Endoplasmic reticulum stress plays a central role in development of leptin resistance

Medium-Chain Fatty Acids Extracted from Black Soldier Fly (Hermetia illucens) Larvae Prevents High-Fat Diet-Induced Obesity In Vivo in C57BL/6J Mice

Obesity is a chronic disease associated with an increased dietary fat intake and reduced physical activity, posing significant health risks, including metabolic disorders, cardiovascular diseases, and diminished quality of life. This study investigated the anti-obesity potential of medium-chain fatty acids (MCFAs) derived from black soldier fly larvae (BSFL-MCFAs) in male C57BL/6J mice fed a high-fat diet (HFD). Lauric acid (>50% of total BSFL lipids) was the predominant fatty acid. Mice supplemented with BSFL-MCFAs exhibited significantly lower weight gain and food efficiency ratios (FERs) than HFD-fed mice, despite similar food intake. Medium-chain fatty acids derived from BSFL supplementation also attenuated HFD-induced increases in triglycerides, total cholesterol, and low-density lipoprotein cholesterol levels while improving cardiac risk indices. Furthermore, BSFL-MCFAs reduced serum glucose and leptin levels, mitigated hypothalamic endoplasmic reticulum stress marker expression, and decreased serum alanine transaminase levels, indicating protective effects against obesity-related metabolic dysregulation. These findings suggest that BSFL-MCFAs enhance energy expenditure and thermogenesis, thereby contributing to effective weight management and obesity prevention. As a sustainable and functional lipid source, BSFL-MCFAs hold promise as a feed additive for animals and as a dietary ingredient for preventing pet obesity, offering an innovative approach to combat obesity and its associated health risks.

Ceramide mediates cell-to-cell ER stress transmission by modulating membrane fluidity

Under endoplasmic reticulum (ER) stress (ERS), cells initiate the unfolded protein response (UPR) to maintain ER homeostasis. Recent studies revealed ERS transmission between cells and tissues, by activating the cell-nonautonomous UPR in cells that do not experience ERS directly. Here, we report that ERS triggers a rapid release of ceramide independent of the UPR, but requiring the acid sphingomyelinase activity. Carried by lipoproteins, ceramide is delivered to receiving cells to induce the UPR and regulate cell functions at multiple aspects, including lipid accumulation, cell death, and cytokine production. Mechanistically, extracellular ceramide stimulates ceramide synthesis at the transcription level in receiving cells, leading to ceramide accumulation in the ER so as to reduce membrane fluidity to disrupt ER calcium homeostasis, thus activating the UPR. Sphingomyelin counterbalanced the effect of ceramide. UPR induction is the frontline response to protect cells from ceramide insult. Our study suggests ceramide-mediated ERS transmission as a universal cell-cell communication model regulating a wide range of physiological events.

Microglial ER stress response via IRE1α regulates diet-induced metabolic imbalance and obesity in mice

BACKGROUND

Chronic high-fat diet (HFD) feeding triggers hypothalamic inflammation and systemic metabolic dysfunction associated with endoplasmic reticulum (ER) stress. Glial cells, specifically microglia and astrocytes, are central mediators of hypothalamic inflammation. However, the role of Inositol-Requiring Enzyme 1α (IRE1α), a primary ER stress sensor, in glial cells and its contributions to metabolic dysfunction remains elusive.

OBJECTIVES

To investigate the role of IRE1α in microglia in mediating HFD-induced metabolic dysfunction.

METHODS

Using novel conditional knockout mouse models (CX3CR1GFPΔIRE1 and TMEM119ERΔIRE1), we deleted IRE1α in immune cells or exclusively in microglia and studied its impact on metabolic health and hypothalamic transcriptional changes in mice fed with HFD for 16 weeks.

RESULTS

Deleting IRE1α in microglia significantly reduced LPS-induced pro-inflammatory cytokine gene expression in vitro. IRE1α deletion in microglia protected male mice from HFD-induced obesity, glucose intolerance, and hypothalamic inflammation, with no metabolic benefits observed in female mice. RNA-sequencing revealed significant transcriptional reprogramming of the hypothalamus, including upregulation of genes related to mitochondrial fatty acid oxidation, metabolic adaptability, and anti-inflammatory responses.

CONCLUSIONS

Our findings reveal that IRE1α-mediated ER stress response in microglia significantly contributes to hypothalamic inflammation and systemic metabolic dysfunction in response to HFD, particularly in males, demonstrating an important role of microglial ER stress response in diet-induced obesity and metabolic diseases.

The extrahepatic markers in postmenopausal women with metabolic dysfunction-associated steatotic liver disease: A systematic review

Metabolic dysfunction-associated steatotic liver disease (MASLD) is a prevalent, multifactorial systemic metabolic disorder, now recognized as the most common chronic liver disease globally. Female susceptibility to MASLD varies across menstrual states, influenced by genetic factors, age, menopausal status, and physical activity. Postmenopausal women, experiencing a significant reduction in estrogen, are particularly vulnerable to metabolic imbalances, increasing their risk of MASLD, disease progression, liver fibrosis, insulin resistance, and adverse cardiovascular events compared to premenopausal women and age-matched men. This review systematically synthesizes current research on extrahepatic abnormalities associated with MASLD in postmenopausal women. This review identifies key extrahepatic markers associated with MASLD in postmenopausal women, highlighting gaps in current research and proposing targeted screening and management strategies. (Graphical Abstract).

Obesity: pathophysiology and therapeutic interventions

Over the past few decades, obesity has transitioned from a localized health concern to a pressing global public health crisis affecting over 650 million adults globally, as documented by WHO epidemiological surveys. As a chronic metabolic disorder characterized by pathological adipose tissue expansion, chronic inflammation, and neuroendocrine dysregulation that disrupts systemic homeostasis and impairs physiological functions, obesity is rarely an isolated condition; rather, it is frequently complicated by severe comorbidities that collectively elevate mortality risks. Despite advances in nutritional science and public health initiatives, sustained weight management success rates and prevention in obesity remain limited, underscoring its recognition as a multifactorial disease influenced by genetic, environmental, and behavioral determinants. Notably, the escalating prevalence of obesity and its earlier onset in younger populations have intensified the urgency to develop novel therapeutic agents that simultaneously ensure efficacy and safety. This review aims to elucidate the pathophysiological mechanisms underlying obesity, analyze its major complications-including type 2 diabetes mellitus (T2DM), cardiovascular diseases (CVD), non-alcoholic fatty liver disease (NAFLD), obesity-related respiratory disorders, obesity-related nephropathy (ORN), musculoskeletal impairments, malignancies, and psychological comorbidities-and critically evaluate current anti-obesity strategies. Particular emphasis is placed on emerging pharmacological interventions, exemplified by plant-derived natural compounds such as berberine (BBR), with a focus on their molecular mechanisms, clinical efficacy, and therapeutic advantages. By integrating mechanistic insights with clinical evidence, this review seeks to provide innovative perspectives for developing safe, accessible, and effective obesity treatments.

A cellular and molecular basis of leptin resistance

Similar to most humans with obesity, diet-induced obese (DIO) mice have high leptin levels and fail to respond to the exogenous hormone, suggesting that their obesity is caused by leptin resistance, the pathogenesis of which is unknown. We found that leptin treatment reduced plasma levels of leucine and methionine, mTOR-activating ligands, leading us to hypothesize that chronic mTOR activation might reduce leptin signaling. Rapamycin, an mTOR inhibitor, reduced fat mass and increased leptin sensitivity in DIO mice but not in mice with defects in leptin signaling. Rapamycin restored leptin's actions on POMC neurons and failed to reduce the weight of mice with defects in melanocortin signaling. mTOR activation in POMC neurons caused leptin resistance, whereas POMC-specific mutations in mTOR activators decreased weight gain of DIO mice. Thus, increased mTOR activity in POMC neurons is necessary and sufficient for the development of leptin resistance in DIO mice, establishing a key pathogenic mechanism leading to obesity.

Aerobic exercise improves energy and glucose homeostasis through hypothalamic Mitofusion 2-rescued endoplasmic reticulum stress in diet-induced obese mice

AIMS

Hypothalamic endoplasmic reticulum stress (ERS) and mitochondrial dysfunction are two important mechanisms involved in the pathophysiology of obesity, which can be reversed by aerobic exercise to improve organ function. Mitofusion 2 (Mfn2), a mitochondrial membrane protein, affects both mitochondrial dynamics and ER morphology. This study explored the contribution of hypothalamic Mfn2 to exercise-induced improvements in energy homeostasis and peripheral metabolism and the underlying mechanisms involved.

