Reduced lipolysis response to adipose afferent reflex involved in impaired activation of adrenoceptor-cAMP-PKA-hormone sensitive lipase pathway in obesity

The interplay of factors in metabolic syndrome: understanding its roots and complexity

Metabolic syndrome (MetS) is an indicator and diverse endocrine syndrome that combines different metabolic defects with clinical, physiological, biochemical, and metabolic factors. Obesity, visceral adiposity and abdominal obesity, dyslipidemia, insulin resistance (IR), elevated blood pressure, endothelial dysfunction, and acute or chronic inflammation are the risk factors associated with MetS. Abdominal obesity, a hallmark of MetS, highlights dysfunctional fat tissue and increased risk for cardiovascular disease and diabetes. Insulin, a vital peptide hormone, regulates glucose metabolism throughout the body. When cells become resistant to insulin's effects, it disrupts various molecular pathways, leading to IR. This condition is linked to a range of disorders, including obesity, diabetes, fatty liver disease, cardiovascular disease, and polycystic ovary syndrome. Atherogenic dyslipidemia is characterized by three key factors: high levels of small, low-dense lipoprotein (LDL) particles and triglycerides, alongside low levels of high-density lipoprotein (HDL), the "good" cholesterol. Such a combination is a major player in MetS, where IR is a driving force. Atherogenic dyslipidemia contributes significantly to the development of atherosclerosis, which can lead to cardiovascular disease. On top of that, genetic alteration and lifestyle factors such as diet and exercise influence the complexity and progression of MetS. To enhance our understanding and consciousness, it is essential to understand the fundamental pathogenesis of MetS. This review highlights current advancements in MetS research including the involvement of gut microbiome, epigenetic regulation, and metabolomic profiling for early detection of Mets. In addition, this review emphasized the epidemiology and fundamental pathogenesis of MetS, various risk factors, and their preventive measures. The goal of this effort is to deepen understanding of MetS and encourage further research to develop effective strategies for preventing and managing complex metabolic diseases.

Inulin may prevent the high-fat diet induced-obesity via suppressing endocannabinoid system in the prefrontal cortex in Wistar rats

High-fat diets contribute to various metabolic disorders. Inulin supplementation has been shown to reduce appetite, lower food intake, and promote weight loss. Although there is evidence that the endocannabinoid system has metabolic effects in the prefrontal cortex, studies investigating the effects of inulin on the endocannabinoid system are limited. This study investigated the impact of inulin on obesity through the endocannabinoid system in the prefrontal cortex. Twenty-four male Wistar rats were fed one of four diets over 12 weeks. Findings indicated that a high-fat diet led to obesity, whereas inulin reduced food intake and supported weight loss. Consequently, inulin supplementation both prevented obesity and significantly decreased the expressions of Adrb3 and Adcy1, and anandamide and 2-arachidonylglycerol levels in the prefrontal cortex. Additionally, inulin lowered leptin in circulation and stimulated Trpv1. Thus, inulin may mitigate obesity development, possibly by modulating gene expressions linked to obesity in the prefrontal cortex via endocannabinoids.

βAR-mTOR-lipin1 pathway mediates PKA-RIIβ deficiency-induced adipose browning

Background: Enhancing white adipose tissue (WAT) browning combats obesity. The RIIβ subunit of cAMP-dependent protein kinase (PKA) is primarily expressed in the brain and adipose tissue. Deletion of the hypothalamic RIIβ gene centrally induces WAT browning, yet the peripheral mechanisms mediating this process remain unexplored. Methods: This study investigates the mechanisms underlying WAT browning in RIIβ-KO mice. Genetic approaches such as β3-adrenergic receptors (β3ARs) deletion and sympathetic denervation of WAT were utilized. Genome-wide transcriptomic sequencing and bioinformatic analysis were employed to identify potential mediators of WAT browning. siRNA assays were employed to knock down mTOR and lipin1 in vitro, while AAV-shRNAs were used for the same purpose in vivo. Results: We found that WAT browning substantially contributes to the lean and obesity-resistant phenotypes of RIIβ-KO mice. The WAT browning can be dampened by β3ARs deletion or WAT sympathetic denervation. We identified that adipocytic mTOR and lipin1 may act as mediators of the WAT browning. Inhibition of mTOR or lipin1 abrogates WAT browning and hinders the lean phenotype of RIIβ-KO mice. In human subcutaneous white adipocytes and mouse white adipocytes, β3AR stimulation can activate mTOR and causes lipin1 nuclear translocation; knockdown of mTOR and Lipin1 mitigates WAT browning-associated gene expression, impedes mitochondrial activity. Moreover, mTOR knockdown reduces lipin1 level and nuclear translocation, indicating that lipin1 may act downstream of mTOR. Additionally, in vivo knockdown of mTOR and Lipin1 diminished WAT browning and increased adiposity. Conclusions: The β3AR-activated mTOR-lipin1 axis mediates WAT browning, offering new insights into the molecular basis of PKA-regulated WAT browning. These findings provide potential adipose target candidates for the development of drugs to treat obesity.

