Leptin administration restores the altered adipose and hepatic expression of aquaglyceroporins improving the non-alcoholic fatty liver of ob/ob mice

The Expanding Role of Aquaporin-1, Aquaporin-3 and Aquaporin-5 as Transceptors: Involvement in Cancer Development and Potential Druggability

Aquaporins (AQPs) are transmembrane proteins that facilitate the transport of water and small solutes, including glycerol, hydrogen peroxide and ions, across cell membranes. Beyond their established physiological roles in water regulation and metabolic processes, AQPs also exhibit receptor-like signaling activities in cancer-associated signaling pathways, integrating the dual roles of transporters and receptors, hence functioning as transceptors. This dual functionality underpins their critical involvement in cancer biology, where AQPs play key roles in promoting cell proliferation, migration, and invasion, contributing significantly to carcinogenesis. Among the AQPs, AQP1, AQP3 and AQP5 have been consistently identified as being aberrantly expressed in various tumor types. Their overexpression is strongly associated with tumor progression, metastasis, and poor patient prognosis. This review explores the pivotal roles of AQP1, AQP3 and AQP5 as transceptors in cancer biology, underscoring their importance as pharmacological targets. It highlights the urgent need for the development of effective modulators to target these AQPs, offering a promising avenue to enhance current therapeutic approaches for cancer treatment.

Astragaloside IV and cycloastragenol promote liver regeneration through regulation of hepatic oxidative homeostasis and glucose/lipid metabolism

BACKGROUND

The regenerative capacity of the liver is pivotal for mitigating various forms of liver injury and requires the rapid proliferation of hepatocytes. Aquaporin-9 (AQP9) provides vital support for hepatocyte proliferation by preserving hydrogen peroxide (H2O2) oxidative balance and glucose/lipid metabolism equilibrium within hepatocytes. Our previous study demonstrated that Radix Astragali (RA) decoction promotes liver regeneration by upregulating hepatic expression of AQP9, possibly via two major active constituents: astragaloside IV (AS-IV) and cycloastragenol (CAG).

PURPOSE

To verify that upregulated AQP9 expression in hepatocytes maintains liver oxidative balance and glucose/lipid metabolism homeostasis, and is the main pharmacological mechanism by which AS-IV and CAG promote liver regeneration.

STUDY DESIGN/METHODS

Effects of AS-IV and CAG on liver regeneration were scrutinized using a mouse model of 70 % partial hepatectomy (PHx). AQP9-targeted liver regeneration mediated by AS-IV and CAG was verified using AQP9 gene knockout mice (AQP9-/-). The AQP9 protein expression pattern in hepatocytes was determined using tdTomato-tagged AQP9 transgenic mice (AQP9-RFP). Potential mechanisms of AS-IV and CAG on liver regeneration were studied using real-time quantitative PCR, immunoblotting, staining with hematoxylin and eosin, oil red O, and periodic acid-Schiff, and immunofluorescence, immunohistochemistry, HyPerRed fluorescence, and biochemical analyses.

RESULTS

AS-IV and CAG promoted substantial liver regeneration and increased hepatic AQP9 expression in wild-type mice (AQP9+/+) following 70 % PHx, but had no discernible benefits in AQP9-/- mice. Both saponin compounds also helped maintain oxidative homeostasis by reducing levels of oxidative stress markers (reactive oxygen species [ROS], H2O2, and malondialdehyde) and elevating levels of ROS scavengers (glutathione and superoxide dismutase) in AQP9+/+ mice post-70 % PHx. This further activated the PI3K-AKT and insulin signaling pathways, thereby fostering liver regeneration. Furthermore, AS-IV and CAG both promoted hepatocyte glycerol uptake, increased gluconeogenesis, facilitated lipolysis, reduced glycolysis, and inhibited glycogen deposition, thus ensuring the energy supply required for liver regeneration.

CONCLUSION

This research is the first to demonstrate AS-IV and CAG as major active ingredients of RA that promote liver regeneration by upregulating hepatocyte AQP9 expression, improving hepatocyte glucose/lipid metabolism, and reducing oxidative stress damage, constituting a crucial pharmacological mechanism underlying the liver-protective effects of RA. The augmentation of hepatocyte AQP9 expression underscores an important aspect of the Qi-tonifying effect of RA. This study establishes AQP9 as an effective target for regulation of liver regeneration and provides a universal strategy for clinical drug intervention aimed at enhancing liver regeneration.

Aquaporins in Biliary Function: Pathophysiological Implications and Therapeutic Targeting

Aquaporins (AQPs) are transmembrane proteins permeable to water and a series of small solutes. AQPs play a key role in pathways of hepatobiliary secretion at the level of the liver, bile ducts, and gallbladder. AQP8 and -9 are pivotal in facilitating the osmotic water movement of hepatic bile, which is composed of 95% water. In the biliary tract, AQP1 and -4 are involved in the rearrangement of bile composition by mechanisms of reabsorption/secretion of water. In the gallbladder, AQP1 and -8 are also involved in trans-epithelial bidirectional water flow with the ultimate goal of bile concentration. Pathophysiologically, AQPs have been indicated as players in several hepatobiliary disorders, including cholestatic diseases and cholesterol cholelithiasis. Research on AQP function and the modulation of AQP expression is in progress, with the identification of potent and homolog-specific compounds modulating the expression or inhibiting these membrane channels with promising pharmacological developments. This review summarizes the contribution of AQPs in physiological and pathophysiological stages related to hepatobiliary function.

The Important Role of Aquaglyceroporin 7 in Health and Disease

Aquaporins (AQPs) are highly conserved small transmembrane proteins that facilitate the transport of water and small solutes across cell membranes. Aquaglyceroporin 7 (AQP7), a significant member of the AQP family, is widely distributed throughout the body. For years, AQP7 was predominantly recognized for its role as a small-molecule transporter, facilitating the passage of small molecular substances. However, growing studies have revealed that AQP7 is also involved in the regulation of lipid synthesis, gluconeogenesis, and energy homeostasis, and it is intimately linked to a variety of diseases, such as obesity, type 2 diabetes mellitus, cardiovascular diseases, cancer, and inflammatory bowel disease. This article presents a comprehensive overview of the structure of AQP7, its regulatory mechanisms, its vital roles in both healthy and diseased states, and potential therapeutic advancements. We hope that these studies will serve as a valuable reference for the development of future treatments and diagnostic protocols targeting AQP7.

Sex-specific effect of AQP9 deficiency on hepatic triglyceride metabolism in mice with diet-induced obesity

Studies in obese rats and human cell models of non-alcoholic fatty liver disease have indicated that knockdown of the hepatic glycerol channel aquaporin 9 (AQP9) leads to decreased hepatic steatosis. However, a study in leptin receptor-deficient mice did not find that knockout (KO) of AQP9 alleviated hepatic steatosis. The aim of this study was to investigate the effect of high-fat diet (HFD) on hepatic glycerol and triglyceride metabolism in male and female AQP9 KO mice. Male and female AQP9 KO mice and wild-type (WT) littermates were fed a HFD for 12 weeks. Weight, food intake and blood glucose were monitored throughout the study and tissue analysis included determination of hepatic triglyceride content and triglyceride secretion. The expression of key molecules for hepatic glycerol and triglyceride metabolism was evaluated using qPCR and western blotting. AQP9 KO and WT mice demonstrated a similar weight gain throughout the study period, and we found no evidence for AQP9 deficiency being associated with a reduced hepatic accumulation of triglyceride or a reduced blood glucose level. Instead, we show that the effect of AQP9 deficiency on hepatic lipid metabolism is sex-specific, with only male AQP9 KO mice having a reduced hepatic secretion of triglycerides and an elevated expression of peroxisome proliferator-activated receptor α. Male AQP9 KO mice had an elevated blood glucose level after 12 weeks of HFD when compared to baseline levels. Thus, we found no evidence for AQP9 inhibition being a target for alleviating the development of hepatic steatosis in mice with diet-induced obesity. KEY POINTS: This study investigates the effect of AQP9 deficiency on hepatic triglyceride metabolism in both male and female mice fed a high-fat diet (HFD) for 12 weeks. No evidence was found for AQP9 deficiency being associated with a reduced hepatic accumulation of triglyceride or a reduced blood glucose level. The effect of AQP9 deficiency on hepatic triglyceride metabolism is sex-specific. Male AQP9 KO mice had a reduced hepatic secretion of triglycerides and an elevated expression of peroxisome proliferator-activated receptor α, which likely promotes an increased hepatic fatty acid oxidation. Male AQP9 KO had an elevated blood glucose level after 12 weeks of HFD when compared to baseline levels.

