Multiomics reveals persistence of obesity-associated immune cell phenotypes in adipose tissue during weight loss and weight regain in mice

Lipid-associated macrophages' promotion of fibrosis resolution during MASH regression requires TREM2

While macrophage heterogeneity during metabolic dysfunction-associated steatohepatitis (MASH) has been described, the fate of these macrophages during MASH regression is poorly understood. Comparing macrophage heterogeneity during MASH progression vs regression, we identified specific macrophage subpopulations that are critical for MASH/fibrosis resolution. We elucidated the restorative pathways and gene signatures that define regression-associated macrophages and establish the importance of TREM2+ macrophages during MASH regression. Liver-resident Kupffer cells are lost during MASH and are replaced by four distinct monocyte-derived macrophage subpopulations. Trem2 is expressed in two macrophage subpopulations: i) monocyte-derived macrophages occupying the Kupffer cell niche (MoKC) and ii) lipid-associated macrophages (LAM). In regression livers, no new transcriptionally distinct macrophage subpopulation emerged. However, the relative macrophage composition changed during regression compared to MASH. While MoKC was the major macrophage subpopulation during MASH, they decreased during regression. LAM was the dominant macrophage subtype during MASH regression and maintained Trem2 expression. Both MoKC and LAM were enriched in disease-resolving pathways. Absence of TREM2 restricted the emergence of LAMs and formation of hepatic crown-like structures. TREM2+ macrophages are functionally important not only for restricting MASH-fibrosis progression but also for effective regression of inflammation and fibrosis. TREM2+ macrophages are superior collagen degraders. Lack of TREM2+ macrophages also prevented elimination of hepatic steatosis and inactivation of HSC during regression, indicating their significance in metabolic coordination with other cell types in the liver. TREM2 imparts this protective effect through multifactorial mechanisms, including improved phagocytosis, lipid handling, and collagen degradation.

Adipose tissue macrophage infiltration and hepatocyte stress increase GDF-15 throughout development of obesity to MASH

Plasma growth differentiation factor-15 (GDF-15) levels increase with obesity and metabolic dysfunction-associated steatotic liver disease (MASLD) but the underlying mechanism remains poorly defined. Using male mouse models of obesity and MASLD, and biopsies from carefully-characterized patients regarding obesity, type 2 diabetes (T2D) and MASLD status, we identify adipose tissue (AT) as the key source of GDF-15 at onset of obesity and T2D, followed by liver during the progression towards metabolic dysfunction-associated steatohepatitis (MASH). Obesity and T2D increase GDF15 expression in AT through the accumulation of macrophages, which are the main immune cells expressing GDF15. Inactivation of Gdf15 in macrophages reduces plasma GDF-15 concentrations and exacerbates obesity in mice. During MASH development, Gdf15 expression additionally increases in hepatocytes through stress-induced TFEB and DDIT3 signaling. Together, these results demonstrate a dual contribution of AT and liver to GDF-15 production in metabolic diseases and identify potential therapeutic targets to raise endogenous GDF-15 levels.

Translational potential of mouse models of human metabolic disease

Obesity causes significant morbidity and mortality globally. Research in the last three decades has delivered a step-change in our understanding of the fundamental mechanisms that regulate energy homeostasis, building on foundational discoveries in mouse models of metabolic disease. However, not all findings made in rodents have translated to humans, hampering drug discovery in this field. Here, we review how studies in mice and humans have informed our current framework for understanding energy homeostasis, discuss their challenges and limitations, and offer a perspective on how human studies may play an increasingly important role in the discovery of disease mechanisms and identification of therapeutic targets in the future.

Weight loss-induced adipose macrophage memory improves local Staphylococcus aureus clearance in male mice

Different stimuli can induce innate immune memory to improve pathogen defense or worsen cardiometabolic disease. However, it is less clear if the same stimuli can induce both the protective and detrimental effects of innate immune memory. We previously showed that weight loss induces innate immune memory in adipose macrophages that correlates with worsened diabetes risk after weight regain. In this study, we investigated the effect of weight loss on macrophage cytokine production and overall survival in a mouse model of infection. Male C57Bl/6J mice were put on high-fat or low-fat diets over 18 weeks to induce weight gain or weight loss. Lean mice served as controls. All mice were then infected IV with 2.5×10^6 CFU Staphylococcus aureus . Tissues were collected from 10 mice/group at day 3 and the remaining animals were followed for survival. Weight gain mice had the highest blood neutrophils and the highest bacterial burden in the kidney. However, there was no significant difference in survival. The weight loss group had the highest plasma TNF-α and a significant reduction in bacterial burden in the adipose tissue that correlated with increased adipose macrophage cytokine production. Thus, weight loss-induced adipose macrophage memory may both improve local S.aureus clearance and worsen diabetes risk upon weight regain. Collectively, these findings support the notion that innate immune memory is an evolutionarily protective mechanism that also contributes to the development of cardiometabolic diseases.