Caffeine: a potential mechanism for anti-obesity

Obesity refers to the excessive accumulation of fat caused by a long-term imbalance between energy intake (EI) and energy expenditure (EE). Over recent years, obesity has become a major public health challenge. Caffeine is a natural product that has been demonstrated to exert anti-obesity effects; however, the mechanisms responsible for the effect of caffeine on weight loss have yet to be fully elucidated. Most obesity-related deaths are due to cardiovascular disease. Recent research has demonstrated that caffeine can reduce the risk of death from cardiovascular disease; thus, it can be hypothesized that caffeine may represent a new therapeutic agent for weight loss. In this review, we synthesize data arising from clinical and animal studies over the last decade and discuss the potential mechanisms by which caffeine may induce weight loss, focusing particularly on increasing energy consumption, suppressing appetite, altering lipid metabolism, and influencing the gut microbiota. Finally, we summarize the major challenges associated with caffeine and anti-obesity research and highlight possible directions for future research and development.

Inhibition of visceral adipose tissue-derived pathogenic signals by activation of adenosine A2AR improves hepatic and cardiac dysfunction of NASH mice

A2AR-disrupted mice is characterized by severe systemic and visceral adipose tissue (VAT) inflammation. Increasing adenosine cyclase (AC), cAMP, and protein kinase A (PKA) formation through A2AR activation suppress systemic/VAT inflammation in obese mice. This study explores the effects of 4 wk A2AR agonist PSB0777 treatment on the VAT-driven pathogenic signals in hepatic and cardiac dysfunction of nonalcoholic steatohepatitis (NASH) obese mice. Among NASH mice with cardiac dysfunction, simultaneous decrease in the A2AR, AC, cAMP, and PKA levels were observed in VAT, liver, and heart. PSB0777 treatment significantly restores AC, cAMP, PKA, and hormone-sensitive lipase (HSL) levels, decreased SREBP-1/FASN, MCP-1, and CD68 levels, reduces infiltrated CD11b+ F4/80+ cells and adipogenesis in VAT of NASH + PSB0777 mice. The changes in VAT were accompanied by the suppression of hepatic and cardiac lipogenic/inflammatory/injury/apoptotic/fibrotic markers, the normalization of cardiac contractile [sarco/endoplasmic reticulum Ca2+ ATPase (SERCA2)] marker, and cardiac dysfunction. The in vitro approach revealed that conditioned media (CM) of VAT of NASH mice (CMnash) trigger palmitic acid (PA)-like lipotoxic (lipogenic/inflammatory/apoptotic/fibrotic) effects in AML-12 and H9c2 cell systems. Significantly, A2AR agonist pretreatment-related normalization of A2AR-AC-cAMP-PKA levels was associated with the attenuation of CMnash-related upregulation of lipotoxic markers and the normalization of lipolytic (AML-12 cells) or contractile (H9C2 cells) marker/contraction. The in vivo and in vitro experiments revealed that A2AR agonists are potential agent to inhibit the effects of VAT inflammation-driven pathogenic signals on the hepatic and cardiac lipogenesis, inflammation, injury, apoptosis, fibrosis, hypocontractility, and subsequently improve hepatic and cardiac dysfunction in NASH mice.NEW & NOTEWORTHY Protective role of adenosine A2AR receptor (A2AR) and AC-cAMP-PKA signaling against nonalcoholic fatty liver disease (NAFLD)/nonalcoholic steatohepatitis (NASH) possibly via its actions on adipocytes is well known in the past decade. Thus, this study evaluates pharmacological activities of A2AR agonist PSB0777, which has already demonstrated to treat NASH. In this study, the inhibition of visceral adipose tissue-derived pathogenic signals by activation of adenosine A2AR with A2AR agonist PSB0777 improves the hepatic and cardiac dysfunction of high-fat diet (HFD)-induced NASH mice.

