Adiponectin and sporadic Alzheimer's disease: Clinical and molecular links

Correlation between Alzheimer's Disease and Gastrointestinal Tract Disorders

Alzheimer's disease is the most common cause of dementia globally. The pathogenesis is multifactorial and includes deposition of amyloid-β in the central nervous system, presence of intraneuronal neurofibrillary tangles and a decreased amount of synapses. It remains uncertain what causes the progression of the disease. Nowadays, it is suggested that the brain is connected to the gastrointestinal tract, especially the enteric nervous system and gut microbiome. Studies have found a positive association between AD and gastrointestinal diseases such as periodontitis, Helicobacter pylori infection, inflammatory bowel disease and microbiome disorders. H. pylori and its metabolites can enter the CNS via the oropharyngeal olfactory pathway and may predispose to the onset and progression of AD. Periodontitis may cause systemic inflammation of low severity with high levels of pro-inflammatory cytokines and neutrophils. Moreover, lipopolysaccharide from oral bacteria accompanies beta-amyloid in plaques that form in the brain. Increased intestinal permeability in IBS leads to neuronal inflammation from transference. Chronic inflammation may lead to beta-amyloid plaque formation in the intestinal tract that spreads to the brain via the vagus nerve. The microbiome plays an important role in many bodily functions, such as nutrient absorption and vitamin production, but it is also an important factor in the development of many diseases, including Alzheimer's disease. Both the quantity and diversity of the microbiome change significantly in patients with AD and even in people in the preclinical stage of the disease, when symptoms are not yet present. The microbiome influences the functioning of the central nervous system through, among other things, the microbiota-gut-brain axis. Given the involvement of the microbiome in the pathogenesis of AD, antibiotic therapy, probiotics and prebiotics, and faecal transplantation are being considered as possible therapeutic options.

[On the road to biological blood diagnosis of Alzheimer's disease?]

The growing number of people suffering from Alzheimer's disease (AD) represents a major public health problem. The diagnosis of AD is multidisciplinary and involves the use of amyloid and tau biomarkers measured in cerebrospinal fluid. Recent advances in analytical techniques now allow us to measure these biomarkers in blood. Blood biomarkers offer particularly promising potential for early, minimally invasive detection of AD, as well as for differential diagnosis of dementia and patient follow-up. The aim of this review is to provide an overview of current and candidate blood biomarkers for AD, their informative value, and their potential to be integrated into clinical practice in the near future.

The complex relationship between obesity and neurodegenerative diseases: an updated review

Obesity is a global epidemic, affecting roughly 30% of the world's population and predicted to rise. This disease results from genetic, behavioral, societal, and environmental factors, leading to excessive fat accumulation, due to insufficient energy expenditure. The adipose tissue, once seen as a simple storage depot, is now recognized as a complex organ with various functions, including hormone regulation and modulation of metabolism, inflammation, and homeostasis. Obesity is associated with a low-grade inflammatory state and has been linked to neurodegenerative diseases like multiple sclerosis (MS), Alzheimer's (AD), and Parkinson's (PD). Mechanistically, reduced adipose expandability leads to hypertrophic adipocytes, triggering inflammation, insulin and leptin resistance, blood-brain barrier disruption, altered brain metabolism, neuronal inflammation, brain atrophy, and cognitive decline. Obesity impacts neurodegenerative disorders through shared underlying mechanisms, underscoring its potential as a modifiable risk factor for these diseases. Nevertheless, further research is needed to fully grasp the intricate connections between obesity and neurodegeneration. Collaborative efforts in this field hold promise for innovative strategies to address this complex relationship and develop effective prevention and treatment methods, which also includes specific diets and physical activities, ultimately improving quality of life and health.

