Suppression of adiponectin receptor 1 promotes memory dysfunction and Alzheimer's disease-like pathologies

Integrin Trafficking, Fibronectin Architecture, and Glomerular Injury upon Adiponectin Receptor 1 Depletion

Key Points

Background

Deficiency of adiponectin and its downstream signaling may contribute to the pathogenesis of kidney injury in type 2 diabetes. Adiponectin activates intracellular signaling using adiponectin receptor 1 (AdipoR1) and adiponectin receptor 2, but the role of adiponectin receptor–mediated signaling in glomerular injury in type 2 diabetes remains unknown.

Methods

The expression of AdipoR1 in the kidneys of people with type 2 diabetes and the expression of podocyte proteins or injury markers in the kidneys of AdipoR1 knockout (AdipoR1-KO) mice and immortalized AdipoR1-deficient human podocytes were investigated by immunohistochemistry and immunoblotting. The functional role of AdipoR1 was studied in AdipoR1-deficient podocytes by performing assays for apoptosis, cytokine secretion, mechanical stress, adhesion, and endocytic trafficking.

Results

Glomerular AdipoR1 expression was lower in type 2 diabetes and associated kidney disease, correlating with higher body mass index and podocyte loss. Male AdipoR1-KO mice showed typical signs of early diabetic kidney disease, including albuminuria, glomerular structural abnormalities, and lower expression of central podocyte proteins; females were less affected. Podocyte apoptosis increased in female and male AdipoR1-KO mice, and excessive podocyte loss, potentially due to detachment, was detected in males. AdipoR1 deficiency impaired the yes-associated protein–mediated mechanoresponse and induced accumulation of the extracellular matrix (ECM) protein fibronectin in the glomeruli in vivo and podocytes in vitro. Functionally, AdipoR1 deficiency impaired endocytosis of the ECM receptor active integrin β1, disturbed focal adhesion turnover, and remodulated podocyte-derived ECM, thereby reducing podocyte adhesion.

Conclusions

AdipoR1 deficiency in mice resulted in the development of kidney injury predominantly in males. Mechanistically, AdipoR1 loss in podocytes impaired endocytosis of active integrin β1, which plausibly compromised focal adhesion dynamics, disturbed fibronectin matrix turnover, and hindered podocyte adhesion.

Adiponectin targets the AMPK/mTOR signaling pathway to alleviate cognitive impairment in epilepsy

Among patients with chronic epilepsy, 70‑80% have cognitive impairment. To investigate the relationship between adiponectin (ADPN) and the cognitive level in epilepsy and its mechanism, 20 epileptic patients and 20 healthy controls were included for the assessment of the cognitive level. An ELISA was used to evaluate the serum ADPN level. An epileptic rat model was established and treated with AdipoRon, an ADPN receptor (AdipoR) agonist, which binds to AdipoR1 and AdipoR2. The Morris water maze test was used to assess the cognitive function of rats, and the expression levels of the synapsis‑associated proteins postsynaptic density protein 95 (PSD95), synaptosomal associated protein 25 (SNAP25) and synaptophysin (SYP), as well as AMP‑activated protein kinase (AMPK), mTOR, phosphorylated (p‑)AMPK and p‑mTOR were determined by immunoblotting. Serum ADPN levels were positively correlated with the Montreal cognitive assessment score. AdipoRon improved the cognitive function of epileptic rats, maintained the structural integrity of hippocampal neurons and reduced neuronal damage. It also promoted the mRNA expression of AdipoR1 and AdipoR2 in the hippocampus. Furthermore, AdipoRon increased the expression of the synapsis‑associated proteins PSD95, SNAP25 and SYP by activating the AMPK/mTOR signaling pathway. ADPN improved cognitive impairment in epilepsy by targeting the AMPK/mTOR signaling pathway, providing novel insights for the treatment of epilepsy.

Transcriptome analysis of early- and late-onset Alzheimer's disease in Korean cohorts

INTRODUCTION

The molecular mechanisms underlying early-onset Alzheimer's disease (EOAD) and late-onset Alzheimer's disease (LOAD) remain incompletely understood, particularly in Asian populations.

METHODS

RNA-sequencing was carried out on blood samples from 248 participants in the Seoul National University Bundang Hospital cohort to perform differential gene expression (DGE) and weighted gene co-expression network analysis. Findings were replicated in an independent Korean cohort (N = 275).

RESULTS

DGE analysis identified 18 and 88 dysregulated genes in EOAD and LOAD, respectively. Network analysis identified a LOAD-associated module showing a significant enrichment in pathways related to mitophagy, 5' adenosine monophosphate-activated protein kinase signaling, and ubiquitin-mediated proteolysis. In the replication cohort, downregulation of SMOX and PLVAP in LOAD was replicated, and the LOAD-associated module was highly preserved. In addition, SMOX and PLVAP were associated with brain amyloid beta deposition.

DISCUSSION

Our findings suggest distinct molecular signatures for EOAD and LOAD in a Korean population, providing deeper understanding of their diagnostic potential and molecular mechanisms.

HIGHLIGHTS

Analysis identified 18 and 88 dysregulated genes in early-onset Alzheimer's disease (EOAD) and late-onset Alzheimer's disease (LOAD), respectively. Expression levels of SMOX and PLVAP were downregulated in LOAD. Expression levels of SMOX and PLVAP were associated with brain amyloid beta deposition. Pathways including mitophagy and 5' adenosine monophosphate-activated protein kinase signaling were enriched in a LOAD module. A LOAD module was highly preserved across two independent cohorts.

Adiponectin receptor 1 regulates endometrial receptivity via the adenosine monophosphate‑activated protein kinase/E‑cadherin pathway

Endometrial receptivity is essential for successful embryo implantation and pregnancy initiation and is regulated via various signaling pathways. Adiponectin, an important adipokine, may be a potential regulator of reproductive system functions. The aim of the present study was to elucidate the regulatory role of adiponectin receptor 1 (ADIPOR1) in endometrial receptivity. The endometrial receptivity between RL95‑2 and AN3CA cell lines was confirmed using an in vitro JAr spheroid attachment model. 293T cells were transfected with control or short hairpin (sh)ADIPOR1 vectors and RL95‑2 cells were transduced with lentiviral particles targeting ADIPOR1. Reverse transcription‑quantitative PCR and immunoblot assays were also performed. ADIPOR1 was consistently upregulated in the endometrium during the mid‑secretory phase compared with that in the proliferative phase and in receptive RL95‑2 cells compared with that in non‑receptive AN3CA cells. Stable cell lines with diminished ADIPOR1 expression caused by shRNA showed reduced E‑cadherin expression and attenuated in vitro endometrial receptivity. ADIPOR1 regulated AMP‑activated protein kinase (AMPK) activity in endometrial epithelial cells. Regulation of AMPK activity via dorsomorphin and 5‑aminoimidazole‑4‑carboxamide ribonucleotide affected E‑cadherin expression and in vitro endometrial receptivity. The ADIPOR1/AMPK/E‑cadherin axis is vital to endometrial receptivity. These findings can help improve fertility treatments and outcomes.

Adiponectin rescues synaptic plasticity in the dentate gyrus of a mouse model of Fragile X Syndrome

Fragile X syndrome (FXS) is the most common inherited cause of intellectual disability and is the leading known single-gene cause of autism spectrum disorder. Patients with FXS display varied behavioural deficits that include mild to severe cognitive impairments in addition to mood disorders. Currently, there is no cure for this condition; however, there is an emerging focus on therapies that inhibit mechanistic target of rapamycin (mTOR)-dependent protein synthesis owing to the clinical effectiveness of metformin for alleviating some behavioural symptoms in FXS. Adiponectin (APN) is a neurohormone that is released by adipocytes and provides an alternative means to inhibit mTOR activation in the brain. In these studies, we show that Fmr1 knockout mice, like patients with FXS, show reduced levels of circulating APN and that both long-term potentiation (LTP) and long-term depression (LTD) in the dentate gyrus (DG) are impaired. Brief (20 min) incubation of hippocampal slices in APN (50 nM) was able to rescue both LTP and LTD in the DG and increased both the surface expression and phosphorylation of GluA1 receptors. These results provide evidence for reduced APN levels in FXS playing a role in decreasing bidirectional synaptic plasticity and show that therapies which enhance APN levels may have therapeutic potential for this and related conditions.This article is part of a discussion meeting issue 'Long-term potentiation: 50 years on'.