MATERIALS AND METHODS

We determined the effects of aerobic exercise on energy metabolism and the expression of Mfn2 and α-MSH in the hypothalamus of diet-induced obesity (DIO) model mice. In addition, hypothalamic ER signalling and insulin signalling in both the hypothalamus and the liver were evaluated following 4 weeks of aerobic exercise. By using an adenovirus carrying shRNA-Mfn2, we further explored the effects of hypothalamic Mfn2 on exercise-induced improvements in energy metabolism, ER signalling and insulin signalling.

RESULTS

Energy metabolism was obviously improved following 4 weeks of aerobic exercise in DIO model mice. However, after hypothalamic Mfn2 knockdown, the effects of exercise on food intake and peripheral metabolism were significantly suppressed. Hypothalamic ER signalling was attenuated significantly, whereas both hypothalamic and hepatic insulin signalling were obviously activated following aerobic exercise. Nevertheless, exercise-induced improvements in ER signalling and insulin signalling were attenuated significantly after Mfn2 knockdown.

CONCLUSION

These data indicate that aerobic exercise improves whole-body metabolism in DIO mice, probably via increased hypothalamic Mfn2, which could be further mediated by attenuated HFD-induced ER stress in the hypothalamus.

Endoplasmic reticulum stress and unfolded protein response in renal lipid metabolism

The endoplasmic reticulum (ER) is a crucial cellular organelle involved in protein synthesis, folding, modification, and transport. Exposure to internal and external stressors can induce endoplasmic reticulum stress (ERS), leading to abnormal protein folding and ER malfunction. This stress can disrupt lipid synthesis, metabolism, and transport processes. Fatty acid oxidation is the primary energy source for the renal system. When energy intake exceeds the storage capacity of adipose tissue, lipids accumulate abnormally in non-adipose tissues, including kidneys, liver, and pancreas. Lipids accumulate in the kidneys of nearly all cell types, including thylakoid membranous, pedunculated, and proximal renal tubular epithelial cells. Intracellular free fatty acids can significantly disrupt renal lipid metabolism, contributing to ischemia-reperfusion acute kidney injury, diabetic nephropathy, renal fibrosis, and lupus nephritis. Consequently, this study delineated the primary signaling pathways and mechanisms of the ERS-induced unfolded protein response, explored the mechanistic link between ERS and lipid metabolism, and elucidated its role in renal lipid metabolism. This study aimed to offer new perspectives on managing and treating renal disorders.

Targeting endoplasmic reticulum stress as a potential therapeutic strategy for diabetic cardiomyopathy

Endoplasmic reticulum (ER) is an essential organelle involved in vesicular transport, calcium handling, protein synthesis and folding, and lipid biosynthesis and metabolism. ER stress occurs when ER homeostasis is disrupted by the accumulation of unfolded and/or misfolded proteins in the ER lumen. Adaptive pathways of the unfolded protein response (UPR) are activated to maintain ER homeostasis. In obesity and type 2 diabetes mellitus (T2DM), accumulating data indicate that persistent ER stress due to maladaptive UPR interacts with insulin/leptin signaling, which may be the potential and central mechanistic link between obesity-/T2DM-induced metabolic dysregulation (chronic hyperglycemia, dyslipidemia and lipotoxicity in cardiomyocytes), insulin/leptin resistance and the development of diabetic cardiomyopathy (DiabCM). Meanwhile, these pathological conditions further exacerbate ER stress. However, their interrelationships and the underlying molecular mechanisms are not fully understood. A deeper understanding of ER stress-mediated pathways in DiabCM is needed to develop novel therapeutic strategies. The aim of this review is to discuss the crosstalk between ER stress and leptin/insulin signaling and their involvement in the development of DiabCM focusing on mitochondria-associated ER membranes and chronic inflammation. We also present the current direction of drug development and important considerations for translational research into targeting ER stress for the treatment of DiabCM.

Regulation of energy balance by leptin as an adiposity signal and modulator of the reward system

BACKGROUND

Leptin is an adipose tissue-derived hormone that plays a crucial role in body weight, appetite, and behaviour regulation. Leptin controls energy balance as an indicator of adiposity levels and as a modulator of the reward system, which is associated with liking palatable foods. Obesity is characterized by expanded adipose tissue mass and consequently, elevated concentrations of leptin in blood. Leptin's therapeutic potential for most forms of obesity is hampered by leptin resistance and a narrow dose-response window.

SCOPE OF REVIEW

This review describes the current knowledge of the brain regions and intracellular pathways through which leptin promotes negative energy balance and restrains neural circuits affecting food reward. We also describe mechanisms that hinder these biological responses in obesity and highlight potential therapeutic interventions.

MAJOR CONCLUSIONS

Additional research is necessary to understand how pathways engaged by leptin in different brain regions are interconnected in the control of energy balance.

The Effects of Yoga on Key Adipocytokines in Obesity: A Narrative Review of Leptin and Adiponectin

Obesity is a global health concern that increases the risk of numerous complications, including type 2 diabetes, hypertension, and cardiovascular diseases. Conventional obesity treatments, such as lifestyle modifications, pharmacotherapy, and surgical interventions, are often insufficient, highlighting the need for more efficient and effective approaches. Yoga, an ancient mind-body practice incorporating physical postures (asanas), breathing exercises (pranayama), and meditation, has emerged as a potential therapeutic intervention for obesity management. This review examines the functions of leptin and adiponectin, two key adipocytokines central to obesity, and evaluates the impact of yoga on these hormones. A literature search was conducted using PubMed, Scopus, and Google Scholar with the keywords "yoga" and "adipocytokine" as of May 5, 2024, resulting in the selection of 12 relevant studies. The majority of studies reviewed demonstrated that yoga significantly decreases leptin levels and increases adiponectin levels. Intensive yoga sessions and combined dietary interventions were found to contribute notably to improvements in these hormonal levels. These findings suggest that yoga may improve the balance between leptin and adiponectin, offering beneficial effects on anti-obesity and chronic inflammation reduction. Yoga, as an economical and non-invasive treatment option, presents a promising approach to managing obesity. Further research is expected to elucidate the underlying mechanisms and explore potential clinical applications.

GC/MS Fatty Acid Profile of Marine-Derived Actinomycetes from Extreme Environments: Chemotaxonomic Insights and Biotechnological Potential

This study investigated the fatty acids (FA) profile of 54 actinomycete strains isolated from marine sediments collected off the Portugal continental coast, specifically from the Estremadura Spur pockmarks field, by GC/MS. Fatty acid methyl esters (FAMEs) were prepared from the ethyl acetate lipidic extracts of these strains and analyzed by gas chromatography-mass spectrometry (GC/MS), with FA identification performed using the NIST library. The identified FAs varied from C12:0 to C20:0, where 32 distinct FAs were identified, including 7 branched-chain fatty acids (BCFAs), 9 odd-chain fatty acids (OCFAs), 8 monounsaturated fatty acids (MUFAs), 6 saturated fatty acids (SFAs), 1 polyunsaturated fatty acid (PUFA), and 1 cyclic chain fatty acid (CCFA). The average expressed content was BCFA (47.54%), MUFA (28.49%), OCFA (26.93%), and SFA (22.16%), of which i-C16:0, C18:1ω9, and C16:0 were predominant, while PUFA (3.58%) and CCFA (0.41%) were identified as minor components. The identified BCFA were i-C16:0, a-C15:0, i-C15:0, i-C15:1ω6, a-C16:0, a-C14:0, and i-C17:0, which include combined branching and unsaturation and branching and odd. SFAs were present in all species, with C16:0 and C18:0 being the most representative. Rare OCFAs C19:1ω9, C17:1ω7, C15:0, and C17:0 were expressed. PUFA C18:1ω9 was detected; within this class, omega families ω9, ω7, ω6, and ω5 were identified, and no ω3 was detected. The only CCFA was benzene-butanoic acid (benzene-C4:0). These findings highlight the metabolic versatility of actinomycetes, providing valuable insights into microbial chemotaxonomy and offering promising biochemical leads for the development of biofuel, nutraceutical, and antifungal agents. Furthermore, these results underline the diversity and biotechnological potential of FAs in actinomycetes, uncovering their potential to be used as microbial cell factories, and paving the way for innovations in biofuels, pharmaceuticals, and eco-friendly industrial products.

