associated with an increased risk for Alzheimer's disease (AD). Metabolic remodeling occurs in the central nervous system (CNS) and periphery, even in the early stages of AD. Mitochondrial dysfunction has been widely accepted as a molecular mechanism underlying metabolic disorders. Therefore, focusing on early metabolic changes, especially from the perspective of mitochondria, could be of interest for early AD diagnosis and intervention. Recent Advances: We and others have identified that the levels of several metabolites are fluctuated in the periphery before their accumulation in the CNS, which plays an important role in the pathogenesis of AD. Mitochondrial remodeling is likely one of the earliest signs of AD, linking nutritional imbalance to cognitive deficits. Notably, by improving mitochondrial function, mitochondrial nutrients efficiently rescue cellular metabolic dysfunction in the CNS and periphery in individuals with AD. Critical Issues: Peripheral metabolic disorders should be intensively explored and evaluated for the early diagnosis of AD. The circulating metabolites derived from mitochondrial remodeling represent novel potential diagnostic biomarkers for AD that are more readily detected than CNS-oriented biomarkers. Moreover, mitochondrial nutrients provide a promising approach to preventing and delaying AD progression. Future Directions: Abnormal mitochondrial metabolism in the CNS and periphery is involved in AD pathogenesis. More clinical studies provide evidence for the suitability and reliability of circulating metabolites and cytokines for the early diagnosis of AD. Targeting mitochondria to rewire cellular metabolism is a promising approach to preventing AD and ameliorating AD-related metabolic disorders.

Small Molecule Amyloid-β Protein Precursor Processing Modulators Lower Amyloid-β Peptide Levels via cKit Signaling

Alzheimer's disease (AD) is characterized by the accumulation of neurotoxic amyloid-β (Aβ) peptides consisting of 39-43 amino acids, proteolytically derived fragments of the amyloid-β protein precursor (AβPP), and the accumulation of the hyperphosphorylated microtubule-associated protein tau. Inhibiting Aβ production may reduce neurodegeneration and cognitive dysfunction associated with AD. We have previously used an AβPP-firefly luciferase enzyme complementation assay to conduct a high throughput screen of a compound library for inhibitors of AβPP dimerization, and identified a compound that reduces Aβ levels. In the present study, we have identified an analog, compound Y10, which also reduced Aβ. Initial kinase profiling assays identified the receptor tyrosine kinase cKit as a putative Y10 target. To elucidate the precise mechanism involved, AβPP phosphorylation was examined by IP-western blotting. We found that Y10 inhibits cKit phosphorylation and increases AβPP phosphorylation mainly on tyrosine residue Y743, according to AβPP751 numbering. A known cKit inhibitor and siRNA specific to cKit were also found to increase AβPP phosphorylation and lower Aβ levels. We also investigated a cKit downstream signaling molecule, the Shp2 phosphatase, and found that known Shp2 inhibitors and siRNA specific to Shp2 also increase AβPP phosphorylation, suggesting that the cKit signaling pathway is also involved in AβPP phosphorylation and Aβ production. We further found that inhibitors of both cKit and Shp2 enhance AβPP surface localization. Thus, regulation of AβPP phosphorylation by small molecules should be considered as a novel therapeutic intervention for AD.

Tau, Diabetes and Insulin

Tau protein which was discovered in 1975 [310] became of great interest when it was identified as the main component of neurofibrillary tangles (NFT), a pathological feature in the brain of patients with Alzheimer's disease (AD) [39, 110, 232]. Tau protein is expressed mainly in the brain as six isoforms generated by alternative splicing [46, 97]. Tau is a microtubule associated proteins (MAPs) and plays a role in microtubules assembly and stability, as well as diverse cellular processes such as cell morphogenesis, cell division, and intracellular trafficking [49]. Additionally, Tau is involved in much larger neuronal functions particularly at the level of synapses and nuclei [11, 133, 280]. Tau is also physiologically released by neurons [233] even if the natural function of extracellular Tau remains to be uncovered (see other chapters of the present book).

Decay in Retinoic Acid Signaling in Varied Models of Alzheimer's Disease and In-Vitro Test of Novel Retinoic Acid Receptor Ligands (RAR-Ms) to Regulate Protective Genes

Retinoic acid has been previously proposed in the treatment of Alzheimer's disease (AD). Here, five transgenic mouse models expressing AD and frontotemporal dementia risk genes (i.e., PLB2APP, PLB2TAU, PLB1Double, PLB1Triple, and PLB4) were used to investigate if consistent alterations exist in multiple elements of the retinoic acid signaling pathway in these models. Many steps of the retinoic acid signaling pathway including binding proteins and metabolic enzymes decline, while the previously reported increase in RBP4 was only consistent at late (6 months) but not early (3 month) ages. The retinoic acid receptors were exceptional in their consistent decline in mRNA and protein with transcript decline of retinoic acid receptors β and γ by 3 months, before significant pathology, suggesting involvement in early stages of disease. Decline in RBP1 transcript may also be an early but not late marker of disease. The decline in the retinoic acid signaling system may therefore be a therapeutic target for AD and frontotemporal dementia. Thus, novel stable retinoic acid receptor modulators (RAR-Ms) activating multiple genomic and non-genomic pathways were probed for therapeutic control of gene expression in rat primary hippocampal and cortical cultures. RAR-Ms promoted the non-amyloidogenic pathway, repressed lipopolysaccharide induced inflammatory genes and induced genes with neurotrophic action. RAR-Ms had diverse effects on gene expression allowing particular RAR-Ms to be selected for maximal therapeutic effect. Overall the results demonstrated the early decline of retinoic acid signaling in AD and frontotemporal dementia models and the activity of stable and potent alternatives to retinoic acid as potential therapeutics.