Putative Molecular Mechanisms Underpinning the Inverse Roles of Mitochondrial Respiration and Heme Function in Lung Cancer and Alzheimer's Disease

Mitochondria are the powerhouse of the cell. Mitochondria serve as the major source of oxidative stress. Impaired mitochondria produce less adenosine triphosphate (ATP) but generate more reactive oxygen species (ROS), which could be a major factor in the oxidative imbalance observed in Alzheimer's disease (AD). Well-balanced mitochondrial respiration is important for the proper functioning of cells and human health. Indeed, recent research has shown that elevated mitochondrial respiration underlies the development and therapy resistance of many types of cancer, whereas diminished mitochondrial respiration is linked to the pathogenesis of AD. Mitochondria govern several activities that are known to be changed in lung cancer, the largest cause of cancer-related mortality worldwide. Because of the significant dependence of lung cancer cells on mitochondrial respiration, numerous studies demonstrated that blocking mitochondrial activity is a potent strategy to treat lung cancer. Heme is a central factor in mitochondrial respiration/oxidative phosphorylation (OXPHOS), and its association with cancer is the subject of increased research in recent years. In neural cells, heme is a key component in mitochondrial respiration and the production of ATP. Here, we review the role of impaired heme metabolism in the etiology of AD. We discuss the numerous mitochondrial effects that may contribute to AD and cancer. In addition to emphasizing the significance of heme in the development of both AD and cancer, this review also identifies some possible biological connections between the development of the two diseases. This review explores shared biological mechanisms (Pin1, Wnt, and p53 signaling) in cancer and AD. In cancer, these mechanisms drive cell proliferation and tumorigenic functions, while in AD, they lead to cell death. Understanding these mechanisms may help advance treatments for both conditions. This review discusses precise information regarding common risk factors, such as aging, obesity, diabetes, and tobacco usage.

The role of adiponectin in Alzheimer's disease: A translational review

Adiponectin is an adipokine playing a central role in the regulation of energy homeostasis, carbohydrate and lipid metabolism, as well as immunomodulation. The relationship between Alzheimer's disease (AD) and body composition has highlighted the bidirectional crosstalk between AD's pathophysiology and metabolic disorders. This review aimed to report the current state of knowledge about cellular and molecular mechanisms linking adiponectin and AD, in preclinical studies. Then, we reviewed human studies to assess the relationship between adiponectin levels and AD diagnosis. We also examined the risk of incident AD regarding the participants' baseline adiponectin level, as well as the relationship of adiponectin and cognitive decline in patients with AD. We conducted a systematic review, in accordance with the Preferred Reporting Items for Systematic Reviews and Meta-analyses reporting guideline, of studies published over the last decade on MEDLINE and Cochrane databases. Overall, we reviewed 34 original works about adiponectin in AD, including 11 preclinical studies, two both preclinical and human studies and 21 human studies. Preclinical studies brought convincing evidence for the neuroprotective role of adiponectin on several key mechanisms of AD. Human studies showed conflicting results regarding the relationship between AD and adiponectin levels, as well as regarding the cross-sectional association between cognitive function and adiponectin levels. Adiponectin did not appear as a predictor of incident AD, nor as a predictor of cognitive decline in patients with AD. Despite solid preclinical evidence suggesting the protective role of adiponectin in AD, inconsistent results in humans supports the need for further research.

Adipose tissue as a therapeutic target for vascular damage in Alzheimer's disease

Adipose tissue has recently been recognized as an important endocrine organ that plays a crucial role in energy metabolism and in the immune response in many metabolic tissues. With this regard, emerging evidence indicates that an important crosstalk exists between the adipose tissue and the brain. However, the contribution of adipose tissue to the development of age-related diseases, including Alzheimer's disease, remains poorly defined. New studies suggest that the adipose tissue modulates brain function through a range of endogenous biologically active factors known as adipokines, which can cross the blood-brain barrier to reach the target areas in the brain or to regulate the function of the blood-brain barrier. In this review, we discuss the effects of several adipokines on the physiology of the blood-brain barrier, their contribution to the development of Alzheimer's disease and their therapeutic potential. LINKED ARTICLES: This article is part of a themed issue From Alzheimer's Disease to Vascular Dementia: Different Roads Leading to Cognitive Decline. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v181.6/issuetoc.

The Role of Adipokines in the Pathologies of the Central Nervous System

Adipokines are protein hormones secreted by adipose tissue in response to disruptions in physiological homeostasis within the body's systems. The regulatory functions of adipokines within the central nervous system (CNS) are multifaceted and intricate, and they have been identified in a number of pathologies. Therefore, specific adipokines have the potential to be used as biomarkers for screening purposes in neurological dysfunctions. The systematic review presented herein focuses on the analysis of the functions of various adipokines in the pathogenesis of CNS diseases. Thirteen proteins were selected for analysis through scientific databases. It was found that these proteins can be identified within the cerebrospinal fluid either by their ability to modify their molecular complex and cross the blood-brain barrier or by being endogenously produced within the CNS itself. As a result, this can correlate with their measurability during pathological processes, including Alzheimer's disease, amyotrophic lateral sclerosis, multiple sclerosis, depression, or brain tumors.

PPARγ/Adiponectin axis attenuates methamphetamine-induced conditional place preference via the hippocampal AdipoR1 signaling pathway

Methamphetamine (METH) is a highly addictive psychostimulant. The adipocyte-derived hormone adiponectin has a broad spectrum of functions in the brain. However, limited research has been conducted on the effect of adiponectin signaling on METH-induced conditioned place preference (CPP) and knowledge of the underlying neural mechanisms is scarce. The METH induced adult male C57/BL6J mice model were used for testing the therapeutic activities of intraperitoneal injection of AdipoRon or Rosiglitazone, and AdipoR1 overexpression in hippocampal dentate gyrus (DG), and chemogenetic inhibiting the neural activity of DG, and the changes of neurotrophic factors, synaptic molecules, and glutamate receptors, and inflammatory cytokines were also measured. We found that adiponectin expression was significantly reduced in METH addicted patients and mice. Our findings also showed that injection of AdipoRon or Rosiglitazone alleviated the METH-induced CPP behavior. Moreover, the expression of AdipoR1 in the hippocampus was also reduced, and AdipoR1 overexpression blocked the development of METH-induced CPP behavior through regulatory effects on neurotrophic factors, synaptic molecules, and glutamate receptors. The observed inhibitory neural activity of the hippocampal dentate gyrus (DG) induced via a chemogenetic approach produced a therapeutic effect on the METH-induced CPP behavior. Finally, we identified an abnormal expression of some key inflammatory cytokines through the PPARγ/Adiponectin/AdipoR1 axis. This study demonstrates that adiponectin signaling is a promising diagnostic and therapeutic target for METH addiction.

Identification of Putative Molecules for Adiponectin and Adiponectin Receptor and Their Roles in Learning and Memory in Lymnaea stagnalis

Adiponectin enhances insulin sensitivity, which improves cognition in mammals. How adiponectin affects the mechanism’s underlying cognition, however, remains unknown. We hypothesized that experiments using the pond snail Lymnaea stagnalis, which has long been used in learning and memory studies and in which the function of insulin-like peptides affect learning and memory, could clarify the basic mechanisms by which adiponectin affects cognition. We first identified putative molecules of adiponectin and its receptor in Lymnaea. We then examined their distribution in the central nervous system and changes in their expression levels when hemolymph glucose concentrations were intentionally decreased by food deprivation. We also applied an operant conditioning protocol of escape behavior to Lymnaea and examined how the expression levels of adiponectin and its receptor changed after the conditioned behavior was established. The results demonstrate that adiponectin and adiponectin’s receptor expression levels were increased in association with a reduced concentration of hemolymph glucose and that expression levels of both adiponectin and insulin-like peptide receptors were increased after the conditioning behavior was established. Thus, the involvement of the adiponectin-signaling cascade in learning and memory in Lymnaea was suggested to occur via changes in the glucose concentrations and the activation of insulin.

Sensogenomics of music and Alzheimer's disease: An interdisciplinary view from neuroscience, transcriptomics, and epigenomics

Introduction

The relationship between music and Alzheimer's disease (AD) has been approached by different disciplines, but most of our outstanding comes from neuroscience.

Methods

First, we systematically reviewed the state-of-the-art of neuroscience and cognitive sciences research on music and AD (>100 studies), and the progress made on the therapeutic impact of music stimuli in memory. Next, we meta-analyzed transcriptomic and epigenomic data of AD patients to search for commonalities with genes and pathways previously connected to music in genome association, epigenetic, and gene expression studies.

Results

Our findings indicate that >93% of the neuroscience/ cognitive sciences studies indicate at least one beneficial effect of music on patients with neurodegenerative diseases, being improvements on memory and cognition the most frequent outcomes; other common benefits were on social behavior, mood and emotion, anxiety and agitation, quality of life, and depression. Out of the 334 music-related genes, 127 (38%) were found to be linked to epigenome/transcriptome analysis in AD (vs. healthy controls); some of them (SNCA, SLC6A4, ASCC2, FTH1, PLAUR and ARHGAP26) have been reported to be associated e.g. with musical aptitude and music effect on the transcriptome. Other music-related genes (GMPR, SELENBP1 and ADIPOR1) associated to neuropsychiatric, neurodegenerative diseases and music performance, emerged as hub genes in consensus co-expression modules detected between AD and music estimulated transcriptomes. In addition, we found connections between music, AD and dopamine related genes, with SCNA being the most remarkable - a gene previously associated with learning and memory, and neurodegenerative disorders (e.g., Parkinson's disease and AD).