Interplay between the brain and adipose tissue: a metabolic conversation

The central nervous system and adipose tissue interact through complex communication. This bidirectional signaling regulates metabolic functions. The hypothalamus, a key homeostatic brain region, integrates exteroceptive and interoceptive signals to control appetite, energy expenditure, glucose, and lipid metabolism. This regulation is partly achieved via the nervous modulation of white (WAT) and brown (BAT) adipose tissue. In this review, we highlight the roles of sympathetic and parasympathetic innervation in regulating WAT and BAT activities, such as lipolysis and thermogenesis. Adipose tissue, in turn, plays a dual role as an energy reservoir and an endocrine organ, secreting hormones that influence brain function and metabolic health. In addition, this review focuses on recently uncovered communication pathways, including extracellular vesicles and neuro-mesenchymal units, which add new layers of regulation and complexity to the brain-adipose tissue interaction. Finally, we also examine the consequences of disrupted communication between the brain and adipose tissue in metabolic disorders like obesity and type-2 diabetes, emphasizing the potential for new therapeutic strategies targeting these pathways to improve metabolic health.

History and future of leptin: Discovery, regulation and signaling

The cloning of leptin 30 years ago in 1994 was an important milestone in obesity research. Prior to the discovery of leptin, obesity was stigmatized as a condition caused by lack of character and self-control. Mutations in either leptin or its receptor were the first single gene mutations found to cause severe obesity, and it is now recognized that obesity is caused mostly by a dysregulation of central neuronal circuits. Since the discovery of the leptin-deficient obese mouse (ob/ob) the cloning of leptin (ob aka lep) and leptin receptor (db aka lepr) genes, we have learned much about leptin and its action in the central nervous system. The first hope that leptin would cure obesity was quickly dampened because humans with obesity have increased leptin levels and develop leptin resistance. Nevertheless, leptin target sites in the brain represent an excellent blueprint to understand how neuronal circuits control energy homeostasis. Our expanding understanding of leptin function, interconnection of leptin signaling with other systems and impact on distinct physiological functions continues to guide and improve the development of safe and effective interventions to treat metabolic illnesses. This review highlights past concepts and current emerging concepts of the hormone leptin, leptin receptor signaling pathways and central targets to mediate distinct physiological functions.

Upregulation of Xbp1 in NPY/AgRP neurons reverses diet-induced obesity and ameliorates leptin and insulin resistance

The molecular mechanisms underlying neuronal leptin and insulin resistance in obesity and diabetes are not fully understood. In this study, we show that induction of the unfolded protein response transcription factor, spliced X-box binding protein 1 (Xbp1s), in Agouti-Related Peptide (AgRP) neurons alone, is sufficient to not only protect against but also significantly reverse diet-induced obesity (DIO) as well as improve leptin and insulin sensitivity, despite activation of endoplasmic reticulum stress. We also demonstrate that constitutive expression of Xbp1s in AgRP neurons contributes to improved insulin sensitivity and glucose tolerance. Together, our results identify critical molecular mechanisms linking ER stress in arcuate AgRP neurons to acute leptin and insulin resistance as well as liver glucose metabolism in DIO and diabetes.

The lipid side of unfolded protein response

Although our current knowledge of the molecular crosstalk between the ER stress, the unfolded protein response (UPR), and lipid homeostasis remains limited, there is increasing evidence that dysregulation of either protein or lipid homeostasis profoundly affects the other. Most research regarding UPR signaling in human diseases has focused on the causes and consequences of disrupted protein folding. The UPR itself consists of very complex pathways that function to not only maintain protein homeostasis, but just as importantly, modulate lipid biogenesis to allow the ER to adjust and promote cell survival. Lipid dysregulation is known to activate many aspects of the UPR, but the complexity of this crosstalk remains a major research barrier. ER lipid disequilibrium and lipotoxicity are known to be important contributors to numerous human pathologies, including insulin resistance, liver disease, cardiovascular diseases, neurodegenerative diseases, and cancer. Despite their medical significance and continuous research, however, the molecular mechanisms that modulate lipid synthesis during ER stress conditions, and their impact on cell fate decisions, remain poorly understood. Here we summarize the current view on crosstalk and connections between altered lipid metabolism, ER stress, and the UPR.

Regulation of leptin signaling and diet-induced obesity by SEL1L-HRD1 ER-associated degradation in POMC expressing neurons

Endoplasmic reticulum (ER) homeostasis in the hypothalamus has been implicated in the pathogenesis of diet-induced obesity (DIO) and type 2 diabetes; however, the underlying molecular mechanism remain vague and debatable. Here we report that SEL1L-HRD1 protein complex of the highly conserved ER-associated protein degradation (ERAD) machinery in POMC-expressing neurons ameliorates diet-induced obesity and its associated complications, partly by regulating the turnover of the long isoform of Leptin receptors (LepRb). Loss of SEL1L in POMC-expressing neurons attenuates leptin signaling and predisposes mice to HFD-associated pathologies including fatty liver, glucose intolerance, insulin and leptin resistance. Mechanistically, nascent LepRb, both wildtype and disease-associated Cys604Ser variant, are misfolding prone and bona fide substrates of SEL1L-HRD1 ERAD. In the absence of SEL1L-HRD1 ERAD, LepRb are largely retained in the ER, in an ER stress-independent manner. This study uncovers an important role of SEL1L-HRD1 ERAD in the pathogenesis of central leptin resistance and leptin signaling.

Neuronal lipid droplets play a conserved and sex-biased role in maintaining whole-body energy homeostasis

Lipids are essential for neuron development and physiology. Yet, the central hubs that coordinate lipid supply and demand in neurons remain unclear. Here, we combine invertebrate and vertebrate models to establish the presence and functional significance of neuronal lipid droplets (LD) in vivo. We find that LD are normally present in neurons in a non-uniform distribution across the brain, and demonstrate triglyceride metabolism enzymes and lipid droplet-associated proteins control neuronal LD formation through both canonical and recently-discovered pathways. Appropriate LD regulation in neurons has conserved and male-biased effects on whole-body energy homeostasis across flies and mice, specifically neurons that couple environmental cues with energy homeostasis. Mechanistically, LD-derived lipids support neuron function by providing phospholipids to sustain mitochondrial and endoplasmic reticulum homeostasis. Together, our work identifies a conserved role for LD as the organelle that coordinates lipid management in neurons, with implications for our understanding of mechanisms that preserve neuronal lipid homeostasis and function in health and disease.

Microglia in physiological conditions and the importance of understanding their homeostatic functions in the arcuate nucleus

Microglia are highly dynamic cells that have been mainly studied under pathological conditions. The present review discusses the possible implication of microglia as modulators of neuronal electrical responses in physiological conditions and hypothesizes how these cells might modulate hypothalamic circuits in health and during obesity. Microglial cells studied under physiological conditions are highly diverse, depending on the developmental stage and brain region. The evidence also suggests that neuronal electrical activity modulates microglial motility to control neuronal excitability. Additionally, we show that the expression of genes associated with neuron-microglia interaction is down-regulated in obese mice compared to control-fed mice, suggesting an alteration in the contact-dependent mechanisms that sustain hypothalamic arcuate-median eminence neuronal function. We also discuss the possible implication of microglial-derived signals for the excitability of hypothalamic neurons during homeostasis and obesity. This review emphasizes the importance of studying the physiological interplay between microglia and neurons to maintain proper neuronal circuit function. It aims to elucidate how disruptions in the normal activities of microglia can adversely affect neuronal health.