Knock-in of Mutated hTAU Causes Insulin Resistance, Inflammation and Proteostasis Disturbance in a Mouse Model of Frontotemporal Dementia

Diabetes and obesity have been implicated as risk factors for dementia. However, metabolic mechanisms and associated signalling pathways have not been investigated in detail in frontotemporal dementia. We therefore here characterised physiological, behavioural and molecular phenotypes of 3- and 8-month-old male tau knock-in (PLB2_TAU) vs wild-type (PLB_WT) mice. Homecage analysis suggested intact habituation but a dramatic reduction in exploratory activity in PLB2_TAU mice. Deficits in motor strength were also observed. At 3 months, PLB2_TAU mice displayed normal glucose handling but developed hyperglycaemia at 8 months, suggesting a progressive diabetic phenotype. Brain, liver and muscle tissue analyses confirmed tissue-specific deregulation of metabolic and homeostatic pathways. In brain, increased levels of phosphorylated tau and inflammation were detected alongside reduced ER regulatory markers, overall suggesting a downregulation in essential cellular defence pathways. We suggest that subtle neuronal expression of mutated human tau is sufficient to disturb systems metabolism and protein handling. Whether respective dysfunctions in tauopathy patients are also a consequence of tau pathology remains to be confirmed, but could offer new avenues for therapeutic interventions.

The Role of Leptin and Adiponectin in Obesity-Associated Cognitive Decline and Alzheimer's Disease

Cross-talk between adipose tissue and central nervous system (CNS) underlies the increased risk of obese people to develop brain diseases such as cognitive and mood disorders. Detailed mechanisms for how peripheral changes caused by adipose tissue accumulation in obesity impact the CNS to cause brain dysfunction are poorly understood. Adipokines are a large group of substances secreted by the white adipose tissue to regulate a wide range of homeostatic processes including, but not limited to, energy metabolism and immunity. Obesity is characterized by a generalized change in the levels of circulating adipokines due to abnormal accumulation and dysfunction of adipose tissue. Altered adipokine levels underlie complications of obesity as well as the increased risk for the development of obesity-related comorbidities such as type 2 diabetes, cardiovascular and neurodegenerative diseases. Here, we review the literature for the role of adipokines as key mediators of the communication between periphery and CNS in health and disease. We will focus on the actions of leptin and adiponectin, two of the most abundant and well studied adipokines, in the brain, with particular emphasis on how altered signaling of these adipokines in obesity may lead to cognitive dysfunction and augmented risk for Alzheimer's disease. A better understanding of adipokine biology in brain disorders may prove of major relevance to diagnostic, prevention and therapy.

BH3 mimetics derived from Bim-BH3 domain core region show PTP1B inhibitory activity

A series of our previously described BH3 peptide mimetics derived from Bim-BH3 domain core region were found to exhibit weak to potent PTP1B binding affinity and inhibitory activities via target-based drug screening. Among these compounds, a 12-aa Bim-BH3 core sequence peptide conjugated to palmitic acid (SM-6) displayed good PTP1B binding affinity (K_D = 8.38 nmol/L), inhibitory activity (IC₅₀ = 1.20 μmol/L) and selectivity against other PTPs (TCPTP, LAR, SHP-1 and SHP-2). Furthermore, SM-6 promoted HepG2 cell glucose uptake and inhibited the expression of PTP1B, indicating that SM-6 could improve the insulin resistance effect in the insulin-resistant HepG2 cell model. These results may indicate a new direction for the application of BH3 peptide mimetics and promising PTP1B peptide inhibitors could be designed and developed based on SM-6.

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.

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.

