Mechanisms of insulin resistance related to white, beige, and brown adipocytes

Are glucose and insulin levels at all time points during OGTT a reliable marker of diabetes mellitus risk in pediatric obesity?

PURPOSE

Childhood overweight and obesity associated with insulin resistance and metabolic syndrome represent the new global pandemic and the main causative factors for dysglycemia, prediabetes, and Type 2 Diabetes Mellitus (T2DM). Predictors, such as HOMA-IR, HOMA-β%, and QUICKI lack specific reference values in children. OGTT is a gold standard for glycometabolic assessment. Recently, a glycemic level higher than 155 mg/dl at + 60' after glucose ingestion has been defined as a risk factor for T2DM in obese adolescents. We aim to analyze and correlate fasting insulin-resistance markers with OGTT results in overweight/obese children and adolescents.

METHODS

We retrospectively evaluated glucose and insulin values during a 2-h OGTT every 30 min in 236 overweight/obese patients. Glucose values and insulin sum during OGTT were compared to glycometabolic indexes and different cut-off values for insulin sum.

RESULTS

A 1-h glucose > 155 mg/dl and insulin sum > 535 microU/ml at all times during OGTT are the best predictors of diabetes risk in obese youths. A1-h glucose > 155 mg/dl is significantly associated with HbA1c > 5.7%, while no association was observed between HbA1c > 5.7% and glucose levels at baseline and 2 h. The ability of the standardized HOMA-IR to predict the prediabetes status is clearly lower than the total insulin sum at OGTT.

CONCLUSION

Our study demonstrates that also 1-h post-OGTT glucose, together with HbA1c, is an effective diabetes predictor.

"Multiomics" Analyses Combined with Systems Pharmacology Reveal the Renoprotection of Mangiferin Monosodium Salt in Rats with Diabetic Nephropathy: Focus on Improvements in Renal Ferroptosis, Renal Inflammation, and Podocyte Insulin Resistance

We explored the protection of mangiferin monosodium salt (MGM) on kidney injury in rats with streptozotocin (STZ)-induced diabetic nephropathy (DN) by "multiomics" analysis combined with systems pharmacology, with a specific focus on ferroptosis, inflammation, and podocyte insulin resistance (IR) signaling events in kidneys. MGM treatment afforded renoprotective effects on rats with STZ-induced DN by alleviating systemic IR-induced renal inflammation and podocyte IR. These mechanisms were correlated mainly with the MGM treatment-induced inhibition of the mitogen-activated protein kinase/nuclear factor-kappa B axis and activation of the phosphorylated insulin receptor substrate 1(Tyr608)/phosphorylated phosphatidylinositol 3-kinase/phosphorylated protein kinase B axis in the kidneys of DN rats. MGM had an ameliorative function in renal ferroptosis in rats with STZ-induced DN by upregulating mevalonate-mediated antioxidant capacities (glutathione peroxidase 4 and ferroptosis suppressor protein 1/coenzyme Q10 axis) and weakening acyl-CoA synthetase long-chain family member 4-mediated proferroptotic generation of lipid drivers in kidneys. MGM may be a promising alternative strategy for the treatment of DN.

RBM43 links adipose inflammation and energy expenditure through translational regulation of PGC1α

Adipose thermogenesis involves specialized mitochondrial function that counteracts metabolic disease through dissipation of chemical energy as heat. However, inflammation present in obese adipose tissue can impair oxidative metabolism. Here, we show that PGC1α, a key governor of mitochondrial biogenesis and thermogenesis, is negatively regulated at the level of mRNA translation by the little-known RNA-binding protein RBM43. Rbm43 is expressed selectively in white adipose depots that have low thermogenic potential, and is induced by inflammatory cytokines. RBM43 suppresses mitochondrial and thermogenic gene expression in a PGC1α-dependent manner and its loss protects cells from cytokine-induced mitochondrial impairment. In mice, adipocyte-selective Rbm43 disruption increases PGC1α translation, resulting in mitochondrial biogenesis and adipose thermogenesis. These changes are accompanied by improvements in glucose homeostasis during diet-induced obesity that are independent of body weight. The action of RBM43 suggests a translational mechanism by which inflammatory signals associated with metabolic disease dampen mitochondrial function and thermogenesis.

Obesity and type 2 diabetes mellitus: connections in epidemiology, pathogenesis, and treatments

The prevalence of obesity and diabetes mellitus (DM) has been consistently increasing worldwide. Sharing powerful genetic and environmental features in their pathogenesis, obesity amplifies the impact of genetic susceptibility and environmental factors on DM. The ectopic expansion of adipose tissue and excessive accumulation of certain nutrients and metabolites sabotage the metabolic balance via insulin resistance, dysfunctional autophagy, and microbiome-gut-brain axis, further exacerbating the dysregulation of immunometabolism through low-grade systemic inflammation, leading to an accelerated loss of functional β-cells and gradual elevation of blood glucose. Given these intricate connections, most available treatments of obesity and type 2 DM (T2DM) have a mutual effect on each other. For example, anti-obesity drugs can be anti-diabetic to some extent, and some anti-diabetic medicines, in contrast, have been shown to increase body weight, such as insulin. Meanwhile, surgical procedures, especially bariatric surgery, are more effective for both obesity and T2DM. Besides guaranteeing the availability and accessibility of all the available diagnostic and therapeutic tools, more clinical and experimental investigations on the pathogenesis of these two diseases are warranted to improve the efficacy and safety of the available and newly developed treatments.

Placental mesenchymal stem cells restore glucose and energy homeostasis in obesogenic adipocytes

Obesity (Ob) depicts a state of energy imbalance(s) being characterized by the accumulation of excessive fat and which predisposes to several metabolic diseases. Mesenchymal stem cells (MSCs) represent a promising option for addressing obesity and its associated metabolic co-morbidities. The present study aims at assessing the beneficial effects of human placental MSCs (P-MSCs) in mitigating Ob-associated insulin resistance (IR) and mitochondrial dysfunction both in vivo and in vitro. Under obesogenic milieu, adipocytes showed a significant reduction in glucose uptake, and impaired insulin signaling with decreased expression of UCP1 and PGC1α, suggestive of dysregulated non-shivering thermogenesis vis-a-vis mitochondrial biogenesis respectively. Furthermore, obesogenic adipocytes demonstrated impaired mitochondrial respiration and energy homeostasis evidenced by reduced oxygen consumption rate (OCR) and blunted ATP/NAD⁺/NADP⁺ production respectively. Interestingly, co-culturing adipocytes with P-MSCs activated PI3K-Akt signaling, improved glucose uptake, diminished ROS production, enhanced mitochondrial OCR, improved ATP/NAD⁺/NADP⁺ production, and promoted beiging of adipocytes evidenced by upregulated expression of PRDM16, UCP1, and PGC1α expression. In vivo, P-MSCs administration increased the peripheral blood glucose uptake and clearance, and improved insulin sensitivity and lipid profile with a coordinated increase in the ratio of ATP/ADP and NAD⁺ and NADP⁺ in the white adipose tissue (WAT), exemplified in WNIN/GR-Ob obese mutant rats. In line with in vitro findings, there was a significant reduction in adipocyte hypertrophy, increased mitochondrial staining, and thermogenesis. Our findings advocate for a therapeutic application of P-MSCs for improving glucose and energy homeostasis, i.e., probably restoring non-shivering thermogenesis towards obesity management.

Epicardial adipocytes in the pathogenesis of atrial fibrillation: An update on basic and translational studies

Epicardial adipose tissue (EAT) is an endocrine organ containing a host of cell types and undoubtedly serving a multitude of important physiologic functions. Aging and obesity cause hypertrophy of EAT. There is great interest in the possible connection between EAT and cardiovascular disease, in particular, atrial fibrillation (AF). Increased EAT is independently associated with AF and adverse events after AF ablation (e.g., recurrence of AF, and stroke). In general, the amount of EAT correlates with BMI or visceral adiposity. Yet on a molecular level, there are similarities and differences between epicardial and abdominal visceral adipocytes. In comparison to subcutaneous adipose tissue, both depots are enriched in inflammatory cells and chemokines, even in normal conditions. On the other hand, in comparison to visceral fat, epicardial adipocytes have an increased rate of fatty acid release, decreased size, and increased vascularity. Several studies have described an association between fibrosis of EAT and fibrosis of the underlying atrial myocardium. Others have discovered paracrine factors released from EAT that could possibly mediate this association. In addition to the adjacent atrial cardiomyocytes, EAT contains a robust stromal-vascular fraction and surrounds the ganglionic plexi of the cardiac autonomic nervous system (cANS). The importance of the cANS in the pathogenesis of atrial fibrillation is well known, and it is quite likely that there is feedback between EAT and the cANS. This complex interplay may be crucial to the maintenance of normal sinus rhythm or the development of atrial fibrillation. The extent the adipocyte is a microcosm of metabolic health in the individual patient may determine which is the predominant rhythm.