Discussion

The present study indicate that the vast majority of neuroscientific studies unambiguously show that music has a beneficial effect on health, being the most common benefits relevant to Alzheimer's disease. These findings illuminate a new roadmap for genetic research in neurosciences, and musical interventions in AD and other neurodegenerative conditions.

Adiponectin, the adiponectin paradox, and Alzheimer's Disease: Is this association biologically plausible?

Dementia, especially Alzheimer's Disease (AD) and vascular dementia, is a major public health problem that continues to expand in both economically emerging and hegemonic countries. In 2017, the World Alzheimer Report estimated that over 50 million people were living with dementia globally. Metabolic dysfunctions of brain structures such as the hippocampus and cerebral cortex have been implicated as risk factors for dementia. Several well-defined metabolic risk factors for AD include visceral obesity, chronic inflammation, peripheral and brain insulin resistance, type 2 diabetes mellitus (T2DM), hypercholesterolemia, and others. In this review, we describe the relationship between the dysmetabolic mechanisms, although still unknown, and dementia, particularly AD. Adiponectin (ADPN), the most abundant circulating adipocytokine, acts as a protagonist in the metabolic dysfunction associated with AD, with unexpected and intriguing dual biological functions. This contradictory role of ADPN has been termed the adiponectin paradox. Some evidence suggests that the adiponectin paradox is important in amyloidogenic evolvability in AD. We present cumulative evidence showing that AD and T2DM share many common features. We also review the mechanistic pathways involving brain insulin resistance. We discuss the importance of the evolvability of amyloidogenic proteins (APs), defined as the capacity of a system for adaptive evolution. Finally, we describe potential therapeutic strategies in AD, based on the adiponectin paradox.

Emerging roles of leptin in Parkinson's disease: Chronic inflammation, neuroprotection and more?

An increasing body of experimental evidence implicates a relationship between immunometabolic deterioration and the progression of Parkinson's disease (PD) with a dysregulation of central and peripheral neuroinflammatory networks mediated by circulating adipokines, in particular leptin. We screened the current literature on the role of adipokines in PD. Hence, we searched known databases (PubMed, MEDLINE/OVID) and reviewed original and review articles using the following terms: "leptin/ObR", "Parkinson's disease", "immune-metabolism", "biomarkers" and "neuroinflammation". Focusing on leptin, we summarize and discuss the existing in vivo and in vitro evidence on how adipokines may be protective against neurodegeneration, but at the same time contribute to the progression of PD. These components of the adipose brain axis represent a hitherto underestimated pathway to study systemic influences on dopaminergic degeneration. In addition, we give a comprehensive update on the potential of adjunctive therapeutics in PD targeting leptin, leptin-receptors, and associated pathways. Further experimental and clinical trials are needed to elucidate the mechanisms of action and the value of central and peripheral adipose-immune-metabolism molecular phenotyping in order to develop and validate the differential roles of different adipokines as potential therapeutic target for PD patients.

Circulating adiponectin levels, expression of adiponectin receptors, and methylation of adiponectin gene promoter in relation to Alzheimer's disease

BACKGROUND

The role of adiponectin (ADIPOQ) in Alzheimer's disease (AD) has been documented, however, demonstrating controversial results. In this study, we investigated blood serum ADIPOQ levels, methylation of the adiponectin gene promoter, and adiponectin receptors (AdipoR1 and AdipoR2) expression in blood samples isolated from AD patients and healthy controls.

METHODS

We performed a case-control study including 248 subjects (98 AD patients and 150 healthy controls); ADIPOQ serum levels, AdipoR1, and AdipoR2 levels in PBMC were measured by ELISA Kits, and ADIPOQ gene methylation was analyzed using methyl-specific PCR.

RESULTS

Serum adiponectin levels were threefold higher in the AD group compared to the controls. We have also found a positive correlation between adiponectin and MMSE scores and high-density lipoprotein cholesterol (HDL-C) in AD patients. A significant difference in the proportion of methylation of the CpG sites at - 74 nt of the ADIPOQ gene promoter was detected in AD cases, and the levels of adiponectin in blood serum were significantly higher in methylated samples in the AD group compared to controls. The amount of AdipoR1 was significantly higher among AD subjects, while the expression of AdipoR2 did not vary between AD patients and controls.

CONCLUSION

These findings may contribute to a deeper understanding of the etiological factors leading to the development of dementia and may serve as a basis for the development of predictive biomarkers of AD.

Neuroprotective Effects of Nicotinamide against MPTP-Induced Parkinson's Disease in Mice: Impact on Oxidative Stress, Neuroinflammation, Nrf2/HO-1 and TLR4 Signaling Pathways

Nicotinamide (NAM) is the amide form of niacin and an important precursor of nicotinamide adenine dinucleotide (NAD), which is needed for energy metabolism and cellular functions. Additionally, it has shown neuroprotective properties in several neurodegenerative diseases. Herein, we sought to investigate the potential protective mechanisms of NAM in an intraperitoneal (i.p) 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-induced Parkinson's disease (PD) mouse model (wild-type mice (C57BL/6N), eight weeks old, average body weight 25-30 g). The study had four groups (n = 10 per group): control, MPTP (30 mg/kg i.p. for 5 days), MPTP treated with NAM (500 mg/kg, i.p for 10 days) and control treated with NAM. Our study showed that MPTP increased the expression of α-synuclein 2.5-fold, decreased tyrosine hydroxylase (TH) 0.5-fold and dopamine transporters (DAT) levels up to 0.5-fold in the striatum and substantia nigra pars compacta (SNpc), and impaired motor function. However, NAM treatment significantly reversed these PD-like pathologies. Furthermore, NAM treatment reduced oxidative stress by increasing the expression of nuclear factor erythroid 2-related factor 2 (Nrf2) and heme oxygenase-1 (HO-1) between 0.5- and 1.0-fold. Lastly, NAM treatment regulated neuroinflammation by reducing Toll-like receptor 4 (TLR-4), phosphorylated nuclear factor-κB, tumor (p-NFκB), and cyclooxygenase-2 (COX-2) levels by 0.5- to 2-fold in the PD mouse brain. Overall, these findings suggest that NAM exhibits neuroprotective properties and may be an effective therapeutic agent for PD.

Potential biomarkers of Alzheimer’s disease and cerebral small vessel disease

Background

Cerebral small vessel disease (CSVD) is associated with the pathogenesis of Alzheimer’s disease (AD). Effective treatments to alleviate AD are still not currently available. Hence, we explored markers and underlying molecular mechanisms associated with AD by utilizing gene expression profiles of AD and CSVD patients from public databases, providing more options for early diagnosis and its treatment.

Methods

Gene expression profiles were collected from GSE63060 (for AD) and GSE162790 (for CSVD). Differential analysis was performed between AD and mild cognitive impairment (MCI) or CSVD progression and CSVD no-progression. In both datasets, differentially expressed genes (DEGs) with the same expression direction were identified as common DEGs. Then protein-protein interaction (PPI) network was constructed for common DEGs. Differential immune cells and checkpoints were calculated between AD and MCI.

Results

A total of 146 common DEGs were identified. Common DEGs were mainly enriched in endocytosis and oxytocin signaling pathways. Interestingly, endocytosis and metabolic pathways were shown both from MCI to AD and from CSVD no-progression to CSVD progression. Moreover, SIRT1 was identified as a key gene by ranking degree of connectivity in the PPI network. SIRT1 was associated with obesity-related genes and metabolic disorders. Additionally, SIRT1 showed correlations with CD8 T cells, NK CD56 bright cells, and checkpoints in AD.

Conclusion

The study revealed that the progression of AD is associated with abnormalities in gene expression and metabolism and that the SIRT1 gene may serve as a promising therapeutic target for the treatment of AD.

Pharmacological Inhibition of Spleen Tyrosine Kinase Suppressed Neuroinflammation and Cognitive Dysfunction in LPS-Induced Neurodegeneration Model

Tyrosine-protein kinase (Syk) plays a potential role in neuroinflammation and adaptive immune responses in several neurodegenerative conditions. Seeing the significant role of Syk in the pathophysiology of neurodegeneration, several pharmacological inhibitors have been developed. One of the known inhibitors of Syk is BAY61-3606, which has shown efficacies in Alzheimer’s disease (AD) through regulating amyloid production. However, little is known about its efficacies in neuroinflammation and neurodegeneration. Our finding showed that Syk expression was up-regulated by lipopolysaccharide (LPS)-dependent manner, and BAY61-3606 significantly suppressed the activated microglia (ionized calcium-binding adaptor molecule 1 [Iba-1]) and the inflammatory cytokines (tumor necrosis factor-alpha [TNF-α], interleukin 1-beta [IL-1β], IL-6) and other inflammatory mediators (nuclear factor kappa B [NF-κB], cyclooxygenase-2 [Cox-2], and inducible nitric axide synthase [iNOS]) in the lipopolysaccharide (LPS)-treated in vivo and in vitro models. Moreover, BAY61-3606 significantly reduced microglia-mediated neuronal cell death by regulating the expression of Cytochrome C and Bim (B-cell lymphoma 2 [BCL-2] interacting mediator of cell death) in the LPS-treated mice brain and HT22 cells. Furthermore, the expression of synaptic markers, synaptosomal-associated protein, 25 kDa (SNAP25), synaptophysin (Syp), and postsynaptic density protein-95 (PSD95) in LPS-challenged mice showed that BAY61-3606 significantly recovered the synaptic markers. Finally, we have analyzed the effects of BAY61-3606 against memory and cognitive dysfunctions in the LPS injected mice. The Y-maze test and Passive avoidance test suggested that BAY61-3606 significantly protected against LPS-induced cognitive and memory dysfunctions. The current findings not only highlight the mechanisms of Syk in the pathophysiology of neuro-inflammation, but also support the therapeutic efficacy of BAY61-3606 in the management of neurodegeneration.