Differential Protein Profiling of Cerebrospinal Fluid in Piglets with Severe Meningoencephalitis Caused by Streptococcus suis Type 2 Compared to Controls

Streptococcus suis serotype 2 (SS2) is a zoonotic pathogen that can cause meningitis both in pigs and in human beings. However, the pathogenesis of central nervous system (CNS) infection caused by SS2 have not yet been elucidated. To find the key molecules in cerebrospinal fluid (CSF) needed for the pathogenesis, a SS2 meningoencephalitic pig model and a SS2 non-meningoencephalitic pig model were established in this study. CSF was collected from infected piglets, and protein profiling was performed with label-free proteomics technology. A total of 813 differential proteins, including 52 up-regulated proteins and 761 down-regulated proteins, were found in the CSF of meningoencephalitic pigs compared with both non-meningoencephalitic pigs and healthy pigs. These 813 differential proteins were clustered into three main categories, namely, cellular component, biological process, and molecular function by gene ontology (GO) analysis. The most enriched subclasses of differential proteins in each category were exosome (44.3%), energy pathway (25.0%) and catalytic activity (11.3%), respectively. The most enriched subclasses of upregulated proteins were extracellular (62.1%), protein metabolism (34.5%) and cysteine-type peptidase activity (6.9%), and of downregulated proteins were exosomes (45.0%), energy pathway (24.0%) and catalytic activity (9.4%). Then, the differential proteins were further investigated by using the KEGG database and were found to participate in 16 KEGGs. The most enriched KEGG was citrate cycle (56.6%), and some of these differential proteins are associated with brain diseases such as Huntington's disease (18.6%), Parkinson's disease (23.8%) and Alzheimer's disease (17.6%). Sixteen of the 813 differential proteins, chosen randomly as examples, were further confirmed by enzyme-linked immunosorbent assay (ELISA) to support the proteomic data. To our knowledge, this is the first study to analyze the differential protein profiling of CSF between SS2 meningoencephalitic piglets and non-meningoencephalitic piglets by employing proteomic technology. The discovery and bioinformatics analysis of these differential proteins provides reference data not only for research on pathogenesis of SS2 CNS infection but also for diagnosis and drug therapy research.

Evidence for altered insulin receptor signaling in Alzheimer's disease

Epidemiological data have shown that metabolic disease can increase the propensity for developing cognitive decline and dementia, particularly Alzheimer's disease (AD). While this interaction is not completely understood, clinical studies suggest that both hyper- and hypoinsulinemia are associated with an increased risk for developing AD. Indeed, insulin signaling is altered in post-mortem brain tissue from AD patients and treatments known to enhance insulin signaling can improve cognitive function. Further, clinical evidence has shown that AD patients and mouse models of AD often display alterations in peripheral metabolism. Since insulin is primarily derived from the periphery, it is likely that changes in peripheral insulin levels lead to alterations in central nervous system (CNS) insulin signaling and could contribute to cognitive decline and pathogenesis. Developing a better understanding of the relationship between alterations in peripheral metabolism and cognitive function might provide a foundation for the development of better treatment options for patients with AD. In this article we will begin to piece together the present data defining this relationship by briefly discussing insulin signaling in the periphery and CNS, its role in cognitive function, insulin's relationship to AD, peripheral metabolic alterations in mouse models of AD and how information from these models helps understand the mechanisms through which these changes potentially lead to impairments in insulin signaling in the CNS, and potential ways to target insulin signaling that could improve cognitive function in AD. This article is part of the Special Issue entitled 'Metabolic Impairment as Risk Factors for Neurodegenerative Disorders.'

Effects of thymol on amyloid-β-induced impairments in hippocampal synaptic plasticity in rats fed a high-fat diet

Obesity and a high-fat diet (HFD) are known to increase the incidence of Alzheimer's disease (AD). Oxidative stress, a major risk factor for AD, is increased with HFD consumption. Thymol (Thy) has antioxidant properties. Therefore, in the present study, we examined the protective and therapeutic effects of Thy on amyloid-β (Aβ)-induced impairments in the hippocampal synaptic plasticity of HFD-fed rats. In this study, 72 adult male Wistar rats were randomly assigned to 9 groups (n = 8 rats/group): Group 1 (control; standard diet); Group 2: Control + phosphate-buffered saline (PBS) + Oil (Thy vehicle); Group 3 (HFD + PBS); Group 4: (HFD + Aβ); Group 5: Control + PBS + Thy; Group 6: (HFD + Aβ + Oil); Group 7: Control + Aβ + Thy; Group 8: HFD + PBS + Thy; Group 9: (HFD + Aβ + Thy). After stereotaxic surgery, the field potentials were recorded after the implantation of the recording and stimulating electrodes in the dentate gyrus (DG) and perforant pathway, respectively. Following high-frequency stimulation, the long-term potentiation (LTP) of the population spike (PS) amplitude and the slope of the excitatory postsynaptic potentials (EPSPs) were measured in the DG. The HFD rats that received Aβ exhibited a significant decrease in their EPSP slope and PS amplitude as compared to the control group. In contrast, Thy administration in the HFD + Aβ rats reduced the decrease in the EPSP slope and PS amplitude. Thy decreased the Aβ-induced LTP impairments in HFD rats. The HFD significantly increased serum malondialdehyde levels and decreased total antioxidant capacity and total glutathione levels; whereas, Thy supplementation significantly reversed these parameters. Therefore, these results suggest that Thy, a natural antioxidant, can be therapeutic against high risk factors for AD, such as HFD.

Mutual Relationship between Tau and Central Insulin Signalling: Consequences for AD and Tauopathies?

