Suppressing adipocyte inflammation promotes insulin resistance in mice

Inflammation-mediated metabolic regulation in adipose tissue

Chronic inflammation of adipose tissue is a prominent characteristic of many metabolic diseases. Lipid metabolism in adipose tissue is consistently dysregulated during inflammation, which is characterized by substantial infiltration by proinflammatory cells and high cytokine concentrations. Adipose tissue inflammation is caused by a variety of endogenous factors, such as mitochondrial dysfunction, reactive oxygen species (ROS) production, endoplasmic reticulum (ER) stress, cellular senescence, ceramides biosynthesis and mediators of lipopolysaccharides (LPS) signaling. Additionally, the gut microbiota also plays a crucial role in regulating adipose tissue inflammation. Essentially, adipose tissue inflammation arises from an imbalance in adipocyte metabolism and the regulation of immune cells. Specific inflammatory signals, including nuclear factor-κB (NF-κB) signaling, inflammasome signaling and inflammation-mediated autophagy, have been shown to be involved in the metabolic regulation. The pathogenesis of metabolic diseases characterized by chronic inflammation (obesity, insulin resistance, atherosclerosis and nonalcoholic fatty liver disease [NAFLD]) and recent research regarding potential therapeutic targets for these conditions are also discussed in this review.

Adipose Tissue Inflammation: Linking Physiological Stressors to Disease Susceptibility

The study of adipose tissue (AT) is enjoying a renaissance. White, brown, and beige adipocytes are being investigated in adult animals, and the critical roles of small depots like perivascular AT are becoming clear. But the most profound revision of the AT dogma has been its cellular composition and regulation. Single-cell transcriptomic studies revealed that adipocytes comprise well under 50% of the cells in white AT, and a substantial portion of the rest are immune cells. Altering the function of AT resident leukocytes can induce or correct metabolic syndrome and, more surprisingly, alter adaptive immune responses to infection. Although the field is dominated by obesity research, conditions such as rapid lipolysis, infection, and heat stress impact AT immune dynamics as well. Recent findings in rodents lead to critical questions that should be explored in domestic livestock as potential avenues for improved animal resilience to stressors, particularly as animals age.

CTRP6 promotes the macrophage inflammatory response, and its deficiency attenuates LPS-induced inflammation

Macrophages play critical roles in inflammation and tissue homeostasis, and their functions are regulated by various autocrine, paracrine, and endocrine factors. We have previously shown that CTRP6, a secreted protein of the C1q family, targets both adipocytes and macrophages to promote obesity-linked inflammation. However, the gene programs and signaling pathways directly regulated by CTRP6 in macrophages remain unknown. Here, we combine transcriptomic and phosphoproteomic analyses to show that CTRP6 activates inflammatory gene programs and signaling pathways in mouse bone marrow-derived macrophages (BMDMs). Treatment of BMDMs with CTRP6 upregulated proinflammatory, and suppressed the antiinflammatory, gene expression. We also showed that CTRP6 activates p44/42-MAPK, p38-MAPK, and NF-κB signaling pathways to promote inflammatory cytokine secretion from BMDMs, and that pharmacologic inhibition of these signaling pathways markedly attenuated the effects of CTRP6. Pretreatment of BMDMs with CTRP6 also sensitized and potentiated the BMDMs response to lipopolysaccharide (LPS)-induced inflammatory signaling and cytokine secretion. Consistent with the metabolic phenotype of proinflammatory macrophages, CTRP6 treatment induced a shift toward aerobic glycolysis and lactate production, reduced oxidative metabolism, and elevated mitochondrial reactive oxygen species production in BMDMs. Importantly, in accordance with our in vitro findings, BMDMs from CTRP6-deficient mice were less inflammatory at baseline and showed a marked suppression of LPS-induced inflammatory gene expression and cytokine secretion. Finally, loss of CTRP6 in mice also dampened LPS-induced inflammation and hypothermia. Collectively, our findings suggest that CTRP6 regulates and primes the macrophage response to inflammatory stimuli and thus may have a role in modulating tissue inflammatory tone in different physiological and disease contexts.

Dual Role of Caspase 8 in Adipocyte Apoptosis and Metabolic Inflammation

Caspases are cysteine-aspartic proteases that were initially discovered to play a role in apoptosis. However, caspase 8, in particular, also has additional nonapoptotic roles, such as in inflammation. Adipocyte cell death and inflammation are hypothesized to be initiating pathogenic factors in type 2 diabetes. Here, we examined the pleiotropic role of caspase 8 in adipocytes and obesity-associated insulin resistance. Caspase 8 expression was increased in adipocytes from mice and humans with obesity and insulin resistance. Treatment of 3T3-L1 adipocytes with caspase 8 inhibitor Z-IETD-FMK decreased both death receptor-mediated signaling and targets of nuclear factor κ-light-chain-enhancer of activated B (NF-κB) signaling. We generated novel adipose tissue and adipocyte-specific caspase 8 knockout mice (aP2Casp8-/- and adipoqCasp8-/-). Both males and females had improved glucose tolerance in the setting of high-fat diet (HFD) feeding. Knockout mice also gained less weight on HFD, with decreased adiposity, adipocyte size, and hepatic steatosis. These mice had decreased adipose tissue inflammation and decreased activation of canonical and noncanonical NF-κB signaling. Furthermore, they demonstrated increased energy expenditure, core body temperature, and UCP1 expression. Adipocyte-specific activation of Ikbkb or housing mice at thermoneutrality attenuated improvements in glucose tolerance. These data demonstrate an important role for caspase 8 in mediating adipocyte cell death and inflammation to regulate glucose and energy homeostasis.

ARTICLE HIGHLIGHTS

Caspase 8 is increased in adipocytes from mice and humans with obesity and insulin resistance. Knockdown of caspase 8 in adipocytes protects mice from glucose intolerance and weight gain on a high-fat diet. Knockdown of caspase 8 decreases Fas signaling, as well as canonical and noncanonical nuclear factor κ-light-chain-enhancer of activated B (NF-κB) signaling in adipose tissue. Improved glucose tolerance occurs via reduced activation of NF-κB signaling and via induction of UCP1 in adipocytes.

Glucose-dependent inflammatory responses in obese compared to lean individuals

PURPOSE

Obesity is characterized by chronic inflammation that may contribute to insulin resistance and promote type 2 diabetes. We have investigated whether inflammatory responses to glycemic and insulinemic variations are altered in obese individuals.

METHODS

Eight obese and eight lean individuals without diabetes had undergone hyperinsulinemic-euglycemic-hypoglycemic and hyperglycemic clamps in a previous study. Using Proximity Extension Assay, 92 inflammatory markers were analyzed from plasma samples at fasting, hyperinsulinemia-euglycemia, hypoglycemia and hyperglycemia.

RESULTS

In all participants, hyperinsulinemia, hypoglycemia and hyperglycemia led to reductions of 11, 19 and 62 out of the 70 fully evaluable biomarkers, respectively. FGF-21 increased during both hypoglycemia and hyperglycemia while IL-6 and IL-10 increased during hypoglycemia. In obese vs lean participants, Oncostatin-M, Caspase-8 and 4E-BP1 were more markedly suppressed during hypoglycemia, whereas VEGF-A was more markedly suppressed during hyperglycemia. BMI correlated inversely with changes of PD-L1 and CD40 during hyperinsulinemia, Oncostatin-M, TNFSF14, FGF-21 and 4EBP-1 during hypoglycemia and CCL23, VEGF-A and CDCP1 during hyperglycemia (Rho ≤ -0.50). HbA1c correlated positively with changes of MCP-2 and IL-15-RA during hyperinsulinemia (Rho ≥ 0.51) and inversely with changes of CXCL1, MMP-1 and Axin-1 during hypoglycemia (Rho ≤ -0.55). M-value correlated positively with changes of IL-12B and VEGF-A during hyperglycemia (Rho ≥ 0.51). Results above were significant (p < 0.05).