LDHB Deficiency Promotes Mitochondrial Dysfunction Mediated Oxidative Stress and Neurodegeneration in Adult Mouse Brain

Age-related decline in mitochondrial function and oxidative stress plays a critical role in neurodegeneration. Lactate dehydrogenase-B (LDHB) is a glycolytic enzyme that catalyzes the conversion of lactate, an important brain energy substrate, into pyruvate. It has been reported that the LDHB pattern changes in the brain during ageing. Yet very little is known about the effect of LDHB deficiency on brain pathology. Here, we have used Ldhb knockout (Ldhb^−/−) mice to test the hypothesis that LDHB deficiency plays an important role in oxidative stress-mediated neuroinflammation and neurodegeneration. LDHB knockout (Ldhb^−/−) mice were generated by the ablation of the Ldhb gene using the Cre/loxP-recombination system in the C57BL/6 genetic background. The Ldhb^−/− mice were treated with either osmotin (15 μg/g of the body; intraperitoneally) or vehicle twice a week for 5-weeks. After behavior assessments, the mice were sacrificed, and the cortical and hippocampal brain regions were analyzed through biochemical and morphological analysis. Ldhb^−/− mice displayed enhanced reactive oxygen species (ROS) and lipid peroxidation (LPO) production, and they revealed depleted stores of cellular ATP, GSH:GSSG enzyme ratio, and downregulated expression of Nrf2 and HO-1 proteins, when compared to WT littermates. Importantly, the Ldhb^−/− mice showed upregulated expression of apoptosis mediators (Bax, Cytochrome C, and caspase-3), and revealed impaired p-AMPK/SIRT1/PGC-1alpha signaling. Moreover, LDHB deficiency-induced gliosis increased the production of inflammatory mediators (TNF-α, Nf-ĸB, and NOS2), and revealed cognitive deficits. Treatment with osmotin, an adipoR1 natural agonist, significantly increased cellular ATP production by increasing mitochondrial function and attenuated oxidative stress, neuroinflammation, and neuronal apoptosis, probably, by upregulating p-AMPK/SIRT1/PGC-1alpha signaling in Ldhb^−/− mice. In brief, LDHB deficiency may lead to brain oxidative stress-mediated progression of neurodegeneration via regulating p-AMPK/SIRT1/PGC-1alpha signaling, while osmotin could improve mitochondrial functions, abrogate oxidative stress and alleviate neuroinflammation and neurodegeneration in adult Ldhb^−/− mice.

Exercise Training Improves Memory Performance in Older Adults: A Narrative Review of Evidence and Possible Mechanisms

As human life expectancy increases, cognitive decline and memory impairment threaten independence and quality of life. Therefore, finding prevention and treatment strategies for memory impairment is an important health concern. Moreover, a better understanding of the mechanisms involved underlying memory preservation will enable the development of appropriate pharmaceuticals drugs for those who are activity limited. Exercise training as a non-pharmacological tool, has been known to increase the mean lifespan by maintaining general body health and improving the cardiovascular and nervous systems function. Among different exercise training protocols, aerobic exercise has been reported to prevent the progression of memory decline, provided adequate exertion level, duration, and frequency. Mechanisms underlying exercise training effects on memory performance have not been understood yet. Convergent evidence suggest several direct and indirect mechanisms at molecular and supramolecular levels. The supramolecular level includes improvement in blood circulation, synaptic plasticity and neurogenesis which are under controls of complex molecular signaling of neurotransmitters, neurotrophic factors, exerkines, and epigenetics factors. Among these various factors, irisin/BDNF signaling seems to be one of the important mediators of crosstalk between contracted skeletal muscles and the brain during exercise training. This review provides an affordable and effective method to improve cognitive function in old ages, particularly those who are most vulnerable to neurodegenerative disorders.

The impact of uremic toxins on Alzheimer's disease

Alzheimer's disease (AD) is the most common type of dementia, pathologically characterized by accumulation of senile plaques and neurofibrillary tangles. Chronic kidney disease (CKD) is highly prevalent in elderly population closely associated with occurrence of dementia. Recent epidemiological and experimental studies suggest a potential association of CKD with AD. Both diseases share a panel of identical risk factors, such as type 2 diabetes; and hypertension. However, the relationship between CKD and AD is unclear. Lower clearance of a panel of uremic toxin including cystatin-C, guanidine, and adiponectin due to CKD is implied to contribute to AD pathogenesis. In this review we summarize the current evidence from epidemiological, experimental and clinical studies on the potential contribution of uremic toxins to AD pathogenesis. We describe outstanding questions and propose an outlook on the link between uremic toxins and AD.

Adiponectin ameliorates hypoperfusive cognitive deficits by boosting a neuroprotective microglial response

Vascular cognitive impairment and dementia (VaD) is the second most common type of dementia caused by chronic vascular hypoperfusion. Adiponectin, one of the cytokines produced by adipocytes (adipocytokine), plays a role in CNS pathologies, but its specific function in VaD is unknown. Here, transcriptomic analyses on human brain tissues showed downregulation of adipocytokine/PPAR signaling in VaD patients, with prominent upregulation of pro-inflammatory responses. Using the murine asymmetric common carotid artery stenosis (ACAS) model, we discovered that the adiponectin/PPARγ axis is essential in reducing chronic hypoperfusion-induced cognitive deficits via modulation of microglial function. Adiponectin levels in the plasma increased early after VaD induction, but decreased in the cerebrospinal fluid in the late phase of VaD. Adiponectin deficiency worsened hippocampus-dependent cognitive deficits, exacerbated neuroinflammation and microglia/macrophage activation, and amplified neuronal loss, but these behavioral and histological outcomes were rescued by adipoRon, a small molecule agonist of the adiponectin receptors. AdipoRon boosted PPARγ expression and inhibited pro-inflammatory microglial responses in vitro, thereby protecting ischemic neurons in primary microglia-neuron cocultures. Microglia/macrophage-specific knockout of PPARγ abolished the neuroprotective effects of adipoRon. Collectively, these data confirm the importance of adiponectin/PPARγ signaling in maintaining cognitive functions in chronic hypoperfusion-induced dementia, and thus provide novel therapeutic targets for VaD.

Chronic oral administration of adipoRon reverses cognitive impairments and ameliorates neuropathology in an Alzheimer's disease mouse model

Circulating adiponectin (APN) levels decrease with age and obesity. On the other hand, a reduction in APN levels is associated with neurodegeneration and neuroinflammation. We previously showed that aged adiponectin knockout (APN-/-) mice developed Alzheimer's like pathologies, cerebral insulin resistance, and cognitive impairments. More recently, we also demonstrated that APN deficiency increased Aβ-induced microglia activation and neuroinflammatory responses in 5xFAD mice. There is compelling evidence that deregulated insulin activities or cerebral insulin resistance contributes to neuroinflammation and Alzheimer's disease (AD) pathogenesis. Here, we demonstrated that APN levels were reduced in the brain of AD patients and 5xFAD mice. We crossbred 5xFAD mice with APN-/- mice to generate APN-deficient 5xFAD (5xFAD;APN-/-). APN deficiency in 5xFAD mice accelerated amyloid loading, increased cerebral amyloid angiopathy, and reduced insulin-signaling activities. Pharmacokinetics study demonstrated adipoRon (APN receptor agonist) was a blood-brain barrier penetrant. AdipoRon improved neuronal insulin-signaling activities and insulin sensitivity in vitro and in vivo. Chronic adipoRon treatment improved spatial memory functions and significantly rescued neuronal and synaptic loss in 5xFAD and 5xFAD;APN-/- mice. AdipoRon lowered plaque and Aβ levels in AD mice. AdipoRon also exerted anti-inflammatory effects by reducing microglial and astrocytes activation as well as suppressing cerebral cytokines levels. The microglial phagocytic activity toward Aβ was restored after adipoRon treatment. Our results indicated that adipoRon exerts multiple beneficial effects providing important therapeutic implications. We propose chronic adipoRon administration as a potential treatment for AD.