Alzheimer disease (AD) is a progressive neurodegenerative disorder mainly characterized by cognitive deficits and neuropathological changes such as Tau lesions and amyloid plaques, but also associated with non-cognitive symptomatology. Metabolic and neuroendocrine abnormalities, such as alterations in body weight, brain insulin impairments, and lower brain glucose metabolism, which often precede clinical diagnosis, have been extensively reported in AD patients. However, the origin of these symptoms and their relation to pathology and cognitive impairments remain misunderstood. Insulin is a hormone involved in the control of energy homeostasis both peripherally and centrally, and insulin-resistant state has been linked to increased risk of dementia. It is now well established that insulin resistance can exacerbate Tau lesions, mainly by disrupting the balance between Tau kinases and phosphatases. On the other hand, the emerging literature indicates that Tau protein can also modulate insulin signalling in the brain, thus creating a detrimental vicious circle. The following review will highlight our current understanding of the role of insulin in the brain and its relation to Tau protein in the context of AD and tauopathies. Considering that insulin signalling is prone to be pharmacologically targeted at multiple levels, it constitutes an appealing approach to improve both insulin brain sensitivity and mitigate brain pathology with expected positive outcome in terms of cognition.

Cdkn2a deficiency promotes adipose tissue browning

Objectives

Genome-wide association studies have reported that DNA polymorphisms at the CDKN2A locus modulate fasting glucose in human and contribute to type 2 diabetes (T2D) risk. Yet the causal relationship between this gene and defective energy homeostasis remains elusive. Here we sought to understand the contribution of Cdkn2a to metabolic homeostasis.

Methods

We first analyzed glucose and energy homeostasis from Cdkn2a-deficient mice subjected to normal or high fat diets. Subsequently Cdkn2a-deficient primary adipose cells and human-induced pluripotent stem differentiated into adipocytes were further characterized for their capacity to promote browning of adipose tissue. Finally CDKN2A levels were studied in adipocytes from lean and obese patients.

Results

We report that Cdkn2a deficiency protects mice against high fat diet-induced obesity, increases energy expenditure and modulates adaptive thermogenesis, in addition to improving insulin sensitivity. Disruption of Cdkn2a associates with increased expression of brown-like/beige fat markers in inguinal adipose tissue and enhances respiration in primary adipose cells. Kinase activity profiling and RNA-sequencing analysis of primary adipose cells further demonstrate that Cdkn2a modulates gene networks involved in energy production and lipid metabolism, through the activation of the Protein Kinase A (PKA), PKG, PPARGC1A and PRDM16 signaling pathways, key regulators of adipocyte beiging. Importantly, CDKN2A expression is increased in adipocytes from obese compared to lean subjects. Moreover silencing CDKN2A expression during human-induced pluripotent stem cells adipogenic differentiation promoted UCP1 expression.

Conclusion

Our results offer novel insight into brown/beige adipocyte functions, which has recently emerged as an attractive therapeutic strategy for obesity and T2D. Modulating Cdkn2a-regulated signaling cascades may be of interest for the treatment of metabolic disorders.

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Cdkn2a deficiency protects mice against high fat diet-induced obesity.

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Cdkn2a modulates brown-like/beige fat gene networks involved in energy production and lipid metabolism.

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Increased CDKN2A expression in human obese adipocytes.

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Increased UCP1 levels in adipocytes differentiated from CDKN2A-silenced hiPS cells.

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.'

Xuefu Zhuyu decoction ameliorates obesity, hepatic steatosis, neuroinflammation, amyloid deposition and cognition impairment in metabolically stressed APPswe/PS1dE9 mice

ETHNOPHARMACOLOGICAL RELEVANCE

Metabolic syndrome and vascular dysfunction was suggested to be the risk factors for Alzheimer's disease (AD). Xuefu Zhuyu decoction (XZD) is a traditional Chinese medicine used to treat metabolic syndrome and cardiac-cerebral vascular disease. The effects of XZD on ameliorating metabolic syndrome, amyloid-related pathologies and cognitive impairment in an animal model of AD with metabolic stress was investigated.

MATERIALS AND METHOD

The animal model of AD with metabolic stress was created by administrating high-fat diet and a low-dose injection of streptozotocin prior to the appearance of senile plaques in APP/PS1 transgenic mice. The diabesity-associated metabolic changes and AD-related pathological alterations were examined.

RESULTS

We found that XZD reduced body weight, insulin and leptin level, HOMA-IR, hepatic triglyceride, serum Aβ42 in the metabolic stressed AD animal. XZD also ameliorated oral glucose tolerant, Aβ deposition, astrocyte and microglia activation in the vicinity of plaques, and nesting behavior in the metabolic stressed AD animal.

CONCLUSION

The results of this study suggest that XZD is able to reduce the peripheral metabolic stress-mediated vascular hypoperfusion, neuroinflammation and AD-related pathology in APP/PS1 mice.

Effects of ABCA1 R219K Polymorphism and Serum Lipid Profiles on Mild Cognitive Impairment in Type 2 Diabetes Mellitus

Background: Accumulated evidence suggests that adverse lipid changes are risk factors for type 2 diabetes mellitus (T2DM) and neurodegenerative disorders. The ATP-binding cassette A1 transporter (ABCA1) gene contributes to both lipid processing and amyloid-β formation and thus shows promise as a biological target in the pathology of mild cognitive impairment (MCI) in T2DM.