Goldfish adiponectin: (I) molecular cloning, tissue distribution, recombinant protein expression, and novel function as a satiety factor in fish model

Adiponectin (AdipoQ) is an adipokine involved in glucose homeostasis and lipid metabolism. In mammals, its role in appetite control is highly controversial. To shed light on the comparative aspects of AdipoQ in lower vertebrates, goldfish was used as a model to study feeding regulation by AdipoQ in fish species. As a first step, goldfish AdipoQ was cloned and found to be ubiquitously expressed at the tissue level. Using sequence alignment, protein modeling, phylogenetic analysis and comparative synteny, goldfish AdipoQ was shown to be evolutionarily related to its fish counterparts and structurally comparable with AdipoQ in higher vertebrates. In our study, recombinant goldfish AdipoQ was expressed in E. coli, purified by IMAC, and confirmed to be bioactive via activation of AdipoQ receptors expressed in HepG2 cells. Feeding in goldfish revealed that plasma levels of AdipoQ and its transcript expression in the liver and brain areas involved in appetite control including the telencephalon, optic tectum, and hypothalamus could be elevated by food intake. In parallel studies, IP and ICV injection of recombinant goldfish AdipoQ in goldfish was effective in reducing foraging behaviors and food consumption. Meanwhile, transcript expression of orexigenic factors (NPY, AgRP, orexin, and apelin) was suppressed with parallel rises in anorexigenic factors (POMC, CART, CCK, and MCH) in the telencephalon, optic tectum and/or hypothalamus. In these brain areas, transcript signals for leptin receptor were upregulated with concurrent drops in the NPY receptor and ghrelin receptors. In the experiment with IP injection of AdipoQ, transcript expression of leptin was also elevated with a parallel drop in ghrelin mRNA in the liver. These findings suggest that AdipoQ can act as a novel satiety factor in goldfish. In this case, AdipoQ signals (both central and peripheral) can be induced by feeding and act within the brain to inhibit feeding behaviors and food intake via differential regulation of orexigenic/anorexigenic factors and their receptors. The feeding inhibition observed may also involve the hepatic action of AdipoQ by modulation of feeding regulators expressed in the liver.

Potential Protective Function of Adiponectin in Diabetic Retinopathy

Adiponectin, one of the most ubiquitous adipokines found in the blood, plays a major role in glucolipid metabolism and energy metabolism and regulation. In recent years, a growing body of research indicates that adiponectin also plays a significant role in diabetic retinopathy. In the present review, we specifically address the protective effects of adiponectin on the development and progression of diabetic retinopathy through improvement in insulin resistance, alleviation of oxidative stress, limiting of inflammation, and prevention of vascular remodeling, with the aim to explore new potential approaches and targets for the prevention and treatment of diabetic retinopathy.

Overview of the blood biomarkers in Alzheimer's disease: Promises and challenges

The increasing number of people with advanced Alzheimer's disease (AD) represents a significant psychological and financial cost to the world population. Accurate detection of the earliest phase of preclinical AD is of major importance for the success of preventive and therapeutic strategies (Cullen et al., 2021). Advances in analytical techniques have been essential for the development of sensitive, specific and reliable diagnostic tests for AD biomarkers in biological fluids (cerebrospinal fluid and blood). Blood biomarkers hold promising potential for early and minimally invasive detection of AD, but also for differential diagnosis of dementia and for monitoring the course of the disease. The aim of this review is to provide an overview of current blood biomarkers of AD, from tau proteins and amyloid peptides to biomarkers of neuronal degeneration and inflammation, reactive and metabolic factors. We thus discuss the informative value of currently candidate blood biomarkers and their potential to be integrated into clinical practice for the management of AD in the near future.

Relationship between the therapeutic potential of various plant-derived bioactive compounds and their related microRNAs in neurological disorders

BACKGROUND

Neurological disorders, such as ischemic stroke, spinal cord injury, neurodegenerative diseases, and glioblastoma often lead to long-term disability and death. MicroRNAs (miRNAs) are small single-stranded non-coding RNAs of approximately 22 nucleotides, known to participate in both normal and pathological development, making them ideal therapeutic targets for clinical intervention. Several recent studies have suggested that plant-derived bioactive compounds (PDBCs) can have anti-atherosclerosis, antioxidant, and anti-inflammatory effects by regulating miRNAs. Thus, miRNAs are novel targets for the action of PDBCs.

