Apolipoprotein A-IV exerts its anorectic action through a PI3K/Akt signaling pathway in the hypothalamus

Apolipoproteins in ischemic stroke progression and recovery: Key molecular mechanisms and therapeutic potential

Ischemic stroke, responsible for 80 % of all strokes, is a leading cause of mortality globally. While altered lipids profiles are recognized as modifiable risk factors, their direct impact on stroke outcomes is less understood due to the brain's distinct lipid metabolism and the selective permeability of the blood-brain barrier for lipoproteins. As key components of lipoproteins, apolipoproteins are essential for lipid transport, redistribution and metabolism in both the central nervous system and peripheral blood circulation. This review provides an updated perspective on the influence of brain-expressed apolipoproteins (such as ApoE, ApoA-I, ApoJ, ApoD, and others) and those that cross the damaged blood-brain barrier following ischemic stroke. We explore hypotheses regarding their involvement in molecular pathways related to lipid metabolism, inflammation, oxidative stress, mitochondrial function and blood-brain barrier integrity. Through this synthesis, we aim to identify potential biomarkers and therapeutic targets, thereby enhancing our understanding of apolipoproteins in ischemic stroke progression and contributing to improved clinical outcomes.

Apolipoprotein A-IV is induced by high-fat diets and mediates positive effects on glucose and lipid metabolism

OBJECTIVE

Low-carbohydrate, high-fat diets under eucaloric conditions are associated with several health-beneficial metabolic effects in humans, particularly in the liver. We recently observed that apolipoprotein A-IV (apoA-IV), a highly abundant apolipoprotein, was among the most upregulated proteins in circulation after six weeks of consuming a high-fat diet in humans. However, the impact of dietary changes in regulating apoA-IV, and the potential effects of apoA-IV on regulation of glucose- and lipid metabolism remain to be fully established.

METHODS

We investigated the regulation of circulating fasting concentrations of apoA-IV in humans in response to diets enriched in either fat or carbohydrates. Moreover, to study the whole-body and tissue-specific glucose and lipid metabolic effects of apoA-IV, we administrered apoA-IV recombinant protein to mice and isolated pancreatic islets.

RESULTS

We demonstrate that in healthy human individuals high-fat intake increased fasting plasma apoA-IV concentrations by up to 54%, while high-carbohydrate intake suppressed plasma apoA-IV concentrations. In mice, administration of apoA-IV acutely lowered blood glucose levels both in lean and obese mice. Interestingly, this was related to a dual mechanism, involving both inhibition of hepatic glucose production and increased glucose uptake into white and brown adipose tissues. In addition to an effect on hepatic glucose production, the apoA-IV-induced liver proteome revealed increased capacity for lipoprotein clearance. The effects of apoA-IV in the liver and adipose tissues were concomitant with increased whole-body fatty acid oxidation. Upon glucose stimulation, an improvement in glucose tolerance by apoA-IV administration was related to potentiation of glucose-induced insulin secretion, while apoA-IV inhibited glucagon secretion ex vivo in islets.

CONCLUSIONS

We find that apoA-IV is potently increased by intake of fat in humans, and that several beneficial metabolic effects, previously associated with high fat intake in humans, are mimicked by administration of apoA-IV protein to mice.

Seasonal and comparative evidence of adaptive gene expression in mammalian brain size plasticity

Contrasting almost all other mammalian wintering strategies, Eurasian common shrews, Sorex araneus, endure winter by shrinking their brain, skull, and most organs, only to then regrow to breeding size the following spring. How such tiny mammals achieve this unique brain size plasticity while maintaining activity through the winter remains unknown. To discover potential adaptations underlying this trait, we analyzed seasonal differential gene expression in the shrew hypothalamus, a brain region that both regulates metabolic homeostasis and drastically changes size, and compared hypothalamus gene expression across species. We discovered seasonal variation in suites of genes involved in energy homeostasis and apoptosis, shrew-specific upregulation of genes involved in the development of the hypothalamic blood-brain barrier and calcium signaling, as well as overlapping seasonal and comparative gene expression divergence in genes implicated in the development and progression of human neurological and metabolic disorders, including CCDC22. With high metabolic rates and facing harsh winter conditions, S. araneus have evolved both adaptive and plastic mechanisms to sense and regulate their energy budget. Many of these changes mirrored those identified in human neurological and metabolic disease, highlighting the interactions between metabolic homeostasis, brain size plasticity, and longevity.