Objective: This study aimed to investigate the interactions among lipids, ABCA1 R219K polymorphism, and cognitive function in T2DM.

Methods: Clinical parameters, including lipids, were measured. The testing scores of different cognitive domains were recorded, and the ABCA1 R219K polymorphisms were analyzed.

Results: A total of 226 patients, including 124 MCI patients and 102 controls, were enrolled in this study. T2DM patients with MCI showed lower cognitive functions, serum high-density lipoprotein (HDL-c), and apolipoprotein A1 (apoA-I) levels; and higher total cholesterol level than the controls. Serum HDL-c (P = 0.001) and apoA-I (P = 0.016) were positively associated with the MoCA score in MCI patients. Further stratification analyses revealed that the subjects with higher HDL-c concentration showed better attention and memory for verbal, visual, and logical functions than the group with lower HDL-c concentration (P < 0.05). No significant differences were observed among the distributions of ABCA1 R219K variants between MCI patients and controls; however, the KK genotype carriers presented higher apoA-I levels than those with RR genotype in MCI individuals.

Conclusion: This study does not support the association between R219K polymorphism and T2DM-related MCI. However, our data suggested that the serum HDL-c level might positively influence cognition, especially memory function, in T2DM patients. Further studies are needed to determine the interaction between lipids and ABCA1 genotype and its effect on cognition in T2DM patients.

Trial registration: Advanced Glycation End Products Induced Cognitive Impairment in Diabetes: BDNF Signal Meditated Hippocampal Neurogenesis ChiCTR-OCC-15006060; http://www.chictr.org.cn/showproj.aspx?proj=10536.

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).

An amylin analog used as a challenge test for Alzheimer's disease

INTRODUCTION

Preclinical studies demonstrate the potential of amylin in the diagnosis of Alzheimer's disease (AD). We aimed to lay the foundation for repurposing the amylin analog and a diabetes drug, pramlintide, for AD in humans.

METHODS

We administered a single subcutaneous injection of 60 μg of pramlintide to nondiabetic subjects under fasting conditions.

RESULTS

None of the participants developed hypoglycemia after the injection of pramlintide. The pramlintide challenge induced a significant surge of amyloid-β peptide and a decrease in total tau in the plasma of AD subjects but not in control participants. The pramlintide injection provoked an increase in interleukin 1 receptor antagonist and a decrease in retinol-binding protein 4, which separates AD subjects from control subjects.

DISCUSSION

Pramlintide use appeared to be safe in the absence of diabetes. The biomarker changes as a result of the pramlintide challenge, which distinguished AD from control subjects and mild cognitive impairment.

Reversal of high fat diet-induced obesity improves glucose tolerance, inflammatory response, β-amyloid accumulation and cognitive decline in the APP/PSEN1 mouse model of Alzheimer's disease

This study assessed the extent to which high fat diet (HFD)-induced β-amyloid accumulation and cognitive decline in APP/PSEN1 mice are reversible through control of fat intake. Ten months of HFD (60% calories from fat) led to significant deficits in a 2-trial Y maze task, and nest building assay, and decreased voluntary locomotor activity. The HFD induced an inflammatory response, indicated by increased expression of several inflammatory markers. Substituting a low fat diet led to pronounced weight loss and correction of glucose intolerance, decreases in the inflammatory response, and improved performance on behavioral tasks in both wild-type and APP/PSEN1 transgenic mice. Insoluble β-amyloid levels, and extent of tau phosphorylation were also lower following dietary reversal in APP/PSEN1 mice compared to high fat-fed animals, indicating that the inflammatory response may have contributed to key pathogenic pathways in the Alzheimer's disease model. The data suggest that weight loss can be a vital strategy for cognitive protection, but also highlight potential mechanisms for intervention when sustained weight loss is not possible.

Neuronal human BACE1 knockin induces systemic diabetes in mice

AIMS

β-Secretase 1 (BACE1) is a key enzyme in Alzheimer's disease pathogenesis that catalyses the amyloidogenic cleavage of amyloid precursor protein (APP). Recently, global Bace1 deletion was shown to protect against diet-induced obesity and diabetes, suggesting that BACE1 is a potential regulator of glucose homeostasis. Here, we investigated whether increased neuronal BACE1 is sufficient to alter systemic glucose metabolism, using a neuron-specific human BACE1 knockin mouse model (PLB4).

METHODS

Glucose homeostasis and adiposity were determined by glucose tolerance tests and EchoMRI, lipid species were measured by quantitative lipidomics, and biochemical and molecular alterations were assessed by western blotting, quantitative PCR and ELISAs. Glucose uptake in the brain and upper body was measured via (18)FDG-PET imaging.