Evidence That Peripheral Leptin Resistance in Omental Adipose Tissue and Liver Correlates with MASLD in Humans

Leptin regulates lipid metabolism, maximizing insulin sensitivity; however, peripheral leptin resistance is not fully understood, and its contribution to metabolic dysfunction-associated steatotic liver disease (MASLD) is unclear. This study evaluated the contribution of the leptin axis to MASLD in humans. Forty-three participants, mostly female (86.04%), who underwent cholecystectomy were biopsied. Of the participants, 24 were healthy controls, 8 had MASLD, and 11 had metabolic dysfunction-associated steatohepatitis (MASH). Clinical and biochemical data and the gene expression of leptin, leptin receptor (LEPR), suppressor of cytokine signaling 3 (SOCS3), sterol regulatory element-binding transcription factor 1 (SREBF1), stearoyl-CoA desaturase-1 (SCD1), and patatin-like phospholipase domain-containing protein 2 (PNPLA2), were determined from liver and adipose tissue. Higher serum leptin and LEPR levels in the omental adipose tissue (OAT) and liver with MASH were found. In the liver, LEPR was positively correlated with leptin expression in adipose tissue, and SOCS3 was correlated with SREBF1-SCD1. In OAT, SOCS3 was correlated with insulin resistance and transaminase enzymes (p < 0.05 for all. In conclusion, we evidenced the correlation between the peripheral leptin resistance axis in OAT-liver crosstalk and the complications of MASLD in humans.

Association of Aquaporin 7 and 9 with Obesity and Fatty Liver in db/db Mice

Aquaporin (AQP) 7 and AQP9 are membrane channel proteins called aquaglyceroporins and are related to glucose and lipid metabolism. AQP7 is mainly expressed in white adipose tissue (WAT) and is involved in releasing glycerol into the bloodstream. AQP9 is the glycerol channel in the liver that supplies glycerol to the hepatic cells. In this study, we investigated the relationship between the expression of aquaglyceroporins and lifestyle-related diseases, such as obesity and fatty liver, using 22-week-old db/db mice. Body weight, WAT, and liver weight showed increases in db/db mice. The levels of liver lipids, plasma lipids, insulin, and leptin were also increased in db/db mice. Gene expression related to fatty acid and triglyceride synthesis in the liver was enhanced in db/db mice. In addition, gene and protein expression of gluconeogenesis-related enzymes was increased. Conversely, lipolysis-related gene expression in WAT was reduced. In the db/db mice, AQP9 expression in the liver was raised; however, AQP7 expression in WAT was reduced. These results suggest that in db/db mice, enhanced hepatic AQP9 expression increased the supply of glycerol to the liver and induced fatty liver and hyperglycemia. Additionally, reduced AQP7 expression in WAT is associated with excessive lipid accumulation in adipocytes. Aquaglyceroporins are essential molecules for glucose and lipid metabolism, and may be potential target molecules for the treatment of obesity and lifestyle-related diseases.

Aquaporin 7 is upregulated through the PI3K-Akt pathway and modulates decidualisation of endometrial stromal cells

CONTEXT

Aquaporin 7 (AQP7) is selectively expressed in decidualised endometrial stromal cells (ESCs) of mice surrounding the embryonic implantation sites. However, the roles of AQP7 and the underlying mechanism that regulates AQP7 expression in endometrial decidualisation after implantation are still unclear.

AIMS

This study aimed to investigate the role of the PI3K-Akt pathway in regulating the expression of AQP7 in ESCs and decidualisation.

METHODS

Primary ESCs of pregnant mice were isolated to establish in vitro decidualisation models. PI3K inhibitor LY294002 was added to the decidualisation models, then AQP7 expression, changes in decidualised ESC morphology and expression of decidualisation marker molecules were examined.

KEY RESULTS

AQP7 knockdown reduced the proliferation and differentiation of ESCs with in vitro induced decidualisation. Furthermore, when the activity of PI3K was inhibited by LY294002, the expression of AQP7 in decidualised ESCs was decreased and both the proliferation and differentiation of ESCs were significantly reduced.

CONCLUSIONS

This indicates that AQP7 is a key molecule involved in endometrial decidualisation and the expression of AQP7 is upregulated through activation of the PI3K-Akt pathways, which promotes the proliferation and differentiation of the ESCs, thus affecting occurrence of decidualisation.

IMPLICATIONS

This study may provide a new biomarker for the diagnosis of infertility and a new drug target for the prevention and treatment of infertility.

Red and golden tomato administration improves fat diet-induced hepatic steatosis in rats by modulating HNF4α, Lepr, and GK expression

Introduction

Nonalcoholic fatty liver disease (NAFLD), characterized by lipid accumulation within hepatocytes exceeding 5% of liver weight, is strongly related to metabolic disorders, obesity, and diabetes and represents a health emergency worldwide. There is no standard therapy available for NAFLD. Lifestyle intervention, including phytonutrient intake, is key in preventing NAFLD development and progression.

Methods

We used a rat model of NAFLD to evaluate the effect of dietary supplementation with red tomato (RT) and golden tomato (GT)-a patented mix of fruit with varying degrees of ripeness and particularly rich in naringenin and chlorogenic acid-after steatosis development. We assessed the effects on body weight, metabolic profile, and hepatic steatosis.

Results and discussion

We found a correlation between the amelioration of all the parameters and the liver gene expression. Our results showed that, together with the reversion of steatosis, the consumption of RT and GT can cause a significant reduction in triglycerides, low-density lipoprotein-cholesterol, fasting glucose, and homeostasis model assessment index. Meanwhile, we observed an increase in high-density lipoprotein-cholesterol according to the amelioration of the general lipidic profile. Regarding hepatic gene expression, we found the upregulation of Gk and Hnf4α involved in metabolic homeostasis, Lepr involved in adipokine signaling, and Il6 and Tnf involved in inflammatory response. Taken together, our results suggest that dietary intake of red and golden tomatoes, as a nutraceutical approach, has potential in preventing and therapeutics of NAFLD.

Effects of multi-organ crosstalk on the physiology and pathology of adipose tissue

In previous studies, adipocytes were found to play an important role in regulating whole-body nutrition and energy balance, and are also important in energy metabolism, hormone secretion, and immune regulation. Different adipocytes have different contributions to the body, with white adipocytes primarily storing energy and brown adipocytes producing heat. Recently discovered beige adipocytes, which have characteristics in between white and brown adipocytes, also have the potential to produce heat. Adipocytes interact with other cells in the microenvironment to promote blood vessel growth and immune and neural network interactions. Adipose tissue plays an important role in obesity, metabolic syndrome, and type 2 diabetes. Dysfunction in adipose tissue endocrine and immune regulation can cause and promote the occurrence and development of related diseases. Adipose tissue can also secrete multiple cytokines, which can interact with organs; however, previous studies have not comprehensively summarized the interaction between adipose tissue and other organs. This article reviews the effect of multi-organ crosstalk on the physiology and pathology of adipose tissue, including interactions between the central nervous system, heart, liver, skeletal muscle, and intestines, as well as the mechanisms of adipose tissue in the development of various diseases and its role in disease treatment. It emphasizes the importance of a deeper understanding of these mechanisms for the prevention and treatment of related diseases. Determining these mechanisms has enormous potential for identifying new targets for treating diabetes, metabolic disorders, and cardiovascular diseases.

Increased Aquaporin-7 Expression Is Associated with Changes in Rat Brown Adipose Tissue Whitening in Obesity: Impact of Cold Exposure and Bariatric Surgery

Glycerol is a key metabolite for lipid accumulation in insulin-sensitive tissues. We examined the role of aquaporin-7 (AQP7), the main glycerol channel in adipocytes, in the improvement of brown adipose tissue (BAT) whitening, a process whereby brown adipocytes differentiate into white-like unilocular cells, after cold exposure or bariatric surgery in male Wistar rats with diet-induced obesity (DIO) (n = 229). DIO promoted BAT whitening, evidenced by increased BAT hypertrophy, steatosis and upregulation of the lipogenic factors Pparg2, Mogat2 and Dgat1. AQP7 was detected in BAT capillary endothelial cells and brown adipocytes, and its expression was upregulated by DIO. Interestingly, AQP7 gene and protein expressions were downregulated after cold exposure (4 °C) for 1 week or one month after sleeve gastrectomy in parallel to the improvement of BAT whitening. Moreover, Aqp7 mRNA expression was positively associated with transcripts of the lipogenic factors Pparg2, Mogat2 and Dgat1 and regulated by lipogenic (ghrelin) and lipolytic (isoproterenol and leptin) signals. Together, the upregulation of AQP7 in DIO might contribute to glycerol influx used for triacylglycerol synthesis in brown adipocytes, and hence, BAT whitening. This process is reversible by cold exposure and bariatric surgery, thereby suggesting the potential of targeting BAT AQP7 as an anti-obesity therapy.