Epigenetics-Driven Appetite System Disorders and PI3K/AKT Signaling Activation Mediate a Weight Gain Resistance Phenotype Induced by a High-Fat Diet in Male Rats

OBJECTIVE

Some patients with anorexia nervosa (AN) exhibit an aversion to high-fat food. The hypothalamus plays a crucial role in feeding behavior. This study investigated the role of epigenetic modifications in the hypothalamus of male rats exhibiting a weight gain resistance (WR) phenotype induced by a high-fat diet (HFD).

METHOD

Male Sprague-Dawley (SD) rats were divided into normal diet (ND) and HFD groups for 9 weeks. Rats in the HFD group were then divided into HFD-induced obese (HFO) or HFD-induced WR phenotype (HFWR) groups, and body weight and food intake were monitored for 24 days. Samples such as hypothalamus and serum were collected.

RESULTS

The hypothalamus of HFWR rats showed increased 5-methylcytosine (5mC) levels. Whole-genome bisulfite sequencing (WGBS) analysis revealed that the level of 5mC in the hypothalamic DNA of HFWR rats was higher than that of HFO rats. The hypothalamus of HFWR rats displayed molecular disturbances in appetite systems. Through integrated analysis of the methylome and transcriptome, we discovered that alterations in methylation levels directly influenced changes in the galanin and IGF systems. Five genes (Aurkb, Cdkn1a, Galr1, ND2, and Tf) with promoter hypermethylation may be involved in appetite system disturbances. Furthermore, HFD-induced alteration of 5mC affects PI3K/Akt signaling activation, resulting in increased neuroinflammation and apoptosis in the ventromedial nucleus of the hypothalamus (VMH) in HFWR rats.

DISCUSSION

Our study suggests that 5mC-mediated molecular disturbances in the hypothalamic appetite system and activation of PI3K/Akt signaling in the VMH may serve as a potential pathogenic basis for HFWR.

The Impact of Cannabidiol (CBD) on Lipid Absorption and Lymphatic Transport in Rats

Background: Cannabidiol (CBD) exerts diverse metabolic effects, yet its influence on intestinal lipid metabolism remains unclear. Methods: In this study, we investigated whether short-term (one-week) CBD treatment affects lipid absorption and transport through the lymphatic system using a validated lymph fistula model. Results: CBD treatment significantly enhanced the transport of radiolabeled triglycerides through the lymphatic system. This effect appeared specific, as CBD did not substantially alter cholesterol output in the lymph. Chemical assays indicated that CBD treatment did not significantly alter total triglycerides, cholesterol, phospholipids, or non-esterified fatty acid levels in the lymph. However, it significantly enhanced the lymphatic output of apolipoprotein A4 (ApoA4) and apolipoprotein A1 (ApoA1). Additionally, gene expression analysis revealed a downregulation of vascular endothelial growth factor receptor 1 (Flt1) in the small intestine, leading to increased lymphatic lacteal permeability and altered lipid transport dynamics. Conclusions: These findings indicate that short-term CBD treatment modulates lymphatic lipid composition and apolipoprotein secretion by regulating lymphatic lacteal function, thereby influencing lipid transport and metabolism. This study provides novel insights into CBD's role in facilitating TG-rich lipoprotein transport via the lymphatic system, highlighting its potential therapeutic applications in lipid-related disorders.

Adiponectin inhibits GnRH secretion via activating AMPK and PI3K signaling pathways in chicken hypothalamic neuron cells