Endoplasmic reticulum stress in diseases

The endoplasmic reticulum (ER) is a key organelle in eukaryotic cells, responsible for a wide range of vital functions, including the modification, folding, and trafficking of proteins, as well as the biosynthesis of lipids and the maintenance of intracellular calcium homeostasis. A variety of factors can disrupt the function of the ER, leading to the aggregation of unfolded and misfolded proteins within its confines and the induction of ER stress. A conserved cascade of signaling events known as the unfolded protein response (UPR) has evolved to relieve the burden within the ER and restore ER homeostasis. However, these processes can culminate in cell death while ER stress is sustained over an extended period and at elevated levels. This review summarizes the potential role of ER stress and the UPR in determining cell fate and function in various diseases, including cardiovascular diseases, neurodegenerative diseases, metabolic diseases, autoimmune diseases, fibrotic diseases, viral infections, and cancer. It also puts forward that the manipulation of this intricate signaling pathway may represent a novel target for drug discovery and innovative therapeutic strategies in the context of human diseases.

Examining the Potential Applicability of Orexigenic and Anorexigenic Peptides in Veterinary Medicine for the Management of Obesity in Companion Animals

This review article comprehensively explores the role of orexigenic and anorexigenic peptides in the management of obesity in companion animals, with a focus on clinical applications. Obesity in domestic animals, particularly dogs and cats, is prevalent, with significant implications for their health and well-being. Factors contributing to obesity include overfeeding, poor-quality diet, lack of physical activity, and genetic predispositions. Despite the seriousness of this condition, it is often underestimated, with societal perceptions sometimes reinforcing unhealthy behaviors. Understanding the regulation of food intake and identifying factors affecting the function of food intake-related proteins are crucial in combating obesity. Dysregulations in these proteins, whether due to genetic mutations, enzymatic dysfunctions, or receptor abnormalities, can have profound health consequences. Molecular biology techniques play a pivotal role in elucidating these mechanisms, offering insights into potential therapeutic interventions. The review categorizes food intake-related proteins into anorexigenic peptides (inhibitors of food intake) and orexigenic peptides (enhancers of food intake). It thoroughly examines current research on regulating energy balance in companion animals, emphasizing the clinical application of various peptides, including ghrelin, phoenixin (PNX), asprosin, glucagon-like peptide 1 (GLP-1), leptin, and nesfatin-1, in veterinary obesity management. This comprehensive review aims to provide valuable insights into the complex interplay between peptides, energy balance regulation, and obesity in companion animals. It underscores the importance of targeted interventions and highlights the potential of peptide-based therapies in improving the health outcomes of obese pets.

Cell non-autonomous control of autophagy and metabolism by glial cells

Glia are the protectors of the nervous system, providing neurons with support and protection from cytotoxic insults. We previously discovered that four astrocyte-like glia can regulate organismal proteostasis and longevity in C. elegans. Expression of the UPRER transcription factor, XBP-1s, in these glia increases stress resistance, and longevity, and activates the UPRER in intestinal cells via neuropeptides. Autophagy, a key regulator of metabolism and aging, has been described as a cell autonomous process. Surprisingly, we find that glial XBP-1s enhances proteostasis and longevity by cell non-autonomously reprogramming organismal lipid metabolism and activating autophagy. Glial XBP-1s regulates the activation of another transcription factor, HLH-30/TFEB, in the intestine. HLH-30 activates intestinal autophagy, increases intestinal lipid catabolism, and upregulates a robust transcriptional program. Our study reveals a novel role for glia in regulating peripheral lipid metabolism, autophagy, and organellar health through peripheral activation of HLH-30 and autophagy.

Association between protein undernutrition and diabetes: Molecular implications in the reduction of insulin secretion

Undernutrition is still a recurring nutritional problem in low and middle-income countries. It is directly associated with the social and economic sphere, but it can also negatively impact the health of the population. In this sense, it is believed that undernourished individuals may be more susceptible to the development of non-communicable diseases, such as diabetes mellitus, throughout life. This hypothesis was postulated and confirmed until today by several studies that demonstrate that experimental models submitted to protein undernutrition present alterations in glycemic homeostasis linked, in part, to the reduction of insulin secretion. Therefore, understanding the changes that lead to a reduction in the secretion of this hormone is essential to prevent the development of diabetes in undernourished individuals. This narrative review aims to describe the main molecular changes already characterized in pancreatic β cells that will contribute to the reduction of insulin secretion in protein undernutrition. So, it will provide new perspectives and targets for postulation and action of therapeutic strategies to improve glycemic homeostasis during this nutritional deficiency.

Microglia in Central Control of Metabolism

Beyond their role as brain immune cells, microglia act as metabolic sensors in response to changes in nutrient availability, thus playing a role in energy homeostasis. This review highlights the evidence and challenges of studying the role of microglia in metabolism regulation.

The Mechanism of Leptin Resistance in Obesity and Therapeutic Perspective

Leptin resistance is induced via leptin signaling blockade by chronic overstimulation of the leptin receptor and intracellular signaling defect or increased hypothalamic inflammation and suppressor of cytokine signaling (SOCS)-3 expression. High-fat diet triggers leptin resistance induced by at least two independent causes: first, the limited ability of peripheral leptin to activate hypothalamic signaling transducers and activators of transcription (STAT) signaling and secondly a signaling defect in leptin-responsive hypothalamic neurons. Central leptin resistance is dependent on decreased leptin transport efficiency across the blood brain barrier (BBB) rather than hypothalamic leptin insensitivity. Since the hypothalamic phosphorylated STAT3 (pSTAT3) represents a sensitive and specific readout of leptin receptor-B signaling, the assessment of pSTAT3 levels is the gold standard. Hypertriglyceridemia is one of important factors to inhibit the transport of leptin across BBB in obesity. Mismatch between high leptin and the amount of leptin receptor expression in obesity triggers brain leptin resistance via increasing hypothalamic inflammation and SOCS-3 expression. Therapeutic strategies that regulate the passage of leptin to the brain include the development of modifications in the structure of leptin analogues as well as the synthesis of new leptin receptor agonists with increased BBB permeability. In the hyperleptinemic state, polyethylene glycol (PEG)-modified leptin is unable to pass through the BBB. Peripheral histone deacetylase (HDAC) 6 inhibitor, tubastatin, and metformin increase central leptin sensitization. While add-on therapy with anagliptin, metformin and miglitol reduce leptin concentrations, the use of long-acting leptin analogs, and exendin-4 lead to the recovery of leptin sensitivity. Contouring surgery with fat removal, and bariatric surgery independently of the type of surgery performed provide significant improvement in leptin concentrations. Although approaches to correcting leptin resistance have shown some success, no clinically effective application has been developed to date. Due to the impairment of central and peripheral leptin signaling, as well as the extensive integration of leptin-sensitive metabolic pathways with other neurons, the effectiveness of methods used to eliminate leptin resistance is extremely limited.

Circumventricular organ-hypothalamic circuit endoplasmic reticulum stress drives hepatic steatosis during obesity

OBJECTIVE

Nonalcoholic fatty liver disease (NAFLD), characterized by excess liver triglyceride accumulation (hepatic steatosis), leads to an increased risk for cardiometabolic diseases and obesity-related mortality. Emerging evidence points to endoplasmic reticulum (ER) stress in the central nervous system as critical in NAFLD pathogenesis. Here, we tested the contribution of ER stress in a circumventricular organ-hypothalamic circuit in NAFLD development during obesity.

METHODS

C57BL/6J male mice were fed a high-fat diet (HFD) or normal chow. A combination of histological, viral tracing, intersectional viral targeting, and in vivo integrative physiological approaches were used to examine the role of ER stress in subfornical organ to hypothalamic paraventricular nucleus projecting neurons (SFO➔PVN) in NAFLD during diet-induced obesity.

RESULTS

Immunohistochemical analysis revealed marked unfolded protein response activation in the SFO, particularly in excitatory SFO➔PVN neurons of HFD-fed animals. Moreover, intersectional viral inhibition of ER stress in SFO➔PVN neurons resulted in a reduction in hepatomegaly, hepatic steatosis, and a blunted increase in body weight gain during diet-induced obesity, independent of changes in food intake, substrate partitioning, energy expenditure, and ambulatory activity.

CONCLUSIONS

These results indicate that ER stress in an SFO➔PVN neural circuit contributes to hepatic steatosis during obesity.