Obese Male Mice Exposed to Early Life Stress Display Sympathetic Activation and Hypertension Independent of Circulating Angiotensin II

BACKGROUND

We have previously reported that male mice exposed to maternal separation and early weaning (MSEW), a model of early life stress, show sympathetic activation and increased blood pressure in response to a chronic high-fat diet. The goal of this study was to investigate the contribution of the renin-angiotensin-aldosterone system to the mechanism by which MSEW increases blood pressure and vasomotor sympathetic tone in obese male mice.

METHODS AND RESULTS

Mice were exposed to MSEW during postnatal life. Undisturbed litters served as controls. At weaning, both control and MSEW offspring were placed on a low-fat diet or a high-fat diet for 20 weeks. Angiotensin peptides in serum were similar in control and MSEW mice regardless of the diet. However, a high-fat diet induced a similar increase in angiotensinogen levels in serum, renal cortex, liver, and fat in both control and MSEW mice. No evidence of renin-angiotensin system activation was found in adipose tissue and renal cortex. After chronic treatment with enalapril (2.5 mg/kg per day, drinking water, 7 days), an angiotensin-converting enzyme inhibitor that does not cross the blood-brain barrier, induced a similar reduction in blood pressure in both groups, while the vasomotor sympathetic tone remained increased in obese MSEW mice. In addition, acute boluses of angiotensin II (1, 10, 50 μg/kg s.c.) exerted a similar pressor response in MSEW and control mice before and after enalapril treatment.

CONCLUSIONS

Overall, elevated blood pressure and vasomotor sympathetic tone remained exacerbated in MSEW mice compared with controls after the peripheral inhibition of angiotensin-converting enzyme, suggesting a mechanism independent of angiotensin II.

Branched-chain amino acid modulation of lipid metabolism, gluconeogenesis, and inflammation in a finishing pig model: targeting leucine and valine

Branched-chain amino acids (BCAAs) play a regulatory role in adipogenesis and energy balance. Therefore, this study aimed to investigate the impact of BCAA supplements, especially leucine (Leu) and valine (Val) supplementation, on lipid metabolism and related disorders in a finishing pig model. The results demonstrated that Leu (1%) and Val decreased serum as well as hepatic lipid accumulation. Moreover, metabolomics and lipidomics analyses revealed that Leu and Val markedly downregulated the level of various lipid species in the liver. This outcome may be explained by Leu and Val promoting cyclic adenosine monophosphate (cAMP)/protein kinase A (PKA)/hormone-sensitive triglyceride lipase (HSL) signaling pathways. Leu and Val altered the fatty acid composition in distinct adipose tissues and decreased the levels of inflammatory factors. Additionally, they significantly decreased back fat thickness, and the results of the fatty acid profiles demonstrated that Leu and Val significantly increased the levels of monounsaturated fatty acids (MUFAs) and polyunsaturated fatty acids (PUFAs) while decreasing those of saturated fatty acids (SFAs), especially in back fat and abdominal fat. Besides, Leu and Val restored glucose homeostasis by suppressing gluconeogenesis through the serine/threonine protein kinase (AKT)/transcription factor forkhead box O1 (FOXO1) signaling pathway in the liver and back fat. In summary, these results suggest that Leu and Val may serve as key regulators for modulating lipid metabolism and steatosis.

The metabolic and functional roles of sensory nerves in adipose tissues

Homeostatic regulation of adipose tissue is critical for the maintenance of energy balance and whole-body metabolism. The peripheral nervous system provides bidirectional neural communication between the brain and adipose tissue, thereby providing homeostatic control. Most research on adipose innervation and nerve functions has been limited to the sympathetic nerves and their neurotransmitter norepinephrine. In recent years, more work has focused on adipose sensory nerves, but the contributions of subsets of sensory nerves to metabolism and the specific roles contributed by sensory neuropeptides are still understudied. Advances in imaging of adipose innervation and newer tissue denervation techniques have confirmed that sensory nerves contribute to the regulation of adipose functions, including lipolysis and browning. Here, we summarize the historical and latest findings on the regulation, function and plasticity of adipose tissue sensory nerves that contribute to metabolically important processes such as lipolysis, vascular control and sympathetic axis cross-talk.