Long Noncoding RNAs in the Pathogenesis of Insulin Resistance

Insulin resistance (IR), designated as the blunted response of insulin target tissues to physiological level of insulin, plays crucial roles in the development and progression of diabetes, nonalcoholic fatty liver disease (NAFLD) and other diseases. So far, the distinct mechanism(s) of IR still needs further exploration. Long non-coding RNA (lncRNA) is a class of non-protein coding RNA molecules with a length greater than 200 nucleotides. LncRNAs are widely involved in many biological processes including cell differentiation, proliferation, apoptosis and metabolism. More recently, there has been increasing evidence that lncRNAs participated in the pathogenesis of IR, and the dysregulated lncRNA profile played important roles in the pathogenesis of metabolic diseases including obesity, diabetes and NAFLD. For example, the lncRNAs MEG3, H19, MALAT1, GAS5, lncSHGL and several other lncRNAs have been shown to regulate insulin signaling and glucose/lipid metabolism in various tissues. In this review, we briefly introduced the general features of lncRNA and the methods for lncRNA research, and then summarized and discussed the recent advances on the roles and mechanisms of lncRNAs in IR, particularly focused on liver, skeletal muscle and adipose tissues.

Adipose Tissue Dysfunction: Impact on Metabolic Changes?

Adipose tissue is a metabolically dynamic organ that is the primary site of storage for excess energy, but it serves as an endocrine organ capable of synthesizing a number of biologically active compounds that regulate metabolic homeostasis. However, when the capacity of expansion of this tissue exceeds, dysfunction occurs, favoring ectopic accumulation of fat in the visceral, which has been implicated in several disease states, most notably obesity. This review highlights the mechanisms involved in the structure of adipose tissue, tissue expandability, adipocyte dysfunction, as well as the impact of these events on the manifestation of important metabolic disorders associated with adipose tissue dysfunction. A literature search using Pubmed, Web of Science, Scopus, and Cochrane databases were used to identify relevant studies, using clinical trials, experimental studies in animals and humans, case-control studies, case series, letters to the editor, and review articles published in English, without restrictions on year of publication. The excessive ectopic lipid accumulation leads to local inflammation and insulin resistance. Indeed, overnutrition triggers uncontrolled inflammatory responses white adipose tissue, leading to chronic low-grade inflammation, therefore fostering the progression of important metabolic disorders. Thus, it is essential to advance the understanding of the molecular mechanisms involved in adipose tissue dysfunction in order to mitigate the negative metabolic consequences of obesity.

Cistanche tubulosa phenylethanoid glycosides suppressed adipogenesis in 3T3-L1 adipocytes and improved obesity and insulin resistance in high-fat diet induced obese mice

Background

Cistanche tubulosa is an editable and medicinal traditional Chinese herb and phenylethanoid glycosides are its major components, which have shown various beneficial effects such as anti-tumor, anti-oxidant and neuroprotective activities. However, the anti-obesity effect of C. tubulosa phenylethanoid glycosides (CTPG) and their regulatory effect on gut microbiota are still unclear. In the present study, we investigated its anti-obesity effect and regulatory effect on gut microbiota by 3T3-L1 cell model and obesity mouse model.

Methods

3T3-L1 adipocytes were used to evaluate CTPG effects on adipogenesis and lipids accumulation. Insulin resistant 3T3-L1 cells were induced and used to measure CTPG effects on glucose consumption and insulin sensitivity. High-fat diet (HFD)-induced C57BL/6 obese mice were used to investigate CTPG effects on fat deposition, glucose and lipid metabolism, insulin resistance and intestinal microorganism.

Results

In vitro data showed that CTPG significantly decreased the triglyceride (TG) and non-esterified fatty acid (NEFA) contents of the differentiated 3T3-L1 adipocytes in a concentration-dependent manner without cytotoxicity, and high concentration (100 µg/ml) of CTPG treatment dramatically suppressed the level of monocyte chemoattractant protein-1 (MCP-1) in 3T3-L1 mature adipocytes. Meanwhile, CTPG increased glucose consumption and decreased NEFA level in insulin resistant 3T3-L1 cells. We further found that CTPG protected mice from the development of obesity by inhibiting the expansion of adipose tissue and adipocyte hypertrophy, and improved hepatic steatosis by activating AMPKα to reduce hepatic fat accumulation. CTPG ameliorated HFD-induced hyperinsulinemia, hyperglycemia, inflammation and insulin resistance by activating IRS1/Akt/GLUT4 insulin signaling pathway in white adipose tissue. Moreover, gut microbiota structure and metabolic functions in HFD-induced obese mice was changed by CTPG, especially short chain fatty acids-producing bacteria including Blautia, Roseburia, Butyrivibrio and Bacteriodes were significantly increased by CTPG treatment.

Conclusions

CTPG effectively suppressed adipogenesis and lipid accumulation in 3T3-L1 adipocytes and ameliorated HFD-induced obesity and insulin resistance through activating AMPKα and IRS1/AKT/GLUT4 signaling pathway and regulating the composition and metabolic functions of gut microbiota.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12906-022-03743-6.

Polymorphism PLIN1 11482 G>A interacts with dietary intake to modulate anthropometric measures and lipid profile in adults with normal-weight obesity syndrome

Evidence shows that genetic polymorphisms in perilipin 1 gene (PLIN1) are associated with excessive accumulation of body fat and disturbances in cardiometabolic markers. Therefore, the aim of this study was to verify whether the SNP PLIN1 11482 G>A (rs894160) interacts with nutrient intake, anthropometric, body composition and cardiometabolic markers in adults with normal-weight obesity (NWO) syndrome. A cross-sectional study was carried out with 116 individuals aged 20-59 years, with normal BMI and high percentage of body fat. Anthropometric and body composition measures, glycaemic control and serum lipid markers, SNP PLIN1 11482 G>A and nutrient intake were evaluated. Interactions between nutrient intake and the SNP were determined by regression models and adjusted for potential confounders. The SNP frequency was 56·0 % GG, 38·8 % GA and 5·2 % AA. Anthropometric measures and biochemical markers were not different according to genotype, except for total cholesterol (TC), LDL-cholesterol and non-HDL-cholesterol concentrations. However, important interactions between the SNP and dietary intake were observed. Carbohydrate intake interacted with the SNP PLIN1 11482 G>A to modulate waist circumference (WC) and the homeostatic model assessment of insulin resistance index. Interaction of lipid intake and the SNP modulated TC and LDL-cholesterol concentrations, and the interaction between protein intake and the SNP tended to modulate weight, WC and BMI. The SNP PLIN1 11482 G>A seems to modulate responses in anthropometric and lipid profile biomarkers of subjects with NWO depending on the dietary macronutrient composition, which may have long-term impact on cardiometabolic markers.

Effects of two triterpenoids from Nigella sativa seeds on insulin resistance of 3T3-L1 adipocytes

Insulin resistance (IR) is a physiological abnormality that occurs when insulin fails to activate the signal transduction pathway in target organs. It was found that supplementation of Nigella sativa seeds with oral antidiabetic medicines helps improve blood glucose control by enhanced β cells activity and alleviation of IR. However, the activities and related mechanisms of phytochemicals from N. sativa seeds have not been thoroughly explored. In this study, the effects of two triterpenoids, 3-O-[β-D-xylopyranose-(1→3)-α-L-rhamnose-(1→2)-α-L-arabinose]-28-O-[α-L-rhamnose-(1→4)-β-D-glucopyranose-L-(1→6)-β-D-glucopyranose]-hederagenin (Hxrarg) and 3-O-[β-D-xylopyranose-(1→3)-α-L-rhamnose-(1→2)-α-L-arabinose]-hederagenin (Hxra), on IR were studied by 3T3-L1 adipocytes model. The results demonstrated that Hxrarg and Hxra inhibited maturation of 3T3-L1 preadipocytes, dramatically stimulated glucose uptake of IR-3T3-L1 adipocytes, promoted transcription of IRS, AKT, PI-3K, and GLUT4 mRNA. Western Blot results suggested that Hxrarg and Hxra were able to markedly up-regulate expression of p-IRS, p-AKT, PI-3K, and GLUT4 proteins. These findings could provide a basic foundation for the continued development and application of N. sativa in medicine and functional foods.

The Stress-Responsive microRNA-34a Alters Insulin Signaling and Actions in Adipocytes through Induction of the Tyrosine Phosphatase PTP1B

Metabolic stresses alter the signaling and actions of insulin in adipocytes during obesity, but the molecular links remain incompletely understood. Members of the microRNA-34 (miR-34 family play a pivotal role in stress response, and previous studies showed an upregulation of miR-34a in adipose tissue during obesity. Here, we identified miR-34a as a new mediator of adipocyte insulin resistance. We confirmed the upregulation of miR-34a in adipose tissues of obese mice, which was observed in the adipocyte fraction exclusively. Overexpression of miR-34a in 3T3-L1 adipocytes or in fat pads of lean mice markedly reduced Akt activation by insulin and the insulin-induced glucose transport. This was accompanied by a decreased expression of VAMP2, a target of miR-34a, and an increased expression of the tyrosine phosphatase PTP1B. Importantly, PTP1B silencing prevented the inhibitory effect of miR-34a on insulin signaling. Mechanistically, miR-34a decreased the NAD⁺ level through inhibition of Naprt and Nampt, resulting in an inhibition of Sirtuin-1, which promoted an upregulation of PTP1B. Furthermore, the mRNA expression of Nampt and Naprt was decreased in adipose tissue of obese mice. Collectively, our results identify miR-34a as a new inhibitor of insulin signaling in adipocytes, providing a potential pathway to target to fight insulin resistance.