It has been reported that adiponectin (AdipoQ), an adipokine secreted by white adipose tissue, plays an important role in the control of animal reproduction in addition to its function in energy homeostasis by binding to its receptors AdipoR1/2. However, the molecular mechanisms of AdipoQ in the regulation of animal reproduction remain elusive. In this study, we investigated the effects of AdipoQ on hypothalamic reproductive hormone (GnRH) secretion and reproduction-related receptor gene (estrogen receptor [ER] and progesterone receptor [PR]) expression in hypothalamic neuronal cells (HNCs) of chickens by using real-time fluorescent quantitative PCR (RT-qPCR), enzyme-linked immunosorbent assay (ELISA), Western blot (WB) and cell counting kit-8 (CCK-8) assays and found that overexpression of AdipoQ could increase the expression levels of AdipoR1/2 and reproduction-related receptor genes (P < 0.05) while decreasing the expression level of GnRH. In contrast, interference with AdipoQ mRNA showed the opposite results in HNCs. Furthermore, we demonstrated that AdipoQ exerts its functions through the AMPK and PI3K signaling pathways. Finally, our in vitro experiments found that AdipoRon (a synthetic substitute for AdipoQ) treatment and AdipoR1/2 RNAi interference co-treatment resulted in no effect on GnRH secretion, suggesting that the inhibition of GnRH secretion by AdipoQ is mediated by the AdipoR1/2 signaling axis. In summary, we uncovered, for the first time, the molecular mechanism of AdipoQ in the regulation of reproductive hormone secretion in hypothalamic neurons in chickens.

Advances in the study of the pathogenesis of obesity: Based on apolipoproteins

Obesity is a state presented by excessive accumulation and abnormal distribution of body fat, with metabolic disorders being one of its distinguishing features. Obesity is associated with dyslipidemia, apolipoproteins are important structural components of plasma lipoproteins, which influence lipid metabolism in the body by participating in lipoprotein metabolism and are closely related to the progression of obesity. Apolipoproteins influence the progression of obesity from lipid metabolism, energy expenditure and inflammatory response. In this review, we discuss the alterations of apolipoproteins in obesity, understand the potential mechanisms by which apolipoproteins affect obesity, as well as provide new targets for the treatment of obesity.

Betaine Reduces Lipid Anabolism and Promotes Lipid Transport in Mice Fed a High-Fat Diet by Influencing Intestinal Protein Expression

Betaine is more efficient than choline and methionine methyl donors, as it can increase nitrogen storage, promote fat mobilisation and fatty acid oxidation and change body fat content and distribution. Lipid is absorbed primarily in the small intestine after consumption, which is also the basis of lipid metabolism. This study was conducted to establish a mouse model of obesity in Kunming mice of the same age and similar body weight, and to assess the effect of betaine on the intestinal protein expression profile of mice using a proteomic approach. Analysis showed that betaine supplementation reversed the reduction in expression of proteins related to lipid metabolism and transport in the intestine of mice induced by a high-fat diet (HFD). For example, the addition of betaine resulted in a significant upregulation of microsomal triglyceride transfer protein (Mttp), apolipoprotein A-IV (Apoa4), fatty-acid-binding protein 1 (Fabp1) and fatty-acid-binding protein 2 (Fabp2) expression compared to the HFD group (p < 0.05), which exhibited accelerated lipid absorption and then translocation from the intestine into the body’s circulation, in addition to a significant increase in Acetyl-CoA acyltransferase (Acaa1a) protein expression, hastening lipid metabolism in the intestine (p < 0.05). Simultaneously, a significant reduction in protein expression of alpha-enolase 1 (Eno1) as the key enzyme for gluconeogenesis in mice in the betaine-supplemented group resulted in a reduction in lipid synthesis in the intestine (p < 0.05). These findings provide useful information for understanding the changes in the protein profile of the small intestine in response to betaine supplementation and the potential physiological regulation of diets’ nutrient absorption.

Inhibition of Vascular Inflammation by Apolipoprotein A-IV

Background

Apolipoprotein (apo) A-IV, the third most abundant apolipoprotein in human high density lipoproteins (HDLs), inhibits intestinal and systemic inflammation. This study asks if apoA-IV also inhibits acute vascular inflammation.

Methods

Inflammation was induced in New Zealand White rabbits by placing a non-occlusive silastic collar around the common carotid artery. A single 1 mg/kg intravenous infusion of lipid-free apoA-IV or saline (control) was administered to the animals 24 h before collar insertion. The animals were euthanised 24 h post-collar insertion. Human coronary artery cells (HCAECs) were pre-incubated with reconstituted HDLs containing apoA-IV complexed with phosphatidylcholine, (A-IV)rHDLs, then activated by incubation with tumour necrosis factor (TNF)-α. Cell surface vascular cell adhesion molecule-1 (VCAM-1) and intercellular adhesion molecule-1 (ICAM-1) in the TNF-α-activated HCAECs was quantified by flow cytometry. VCAM-1, ICAM-1 and 3β-hydroxysteroid-Δ24 reductase (DHCR24) mRNA levels were quantified by real time PCR.