Anterior Pituitary Transcriptomics Following a High-Fat Diet: Impact of Oxidative Stress on Cell Metabolism

Anterior pituitary cell function requires a high level of protein synthesis and secretion which depend heavily on mitochondrial adenosine triphosphate production and functional endoplasmic reticula. Obesity adds stress to tissues, requiring them to adapt to inflammation and oxidative stress, and adding to their allostatic load. We hypothesized that pituitary function is vulnerable to the stress of obesity. Here, we utilized a 10- to 15-week high-fat diet (HFD, 60%) in a thermoneutral environment to promote obesity, testing both male and female FVB.129P mice. We quantified serum hormones and cytokines, characterized the metabolic phenotype, and defined changes in the pituitary transcriptome using single-cell RNA-sequencing analysis. Weight gain was significant by 3 weeks in HFD mice, and by 10 weeks all HFD groups had gained 20 g. HFD females (15 weeks) had increased energy expenditure and decreased activity. All HFD groups showed increases in serum leptin and decreases in adiponectin. HFD caused increased inflammatory markers: interleukin-6, resistin, monocyte chemoattractant protein-1, and tumor necrosis factorα. HFD males and females also had increased insulin and increased TSH, and HFD females had decreased serum prolactin and growth hormone pulse amplitude. Pituitary single-cell transcriptomics revealed modest or no changes in pituitary cell gene expression from HFD males after 10 or 15 weeks or from HFD females after 10 weeks. However, HFD females (15 weeks) showed significant numbers of differentially expressed genes in lactotropes and pituitary stem cells. Collectively, these studies reveal that pituitary cells from males appear to be more resilient to the oxidative stress of obesity than females and identify the most vulnerable pituitary cell populations in females.

HFD-exacerbated Metabolic Side Effects of Olanzapine Are Suppressed by ER Stress Inhibitor

OBJECTIVE

Numerous schizophrenic patients are suffering from obesity primarily attributed to antipsychotic medication and poor dietary habits. This study investigated the progressive deterioration of olanzapine-induced metabolic disorders in the presence of a high-fat diet (HFD) and explored the involvement of endoplasmic reticulum (ER) stress.

METHODS

Female Sprague-Dawley rats fed on a standard chow diet or HFD were treated with olanzapine (3 mg/kg/day) and the ER stress inhibitor 4-phenylbutyric acid (4-PBA, 1 and 0.5 g/kg/day) for 8 days. Changes in body weight, food intake, and plasma lipids were assessed. Hepatic fat accumulation was evaluated using oil red O staining. Western blotting and immunofluorescence assays were employed to examine the expression of ER stress markers, NOD-like receptor pyrin domain-containing protein 3 (NLRP3), and proopiomelanocortin (POMC) in the hypothalamus or liver.

RESULTS

Compared to olanzapine alone, olanzapine+HFD induced greater weight gain, increased hyperlipidemia, and enhanced hepatic fat accumulation (P<0.05). Co-treatment with 4-PBA exhibited a dose-dependent inhibition of these effects (P<0.05). Further mechanistic investigations revealed that olanzapine alone activated ER stress, upregulated NLRP3 expression in the hypothalamus and liver, and downregulated hypothalamic POMC expression. The HFD exacerbated these effects by 50%-100%. Moreover, co-administration of 4-PBA dose-dependently attenuated the olanzapine+HFD-induced alterations in ER stress, NLRP3, and POMC expression in the hypothalamus and liver (P<0.05).

CONCLUSION

HFD worsened olanzapine-induced weight gain and lipid metabolic disorders, possibly through ER stress-POMC and ER stress-NLRP3 signaling. ER stress inhibitors could be effective in preventing olanzapine+HFD-induced metabolic disorders.

An investigation of the endoplasmic reticulum stress in obesity exposure in the prenatal period

OBJECTIVES

Exposure to maternal obesity has been shown to make offspring more prone to cognitive and metabolic disorders later in life. Although the underlying mechanisms are unclear, the role of endoplasmic reticulum (ER) stress in the fetal programming process is remarkable. ER stress can be activated by many chronic diseases, including obesity and diabetes. Therefore, our study aimed to investigate the role of ER stress caused by maternal diet-induced obesity in the offspring hippocampus. We also evaluated the protective effect of N-acetylcysteine (NAC) against ER stress.

METHODS

A rat obesity model was created by providing a high-fat (60 % kcal) diet. N-acetylcysteine (NAC) was administered at a dosage of 150 mg/kg via the intragastric route. The animals were mated at the age of 12 weeks. The same diet was maintained during pregnancy and lactation. The experiment was terminated on the postnatal 28th day, and the offspring's brain tissues were examined. Immunohistochemical staining for ER stress markers was performed on sections taken from tissues after routine histological procedures.

RESULTS

The results revealed increased GRP78, PERK, and eIF2α immunoreactivities in the hippocampal dentate gyrus (DG) and cornu ammonis 1 (CA1) regions in the obese group offspring, while the expression of those markers in those regions normalized with NAC supplementation (p < 0.01). Statistical analysis of XBP1 immunoreactivity H-scores revealed no difference between the study groups (p > 0.05).

DISCUSSION

These results suggest that exposure to obesity during the prenatal period may cause increased ER stress in hippocampal neurons, which have an important role in the regulation of learning, memory and behavior, and this may contribute to decreased cognitive performance. On the other hand, NAC stands out as an effective agent that can counteract hippocampal ER stress.

CerS6-dependent ceramide synthesis in hypothalamic neurons promotes ER/mitochondrial stress and impairs glucose homeostasis in obese mice

Dysregulation of hypothalamic ceramides has been associated with disrupted neuronal pathways in control of energy and glucose homeostasis. However, the specific ceramide species promoting neuronal lipotoxicity in obesity have remained obscure. Here, we find increased expression of the C16:0 ceramide-producing ceramide synthase (CerS)6 in cultured hypothalamic neurons exposed to palmitate in vitro and in the hypothalamus of obese mice. Conditional deletion of CerS6 in hypothalamic neurons attenuates high-fat diet (HFD)-dependent weight gain and improves glucose metabolism. Specifically, CerS6 deficiency in neurons expressing pro-opiomelanocortin (POMC) or steroidogenic factor 1 (SF-1) alters feeding behavior and alleviates the adverse metabolic effects of HFD feeding on insulin sensitivity and glucose tolerance. POMC-expressing cell-selective deletion of CerS6 prevents the diet-induced alterations of mitochondrial morphology and improves cellular leptin sensitivity. Our experiments reveal functions of CerS6-derived ceramides in hypothalamic lipotoxicity, altered mitochondrial dynamics, and ER/mitochondrial stress in the deregulation of food intake and glucose metabolism in obesity.

Melatonin Alleviates the Impairment of Muscle Bioenergetics and Protein Quality Control Systems in Leptin-Deficiency-Induced Obesity

Leptin is critically compromised in the major common forms of obesity. Skeletal muscle is the main effector tissue for energy modification that occurs as a result of the effect of endocrine axes, such as leptin signaling. Our study was carried out using skeletal muscle from a leptin-deficient animal model, in order to ascertain the importance of this hormone and to identify the major skeletal muscle mechanisms affected. We also examined the therapeutic role of melatonin against leptin-induced muscle wasting. Here, we report that leptin deficiency stimulates fatty acid β-oxidation, which results in mitochondrial uncoupling and the suppression of mitochondrial oxidative damage; however, it increases cytosolic oxidative damage. Thus, different nutrient-sensing pathways are disrupted, impairing proteostasis and promoting lipid anabolism, which induces myofiber degeneration and drives oxidative type I fiber conversion. Melatonin treatment plays a significant role in reducing cellular oxidative damage and regulating energy homeostasis and fuel utilization. Melatonin is able to improve both glucose and mitochondrial metabolism and partially restore proteostasis. Taken together, our study demonstrates melatonin to be a decisive mitochondrial function-fate regulator in skeletal muscle, with implications for resembling physiological energy requirements and targeting glycolytic type II fiber recovery.