Cytochrome P450 2E1 gene knockout or inhibition prevents obesity induced by high-fat diet via regulating energy expenditure

Cytochrome P450 2E1 (CYP2E1), an important member of the CYP metabolic enzyme family in the liver, regulates the disposal of drugs and the biotransformation of endogenous substances. Although previous studies have found that CYP2E1 is related to energy metabolism, the role of CYP2E1 in energy homeostasis remains unclear. Herein this study shows that the deletion of Cyp2e1 gene in rats can prevent obesity, fatty liver and insulin resistance induced by high-fat diet. Mechanism studies uncover that Cyp2e1 deficiency not only increases the expression of thermogenic genes in brown adipose tissue (BAT) and subcutaneous adipose tissue (SAT), but also promotes fatty acid metabolism in the liver and BAT. In particular, Cyp2e1 deficiency elevates energy expenditure through an increase of liver-generated acylcarnitines, which promote BAT thermogenesis and increase β-oxidation. Interestingly, disulfiram as a CYP2E1 inhibitor can also prevent obesity induced by high-fat diet in normal rats. In general, this study explains the relationship between CYP2E1 and energy metabolism, and provides a new perspective for the prevention and treatment of obesity.

The Translational Role of miRNA in Polycystic Ovary Syndrome: From Bench to Bedside—A Systematic Literature Review

MicroRNAs (miRNAs) are small, non-coding RNAs that are essential for the regulation of post-transcriptional gene expression during tissue development and differentiation. They are involved in the regulation of manifold metabolic and hormonal processes and, within the female reproductive tract, in oocyte maturation and folliculogenesis. Altered miRNA levels have been observed in oncological and inflammatory diseases, diabetes or polycystic ovary syndrome (PCOS). Therefore, miRNAs are proving to be promising potential biomarkers. In women with PCOS, circulating miRNAs can be obtained from whole blood, serum, plasma, urine, and follicular fluid. Our systematic review summarizes data from 2010–2021 on miRNA expression in granulosa and theca cells; the relationship between miRNAs, hormonal changes, glucose and lipid metabolism in women with PCOS; and the potential role of altered miRNAs in fertility (oocyte quality) in PCOS. Furthermore, we discuss miRNAs as a potential therapeutic target in PCOS and as a diagnostic marker for PCOS.

Does the RGD region of certain proteins affect metabolic activity?

A better understanding of the role of mineralized tissues and their associated factors in governing whole-body metabolism should be of value toward informing clinical strategies to treat mineralized tissue and metabolic disorders, such as diabetes and obesity. This perspective provides evidence suggesting a role for the arginine-glycine-aspartic acid (RGD) region, a sequence identified in several proteins secreted by bone cells, as well as other cells, in modulating systemic metabolic activity. We focus on (a) two of the SIBLING (small integrin-binding ligand, N-linked glycoprotein) family genes/proteins, bone sialoprotein (BSP) and osteopontin (OPN), (b) insulin-like growth factor-binding protein-1 & 2 (IGFBP-1, IGFBP-2) and (c) developmental endothelial locus 1 (DEL1) and milk fat globule–EGF factor-8 (MFG-E8). In addition, for our readers to appreciate the mounting evidence that a multitude of bone secreted factors affect the activity of other tissues, we provide a brief overview of other proteins, to include fibroblast growth factor 23 (FGF23), phosphatase orphan 1 (PHOSPHO1), osteocalcin (OCN/BGLAP), tissue non-specific alkaline phosphatase (TNAP) and acidic serine aspartic-rich MEPE-associated motif (ASARM), along with known/suggested functions of these factors in influencing energy metabolism.

Angiogenesis in adipose tissue and obesity

While most tissues exhibit their greatest growth during development, adipose tissue is capable of additional massive expansion in adults. Adipose tissue expandability is advantageous when temporarily storing fuel for use during fasting, but becomes pathological upon continuous food intake, leading to obesity and its many comorbidities. The dense vasculature of adipose tissue provides necessary oxygen and nutrients, and supports delivery of fuel to and from adipocytes under fed or fasting conditions. Moreover, the vasculature of adipose tissue comprises a major niche for multipotent progenitor cells, which give rise to new adipocytes and are necessary for tissue repair. Given the multiple, pivotal roles of the adipose tissue vasculature, impairments in angiogenic capacity may underlie obesity-associated diseases such as diabetes and cardiometabolic disease. Exciting new studies on the single-cell and single-nuclei composition of adipose tissues in mouse and humans are providing new insights into mechanisms of adipose tissue angiogenesis. Moreover, new modes of intercellular communication involving micro vesicle and exosome transfer of proteins, nucleic acids and organelles are also being recognized to play key roles. This review focuses on new insights on the cellular and signaling mechanisms underlying adipose tissue angiogenesis, and on their impact on obesity and its pathophysiological consequences.

Distinct Effects of Cannabidiol on Sphingolipid Metabolism in Subcutaneous and Visceral Adipose Tissues Derived from High-Fat-Diet-Fed Male Wistar Rats

Available data suggest that cannabidiol (CBD) may ameliorate symptoms of insulin resistance by modulating the sphingolipid concentrations in particular organs. However, it is not entirely clear whether its beneficial actions also involve adipose tissues in a state of overnutrition. The aim of the study was to evaluate the effect of CBD on sphingolipid metabolism pathways and, as a result, on the development of insulin resistance in subcutaneous (SAT) and visceral (VAT) adipose tissues of an animal model of HFD-induced insulin resistance. Our experiment was performed on Wistar rats that were fed with a high-fat diet and/or received intraperitoneal CBD injections. We showed that CBD significantly lowered the ceramide content in VAT by reducing its de novo synthesis and increasing its catabolism. However, in SAT, CBD decreased the ceramide level through the inhibition of salvage and de novo synthesis pathways. All of these changes restored adipose tissues’ sensitivity to insulin. Our study showed that CBD sensitized adipose tissue to insulin by influencing the metabolism of sphingolipids under the conditions of increased availability of fatty acids in the diet. Therefore, we believe that CBD use may be considered as a potential therapeutic strategy for treating or reducing insulin resistance, T2DM, and metabolic syndrome.

Beta-hydroxybutyrate dampens adipose progenitors' profibrotic activation through canonical Tgfβ signaling and non-canonical ZFP36-dependent mechanisms

BACKGROUND/PURPOSE

Adipose tissue contains progenitor cells that contribute to beneficial tissue expansion when needed by de novo adipocyte formation (classical white or beige fat cells with thermogenic potential). However, in chronic obesity, they can exhibit an activated pro-fibrotic, extracellular matrix (ECM)-depositing phenotype that highly aggravates obesity-related adipose tissue dysfunction.

METHODS

Given that progenitors' fibrotic activation and fat cell browning appear to be antagonistic cell fates, we have examined the anti-fibrotic potential of pro-browning agents in an obesogenic condition.

RESULTS

In obese mice fed a high fat diet, thermoneutral housing, which induces brown fat cell dormancy, increases the expression of ECM gene programs compared to conventionally raised animals, indicating aggravation of obesity-related tissue fibrosis at thermoneutrality. In a model of primary cultured murine adipose progenitors, we found that exposure to β-hydroxybutyrate selectively reduced Tgfβ-dependent profibrotic responses of ECM genes like Ctgf, Loxl2 and Fn1. This effect is observed in both subcutaneous and visceral-derived adipose progenitors, as well as in 3T3-L1 fibroblasts. In 30 patients with obesity eligible for bariatric surgery, those with higher circulating β-hydroxybutyrate levels have lower subcutaneous adipose tissue fibrotic scores. Mechanistically, β-hydroxybutyrate limits Tgfβ-dependent collagen accumulation and reduces Smad2-3 protein expression and phosphorylation in visceral progenitors. Moreover, β-hydroxybutyrate induces the expression of the ZFP36 gene, encoding a post-transcriptional regulator that promotes the degradation of mRNA by binding to AU-rich sites within 3'UTRs. Importantly, complete ZFP36 deficiency in a mouse embryonic fibroblast line from null mice, or siRNA knock-down in primary progenitors, indicate that ZFP36 is required for β-hydroxybutyrate anti-fibrotic effects.

CONCLUSION

These data unravel the potential of β-hydroxybutyrate to limit adipose tissue matrix deposition, a finding that might exploited in an obesogenic context.

Many Ways to Rome: Exercise, Cold Exposure and Diet-Do They All Affect BAT Activation and WAT Browning in the Same Manner?