CONCLUSION

Overall, hyperinsulinemia, hypo- and hyperglycemia led to suppression of several inflammatory markers and this tended to be more marked in individuals with obesity, insulin resistance and dysglycemia. Thus, acute glycemic or insulinemic variations do not seem to potentiate possible inflammatory pathways in the development of insulin resistance and disturbed glucose metabolism.

Targeting the gut microbiota and its metabolites for type 2 diabetes mellitus

Type 2 diabetes mellitus (T2DM) is a metabolic disorder characterized by hyperglycemia and insulin resistance. The incidence of T2DM is increasing globally, and a growing body of evidence suggests that gut microbiota dysbiosis may contribute to the development of this disease. Gut microbiota-derived metabolites, including bile acids, lipopolysaccharide, trimethylamine-N-oxide, tryptophan and indole derivatives, and short-chain fatty acids, have been shown to be involved in the pathogenesis of T2DM, playing a key role in the host-microbe crosstalk. This review aims to summarize the molecular links between gut microbiota-derived metabolites and the pathogenesis of T2DM. Additionally, we review the potential therapy and treatments for T2DM using probiotics, prebiotics, fecal microbiota transplantation and other methods to modulate gut microbiota and its metabolites. Clinical trials investigating the role of gut microbiota and its metabolites have been critically discussed. This review highlights that targeting the gut microbiota and its metabolites could be a potential therapeutic strategy for the prevention and treatment of T2DM.

An adipocentric perspective on the development and progression of non-alcoholic fatty liver disease

Alongside the liver, white adipose tissue (WAT) is critical in regulating systemic energy homeostasis. Although each organ has its specialised functions, they must work coordinately to regulate whole-body metabolism. Adipose tissues and the liver are relatively resilient and can adapt to an energy surplus by facilitating triglyceride (TG) storage up to a certain threshold level without significant metabolic disturbances. However, lipid storage in WAT beyond a "personalised" adiposity threshold becomes dysfunctional, leading to metabolic inflexibility, progressive inflammation, and aberrant adipokine secretion. Moreover, the failure of adipose tissue to store and mobilise lipids results in systemic knock-on lipid overload, particularly in the liver. Factors contributing to hepatic lipid overload include lipids released from WAT, dietary fat intake, and enhanced de novo lipogenesis. In contrast, extrahepatic mechanisms counteracting toxic hepatic lipid overload entail coordinated compensation through oxidation of surplus fatty acids in brown adipose tissue and storage of fatty acids as TGs in WAT. Failure of these integrated homeostatic mechanisms leads to quantitative increases and qualitative alterations to the lipidome of the liver. Initially, hepatocytes preferentially accumulate TG species leading to a relatively "benign" non-alcoholic fatty liver. However, with time, inflammatory responses ensue, progressing into more severe conditions such as non-alcoholic steatohepatitis, cirrhosis, and hepatocellular carcinoma, in some individuals (often without an early prognostic clue). Herein, we highlight the pathogenic importance of obesity-induced "adipose tissue failure", resulting in decreased adipose tissue functionality (i.e. fat storage capacity and metabolic flexibility), in the development and progression of NAFL/NASH.

Obese visceral fat tissue inflammation: from protective to detrimental?

Obesity usually is accompanied by inflammation of fat tissue, with a prominent role of visceral fat. Chronic inflammation in obese fat tissue is of a lower grade than acute immune activation for clearing the tissue from an infectious agent. It is the loss of adipocyte metabolic homeostasis that causes activation of resident immune cells for supporting tissue functions and regaining homeostasis. Initially, the excess influx of lipids and glucose in the context of overnutrition is met by adipocyte growth and proliferation. Eventual lipid overload of hypertrophic adipocytes leads to endoplasmic reticulum stress and the secretion of a variety of signals causing increased sympathetic tone, lipolysis by adipocytes, lipid uptake by macrophages, matrix remodeling, angiogenesis, and immune cell activation. Pro-inflammatory signaling of adipocytes causes the resident immune system to release increased amounts of pro-inflammatory and other mediators resulting in enhanced tissue-protective responses. With chronic overnutrition, these protective actions are insufficient, and death of adipocytes as well as senescence of several tissue cell types is seen. This structural damage causes the expression or release of immunostimulatory cell components resulting in influx and activation of monocytes and many other immune cell types, with a contribution of stromal cells. Matrix remodeling and angiogenesis is further intensified as well as possibly detrimental fibrosis. The accumulation of senescent cells also may be detrimental via eventual spread of senescence state from affected to neighboring cells by the release of microRNA-containing vesicles. Obese visceral fat inflammation can be viewed as an initially protective response in order to cope with excess ambient nutrients and restore tissue homeostasis but may contribute to tissue damage at a later stage.

The rheumatoid arthritis drug auranofin lowers leptin levels and exerts antidiabetic effects in obese mice

Low-grade, sustained inflammation in white adipose tissue (WAT) characterizes obesity and coincides with type 2 diabetes mellitus (T2DM). However, pharmacological targeting of inflammation lacks durable therapeutic effects in insulin-resistant conditions. Through a computational screen, we discovered that the FDA-approved rheumatoid arthritis drug auranofin improved insulin sensitivity and normalized obesity-associated abnormalities, including hepatic steatosis and hyperinsulinemia in mouse models of T2DM. We also discovered that auranofin accumulation in WAT depleted inflammatory responses to a high-fat diet without altering body composition in obese wild-type mice. Surprisingly, elevated leptin levels and blunted beta-adrenergic receptor activity achieved by leptin receptor deletion abolished the antidiabetic effects of auranofin. These experiments also revealed that the metabolic benefits of leptin reduction were superior to immune impacts of auranofin in WAT. Our studies uncover important metabolic properties of anti-inflammatory treatments and contribute to the notion that leptin reduction in the periphery can be accomplished to treat obesity and T2DM.

Adipose tissue macrophages exert systemic metabolic control by manipulating local iron concentrations

Iron is essential to many fundamental biological processes, but its cellular compartmentalization and concentration must be tightly controlled. Although iron overload can contribute to obesity-associated metabolic deterioration, the subcellular localization and accumulation of iron in adipose tissue macrophages is largely unknown. Here, we show that macrophage mitochondrial iron levels control systemic metabolism in male mice by altering adipocyte iron concentrations. Using various transgenic mouse models to manipulate the macrophage mitochondrial matrix iron content in an inducible fashion, we demonstrate that lowering macrophage mitochondrial matrix iron increases numbers of M2-like macrophages in adipose tissue, lowers iron levels in adipocytes, attenuates inflammation and protects from high-fat-diet-induced metabolic deterioration. Conversely, elevating macrophage mitochondrial matrix iron increases M1-like macrophages and iron levels in adipocytes, exacerbates inflammation and worsens high-fat-diet-induced metabolic dysfunction. These phenotypes are robustly reproduced by transplantation of a small amount of fat from transgenic to wild-type mice. Taken together, we identify macrophage mitochondrial iron levels as a crucial determinant of systemic metabolic homeostasis in mice.

The Nrf2 in Obesity: A Friend or Foe?