RESULTS

Physiological and molecular analyses demonstrated that centrally expressed human BACE1 induced systemic glucose intolerance in mice from 4 months of age onward, alongside a fatty liver phenotype and impaired hepatic glycogen storage. This diabetic phenotype was associated with hypothalamic pathology, i.e. deregulation of the melanocortin system, and advanced endoplasmic reticulum (ER) stress indicated by elevated central C/EBP homologous protein (CHOP) signalling and hyperphosphorylation of its regulator eukaryotic translation initiation factor 2α (eIF2α). In vivo (18)FDG-PET imaging further confirmed brain glucose hypometabolism in these mice; this corresponded with altered neuronal insulin-related signalling, enhanced protein tyrosine phosphatase 1B (PTP1B) and retinol-binding protein 4 (RBP4) levels, along with upregulation of the ribosomal protein and lipid translation machinery. Increased forebrain and plasma lipid accumulation (i.e. ceramides, triacylglycerols, phospholipids) was identified via lipidomics analysis.

CONCLUSIONS/INTERPRETATION

Our data reveal that neuronal BACE1 is a key regulator of metabolic homeostasis and provide a potential mechanism for the high prevalence of metabolic disturbance in Alzheimer's disease.

Increased susceptibility to metabolic dysregulation in a mouse model of Alzheimer's disease is associated with impaired hypothalamic insulin signaling and elevated BCAA levels

INTRODUCTION

Epidemiologic studies have demonstrated an association between diabetes and dementia. Insulin signaling within the brain, in particular within the hypothalamus regulates carbohydrate, lipid, and branched chain amino acid (BCAA) metabolism in peripheral organs such as the liver and adipose tissue. We hypothesized that cerebral amyloidosis impairs central nervous system control of metabolism through disruption of insulin signaling in the hypothalamus, which dysregulates glucose and BCAA homeostasis resulting in increased susceptibility to diabetes.

METHODS

We examined whether APP/PS1 mice exhibit increased susceptibility to aging or high-fat diet (HFD)-induced metabolic impairment using metabolic phenotyping and insulin-signaling studies.

RESULTS

APP/PS1 mice were more susceptible to high-fat feeding and aging-induced metabolic dysregulation including disrupted BCAA homeostasis and exhibited impaired hypothalamic insulin signaling.

DISCUSSION

Our data suggest that AD pathology increases susceptibility to diabetes due to impaired hypothalamic insulin signaling, and that plasma BCAA levels could serve as a biomarker of hypothalamic insulin action in patients with AD.

Unexpected partial correction of metabolic and behavioral phenotypes of Alzheimer's APP/PSEN1 mice by gene targeting of diabetes/Alzheimer's-related Sorcs1

Introduction

Insulin resistance and type 2 diabetes mellitus (T2D) are associated with increased risk for cognitive impairment, Alzheimer’s disease (AD) and vascular dementia. SORCS1 encodes a protein-sorting molecule genetically linked to both T2D and AD. The association of SORCS1 with both AD and T2D is sexually dimorphic in humans, with both disease associations showing more robust effects in females. Based on published evidence that manipulation of the mouse genome combining multiple genes related to cerebral amyloidosis, to T2D, or both, might provide novel mouse models with exacerbated amyloid and/or diabetes phenotypes, we assessed memory, glucose homeostasis, and brain biochemistry and pathology in male and female wild-type, Sorcs1 -/-, APP/PSEN1, and Sorcs1 -/- X APP/PSEN1 mice.

Results

Male mice with either the APP/PSEN1 or Sorcs1 -/- genotype displayed earlier onset and persistent impairment in both learning behavior and glucose homeostasis. Unlike prior examples in the literature, the behavioral and metabolic abnormalities in male mice were not significantly exacerbated when the two disease model mice (Sorcs1 -/- models T2D; APP/PSEN1 models AD) were crossed. However, female Sorcs1 -/- X APP/PSEN1 mice exhibited worse metabolic dysfunction than Sorcs1 -/- knockout mice and worse memory than wild-type mice. The deletion of Sorcs1 from APP/PSEN1 mutant mice led to no obvious changes in brain levels of total or oligomeric amyloid-beta (Aβ) peptide.

Conclusions

In general, unexpectedly, there was a trend for gene targeting of Sorcs1-/- to partially mitigate, not exacerbate, the metabolic and amyloid pathologies. These results indicate that crossing AD model mice and T2D model mice may not always cause exacerbation of both the amyloidosis phenotype and the metabolic phenotype and highlight the unexpected pitfalls of creating mixed models of disease.

Electronic supplementary material

The online version of this article (doi:10.1186/s40478-016-0282-y) contains supplementary material, which is available to authorized users.