The discovery of functional brown adipose tissue (BAT) in adult humans and the possibility to recruit beige cells with high thermogenic potential within white adipose tissue (WAT) depots opened the field for new strategies to combat obesity and its associated comorbidities. Exercise training as well as cold exposure and dietary components are associated with the enhanced accumulation of metabolically-active beige adipocytes and BAT activation. Both activated beige and brown adipocytes increase their metabolic rate by utilizing lipids to generate heat via non-shivering thermogenesis, which is dependent on uncoupling protein 1 (UCP1) in the inner mitochondrial membrane. Non-shivering thermogenesis elevates energy expenditure and promotes a negative energy balance, which may ameliorate metabolic complications of obesity and Type 2 Diabetes Mellitus (T2DM) such as insulin resistance (IR) in skeletal muscle and adipose tissue. Despite the recent advances in pharmacological approaches to reduce obesity and IR by inducing non-shivering thermogenesis in BAT and WAT, the administered pharmacological compounds are often associated with unwanted side effects. Therefore, lifestyle interventions such as exercise, cold exposure, and/or specified dietary regimens present promising anchor points for future disease prevention and treatment of obesity and T2DM. The exact mechanisms where exercise, cold exposure, dietary interventions, and pharmacological treatments converge or rather diverge in their specific impact on BAT activation or WAT browning are difficult to determine. In the past, many reviews have demonstrated the mechanistic principles of exercise- and/or cold-induced BAT activation and WAT browning. In this review, we aim to summarize not only the current state of knowledge on the various mechanistic principles of diverse external stimuli on BAT activation and WAT browning, but also present their translational potential in future clinical applications.

Transcriptome-wide analyses of adipose tissue in outbred rats reveal genetic regulatory mechanisms relevant for human obesity

Transcriptomic analysis in metabolically active tissues allows a systems genetics approach to identify causal genes and networks involved in metabolic disease. Outbred heterogeneous stock (HS) rats are used for genetic mapping of complex traits, but to-date, a systems genetics analysis of metabolic tissues has not been done. We investigated whether adiposity-associated genes and gene co-expression networks in outbred heterogeneous stock (HS) rats overlap those found in humans. We analyzed RNAseq data from adipose tissue of 415 male HS rats, correlated these transcripts with body weight (BW) and compared transcriptome signatures to two human cohorts: the "African American Genetics of Metabolism and Expression" and "Metabolic Syndrome in Men". We used weighted gene co-expression network analysis to identify adiposity-associated gene networks and mediation analysis to identify genes under genetic control whose expression drives adiposity. We identified 554 orthologous "consensus genes" whose expression correlates with BW in the rat and with body mass index (BMI) in both human cohorts. Consensus genes fell within eight co-expressed networks and were enriched for genes involved in immune system function, cell growth, extracellular matrix organization and lipid metabolic processes. We identified 19 consensus genes for which genetic variation may influence BW via their expression, including those involved in lipolysis (e.g., Hcar1), inflammation (e.g., Rgs1), adipogenesis (e.g., Tmem120b) or no previously known role in obesity (e.g., St14, Msa4a6). Strong concordance between HS rat and human BW/BMI associated transcripts demonstrates translational utility of the rat model, while identification of novel genes expands our knowledge of the genetics underlying obesity.

Beige Adipocyte as the Flame of White Adipose Tissue: Regulation of Browning and Impact of Obesity

Beige adipocyte, the third and relatively new type of adipocyte, can emerge in white adipose tissue (WAT) under thermogenic stimulations that is termed as browning of WAT. Recent studies suggest that browning of WAT deserves more attention and therapies targeting browning of WAT can be helpful for reducing obesity. Beyond the major inducers of browning, namely cold and β 3-adrenergic stimulation, beige adipocytes are affected by several factors, and excess adiposity per se may also influence the browning process. The objective of the present review is to provide an overview of recent clinical and preclinical studies on the hormonal and nonhormonal factors that affect the browning of WAT. This review further focuses on the role of obesity per se on browning process.

The Role of Glp-1 Receptor Agonists in Insulin Resistance with Concomitant Obesity Treatment in Polycystic Ovary Syndrome

Insulin resistance is documented in clamp studies in 75% of women with polycystic ovary syndrome (PCOS). Although it is not included in the diagnostic criteria of PCOS, there is a crucial role of this metabolic impairment, which along with hormonal abnormalities, increase each other in a vicious circle of PCOS pathogenesis. Insulin resistance in this group of patients results from defects at the molecular level, including impaired insulin receptor-related signaling pathways enhanced by obesity and its features: Excess visceral fat, chronic inflammation, and reactive oxygen species. While lifestyle intervention has a first-line role in the prevention and management of excess weight in PCOS, the role of anti-obesity pharmacological agents in achieving and maintaining weight loss is being increasingly recognized. Glucagon-like peptide-1 receptor agonists (GLP1-RAs) not only act by reducing body weight but also can affect the mechanisms involved in insulin resistance, like an increasing expression of glucose transporters in insulin-dependent tissues, decreasing inflammation, reducing oxidative stress, and modulating lipid metabolism. They also tend to improve fertility either by increasing LH surge in hypothalamus-pituitary inhibition due to estrogen excess connected with obesity or decreasing too high LH levels accompanying hyperinsulinemia. GLP1-RAs seem promising for effective treatment of obese PCOS patients, acting on one of the primary causes of PCOS at the molecular level.

Deconstructing Adipose Tissue Heterogeneity One Cell at a Time

As a central coordinator of physiologic metabolism, adipose tissue has long been appreciated as a highly plastic organ that dynamically responds to environmental cues. Once thought of as a homogenous storage depot, recent advances have enabled deep characterizations of the underlying structure and composition of adipose tissue depots. As the obesity and metabolic disease epidemics continue to accelerate due to modern lifestyles and an aging population, elucidation of the underlying mechanisms that control adipose and systemic homeostasis are of critical importance. Within the past decade, the emergence of deep cell profiling at tissue- and, recently, single-cell level has furthered our understanding of the complex dynamics that contribute to tissue function and their implications in disease development. Although many paradigm-shifting findings may lie ahead, profound advances have been made to forward our understanding of the adipose tissue niche in both health and disease. Now widely accepted as a highly heterogenous organ with major roles in metabolic homeostasis, endocrine signaling, and immune function, the study of adipose tissue dynamics has reached a new frontier. In this review, we will provide a synthesis of the latest advances in adipose tissue biology made possible by the use of single-cell technologies, the impact of epigenetic mechanisms on adipose function, and suggest what next steps will further our understanding of the role that adipose tissue plays in systemic physiology.

The Effects of Prolonged Water-Only Fasting and Refeeding on Markers of Cardiometabolic Risk

(1) Background: Cardiometabolic disease, including insulin resistance, hyperlipidemia, and hypertension, are major contributors to adverse health outcomes. Fasting has gained interest as a nonpharmacological therapeutic adjunct for these disorders. (2) Methods: We conducted a prospective, single-center study on the effects of prolonged water-only fasting followed by an exclusively whole-plant-food refeeding diet on accepted measures of cardiovascular risk and metabolic health. Participants were recruited from patients who had voluntarily elected to complete a water-only fast in order to improve their overall health according to an established protocol at an independent, residential medical center. Median fasting and refeed lengths were 17 and 8 days, respectively. The primary endpoint was to describe the mean glucose tolerance as indicated by Homeostatic Model Assessment of Insulin Resistance (HOMA-IR) scores at baseline, end-of-fast (EOF), and end-of-refeed (EOR) visits. Secondary endpoints were to describe the mean weight, body mass index (BMI), abdominal circumference (AC), systolic blood pressure (SBP), diastolic blood pressure (DBP), lipid panel, and high-sensitivity C-reactive protein (hsCRP) at the same time points. (3) Results: The study enrolled 48 overweight/obese non-diabetic participants, of which 26 completed the full study protocol. At the EOF visit, the median SBP, AC, low-density lipoprotein (LDL), and hsCRP were decreased and triglycerides (TG) and HOMA-IR scores were increased. Conclusion: Prolonged water-only fasting and whole-plant-food refeeding holds potential as a clinical therapy for cardiometabolic disease but increased TG and HOMA-IR values after refeeding necessitate further inquiry.

Adipose-tissue plasticity in health and disease

Adipose tissue, colloquially known as "fat," is an extraordinarily flexible and heterogeneous organ. While historically viewed as a passive site for energy storage, we now appreciate that adipose tissue regulates many aspects of whole-body physiology, including food intake, maintenance of energy levels, insulin sensitivity, body temperature, and immune responses. A crucial property of adipose tissue is its high degree of plasticity. Physiologic stimuli induce dramatic alterations in adipose-tissue metabolism, structure, and phenotype to meet the needs of the organism. Limitations to this plasticity cause diminished or aberrant responses to physiologic cues and drive the progression of cardiometabolic disease along with other pathological consequences of obesity.