Aquaporins in Obesity

Obesity is one of the most important metabolic disorders of this century and is associated with a cluster of the most dangerous cardiovascular disease risk factors, such as insulin resistance and diabetes, dyslipidemia, and hypertension, collectively named Metabolic Syndrome. The role of aquaporins (AQP) in glycerol metabolism facilitating glycerol release from the adipose tissue and distribution to various tissues and organs unveils these membrane channels as important players in lipid balance and energy homeostasis and points to their involvement in a variety of pathophysiological mechanisms including insulin resistance, obesity, and diabetes. This review summarizes the physiologic role of aquaglyceroporins in glycerol metabolism and lipid homeostasis, describing their specific tissue distribution, involvement in glycerol balance, and implication in obesity and fat-related metabolic complications. The development of specify pharmacologic modulators able to regulate aquaglyceroporins expression and function, in particular AQP7 in adipose tissue, might constitute a novel approach for controlling obesity and other metabolic disorders.

Growth-Promoting Effects of Zhenqi Granules on Finishing Pigs

Developing nonantibiotic livestock growth promoters attracts intensive interest in the post-antibiotic era. In this study, we investigated the growth-promoting efficacy of Zhenqi granules (ZQ) in pigs and further explored the possible mechanisms by transcriptomics analysis. Weaned piglets (52 days old with an average body weight of 17.92 kg) were fed with diets supplemented with different doses of ZQ (0 g/kg, 1 g/kg, and 2 g/kg) for 30 days and continued observations for an additional 32 days after removing ZQ from the diets. Compared with the control group, the average daily gain, carcass weight, average back fat thickness, and fat meat percentage of the group supplemented with 1 g/kg of ZQ showed a significant increase, and the feed/gain ratio was lower. The group supplemented with 2 g/kg of ZQ also showed a significant increase in average daily gain and average backfat thickness. A transcriptomics analysis revealed that the supplementation of ZQ at 1 g/kg upregulated the expression of genes related to collagen biosynthesis and lipid biosynthesis in skeletal muscle and liver. This effect was primarily through upregulating the mRNA levels of structural proteins and lipid-related enzymes. This study demonstrates the growth-promoting efficacy of ZQ and provides some insights of the mechanism of growth promotion.

Adipose tissue plays a major role in retinoic acid-mediated metabolic homoeostasis

Retinoic acid (RA), a bioactive metabolite of vitamin A, has shown therapeutic effects in liver disease, and its effect in improving non-alcoholic fatty liver disease (NAFLD) is associated with the inhibition of adipogenesis in the white adipose tissue (WAT) and fatty acid oxidation induction in the liver. However, the major target organ of RA is unknown. We performed chronic administration of RA in high-fat diet (HFD)-induced NAFLD mice. Further, hepatic and adipose cells were used to study the direct effect of RA on lipid metabolism. In addition, qRT-PCR was performed to examine differential gene expression in mouse adipose tissue. RA administration ameliorated NAFLD in HFD-induced obese mice and increased mouse energy expenditure. Although RA had therapeutic effects on liver histology and lipid accumulation, it did not directly affect lipid metabolism in HepG2 cells. In contrast, RA reduced the weight of several adipose tissues and improved lipid accumulation in OP9 cells. In addition, RA upregulated genes responsible for fatty acid oxidation and thermogenesis in three different WATs. Our work suggests that the liver may not be the main target organ of RA during NAFLD treatment. WAT browning induced by RA may be the primary contributor towards the amelioration of NAFLD in HFD-induced obese mice.

Hepatobiliary Thyroid Hormone Deficiency Impacts Bile Acid Hydrophilicity and Aquaporins in Cholestatic C57BL/6J Mice

Women are more prone to develop either hypothyroidism or cholesterol gallstones than men. However, a male predominance in cholesterol gallstones under hypothyroidism was reported. Recently, a novel pathogenic link between thyroid hormone (TH) deficiency and cholesterol gallstones has been described in male mice. Here, we investigate if TH deficiency impacts cholesterol gallstone formation in females by the same mechanism. Three-month-old C57BL/6J mice were randomly divided into a control, a TH deficient, a lithogenic, and a lithogenic + TH deficient group and diet-treated for two, four, and six weeks. Gallstone prevalence, liver function tests, bile composition, hepatic gene expression, and gallbladder aquaporin expression and localization were investigated. Cholesterol gallstones were observed in lithogenic + TH deficient but not lithogenic only female mice. Diminished hydrophilicity of primary bile acids due to decreased gene expression of hepatic detoxification phase II enzymes was observed. A sex-specific expression and localization of hepatobiliary aquaporins involved in transcellular water and glycerol permeability was observed under TH deficient and lithogenic conditions. TH deficiency promotes cholesterol gallstone formation in female C57BL/6J mice by the same mechanism as observed in males. However, cholesterol gallstone prevalence was lower in female than male C57BL/6J mice. Interestingly, the sex-specific expression and localization of hepatobiliary aquaporins could protect female C57BL/6J mice to cholestasis and could reduce biliary water transport in male C57BL/6J mice possibly contributing to the sex-dependent cholesterol gallstone prevalence under TH deficiency.

Characterization of the Aquaporin-9 Inhibitor RG100204 In Vitro and in db/db Mice

Aquaporin-9 (AQP9) is a facilitator of glycerol and other small neutral solute transmembrane diffusion. Identification of specific inhibitors for aquaporin family proteins has been difficult, due to high sequence similarity between the 13 human isoforms, and due to the limited channel surface areas that permit inhibitor binding. The few AQP9 inhibitor molecules described to date were not suitable for in vivo experiments. We now describe the characterization of a new small molecule AQP9 inhibitor, RG100204 in cell-based calcein-quenching assays, and by stopped-flow light-scattering recordings of AQP9 permeability in proteoliposomes. Moreover, we investigated the effects of RG100204 on glycerol metabolism in mice. In cell-based assays, RG100204 blocked AQP9 water permeability and glycerol permeability with similar, high potency (~5 × 10-8 M). AQP9 channel blocking by RG100204 was confirmed in proteoliposomes. After oral gavage of db/db mice with RG100204, a dose-dependent elevation of plasma glycerol was observed. A blood glucose-lowering effect was not statistically significant. These experiments establish RG100204 as a direct blocker of the AQP9 channel, and suggest its use as an experimental tool for in vivo experiments on AQP9 function.

Untargeted metabolomics reveals the role of AQP9 in nonalcoholic fatty liver disease in a mice model

Previous studies have shown that AQP9 plays an important role in energy metabolism in nonalcoholic fatty liver disease (NAFLD). Recently, metabolomic analyses were used to determine the slight changes in metabolic profiles and helped to understand the disease progression, therapeutic intervention of NAFLD. A mouse model of NAFLD was established with a high-fat diet (HFD), and Aqp9 knockout mice were constructed. Untargeted metabolomics techniques were used to evaluate the potential mechanism of the effect of AQP9 in NAFLD. The results indicated that AQP9 plays a regulatory role in the occurrence of NAFLD. Moreover, a total of 220 candidate biomarkers were screened and identified. Cluster analysis and enrichment analysis of differential metabolites indicated that fatty acid biosynthesis was mainly disturbed when compared against the control group, which was mitigated by knockout of Aqp9. These results show that untargeted metabolomics help to understand the effects of AQP9 in NAFLD.

Appetite regulating genes in zebrafish gut; a gene expression study

The underlying molecular pathophysiology of feeding disorders, particularly in peripheral organs, is still largely unknown. A range of molecular factors encoded by appetite-regulating genes are already described to control feeding behaviour in the brain. However, the important role of the gastrointestinal tract in the regulation of appetite and feeding in connection to the brain has gained more attention in the recent years. An example of such inter-organ connection can be the signals mediated by leptin, a key regulator of body weight, food intake and metabolism, with conserved anorexigenic effects in vertebrates. Leptin signals functions through its receptor (lepr) in multiple organs, including the brain and the gastrointestinal tract. So far, the regulatory connections between leptin signal and other appetite-regulating genes remain unclear, particularly in the gastrointestinal system. In this study, we used a zebrafish mutant with impaired function of leptin receptor to explore gut expression patterns of appetite-regulating genes, under different feeding conditions (normal feeding, 7-day fasting, 2 and 6-hours refeeding). We provide evidence that most appetite-regulating genes are expressed in the zebrafish gut. On one hand, we did not observed significant differences in the expression of orexigenic genes (except for hcrt) after changes in the feeding condition. On the other hand, we found 8 anorexigenic genes in wild-types (cart2, cart3, dbi, oxt, nmu, nucb2a, pacap and pomc), as well as 4 genes in lepr mutants (cart3, kiss1, kiss1r and nucb2a), to be differentially expressed in the zebrafish gut after changes in feeding conditions. Most of these genes also showed significant differences in their expression between wild-type and lepr mutant. Finally, we observed that impaired leptin signalling influences potential regulatory connections between anorexigenic genes in zebrafish gut. Altogether, these transcriptional changes propose a potential role of leptin signal in the regulation of feeding through changes in expression of certain anorexigenic genes in the gastrointestinal tract of zebrafish.