A three-dimensional human adipocyte model of fatty acid-induced obesity

Obesity prevalence has reached pandemic proportions, leaving individuals at high risk for the development of diseases such as cancer and type 2 diabetes. In obesity, to accommodate excess lipid storage, adipocytes become hypertrophic, which is associated with an increased pro-inflammatory cytokine secretion and dysfunction of metabolic processes such as insulin signaling and lipolysis. Targeting adipocyte dysfunction is an important strategy to prevent the development of obesity-associated disease. However, it is unclear how accurately animal models reflect human biology, and the long-term culture of human hypertrophic adipocytes in an in vitro 2D monolayer is challenging due to the buoyant nature of adipocytes. Here we describe the development of a human 3D in vitro disease model that recapitulates hallmarks of obese adipocyte dysfunction. First, primary human adipose-derived mesenchymal stromal cells are embedded in hydrogel, and infiltrated into a thin cellulose scaffold. The thin microtissue profile allows for efficient assembly and image-based analysis. After adipocyte differentiation, the scaffold is stimulated with oleic or palmitic acid to mimic caloric overload. Using functional assays, we demonstrated that this treatment induced important obese adipocyte characteristics such as a larger lipid droplet size, increased basal lipolysis, insulin resistance and a change in macrophage gene expression through adipocyte-conditioned media. This 3D disease model mimics physiologically relevant hallmarks of obese adipocytes, to enable investigations into the mechanisms by which dysfunctional adipocytes contribute to disease.

Intestinal AMPK modulation of microbiota mediates crosstalk with brown fat to control thermogenesis

The energy-dissipating capacity of brown adipose tissue through thermogenesis can be targeted to improve energy balance. Mammalian 5'-AMP-activated protein kinase, a key nutrient sensor for maintaining cellular energy status, is a known therapeutic target in Type II diabetes. Despite its well-established roles in regulating glucose metabolism in various tissues, the functions of AMPK in the intestine remain largely unexplored. Here we show that AMPKα1 deficiency in the intestine results in weight gain and impaired glucose tolerance under high fat diet feeding, while metformin administration fails to ameliorate these metabolic disorders in intestinal AMPKα1 knockout mice. Further, AMPKα1 in the intestine communicates with brown adipose tissue to promote thermogenesis. Mechanistically, we uncover a link between intestinal AMPKα1 activation and BAT thermogenic regulation through modulating anti-microbial peptide-controlled gut microbiota and the metabolites. Our findings identify AMPKα1-mediated mechanisms of intestine-BAT communication that may partially underlie the therapeutic effects of metformin.

The regulation of PKA signaling in obesity and in the maintenance of metabolic health

The cAMP-dependent protein kinase (PKA) system represents a primary cell-signaling pathway throughout systems and across species. PKA facilitates the actions of hormones, neurotransmitters and other signaling molecules that bind G-protein coupled receptors (GPCR) to modulate cAMP levels. Through its control of synaptic events, exocytosis, transcriptional regulation, and more, PKA signaling regulates cellular metabolism and emotional and stress responses making it integral in the maintenance and dysregulation of energy homeostasis. Neural PKA signaling is regulated by afferent and peripheral efferent signals that link specific neural cell populations to the regulation of metabolic processes in adipose tissue, liver, pancreas, adrenal, skeletal muscle, and gut. Mouse models have provided invaluable information on the roles for PKA subunits in brain and key metabolic organs. While limited, human studies infer differential regulation of the PKA system in obese compared to lean individuals. Variants identified in PKA subunit genes cause Cushing syndrome that is characterized by metabolic dysregulation associated with endogenous glucocorticoid excess. Under healthy physiologic conditions, the PKA system is exquisitely regulated by stimuli that activate GPCRs to alter intracellular cAMP concentrations, and by PKA cellular localization and holoenzyme stability. Adenylate cyclase activity generates cAMP while phosphodiesterase-mediated cAMP degradation to AMP decreases cAMP levels downstream of GPCRs. Chronic perturbations in PKA signaling appear to be capable of resetting PKA regulation at several levels; in addition, sex differences in PKA signaling regulation, while not well understood, impact the physiologic consequences of metabolic dysregulation and obesity. This review explores the roles for PKA signaling in the pathogenesis of metabolic diseases including obesity, type 2 diabetes mellitus and associated co-morbidities through neural-peripheral crosstalk and cAMP/PKA signaling pathway targets that hold therapeutic potential.