The role of mitochondrial reactive oxygen species in insulin resistance

Insulin resistance is one of the earliest pathological features of a suite of diseases including type 2 diabetes collectively referred to as metabolic syndrome. There is a growing body of evidence from both pre-clinical studies and human cohorts indicating that reactive oxygen species, such as the superoxide radical anion and hydrogen peroxide are key players in the development of insulin resistance. Here we review the evidence linking mitochondrial reactive oxygen species generated within mitochondria with insulin resistance in adipose tissue and skeletal muscle, two major insulin sensitive tissues. We outline the relevant mitochondria-derived reactive species, how the mitochondrial redox state is regulated, and methodologies available to measure mitochondrial reactive oxygen species. Importantly, we highlight key experimental issues to be considered when studying the role of mitochondrial reactive oxygen species in insulin resistance. Evaluating the available literature on both mitochondrial reactive oxygen species/redox state and insulin resistance in a variety of biological systems, we conclude that the weight of evidence suggests a likely role for mitochondrial reactive oxygen species in the etiology of insulin resistance in adipose tissue and skeletal muscle. However, major limitations in the methods used to study reactive oxygen species in insulin resistance as well as the lack of data linking mitochondrial reactive oxygen species and cytosolic insulin signaling pathways are significant obstacles in proving the mechanistic link between these two processes. We provide a framework to guide future studies to provide stronger mechanistic information on the link between mitochondrial reactive oxygen species and insulin resistance as understanding the source, localization, nature, and quantity of mitochondrial reactive oxygen species, their targets and downstream signaling pathways may pave the way for important new therapeutic strategies.

Gene deletion of γ-actin impairs insulin-stimulated skeletal muscle glucose uptake in growing mice but not in mature adult mice

The cortical cytoskeleton, consisting of the cytoplasmic actin isoforms β and/or γ-actin, has been implicated in insulin-stimulated GLUT4 translocation and glucose uptake in muscle and adipose cell culture. Furthermore, transgenic inhibition of multiple actin-regulating proteins in muscle inhibits insulin-stimulated muscle glucose uptake. The current study tested if γ-actin was required for insulin-stimulated glucose uptake in mouse skeletal muscle. Based on our previously reported age-dependent phenotype in muscle-specific β-actin gene deletion (^-/- ) mice, we included cohorts of growing 8-14 weeks old and mature 18-32 weeks old muscle-specific γ-actin^-/- mice or wild-type littermates. In growing mice, insulin significantly increased the glucose uptake in slow-twitch oxidative soleus and fast-twitch glycolytic EDL muscles from wild-type mice, but not γ-actin^-/- . In relative values, the maximal insulin-stimulated glucose uptake was reduced by ~50% in soleus and by ~70% in EDL muscles from growing γ-actin^-/- mice compared to growing wild-type mice. In contrast, the insulin-stimulated glucose uptake responses in mature adult γ-actin^-/- soleus and EDL muscles were indistinguishable from the responses in wild-type muscles. Mature adult insulin-stimulated phosphorylations on Akt, p70S6K, and ULK1 were not significantly affected by genotype. Hence, insulin-stimulated muscle glucose uptake shows an age-dependent impairment in young growing but not in fully grown γ-actin^-/- mice, bearing phenotypic resemblance to β-actin^-/- mice. Overall, γ-actin does not appear required for insulin-stimulated muscle glucose uptake in adulthood. Furthermore, our data emphasize the need to consider the rapid growth of young mice as a potential confounder in transgenic mouse phenotyping studies.

Lipogenesis inhibitors: therapeutic opportunities and challenges

Fatty acids are essential for survival, acting as bioenergetic substrates, structural components and signalling molecules. Given their vital role, cells have evolved mechanisms to generate fatty acids from alternative carbon sources, through a process known as de novo lipogenesis (DNL). Despite the importance of DNL, aberrant upregulation is associated with a wide variety of pathologies. Inhibiting core enzymes of DNL, including citrate/isocitrate carrier (CIC), ATP-citrate lyase (ACLY), acetyl-CoA carboxylase (ACC) and fatty acid synthase (FAS), represents an attractive therapeutic strategy. Despite challenges related to efficacy, selectivity and safety, several new classes of synthetic DNL inhibitors have entered clinical-stage development and may become the foundation for a new class of therapeutics.

De novo lipogenesis (DNL) is vital for the maintenance of whole-body and cellular homeostasis, but aberrant upregulation of the pathway is associated with a broad range of conditions, including cardiovascular disease, metabolic disorders and cancers. Here, Steinberg and colleagues provide an overview of the physiological and pathological roles of the core DNL enzymes and assess strategies and agents currently in development to therapeutically target them.

Galanin enhanced insulin-mediated intracellular signaling by regulating the stability of membrane-localized insulin/IR

Previous studies have shown that insulin has the important regulatory effect on the intestinal tract. However, until now, the biological properties of insulin on intestinal cell has not been revealed. Therefore, in the current research, we first studied the cell characteristics and signaling profiles of insulin in the intestinal cell model, and found that insulin can be internalized into the cytoplasm in a time-dependent manner. After internalization, insulin transported into different type of endosomes. More importantly, we explored the effect of galanin on insulin-mediated signaling pathways (galanin is a polypeptide composed of 29 amino acid residues, galanin is widely distributed in the central and peripheral nervous system and has a variety of biological activities), and found that galanin can increase insulin sensitivity by regulating insulin receptor (IR)-mediated signal transduction pathways. We further study the potential molecular mechanism by which galanin enhances insulin sensitivity, and found that galanin could increase the time of insulin acting on the cell membrane. Further experiments showed that galanin could stabilize the membrane-localized insulin/IR, which may be an important new potential mechanism by which galanin improves the biological activity of insulin. This study laid the foundation for exploring the relationship between galanin and insulin sensitivity.

Elevated SAA1 promotes the development of insulin resistance in ovarian granulosa cells in polycystic ovary syndrome

BACKGROUND

Insulin resistance (IR) contributes to ovarian dysfunctions in polycystic ovarian syndrome (PCOS) patients. Serum amyloid A1 (SAA1) is an acute phase protein produced primarily by the liver in response to inflammation. In addition to its role in inflammation, SAA1 may participate in IR development in peripheral tissues. Yet, expressional regulation of SAA1 in the ovary and its role in the pathogenesis of ovarian IR in PCOS remain elusive.

METHODS

Follicular fluid, granulosa cells and peripheral venous blood were collected from PCOS and non-PCOS patients with and without IR to measure SAA1 abundance for analysis of its correlation with IR status. The effects of SAA1 on its own expression and insulin signaling pathway were investigated in cultured primary granulosa cells.

RESULTS

Ovarian granulosa cells were capable of producing SAA1, which could be induced by SAA1 per se. Moreover, the abundance of SAA1 significantly increased in granulosa cells and follicular fluid in PCOS patients with IR. SAA1 treatment significantly attenuated insulin-stimulated membrane translocation of glucose transporter 4 and glucose uptake in granulosa cells through induction of phosphatase and tensin homolog deleted on chromosome 10 (PTEN) expression with subsequent inhibition of Akt phosphorylation. These effects of SAA1 could be blocked by inhibitors for toll-like receptors 2/4 (TLR 2/4) and nuclear factor kappa light chain enhancer of activated B (NF-κB).

CONCLUSIONS

Human granulosa cells are capable of feedforward production of SAA1, which significantly increased in PCOS patients with IR. Excessive SAA1 reduces insulin sensitivity in granulosa cells via induction of PTEN and subsequent inhibition of Akt phosphorylation upon activation of TLR2/4 and NF-κB pathway. These findings highlight that elevation of SAA1 in the ovary promotes the development of IR in granulosa cells of PCOS patients.

Probing Insulin Sensitivity with Metabolically Competent Human Stem Cell-Derived White Adipose Tissue Microphysiological Systems

Impaired white adipose tissue (WAT) function has been recognized as a critical early event in obesity-driven disorders, but high buoyancy, fragility, and heterogeneity of primary adipocytes have largely prevented their use in drug discovery efforts highlighting the need for human stem cell-based approaches. Here, human stem cells are utilized to derive metabolically functional 3D adipose tissue (iADIPO) in a microphysiological system (MPS). Surprisingly, previously reported WAT differentiation approaches create insulin resistant WAT ill-suited for type-2 diabetes mellitus drug discovery. Using three independent insulin sensitivity assays, i.e., glucose and fatty acid uptake and suppression of lipolysis, as the functional readouts new differentiation conditions yielding hormonally responsive iADIPO are derived. Through concomitant optimization of an iADIPO-MPS, it is abled to obtain WAT with more unilocular and significantly larger (≈40%) lipid droplets compared to iADIPO in 2D culture, increased insulin responsiveness of glucose uptake (≈2-3 fold), fatty acid uptake (≈3-6 fold), and ≈40% suppressing of stimulated lipolysis giving a dynamic range that is competent to current in vivo and ex vivo models, allowing to identify both insulin sensitizers and desensitizers.