On cognitive ecology and the environmental factors that promote Alzheimer disease: lessons from Octodon degus (Rodentia: Octodontidae)

Cognitive ecologist posits that the more efficiently an animal uses information from the biotic and abiotic environment, the more adaptive are its cognitive abilities. Nevertheless, this approach does not test for natural neurodegenerative processes under field or experimental conditions, which may recover animals information processing and decision making and may explain, mechanistically, maladaptive behaviors. Here, we call for integrative approaches to explain the relationship between ultimate and proximate mechanisms behind social behavior. We highlight the importance of using the endemic caviomorph rodent Octodon degus as a valuable natural model for mechanistic studies of social behavior and to explain how physical environments can shape social experiences that might influence impaired cognitive abilities and the onset and progression of neurodegenerative disorders such as Alzheimer disease. We consequently suggest neuroecological approaches to examine how key elements of the environment may affect neural and cognitive mechanisms associated with learning, memory processes and brain structures involved in social behavior. We propose the following three core objectives of a program comprising interdisciplinary research in O. degus, namely: (1) to determine whether diet types provided after weaning can lead to cognitive impairment associated with spatial memory, learning and predisposing to develop Alzheimer disease in younger ages; (2) to examine if early life social experience has long term effects on behavior and cognitive responses and risk for development Alzheimer disease in later life and (3) To determine if an increase of social interactions in adult degu reared in different degree of social stressful conditions alter their behavior and cognitive responses.

Neuroprotective effects of metformin against Aβ-mediated inhibition of long-term potentiation in rats fed a high-fat diet

Metformin (Met) is used to treat neurodegenerative disorders such as Alzheimer's disease (AD). Conversely, high-fat diets (HFD) have been shown to increase AD risk. In this study, we investigated the neuroprotective effects of Met on β-amyloid (Aβ)-induced impairments in hippocampal synaptic plasticity in AD model rats that were fed a HFD. In this study, 32 adult male Wistar rats were randomly assigned to four groups: group I (control group, regular diet); group II (HFD+vehicle); group III (HFD+Aβ); or group IV (Met+HFD+Aβ). Rats fed a HFD were injected with Aβ to induce AD, allowed to recover, and treated with Met for 8 weeks. The rats were then anesthetized with intraperitoneal injections of urethane and placed in a stereotaxic apparatus for surgery, electrode implantation, and field potential recording. In vivo electrophysiological recordings were then performed to measure population spike (PS) amplitude and excitatory postsynaptic potential (EPSP) slope in the hippocampal dentate gyrus. Long-term potentiation (LTP) was induced by high-frequency stimulation of the perforant pathway. Blood samples were then collected to measure plasma levels of triglycerides, low-density lipoproteins, very low-density lipoprotein, and cholesterol. After induction of LTP, PS amplitude and EPSP slope were significantly decreased in Aβ-injected rats fed a HFD compared to vehicle-injected animals or untreated animals that were fed a normal diet. Met treatment of Aβ-injected rats significantly attenuated these decreases, suggesting that Met decreased the effects of Aβ on LTP. These findings suggest that Met treatment is neuroprotective against the detrimental effects of Aβ and HFDs on hippocampal synaptic plasticity.

Early inflammation-associated factors blunt sterol regulatory element-binding proteins-1-mediated lipogenesis in high-fat diet-fed APPSWE /PSEN1dE9 mouse model of Alzheimer's disease

Alzheimer's disease (AD) patients have an increased incidence of Type 2 diabetes (T2D); however, the underlying mechanisms are not well understood. Since AD is considered a multifactorial disease that affects both the central nerves system and periphery and the dysregulation of hepatic lipid and glucose metabolism play critical roles in T2D, we, therefore, aim to explore the influence of AD genotype on the liver during the progress of high-fat diet (HFD)-induced T2D. Fourteen-week-old female APP_SWE /PSEN1dE9 (AD) mice and age-, gender-matched wild-type controls C57BL/6J (WT) mice were fed a HFD (45% kcal fat content) or a standard chow diet (chow, 12% kcal fat content) for 22 weeks. The effects of diet and genotype were analyzed. Mouse primary hepatocytes were used to decipher the underlying mechanisms. HFD induced significantly higher body weight gain, more severe hyperglycemia, glucose intolerance and hepatic insulin resistance in AD mice than in WT mice. However, AD mice showed reduced HFD-induced hepatic steatosis, and SREBP-1-mediated lipogenic signaling was activated by HFD in WT mice but not in AD mice. In addition, 14-week-old AD mice exhibited higher expression of NF-κB p65, p-JNK and p-p38MAPK, as well as higher hepatic and serum contents of IL-6 and TNFα. In mouse primary hepatocyte cultures, IL-6 and TNFα inhibited high-glucose plus insulin-induced activation of SREBP-1-mediated lipogenic signaling and biosynthesis of non-esterified fatty acid and triglyceride. Early inflammation-associated factors most likely diminish HFD-induced hepatic lipid deposition by inhibiting SREBP-1-mediated de novo lipogenesis, thus driving substrate flux to glucose production for hyperglycemia and hepatic insulin resistance in T2D development. Alzheimer's disease (AD) is a multifactorial disease affecting both central nerves system and periphery organs. Therefore, we explored the hepatic susceptibility to high-fat diet (HFD) in AD mice. We found that AD mice were resistant to HFD-induced hepatic fat accumulation in spite of more severe obesity, hyperglycemia, glucose intolerance and hepatic insulin resistance. Mechanistically, AD mice exhibited hepatic inflammation at an early stage, which inhibited sterol regulatory element-binding proteins-1 (SREBP-1)-mediated de novo lipogenesis, and most likely drive substrate flux to glucose production for hyperglycemia and hepatic insulin resistance. Cover Image for this issue: doi: 10.1111/jnc.13306.