Obesity and its complications have become serious global health concerns recently and increasing work has been carried out to explicate the underlying mechanism of the disease development. The recognized correlations suggest oxidative stress and inflammation in expanding adipose tissue with excessive fat accumulation play important roles in the pathogenesis of obesity, as well as its associated metabolic syndromes. In adipose tissue, obesity-mediated insulin resistance strongly correlates with increased oxidative stress and inflammation. Nuclear factor erythroid 2-related factor 2 (Nrf2) has been described as a key modulator of antioxidant signaling, which regulates the transcription of various genes coding antioxidant enzymes and cytoprotective proteins. Furthermore, an increasing number of studies have demonstrated that Nrf2 is a pivotal target of obesity and its related metabolic disorders. However, its effects are controversial and even contradictory. This review aims to clarify the complicated interplay among Nrf2, oxidative stress, lipid metabolism, insulin signaling and chronic inflammation in obesity. Elucidating the implications of Nrf2 modulation on obesity would provide novel insights for potential therapeutic approaches in obesity and its comorbidities.

Adipose Tissue Plasticity in Aging

As a dynamic endocrine organ, white adipose tissue (WAT) stores lipids and plays a critical role in maintaining whole-body energy homeostasis and insulin sensitivity. A large group of the population over 65 years old suffer from increased WAT mass, especially in the visceral location. Visceral adiposity accelerates aging through promoting age-associated chronic conditions, significantly shortening life expectancy. Unlike WAT, brown adipose tissue (BAT) functions as an effective energy sink that burns and disposes of excess lipids and glucose upon activation of thermogenesis. Unfortunately, the thermogenic activity of BAT declines during aging. New appreciation of cellular and functional remodeling of WAT and BAT during aging has emerged in recent years. Efforts are underway to explore the potential underlying mechanisms behind these age-associated alterations in WAT and BAT and the impact of these alterations on whole-body metabolism. Lastly, it is intriguing to translate our knowledge obtained from animal models to the clinic to prevent and treat age-associated metabolic disorders. © 2022 American Physiological Society. Compr Physiol 12: 4119-4132, 2022.

Importance of the Microenvironment and Mechanosensing in Adipose Tissue Biology

The expansion of adipose tissue is an adaptive mechanism that increases nutrient buffering capacity in response to an overall positive energy balance. Over the course of expansion, the adipose microenvironment undergoes continual remodeling to maintain its structural and functional integrity. However, in the long run, adipose tissue remodeling, typically characterized by adipocyte hypertrophy, immune cells infiltration, fibrosis and changes in vascular architecture, generates mechanical stress on adipose cells. This mechanical stimulus is then transduced into a biochemical signal that alters adipose function through mechanotransduction. In this review, we describe the physical changes occurring during adipose tissue remodeling, and how they regulate adipose cell physiology and promote obesity-associated dysfunction in adipose tissue.

Greasing the inflammatory pathogenesis of viral pneumonias in diabetes

Type 2 diabetes (T2D) and obesity are independent risk factors for increased morbidity and mortality associated with influenza and SARS-CoV-2 infection. Skewed cellular metabolism shapes immune cell inflammatory responsiveness and function in obesity, T2D, and infection. However, altered immune cell responsiveness and levels of systemic proinflammatory mediators, partly independent of peripheral immune cell contribution, are linked with SARS-CoV-2-associated disease severity. Despite such knowledge, the role of tissue parenchymal cell-driven inflammatory responses, and specifically those dominantly modified in obesity (e.g., adipocytes), in influenza and SARS-CoV-2 infection pathogenesis remain poorly defined. Whether obesity-dependent skewing of adipocyte cellular metabolism uncovers inflammatory clades and promotes the existence of a 'pathogenic-inflammatory' adipocyte phenotype that amplifies SARS-CoV-2 infection diseases severity in individuals with obesity and individuals with obesity and T2D has not been examined. Here, using the knowledge gained from studies of immune cell responses in obesity, T2D, and infection, we highlight the key knowledge gaps underlying adipocyte cellular functions that may sculpt and grease pathogenic processes associated with influenza and SARS-CoV-2 disease severity in diabetes.

Lactate Is a Key Mediator That Links Obesity to Insulin Resistance via Modulating Cytokine Production From Adipose Tissue

Numerous evidence indicates that inflammation in adipose tissue is the primary cause of systemic insulin resistance induced by obesity. Obesity-associated changes in circulating LPS level and hypoxia/HIF-1α activation have been proposed to be involved in boosting obesity-induced inflammation. However, there is poor understanding of what triggers obesity-induced inflammation. In this study, we pinpoint lactate as a key trigger to mediate obesity-induced inflammation and systemic insulin resistance. Specific deletion of Slc16a1 that encodes MCT1, the primary lactate transporter in adipose tissues, robustly elevates blood levels of proinflammatory cytokines and aggravates systemic insulin resistance without alteration of adiposity in mice fed high-fat diet. Slc16a1 deletion in adipocytes elevates intracellular lactate level while reducing circulating lactate concentration. Mechanistically, lactate retention due to Slc16a1 deletion initiates adipocyte apoptosis and cytokine release. The locally recruited macrophages amplify the inflammation by release of proinflammatory cytokines to the circulation, leading to insulin resistance in peripheral tissues. This study, therefore, indicates that lactate within adipocytes has a key biological function linking obesity to insulin resistance, and harnessing lactate in adipocytes can be a promising strategy to break this link.

Changes in mechanical properties of adipose tissue after bariatric surgery driven by extracellular matrix remodelling and neovascularization are associated with metabolic improvements

Biomechanical properties of adipose tissue (AT) are closely involved in the development of obesity-associated comorbidities. Bariatric surgery (BS) constitutes the most effective option for a sustained weight loss in addition to improving obesity-associated metabolic diseases including type 2 diabetes (T2D). We aimed to determine the impact of weight loss achieved by BS and caloric restriction (CR) on the biomechanical properties of AT. BS but not CR changed the biomechanical properties of epididymal white AT (EWAT) from a diet-induced obesity rat model, which were associated with metabolic improvements. We found decreased gene expression levels of collagens and Lox together with increased elastin and Mmps mRNA levels in EWAT after BS, which were also associated with the biomechanical properties. Moreover, an increased blood vessel density was observed in EWAT after surgery, confirmed by an upregulation of Acta2 and Antxr1 gene expression levels, which was also correlated with the biomechanical properties. Visceral AT from patients with obesity showed increased stiffness after tensile tests compared to the EWAT from the animal model. This study uncovers new insights into EWAT adaptation after BS with decreased collagen crosslink and synthesis as well as an increased degradation together with enhanced blood vessel density providing, simultaneously, higher stiffness and more ductility. STATEMENT OF SIGNIFICANCE: Biomechanical properties of the adipose tissue (AT) are closely involved in the development of obesity-associated comorbidities. In this study, we show for the first time that biomechanical properties of AT determined by E, UTS and strain at UTS are decreased in obesity, being increased after bariatric surgery by the promotion of ECM remodelling and neovascularization. Moreover, these changes in biomechanical properties are associated with improvements in metabolic homeostasis. Consistently, a better characterization of the plasticity and biomechanical properties of the AT after bariatric surgery opens up a new field for the development of innovative strategies for the reduction of fibrosis and inflammation in AT as well as to better understand obesity and its associated comorbidities.

The Shades of Grey in Adipose Tissue Reprogramming

The adipose tissue (AT) has a major role in contributing to obesity-related pathologies through regulating systemic immunometabolism. The pathogenicity of the AT is underpinned by its remarkable plasticity to be reprogrammed during obesity, in the perspectives of tissue morphology, extracellular matrix (ECM) composition, angiogenesis, immunometabolic homoeostasis and circadian rhythmicity. Dysregulation in these features escalates the pathogenesis conferred by this endometabolic organ. Intriguingly, the potential to be reprogrammed appears to be an Achilles’ heel of the obese AT that can be targeted for the management of obesity and its associated comorbidities. Here, we provide an overview of the reprogramming processes of white AT (WAT), with a focus on their dynamics and pleiotropic actions over local and systemic homoeostases, followed by a discussion of potential strategies favouring therapeutic reprogramming. The potential involvement of AT remodelling in the pathogenesis of COVID-19 is also discussed.