Deciphering the Role of Selenoprotein M

Selenocysteine (Sec), the 21st amino acid, is structurally similar to cysteine but with a sulfur to selenium replacement. This single change retains many of the chemical properties of cysteine but often with enhanced catalytic and redox activity. Incorporation of Sec into proteins is unique, requiring additional translation factors and multiple steps to insert Sec at stop (UGA) codons. These Sec-containing proteins (selenoproteins) are found in all three domains of life where they often are involved in cellular homeostasis (e.g., reducing reactive oxygen species). The essential role of selenoproteins in humans requires us to maintain appropriate levels of selenium, the precursor for Sec, in our diet. Too much selenium is also problematic due to its toxic effects. Deciphering the role of Sec in selenoproteins is challenging for many reasons, one of which is due to their complicated biosynthesis pathway. However, clever strategies are surfacing to overcome this and facilitate production of selenoproteins. Here, we focus on one of the 25 human selenoproteins, selenoprotein M (SELENOM), which has wide-spread expression throughout our tissues. Its thioredoxin motif suggests oxidoreductase function; however, its mechanism and functional role(s) are still being uncovered. Furthermore, the connection of both high and low expression levels of SELENOM to separate diseases emphasizes the medical application for studying the role of Sec in this protein. In this review, we aim to decipher the role of SELENOM through detailing and connecting current evidence. With multiple proposed functions in diverse tissues, continued research is still necessary to fully unveil the role of SELENOM.

Integrative neurocircuits that control metabolism and food intake

Systemic metabolism has to be constantly adjusted to the variance of food intake and even be prepared for anticipated changes in nutrient availability. Therefore, the brain integrates multiple homeostatic signals with numerous cues that predict future deviations in energy supply. Recently, our understanding of the neural pathways underlying these regulatory principles-as well as their convergence in the hypothalamus as the key coordinator of food intake, energy expenditure, and glucose metabolism-have been revealed. These advances have changed our view of brain-dependent control of metabolic physiology. In this Review, we discuss new concepts about how alterations in these pathways contribute to the development of prevalent metabolic diseases such as obesity and type 2 diabetes mellitus and how this emerging knowledge may provide new targets for their treatment.

Control of immune cell function by the unfolded protein response

Initiating and maintaining optimal immune responses requires high levels of protein synthesis, folding, modification and trafficking in leukocytes, which are processes orchestrated by the endoplasmic reticulum. Importantly, diverse extracellular and intracellular conditions can compromise the protein-handling capacity of this organelle, inducing a state of 'endoplasmic reticulum stress' that activates the unfolded protein response (UPR). Emerging evidence shows that physiological or pathological activation of the UPR can have effects on immune cell survival, metabolism, function and fate. In this Review, we discuss the canonical role of the adaptive UPR in immune cells and how dysregulation of this pathway in leukocytes contributes to diverse pathologies such as cancer, autoimmunity and metabolic disorders. Furthermore, we provide an overview as to how pharmacological approaches that modulate the UPR could be harnessed to control or activate immune cell function in disease.

Recent progress on action and regulation of anorexigenic adipokine leptin

Organismal energy balance is controlled by inter-tissue communication mediated by the nervous system and hormones, the disruption of which causes metabolic syndrome exemplified by diabetes and obesity. Fat-storing adipose tissue, especially those located in subcutaneous white adipose tissue, secretes leptin in a proportion of fat mass, inhibiting the accumulation of organismal fat by suppressing appetite and promoting energy expenditure. With a prevalence of obesity that exhibits hyperleptinemia, most of the investigation on leptin has been focused on how it works and how it does not, which is expected to be a clue for treating obesity. In contrast, how it is synthesized, transported, and excreted, all of which are relevant to the homeostasis of blood leptin concentration, are not much understood. Of note, acute leptin reduction after hyperleptinemia in the context of obesity exhibited a beneficial effect on obesity and insulin sensitivity, indicating that manipulation of circulating leptin level may provide a therapeutic strategy. Technological advances such as "omics" analysis combined with sophisticated gene-engineered mice studies in the past decade enabled a deeper understanding of leptin's action in more detail. Here, we summarize the updated understanding of the action as well as regulation of leptin and point out the emerging direction of research on leptin.

Effects of the polypeptide from peanut meal mixed fermentation on lipid metabolism and intestinal flora of hyperlipidemic mice

BACKGROUND

Hyperlipidemia is one of the metabolic disorders posing great threat to human health. Our previous studies have shown that the nutritional properties of peanut meal after fermentation are markedly improved, and can effectively improve hyperlipidemia caused by high-fat diet in mice. In this study, in order to facilitate the further utilization of peanut meal, the effect of peanut polypeptide (PP) from peanut meal mixed fermentation on lipid metabolism in mice fed with high-fat diet (HFD) and its possible mechanism were investigated. Fifty male C57BL/6J mice were randomly divided into five groups: normal control group (N), high-fat model group (M), PP low-dose group (PL), PP high-dose group (PH), and atorvastatin positive control group (Y).

RESULTS

The results show that PP supplementation can effectively reduce the body weight of mice, decrease the serum total cholesterol (TC), triglyceride (TG), low-density lipoprotein cholesterol (LDL-C) and leptin levels (P < 0.05), increase the high-density lipoprotein cholesterol (HDL-C) levels (P < 0.05), up-regulate the expression levels of ileal tight junction proteins ZO-1 and occludin (P < 0.05), reduce the hepatocyte injury and lipid accumulation caused by high-fat diet and increase the species richness of intestinal flora.

CONCLUSION

PP can significantly improve hyperlipidemia and regulate intestinal flora disorders caused by hyperlipidemia. The possible mechanism may be related to the reduction of serum leptin levels and up-regulating the expression levels of the ileal tight junction proteins ZO-1 and occludin. This study provides evidence for its regulatory role in lipid metabolism and intestinal function, and provides a research basis for the potential nutritional benefits of underutilized food by-products. © 2023 Society of Chemical Industry.

Longan extract suppresses food intake through regulation of POMC/AgRP neuronal activities and endoplasmic reticulum stress in hypothalamus of db/db mice

Type 2 diabetes mellitus (T2DM) is one of the biggest public health issues worldwide and closely related to development of other chronic diseases such as cardiovascular diseases, cancer and neurodegenerative diseases. Considerable percentage of T2DM patients undergo have suffered from binge eating disorder which exacerbates insulin resistance and metabolic challenges. Longan (Dimocarpus longan L.) and its constituents are reported for their various health benefits. However, it is still unknown whether longan fruit supplementation can ameliorate glucose homeostasis and binge eating disorder found in T2DM. The current study aimed to investigate whether longan fruit extract (LE) supplementation can improve diabetic hyperglycemia through modulation of feeding center located in hypothalamus of db/db T2DM mice. As a result, LE supplementation ameliorated fasting blood glucose levels and reduced excessive epididymal fat accumulation. In addition, LE administration improved glucose tolerance and insulin sensitivity in db/db mice. Especially, LE supplemented mice showed less food consumption which was in line with increase of pro-opiomelanocortin (POMC) neuronal activities and decrease of agouti-related peptide (AgRP) neuronal activities. Furthermore, LE supplementation reduced hypothalamic endoplasmic reticulum (ER) stress which was stimulated in db/db mice. As ER stress is a crucial factor involving in appetite control and glucose homeostasis, the effect of LE supplementation on circulating glucose levels and feeding behavior might be mediated by suppression of hypothalamic ER stress. Collectively, these findings suggest that LE could be a potential nutraceutical for improvement of T2DM as well as patients with satiety issues.

Diallyl disulfide alleviates hypercholesterolemia induced by a western diet by suppressing endoplasmic reticulum stress in apolipoprotein E-deficient mice

BACKGROUND

The endoplasmic reticulum (ER) plays a pivotal role in maintaining cellular metabolic homeostasis. ER stress refers to the accumulation of misfolded proteins, which can trigger an unfolded protein response for survival or death in the cells. Diallyl disulfide (DADS), a major active compound in garlic, has many health benefits for patients with metabolic diseases, especially cardiovascular or fatty liver diseases. However, its role in attenuating hypercholesterolemia by suppressing ER stress remains unknown. Therefore, in this study, we determined whether DADS supplementation could reduce ER stress in apolipoprotein E-deficient (ApoE^-/-) mice fed a Western-type diet (WD).

METHODS

ApoE^-/- mice were fed either a WD alone or a WD supplemented with 0.1% DADS for 12 weeks (n = 10). Levels of plasma total cholesterol, triglyceride, leptin, and insulin were determined. Western blotting was performed to measure protein levels involved in ER stress markers. Histology and Immunostaining were performed on aortic root sections to confirm the effect of DADS on histology and expression of ER chaperone protein GRP78.

RESULTS

The metabolic parameters showed that increases in fat weight, leptin resistance, and hypercholesterolemia were reversed in DADS-supplemented mice (p < 0.05). In addition, DADS ameliorated not only the protein of ER stress markers, phospho-eukaryotic initiation factor 2 subunit alpha and C/EBP homologous protein in the liver (p < 0.05) but also glucose-related protein 78 localization in the aorta.