Melatonin improves the maturation and developmental ability of bovine oocytes by up-regulating GJA4 to enhance gap junction intercellular communication

Melatonin (MT) increases oocyte maturation by reducing reactive oxygen species level and enhancing oocyte antioxidant capacity. However, the mechanisms via which MT works are still poorly understood. In the present study, the effects of MT on the maturation rate and development ability of bovine oocytes were investigated. Then, the transcriptome of oocytes treated by MT was sequenced. Finally, the expression of gap junction protein alpha 4 (GJA4) protein and cAMP level were detected in bovine oocytes, and isoprenaline (enhancer of gap junctional intercellular communication (GJIC)) and heptanol (inhibitor of GJIC) were used to investigate the effect of MT on GJIC activity in bovine oocytes. Our results showed that MT significantly improved the maturation, developmental ability and mRNA expression of GJA4 of bovine oocytes. Meanwhile, MT significantly increased GJA4 protein level and cAMP level in bovine oocytes. In contrast to heptanol, both isoproterenol and MT significantly increased GJIC activity, nuclear maturation and the development ability of bovine oocytes. However, MT significantly restored the nuclear maturation and developmental ability of oocytes treated by heptanol. In conclusion, our results showed that MT improves the maturation and developmental ability of bovine oocytes by enhancing GJIC activity via up-regulating GJA4 protein expression in IVM progress.

Increased energy expenditure and activated β3-AR-cAMP-PKA signaling pathway in the interscapular brown adipose tissue of 6-OHDA-induced Parkinson's disease model rats

To explore the possible mechanism of weight loss in Parkinson's disease (PD). Bilateral injections of 6-hydroxydopamine (6-OHDA) into substantia nigra (SN) were performed to induce the PD model rats. The rotarod test, food intake, body weight, and interscapular brown adipose tissue (IBAT) weight were recorded 6 weeks postoperation. HE staining was performed to observe the morphology of multilocular adipose cells in IBAT. Immunohistochemistry and western blot were used to determine the protein levels of tyrosine hydroxylase (TH) in the SN, and the levels of uncoupling protein 1 (UCP1), peroxisome proliferator-activated receptor gamma coactivator-1α (PGC-1α), phosphorylated-hormone sensitive lipase (p-HSL), HSL, TH, β3-adrenergic receptor (β3-AR), cyclic adenosine monophosphate (cAMP), and protein kinase A (PKA) in IBAT. After treatment with 6-OHDA for 6 weeks, 6-OHDA rats exhibited decreased TH expression in SN accompanied with shortened staying time on the rotating rod. This motor impairment paralleled with no significant alteration in body mass, IBAT weight, and food intake until the end of the experimental protocol. However, the decreasing diameter of the single fat vesicle in IBAT was observed in the 6-OHDA group. Meanwhile, compared with the control group, the protein expression of UCP1, PGC-1α, p-HSL, TH, β3-AR, cAMP, and PKA in IBAT were increased significantly in the 6-OHDA group, whereas no obvious change in the expression of HSL. The present study suggested an increased energy expenditure and activation of the β3-AR-cAMP-PKA signaling pathway in the IBAT after the destruction of the dopamine system in the SN of the rat.