Impaired phosphocreatine metabolism in white adipocytes promotes inflammation

The mechanisms promoting disturbed white adipocyte function in obesity remain largely unclear. Herein, we integrate white adipose tissue (WAT) metabolomic and transcriptomic data from clinical cohorts and find that the WAT phosphocreatine/creatine ratio is increased and creatine kinase-B expression and activity is decreased in the obese state. In human in vitro and murine in vivo models, we demonstrate that decreased phosphocreatine metabolism in white adipocytes alters adenosine monophosphate-activated protein kinase activity via effects on adenosine triphosphate/adenosine diphosphate levels, independently of WAT beigeing. This disturbance promotes a pro-inflammatory profile characterized, in part, by increased chemokine (C-C motif) ligand 2 (CCL2) production. These data suggest that the phosphocreatine/creatine system links cellular energy shuttling with pro-inflammatory responses in human and murine white adipocytes. Our findings provide unexpected perspectives on the mechanisms driving WAT inflammation in obesity and may present avenues to target adipocyte dysfunction.

Why does obesity cause diabetes?

The accumulation of an excessive amount of body fat can cause type 2 diabetes, and the risk of type 2 diabetes increases linearly with an increase in body mass index. Accordingly, the worldwide increase in the prevalence of obesity has led to a concomitant increase in the prevalence of type 2 diabetes. The cellular and physiological mechanisms responsible for the link between obesity and type 2 diabetes are complex and involve adiposity-induced alterations in β cell function, adipose tissue biology, and multi-organ insulin resistance, which are often ameliorated and can even be normalized with adequate weight loss.

Comparative Analysis of Gene Expression Profiles in the Adipose Tissue of Obese Adult Mice With Rapid Infantile Growth After Undernourishment In Utero

Rapid infantile growth (RG) markedly increases the risk of obesity and metabolic disorders in adulthood, particularly among neonates born small. To elucidate the molecular mechanisms by which RG following undernourishment in utero (UN) contributes to the deterioration of adult fat deposition, we developed a UN mouse model using maternal energy restriction, followed by RG achieved by adjustments to 4 pups per litter soon after birth. A high-fat diet (HFD) was fed to weaned pups treated or not (Veh) with tauroursodeoxycholic acid (TU). UN-RG pups showed the deterioration of diet-induced obesity and fat deposition, which was ameliorated by TU. We performed a microarray analysis of epididymal adipose tissue and two gene enrichment analyses (NN-Veh vs UN-RD-Veh and UN-RG-Veh vs UN-RG-TU). The results obtained identified 4 common gene ontologies (GO) terms of inflammatory pathways. In addition to the inflammatory characteristics of 4 GO terms, the results of heatmap and principal component analyses of the representative genes from 4 GO terms, genes of interest (GOI; Saa3, Ubd, S100a8, Hpx, Casp1, Agt, Ptgs2) selected from the 4 GO terms, and immunohistochemistry of macrophages collectively suggested the critical involvement of inflammation in the regulation of fat deposition in the responses to UN and TU. Therefore, the present results support the 'Developmental Origins of Metaflammation', the last word of which was recently proposed by the concept of metabolic disorders induced by low-grade systemic inflammation.

Which BMI for Diabetes Patients is Better? From the View of the Adipose Tissue Macrophage-Derived Exosome

PURPOSE

Diabetes, as a group of metabolic diseases, can elevate blood glucose, thus leading to the development of life-threatening complications. It is difficult to define the outcome for diabetics with different BMI. This review will illustrate the adipose tissue macrophage-derived exosome in the diabetics with different BMI.

PATIENTS AND METHODS

Insulin resistance in peripheral tissues can cause diabetes. The peripheral tissues include liver, muscle, or the adipose depots. Communication between these organs is fatal to the maintenance of glucose homeostasis. This review will illustrate this communication. Obesity is closely linked with diabetes. There are different changes in fat distribution in diabetic patients. Adipose tissue macrophages can secrete various hormones, including adiponectin, leptin, resistin and other classical cytokines, such as TNF-α and IL-6. Studies illustrated that exosomes from the adipose tissue, can modulate inter-organ cross-talk by regulating gene expression in other tissues.

RESULTS

Adipose tissue macrophages exosomes links thin and fat individuals in the development of diabetes.

CONCLUSION

The molecular pathways initiated by exosomes such as miRNA in the situations of metabolic stress could help us gain a deeper knowledge of the pathophysiology of diabetes.

The Role of Bioactive Compounds from Dietary Spices in the Management of Metabolic Syndrome: An Overview

Metabolic syndrome (MetS) is a combination of physiologically dysregulated parameters that can include elevated fasting blood glucose, high blood pressure, central obesity, increased triglyceride levels, insulin resistance, diabetes, elevated low density lipoprotein levels, and reduced high density lipoprotein levels in the blood. Effective clinical management of MetS is critical as it is strongly associated with long lasting and fatal complications in patients. Alongside standard care of lifestyle changes and medication, dietary supplements derived from herbal resources could be an alternative therapeutic strategy that is safe, efficient, culturally acceptable, and has few side effects. Of the dietary supplements, spicy foods have always been considered a great source of functional bioactive compounds. Herbal therapy is broadly used in many countries as a treatment or as a preventive measure in the management of MetS risk factors, including blood glucose, blood pressure, and blood lipid levels. Herein, an attempt is made to evaluate the recent studies in the management of MetS with herbal alternatives, and to explore the possibility of their use as therapeutic treatments or supplements.

Adipocyte inflammation and pathogenesis of viral pneumonias: an overlooked contribution

Epidemiological evidence establishes obesity as an independent risk factor for increased susceptibility and severity to viral respiratory pneumonias associated with H1N1 influenza and SARS-CoV-2 pandemics. Given the global obesity prevalence, a better understanding of the mechanisms behind obese susceptibility to infection is imperative. Altered immune cell metabolism and function are often perceived as a key causative factor of dysregulated inflammation. However, the contribution of adipocytes, the dominantly altered cell type in obesity with broad inflammatory properties, to infectious disease pathogenesis remains largely ignored. Thus, skewing of adipocyte-intrinsic cellular metabolism may lead to the development of pathogenic inflammatory adipocytes, which shape the overall immune responses by contributing to either premature immunosenescence, delayed hyperinflammation, or cytokine storm in infections. In this review, we discuss the underappreciated contribution of adipocyte cellular metabolism and adipocyte-produced mediators on immune system modulation and how such interplay may modify disease susceptibility and pathogenesis of influenza and SARS-CoV-2 infections in obese individuals.