Shared Neuropathological Characteristics of Obesity, Type 2 Diabetes and Alzheimer's Disease: Impacts on Cognitive Decline

In the past few decades, the prevalence of obesity and type 2 diabetes mellitus (T2DM), as well as older individuals at risk for Alzheimer’s disease (AD), has increased. While the consumption of diets high in fat (total and saturated) have been linked to increased risk of AD, diets rich in antioxidants, polyunsaturated fats, and omega-3 fatty acids are associated with decreased risk. Additionally, AD patients are at increased risk for developing T2DM. Recent research suggests that there are stronger similarities between AD and T2DM than have previously been considered. Here we review the neurocognitive and inflammatory effects of high-fat diet consumption, its relationship to AD, and the treatment potential of dietary interventions that may decrease risk of cognitive decline and other associated neuropathological changes, such as insulin resistance, oxidative stress, and chronic inflammatory processes.

Obesity and Hepatic Steatosis Are Associated with Elevated Serum Amyloid Beta in Metabolically Stressed APPswe/PS1dE9 Mice

Diabesity-associated metabolic stresses modulate the development of Alzheimer’s disease (AD). For further insights into the underlying mechanisms, we examine whether the genetic background of APPswe/PS1dE9 at the prodromal stage of AD affects peripheral metabolism in the context of diabesity. We characterized APPswe/PS1dE9 transgenic mice treated with a combination of high-fat diet with streptozotocin (HFSTZ) in the early stage of AD. HFSTZ-treated APPswe/PS1dE9 transgenic mice exhibited worse metabolic stresses related to diabesity, while serum β-amyloid levels were elevated and hepatic steatosis became apparent. Importantly, two-way analysis of variance shows a significant interaction between HFSTZ and genetic background of AD, indicating that APPswe/PS1dE9 transgenic mice are more vulnerable to HFSTZ treatment. In addition, body weight gain, high hepatic triglyceride, and hyperglycemia were positively associated with serum β-amyloid, as validated by Pearson’s correlation analysis. Our data suggests that the interplay between genetic background of AD and HFSTZ-induced metabolic stresses contributes to the development of obesity and hepatic steatosis. Alleviating metabolic stresses including dysglycemia, obesity, and hepatic steatosis could be critical to prevent peripheral β-amyloid accumulation at the early stage of AD.

Role of insulin resistance in Alzheimer's disease

A critical role of insulin resistance (IR) in Alzheimer's disease (AD) includes beta-amyloid (Aβ) production and accumulation, the formation of neurofibrillary tangles (NFTs), failure of synaptic transmission and neuronal degeneration. Aβ is sequentially cleavaged from APP by two proteolytic enzymes: β-secretase and γ-secretase. IR could regulate Aβ production via enhancing β- and γ-secretase activity. Meanwhile, IR induces oxidative stress and inflammation in the brain which contributes to Aβ and tau pathology. Aβ accumulation can enhance IR through Aβ-mediated inflammation and oxidative stress. IR is a possible linking between amyloid plaques and NFTs pathology via oxidative stress and neuroinflammation. Additionally, IR could disrupt acetylcholine activity, and accelerate axon degeneration and failures in axonal transport, and lead to cognitive impairment in AD. Preclinical and clinical studies have supported that insulin could be useful in the treatment of AD. Thus, an effective measure to inhibit IR may be a novel drug target in AD.

PTP1B inhibition suggests a therapeutic strategy for Rett syndrome

The X-linked neurological disorder Rett syndrome (RTT) presents with autistic features and is caused primarily by mutations in a transcriptional regulator, methyl CpG-binding protein 2 (MECP2). Current treatment options for RTT are limited to alleviating some neurological symptoms; hence, more effective therapeutic strategies are needed. We identified the protein tyrosine phosphatase PTP1B as a therapeutic candidate for treatment of RTT. We demonstrated that the PTPN1 gene, which encodes PTP1B, was a target of MECP2 and that disruption of MECP2 function was associated with increased levels of PTP1B in RTT models. Pharmacological inhibition of PTP1B ameliorated the effects of MECP2 disruption in mouse models of RTT, including improved survival in young male (Mecp2-/y) mice and improved behavior in female heterozygous (Mecp2-/+) mice. We demonstrated that PTP1B was a negative regulator of tyrosine phosphorylation of the tyrosine kinase TRKB, the receptor for brain-derived neurotrophic factor (BDNF). Therefore, the elevated PTP1B that accompanies disruption of MECP2 function in RTT represents a barrier to BDNF signaling. Inhibition of PTP1B led to increased tyrosine phosphorylation of TRKB in the brain, which would augment BDNF signaling. This study presents PTP1B as a mechanism-based therapeutic target for RTT, validating a unique strategy for treating the disease by modifying signal transduction pathways with small-molecule drugs.