PKA functions in metabolism and resistance to obesity: lessons from mouse and human studies

Both direct and indirect evidence demonstrate a central role for the cAMP-dependent protein kinase (PKA) signaling pathway in the regulation of energy balance and metabolism across multiple systems. However, the ubiquitous pattern of PKA expression across cell types poses a challenge in pinpointing its tissue-specific regulatory functions and further characterizing its many downstream effects in certain organs or cells. Mouse models of PKA deficiency and over-expression and studies in living cells have helped clarify PKA function in adipose tissue (AT), liver, adrenal, pancreas, and specific brain nuclei, as they pertain to energy balance and metabolic dysregulation. Limited studies in humans suggest differential regulation of PKA in AT of obese compared to lean individuals and an overall dysregulation of PKA signaling in obesity. Despite its complexity, under normal physiologic conditions, the PKA system is tightly regulated by changes in cAMP concentrations upstream via adenylate cyclase and downstream by phosphodiesterase-mediated cAMP degradation to AMP and by changes in PKA holoenzyme stability. Adjustments in the PKA system appear to be important to the development and maintenance of the obese state and its associated metabolic perturbations. In this review we discuss the important role of PKA in obesity and its involvement in resistance to obesity, through studies in humans and in mouse models, with a focus on the regulation of PKA in energy expenditure, intake behavior, and lipid and glucose metabolism.

Nuclear Factor E2-Related Factor 2 Mediates Oxidative Stress-Induced Lipid Accumulation in Adipocytes by Increasing Adipogenesis and Decreasing Lipolysis

Aims: Nuclear factor E2-related factor 2 (Nrf2) is a regulator of cellular oxidative stress and is also involved in lipid metabolism in adipocytes. However, it remains unknown as to whether Nrf2 is the link between oxidative stress and the induction of lipid accumulation in adipocytes. Results: Here, we show that oxidative stress is markedly increased in white adipose tissue from mice with high-fat diet-induced or genetically (ob/ob)-induced obesity and from human subjects with obesity. Notably, in response to oxidative stress, Nrf2 expression and activity were induced, further promoting lipid accumulation in adipocytes and exacerbating the development of obesity. In contrast, Nrf2 ablation alleviated oxidative stress-induced lipid accumulation. Mechanistically, oxidative stress promoted Nrf2 recruitment to the sterol regulatory element binding protein 1 promoter, inducing target gene transcription and subsequent lipogenesis. In addition, Nrf2 mediated oxidative stress-inhibited lipolysis in adipocytes via the protein kinase A pathway. Innovation and Conclusion: Our data provide a novel insight that Nrf2, as a critical signaling node, links oxidative stress to the induction of fat accumulation in adipocytes.

Cytoplasm lipids can be modulated through hormone-sensitive lipase and are related to mitochondrial function in porcine IVM oocytes

Intracellular lipids provide energy for oocyte maturation and development. Triglycerides are the main components of cytoplasm lipid droplets, and hydrolysis of triglycerides requires several lipase-mediated steps. The aim of this study was to determine the effects of the β-adrenoceptor agonist isoproterenol (ISO) and the hormone-sensitive lipase (HSL) inhibitor CAY10499 on the IVM of porcine oocytes. ISO (5mg L−1) and CAY10499 (20mg L−1) had positive and negative effects respectively on invitro oocyte maturation and subsequent embryo development. The rates of polar body extrusion, cleavage and blastocyst formation were significantly higher in the ISO-treated group than the control and CAY10499-treated groups. ISO treatment also upregulated intracellular cAMP levels in comparison with the control group, while CAY10499 significantly increased the triglyceride content of matured oocytes when compared with other groups, consistent with the observed decrease in LIPE (HSL) mRNA levels. Furthermore, the inhibitory effects of CAY10499 included decreases in mitochondrial membrane potential and mitochondrial temperature. These results indicate that ISO has a positive effect on the IVM of porcine oocytes, and that intracellular lipid metabolism can be modulated by CAY10499 through inhibition of HSL and is closely related to mitochondrial function.

Sensory signals mediating high blood pressure via sympathetic activation: role of adipose afferent reflex

Blood pressure regulation in health and disease involves a balance between afferent and efferent signals from multiple organs and tissues. Although there are numerous reviews focused on the role of sympathetic nerves in different models of hypertension, few have revised the contribution of afferent nerves innervating adipose tissue and their role in the development of obesity-induced hypertension. Both clinical and basic research support the beneficial effects of bilateral renal denervation in lowering blood pressure. However, recent studies revealed that afferent signals from adipose tissue, in an adipose-brain-peripheral pathway, could contribute to the increased sympathetic activation and blood pressure during obesity. This review focuses on the role of adipose tissue afferent reflexes and briefly describes a number of other afferent reflexes modulating blood pressure. A comprehensive understanding of how multiple afferent reflexes contribute to the pathophysiology of essential and/or obesity-induced hypertension may provide significant insights into improving antihypertensive therapeutic approaches.