CTRP6 rapidly responds to acute nutritional changes, regulating adipose tissue expansion and inflammation in mice

In chronic obesity, activated adipose tissue proinflammatory cascades are tightly linked to metabolic dysfunction. Yet, close temporal analyses of the responses to obesogenic environment such as high-fat feeding (HFF) in susceptible mouse strains question the causal relationship between inflammation and metabolic dysfunction, and/or raises the possibility that certain inflammatory cascades play adaptive/homeostatic, rather than pathogenic roles. Here, we hypothesized that CTRP6, a C1QTNF family member, may constitute an early responder to acute nutritional changes in adipose tissue, with potential physiological roles. Both 3-days high-fat feeding (3dHFF) and acute obesity reversal [2-wk switch to low-fat diet after 8-wk HFF (8wHFF)] already induced marked changes in whole body fuel utilization. Although adipose tissue expression of classical proinflammatory cytokines (Tnf-α, Ccl2, and Il1b) exhibited no, or only minor, change, C1qtnf6 uniquely increased, and decreased, in response to 3dHFF and acute obesity reversal, respectively. CTRP6 knockout (KO) mouse embryonic fibroblasts (MEFs) exhibited increased adipogenic gene expression (Pparg, Fabp4, and Adipoq) and markedly reduced inflammatory genes (Tnf-α, Ccl2, and Il6) compared with wild-type MEFs, and recombinant CTRP6 induced the opposite gene expression signature, as assessed by RNA sequencing. Consistently, 3dHFF of CTRP6-KO mice induced a greater whole body and adipose tissue weight gain compared with wild-type littermates. Collectively, we propose CTRP6 as a gene that rapidly responds to acute changes in caloric intake, acting in acute overnutrition to induce a "physiological inflammatory response" that limits adipose tissue expansion.NEW & NOTEWORTHY CTRP6 (C1qTNF6), a member of adiponectin gene family, regulates inflammation and metabolism in established obesity. Here, short-term high-fat feeding in mice is shown to increase adipose tissue expression of CTRP6 before changes in the expression of classical inflammatory genes occur. Conversely, CTRP6 expression in adipose tissue decreases early in the course of obesity reversal. Gain- and loss-of-function models suggest CTRP6 as a positive regulator of inflammatory cascades, and a negative regulator of adipogenesis and adipose tissue expansion.

Torreya nucifera seed oil improves 3T3-L1 adipocyte differentiation

BACKGROUND

Adipose tissue is a critical regulator of lipid storage and endocrine function. Impairment of the recruitment of new adipocytes in the adipose tissue is associated with ectopic fat accumulation, diabetes and insulin resistance. Torreya nucifera, an evergreen conifer that grows in warm temperate climates, has been found to exert beneficial effects against inflammation, infection and diabetes. However, the molecular mechanisms responsible for these effects at the cellular level remain unknown. This study aimed to investigate effects of Torreya nucifera seed oil (TNSO) on 3T3-L1 adipocyte differentiation and its underlying regulatory mechanism.

METHODS

To investigate the effects of TNSO on adipocyte differentiation, 3T3-L1 cells were induced to differentiate for 5 days in the presence of 0.75 μL/mL TNSO. Oil Red O staining and an assay for intracellular triglyceride were performed to determine the extent of lipid accumulation in 3T3-L1 cells. To elucidate the underlying mechanism of TNSO, adipogenic gene expression was analyzed using quantitative real-time PCR. Moreover, we monitored TNSO-derived activation of PPARγ and STAT3 with 3T3-L1 reporter cell lines engineered to secrete Gaussia luciferase upon the interaction of a transcription factor to its DNA binding element.

RESULTS

Oil Red O staining revealed that TNSO improved the differentiation of 3T3-L1 preadipocytes into mature adipocytes. The mRNA levels of adipogenic genes, including adiponectin, fatty acid synthase (FAS) and adipocyte fatty acid-binding protein (FABP4), were upregulated and intracellular triglyceride levels increased upon TNSO treatment. We also established that adipocyte differentiation was improved by TNSO-derived activation of PPARγ and STAT3.

CONCLUSIONS

Our results suggest that TNSO improves adipocyte differentiation by regulating the activation of adipogenic transcription factors, indicating that it may serve as a potential treatment strategy for adipocyte dysfunction.

α1-Antitrypsin A treatment attenuates neutrophil elastase accumulation and enhances insulin sensitivity in adipose tissue of mice fed a high-fat diet

Neutrophils accumulate in insulin-sensitive tissues during obesity and may play a role in impairing insulin sensitivity. The major serine protease expressed by neutrophils is neutrophil elastase (NE), which is inhibited endogenously by α1-antitrypsin A (A1AT). We investigated the effect of exogenous (A1AT) treatment on diet-induced metabolic dysfunction. Male C57Bl/6j mice fed a chow or a high-fat diet (HFD) were randomized to receive intraperitoneal injections three times weekly of either Prolastin (human A1AT; 2 mg) or vehicle (PBS) for 10 wk. Prolastin treatment did not affect plasma NE concentration, body weight, glucose tolerance, or insulin sensitivity in chow-fed mice. In contrast, Prolastin treatment attenuated HFD-induced increases in plasma and white adipose tissue (WAT) NE without affecting circulatory neutrophil levels or increases in body weight. Prolastin-treated mice fed a HFD had improved insulin sensitivity, as assessed by insulin tolerance test, and this was associated with higher insulin-dependent IRS-1 (insulin receptor substrate) and Akt^Ser473 phosphorylation, and reduced inflammation markers in WAT but not liver or muscle. In 3T3-L1 adipocytes, Prolastin reversed recombinant NE-induced impairment of insulin-stimulated glucose uptake and IRS-1 phosphorylation. Furthermore, PDGF mediated p-Akt^Ser473 activation and glucose uptake (which is independent of IRS-1) was not affected by recombinant NE treatment. Collectively, our findings suggest that NE infiltration of WAT during metabolic overload contributes to insulin resistance by impairing insulin-induced IRS-1 signaling.NEW & NOTEWORTHY Neutrophils accumulate in peripheral tissues during obesity and are critical coordinators of tissue inflammatory responses. Here, we provide evidence that inhibition of the primary neutrophil protease, neutrophil elastase, with α1-antitrypsin A (A1AT) can improve insulin sensitivity and glucose homeostasis of mice fed a high-fat diet. This was attributed to improved insulin-induced IRS-1 phosphorylation in white adipose tissue and provides further support for a role of neutrophils in mediating diet-induced peripheral tissue insulin resistance.

Chronic tissue inflammation and metabolic disease

In this review, Lee and Olefsky discuss the characteristics of chronic inflammation in the major metabolic tissues and how obesity triggers these events, including a focus on the role of adipose tissue hypoxia and macrophage-derived exosomes.

Obesity is the most common cause of insulin resistance, and the current obesity epidemic is driving a parallel rise in the incidence of T2DM. It is now widely recognized that chronic, subacute tissue inflammation is a major etiologic component of the pathogenesis of insulin resistance and metabolic dysfunction in obesity. Here, we summarize recent advances in our understanding of immunometabolism. We discuss the characteristics of chronic inflammation in the major metabolic tissues and how obesity triggers these events, including a focus on the role of adipose tissue hypoxia and macrophage-derived exosomes. Last, we also review current and potential new therapeutic strategies based on immunomodulation.