Maternal Midpregnancy Leptin and Adiponectin Levels as Predictors of Autism Spectrum Disorders: A Prenatal Cohort Study

CONTEXT

Autism spectrum disorders (ASDs) are a group of conditions characterized by impaired social function and repetitive behaviors. Their etiology is largely unknown.

OBJECTIVE

This work aims to examine the associations of maternal second-trimester and cord blood leptin and adiponectin levels with ASDs in offspring.

METHODS

We used data from 1164 mother-child pairs enrolled in Project Viva, a prospective prebirth cohort. We used logistic regression analysis to examine the associations of leptin and adiponectin levels in maternal second-trimester blood and cord blood obtained at birth with ASDs. Additionally, we examined the association of maternal prepregnancy body mass index (BMI) as an exposure. Main outcome measures included doctor-diagnosed ASDs reported by mothers using questionnaires in midchildhood and early adolescence.

RESULTS

The cumulative incidence of ASDs was 3.4%. Maternal prepregnancy BMI (per 5 points) was positively associated with ASDs in a logistic regression model adjusted for maternal race/ethnicity, education, smoking status and child sex (adjusted odds ratio [OR] 1.38; 95% CI, 1.06-1.79). Higher second-trimester adiponectin was associated with lower odds of ASD in offspring (unadjusted OR 0.49; 95% CI, 0.30-0.78; and OR 0.54; 95% CI, 0.32-0.91 after adjusting for maternal race/ethnicity, education, child sex, OR 0.55; 95% CI, 0.33-0.93 after adjusting for BMI, gestational weight gain, gestational diabetes, and smoking status). Maternal leptin and cord blood leptin and adiponectin levels were not associated with ASDs.

CONCLUSION

Prepregnancy BMI and adiponectin during pregnancy may be useful as a tool to monitor the risk of autism. Increasing adiponectin levels prenatally may play a role in the prevention of ASDs.

Adiponectin improves amyloid-β 31-35-induced circadian rhythm disorder in mice

Adiponectin is an adipocyte‐derived hormone, which is closely associated with the development of Alzheimer's disease (AD) and has potential preventive and therapeutic significance. In the present study, we explored the relationship between adiponectin and circadian rhythm disorder in AD, the effect of adiponectin on the abnormal expression of Bmal1 mRNA/protein induced by amyloid‐β protein 31‐35 (Aβ31‐35), and the underlying mechanism of action. We found that adiponectin‐knockout mice exhibited amyloid‐β deposition, circadian rhythm disorders and abnormal expression of Bmal1. Adiponectin ameliorated the abnormal expression of the Bmal1 mRNA/protein caused by Aβ31‐35 by inhibiting the activity of glycogen synthase kinase 3β (GSK3β). These results suggest that adiponectin deficiency could induce circadian rhythm disorders and abnormal expression of the Bmal1 mRNA/protein, whilst exogenous administration of adiponectin may improve Aβ31‐35‐induced abnormal expression of Bmal1 by inhibiting the activity of GSK3β, thus providing a novel idea for the treatment of AD.

Sex-Specific Linear Polyubiquitination Is a Critical Regulator of Contextual Fear Memory Formation

Strong evidence supports that protein ubiquitination is a critical regulator of fear memory formation. However, as this work has focused on protein degradation, it is currently unknown whether polyubiquitin modifications that are independent of the proteasome are involved in learning-dependent synaptic plasticity. Here, we present the first evidence that atypical linear (M1) polyubiquitination, the only ubiquitin chain that does not occur at a lysine site and is largely independent of the proteasome, is critically involved in contextual fear memory formation in the amygdala in a sex-specific manner. Using immunoblot and unbiased proteomic analyses, we found that male (49) and female (14) rats both had increased levels of linear polyubiquitinated substrates following fear conditioning, though none of these protein targets overlapped between sexes. In males, target protein functions involved cell junction and axonal guidance signaling, while in females the primary target was Adiponectin A, a critical regulator of neuroinflammation, synaptic plasticity, and memory, suggesting sex-dependent functional roles for linear polyubiquitination during fear memory formation. Consistent with these increases, in vivo siRNA-mediated knockdown of Rnf31, an essential component of the linear polyubiquitin E3 complex LUBAC, in the amygdala impaired contextual fear memory in both sexes without affecting memory retrieval. Collectively, these results provide the first evidence that proteasome-independent linear polyubiquitination is a critical regulator of fear memory formation, expanding the potential roles of ubiquitin-signaling in learning-dependent synaptic plasticity. Importantly, our data identify a novel sex difference in the functional role of, but not a requirement for, linear polyubiquitination in fear memory formation.

Adiponectin Modulation by Genotype and Maternal Choline Supplementation in a Mouse Model of Down Syndrome and Alzheimer's Disease

Down syndrome (DS) is a genetic disorder caused by the triplication of human chromosome 21, which results in neurological and physiological pathologies. These deficits increase during aging and are exacerbated by cognitive decline and increase of Alzheimer's disease (AD) neuropathology. A nontoxic, noninvasive treatment, maternal choline supplementation (MCS) attenuates cognitive decline in mouse models of DS and AD. To evaluate potential underlying mechanisms, laser capture microdissection of individual neuronal populations of MCS offspring was performed, followed by RNA sequencing and bioinformatic inquiry. Results at ~6 months of age (MO) revealed DS mice (the well-established Ts65Dn model) have significant dysregulation of select genes within the Type 2 Diabetes Mellitus (T2DM) signaling pathway relative to normal disomic (2N) littermates. Accordingly, we interrogated key T2DM protein hormones by ELISA assay in addition to gene and encoded protein levels in the brain. We found dysregulation of adiponectin (APN) protein levels in the frontal cortex of ~6 MO trisomic mice, which was attenuated by MCS. APN receptors also displayed expression level changes in response to MCS. APN is a potential biomarker for AD pathology and may be relevant in DS. We posit that changes in APN signaling may be an early marker of cognitive decline and neurodegeneration.

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.

Adiponectin-mimetic novel nonapeptide rescues aberrant neuronal metabolic-associated memory deficits in Alzheimer's disease

Background

Recently, we and other researchers reported that brain metabolic disorders are implicated in Alzheimer’s disease (AD), a progressive, devastating and incurable neurodegenerative disease. Hence, novel therapeutic approaches are urgently needed to explore potential and novel therapeutic targets/agents for the treatment of AD. The neuronal adiponectin receptor 1 (AdipoR1) is an emerging potential target for intervention in metabolic-associated AD. We aimed to validate this hypothesis and explore in-depth the therapeutic effects of an osmotin-derived adiponectin-mimetic novel nonapeptide (Os-pep) on metabolic-associated AD.

Methods

We used an Os-pep dosage regimen (5 μg/g, i.p., on alternating days for 45 days) for APP/PS1 in amyloid β oligomer-injected, transgenic adiponectin knockout (Adipo−/−) and AdipoR1 knockdown mice. After behavioral studies, brain tissues were subjected to biochemical and immunohistochemical analyses. In separate cohorts of mice, electrophysiolocal and Golgi staining experiments were performed. To validate the in vivo studies, we used human APP Swedish (swe)/Indiana (ind)-overexpressing neuroblastoma SH-SY5Y cells, which were subjected to knockdown of AdipoR1 and APMK with siRNAs, treated with Os-pep and other conditions as per the mechanistic approach, and we proceeded to perform further biochemical analyses.

Results

Our in vitro and in vivo results show that Os-pep has good safety and neuroprotection profiles and crosses the blood-brain barrier. We found reduced levels of neuronal AdipoR1 in human AD brain tissue. Os-pep stimulates AdipoR1 and its downstream target, AMP-activated protein kinase (AMPK) signaling, in AD and Adipo−/− mice. Mechanistically, in all of the in vivo and in vitro studies, Os-pep rescued aberrant neuronal metabolism by reducing neuronal insulin resistance and activated downstream insulin signaling through regulation of AdipoR1/AMPK signaling to consequently improve the memory functions of the AD and Adipo−/− mice, which was associated with improved synaptic function and long-term potentiation via an AdipoR1-dependent mechanism.

Conclusion

Our findings show that Os-pep activates AdipoR1/AMPK signaling and regulates neuronal insulin resistance and insulin signaling, which subsequently rescues memory deficits in AD and adiponectin-deficient models. Taken together, the results indicate that Os-pep, as an adiponectin-mimetic novel nonapeptide, is a valuable and promising potential therapeutic candidate to treat aberrant brain metabolism associated with AD and other neurodegenerative diseases.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13024-021-00445-4.