CONCLUSIONS

This indicates that DADS inhibits diet-induced hypercholesterolemia, at least in parts by regulating ER stress markers. DADS may be a good candidate for treating individuals with diet-induced hypercholesterolemia.

Alkannin Attenuates Amyloid β Aggregation and Alzheimer's Disease Pathology

Alzheimer's disease (AD) is a neurodegenerative disease that is accompanied by memory decline and cognitive dysfunction. Aggregated amyloid β formation and accumulation may be one of the underlying mechanisms of the pathophysiology of AD. Therefore, compounds that can inhibit amyloid β aggregation may be useful for treatment. Based on this hypothesis, we screened plant compounds used in Kampo medicine for chemical chaperone activity and identified that alkannin had this property. Further analysis indicated that alkannin could inhibit amyloid β aggregation. Importantly, we also found that alkannin inhibited amyloid β aggregation after aggregates had already formed. Through the analysis of circular dichroism spectra, alkannin was found to inhibit β-sheet structure formation, which is an aggregation-prone toxic structure. Furthermore, alkannin attenuated amyloid β-induced neuronal cell death in PC12 cells, ameliorated amyloid β aggregation in the AD model of Caenorhabditis elegans (C. elegans), and inhibited chemotaxis observed in AD C. elegans, suggesting that alkannin could potentially inhibit neurodegeneration in vivo. Overall, these results suggest that alkannin may have novel pharmacological properties for inhibiting amyloid β aggregation and neuronal cell death in AD. SIGNIFICANCE STATEMENT: Aggregated amyloid β formation and accumulation is one of the underlying mechanisms of the pathophysiology of Alzheimer's disease. We found that alkannin had chemical chaperone activity, which can inhibit β-sheet structure formation of amyloid β and its aggregation, neuronal cell death, and Alzheimer's disease phenotype in C. elegans. Overall, alkannin may have novel pharmacological properties for inhibiting amyloid β aggregation and neuronal cell death in Alzheimer's disease.

Fatty Liver Disease, Metabolism and Alcohol Interplay: A Comprehensive Review

Non-alcoholic fatty liver disease (NAFLD) is the most common cause of chronic liver disease worldwide, and its incidence has been increasing in recent years because of the high prevalence of obesity and metabolic syndrome in the Western population. Alcohol-related liver disease (ArLD) is the most common cause of cirrhosis and constitutes the leading cause of cirrhosis-related deaths worldwide. Both NAFLD and ArLD constitute well-known causes of liver damage, with some similarities in their pathophysiology. For this reason, they can lead to the progression of liver disease, being responsible for a high proportion of liver-related events and liver-related deaths. Whether ArLD impacts the prognosis and progression of liver damage in patients with NAFLD is still a matter of debate. Nowadays, the synergistic deleterious effect of obesity and diabetes is clearly established in patients with ArLD and heavy alcohol consumption. However, it is still unknown whether low to moderate amounts of alcohol are good or bad for liver health. The measurement and identification of the possible synergistic deleterious effect of alcohol consumption in the assessment of patients with NAFLD is crucial for clinicians, since early intervention, advising abstinence and controlling cardiovascular risk factors would improve the prognosis of patients with both comorbidities. This article seeks to perform a comprehensive review of the pathophysiology of both disorders and measure the impact of alcohol consumption in patients with NAFLD.

Amyloid β-Peptide Effects on Glucose Regulation Are Dependent on Apolipoprotein E Genotype

The apolipoprotein E gene (APOE) confers the greatest genetic risk factor for Alzheimer's disease (AD), wherein the ε4 allele confers an elevated risk compared with the ε3 allele. Biological mechanisms that differ across these alleles have been explored in mouse models wherein the murine Apoe gene has undergone targeted replacement with sequences encoding human ApoE3 or ApoE4 (ApoE-TR mice). Such models have indicated that the two variants of ApoE produce differential effects on energy metabolism, including metabolic syndrome. However, glucose regulation has not been compared in ApoE-TR mice with and without amyloid β-peptide (Aβ) accumulation. We crossed ApoE3-TR and ApoE4-TR mice with a transgenic line that accumulates human Aβ1-42 In male ApoE3-TR mice, introduction of Aβ caused aberrations in glucose tolerance and in membrane translocation of astrocytic glucose transporter 1 (GLUT1). Phosphorylation of Tau at AD-relevant sites was correlated with glucose intolerance. These effects appeared independent of insulin dysregulation and were not observed in females. In ApoE4-TR mice, the addition of Aβ had no significant effects because of a trend toward perturbation of the baseline values.

Correlation between improved leptin signaling and cognitive function post bariatric surgery

Determining whether changes in leptin signaling plays a role in the improvement of cognitive function post-bariatric surgery may aid in the understanding and development of novel therapeutic approaches targeting cognitive dysfunction through the greater understanding of processes connecting obesity and brain health. Several studies have explored the effects of cognition post bariatric surgery, and others have studied leptin and its changes post surgery. However the amalgamation of the effects of leptin signaling in relation to cognition post bariatric surgery have yet to be considered as key tools in the understanding of cognitive dysfunction in obese subjects with leptin resistance or insensitivity. This review serves to highlight the potential correlations, to further elucidate the effect of improved leptin signaling on cognition post bariatric surgery, and to propose a direct cause for the improvement of cognitive function via the amelioration of the leptin Janus kinase/Signal transducer and activator of transcription (JAK/STAT) signaling pathway as a result of the reversal of inflammatory processes involved in diseased individuals.

Phenylbutyric acid robustly increases Npy mRNA expression in hypothalamic neurons by increasing H3K9/14 acetylation at the Npy promoter

Phenylbutyric acid (PBA) is a commonly used inhibitor of endoplasmic reticulum stress, as well as a histone deacetylase (HDAC) inhibitor, that increases hypothalamic expression of orexigenic neuropeptide Y (Npy). Elucidation of the dose-response relationship and mechanism of action of PBA may position this compound as a potential therapeutic for eating disorders where Npy is dysregulated, such as anorexia nervosa. The hypothalamic neuronal model mHypoE-41 was exposed to PBA (5 μM-5 mM) to assess the maximal Npy upregulation. Transcription factors and histone acetylation-related genes were assessed by qRT-PCR, as well as the involvement estrogen receptors (ER) using siRNA knockdown. Changes in global and Npy promoter-specific H3K9/14 acetylation were detected using western analysis and chromatin immunoprecipitation. Treatment with 5 mM PBA led to a 10-fold and 206-fold increase in Npy mRNA at 4 and 16 h, respectively, as well as increased NPY secretion. This induction was not observed with another orexigenic neuropeptide Agrp. PBA significantly increased the expression of Foxo1, Socs3 and Atf3 and the ERs Esr1 and Esr2 mRNA, but the PBA-mediated induction of Npy was not dependent on ERα or ERβ. PBA induced histone H3K9/14 acetylation at 3 distinct Npy promoter regions, suggesting increased Npy transcriptional activation due to a more open chromatin structure. We also report changes in Hdac mRNAs by PBA and the fatty acid palmitate, highlighting the importance of epigenetic regulation in Npy transcription. Overall, we conclude that PBA has strong orexigenic potential and can robustly and specifically induce Npy in hypothalamic neurons through a mechanism likely involving histone H3 acetylation.

Fecal Metagenomics and Metabolomics Identifying Microbial Signatures in Non-Alcoholic Fatty Liver Disease

The frequency of non-alcoholic fatty liver disease (NAFLD) has intensified, creating diagnostic challenges and increasing the need for reliable non-invasive diagnostic tools. Due to the importance of the gut-liver axis in the progression of NAFLD, studies attempt to reveal microbial signatures in NAFLD, evaluate them as diagnostic biomarkers, and to predict disease progression. The gut microbiome affects human physiology by processing the ingested food into bioactive metabolites. These molecules can penetrate the portal vein and the liver to promote or prevent hepatic fat accumulation. Here, the findings of human fecal metagenomic and metabolomic studies relating to NAFLD are reviewed. The studies present mostly distinct, and even contradictory, findings regarding microbial metabolites and functional genes in NAFLD. The most abundantly reproducing microbial biomarkers include increased lipopolysaccharides and peptidoglycan biosynthesis, enhanced degradation of lysine, increased levels of branched chain amino acids, as well as altered lipid and carbohydrate metabolism. Among other causes, the discrepancies between the studies may be related to the obesity status of the patients and the severity of NAFLD. In none of the studies, except for one, was diet considered, although it is an important factor driving gut microbiota metabolism. Future studies should consider diet in these analyses.