PURPOSE

The aim of this review was to evaluate the current status of PDBCs targeted miRNAs by dissecting their development status through a literature review.

METHODS

A manual and electronic search was performed for English articles available from inception up to June 2022 reporting PDBCs and their regulating relationship with miRNAs for the therapeutic potential of neurological disorders. Information was retrieved from scientific databases including PubMed, ScienceDirect, Web of Science, Google Scholar and Chemical Abstracts Services. Keywords used for the search engines were "miRNAs" AND "Plant-derived bioactive compounds" in conjunction with "(native weeds OR alien invasive)" AND "traditional herbal medicine".

RESULTS

A total of 37 articles were retrieved on PDBCs and their related miRNAs in neurological disorders. These PDBCs from traditional herbal medicine may play a therapeutic role in neurological disorders in a variety of mechanisms by regulating the corresponding miRNAs. These mechanisms mainly include inhibiting oxidative stress, anti-neuroinflammation, anti-autophagy, and anti-apoptosis. PDBC are a group of chemically distinct compounds derived from medicinal plants, some of which have therapeutic effects on neurological disorders.

CONCLUSION

The emergence of miRNAs as pathological regulatory factors provides a new direction for the study of bioactive compounds in Traditional Chinese medicine and the elucidating of their epigenetic effects. Elucidating the regulatory relationship between bioactive compounds and miRNAs may help to identify new therapeutic targets and promoting the application of these compounds in precision medicine through their targeted molecular activity.

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.

Bidirectional communication between brain and visceral white adipose tissue: Its potential impact on Alzheimer's disease

A variety of axes between brain and abdominal organs have been reported, but the interaction between brain and visceral white adipose tissue (vWAT) remains unclear. In this review, we summarized human studies on the association between brain and vWAT, and generalized their interaction and the underlying mechanisms according to animal and cell experiments. On that basis, we come up with the concept of the brain-vWAT axis (BVA). Furthermore, we analyzed the potential mechanisms of involvement of BVA in the pathogenesis of Alzheimer's disease (AD), including vWAT-derived fatty acids, immunological properties of vWAT, vWAT-derived retinoic acid and vWAT-regulated insulin resistance. The proposal of BVA may expand our understanding to some extent of how the vWAT impacts on brain health and diseases, and provide a novel approach to study the pathogenesis and treatment strategies of neurodegenerative disorders.

Adiponectin/AdiopR1 signaling prevents mitochondrial dysfunction and oxidative injury after traumatic brain injury in a SIRT3 dependent manner

Mitochondrial dysfunction and oxidative injury, which contribute to worsening of neurological deficits and poor clinical outcomes, are hallmarks of secondary brain injury after TBI. Adiponectin (APN), beyond its well-established regulatory effects on metabolism, is also essential for maintaining normal brain functions by binding APN receptors that are ubiquitously expressed in the brain. Currently, the significance of the APN/APN receptor (AdipoR) signaling pathway in secondary injury after TBI and the specific mechanisms have not been conclusively determined. In this study, we found that APN knockout aggravated brain functional deficits, increased brain edema and lesion volume, and exacerbated oxidative stress as well as apoptosis after TBI. These effects were significantly alleviated after APN receptor agonist (AdipoRon) treatment. Moreover, we found that AdipoR1, rather than AdipoR2, mediated the protective effects of APN/AdipoR signaling against oxidative stress and brain injury after TBI. In neuron-specific AdipoR1 knockout mice, mitochondrial damage was more severe after TBI, indicating a potential association between APN/AdipoR1 signaling inactivation and mitochondrial damage. Mechanistically, neuron-specific knockout of SIRT3, the most important deacetylase in the mitochondria, reversed the neuroprotective effects of AdipoRon after TBI. Then, PRDX3, a critical antioxidant enzyme in the mitochondria, was identified as a vital downstream target of the APN/SIRT3 axis to alleviate oxidative injury after TBI. Finally, we revealed that APN/AdipoR1 signaling promotes SIRT3 transcription by activating the AMPK-PGC pathway. In conclusion, APN/AdipoR1 signaling plays a protective role in post-TBI oxidative damage by restoring the SIRT3-mediated mitochondrial homeostasis and antioxidant system.