Adenosine monophosphate activated protein kinase (AMPK) is essential for the memory improving effect of adiponectin

Adiponectin (APN) plays a major role in the regulation of insulin sensitivity and glucose homeostasis. Insulin and APN have a positive effect on memory. In this study, we examined whether the inhibition of AMPK could block the memory improving effect of APN or affect the IRS1 expression. Animal model of AD was developed by intracerebroventricular (icv) injection of 3 mg/kg streptozotocin (STZ), in 12 weeks old Wistar rats, on days 1 and 3 after cannulation. Dorsomorphin (DM) and APN (600 nM) were injected 30 and 20 min before the acquisition phase, respectively. DM was applied in 3 different doses (0.2, 2 and 20 μM). All behavioral tests were performed on days 15 and 16; the Preference Index (PI) was calculated for novel object recognition (NOR) test, while the step through latency (STL) and total time in dark compartment (TDC) were recorded and analyzed for the passive avoidance task. Relative expression of insulin receptor substrate-1 (IRS-1) protein in the hippocampus was measured by western blotting. In early retrieval test, STZ + APN treatment increased STL (P < 0.0001) and decreased TDC (P < 0.05) in comparison to STZ group, while STZ + APN + DM (2μM) caused a decrease in STL (P < 0.05) and increase in TDC (0.2μM and 2μM DM; P < 0.05). Icv injection of DM (0.2μM and 2μM) before APN decreased the PI significantly (P < 0.05) in comparison to STZ + APN group. APN treatment raised the IRS-1 expression and DM reversed this increment, significantly (P < 0.0001). It is concluded that the memory improving effect of APN is mediated, at least in part, by the AMPK pathway. APN is also able to boost insulin signaling by overexpression of IRS-1 in the hippocampus.

Protective effects of intracerebroventricular adiponectin against olfactory impairments in an amyloid β1-42 rat model

BACKGROUND

Alzheimer's disease (AD) is characterized by cognitive impairment that eventually develops into dementia. Amyloid-beta (Aβ) accumulation is a widely described hallmark in AD, and has been reported to cause olfactory dysfunction, a condition considered an early marker of the disease associated with injuries in the olfactory bulb (OB), the hippocampus (HIPP) and other odor-related cortexes. Adiponectin (APN) is an adipokine with neuroprotective effects. Studies have demonstrated that APN administration decreases Aβ neurotoxicity and Tau hyperphosphorylation in the HIPP, reducing cognitive impairment. However, there are no studies regarding the neuroprotective effects of APN in the olfactory dysfunction observed in the Aβ rat model. The aim of the present study is to determine whether the intracerebroventricular (i.c.v) administration of APN prevents the early olfactory dysfunction in an i.c.v Amyloid-beta1-42 (Aβ1-42) rat model. Hence, we evaluated olfactory function by using a battery of olfactory tests aimed to assess olfactory memory, discrimination and detection in the Aβ rat model treated with APN. In addition, we determined the number of cells expressing the neuronal nuclei (NeuN), as well as the number of microglial cells by using the ionized calcium-binding adapter molecule 1 (Iba-1) marker in the OB and, CA1, CA3, hilus and dentate gyrus (DG) in the HIPP. Finally, we determined Arginase-1 expression in both nuclei through Western blot.

RESULTS

We observed that the i.c.v injection of Aβ decreased olfactory function, which was prevented by the i.c.v administration of APN. In accordance with the olfactory impairment observed in i.c.v Aβ-treated rats, we observed a decrease in NeuN expressing cells in the glomerular layer of the OB, which was also prevented with the i.c.v APN. Furthermore, we observed an increase of Iba-1 cells in CA1, and DG in the HIPP of the Aβ rats, which was prevented by the APN treatment.

CONCLUSION

The present study describes the olfactory impairment of Aβ treated rats and evidences the protective role that APN plays in the brain, by preventing the olfactory impairment induced by Aβ1-42. These results may lead to APN-based pharmacological therapies aimed to ameliorate AD neurotoxic effects.

Energy sensors in drug addiction: A potential therapeutic target

Addiction is defined as the repeated exposure and compulsive seek of psychotropic drugs that, despite the harmful effects, generate relapse after the abstinence period. The psychophysiological processes associated with drug addiction (acquisition/expression, withdrawal, and relapse) imply important alterations in neurotransmission and changes in presynaptic and postsynaptic plasticity and cellular structure (neuroadaptations) in neurons of the reward circuits (dopaminergic neuronal activity) and other corticolimbic regions. These neuroadaptation mechanisms imply important changes in neuronal energy balance and protein synthesis machinery. Scientific literature links drug-induced stimulation of dopaminergic and glutamatergic pathways along with presence of neurotrophic factors with alterations in synaptic plasticity and membrane excitability driven by metabolic sensors. Here, we provide current knowledge of the role of molecular targets that constitute true metabolic/energy sensors such as AMPK, mTOR, ERK, or K_ATP in the development of the different phases of addiction standing out the main brain regions (ventral tegmental area, nucleus accumbens, hippocampus, and amygdala) constituting the hubs in the development of addiction. Because the available treatments show very limited effectiveness, evaluating the drug efficacy of AMPK and mTOR specific modulators opens up the possibility of testing novel pharmacotherapies for an individualized approach in drug abuse.

Diabetes, stroke, and neuroresilience: looking beyond hyperglycemia

Ischemic stroke is a leading cause of morbidity and mortality among type 2 diabetic patients. Preclinical and translational studies have identified critical pathophysiological mediators of stroke risk, recurrence, and poor outcome in diabetic patients, including endothelial dysfunction and inflammation. Most clinical trials of diabetes and stroke have focused on treating hyperglycemia alone. Pioglitazone has shown promise in secondary stroke prevention for insulin-resistant patients; however, its use is not yet widespread. Additional research into clinical therapies directed at diabetic pathophysiological processes to prevent stroke and improve outcome for diabetic stroke survivors is necessary. Resilience is the process of active adaptation to a stressor. In patients with diabetes, stroke recovery is impaired by insulin resistance, endothelial dysfunction, and inflammation, which impair key neuroresilience pathways maintaining cerebrovascular integrity, resolving poststroke inflammation, stimulating neural plasticity, and preventing neurodegeneration. Our review summarizes the underpinnings of stroke risk in diabetes, the clinical consequences of stroke in diabetic patients, and proposes hypotheses and new avenues of research for therapeutics to stimulate neuroresilience pathways and improve stroke outcome in diabetic patients.

AdipoRon Treatment Induces a Dose-Dependent Response in Adult Hippocampal Neurogenesis

AdipoRon, an adiponectin receptor agonist, elicits similar antidiabetic, anti-atherogenic, and anti-inflammatory effects on mouse models as adiponectin does. Since AdipoRon can cross the blood-brain barrier, its chronic effects on regulating hippocampal function are yet to be examined. This study investigated whether AdipoRon treatment promotes hippocampal neurogenesis and spatial recognition memory in a dose-dependent manner. Adolescent male C57BL/6J mice received continuous treatment of either 20 mg/kg (low dose) or 50 mg/kg (high dose) AdipoRon or vehicle intraperitoneally for 14 days, followed by the open field test to examine anxiety and locomotor activity, and the Y maze test to examine hippocampal-dependent spatial recognition memory. Immunopositive cell markers of neural progenitor cells, immature neurons, and newborn cells in the hippocampal dentate gyrus were quantified. Immunosorbent assays were used to measure the serum levels of factors that can regulate hippocampal neurogenesis, including adiponectin, brain-derived neurotrophic factor (BDNF), and corticosterone. Our results showed that 20 mg/kg AdipoRon treatment significantly promoted hippocampal cell proliferation and increased serum levels of adiponectin and BDNF, though there were no effects on spatial recognition memory and locomotor activity. On the contrary, 50 mg/kg AdipoRon treatment impaired spatial recognition memory, suppressed cell proliferation, neuronal differentiation, and cell survival associated with reduced serum levels of BDNF and adiponectin. The results suggest that a low-dose AdipoRon treatment promotes hippocampal cell proliferation, while a high-dose AdipoRon treatment is detrimental to the hippocampus function.

Exploring the New Horizon of AdipoQ in Obesity-Related Alzheimer's Dementia

Alzheimer's disease (AD) is the most common form of dementia, which causes abnormalities in learning, thinking, memory, as well as behavior. Generally, symptoms of AD develop gradually and aggravate over time, and consequently severely interfere with daily activities. Furthermore, obesity is one of the common risk factors for dementia. Dysregulation of adipokine and adipocyte dysfunction are assumed to be accountable for the high risk of obesity in people that develop many related disorders such as AD. Moreover, it has been observed that the dysfunction of adipose is connected with changes in brain metabolism, brain atrophy, cognitive decline, impaired mood, neuroinflammation, impaired insulin signaling, and neuronal dysfunction in people with obesity. Conversely, the pathological mechanisms, as well as the molecular players which are involved in this association, have been unclear until now. In this article, we discuss the impact of adiponectin (AdipoQ) on obesity-related Alzheimer's dementia.