Zeaxanthin Remodels Cytoplasmic Lipid Droplets via β3-Adrenergic Receptor Signaling and Enhances Perilipin 5-Mediated Lipid Droplet–Mitochondria Interactions in Adipocytes

Cytoplasmic lipid droplets (LDs), which are remarkably dynamic, neutral lipid storage organelles, play fundamental roles in lipid metabolism and energy homeostasis. Both the dynamic remodeling of LDs and LD–mitochondria interactions...

In Vitro and In Vivo Antidiabetic Potential of Monoterpenoids: An Update

Diabetes mellitus (DM) is a chronic metabolic condition characterized by persistent hyperglycemia due to insufficient insulin levels or insulin resistance. Despite the availability of several oral and injectable hypoglycemic agents, their use is associated with a wide range of side effects. Monoterpenes are compounds extracted from different plants including herbs, vegetables, and fruits and they contribute to their aroma and flavor. Based on their chemical structure, monoterpenes are classified into acyclic, monocyclic, and bicyclic monoterpenes. They have been found to exhibit numerous biological and medicinal effects such as antipruritic, antioxidant, anti-inflammatory, and analgesic activities. Therefore, monoterpenes emerged as promising molecules that can be used therapeutically to treat a vast range of diseases. Additionally, monoterpenes were found to modulate enzymes and proteins that contribute to insulin resistance and other pathological events caused by DM. In this review, we highlight the different mechanisms by which monoterpenes can be used in the pharmacological intervention of DM via the alteration of certain enzymes, proteins, and pathways involved in the pathophysiology of DM. Based on the fact that monoterpenes have multiple mechanisms of action on different targets in in vitro and in vivo studies, they can be considered as lead compounds for developing effective hypoglycemic agents. Incorporating these compounds in clinical trials is needed to investigate their actions in diabetic patients in order to confirm their ability in controlling hyperglycemia.

Systematisation of biological protectors for managing the metabolic syndrome development

BACKGROUND

Metabolic syndrome (MS) is becoming a major health risk in the world. Disorders of homeostasis are a trigger for MS and subsequent cardiometabolic diseases (CMDs). Its physiological role can be supported by biological protectors (BP). The purpose of this study is to develop a BP system for managing the MS development.

METHODS

Within the framework of the case-control study, 3000 participants aged 20-60 years formed 2 groups: the main group and the control group.

RESULTS

The study compared traditional markers of oxidative stress, chronic inflammation, and insulin resistance, which reflect the state of homeostasis. The BP system, proposed based on the concept of maintaining homeostasis, offers the following points for investigating the possibilities of therapeutic intervention: confronting dysregulation of homeostasis, resisting chronic inflammation and oxidative stress, resisting the consequences of disturbed homeostasis. This approach not only contributed to the understanding of general biological processes, but also provided a targeted search and development of BP to maintain the stability of homeostasis with MS.

CONCLUSIONS

The study results provided insight into new opportunities in the MS management.

URAT1-selective inhibition ameliorates insulin resistance by attenuating diet-induced hepatic steatosis and brown adipose tissue whitening in mice

Objective

Accumulating evidence indicates that high uric acid (UA) is strongly associated with obesity and metabolic syndrome and drives the development of nonalcoholic fatty liver disease (NAFLD) and insulin resistance. Although urate transporter-1 (URAT1), which is primarily expressed in the kidneys, plays a critical role in the development of hyperuricemia, its pathophysiological implication in NAFLD and insulin resistance remains unclear. We herein investigated the role and functional significance of URAT1 in diet-induced obese mice.

Methods

Mice fed a high-fat diet (HFD) for 16–18 weeks or a normal-fat diet (NFD) were treated with or without a novel oral URAT1-selective inhibitor (dotinurad [50 mg/kg/day]) for another 4 weeks.

Results

We found that URAT1 was also expressed in the liver and brown adipose tissue (BAT) other than the kidneys. Dotinurad administration significantly ameliorated HFD-induced obesity and insulin resistance. HFD markedly induced NAFLD, which was characterized by severe hepatic steatosis as well as the elevation of serum ALT activity and tissue inflammatory cytokine genes (chemokine ligand 2 (Ccl2) and tissue necrosis factor α (TNFα)), all of which were attenuated by dotinurad. Similarly, HFD significantly increased URAT1 expression in BAT, resulting in lipid accumulation (whitening of BAT), and increased the production of tissue reactive oxygen species (ROS), which were reduced by dotinurad via UCP1 activation.

Conclusions

In conclusion, a novel URAT1-selective inhibitor, dotinurad, ameliorates insulin resistance by attenuating hepatic steatosis and promoting rebrowning of lipid-rich BAT in HFD-induced obese mice. URAT1 serves as a key regulator of the pathophysiology of metabolic syndrome and may be a new therapeutic target for insulin-resistant individuals, particularly those with concomitant NAFLD.

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URAT1 is expressed in the liver and brown adipose tissue other than in the kidneys.

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URAT1-selective inhibitor ameliorates HFD-induced insulin resistance.

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URAT1-selective inhibitor improves NAFLD through the inhibition of Ccl2 and TNFα.

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URAT1-selective inhibitor promotes rebrowning of HFD-induced lipid-rich BAT.

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URAT1 serves as a key regulator of the pathophysiology of metabolic syndrome.

Leptin Signaling in the Ovary of Diet-Induced Obese Mice Regulates Activation of NOD-Like Receptor Protein 3 Inflammasome

Obesity leads to ovarian dysfunction and the establishment of local leptin resistance. The aim of our study was to characterize the levels of NOD-like receptor protein 3 (NLRP3) inflammasome activation in ovaries and liver of mice during obesity progression. Furthermore, we tested the putative role of leptin on NLRP3 regulation in those organs. C57BL/6J female mice were treated with equine chorionic gonadotropin (eCG) or human chorionic gonadotropin (hCG) for estrous cycle synchronization and ovary collection. In diet-induced obesity (DIO) protocol, mice were fed chow diet (CD) or high-fat diet (HFD) for 4 or 16 weeks, whereas in the hyperleptinemic model (LEPT), mice were injected with leptin for 16 days (16 L) or saline (16 C). Finally, the genetic obese leptin-deficient ob/ob (+/? and −/−) mice were fed CD for 4 week. Either ovaries and liver were collected, as well as cumulus cells (CCs) after superovulation from DIO and LEPT. The estrus cycle synchronization protocol showed increased protein levels of NLRP3 and interleukin (IL)-18 in diestrus, with this stage used for further sample collections. In DIO, protein expression of NLRP3 inflammasome components was increased in 4 week HFD, but decreased in 16 week HFD. Moreover, NLRP3 and IL-1β were upregulated in 16 L and downregulated in ob/ob. Transcriptome analysis of CC showed common genes between LEPT and 4 week HFD modulating NLRP3 inflammasome. Liver analysis showed NLRP3 protein upregulation after 16 week HFD in DIO, but also its downregulation in ob/ob−/−. We showed the link between leptin signaling and NLRP3 inflammasome activation in the ovary throughout obesity progression in mice, elucidating the molecular mechanisms underpinning ovarian failure in maternal obesity.

The aetiology and molecular landscape of insulin resistance

Insulin resistance, defined as a defect in insulin-mediated control of glucose metabolism in tissues - prominently in muscle, fat and liver - is one of the earliest manifestations of a constellation of human diseases that includes type 2 diabetes and cardiovascular disease. These diseases are typically associated with intertwined metabolic abnormalities, including obesity, hyperinsulinaemia, hyperglycaemia and hyperlipidaemia. Insulin resistance is caused by a combination of genetic and environmental factors. Recent genetic and biochemical studies suggest a key role for adipose tissue in the development of insulin resistance, potentially by releasing lipids and other circulating factors that promote insulin resistance in other organs. These extracellular factors perturb the intracellular concentration of a range of intermediates, including ceramide and other lipids, leading to defects in responsiveness of cells to insulin. Such intermediates may cause insulin resistance by inhibiting one or more of the proximal components in the signalling cascade downstream of insulin (insulin receptor, insulin receptor substrate (IRS) proteins or AKT). However, there is now evidence to support the view that insulin resistance is a heterogeneous disorder that may variably arise in a range of metabolic tissues and that the mechanism for this effect likely involves a unified insulin resistance pathway that affects a distal step in the insulin action pathway that is more closely linked to the terminal biological response. Identifying these targets is of major importance, as it will reveal potential new targets for treatments of diseases associated with insulin resistance.

Adipocyte CAMK2 deficiency improves obesity-associated glucose intolerance

OBJECTIVE

Obesity-related adipose tissue dysfunction has been linked to the development of insulin resistance, type 2 diabetes, and cardiovascular disease. Impaired calcium homeostasis is associated with altered adipose tissue metabolism; however, the molecular mechanisms that link disrupted calcium signaling to metabolic regulation are largely unknown. Here, we investigated the contribution of a calcium-sensing enzyme, calcium/calmodulin-dependent protein kinase II (CAMK2), to adipocyte function, obesity-associated insulin resistance, and glucose intolerance.