Histone Deacetylase 3 Regulates Adipocyte Phenotype at Early Stages of Differentiation

Obesity is a condition characterized by uncontrolled expansion of adipose tissue mass resulting in pathological weight gain. Histone deacetylases (HDACs) have emerged as crucial players in epigenetic regulation of adipocyte metabolism. Previously, we demonstrated that selective inhibition of class I HDACs improves white adipocyte functionality and promotes the browning phenotype of murine mesenchymal stem cells (MSCs) C3H/10T1/2 differentiated to adipocytes. These effects were also observed in db/db and diet induced obesity mouse models and in mice with adipose-selective inactivation of HDAC3, a member of class I HDACs. The molecular basis of class I HDACs action in adipose tissue is not deeply characterized and it is not known whether the effects of their inhibition are exerted on adipocyte precursors or mature adipocytes. Therefore, the aim of the present work was to explore the molecular mechanism of class I HDAC action in adipocytes by evaluating the effects of HDAC3-specific silencing at different stages of differentiation. HDAC3 was silenced in C3H/10T1/2 MSCs at different stages of differentiation to adipocytes. shRNA targeting HDAC3 was used to generate the knock-down model. Proper HDAC3 silencing was assessed by measuring both mRNA and protein levels of mouse HDAC3 via qPCR and western blot, respectively. Mitochondrial DNA content and gene expression were quantified via qPCR. HDAC3 silencing at the beginning of differentiation enhanced adipocyte functionality by amplifying the expression of genes regulating differentiation, oxidative metabolism, browning and mitochondrial activity, starting from 72 h after induction of differentiation and silencing. Insulin signaling was enhanced as demonstrated by increased AKT phosphorylation following HDAC3 silencing. Mitochondrial content/density did not change, while the increased expression of the transcriptional co-activator Ppargc1b suggests the observed phenotype was related to enhanced mitochondrial activity, which was confirmed by increased maximal respiration and proton leak linked to reduced coupling efficiency. Moreover, the expression of pro-inflammatory markers increased with HDAC3 early silencing. To the contrary, no differences in terms of gene expression were found when HDAC3 silencing occurred in terminally differentiated adipocyte. Our data demonstrated that early epigenetic events mediated by class I HDAC inhibition/silencing are crucial to commit adipocyte precursors towards the above-mentioned metabolic phenotype. Moreover, our data suggest that these effects are exerted on adipocyte precursors.

Effects of sleeve gastrectomy on bone mass, microstructure of femurs and bone metabolism associated serum factors in obese rats

BACKGROUND

Sleeve gastrectomy (SG) is a profoundly effective operation for severe obese patients, but is closely associated with bone mass loss. Previous studies have reported changes of various serum factors which may be associated with bone mass loss after SG. However, those results are contradictory. In this study, we assessed the effects of SG on bone mass, microstructure of femurs, and changes in bone turnover markers (BTMs), serum adipokines, inflammatory factors and gastrointestinal hormones after SG in high-fat diet (HFD) induced obese rats.

METHODS

Eight-week-old male Sprague-Dawley (SD) rats were fed with HFD to induce obesity. Then, SG and sham surgery were performed in anesthetized obese rats. SD rats in control group were fed with standard chow. Microstructure of femurs was scanned and analyzed by micro-computed tomography in control group, HFD sham group and HFD SG group. Serum inflammatory factors, adipokines markers, gastrointestinal hormones and BTMs were also measured.

RESULTS

Bone mineral density (BMD) of trabecular bone in both HFD sham group and HFD SG group were remarkably decreased compared with control group. All serum BTMs were significantly higher in HFD SG group than HFD sham group. In the meantime, serum levels of several important inflammatory factors, gastrointestinal hormones and adipokines such as tumor necrosis factor-α (TNF-α), interleukin (IL)-6, monocyte chemoattractant protein-1(MCP-1), ghrelin, insulin and leptin in HFD SG group were remarkably reduced compared with HFD sham group, whereas glucagon-like peptide-1 (GLP-1), adiponectin, fibroblast growth factor (FGF)-19 and FGF-21 were dramatically increased after SG. Protein tyrosine phosphatase 1B (PTP1B) was significantly increased in the HFD sham group than control group. Spearman's correlation analysis indicated that serum osteocalcin (OC) and 25-hydroxy vitamin D₃ (25(OH)D₃) were positively correlated with BMD of trabecular bone, whereas serum PTP1B and TNF-α were negatively related to BMD of trabecular bone.

CONCLUSIONS

SG aggravates bone mass loss and activates bone remodeling in obese rats. Levels of BTMs, adipokines, inflammatory factors, and gastrointestinal hormones could be affected by SG in obese rats. Serum PTP1B level might be associated with abnormal bone mass in obese rats.

Fight against fibrosis in adipose tissue remodeling

Adipose is a key tissue regulating energy homeostasis. In states of obesity, caloric intake exceeds energy expenditure, thereby accelerating lipid accumulation with ongoing extracellular matrix (ECM) remodeling. Excess deposition of lipids and expansion of adipocytes potentially decrease ECM flexibility with local hypoxia and inflammation. Hypoxia and chronic low-grade inflammation accelerate the development of adipose tissue fibrosis and related metabolic dysfunctions. Recent research investigated that some cytokines and proteins are functional in regulating energy homeostasis, meanwhile, are potential targets to fight against adipose tissue fibrosis and insulin resistance. In this review, we focused on the regulatory mechanisms and mediators in remodeling of adipose tissue fibrosis, along with their relevance to clinical manifestations.

Macrophage tumor necrosis factor-alpha deletion does not protect against obesity-associated metabolic dysfunction

The pro-inflammatory cytokine, tumor necrosis factor-alpha (TNF-α), has been suggested to be a key factor in the induction of obesity-associated metabolic dysfunction. However, the role that macrophage-derived TNF-α has on regulating metabolic perturbations in obesity is not completely understood. Therefore, we utilized the TNF-αFlox/Flox(F/F) , LyzMcre± mouse model to determine the impact that macrophage TNF-α deletion has on the development of high-fat diet (HFD)-induced obesity. At 10 weeks of age, male littermates were randomly assigned to 1 of 4 groups: TNF-αF/F low-fat diet (TNF-αF/F LFD), TNF-αF/F,LyzMCre LFD, TNF-αF/F HFD, or TNF-αF/F,LyzMCre HFD (n = 16-28/group) and were fed their respective diets for 18 weeks. Body weight was assessed throughout the course of the experiment. Body composition, hepatic lipid accumulation, and metabolic outcomes were also examined. A microarray gene expression experiment was performed from RNA isolated from epididymal adipose tissue of the HFD-fed groups (n = 10/group) and results were verified via qRT-PCR for all groups. Macrophage-derived TNF-α deletion significantly reduced adipose tissue TNF-α gene expression and circulating TNF-α and downregulated genes linked to the toll-like receptor (TLR) and NFκB signaling pathways. However, macrophage TNF-α deletion had no effect on hindering the development of obesity, hepatic lipid accumulation, or improving glucose metabolism or insulin sensitivity. In conclusion, macrophage-derived TNF-α is not a causative factor for the induction of obesity-associated metabolic dysfunction.

Adipose tissue macrophage populations and inflammation are associated with systemic inflammation and insulin resistance in obesity

Obesity is accompanied by numerous systemic and tissue-specific derangements, including systemic inflammation, insulin resistance, and mitochondrial abnormalities in skeletal muscle. Despite growing recognition that adipose tissue dysfunction plays a role in obesity-related disorders, the relationship between adipose tissue inflammation and other pathological features of obesity is not well-understood. We assessed macrophage populations and measured the expression of inflammatory cytokines in abdominal adipose tissue biopsies in 39 nondiabetic adults across a range of body mass indexes (BMI 20.5-45.8 kg/m²). Skeletal muscle biopsies were used to evaluate mitochondrial respiratory capacity, ATP production capacity, coupling, and reactive oxygen species production. Insulin sensitivity (S_I) and β cell responsivity were determined from test meal postprandial glucose, insulin, c-peptide, and triglyceride kinetics. We examined the relationships between adipose tissue inflammatory markers, systemic inflammatory markers, S_I, and skeletal muscle mitochondrial physiology. BMI was associated with increased adipose tissue and systemic inflammation, reduced S_I, and reduced skeletal muscle mitochondrial oxidative capacity. Adipose-resident macrophage numbers were positively associated with circulating inflammatory markers, including tumor necrosis factor-α (TNFα) and C-reactive protein (CRP). Local adipose tissue inflammation and circulating concentrations of TNFα and CRP were negatively associated with S_I, and circulating concentrations of TNFα and CRP were also negatively associated with skeletal muscle oxidative capacity. These results demonstrate that obese humans exhibit increased adipose tissue inflammation concurrently with increased systemic inflammation, reduced insulin sensitivity, and reduced muscle oxidative capacity and suggest that adipose tissue and systemic inflammation may drive obesity-associated metabolic derangements.NEW AND NOTEWORTHY Adipose inflammation is proposed to be at the nexus of the systemic inflammation and metabolic derangements associated with obesity. The present study provides evidence to support adipose inflammation as a central feature of the pathophysiology of obesity. Adipose inflammation is associated with systemic and peripheral metabolic derangements, including increased systemic inflammation, reduced insulin sensitivity, and reduced skeletal muscle mitochondrial respiration.