From Obesity to Hippocampal Neurodegeneration: Pathogenesis and Non-Pharmacological Interventions

High-caloric diet and physical inactivity predispose individuals to obesity and diabetes, which are risk factors of hippocampal neurodegeneration and cognitive deficits. Along with the adipose-hippocampus crosstalk, chronically inflamed adipose tissue secretes inflammatory cytokine could trigger neuroinflammatory responses in the hippocampus, and in turn, impairs hippocampal neuroplasticity under obese and diabetic conditions. Hence, caloric restriction and physical exercise are critical non-pharmacological interventions to halt the pathogenesis from obesity to hippocampal neurodegeneration. In response to physical exercise, peripheral organs, including the adipose tissue, skeletal muscles, and liver, can secret numerous exerkines, which bring beneficial effects to metabolic and brain health. In this review, we summarized how chronic inflammation in adipose tissue could trigger neuroinflammation and hippocampal impairment, which potentially contribute to cognitive deficits in obese and diabetic conditions. We also discussed the potential mechanisms underlying the neurotrophic and neuroprotective effects of caloric restriction and physical exercise by counteracting neuroinflammation, plasticity deficits, and cognitive impairments. This review provides timely insights into how chronic metabolic disorders, like obesity, could impair brain health and cognitive functions in later life.

Adiponectin: The Potential Regulator and Therapeutic Target of Obesity and Alzheimer's Disease

Animal and human mechanistic studies have consistently shown an association between obesity and Alzheimer's disease (AD). AD, a degenerative brain disease, is the most common cause of dementia and is characterized by the presence of extracellular amyloid beta (Aβ) plaques and intracellular neurofibrillary tangles disposition. Some studies have recently demonstrated that Aβ and tau cannot fully explain the pathophysiological development of AD and that metabolic disease factors, such as insulin, adiponectin, and antioxidants, are important for the sporadic onset of nongenetic AD. Obesity prevention and treatment can be an efficacious and safe approach to AD prevention. Adiponectin is a benign adipokine that sensitizes the insulin receptor signaling pathway and suppresses inflammation. It has been shown to be inversely correlated with adipose tissue dysfunction and may enhance the risk of AD because a range of neuroprotection adiponectin mechanisms is related to AD pathology alleviation. In this study, we summarize the recent progress that addresses the beneficial effects and potential mechanisms of adiponectin in AD. Furthermore, we review recent studies on the diverse medications of adiponectin that could possibly be related to AD treatment, with a focus on their association with adiponectin. A better understanding of the neuroprotection roles of adiponectin will help clarify the precise underlying mechanism of AD development and progression.

Brain energy rescue: an emerging therapeutic concept for neurodegenerative disorders of ageing

The brain requires a continuous supply of energy in the form of ATP, most of which is produced from glucose by oxidative phosphorylation in mitochondria, complemented by aerobic glycolysis in the cytoplasm. When glucose levels are limited, ketone bodies generated in the liver and lactate derived from exercising skeletal muscle can also become important energy substrates for the brain. In neurodegenerative disorders of ageing, brain glucose metabolism deteriorates in a progressive, region-specific and disease-specific manner - a problem that is best characterized in Alzheimer disease, where it begins presymptomatically. This Review discusses the status and prospects of therapeutic strategies for countering neurodegenerative disorders of ageing by improving, preserving or rescuing brain energetics. The approaches described include restoring oxidative phosphorylation and glycolysis, increasing insulin sensitivity, correcting mitochondrial dysfunction, ketone-based interventions, acting via hormones that modulate cerebral energetics, RNA therapeutics and complementary multimodal lifestyle changes.

Insulin deficiency, but not resistance, exaggerates cognitive deficits in transgenic mice expressing human amyloid and tau proteins. Reversal by Exendin-4 treatment

Epidemiological studies have pointed at diabetes as a risk factor for Alzheimer's disease (AD) and this has been supported by several studies in animal models of both type 1 and type 2 diabetes. However, side-by-side comparison of the two types of diabetes is limited. We investigated the role of insulin deficiency and insulin resistance in the development of memory impairments and the effect of Exendin-4 (Ex4) treatment in a mouse model of AD. Three-4-month-old female wild type (WT) mice and mice overexpressing human tau and amyloid precursor protein (TAPP) were injected with streptozotocin (STZ) or fed a high-fat diet (HFD). A second study was performed in TAPP-STZ mice treated with Ex4, a long-lasting analog of GLP-1. Plasma and brain were collected at study termination for ELISA, Western blot, and immunohistochemistry analysis. Learning and memory deficits were impaired in TAPP transgenic mice compared with WT mice at the end of the study. Deficits were exaggerated by insulin deficiency in TAPP mice but 12 weeks of insulin resistance did not affect memory performances in either WT or TAPP mice. Levels of phosphorylated tau were increased in the brain of WT-STZ and TAPP-STZ mice but not in the brain of WT or TAPP mice on HFD. In the TAPP-STZ mice, treatment with Ex4 initiated after established cognitive deficits ameliorated learning, but not memory, impairments. This was accompanied by the reduction of amyloid β and phosphorylated tau expression. Theses studies support the role of Ex4 in AD, independently from its actions on diabetes.

Altered Brain Adiponectin Receptor Expression in the 5XFAD Mouse Model of Alzheimer's Disease

Metabolic syndromes share common pathologies with Alzheimer's disease (AD). Adiponectin, an adipocyte-derived protein, regulates energy metabolism via its receptors, AdipoR1 and AdipoR2. To investigate the distribution of adiponectin receptors (AdipoRs) in Alzheimer's, we examined their expression in the aged 5XFAD mouse model of AD. In age-matched wild-type mice, we observed neuronal expression of both ARs throughout the brain as well as endothelial expression of AdipoR1. The pattern of receptor expression in the aged 5XFAD brain was significantly perturbed. Here, we observed decreased neuronal expression of both ARs and decreased endothelial expression of AdipoR1, but robust expression of AdipoR2 in activated astrocytes. We also observed AdipoR2-expressing astrocytes in the dorsomedial hypothalamic and thalamic mediodorsal nuclei, suggesting the possibility that astrocytes utilise AdipoR2 signalling to fuel their activated state in the AD brain. These findings provide further evidence of a metabolic disturbance and demonstrate a potential shift in energy utilisation in the AD brain, supporting imaging studies performed in AD patients.

Genistein inhibits high fat diet-induced obesity through miR-222 by targeting BTG2 and adipor1

Obesity and diabetes mellitus have become major health problems worldwide. In recent years, genistein has been found to be capable of inhibiting obesity and alleviating insulin resistance. However, the molecular mechanism of genistein against obesity is still not fully understood. In this study, we used 3T3-L1 preadipocytes and obese mice as models to explore the molecular mechanism of genistein against obesity. We found that genistein can inhibit obesity and downregulate the expression of miR-222 in mouse adipose tissue. In 3T3-L1 preadipocytes, treatment with miR-222 inhibitor or genistein reduced the expression of miR-222 and promoted lipid decomposition, while miR-222 treatment increased the expression of miR-222 and inhibited lipolysis. Moreover, the dual-luciferase reporter assay system confirmed that BTG2 and adipor1 are the target genes of miR-222. Experiments conducted in vitro and in vivo suggest that genistein may regulate lipid metabolism in the adipose tissue of obese mice by regulating the expression of miR-222 and its target genes, BTG2 and adipor1. Our findings provide a new epigenetic mechanism underpinning the ability of genistein to resist obesity. These results may provide a reference point for the dietary treatment of obesity and type 2 diabetes mellitus.

Metabolic Stress Alters Antioxidant Systems, Suppresses the Adiponectin Receptor 1 and Induces Alzheimer's Like Pathology in Mice Brain

Oxidative stress and insulin resistance play major roles in numerous neurodegenerative diseases, including Alzheimer’s disease (AD). A high-fat diet induces obesity-associated oxidative stress, neuronal insulin resistance, microglial activation, and neuroinflammation, which are considered important risk factors for neurodegeneration. Obesity-related metabolic dysfunction is a risk factor for cognitive decline. The present study aimed to elucidate whether chronic consumption of a high-fat diet (HFD; 24 weeks) can induce insulin resistance, neuroinflammation, and amyloid beta (Aβ) deposition in mouse brains. Male C57BL/6N mice were used for a high-fat diet (HFD)-induced pre-clinical model of obesity. The protein expression levels were examined via Western blot, immunofluorescence, and the behavior analysis was performed using the Morris water maze test. To obtain metabolic parameters, insulin sensitivity and glucose tolerance tests were performed. We found that metabolic perturbations from the chronic consumption of HFD elevated neuronal oxidative stress and insulin resistance through adiponectin receptor (AdipoR1) suppression in HFD-fed mice. Similarly, our in vitro results also indicated that knockdown of AdipoR1 in the embryonic mouse hippocampal cell line mHippoE-14 leads to increased oxidative stress in neurons. In addition, HFD markedly increased neuroinflammatory markers’ glial activation in the cortex and hippocampus regions of HFD mouse brains. More importantly, we observed that AdipoR1 suppression increased the amyloidogenic pathway both in vivo and in vitro. Furthermore, deregulated synaptic proteins and behavioral deficits were observed in the HFD mouse brains. Taken together, our findings suggest that excessive consumption of an HFD has a profound impact on brain function, which involves the acceleration of cognitive impairment due to increased obesity-associated oxidative stress, insulin resistance, and neuroinflammation, which ultimately may cause early onset of Alzheimer’s pathology via the suppression of AdipoR1 signaling in the brain.