METHODS

To determine the impact of adipocyte CAMK2 deficiency on metabolic regulation, we generated a conditional knockout mouse model and acutely deleted CAMK2 in mature adipocytes. We further used in vitro differentiated adipocytes to dissect the mechanisms by which CAMK2 regulates adipocyte function.

RESULTS

CAMK2 activity was increased in obese adipose tissue, and depletion of adipocyte CAMK2 in adult mice improved glucose intolerance and insulin resistance without an effect on body weight. Mechanistically, we found that activation of CAMK2 disrupted adipocyte insulin signaling and lowered the amount of insulin receptor. Further, our results revealed that CAMK2 contributed to adipocyte lipolysis, tumor necrosis factor alpha (TNFα)-induced inflammation, and insulin resistance.

CONCLUSIONS

These results identify a new link between adipocyte CAMK2 activity, metabolic regulation, and whole-body glucose homeostasis.

Coffee Bioactive N-Methylpyridinium Attenuates Tumor Necrosis Factor (TNF)-α-Mediated Insulin Resistance and Inflammation in Human Adipocytes

Although coffee consumption has been historically associated with negative health outcomes, recent evidence suggests a lower risk of metabolic syndrome, obesity and diabetes among regular coffee drinkers. Among the plethora of minor organic compounds assessed as potential mediators of coffee health benefits, trigonelline and its pyrolysis product N-methylpyridinium (NMP) were preliminary shown to promote glucose uptake and exert anti-adipogenic properties. Against this background, we aimed at characterizing the effects of trigonelline and NMP in inflamed and dysfunctional human adipocytes. Human Simpson-Golabi-Behmel syndrome (SGBS) adipocytes were treated with NMP or, for comparison, trigonelline, for 5 h before stimulation with tumor necrosis factor (TNF)-α. NMP at concentrations as low as 1 µmol/L reduced the stimulated expression of several pro-inflammatory mediators, including C-C Motif chemokine ligand (CCL)-2, C-X-C Motif chemokine ligand (CXCL)-10, and intercellular adhesion Molecule (ICAM)-1, but left the induction of prostaglandin G/H synthase (PTGS)2, interleukin (IL)-1β, and colony stimulating factor (CSF)1 unaffected. Furthermore, NMP restored the downregulated expression of adiponectin (ADIPOQ). These effects were functionally associated with downregulation of the adhesion of monocytes to inflamed adipocytes. Under the same conditions, NMP also reversed the TNF-α-mediated suppression of insulin-stimulated Ser473 Akt phosphorylation and attenuated the induction of TNF-α-stimulated lipolysis restoring cell fat content. In an attempt to preliminarily explore the underlying mechanisms of its action, we show that NMP restores the expression of the master regulator of adipocyte differentiation peroxisome proliferator-activated receptor (PPAR)γ and downregulates activation of the pro-inflammatory mitogen-activated protein jun N-terminal kinase (JNK). In conclusion, NMP reduces adipose dysfunction in pro-inflammatory activated adipocytes. These data suggest that bioactive NMP in coffee may improve the inflammatory and dysmetabolic milieu associated with obesity.

Microtubules in insulin action: what's on the tube?

Microtubules (MT) have a role in the intracellular response to insulin stimulation and subsequent glucose transport by glucose transporter 4 (GLUT4), which resides in specialized storage vesicles that travel through the cell. Before GLUT4 is inserted into the plasma membrane for glucose transport, it undergoes complex trafficking through the cell via the integration of cytoskeletal networks. In this review, we highlight the importance of MT elements in insulin action in adipocytes through a summary of MT depolymerization studies, MT-based GLUT4 movement, molecular motor proteins involved in GLUT4 trafficking, as well as MT-related phenomena in response to insulin and links between insulin action and MT-associated proteins.

Treatment with atrial natriuretic peptide induces adipose tissue browning and exerts thermogenic actions in vivo

Increasing evidence suggests natriuretic peptides (NPs) coordinate inter-organ metabolic crosstalk with adipose tissues and play a critical role in energy metabolism. We recently reported A-type NP (ANP) raises intracellular temperature in cultured adipocytes in a low-temperature-sensitive manner. We herein investigated whether exogenous ANP-treatment exerts a significant impact on adipose tissues in vivo. Mice fed a high-fat-diet (HFD) or normal-fat-diet (NFD) for 13 weeks were treated with or without ANP infusion subcutaneously for another 3 weeks. ANP-treatment significantly ameliorated HFD-induced insulin resistance. HFD increased brown adipose tissue (BAT) cell size with the accumulation of lipid droplets (whitening), which was suppressed by ANP-treatment (re-browning). Furthermore, HFD induced enlarged lipid droplets in inguinal white adipose tissue (iWAT), crown-like structures in epididymal WAT, and hepatic steatosis, all of which were substantially attenuated by ANP-treatment. Likewise, ANP-treatment markedly increased UCP1 expression, a specific marker of BAT, in iWAT (browning). ANP also further increased UCP1 expression in BAT with NFD. Accordingly, cold tolerance test demonstrated ANP-treated mice were tolerant to cold exposure. In summary, exogenous ANP administration ameliorates HFD-induced insulin resistance by attenuating hepatic steatosis and by inducing adipose tissue browning (activation of the adipose tissue thermogenic program), leading to in vivo thermogenesis during cold exposure.

Phytochemicals: Targeting Mitophagy to Treat Metabolic Disorders

Metabolic disorders include metabolic syndrome, obesity, type 2 diabetes mellitus, non-alcoholic fatty liver disease and cardiovascular diseases. Due to unhealthy lifestyles such as high-calorie diet, sedentary and physical inactivity, the prevalence of metabolic disorders poses a huge challenge to global human health, which is the leading cause of global human death. Mitochondrion is the major site of adenosine triphosphate synthesis, fatty acid β-oxidation and ROS production. Accumulating evidence suggests that mitochondrial dysfunction-related oxidative stress and inflammation is involved in the development of metabolic disorders. Mitophagy, a catabolic process, selectively degrades damaged or superfluous mitochondria to reverse mitochondrial dysfunction and preserve mitochondrial function. It is considered to be one of the major mechanisms responsible for mitochondrial quality control. Growing evidence shows that mitophagy can prevent and treat metabolic disorders through suppressing mitochondrial dysfunction-induced oxidative stress and inflammation. In the past decade, in order to expand the range of pharmaceutical options, more and more phytochemicals have been proven to have therapeutic effects on metabolic disorders. Many of these phytochemicals have been proved to activate mitophagy to ameliorate metabolic disorders. Given the ongoing epidemic of metabolic disorders, it is of great significance to explore the contribution and underlying mechanisms of mitophagy in metabolic disorders, and to understand the effects and molecular mechanisms of phytochemicals on the treatment of metabolic disorders. Here, we investigate the mechanism of mitochondrial dysfunction in metabolic disorders and discuss the potential of targeting mitophagy with phytochemicals for the treatment of metabolic disorders, with a view to providing a direction for finding phytochemicals that target mitophagy to prevent or treat metabolic disorders.

3D Adipose Tissue Culture Links the Organotypic Microenvironment to Improved Adipogenesis

Obesity and type 2 diabetes are strongly associated with adipose tissue dysfunction and impaired adipogenesis. Understanding the molecular underpinnings that control adipogenesis is thus of fundamental importance for the development of novel therapeutics against metabolic disorders. However, translational approaches are hampered as current models do not accurately recapitulate adipogenesis. Here, a scaffold-free versatile 3D adipocyte culture platform with chemically defined conditions is presented in which primary human preadipocytes accurately recapitulate adipogenesis. Following differentiation, multi-omics profiling and functional tests demonstrate that 3D adipocyte cultures feature mature molecular and cellular phenotypes similar to freshly isolated mature adipocytes. Spheroids exhibit physiologically relevant gene expression signatures with 4704 differentially expressed genes compared to conventional 2D cultures (false discovery rate < 0.05), including the concerted expression of factors shaping the adipogenic niche. Furthermore, lipid profiles of >1000 lipid species closely resemble patterns of the corresponding isogenic mature adipocytes in vivo (R2 = 0.97). Integration of multi-omics signatures with analyses of the activity profiles of 503 transcription factors using global promoter motif inference reveals a complex signaling network, involving YAP, Hedgehog, and TGFβ signaling, that links the organotypic microenvironment in 3D culture to the activation and reinforcement of PPARγ and CEBP activity resulting in improved adipogenesis.