Exercise and Adipose Tissue Immunity: Outrunning Inflammation

Chronic inflammation is considered a precipitating factor and possibly an underlying cause of many noncommunicable diseases, including cardiovascular disease, metabolic diseases, and some cancers. Obesity, which manifests in more than 650 million people worldwide, is the most common chronic inflammatory condition, with visceral adiposity thought to be the major inflammatory hub that links obesity and chronic disease. Adipose tissue (AT) inflammation is triggered or heightened in large part by (1) accelerated immune cell recruitment, (2) reshaping of the AT stromal-immuno landscape (e.g., immune cells, endothelial cells, fibroblasts, adipocyte progenitors), and (3) perturbed AT immune cell function. Exercise, along with diet management, is a cornerstone in promoting weight loss and preventing weight regain. This review focuses on evidence that increased physical activity reduces AT inflammation caused by hypercaloric diets or genetic obesity. The precise cell types and mechanisms responsible for the therapeutic effects of exercise on AT inflammation remain poorly understood. This review summarizes what is known about obesity-induced AT inflammation and immunomodulation and highlights mechanisms by which aerobic exercise combats inflammation by remodeling the AT immune landscape. Furthermore, key areas are highlighted that require future exploration and novel discoveries into the burgeoning field of how the biology of exercise affects AT immunity.

Adipocyte Oncostatin Receptor Regulates Adipose Tissue Homeostasis and Inflammation

Adipocytes are the largest cell type in terms of volume, but not number, in adipose tissue. Adipocytes are prominent contributors to systemic metabolic health. Obesity, defined by excess adipose tissue (AT), is recognized as a low-grade chronic inflammatory state. Cytokines are inflammatory mediators that are produced in adipose tissue (AT) and function in both AT homeostatic as well as pathological conditions. AT inflammation is associated with systemic metabolic dysfunction and obesity-associated infiltration and proliferation of immune cells occurs in a variety of fat depots in mice and humans. AT immune cells secrete a variety of chemokines and cytokines that act in a paracrine manner on adjacent adipocytes. TNFα, IL-6, and MCP-1, are well studied mediators of AT inflammation. Oncostatin M (OSM) is another proinflammatory cytokine that is elevated in AT in human obesity, and its specific receptor (OSMRβ) is also induced in conditions of obesity and insulin resistance. OSM production and paracrine signaling in AT regulates adipogenesis and the functions of AT. This review summarizes the roles of the oncostatin M receptor (OSMRβ) as a modulator of adipocyte development and function its contributions to immunological adaptations in AT in metabolic disease states.

Chemically Defined Xeno- and Serum-Free Cell Culture Medium to Grow Human Adipose Stem Cells

Adipose tissue is an abundant source of stem cells. However, liposuction cannot yield cell quantities sufficient for direct applications in regenerative medicine. Therefore, the development of GMP-compliant ex vivo expansion protocols is required to ensure the production of a "cell drug" that is safe, reproducible, and cost-effective. Thus, we developed our own basal defined xeno- and serum-free cell culture medium (UrSuppe), specifically formulated to grow human adipose stem cells (hASCs). With this medium, we can directly culture the stromal vascular fraction (SVF) cells in defined cell culture conditions to obtain hASCs. Cells proliferate while remaining undifferentiated, as shown by Flow Cytometry (FACS), Quantitative Reverse Transcription PCR (RT-qPCR) assays, and their secretion products. Using the UrSuppe cell culture medium, maximum cell densities between 0.51 and 0.80 × 10⁵ cells/cm² (=2.55-4.00 × 10⁵ cells/mL) were obtained. As the expansion of hASCs represents only the first step in a cell therapeutic protocol or further basic research studies, we formulated two chemically defined media to differentiate the expanded hASCs in white or beige/brown adipocytes. These new media could help translate research projects into the clinical application of hASCs and study ex vivo the biology in healthy and dysfunctional states of adipocytes and their precursors. Following the cell culture system developers' practice and obvious reasons related to the formulas' patentability, the defined media's composition will not be disclosed in this study.

Dermal Drivers of Injury-Induced Inflammation: Contribution of Adipocytes and Fibroblasts

Irregular inflammatory responses are a major contributor to tissue dysfunction and inefficient repair. Skin has proven to be a powerful model to study mechanisms that regulate inflammation. In particular, skin wound healing is dependent on a rapid, robust immune response and subsequent dampening of inflammatory signaling. While injury-induced inflammation has historically been attributed to keratinocytes and immune cells, a vast body of evidence supports the ability of non-immune cells to coordinate inflammation in numerous tissues and diseases. In this review, we concentrate on the active participation of tissue-resident adipocytes and fibroblasts in pro-inflammatory signaling after injury, and how altered cellular communication from these cells can contribute to irregular inflammation associated with aberrant wound healing. Furthering our understanding of how tissue-resident mesenchymal cells contribute to inflammation will likely reveal new targets that can be manipulated to regulate inflammation and repair.

Adiponectin, Leptin and Cardiovascular Disorders

The landmark discoveries of leptin and adiponectin firmly established adipose tissue as a sophisticated and highly active endocrine organ, opening a new era of investigating adipose-mediated tissue crosstalk. Both obesity-associated hyperleptinemia and hypoadiponectinemia are important biomarkers to predict cardiovascular outcomes, suggesting a crucial role for adiponectin and leptin in obesity-associated cardiovascular disorders. Normal physiological levels of adiponectin and leptin are indeed essential to maintain proper cardiovascular function. Insufficient adiponectin and leptin signaling results in cardiovascular dysfunction. However, a paradox of high levels of both leptin and adiponectin is emerging in the pathogenesis of cardiovascular disorders. Here, we (1) summarize the recent progress in the field of adiponectin and leptin and its association with cardiovascular disorders, (2) further discuss the underlying mechanisms for this new paradox of leptin and adiponectin action, and (3) explore the possible application of partial leptin reduction, in addition to increasing the adiponectin/leptin ratio as a means to prevent or reverse cardiovascular disorders.

The Role of iRhom2 in Metabolic and Cardiovascular-Related Disorders

Chronic obesity is associated with metabolic imbalance leading to diabetes, dyslipidemia, and cardiovascular diseases (CVDs), in which inflammation is caused by exposure to inflammatory stimuli, such as accumulating sphingolipid ceramides or intracellular stress. This inflammatory response is likely to be prolonged by the effects of dietary and blood cholesterol, thereby leading to chronic low-grade inflammation and endothelial dysfunction. Elevated levels of pro-inflammatory cytokines such as tumor necrosis factor (TNF) are predictive of CVDs and have been widely studied for potential therapeutic strategies. The release of TNF is controlled by a disintegrin and metalloprotease (ADAM) 17 and both are positively associated with CVDs. ADAM17 also cleaves most of the ligands of the epidermal growth factor receptor (EGFR) which have been associated with hypertension, atherogenesis, vascular dysfunction, and cardiac remodeling. The inactive rhomboid protein 2 (iRhom2) regulates the ADAM17-dependent shedding of TNF in immune cells. In addition, iRhom2 also regulates the ADAM17-mediated cleavage of EGFR ligands such as amphiregulin and heparin-binding EGF-like growth factor. Targeting iRhom2 has recently become a possible alternative therapeutic strategy in chronic inflammatory diseases such as lupus nephritis and rheumatoid arthritis. However, what role this intriguing interacting partner of ADAM17 plays in the vasculature and how it functions in the pathologies of obesity and associated CVDs, are exciting questions that are only beginning to be elucidated. In this review, we discuss the role of iRhom2 in cardiovascular-related pathologies such as atherogenesis and obesity by providing an evaluation of known iRhom2-dependent cellular and inflammatory pathways.