Integrative metabolomics-genomics approach reveals key metabolic pathways and regulators of Alzheimer's disease

Metabolites, the biochemical products of the cellular process, can be used to measure alterations in biochemical pathways related to the pathogenesis of Alzheimer's disease (AD). However, the relationships between systemic abnormalities in metabolism and the pathogenesis of AD are poorly understood. In this study, we aim to identify AD-specific metabolomic changes and their potential upstream genetic and transcriptional regulators through an integrative systems biology framework for analyzing genetic, transcriptomic, metabolomic, and proteomic data in AD. Metabolite co-expression network analysis of the blood metabolomic data in the Alzheimer's Disease Neuroimaging Initiative (ADNI) shows short-chain acylcarnitines/amino acids and medium/long-chain acylcarnitines are most associated with AD clinical outcomes, including episodic memory scores and disease severity. Integration of the gene expression data in both the blood from the ADNI and the brain from the Accelerating Medicines Partnership Alzheimer's Disease (AMP-AD) program reveals ABCA1 and CPT1A are involved in the regulation of acylcarnitines and amino acids in AD. Gene co-expression network analysis of the AMP-AD brain RNA-seq data suggests the CPT1A- and ABCA1-centered subnetworks are associated with neuronal system and immune response, respectively. Increased ABCA1 gene expression and adiponectin protein, a regulator of ABCA1, correspond to decreased short-chain acylcarnitines and amines in AD in the ADNI. In summary, our integrated analysis of large-scale multiomics data in AD systematically identifies novel metabolites and their potential regulators in AD and the findings pave a way for not only developing sensitive and specific diagnostic biomarkers for AD but also identifying novel molecular mechanisms of AD pathogenesis.

Role of Cholinergic Signaling in Alzheimer's Disease

Acetylcholine, a neurotransmitter secreted by cholinergic neurons, is involved in signal transduction related to memory and learning ability. Alzheimer’s disease (AD), a progressive and commonly diagnosed neurodegenerative disease, is characterized by memory and cognitive decline and behavioral disorders. The pathogenesis of AD is complex and remains unclear, being affected by various factors. The cholinergic hypothesis is the earliest theory about the pathogenesis of AD. Cholinergic atrophy and cognitive decline are accelerated in age-related neurodegenerative diseases such as AD. In addition, abnormal central cholinergic changes can also induce abnormal phosphorylation of ttau protein, nerve cell inflammation, cell apoptosis, and other pathological phenomena, but the exact mechanism of action is still unclear. Due to the complex and unclear pathogenesis, effective methods to prevent and treat AD are unavailable, and research to explore novel therapeutic drugs is various and active in the world. This review summaries the role of cholinergic signaling and the correlation between the cholinergic signaling pathway with other risk factors in AD and provides the latest research about the efficient therapeutic drugs and treatment of AD.

Plasma levels of sirtuin and adiponectin in patients with primary open-angle glaucoma, exfoliative glaucoma, and healthy controls

PURPOSE

To compare plasma levels of sirtuin 1 (SIRT1) and adiponectin (APN) in patients with primary open-angle glaucoma (POAG), exfoliative glaucoma (XFG), and healthy control subjects.

METHODS

This prospective case-control study collected plasma samples from 118 participants. All subjects underwent a comprehensive ophthalmologic examination before the acquisition of a plasma sample. Plasma samples were obtained from 40 POAG, 38 XFG, and 40 healthy control subjects without any evidence of systemic or ocular disease. Serum SIRT1 and APN levels were estimated by an enzyme-linked immunosorbent assay, ELISA (Elabscience, Houston, USA) method. Statistical analysis of results relied on Kolmogorov-Smirnov, Kruskal-Wallis, Chi-square, analysis of variance (ANOVA) tests, and linear regression analysis, where appropriate.