Adipose tissue cadmium concentrations as a potential risk factor for insulin resistance and future type 2 diabetes mellitus in GraMo adult cohort

Adipose tissue has been recently highlighted as a promising matrix for evaluation of cadmium's (Cd) long-term exposure although not frequently considered in epidemiological studies. The association between Cd exposure and type 2 Diabetes Mellitus (T2DM) remains unclear. This work aimed to explore the association between adipose tissue Cd levels and T2DM incidence over a 16-year follow-up in an adult cohort from Southern Spain considering smoking status. We also performed complementary cross-sectional analyses focused on subclinical markers of glucose homeostasis at recruitment. Clinical information was obtained from hospital databases. Socio-demographic characteristics, lifestyle and diet were collected by face-to-face interviews. Homeostatic model assessment (HOMA) values of insulin sensitivity/resistance and β-cell function were calculated using fasting serum glucose, insulin, and C-peptide levels at recruitment. Adipose tissue Cd concentrations were quantified by inductively coupled plasma mass spectrometry. Statistical analyses were performed by means of Cox-regression and multivariable linear regression models. Participants in the 4th quartile (Q4) of Cd concentrations showed a non statistically-significant increased T2DM risk (Hazard Ratio (HR) Q4 vs Q1: 1.97; 95% Confidence Interval (CI): 0.69, 5.66). This association was particularly strong and suggestive in current smokers (HR: 2.19; 95% CI: 0.98, 4.98). Interestingly, smokers in the 2nd tertile (T2) of adipose tissue Cd levels showed increased log-transformed insulin resistance (beta T2 vs T1: 0.52; 95% CI: 0.07, 0.97), as well as higher log-transformed insulin levels (beta T2 vs T1: 0.52; 95% CI: 0.08, 0.95). We found evidences supporting that Cd exposure, particularly from tobacco smoking, could be a risk factor for T2DM. In addition, our results support the potential relevance of adipose tissue as a matrix for Cd exposure assessment.

hTERT-immortalized adipose-derived stem cell line ASC52Telo demonstrates limited potential for adipose biology research

In the modern world obesity and insulin resistance contribute to a high impact on the structure of mortality. Basic research and pharmacological screenings for the search of new targets and insulin sensitizers require relevant cell models of adipocytes. Today the 3T3-L1 preadipocytes cell line is a widely used mouse-based model for investigation of adipocyte biology. Nonetheless, animal studies cannot be transferred directly in human research and nowadays the search for relevant and renewable cell models of human adipocyte is of undeniable importance. In the present study, we have compared pooled culture of human adipose-derived stem cells (ADSC) with immortalized ADSC cell line ASC52Telo. Both cell types had mesenchymal stem cell phenotype verified by flow cytometry. However, the efficacy of adipogenic differentiation, stimulation of FABP4 and PPARg protein expressions, and glucose uptake stimulation by insulin were reduced for ASC52Telo-derived adipocytes in comparison with ADSC-derived adipocytes. In addition, the analysis of insulin signaling has shown impaired phosphorylation of IRS1 and AS160 in ASC52Telo-derived cells. In summary, we have shown that immortalized cell line of human ADSC ASC52Telo have mesenchymal stem cell phenotype. Nevertheless, ASC52Telo-derived adipocytes demonstrate impaired adipogenesis and insulin sensitivity that are the main properties of healthy adipocytes.

The Roles of Dietary, Nutritional and Lifestyle Interventions in Adipose Tissue Adaptation and Obesity

The obesity and the associated non-communicable diseases (NCDs) are globally increasing in their prevalence. While the modern-day lifestyle required less ventilation of metabolic energy through muscular activities, this lifestyle transition also provided the unlimited accession to foods around the clock, which prolong the daily eating period of foods that contained high calorie and high glycemic load. These situations promote the high continuous flux of carbon substrate availability in mitochondria and induce the indecisive bioenergetic switches. The disrupted bioenergetic milieu increases the uncoupling respiration due to the excess flow of the substrate-derived reducing equivalents and reduces ubiquinones into the respiratory chain. The diversion of the uncoupling proton gradient through adipocyte thermogenesis will then alleviate the damaging effects of free radicals to mitochondria and other organelles. The adaptive induction of white adipose tissues (WAT) to beige adipose tissues (beAT) has shown beneficial effects on glucose oxidation, ROS protection and mitochondrial function preservation through the uncoupling protein 1 (UCP1)-independent thermogenesis of beAT. However, the maladaptive stage can eventually initiate with the persistent unhealthy lifestyles. Under this metabolic gridlock, the low oxygen and pro-inflammatory environments promote the adipose breakdown with sequential metabolic dysregulation, including insulin resistance, systemic inflammation and clinical NCDs progression. It is unlikely that a single intervention can reverse all these complex interactions. A comprehensive protocol that includes dietary, nutritional and all modifiable lifestyle interventions, can be the preferable choice to decelerate, stop, or reverse the NCDs pathophysiologic processes.

Loss of FOXO transcription factors in the liver mitigates stress-induced hyperglycemia

Objective

Stress-induced hyperglycemia is associated with poor outcomes in nearly all critical illnesses. This acute elevation in glucose after injury or illness is associated with increased morbidity and mortality, including multiple organ failure. Stress-induced hyperglycemia is often attributed to insulin resistance as controlling glucose levels via exogenous insulin improves outcomes, but the mechanisms are unclear. Forkhead box O (FOXO) transcription factors are direct targets of insulin signaling in the liver that regulate glucose homeostasis via direct and indirect pathways. Loss of hepatic FOXO transcription factors reduces hyperglycemia in chronic insulin resistance; however, the role of FOXOs in stress-induced hyperglycemia is unknown.

Methods

We subjected mice lacking FOXO transcription factors in the liver to a model of injury known to cause stress-induced hyperglycemia. Glucose, insulin, glycerol, fatty acids, cytokines, and adipokines were assessed before and after injury. Liver and adipose tissue were analyzed for changes in glycogen, FOXO target gene expression, and insulin signaling.

Results

Stress-induced hyperglycemia was associated with reduced hepatic insulin signaling and increased hepatic FOXO target gene expression while loss of FOXO1, 3, and 4 in the liver attenuated hyperglycemia and prevented hyperinsulinemia. Mechanistically, the loss of FOXO transcription factors mitigated the stress-induced hyperglycemia response by directly altering gene expression and glycogenolysis in the liver and indirectly suppressing lipolysis in adipose tissue. Reductions were associated with decreased IL-6, TNF-α, and follistatin and increased FGF21, suggesting that cytokines and FOXO-regulated hepatokines contribute to the stress-induced hyperglycemia response.

Conclusions

This study implicates FOXO transcription factors as a predominant driver of stress-induced hyperglycemia through means that include cross-talk between the liver and adipose, highlighting a novel mechanism underlying acute hyperglycemia and insulin resistance in stress.

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Liver forkhead box O (FOXO) target gene expression is increased in critical illness.

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Loss of FOXO1, 3, and 4 in the liver mitigates stress-induced hyperglycemia (SIH).

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Hepatic FOXO drives SIH via direct and indirect means in the liver and adipose.

Single-Cell RNA Profiling Reveals Adipocyte to Macrophage Signaling Sufficient to Enhance Thermogenesis

Adipocytes deficient in fatty acid synthase (iAdFASNKO) emit signals that mimic cold exposure to enhance the appearance of thermogenic beige adipocytes in mouse inguinal white adipose tissues (iWATs). Both cold exposure and iAdFASNKO upregulate the sympathetic nerve fiber (SNF) modulator Neuregulin 4 (Nrg4), activate SNFs, and require adipocyte cyclic AMP/protein kinase A (cAMP/PKA) signaling for beige adipocyte appearance, as it is blocked by adipocyte Gsα deficiency. Surprisingly, however, in contrast to cold-exposed mice, neither iWAT denervation nor Nrg4 loss attenuated adipocyte browning in iAdFASNKO mice. Single-cell transcriptomic analysis of iWAT stromal cells revealed increased macrophages displaying gene expression signatures of the alternately activated type in iAdFASNKO mice, and their depletion abrogated iWAT beiging. Altogether, these findings reveal that divergent cellular pathways are sufficient to cause adipocyte browning. Importantly, adipocyte signaling to enhance alternatively activated macrophages in iAdFASNKO mice is associated with enhanced adipose thermogenesis independent of the sympathetic neuron involvement this process requires in the cold.

Henriques et al. show an alternative pathway to enhance thermogenesis through an adipocyte cAMP/PKA axis in denervated iWAT. Signals emanating from this pathway generate M2-type macrophages associated with iWAT browning.

Maternal obesity as a risk factor for developing diabetes in offspring: An epigenetic point of view

According to the developmental origin of health and disease concept, the risk of many age-related diseases is not only determined by genetic and adult lifestyle factors but also by factors acting during early development. In particular, maternal obesity and neonatal accelerated growth predispose offspring to overweight and type 2 diabetes (T2D) in adulthood. This concept mainly relies on the developmental plasticity of adipose tissue and pancreatic β-cell programming in response to suboptimal milieu during the perinatal period. These changes result in unhealthy hypertrophic adipocytes with decreased capacity to store fat, low-grade inflammation and loss of insulin-producing pancreatic β-cells. Over the past years, many efforts have been made to understand how maternal obesity induces long-lasting adipose tissue and pancreatic β-cell dysfunction in offspring and what are the molecular basis of the transgenerational inheritance of T2D. In particular, rodent studies have shed light on the role of epigenetic mechanisms in linking maternal nutritional manipulations to the risk for T2D in adulthood. In this review, we discuss epigenetic adipocyte and β-cell remodeling during development in the progeny of obese mothers and the persistence of these marks as a basis of obesity and T2D predisposition.