Meta-Inflammation and De Novo Lipogenesis Markers Are Involved in Metabolic Associated Fatty Liver Disease Progression in BTBR ob/ob Mice

Metabolic associated fatty liver disease (MAFLD) is a hepatic manifestation of metabolic syndrome and usually associated with obesity and diabetes. Our aim is to characterize the pathophysiological mechanism involved in MAFLD development in Black Tan and brachyuric (BTBR) insulin-resistant mice in combination with leptin deficiency (ob/ob). We studied liver morphology and biochemistry on our diabetic and obese mice model (BTBR ob/ob) as well as a diabetic non-obese control (BTBR + streptozotocin) and non-diabetic control mice (BTBR wild type) from 4–22 weeks. Lipid composition was assessed, and lipid related pathways were studied at transcriptional and protein level. Microvesicular steatosis was evident in BTBR ob/ob from week 6, progressing to macrovesicular in the following weeks. At 12th week, inflammatory clusters, activation of STAT3 and Nrf2 signaling pathways, and hepatocellular ballooning. At 22 weeks, the histopathological features previously observed were maintained and no signs of fibrosis were detected. Lipidomic analysis showed profiles associated with de novo lipogenesis (DNL). BTBR ob/ob mice develop MAFLD profile that resemble pathological features observed in humans, with overactivation of inflammatory response, oxidative stress and DNL signaling pathways. Therefore, BTBR ob/ob mouse is an excellent model for the study of the steatosis to steatohepatitis transition.

Localization of aquaglyceroporins in human and murine white adipose tissue

The glycerol channel AQP7 facilitates glycerol efflux from adipose tissue (AT), and AQP7 deficiency has been suggested to promote obesity. However, the release of glycerol from AT is not fully blocked in AQP7-deficient mice, which suggests that either alternative glycerol channels are present in AT or significant simple diffusion of glycerol occurs. Previous investigations of the expression of other aquaglyceroporins (AQP3, AQP9, AQP10) than AQP7 in AT are contradictory. Therefore, we here aim at determining the cellular localization of AQP3 and AQP9 in addition to AQP7 in human and mouse AT using well-characterized antibodies for immunohistochemistry (IHC) and immunoblotting as well as available single-cell transcriptomic data from human and mouse AT. We confirm that AQP7 is expressed in endothelial cells and adipocytes in human AT and find ex vivo evidence for interaction between AQP7 and perilipin-1 in adipocytes. In addition, labeling for AQP7 in human AT also includes CD68-positive cells. No labeling for AQP3 or AQP9 was identified in endothelial cells or adipocytes in human or mouse AT using IHC. Instead, in human AT, AQP3 was predominantly found in erythrocytes, whereas AQP9 expression was observed in a small number of CD15-positive cells. The transcriptomic data revealed that AQP3 mRNA was found in a low number of cells in most of the identified cell clusters, whereas AQP9 mRNA was found in myeloid cell clusters as well as in clusters likely representing mesothelial progenitor cells. No AQP10 mRNA was identified in human AT. In conclusion, the presented results do not suggest a functional overlap between AQP3/AQP9/AQP10 and AQP7 in human or mouse white AT.

Aquaglyceroporin Modulators as Emergent Pharmacological Molecules for Human Diseases

Aquaglyceroporins, a sub-class of aquaporins that facilitate the diffusion of water, glycerol and other small uncharged solutes across cell membranes, have been recognized for their important role in human physiology and their involvement in multiple disorders, mostly related to disturbed energy homeostasis. Aquaglyceroporins dysfunction in a variety of pathological conditions highlighted their targeting as novel therapeutic strategies, boosting the search for potent and selective modulators with pharmacological properties. The identification of selective inhibitors with potential clinical applications has been challenging, relying on accurate assays to measure membrane glycerol permeability and validate effective functional blockers. Additionally, biologicals such as hormones and natural compounds have been revealed as alternative strategies to modulate aquaglyceroporins via their gene and protein expression. This review summarizes the current knowledge of aquaglyceroporins’ involvement in several pathologies and the experimental approaches used to evaluate glycerol permeability and aquaglyceroporin modulation. In addition, we provide an update on aquaglyceroporins modulators reported to impact disease, unveiling aquaglyceroporin pharmacological targeting as a promising approach for innovative therapeutics.

The Physiological Role of Irisin in the Regulation of Muscle Glucose Homeostasis

Irisin is a myokine that primarily targets adipose tissue, where it increases energy expenditure and contributes to the beneficial effects of exercise through the browning of white adipose tissue. As our knowledge has deepened in recent years, muscle has been found to be a major target organ for irisin as well. Several studies have attempted to characterize the role of irisin in muscle to improve glucose metabolism through mechanisms such as reducing insulin resistance. Although they are very intriguing reports, some contradictory results make it difficult to grasp the whole picture of the action of irisin on muscle. In this review, we attempted to organize the current knowledge of the role of irisin in muscle glucose metabolism. We discussed the direct effects of irisin on glucose metabolism in three types of muscle, that is, skeletal muscle, smooth muscle, and the myocardium. We also describe irisin’s effects on mitochondria and its interactions with other hormones. Furthermore, to consider the relationship between the irisin-induced improvement of glucose metabolism in muscle and systemic disorders of glucose metabolism, we reviewed the results from animal interventional studies and human clinical studies.

Role of Leptin in the Digestive System

Leptin is a pluripotent peptide hormone produced mainly by adipocytes, as well as by other tissues such as the stomach. Leptin primarily acts on the central nervous system, particularly the hypothalamus, where this hormone regulates energy homeostasis and neuroendocrine function. Owing to this, disruption of leptin signaling has been linked with numerous pathological conditions. Recent studies have also highlighted the diverse roles of leptin in the digestive system including immune regulation, cell proliferation, tissue healing, and glucose metabolism. Of note, leptin acts differently under physiological and pathological conditions. Here, we review the current knowledge on the functions of leptin and its downstream signaling in the gastrointestinal tract and accessory digestive organs, with an emphasis on its physiological and pathological implications. We also discuss the current therapeutic uses of recombinant leptin, as well as its limitations.

Aquaporin regulation in metabolic organs

Aquaporins (AQPs) are a family of 13 small trans-membrane proteins, which facilitate shuttling of glycerol, water and urea. The peculiar role of AQPs in glycerol transport makes them attractive targets in metabolic organs since glycerol represents the backbone of triglyceride synthesis. Importantly, AQPs are known to be regulated by various nuclear receptors which in turn govern lipid and glucose metabolism as well as inflammatory cascades. Here, we review the role of AQPs regulation in metabolic organs exploring their physiological impact in health and disease.

Pathophysiology of NAFLD and NASH in Experimental Models: The Role of Food Intake Regulating Peptides

Obesity, diabetes, insulin resistance, sedentary lifestyle, and Western diet are the key factors underlying non-alcoholic fatty liver disease (NAFLD), one of the most common liver diseases in developed countries. In many cases, NAFLD further progresses to non-alcoholic steatohepatitis (NASH), fibrosis, cirrhosis, and to hepatocellular carcinoma. The hepatic lipotoxicity and non-liver factors, such as adipose tissue inflammation and gastrointestinal imbalances were linked to evolution of NAFLD. Nowadays, the degree of adipose tissue inflammation was shown to directly correlate with the severity of NAFLD. Consumption of higher caloric intake is increasingly emerging as a fuel of metabolic inflammation not only in obesity-related disorders but also NAFLD. However, multiple causes of NAFLD are the reason why the mechanisms of NAFLD progression to NASH are still not well understood. In this review, we explore the role of food intake regulating peptides in NAFLD and NASH mouse models. Leptin, an anorexigenic peptide, is involved in hepatic metabolism, and has an effect on NAFLD experimental models. Glucagon-like peptide-1 (GLP-1), another anorexigenic peptide, and GLP-1 receptor agonists (GLP-1R), represent potential therapeutic agents to prevent NAFLD progression to NASH. On the other hand, the deletion of ghrelin, an orexigenic peptide, prevents age-associated hepatic steatosis in mice. Because of the increasing incidence of NAFLD and NASH worldwide, the selection of appropriate animal models is important to clarify aspects of pathogenesis and progression in this field.