RESULTS

A significant decrease in SIRT1 levels was observed in POAG patients compared to healthy controls (p = 0.004, Dunn's test). In contrast, no difference was detected between XFG and POAG patients or healthy controls (p = 0.32 and p = 0.34, respectively, Dunn's test). There was no significant difference in plasma APN levels between the three groups under investigation (p = 0.59, ANOVA).

CONCLUSION

Alterations in serum level of SIRT1 may suggest a possible role in POAG via potential effects in neuroprotection and oxidative stress.

An Explanation for the Adiponectin Paradox

The adipokine adiponectin improves insulin sensitivity. Functional signal transduction of adiponectin requires at least one of the receptors AdipoR1 or AdipoR2, but additionally the glycosyl phosphatidylinositol-anchored molecule, T-cadherin. Overnutrition causes a reduction in adiponectin synthesis and an increase in the circulating levels of the enzyme glycosyl phosphatidylinositol-phospholipase D (GPI-PLD). GPI-PLD promotes the hydrolysis of T-cadherin. The functional consequence of T-cadherin hydrolysis is a reduction in adiponectin sequestration by responsive tissues, an augmentation of adiponectin levels in circulation and a (further) reduction in signal transduction. This process creates the paradoxical situation that adiponectin levels are augmented, whereas the adiponectin signal transduction and insulin sensitivity remain strongly impaired. Although both hypoadiponectinemia and hyperadiponectinemia reflect a situation of insulin resistance, the treatments are likely to be different.

Adiponectin: Structure, Physiological Functions, Role in Diseases, and Effects of Nutrition

Adiponectin (a protein consisting of 244 amino acids and characterized by a molecular weight of 28 kDa) is a cytokine that is secreted from adipose tissues (adipokine). Available evidence suggests that adiponectin is involved in a variety of physiological functions, molecular and cellular events, including lipid metabolism, energy regulation, immune response and inflammation, and insulin sensitivity. It has a protective effect on neurons and neural stem cells. Adiponectin levels have been reported to be negatively correlated with cancer, cardiovascular disease, and diabetes, and shown to be affected (i.e., significantly increased) by proper healthy nutrition. The present review comprehensively overviews the role of adiponectin in a range of diseases, showing that it can be used as a biomarker for diagnosing these disorders as well as a target for monitoring the effectiveness of preventive and treatment interventions.

Association between Adipokines and Biomarkers of Alzheimer's Disease: A Cross-Sectional Study

BACKGROUND

Adipose tissue dysfunction has been implicated in the pathophysiology of Alzheimer's disease. However, the involvement of adipokines, particularly adiponectin, remains unclear.

OBJECTIVE

To compare serum and cerebrospinal fluid (CSF) levels of adiponectin, leptin and leptin-to-adiponectin ratio in patients within the spectrum of Alzheimer's disease and evaluate their relationship with classical biomarkers and their value as markers of progression.

METHODS

Amnestic mild cognitive impairment (MCI, n = 71) and Alzheimer's dementia (AD, n = 53) subjects were consecutively recruited for serum and CSF adiponectin and leptin determination using an analytically validated commercial enzyme-linked immunosorbent assay (ELISA). Correlations were explored using adjusted Spearman's correlation coefficients. A logistic regression model and ROC analysis were performed to evaluate the staging predictive value of adipokines.

RESULTS

Serum adiponectin was 33% higher in AD when compared to MCI patients. Adiponectin CSF levels, similar in both groups, were positively correlated with Aβ42 and cognitive function, though only in women. The area under the ROC curve was 0.673 (95% CI:0.57-0.78) for serum adiponectin as predictor of dementia stage and the cut-off 10.85μg/ml maximized the sum of specificity (87%) and sensitivity (44%).

CONCLUSION

Although longitudinal studies are required, we hypothesize that higher serum adiponectin in AD patients constitutes a strategy to compensate possible central signaling defects. In addition, adiponectin might be specifically assigned to neuroprotective functions in women and eventually involved in the female-biased incidence of Alzheimer's disease.

Adipose Tissue and Brain Metabolic Responses to Western Diet-Is There a Similarity between the Two?