Results

Apolipoprotein ApoA-IV treatment significantly decreased collar-induced endothelial expression of VCAM-1, ICAM-1 and neutrophil infiltration into the arterial intima by 67.6 ± 9.9% (p < 0.01), 75.4 ± 6.9% (p < 0.01) and 74.4 ± 8.5% (p < 0.05), respectively. It also increased endothelial expression of DHCR24 by 2.6-fold (p < 0.05). Pre-incubation of HCAECs with (A-IV)rHDLs prior to stimulation with TNF-α inhibited VCAM-1 and ICAM-1 protein levels by 62.2 ± 12.1% and 33.7 ± 5.7%, respectively. VCAM-1 and ICAM-1 mRNA levels were decreased by 55.8 ± 7.2% and 49.6 ± 7.9%, respectively, while DHCR24 mRNA expression increased by threefold. Transfection of HCAECs with DHCR24 siRNA attenuated the anti-inflammatory effects of (A-IV)rHDLs. Pre-incubation of TNF-α-activated HCAECs with (A-IV)rHDLs also inhibited nuclear translocation of the p65 subunit of nuclear factor-κB (NF-κB), and decreased IκBα phosphorylation.

Conclusion

These results indicate that apoA-IV inhibits vascular inflammation in vitro and in vivo by inhibiting NF-κB activation in a DHCR24-dependent manner.

Old Paradoxes and New Opportunities for Appetite Control in Obesity

Human obesity is accompanied by alterations in the blood concentrations of multiple circulating appetite regulators. Paradoxically, most of the appetite-inhibitory hormones are elevated in nonsyndromic obesity, while most of the appetite stimulatory hormones are reduced, perhaps reflecting vain attempts of regulation by inefficient feedback circuitries. In this context, it is important to understand which appetite regulators exhibit a convergent rather than paradoxical behavior and hence are likely to contribute to the maintenance of the obese state. Pharmacological interventions in obesity should preferentially consist of the supplementation of deficient appetite inhibitors or the neutralization of excessive appetite stimulators. Here, we critically analyze the current literature on appetite-regulatory peptide hormones. We propose a short-list of appetite modulators that may constitute the best candidates for therapeutic interventions.

Apolipoprotein A-IV acts as an endogenous anti-inflammatory protein and is reduced in treatment-naïve allergic patients and allergen-challenged mice

Background

Recent studies pointed to a crucial role for apolipoproteins in the pathogenesis of inflammatory diseases. However, the role of apolipoprotein‐IV (ApoA‐IV) in allergic inflammation has not been addressed thoroughly thus far.

Objective

Here, we explored the anti‐inflammatory effects and underlying signaling pathways of ApoA‐IV on eosinophil effector function in vitro and in vivo.

Methods

Migratory responsiveness, Ca²⁺‐flux and apoptosis of human peripheral blood eosinophils were assessed in vitro. Allergen‐driven airway inflammation was assessed in a mouse model of acute house dust mite‐induced asthma. ApoA‐IV serum levels were determined by ELISA.

Results

Recombinant ApoA‐IV potently inhibited eosinophil responsiveness in vitro as measured by Ca²⁺‐flux, shape change, integrin (CD11b) expression, and chemotaxis. The underlying molecular mechanism involved the activation of Rev‐ErbA‐α and induced a PI3K/PDK1/PKA‐dependent signaling cascade. Systemic application of ApoA‐IV prevented airway hyperresponsiveness (AHR) and airway eosinophilia in mice following allergen challenge. ApoA‐IV levels were decreased in serum from allergic patients compared to healthy controls.

Conclusion

Our data suggest that ApoA‐IV is an endogenous anti‐inflammatory protein that potently suppresses effector cell functions in eosinophils. Thus, exogenously applied ApoA‐IV may represent a novel pharmacological approach for the treatment of allergic inflammation and other eosinophil‐driven disorders.