Dim Light at Night Disturbs Molecular Pathways of Lipid Metabolism

Dim light at night (dLAN) is associated with metabolic risk but the specific effects on lipid metabolism have only been evaluated to a limited extent. Therefore, to explore whether dLAN can compromise lipid metabolic homeostasis in healthy individuals, we exposed Wistar rats to dLAN (~2 lx) for 2 and 5 weeks and analyzed the main lipogenic pathways in the liver and epididymal fat pad, including the control mechanisms at the hormonal and molecular level. We found that dLAN promoted hepatic triacylglycerol accumulation, upregulated hepatic genes involved in de novo synthesis of fatty acids, and elevated glucose and fatty acid uptake. These observations were paralleled with suppressed fatty acid synthesis in the adipose tissue and altered plasma adipokine levels, indicating disturbed adipocyte metabolic function with a potential negative impact on liver metabolism. Moreover, dLAN-exposed rats displayed an elevated expression of two peroxisome proliferator-activated receptor family members (Pparα and Pparγ) in the liver and adipose tissue, suggesting the deregulation of important metabolic transcription factors. Together, our results demonstrate that an impaired balance of lipid biosynthetic pathways caused by dLAN can increase lipid storage in the liver, thereby accounting for a potential linking mechanism between dLAN and metabolic diseases.

AQP3 Facilitates Proliferation and Adipogenic Differentiation of Porcine Intramuscular Adipocytes

The meat quality of animal products is closely related to the intramuscular fat content. Aquaglyceroporin (AQP) defines a class of water/glycerol channels that primarily facilitate the passive transport of glycerol and water across biological membranes. In this study, the AQP3 protein of the AQP family was mainly studied in the adipogenic function of intramuscular adipocytes in pigs. Here, we found that AQP3 was increased at both mRNA and protein levels upon adipogenic stimuli in porcine intramuscular adipocytes in vitro. Western blot results showed knockdown of AQP3 by siRNA significantly suppressed the expression of adipogenic genes (PPARγ, aP2, etc.), repressed Akt phosphorylation, as well as reducing lipid accumulation. Furthermore, deletion of AQP3 by siRNA significantly downregulated expression of cell cycle genes (cyclin D, E), and decreased the number of EdU-positive cells as well as cell viability. Collectively, our data indicate that AQP3 is of great importance in both adipogenic differentiation and proliferation in intramuscular adipocytes, providing a potential target for modulating fat infiltration in skeletal muscles.

Effects of gut microbiota on leptin expression and body weight are lessened by high-fat diet in mice

Aberration in leptin expression is one of the most frequent features in the onset and progression of obesity, but the underlying mechanisms are still unclear and need to be clarified. This study investigated the effects of the absence of gut microbiota on body weight and the expression and promoter methylation of the leptin. Male C57 BL/6 J germ-free (GF) and conventional (CV) mice (aged 4-5 weeks) were fed either a normal-fat diet (NFD) or a high-fat diet (HFD) for 16 weeks. Six to eight mice from each group, at 15 weeks, were administered exogenous leptin for 7 d. Leptin expression and body weight gain in GF mice were increased by NFD with more CpG sites hypermethylated at the leptin promoter, whereas there was no change with HFD, compared with CV mice. Adipose or hepatic expression of genes associated with fat synthesis (Acc1, Fas and Srebp-1c), hydrolysis and oxidation (Atgl, Cpt1a, Cpt1c, Ppar-α and Pgc-1α) was lower, and hypothalamus expression of Pomc and Socs3 was higher in GF mice than levels in CV mice, particularly with NFD feeding. Exogenous leptin reduced body weight in both types of mice, with a greater effect on CV mice with NFD. Adipose Lep-R expression was up-regulated, and hepatic Fas and hypothalamic Socs3 were down-regulated in both types of mice. Expression of fat hydrolysis and oxidative genes (Atgl, Hsl, Cpt1a, Cpt1c, Ppar-α and Pgc-1α) was up-regulated in CV mice. Therefore, the effects of gut microbiota on the leptin expression and body weight were affected by dietary fat intake.

Aquaporin-9 is involved in the lipid-lowering activity of the nutraceutical silybin on hepatocytes through modulation of autophagy and lipid droplets composition

Hepatic steatosis is the hallmark of non-alcoholic fatty liver disease (NAFLD), the hepatic manifestation of the metabolic syndrome and insulin resistance with potential evolution towards non-alcoholic steatohepatitis (NASH), cirrhosis and hepatocellular carcinoma. Key roles of autophagy and oxidative stress in hepatic lipid accumulation and NAFLD progression are recognized. Here, we employed a rat hepatoma cell model of NAFLD progression made of FaO cells exposed to oleate/palmitate followed or not by TNFα treatment to investigate the molecular mechanisms through which silybin, a lipid-lowering nutraceutical, may improve hepatic lipid dyshomeostasis. The beneficial effect of silybin was found to involve amelioration of the fatty acids profile of lipid droplets, stimulation of the mitochondrial oxidation and upregulation of a microRNA of pivotal relevance in hepatic fat metabolism, miR-122. Silybin was also found to restore the levels of Aquaporin-9 (AQP9) and glycerol permeability while reducing the activation of the oxidative stress-dependent transcription factor NF-κB, and autophagy turnover. In conclusion, silybin was shown to have molecular effects on signaling pathways that were previously unknown and potentially protect the hepatocyte. These actions intersect TG metabolism, fat-induced autophagy and AQP9-mediated glycerol transport in hepatocytes.

Sex-Specific Effect of High-Fat Diet on Glycerol Metabolism in Murine Adipose Tissue and Liver

Obesity is associated with increased plasma glycerol levels. The coordinated regulation of glycerol channels in adipose tissue (AQP7) and the liver (AQP9) has been suggested as an important contributor to the pathophysiology of type-2-diabetes mellitus, as it would provide glycerol for hepatic synthesis of glucose and triglycerides. The regulation of AQP7 and AQP9 is influenced by sex. This study investigates the effect of a high-fat diet (HFD) on glycerol metabolism in mice and the influence of sex and GLP-1-receptor agonist treatment. Female and male C57BL/6JRj mice were fed either a control diet or a HFD for 12 or 24 weeks. Liraglutide was administered (1 mg/kg/day) to a subset of female mice. After 12 weeks of HFD, females had gained less weight than males. In adipose tissue, only females demonstrated an increased abundance of AQP7, whereas only males demonstrated a significant increase in glycerol kinase abundance and adipocyte size. 24 weeks of HFD resulted in a more comparable effect on weight gain and adipose tissue in females and males. HFD resulted in marked hepatic steatosis in males only and had no significant effect on the hepatic abundance of AQP9. Liraglutide treatment generally attenuated the effects of HFD on glycerol metabolism. In conclusion, no coordinated upregulation of glycerol channels in adipose tissue and liver was observed in response to HFD. The effect of HFD on glycerol metabolism is sex-specific in mice, and we propose that the increased AQP7 abundance in female adipose tissue could contribute to their less severe response to HFD.

Effects of probiotics on nonalcoholic fatty liver disease: a systematic review and meta-analysis

BACKGROUND

Nonalcoholic fatty liver disease (NAFLD) has become prevalent in recent decades, especially in developed countries, and approaches for the prevention and treatment of NAFLD are not clear. The aim of this research was to analyze and summarize randomized controlled trials that investigated the effects of probiotics on NAFLD.

METHODS

Seven databases (PubMed, Embase, the Web of Science, the Cochrane Library, China National Knowledge Infrastructure, Wan Fang Data, and VIP Database) were searched. Then, eligible studies were identified. Finally, proper data extraction, synthesis and analysis were performed by trained researchers.

RESULTS

Anthropometric parameters: with use of probiotics weight was reduced by 2.31 kg, and body mass index (BMI) was reduced by 1.08 kg/m². Liver function: probiotic treatment reduced the alanine aminotransferase level by 7.22 U/l, the aspartate aminotransferase level by 7.22 U/l, the alkaline phosphatase level by 25.87 U/l, and the glutamyl transpeptidase level by -5.76 U/l. Lipid profiles: total cholesterol, low-density lipoprotein cholesterol, and triglycerides were significantly decreased after probiotic treatment. Their overall effects (shown as standard mean difference) were -0.73, -0.54, and -0.36, respectively. Plasma glucose: probiotics reduced the plasma glucose level by 4.45 mg/dl and the insulin level by 0.63. Cytokines: probiotic treatment decreased tumor necrosis factor alpha by 0.62 and leptin by 1.14. Degree of liver fat infiltration (DFI): the related risk of probiotics for restoring DFI was 2.47 (95% confidence interval, 1.61-3.81, p < 0.001).