Dietary fats and sugars were identified as risk factors for overweight and neurodegeneration, especially in middle-age, an earlier stage of the aging process. Therefore, our aim was to study the metabolic response of both white adipose tissue and brain in middle aged rats fed a typical Western diet (high in saturated fats and fructose, HFF) and verify whether a similarity exists between the two tissues. Specific cyto/adipokines (tumor necrosis factor alpha (TNF-α), adiponectin), critical obesity-inflammatory markers (haptoglobin, lipocalin), and insulin signaling or survival protein network (insulin receptor substrate 1 (IRS), Akt, Erk) were quantified in epididymal white adipose tissue (e-WAT), hippocampus, and frontal cortex. We found a significant increase of TNF-α in both e-WAT and hippocampus of HFF rats, while the expression of haptoglobin and lipocalin was differently affected in the various tissues. Interestingly, adiponectin amount was found significantly reduced in e-WAT, hippocampus, and frontal cortex of HFF rats. Insulin signaling was impaired by HFF diet in e-WAT but not in brain. The above changes were associated with the decrease in brain derived neurotrophic factor (BDNF) and synaptotagmin I and the increase in post-synaptic protein PSD-95 in HFF rats. Overall, our investigation supports for the first time similarities in the response of adipose tissue and brain to Western diet.

Links Between Adiponectin and Dementia: From Risk Factors to Pathophysiology

With the aging population, dementia is becoming one of the most serious and troublesome global public health issues. Numerous studies have been seeking for effective strategies to delay or block its progression, but with little success. In recent years, adiponectin (APN) as one of the most abundant and multifunctional adipocytokines related to anti-inflammation, regulating glycogen metabolism and inhibiting insulin resistance (IR) and anti-atherosclerosis, has attracted widespread attention. In this article, we summarize recent studies that have contributed to a better understanding of the extent to which APN influences the risks of developing dementia as well as its pathophysiological progression. In addition, some controversial results interlinked with its effects on cognitive dysfunction diseases will be critically discussed. Ultimately, we aim to gain a novel insight into the pleiotropic effects of APN levels in circulation and suggest potential therapeutic target and future research strategies.

Organokines in disease

Studies have linked obesity, metabolic syndrome, type 2 diabetes, cardiovascular disease (CVD), nonalcoholic fatty liver disease (NAFLD) and dementia. Their relationship to the incidence and progression of these disease states suggests an interconnected pathogenesis involving chronic low-grade inflammation and oxidative stress. Metabolic syndrome represents comorbidities of central obesity, insulin resistance, dyslipidemia, hypertension and hyperglycemia associated with increased risk of type 2 diabetes, NAFLD, atherosclerotic CVD and neurodegenerative disease. As the socioeconomic burden for these diseases has grown signficantly with an increasing elderly population, new and alternative pharmacologic solutions for these cardiometabolic diseases are required. Adipose tissue, skeletal muscle and liver are central endocrine organs that regulate inflammation, energy and metabolic homeostasis, and the neuroendocrine axis through synthesis and secretion of adipokines, myokines, and hepatokines, respectively. These organokines affect each other and communicate through various endocrine, paracrine and autocrine pathways. The ultimate goal of this review is to provide a comprehensive understanding of organ crosstalk. This will include the roles of novel organokines in normal physiologic regulation and their pathophysiological effect in obesity, metabolic syndrome, type 2 diabetes, CVD, NAFLD and neurodegenerative disorders.

Adiponectin, exercise and eye diseases

Adiponectin, one kind of adipokines, has been shown to be neuroprotective in different neurodegenerative diseases. Adiponectin exerts its role through combination with its receptors and activates downstream molecular pathways. In the retinas, the expression of adiponectin can be detected and adiponectin receptors (AdipoRs) locate in different retinal cells. Adiponectin is mainly produced by adipose tissue, enters the circulation and passes through blood-brain barrier (BBB) without injury. It can also be produced locally in the brains as well as in the retinas. Therefore, it is possible that adiponectin from blood as well as that produced locally in the retinas take part in defense of different eye diseases. Here we have summarized the published data about the protective effects of adiponectin in eye diseases. Because exercise can increase the production of adiponectin systemically in the whole body and locally in the brain although no evidence has shown that exercise can increase the production of adiponectin in the eyes until now, we hypothesize that exercise will have a potential protective effect for the eyes via increasing the levels of adiponectin which needs further investigation.