Adipose tissue in health and disease

Adipose, or fat, tissue (AT) was once considered an inert tissue that primarily existed to store lipids, and was not historically recognized as an important organ in the regulation and maintenance of health. With the rise of obesity and more rigorous research, AT is now recognized as a highly complex metabolic organ involved in a host of important physiological functions, including glucose homeostasis and a multitude of endocrine capabilities. AT dysfunction has been implicated in several disease states, most notably obesity, metabolic syndrome and type 2 diabetes. The study of AT has provided useful insight in developing strategies to combat these highly prevalent metabolic diseases. This review highlights the major functions of adipose tissue and the consequences that can occur when disruption of these functions leads to systemic metabolic dysfunction.

Obesity, kidney dysfunction, and inflammation: interactions in hypertension

Obesity contributes 65-75% of the risk for human primary (essential) hypertension (HT) which is a major driver of cardiovascular and kidney diseases. Kidney dysfunction, associated with increased renal sodium reabsorption and compensatory glomerular hyperfiltration, plays a key role in initiating obesity-HT and target organ injury. Mediators of kidney dysfunction and increased blood pressure include (i) elevated renal sympathetic nerve activity (RSNA); (ii) increased antinatriuretic hormones such as angiotensin II and aldosterone; (iii) relative deficiency of natriuretic hormones; (iv) renal compression by fat in and around the kidneys; and (v) activation of innate and adaptive immune cells that invade tissues throughout the body, producing inflammatory cytokines/chemokines that contribute to vascular and target organ injury, and exacerbate HT. These neurohormonal, renal, and inflammatory mechanisms of obesity-HT are interdependent. For example, excess adiposity increases the adipocyte-derived cytokine leptin which increases RSNA by stimulating the central nervous system proopiomelanocortin-melanocortin 4 receptor pathway. Excess visceral, perirenal and renal sinus fat compress the kidneys which, along with increased RSNA, contribute to renin-angiotensin-aldosterone system activation, although obesity may also activate mineralocorticoid receptors independent of aldosterone. Prolonged obesity, HT, metabolic abnormalities, and inflammation cause progressive renal injury, making HT more resistant to therapy and often requiring multiple antihypertensive drugs and concurrent treatment of dyslipidaemia, insulin resistance, diabetes, and inflammation. More effective anti-obesity drugs are needed to prevent the cascade of cardiorenal, metabolic, and immune disorders that threaten to overwhelm health care systems as obesity prevalence continues to increase.

Glutamine metabolism in adipocytes: a bona fide epigenetic modulator of inflammation

A chronic low-grade inflammation of white adipose tissue (WAT) is one of the hallmarks of obesity and is proposed to contribute to insulin resistance and type 2 diabetes. Despite this, the causal mechanisms underlying WAT inflammation remain unclear. Based on metabolomic analyses of human WAT, Petrus et al. showed that the amino acid glutamine was the most markedly reduced polar metabolite in the obese state. Reduced glutamine levels in adipocytes induce an increase of Uridine diphosphate N-acetylglucosamine (UDP-GlcNAc) levels via induction of glycolysis and the hexosamine biosynthetic pathways. This promotes nuclear O-GlcNAcylation, a posttranslational modification that activates the transcription of pro-inflammatory genes. Conversely, glutamine supplementation in vitro and in vivo, reversed these effects. Altogether, dysregulation of intracellular glutamine metabolism in WAT establishes an epigenetic link between adipocytes and inflammation. This commentary discusses these findings and their possibly therapeutic relevance in relation to insulin resistance and type 2 diabetes.

Putative positive role of inflammatory genes in fat deposition supported by altered gene expression in purified human adipocytes and preadipocytes from lean and obese adipose tissues

Background

Obesity is a chronic low-grade inflammatory disease that is generally characterized by enhanced inflammation in obese adipose tissue (AT). Here, we investigated alterations in gene expression between lean and obese conditions using mRNA-Seq data derived from human purified adipocytes (ACs) and preadipocytes (preACs).

Results

Total mRNA-seq data were generated with 27 AC and 21 preAC samples purified from human visceral AT collected during resection surgery in cancer patients, where the samples were classified into lean and obese categories by BMI > 25 kg/m². We defined four classes of differentially expressed genes (DEGs) by comparing gene expression between (1) lean and obese ACs, (2) lean and obese preACs, (3) lean ACs and lean preACs, and 4) obese ACs and obese preACs. Based on an analysis of comparison 1, numerous canonical obesity-related genes, particularly inflammatory genes including IL-6, TNF-α and IL-1β, i.e., the genes that are expected to be upregulated in obesity conditions, were found to be expressed at significantly lower levels in obese ACs than in lean ACs. In contrast, some inflammatory genes were found to be expressed at higher levels in obese preACs than lean preACs in the analysis of comparison 2. The analysis of comparisons 3 and 4 showed that inflammatory gene classes were expressed at higher levels in differentiated ACs than undifferentiated preACs under both lean and obese conditions; however, the degree of upregulation was significantly greater for lean than for obese conditions. We validated our observations using previously published microarray transcriptome data deposited in the GEO database (GSE80654).

Conclusions

Taken together, our analyses suggest that inflammatory genes are expressed at lower levels in obese ACs than in lean ACs because lean adipogenesis involves even greater enhancement of inflammatory responses than does obese adipogenesis.

Permanent cystathionine-β-Synthase gene knockdown promotes inflammation and oxidative stress in immortalized human adipose-derived mesenchymal stem cells, enhancing their adipogenic capacity

In the present study, we aimed to investigate the impact of permanent cystathionine-β-Synthase (CBS) gene knockdown in human telomerase reverse transcriptase (hTERT) immortalized human adipose-derived mesenchymal stem cells (ASC52telo) and in their capacity to differentiate into adipocytes. CBS gene KD in ASC52telo cells led to increased cellular inflammation (IL6, CXCL8, TNF) and oxidative stress markers (increased intracellular reactive oxygen species and decreased reduced glutathione levels) in parallel to decreased H₂S production and rejuvenation (LC3 and SIRT1)-related gene expression. In addition, CBS gene KD in ASC52telo cells resulted in altered mitochondrial respiratory function, characterised by decreased basal respiration (specifically proton leak) and spare respiratory capacity, without significant effects on cell viability and proliferation. In this context, shCBS-ASC52telo cells displayed enhanced adipogenic (FABP4, ADIPOQ, SLC2A4, CEBPA, PPARG)-, lipogenic (FASN, DGAT1)- and adipocyte (LEP, LBP)-related gene expression markers, decreased expression of proinflammatory cytokines, and increased intracellular lipid accumulation during adipocyte differentiation compared to control ASC52telo cells. Otherwise, the increased adipogenic potential of shCBS-ASC52telo cells was detrimental to the ability to differentiate into osteogenic linage. In conclusion, this study demonstrated that permanent CBS gene KD in ASC52telo cells promotes a cellular senescence phenotype with a very increased adipogenic potential, promoting a non-physiological enhanced adipocyte differentiation with excessive lipid storage.