CONCLUSION

Probiotic treatment or supplementation is a promising therapeutic method for NAFLD.

Functional Relationship between Leptin and Nitric Oxide in Metabolism

Leptin, the product of the ob gene, was originally described as a satiety factor, playing a crucial role in the control of body weight. Nevertheless, the wide distribution of leptin receptors in peripheral tissues supports that leptin exerts pleiotropic biological effects, consisting of the modulation of numerous processes including thermogenesis, reproduction, angiogenesis, hematopoiesis, osteogenesis, neuroendocrine, and immune functions as well as arterial pressure control. Nitric oxide (NO) is a free radical synthesized from L-arginine by the action of the NO synthase (NOS) enzyme. Three NOS isoforms have been identified: the neuronal NOS (nNOS) and endothelial NOS (eNOS) constitutive isoforms, and the inducible NOS (iNOS). NO mediates multiple biological effects in a variety of physiological systems such as energy balance, blood pressure, reproduction, immune response, or reproduction. Leptin and NO on their own participate in multiple common physiological processes, with a functional relationship between both factors having been identified. The present review describes the functional relationship between leptin and NO in different physiological processes.

Impact of leptin deficiency compared with neuronal-specific leptin receptor deletion on cardiometabolic regulation

The main goal of this study was to compare the impact of total body leptin deficiency with neuronal-specific leptin receptor (LR) deletion on metabolic and cardiovascular regulation. Liver fat, diacylglycerol acyltransferase-2 (DGTA2), and CD36 protein content were measured in wild-type (WT), nervous system LR-deficient (LR/Nestin-Cre), and leptin deficient (ob/ob) mice. Blood pressure (BP) and heart rate (HR) were recorded by telemetry, and motor activity (MA) and oxygen consumption (V̇o₂) were monitored at 24 wk of age. Female and male LR/Nestin-Cre and ob/ob mice were heavier than WT mice (62 ± 5 and 61 ± 3 vs. 31 ± 1 g) and hyperphagic (6.2 ± 0.5 and 6.1 ± 0.7 vs. 3.5 ± 1.0 g/day), with reduced V̇o₂ (27 ± 1 and 33 ± 1 vs 49 ± 3 ml·kg^-1·min^-1) and decreased MA (3 ± 1 and 7 ± 2 vs 676 ± 105 cm/h). They were also hyperinsulinemic and hyperglycemic compared with WT mice. LR/Nestin-Cre mice had high levels of plasma leptin, while ob/ob mice had undetectable leptin levels. Despite comparable obesity, LR/Nestin-Cre mice had lower liver fat content, DGTA2, and CD36 protein levels than ob/ob mice. Male WT, LR/Nestin-Cre, and ob/ob mice exhibited similar BP (111 ± 3, 110 ± 1 and 109 ± 2 mmHg). Female LR/Nestin-Cre and ob/ob mice, however, had higher BP than WT females despite similar metabolic phenotypes compared with male LR/Nestin-Cre and ob/ob mice. These results indicate that although nervous system LRs play a crucial role in regulating body weight and glucose homeostasis, peripheral LRs regulate liver fat deposition. In addition, our results suggest potential sex differences in the impact of obesity on BP regulation.

Modulation of Aquaporins by Dietary Patterns and Plant Bioactive Compounds

Healthful dietary patterns and bioactive compounds supplementation can be adopted as simple and easy intervention to prevent, attenuate or cure clinical disorders, especially when it comes to degenerative and chronic diseases. In the recent years, a growing body of evidence indicates Aquaporins (AQPs), a family of membrane channel proteins widely expressed in the human body, among the targets underlying the beneficial action played by some food nutrients and phytochemical compounds. Here, we provide an overview of what is known regarding the AQP modulation exerted by healthful dietary patterns and plant polyphenols.

COUP-TFII revisited: Its role in metabolic gene regulation

Chicken Ovalbumin Upstream Promoter Transcription Factor II (COUP-TFII) is an orphan member of the nuclear receptor family of transcriptional regulators. Although hormonal activation of COUP-TFII has not yet been identified, rodent genetic models have uncovered vital and diverse roles for COUP-TFII in biological processes. These include control of cardiac function and angiogenesis, reproduction, neuronal development, cell fate and organogenesis. Recently, an emerging body of evidence has demonstrated COUP-TFII involvement in various metabolic systems such as adipogenesis, lipid metabolism, hepatic gluconeogenesis, insulin secretion, and regulation of blood pressure. The potential relevance of these observations to human pathology has been corroborated by the identification of single nucleotide polymorphism in the human COUP-TFII promoter controlling insulin sensitivity. Of particular interest to metabolism is the ability of COUP-TFII to interact with the Glucocorticoid Receptor (GR). This interaction is known to control gluconeogenesis, principally through direct binding of COUP-TFII/GR complexes to the promoters of gluconeogenic enzyme genes. However, it is likely that this interaction is critical to other metabolic processes, since GR, like COUP-TFII, is an essential regulator of adipogenesis, insulin sensitivity, and blood pressure. This review will highlight these unique roles of COUP-TFII in metabolic gene regulation.

Effects of Diets on Adipose Tissue

BACKGROUND

Obesity is a major health problem that has become a global epidemic. Overweight and obesity are commonly associated with the development of several pathologies, such as insulin resistance, cardiovascular diseases, sleep apnea and several types of cancer, which can lead to further morbidity and mortality. An increased abdominal adiposity renders overweight and obese individuals more prone to metabolic and cardiovascular problems.

OBJECTIVE

This Review aims to describe the dietary strategies to deal with excess adiposity given the medical, social and economic consequences of obesity.

METHODS

One hundred and eighty-five papers were included in the present Review.

RESULTS

Excess adiposity leads to several changes in the biology, morphology and function of the adipose tissue, such as adipocyte hypertrophy and hyperplasia, adipose tissue inflammation and fibrosis and an impaired secretion of adipokines, contributing to the onset of obesity- related comorbidities. The first approach for obesity management and prevention is the implementation of a diet combined with physical activity. The present review summarizes the compelling evidence showing body composition changes, impact on cardiometabolism and potential adverse effects of very-low calorie, low- and high-carbohydrate, high-protein or low-fat diets. The use of macronutrients during the preprandial and postprandial state has been also reviewed to better understand the metabolic changes induced by different dietary interventions.

CONCLUSION

Dietary changes should be individualised, tailored to food preferences and allow for flexible approaches to reducing calorie intake in order to increase the motivation and compliance of overweight and obese patients.

Modulation of aquaporin gene expression by n-3 long-chain PUFA lipid structures in white and brown adipose tissue from hamsters

EPA (20 : 5n-3) and DHA (22 : 6n-3) fatty acids have weight-reducing properties with physiological activity depending on their molecular structure – that is, as TAG or ethyl esters (EE). Aquaporins (AQP) are membrane protein channels recognised as important players in fat metabolism, but their differential expression in white adipose tissue (WAT) and brown adipose tissue (BAT), as well as their modulation by dietary n-3 long-chain PUFA (LCPUFA) such as EPA and DHA, has never been investigated. In this study, the transcriptional profiles of AQP3, AQP5, AQP7 and selected lipid markers of WAT (subcutaneous and visceral) and BAT (interscapular) from hamsters fed diets containing n-3 LCPUFA in different lipid structures such as fish oil (FO, rich in EPA and DHA in the TAG form) and FO-EE (rich in EPA and DHA in the EE form) were used and compared with linseed oil (LSO) as the reference group. A clear effect of fat depot was observed for AQP3 and leptin (LEP), with the lowest values of mRNA found in BAT relative to WAT. The opposite occurred for PPARα. AQP7 was affected by diet, with FO-fed hamsters having higher mRNA levels compared with LSO-fed hamsters. The relative gene expression of AQP5, adiponectin (ADIPO), GLUT4 and PPARγ was influenced by both fat tissue and diet. Taken together, our results revealed a differential expression profile of AQP and some markers of lipid metabolism in both WAT and BAT in response to feeding n-3 LCPUFA in two different structural formats: TAG v. EE.