Upregulation of microRNA-196a improves cognitive impairment and alleviates neuronal damage in hippocampus tissues of Alzheimer's disease through downregulating LRIG3 expression

PURPOSE

This study is launched to uncover the inner function of microRNA-196a (miR-196a) on cognitive dysfunction and neuronal damage in Alzheimer's disease (AD) rats through regulating the PI3K/Akt signaling pathway.

METHODS

The establishment of AD rat model was performed by a microinjection of Aβ_25-35 . miR-196a and LRIG3 expression was detected, and the putative binding site between them was also determined. The spatial learning and memory capability, the hippocampal neurons ultrastructure as well as the survival, and apoptosis of hippocampal neurons of rats were observed. The expression of apoptosis-associated protein, oxidative stress index, and inflammatory factors as well as the PI3K/Akt pathway-related factors was determined.

RESULTS

Initially, decreased miR-196a and increased LRIG3 were exhibited in hippocampus tissues of AD rats. In addition, restored miR-196a and deleted LRIG3 ameliorated spatial learning and memory capability, suppressed the pathological injury, induced the survival, and suppressed the apoptosis of hippocampal neurons, as well as inhibited oxidative stress injury together with inflammatory injury in AD rats. Furthermore, upregulation of miR-196a activated the PI3/Akt pathway in AD rats.

CONCLUSION

This current study suggests that upregulation of miR-196a and downregulation of LRIG3 improve cognitive impairment and alleviate neuronal damage in hippocampus tissues in AD rats via the modulation of the PI3K/Akt pathway.

Ethanol Extract of Centipeda minima Exerts Antioxidant and Neuroprotective Effects via Activation of the Nrf2 Signaling Pathway

Oxidative stress is implicated in the pathogenesis of neurodegeneration and other aging-related diseases. Previous studies have found that the whole herb of Centipeda minima has remarkable antioxidant activities. However, there have been no reports on the neuroprotective effects of C. minima, and the underlying mechanism of its antioxidant properties is unclear. Here, we examined the underlying mechanism of the antioxidant activities of the ethanol extract of C. minima (ECM) both in vivo and in vitro and found that ECM treatment attenuated glutamate and tert-butyl hydroperoxide (tBHP)-induced neuronal death, reactive oxygen species (ROS) production, and mitochondria dysfunction. tBHP-induced phosphorylation of p38 mitogen-activated protein kinase (p38 MAPK) and c-Jun N-terminal kinases (JNK) was reduced by ECM, and ECM sustained phosphorylation level of extracellular signal regulated kinase (ERK) in SH-SY5Y and PC12 cells. Moreover, ECM induced the activation of nuclear factor erythroid 2-related factor 2 (Nrf2) and the upregulation of phase II detoxification enzymes, including heme oxygenase-1 (HO-1), superoxide dismutase-2 (SOD2), and NAD(P)H quinone oxidoreductase-1 (NQO-1) in both two cell types. In a D-galactose (D-gal) and aluminum muriate (AlCl₃)-induced neurodegenerative mouse model, administration of ECM improved the learning and memory of mice in the Morris water maze test and ameliorated the effects of neurodegenerative disorders. ECM sustained the expression level of postsynaptic density 95 (PSD95) and synaptophysin (SYN), activated the Nrf2 signaling pathway, and restored the levels of cellular antioxidants in the hippocampus of mice. In addition, four sesquiterpenoids were isolated from C. minima to identify the bioactive components responsible for the antioxidant activity of C. minima; 6-O-angeloylplenolin and arnicolide D were found to be the active compounds responsible for the activation of the Nrf2 signaling pathway and inhibition of ROS production. Our study examined the mechanism of C. minima and its active components in the amelioration of oxidative stress, which holds the promise for the treatment of neurodegenerative disease.

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.