The Novel Perspectives of Adipokines on Brain Health

First seen as a fat-storage tissue, the adipose tissue is considered as a critical player in the endocrine system. Precisely, adipose tissue can produce an array of bioactive factors, including cytokines, lipids, and extracellular vesicles, which target various systemic organ systems to regulate metabolism, homeostasis, and immune response. The global effects of adipokines on metabolic events are well defined, but their impacts on brain function and pathology remain poorly defined. Receptors of adipokines are widely expressed in the brain. Mounting evidence has shown that leptin and adiponectin can cross the blood–brain barrier, while evidence for newly identified adipokines is limited. Significantly, adipocyte secretion is liable to nutritional and metabolic states, where defective circuitry, impaired neuroplasticity, and elevated neuroinflammation are symptomatic. Essentially, neurotrophic and anti-inflammatory properties of adipokines underlie their neuroprotective roles in neurodegenerative diseases. Besides, adipocyte-secreted lipids in the bloodstream can act endocrine on the distant organs. In this article, we have reviewed five adipokines (leptin, adiponectin, chemerin, apelin, visfatin) and two lipokines (palmitoleic acid and lysophosphatidic acid) on their roles involving in eating behavior, neurotrophic and neuroprotective factors in the brain. Understanding and regulating these adipokines can lead to novel therapeutic strategies to counteract metabolic associated eating disorders and neurodegenerative diseases, thus promote brain health.

A novel kit for early diagnosis of Alzheimer's disease using a fluorescent nanoparticle imaging

Alzheimer's disease (AD) is a progressive neurodegenerative disease and chronic illness with long preclinical phases and a long clinical duration. Until recently, a lack of potential therapeutic agents against AD was the primary focus of research, which resulted in less effort directed towards developing useful diagnostic approaches. In this study, we developed a WO2002/088706 kit that is composed of fluorescent nanoparticles for the early detection of AD. We provided a fluorescent nanoparticle for detecting markers and a kit for the early diagnosis of AD. The kit consists of a probe molecule comprising an oligonucleotide capable of detecting one or more AD-specific microRNAs (miRNAs) and biomarkers related to AD. Through screening, we selected miR-106b, miR-146b, miR-181a, miR-200a, miR-34a, miR-124b, miR-153, miR-155, Aβ_1-42 monomer (mAβ), Aβ_1-42 oligomer (oAβ), UCHL1, NLRP3, Tau, STAT3, SORL1, Clusterin, APOE3, APOE4, Nogo-A, IL-13, and Visfatin to serve as AD- and inflammation-related markers. For detection of kit-binding properties, we checked the expression levels of amyloid beta (Aβ), tau protein, and inflammatory mediators in APP/PS/ApoE knockdown (KD) mice and a control group using co-localisation analysis conducted with a confocal microscope. Using a similar approach, we checked the expression levels of miRNAs in HT22 cells. Finally, we used the plasma from AD patients to confirm that our fluorescent nanoparticles and the WO2002/088706 kit will provide a possible early diagnosis to serve as an AD detector that can be further improved for future studies on targeting AD.

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.

Adiponectin Knockout Mice Display Cognitive and Synaptic Deficits

Adiponectin is an adipokine that has recently been under investigation for potential neuroprotective effects in various brain disorders including Alzheimer's disease, stroke, and depression. Adiponectin receptors (AdipoR1 and AdipoR2) are found throughout various brain regions, including the hippocampus. However, the role of these receptors in synaptic and cognitive function is not clear. Therefore, the goal of the current study was to evaluate synaptic and cognitive function in the absence of adiponectin. The current study utilized 12-month-old adiponectin knockout (APN-KO) mice and age-matched controls to study cognitive and hippocampal synaptic alterations. We determined that AdipoR1 and AdipoR2 are present in the synaptosome, with AdipoR2 displaying increased presynaptic vs. postsynaptic localization, whereas AdipoR1 was enriched in both the presynaptic and postsynaptic fractions. APN-KO mice displayed cognitive deficits in the novel object recognition (NOR) and Y-maze tests. This was mirrored by deficits in long-term potentiation (LTP) of the hippocampal Schaefer collateral pathway in APN-KO mice. APN-KO mice also displayed a reduction in basal synaptic transmission and an increase in presynaptic release probability. Deficits in LTP were rescued through hippocampal slice incubation with the adiponectin receptor agonist, AdipoRon, indicating that acute alterations in adiponectin receptor signaling influence synaptic function. Along with the deficits in LTP, altered levels of key presynaptic and postsynaptic proteins involved in glutamatergic neurotransmission were observed in APN-KO mice. Taken together, these results indicate that adiponectin is an important regulator of cognition and synaptic function in the hippocampus. Future studies should examine the role of specific adiponectin receptors in synaptic processes.

Gintonin Mitigates MPTP-Induced Loss of Nigrostriatal Dopaminergic Neurons and Accumulation of α-Synuclein via the Nrf2/HO-1 Pathway

Gintonin, a ginseng-derived glycolipoprotein isolated from ginseng, has been shown to be neuroprotective in several neurological disorders such as Alzheimer's disease models and depressive-like behaviors. In this study, we sought to investigate the potential protective mechanisms of gintonin in an in vivo MPTP and in vitro MPP+-mediated Parkinson's disease (PD) model. We hypothesized that activation of nuclear factor erythroid 2-related factor 2/heme oxygenase-1 (Nrf2/HO-1, potential therapeutic targets for neurodegeneration) with gintonin could abrogate PD-associated neurotoxicity by modulating the accumulation of α-synuclein, neuroinflammation, and apoptotic cell death in an MPTP/MPP+ models of PD. Our in vivo and in vitro findings suggest that the neuroprotective effects of gintonin were associated with the regulation of the Nrf2/HO-1 pathway, which regulated the expression of proinflammatory cytokines and nitric oxide synthase and apoptotic markers in the substantia nigra and striatum of the mice. Moreover, the neuroprotective effects of gintonin were also associated with a reduction in α-synuclein accumulation in the mouse substantia nigra and striatum. The neuroprotective effects of gintonin were further validated by analyzing the effects of gintonin on MPP+-treated SH-SY5Y cells, which confirmed the protective effects of gintonin. It remains for future basic and clinical research to determine the potential use of gintonin in Parkinson's disease. However, to the best of our knowledge, marked alterations in biochemical and morphological setup of midbrain dopaminergic pathways by gintonin in MPTP mice model have not been previously reported. We believe that gintonin might be explored as an important therapeutic agent in the treatment of PD.

Lipid metabolism in Alzheimer's disease

Since the metabolic disorder may be the high risk that contribute to the progress of Alzheimer's disease (AD). Overtaken of High-fat, high-glucose or high-cholesterol diet may hasten the incidence of AD in later life, due to the metabolic dysfunction. But the metabolism of lipid in brain and the exact effect of lipid to brain or to the AD's pathological remain controversial. Here we summarize correlates of lipid metabolism and AD to provide more foundation for the daily nursing of AD sensitive patients.

Next-generation biomarker discovery in Alzheimer's disease using metabolomics - from animal to human studies

Alzheimer's disease (AD) is a complex disease driven mainly by neuronal loss due to accumulation of intracellular neurofibrillary tangles and amyloid β aggregates in the brain. The diagnosis of AD currently relies on clinical symptoms while the disease can only be confirmed at autopsy. The few available biomarkers allowing for diagnosis are typically detected many years after the onset of the disease. New diagnostic approaches, particularly in easily-accessible biofluids, are essential. By providing an exhaustive information of the phenotype, metabolomics is an ideal approach for identification of new biomarkers. This review investigates the current position of metabolomics in the field of AD research, focusing on animal and human studies, and discusses the improvements carried out over the past decade.

Role of Adiponectin in Central Nervous System Disorders

Adiponectin, the most abundant plasma adipokine, plays an important role in the regulation of glucose and lipid metabolism. Adiponectin also possesses insulin-sensitizing, anti-inflammatory, angiogenic, and vasodilatory properties which may influence central nervous system (CNS) disorders. Although initially not thought to cross the blood-brain barrier, adiponectin enters the brain through peripheral circulation. In the brain, adiponectin signaling through its receptors, AdipoR1 and AdipoR2, directly influences important brain functions such as energy homeostasis, hippocampal neurogenesis, and synaptic plasticity. Overall, based on its central and peripheral actions, recent evidence indicates that adiponectin has neuroprotective, antiatherogenic, and antidepressant effects. However, these findings are not without controversy as human observational studies report differing correlations between plasma adiponectin levels and incidence of CNS disorders. Despite these controversies, adiponectin is gaining attention as a potential therapeutic target for diverse CNS disorders, such as stroke, Alzheimer's disease, anxiety, and depression. Evidence regarding the emerging role for adiponectin in these disorders is discussed in the current review.