Advanced Glycated apoA-IV Loses Its Ability to Prevent the LPS-Induced Reduction in Cholesterol Efflux-Related Gene Expression in Macrophages

We addressed how advanced glycation (AGE) affects the ability of apoA-IV to impair inflammation and restore the expression of genes involved in cholesterol efflux in lipopolysaccharide- (LPS-) treated macrophages. Recombinant human apoA-IV was nonenzymatically glycated by incubation with glycolaldehyde (GAD), incubated with cholesterol-loaded bone marrow-derived macrophages (BMDMs), and then stimulated with LPS prior to measurement of proinflammatory cytokines by ELISA. Genes involved in cholesterol efflux were quantified by RT-qPCR, and cholesterol efflux was measured by liquid scintillation counting. Carboxymethyllysine (CML) and pyrraline (PYR) levels, determined by Liquid Chromatography-Mass Spectrometry (LC-MS/MS), were greater in AGE-modified apoA-IV (AGE-apoA-IV) compared to unmodified-apoA-IV. AGE-apoA-IV inhibited expression of interleukin 6 (Il6), TNF-alpha (Tnf), IL-1 beta (Il1b), toll-like receptor 4 (Tlr4), tumor necrosis factor receptor-associated factor 6 (Traf6), Janus kinase 2/signal transducer and activator of transcription 3 (Jak2/Stat3), nuclear factor kappa B (Nfkb), and AGE receptor 1 (Ddost) as well as IL-6 and TNF-alpha secretion. AGE-apoA-IV alone did not change cholesterol efflux or ABCA-1 levels but was unable to restore the LPS-induced reduction in expression of Abca1 and Abcg1. AGE-apoA-IV inhibited inflammation but lost its ability to counteract the LPS-induced changes in expression of genes involved in macrophage cholesterol efflux that may contribute to atherosclerosis.

Apolipoprotein A-IV: A Multifunctional Protein Involved in Protection against Atherosclerosis and Diabetes

Apolipoprotein A-IV (apoA-IV) is a lipid-binding protein, which is primarily synthesized in the small intestine, packaged into chylomicrons, and secreted into intestinal lymph during fat absorption. In the circulation, apoA-IV is present on chylomicron remnants, high-density lipoproteins, and also in lipid-free form. ApoA-IV is involved in a myriad of physiological processes such as lipid absorption and metabolism, anti-atherosclerosis, platelet aggregation and thrombosis, glucose homeostasis, and food intake. ApoA-IV deficiency is associated with atherosclerosis and diabetes, which renders it as a potential therapeutic target for treatment of these diseases. While much has been learned about the physiological functions of apoA-IV using rodent models, the action of apoA-IV at the cellular and molecular levels is less understood, let alone apoA-IV-interacting partners. In this review, we will summarize the findings on the molecular function of apoA-IV and apoA-IV-interacting proteins. The information will shed light on the discovery of apoA-IV receptors and the understanding of the molecular mechanism underlying its mode of action.

Implications of PI3K/AKT/PTEN Signaling on Superoxide Dismutases Expression and in the Pathogenesis of Alzheimer's Disease

Alzheimer’s disease is a neurodegenerative sickness, where the speed of personal disease progression differs prominently due to genetic and environmental factors such as life style. Alzheimer’s disease is described by the construction of neuronal plaques and neurofibrillary tangles composed of phosphorylated tau protein. Mitochondrial dysfunction may be a noticeable feature of Alzheimer’s disease and increased production of reactive oxygen species has long been described. Superoxide dismutases (SODs) protect from excess reactive oxygen species to form less reactive hydrogen peroxide. It is suggested that SODs can play a protective role in neurodegeneration. In addition, PI3K/AKT pathway has been shown to play a critical role on the neuroprotection and inhibiting apoptosis via the enhancing expression of the SODs. This pathway appears to be crucial in Alzheimer’s disease because it is related to the tau protein hyper-phosphorylation. Dietary supplementation of several ordinary compounds may provide a novel therapeutic approach to brain disorders by modulating the function of the PI3K/AKT pathway. Understanding these systems may offer a better efficacy of new therapeutic approaches. In this review, we summarize recent progresses on the involvement of the SODs and PI3K/AKT pathway in neuroprotective signaling against Alzheimer’s disease.