Adipogenesis: A Necessary but Harmful Strategy

Obesity is considered to significantly increase the risk of the development of a vast range of metabolic diseases. However, adipogenesis is a complex physiological process, necessary to sequester lipids effectively to avoid lipotoxicity in other tissues, like the liver, heart, muscle, essential for maintaining metabolic homeostasis and has a crucial role as a component of the innate immune system, far beyond than only being an inert mass of energy storage. In pathophysiological conditions, adipogenesis promotes a pro-inflammatory state, angiogenesis and the release of adipokines, which become dangerous to health. It results in a hypoxic state, causing oxidative stress and the synthesis and release of harmful free fatty acids. In this review, we try to explain the mechanisms occurring at the breaking point, at which adipogenesis leads to an uncontrolled lipotoxicity. This review highlights the types of adipose tissue and their functions, their way of storing lipids until a critical point, which is associated with hypoxia, inflammation, insulin resistance as well as lipodystrophy and adipogenesis modulation by Krüppel-like factors and miRNAs.

Beneficial Effects of an Aged Black Garlic Extract in the Metabolic and Vascular Alterations Induced by a High Fat/Sucrose Diet in Male Rats

Aged black garlic (ABG) is a functional food with antioxidant and anti-inflammatory properties. Recent studies also report its beneficial metabolic effects in a context of obesity or diabetes, although the mechanisms involved are poorly understood. The aim of this work was to analyze the effects of an ABG extract in the vascular and metabolic alterations induced by a high-fat/sucrose diet in rats. For this purpose, male Sprague–Dawley rats were fed either a standard chow (controls; n = 12) or a high-fat/sucrose diet (HFD; n = 24) for 16 weeks. From week 8 on, half of the HFD rats were treated with a commercial ABG extract concentrated in S-allyl cysteine and melanoidins (ABG10+®; 250 mg/kg daily by gavage; 5 mL/kg). ABG10+®-treated rats showed lower mean caloric intake, body weight, triglycerides, low density lipoprotein cholesterol (LDL-c), insulin and leptin serum concentrations and higher high density lipoprotein cholesterol (HDL-c) and adiponectin serum concentrations than non-treated rats. In the hypothalamus, ABG10+® treatment induced an increase in the gene expression of proopiomelanocortin (POMC) and a decrease in leptin receptor (ObR) mRNA levels. No significant changes were found in visceral adipose tissue except for an overexpression of β3-adrenergic receptor (β3-ADR) in ABG-treated rats. In subcutaneous adipose tissue, ABG10+® treatment decreased adipose weight and downregulated the gene expression of PPAR-γ, LPL, ObR and HSL. In brown adipose tissue, an overexpression of InsR, GLUT-4, UCP-1 and β3-ADR in ABG10+®-treated rats was found, whereas PPAR-γ mRNA levels were significantly decreased. Regarding vascular function, ABG10+® treatment attenuated the obesity-induced vasoconstriction in response to potassium chloride both in presence/absence of perivascular adipose tissue (PVAT). On the contrary, aorta segments from ABG-treated rats showed and improved relaxation in response to acetylcholine only when PVAT was present, with this fact possible being related to the decreased gene expression of proinflammatory cytokines in this tissue. In conclusion, ABG10+® administration partially improves the metabolic and vascular alterations induced by a high-fat/high-sucrose diet in rats through modifications in the gene expression of proteins and neuropeptides involved in inflammation, fat metabolism and food intake regulation. Further studies are required to assess the bioavailability of ABG between rats and humans.

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.

Measurement of Basal and Forskolin-stimulated Lipolysis in Inguinal Adipose Fat Pads

Lipolysis is a process by which the lipid stored as triglycerides in adipose tissues are hydrolyzed into glycerol and fatty acids. This article describes the method for the measurement of basal and forskolin (FSK)-stimulated lipolysis in the inguinal fat pads isolated from wild type mice fed either normal chow diet (NCD), high fat diet (HFD) or a high fat diet containing 0.01% of capsaicin (CAP; transient receptor potential vanilloid subfamily 1 (TRPV1) agonist) for 32 weeks. The method described here for performing ex vivo lipolysis is adopted from Schweiger et al.¹ We present a detailed protocol for measuring glycerol levels by UV-Visible (UV/VIS) spectrophotometry. The method described here can be used to successfully isolate inguinal fat pads for lipolysis measurements to obtain consistent results. The protocol described for inguinal fat pads can readily be extended to measure lipolysis in other tissues.