Resveratrol and Pterostilbene, Two Analogue Phenolic Compounds, Affect Aquaglyceroporin Expression in a Different Manner in Adipose Tissue

Aquaglyceroporins (AQPs) are transmembrane channels that mediate glycerol release and glycerol uptake. They are involved in fat metabolism, with implications in obesity. The aim was to determine whether the administration of resveratrol and pterostilbene during the six weeks of the experimental period would modify AQPs expression in white and brown adipose tissues from Wistar rats fed an obesogenic diet, and to establish a potential relationship with the delipidating properties of these compounds. Consequently, thirty-six rats were divided into four groups: (a) group fed a standard diet; and three more groups fed a high-fat high-sucrose diet: (b) high-fat high-sucrose group: (c) pterostilbene-treated group (30 mg/kg/d): (d) resveratrol-treated group (30 mg/kg/d). Epididymal, subcutaneous white adipose tissues and interscapular brown adipose tissue were dissected. AQPs gene expression (RT-PCR) and protein expression (western-blot) were measured. In white adipose tissue, pterostilbene reduced subcutaneous adipose tissue weight and prevented the decrease in AQP9 induced by obesogenic feeding, and thus glycerol uptake for triglyceride accumulation. Resveratrol reduced epididymal adipose tissue weight and avoided the decrease in AQPs related to glycerol release induced by high-fat high-sucrose feeding, suggesting the involvement of lipolysis in its body-fat lowering effect. Regarding brown adipose tissue, AQP7 seemed not to be involved in the previously reported thermogenic activity of both phenolic compounds.

Increased AQP7 abundance in skeletal muscle from obese men with type 2 diabetes

Aquaglyceroporin 7 (AQP7) facilitates the transport of glycerol across cell membranes. In mice, fasting and refeeding regulate adipose tissue AQP7 abundance, and a role in controlling triglyceride accumulation in adipose tissue has been proposed. AQP7 is also expressed in skeletal muscle, where its function remains to be determined. Here, the abundance of AQP7 in abdominal subcutaneous adipose tissue (SAT) and skeletal muscle was evaluated in the overnight fasted and postprandial state in eight lean and eight obese men with type 2 diabetes (T2D). A biopsy from SAT and muscle was collected after an overnight fast and 2 h after ingestion of a low-fat test meal. Palmitate turnover was evaluated using a [9,10-³H] palmitate dilution technique. Tissue samples were analyzed by immunoblotting. Meal intake did not affect AQP7 expression in SAT or skeletal muscle. No association between the SAT AQP7 abundance and palmitate turnover was found. SAT AQP7 abundance was similar in lean and obese T2D men, whereas muscle AQP7 abundance was more than fourfold higher in obese T2D men. In conclusion, meal intake did not affect AQP7 protein abundance in SAT or skeletal muscle. In addition, SAT AQP7 expression does not appear to be involved in the regulation of adipose tissue lipolysis. However, in contrast to SAT AQP7, skeletal muscle AQP7 protein abundance is markedly increased in obese T2D men, potentially contributing to the excess lipid accumulation in skeletal muscle in type 2 diabetes.

Aquaglyceroporins: Drug Targets for Metabolic Diseases?

Aquaporins (AQPs) are a family of transmembrane channel proteins facilitating the transport of water, small solutes, and gasses across biological membranes. AQPs are expressed in all tissues and ensure multiple roles under normal and pathophysiological conditions. Aquaglyceroporins are a subfamily of AQPs permeable to glycerol in addition to water and participate thereby to energy metabolism. This review focalizes on the present knowledge of the expression, regulation and physiological roles of AQPs in adipose tissue, liver and endocrine pancreas, that are involved in energy metabolism. In addition, the review aims at summarizing the involvement of AQPs in metabolic disorders, such as obesity, diabetes and liver diseases. Finally, challenges and recent advances related to pharmacological modulation of AQPs expression and function to control and treat metabolic diseases are discussed.

Nuclear Receptor Regulation of Aquaglyceroporins in Metabolic Organs

Nuclear receptors, such as the farnesoid X receptor (FXR) and the peroxisome proliferator-activated receptors gamma and alpha (PPAR-γ, -α), are major metabolic regulators in adipose tissue and the liver, where they govern lipid, glucose, and bile acid homeostasis, as well as inflammatory cascades. Glycerol and free fatty acids are the end products of lipid droplet catabolism driven by PPARs. Aquaporins (AQPs), a family of 13 small transmembrane proteins, facilitate the shuttling of water, urea, and/or glycerol. The peculiar role of AQPs in glycerol transport makes them pivotal targets in lipid metabolism, especially considering their tissue-specific regulation by the nuclear receptors PPARγ and PPARα. Here, we review the role of nuclear receptors in the regulation of glycerol shuttling in liver and adipose tissue through the function and expression of AQPs.

Revisiting the metabolic syndrome: the emerging role of aquaglyceroporins

The metabolic syndrome (MetS) includes a group of medical conditions such as insulin resistance (IR), dyslipidemia and hypertension, all associated with an increased risk for cardiovascular disease. Increased visceral and ectopic fat deposition are also key features in the development of IR and MetS, with pathophysiological sequels on adipose tissue, liver and muscle. The recent recognition of aquaporins (AQPs) involvement in adipose tissue homeostasis has opened new perspectives for research in this field. The members of the aquaglyceroporin subfamily are specific glycerol channels implicated in energy metabolism by facilitating glycerol outflow from adipose tissue and its systemic distribution and uptake by liver and muscle, unveiling these membrane channels as key players in lipid balance and energy homeostasis. Being involved in a variety of pathophysiological mechanisms including IR and obesity, AQPs are considered promising drug targets that may prompt novel therapeutic approaches for metabolic disorders such as MetS. This review addresses the interplay between adipose tissue, liver and muscle, which is the basis of the metabolic syndrome, and highlights the involvement of aquaglyceroporins in obesity and related pathologies and how their regulation in different organs contributes to the features of the metabolic syndrome.

Pancreatic Aquaporin-7: A Novel Target for Anti-diabetic Drugs?

Aquaporins comprise a family of 13 members of water channels (AQP0-12) that facilitate a rapid transport of water across cell membranes. In some cases, these pores are also permeated by small solutes, particularly glycerol, urea or nitric oxide, among other solutes. Several aquaporins have been identified in the pancreas, an exocrine and endocrine organ that plays an essential role in the onset of insulin resistance and type 2 diabetes. The exocrine pancreas, which accounts for 90% of the total pancreas, secretes daily large volumes of a near-isotonic fluid containing digestive enzymes into the duodenum. AQP1, AQP5, and AQP8 contribute to fluid secretion especially from ductal cells, whereas AQP12 allows the proper maturation and exocytosis of secretory granules in acinar cells of the exocrine pancreas. The endocrine pancreas (10% of the total pancreatic cells) is composed by the islets of Langerhans, which are distributed in α, β, δ, ε, and pancreatic polypeptide (PP) cells that secrete glucagon, insulin, somatostatin, ghrelin and PP, respectively. AQP7, an aquaglyceroporin permeated by water and glycerol, is expressed in pancreatic β-cells and murine studies have confirmed its participation in insulin secretion, triacylglycerol synthesis and proliferation of these endocrine cells. In this regard, transgenic AQP7-knockout mice develop adult-onset obesity, hyperinsulinemia, increased intracellular triacylglycerol content and reduced β-cell mass in Langerhans islets. Moreover, we have recently reported that AQP7 upregulation in β-cells after bariatric surgery, an effective weight loss surgical procedure, contributes, in part, to the improvement of pancreatic steatosis and insulin secretion through the increase of intracytoplasmic glycerol in obese rats. Human studies remain scarce and controversial, with some rare cases of loss-of function mutations of the AQP7 gene being associated with the onset of type 2 diabetes. The present Review is focused on the role of aquaporins in the physiology and pathophysiology of the pancreas, highlighting the role of pancreatic AQP7 as a novel player in the control of β-cell function and a potential anti-diabetic-drug.

Gastric Plication Improves Glycemia Partly by Restoring the Altered Expression of Aquaglyceroporins in Adipose Tissue and the Liver in Obese Rats

BACKGROUND

Gastric plication is a minimally invasive bariatric surgical procedure, where the greater curvature is plicated inside the gastric lumen. Our aims were to analyze the effectiveness of gastric plication on the resolution of obesity, impaired glucose tolerance, and fatty liver in an experimental model of diet-induced obesity (DIO) and to evaluate changes in glycerol metabolism, a key substrate for adiposity and gluconeogenesis, in adipose tissue and the liver.

METHODS

Male Wistar DIO rats (n = 58) were subjected to surgical (sham operation and gastric plication) or dietary interventions [fed a normal diet (ND) or high-fat diet (HFD) or pair-fed to the amount of food eaten by gastric-plicated animals]. The expression of aquaglyceroporins (AQPs) in epididymal (EWAT) and subcutaneous (SCWAT) fat and the liver was analyzed by real-time PCR and Western blot.