Maternal obesity and ovarian failure: is leptin the culprit?

At the time of its discovery and characterization in 1994, leptin was mostly considered a metabolic hormone able to regulate body weight and energy homeostasis. However, in recent years, a great deal of literature has revealed leptin's pleiotropic nature, through its involvement in numerous physiological contexts including the regulation of the female reproductive tract and ovarian function. Obesity has been largely associated with infertility, and leptin signalling is known to be dysregulated in the ovaries of obese females. Hence, the disruption of ovarian leptin signalling was shown to contribute to the pathophysiology of ovarian failure in obese females, affecting transcriptional programmes in the gamete and somatic cells. This review attempts to uncover the underlying mechanisms contributing to female infertility associated with obesity, as well as to shed light on the role of leptin in the metabolic dysregulation within the follicle, the effects on the oocyte epigenome, and the potential long-term consequence to embryo programming.

Endoplasmic reticulum stress inhibition ameliorated WFS1 expression alterations and reduced pancreatic islets' insulin secretion induced by high-fat diet in rats

Endoplasmic reticulum (ER) stress is involved in the development of glucose homeostasis impairment. When ER stress occurs, the unfolded protein response (UPR) is activated to cope with it. One of the UPR components is WFS1 (Wolfram syndrome 1), which plays important roles in ER homeostasis and pancreatic islets glucose-stimulated insulin secretion (GSIS). Accordingly and considering that feeding high-fat food has a major contribution in metabolic disorders, this study aimed to investigate the possible involvement of pancreatic ER stress in glucose metabolism impairment induced by feeding high-fat diet (HFD) in male rats. After weaning, the rats were divided into six groups, and fed on normal diet and HFD for 20 weeks, then 4-phenyl butyric acid (4-PBA, an ER stress inhibitor) was administered. Subsequently, in all groups, after performing glucose tolerance test, the animals were dissected and their pancreases were removed to extract ER, islets isolation and assessment of GSIS. Moreover, the pancreatic ER stress [binding of immunoglobulin protein (BIP) and enhancer-binding protein homologous protein (CHOP)] and oxidative stress [malondialdehyde (MDA), glutathione (GSH) and catalase] biomarkers as well as WFS1 expression level were evaluated. HFD decreased pancreatic WFS1 protein and GSH levels, and enhanced pancreatic catalase activity, MDA content, BIP and CHOP protein and mRNA levels as well as Wfs1 mRNA amount. Accordingly, it increased BIP, CHOP and WFS1 protein levels in the extracted ER of pancreas. In addition, the HFD caused glucose intolerance, and decreased the islets' GSIS and insulin content. However, 4-PBA administration restored the alterations. It seems that, HFD consumption through inducing pancreatic ER stress, altered WFS1 expression levels, reduced the islets' GSIS and insulin content and finally impaired glucose homeostasis.

Endoplasmic Reticulum Stress-induced Endothelial Dysfunction Promotes Neointima Formation after Arteriovenous Grafts in Mice on High-fat Diet

OBJECTIVE

Endothelial dysfunction is one candidate for triggering neointima formation after arteriovenous grafts (AVGs), but the factors mediating this process are unclear. The purpose of this study was to investigate the role of endoplasmic reticulum stress (ERS)-induced endothelial dysfunction in neointima formation following AVGs in high-fat diet (HFD) mice.

METHODS

CCAAT-enhancer-binding protein-homologous protein (CHOP) knockout (KO) mice were created. Mice were fed with HFD to produce HFD model. AVGs model were applied in the groups of WT ND, WT HFD, and CHOP KO HFD. Human umbilical vein endothelial cells (HUVECs) were cultured with oxidized low density lipoprotein (ox-LDL) (40 mg/L) for the indicated time lengths (0, 6, 12, 24 h). ERS inhibitor tauroursodeoxycholic acid (TUDCA) was used to block ERS. Immunohistochemical staining was used to observe the changes of ICAM1. Changes of ERS were detected by real-time RT-PCR. Protein expression levels and ERS activation were detected by Western blotting. Endothellial cell function was determined by endothelial permeability assay and transendothelial migration assay.

RESULTS

HFD increased neointima formation in AVGs associated with endothelial dysfunction. At the same time, ERS was increased in endothelial cells (ECs) after AVGs in mice consuming the HFD. In vitro, ox-LDL was found to stimulate ERS, increase the permeability of the EC monolayer, and cause endothelial dysfunction. Blocking ERS with TUDCA or CHOP siRNA reversed the EC dysfunction caused by ox-LDL. In vivo, knockout of CHOP (CHOP KO) protected the function of ECs and decreased neointima formation after AVGs in HFD mice.

CONCLUSION

Inhibiting ERS in ECs could improve the function of AVGs.

Drosophila melanogaster as a model for unraveling unique molecular features of epilepsy elicited by human GABA transporter 1 variants

Mutations in the human γ-aminobutyric acid (GABA) transporter 1 (hGAT-1) can instigate myoclonic-atonic and other generalized epilepsies in the afflicted individuals. We systematically examined fifteen hGAT-1 disease variants, all of which dramatically reduced or completely abolished GABA uptake activity. Many of these loss-of-function variants were absent from their regular site of action at the cell surface, due to protein misfolding and/or impaired trafficking machinery (as verified by confocal microscopy and de-glycosylation experiments). A modest fraction of the mutants displayed correct targeting to the plasma membrane, but nonetheless rendered the mutated proteins devoid of GABA transport, possibly due to structural alterations in the GABA binding site/translocation pathway. We here focused on a folding-deficient A288V variant. In flies, A288V reiterated its impeded expression pattern, closely mimicking the ER-retention demonstrated in transfected HEK293 cells. Functionally, A288V presented a temperature-sensitive seizure phenotype in fruit flies. We employed diverse small molecules to restore the expression and activity of folding-deficient hGAT-1 epilepsy variants, in vitro (in HEK293 cells) and in vivo (in flies). We identified three compounds (chemical and pharmacological chaperones) conferring moderate rescue capacity for several variants. Our data grant crucial new insights into: (i) the molecular basis of epilepsy in patients harboring hGAT-1 mutations, and (ii) a proof-of-principle that protein folding deficits in disease-associated hGAT-1 variants can be corrected using the pharmacochaperoning approach. Such innovative pharmaco-therapeutic prospects inspire the rational design of novel drugs for alleviating the clinical symptoms triggered by the numerous emerging pathogenic mutations in hGAT-1.

The PTP1B selective inhibitor MSI-1436 mitigates Tunicamycin-induced ER stress in human hepatocarcinoma cell line through XBP1 splicing modulation

Protein tyrosine phosphatase PTP1B is considered as a key metabolic enzyme that has been reported to be associated with insulin resistance onset, and underlying cellular metabolic malfunctions, including ER stress and mitochondrial failure. In this study, effects of selective PTP1B inhibition using MSI-1436 on cellular apoptosis, oxidative stress, mitochondrial dysfunction and ER stress have been assessed using an in vitro model of Tunicamycin induced ER stress in HepG2 cell line. Inhibition of PTP1B using MSI-1436 significantly increased cell viability and reduced the number of apoptotic cells as well as the expression of key apoptosis initiators and effectors. MSI-1436 further mitigated ER stress, by downregulating the expression of IRE1, ATF6 and PERK transcripts, all being key ER stress sensors. Interestingly, MSI-1436 inhibited the XBP1 splicing, and thus its UPR-associated transcriptional activity. PTP1B inhibition further enabled to restore proper mitochondrial biogenesis, by improving transmembrane potential, and diminishing intracellular ROS while restoring of endogenous antioxidant enzymes genes expression. PTP1B inhibition using MSI-1436 could improve cellular apoptosis and metabolic integrity through the mitigation of ER and mitochondrial stress signalling pathways, and excessive ROS accumulation. This strategy may be useful for the treatment of metabolic disorders including IR, NAFLD and diabetes.