The resolution of acute inflammation induced by cyclic AMP is dependent on annexin A1

Annexin A1 (AnxA1) is a glucocorticoid-regulated protein known for its anti-inflammatory and pro-resolving effects. We have shown previously that the cAMP-enhancing compounds rolipram (ROL; a PDE4 inhibitor) and Bt₂cAMP (a cAMP mimetic) drive caspase-dependent resolution of neutrophilic inflammation. In this follow-up study, we investigated whether AnxA1 could be involved in the pro-resolving properties of these compounds using a model of LPS-induced inflammation in BALB/c mice. The treatment with ROL or Bt₂cAMP at the peak of inflammation shortened resolution intervals, improved resolution indices, and increased AnxA1 expression. In vitro studies showed that ROL and Bt₂cAMP induced AnxA1 expression and phosphorylation, and this effect was prevented by PKA inhibitors, suggesting the involvement of PKA in ROL-induced AnxA1 expression. Akin to these in vitro findings, H89 prevented ROL- and Bt₂cAMP-induced resolution of inflammation, and it was associated with decreased levels of intact AnxA1. Moreover, two different strategies to block the AnxA1 pathway (by using N-t-Boc-Met-Leu-Phe, a nonselective AnxA1 receptor antagonist, or by using an anti-AnxA1 neutralizing antiserum) prevented ROL- and Bt₂cAMP-induced resolution and neutrophil apoptosis. Likewise, the ability of ROL or Bt₂cAMP to induce neutrophil apoptosis was impaired in AnxA-knock-out mice. Finally, in in vitro settings, ROL and Bt₂cAMP overrode the survival-inducing effect of LPS in human neutrophils in an AnxA1-dependent manner. Our results show that AnxA1 is at least one of the endogenous determinants mediating the pro-resolving properties of cAMP-elevating agents and cAMP-mimetic drugs.

Autophagy regulates turnover of lipid droplets via ROS-dependent Rab25 activation in hepatic stellate cell

Activation of hepatic stellate cells (HSCs) is a pivotal event in liver fibrosis, characterized by dramatic disappearance of lipid droplets (LDs). Although LD disappearance has long been considered one of the hallmarks of HSC activation, the underlying molecular mechanisms are largely unknown. In this study, we sought to investigate the role of autophagy in the process of LD disappearance, and to further examine the underlying mechanisms in this molecular context. We found that LD disappearance during HSC activation was associated with a coordinate increase in autophagy. Inhibition or depletion of autophagy by Atg5 siRNA impaired LD disappearance of quiescent HSCs, and also restored lipocyte phenotype of activated HSCs. In contrast, induction of autophagy by Atg5 plasmid accelerated LD loss of quiescent HSCs. Importantly, our study also identified a crucial role for reactive oxygen species (ROS) in the facilitation of autophagy activation. Antioxidants, such as glutathione and N-acetyl cysteine, significantly abrogated ROS production, and in turn, prevented autophagosome generation and autophagic flux during HSC activation. Besides, we found that HSC activation triggered Rab25 overexpression, and promoted the combination of Rab25 and PI3KCIII, which direct autophagy to recognize, wrap and degrade LDs. Down-regulation of Rab25 activity, using Rab25 siRNA, blocked the target recognition of autophagy on LDs, and inhibited LD disappearance of quiescent HSCs. Moreover, the scavenging of excessive ROS could disrupt the interaction between autophagy and Rab25, and increase intracellular lipid content. Overall, these results provide novel implications to reveal the molecular mechanism of LD disappearance during HSC activation, and also identify ROS-Rab25-dependent autophagy as a potential target for the treatment of liver fibrosis.

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Autophagosome generation and autophagic flux are increased during HSC activation.

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The inhibition of autophagy blocks LD disappearance of quiescent HSCs.

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The induction of autophagy accelerates LD disappearance of quiescent HSCs.

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Rab25 activation is required for autophagy to degrade LDs during HSC activation.

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Mitochondrial H₂O₂ production triggers autophagy activation during HSC activation.