RESULTS

Gastric plication did not result in a significant weight loss in DIO rats, showing a modest reduction in whole-body adiposity and hepatic steatosis. However, gastric-plicated animals exhibited an improvement in basal glycemia and glucose clearance, without changes in hepatic gluconeogenic genes. DIO was associated with an increase in glycerol, higher AQP3 and AQP7 in EWAT and SCWAT, and a decrease in hepatic AQP9. Gastric plication downregulated AQP3 in both fat depots without changes in adipose AQP7 and hepatic AQP9.

CONCLUSION

Gastric plication results in a modest reduction in adiposity and hepatosteatosis but restores glycemia by downregulating AQP3, which entails lower efflux of glycerol from fat, lower plasma glycerol availability, and a reduced use of glycerol as a substrate for hepatic gluconeogenesis.

Implications of Aquaglyceroporin 7 in Energy Metabolism

The aquaglyceroporin AQP7 is a pore-forming transmembrane protein that facilitates the transport of glycerol across cell membranes. Glycerol is utilized both in carbohydrate and lipid metabolism. It is primarily stored in white adipose tissue as part of the triglyceride molecules. During states with increased lipolysis, such as fasting and diabetes, glycerol is released from adipose tissue and metabolized in other tissues. AQP7 is expressed in adipose tissue where it facilitates the efflux of glycerol, and AQP7 deficiency has been linked to increased glycerol kinase activity and triglyceride accumulation in adipose tissue, leading to obesity and secondary development of insulin resistance. However, AQP7 is also expressed in a wide range of other tissues, including kidney, muscle, pancreatic β-cells and liver, where AQP7 also holds the potential to influence whole body energy metabolism. The aim of the review is to summarize the current knowledge on AQP7 in adipose tissue, as well as AQP7 expressed in other tissues where AQP7 might play a significant role in modulating whole body energy metabolism.

Ilex latifolia Thunb protects mice from HFD-induced body weight gain

Kuding tea is implicated in alleviating metabolic disorders in traditional Chinese medicine. However, the role of Ilex latifolia Thunb (kuding tea), one of the large leaf kuding tea species, in the prevention of the development of obesity remains to be determined. We show here that 7-week-old male mice treated with an Ilex latifolia Thunb supplement for 14 weeks were resistant to HFD-induced body weight gain and hepatic steatosis, accompanied by improved insulin sensitivity. Ilex latifolia Thunb supplementation dramatically reduced the systemic and tissue inflammation levels of mice via reducing pro-inflammatory cytokine levels, increasing anti-inflammatory cytokine levels in the circulation and inhibiting p38 MAPK and p65 NF-κB signaling in adipose tissue. Together, these results indicate that Ilex latifolia Thunb protects mice from the development of obesity and is a potential compound pool for the development of novel anti-obesity drugs.

AQP3 is regulated by PPARγ and JNK in hepatic stellate cells carrying PNPLA3 I148M

Aquaglyceroporins (AQPs) allow the movement of glycerol that is required for triglyceride formation in hepatic stellate cells (HSC), as key cellular source of fibrogenesis in the liver. The genetic polymorphism I148M of the patatin-like phospholipase domain-containing 3 (PNPLA3) is associated with hepatic steatosis and its progression to steatohepatitis (NASH), fibrosis and cancer. We aimed to explore the role of AQP3 for HSC activation and unveil its potential interactions with PNPLA3. HSC were isolated from human liver, experiments were performed in primary HSC and human HSC line LX2. AQP3 was the only aquaglyceroporin present in HSC and its expression decreased during activation. The PPARγ agonist, rosiglitazone, recovered AQP3 expression also in PNPLA3 I148M carrying HSC. When PNPLA3 was silenced, AQP3 expression increased. In liver sections from patients with NASH, the decreased amount of AQP3 was proportional to the severity of fibrosis and presence of the PNPLA3 I148M variant. In PNPLA3 I148M cells, the blockade of JNK pathway upregulated AQP3 in synergism with PPARγ. In conclusion, we demonstrated profound reduction of AQP3 in HSC carrying the PNPLA3 I148M variant in parallel to decreased PPARγ activation, which could be rescued by rosiglitazone and blockade of JNK.

Profiles of metabolic gene expression in the white adipose tissue, liver and hypothalamus in leptin knockout (LepΔI14/ΔI14 ) rats

Leptin deficiency is principally linked to metabolic disorders. Leptin knockout (LepΔI14/ΔI14) Sprague Dawley rats created by CRISPR/Cas9 is a new model to study metabolic disorders. We used a whole rat genome oligonucleotide microarray to obtain tissue-specific gene expression profiles of the white adipose tissue, liver and hypothalamus in LepΔI14/ΔI14 and wild-type (WT) rats. We found 1,651 differentially expressed (enriched) genes in white adipose tissue, 916 in the liver, and 306 in the hypothalamus in the LepΔI14/ΔI14 rats compared to WT. Gene ontology category and KEGG pathway analysis of the relationships among differentially expressed genes showed that these genes were represented in a variety of functional categories, including fatty acid metabolism, molecular transducers and cellular processes. The reliability of the data obtained from microarray was verified by quantitative real-time PCR on 14 representative genes. These data will contribute to a greater understanding of different metabolic disorders, such as obesity and diabetes.

Role of aquaporin-7 in ghrelin- and GLP-1-induced improvement of pancreatic β-cell function after sleeve gastrectomy in obese rats

BACKGROUND/OBJECTIVES

Glycerol is a key metabolite for lipid accumulation in insulin-sensitive tissues as well as for pancreatic insulin secretion. We examined the role of aquaporin-7 (AQP7), the main glycerol channel in β-cells, and AQP12, an aquaporin related to pancreatic damage, in the improvement of pancreatic function and steatosis after sleeve gastrectomy in diet-induced obese rats.

SUBJECTS/METHODS

Male Wistar obese rats (n=125) were subjected to surgical (sham operation and sleeve gastrectomy) or dietary (pair-fed to the amount of food eaten by sleeve-gastrectomized animals) interventions. The tissue distribution and expression of AQPs in the rat pancreas were analyzed by real-time PCR, western blotting and immunohistochemistry. The effect of ghrelin isoforms and glucagon-like peptide 1 (GLP-1) on insulin secretion, triacylglycerol (TG) accumulation and AQP expression was determined in vitro in RIN-m5F β-cells.

RESULTS

Sleeve gastrectomy reduced pancreatic β-cell apoptosis, steatosis and insulin secretion. Lower ghrelin and higher GLP-1 concentrations were also found after bariatric surgery. Acylated and desacyl ghrelin increased TG content, whereas GLP-1 increased insulin release in RIN-m5F β-cells. Sleeve gastrectomy was associated with an upregulation of AQP7 together with a normalization of the increased AQP12 levels in the rat pancreas. Interestingly, ghrelin and GLP-1 repressed AQP7 and AQP12 expression in RIN-m5F β-cells. AQP7 protein was negatively correlated with intracellular lipid accumulation in acylated ghrelin-treated cells and with insulin release in GLP-1-stimulated β-cells.

CONCLUSIONS

AQP7 upregulation in β-cells after sleeve gastrectomy contributes, in part, to the improvement of pancreatic steatosis and insulin secretion by increasing intracellular glycerol used for insulin release triggered by GLP-1 rather than for ghrelin-induced TG biosynthesis.

Normalization of adiponectin concentrations by leptin replacement in ob/ob mice is accompanied by reductions in systemic oxidative stress and inflammation

The circulating concentrations of adiponectin, an antidiabetic adipokine, have been shown to be reduced in obesity, in relation to an increase in inflammation. The aim of the present work was to assess the effect of leptin replacement on adiponectin levels and expression as well as on markers of oxidative stress and inflammation in leptin-deficient ob/ob mice. Twelve-week-old male mice (n = 7-10 per group) were treated with either saline (wild type and ob/ob mice) or leptin (ob/ob mice) for 18 days. A third group of ob/ob mice was treated with saline and pair-fed to the amount of food consumed by the leptin-treated group. Leptin replacement restored values of adiponectin (P < 0.001), reduced circulating 8-isoprostane and serum amyloid A (SAA) levels (P < 0.05 for both), and significantly downregulated the increased gene expression of osteopontin (Spp1, P < 0.05), Saa3 (P < 0.05), Cd68 (P < 0.01), Il6 (P < 0.01) and NADPH oxidase (Nox1 and Nox2, P < 0.01) in the perirenal WAT and Spp1 (P < 0.05) in the liver of ob/ob mice. In cultured adipocytes from ob/ob mice, leptin increased (P < 0.05) the mRNA expression and secretion of adiponectin. We concluded that circulating concentrations of adiponectin are positively regulated by leptin and ameliorate obesity-associated oxidative stress and inflammation in mice.