The metabolic consequences of 'yo-yo' dieting are markedly influenced by genetic diversity

BACKGROUND

Weight loss can improve the metabolic complications of obesity. However, it is unclear whether insulin resistance persists despite weight loss and whether any protective benefits are preserved following weight regain (weight cycling). The impact of genetic background on weight cycling is undocumented. We aimed to investigate the effects of weight loss and weight cycling on metabolic outcomes and sought to clarify the role of genetics in this relationship.

METHOD

Both C57BL/6 J and genetically heterogeneous Diversity Outbred Australia (DOz) mice were alternately fed high fat Western-style diet (WD) and a chow diet at 8-week intervals. Metabolic measures including body composition, glucose tolerance, pancreatic beta cell activity, liver lipid levels and adipose tissue insulin sensitivity were determined.

RESULTS

After diet switch from WD (8-week) to chow (8-week), C57BL/6 J mice displayed a rapid normalisation of body weight, adiposity, hyperinsulinemia, liver lipid levels and glucose uptake into adipose tissue comparable to chow-fed controls. In response to the same dietary intervention, genetically diverse DOz mice conversely maintained significantly higher fat mass and insulin levels compared to chow-fed controls and exhibited much more profound interindividual variability than C57BL/6 J mice. Weight cycled (WC) animals were re-exposed to WD (8-week) and compared to age-matched controls fed 8-week WD for the first time (LOb). In C57BL/6 J but not DOz mice, WC animals had significantly higher blood insulin levels than LOb controls. All WC animals exhibited significantly greater beta cell activity than LOb controls despite similar fat mass, glucose tolerance, liver lipid levels and insulin-stimulated glucose uptake in adipose tissue.

CONCLUSION

Following weight loss, metabolic outcomes return to baseline in C57BL/6 J mice with obesity. However, genetic diversity significantly impacts this response. A period of weight loss does not provide lasting benefits after weight regain, and weight cycling is detrimental and associated with hyperinsulinemia and elevated basal insulin secretion.

Adrenomedullin improved endothelial dysfunction via receptor-Akt pathway in rats with obesity-related hypertension

Obesity-related hypertension (OH) is accompanied by obvious endothelial dysfunction, which contributes to increased peripheral vascular resistance and hypertension. Adrenomedullin (ADM), a multifunctional active peptide, is elevated in obese humans. The OH rats induced by high fat diet (HFD) for 28 weeks and the human umbilical vein endothelial cells (HUVECs)-treated by palmitic acid (PA) were used to investigate the effects of ADM on endothelial dysfunction and the underlying mechanisms. Vascular reactivity was assessed using mesenteric arteriole rings, and the protein expression levels were examined by Western blot analysis. Compared with the control rats, OH rats exhibited hypertension and endothelial dysfunction, along with reduced eNOS protein expression and Akt activation, and increased protein expression of proinflammatory cytokines and ROS levels. Four-week ADM administration improved hypertension and endothelial function, increased eNOS protein expression and Akt activation, and attenuated endothelial inflammation and oxidative stress in OH rats. In vitro experiment, the antagonism of ADM receptors with ADM22-52 and the suppression of Akt signaling with A6730 significantly blocked ADM-caused increase of NO content and activation of eNOS and Akt, and inhibited the anti-inflammatory and anti-oxidant effect of ADM in PA-stimulated HUVECs. These data indicate that endothelial dysfunction in OH rats is partially attributable to the decreased NO level, and the increased inflammation and oxidative stress. ADM improves endothelial function and exerts hypotensive effect depending on the increase of NO, and its anti-inflammatory and anti-oxidant effect via receptor-Akt pathway.

Intermittent fasting, exercise, and dietary modification induce unique transcriptomic signatures of multiple tissues governing metabolic homeostasis during weight loss and rebound weight gain

Obesity and its related metabolic diseases bring great challenges to public health. In-depth understanding on the efficacy of weight-loss interventions is critical for long-term weight control. Our study demonstrated the comparable efficacy of exercise (EX), intermittent fasting (IF), or the change of daily diet from an unhealthy to a normal chow (DR) for weight reduction, but largely divergently affected metabolic status and transcriptome of subcutaneous fat, scapular brown fat, skeletal muscles and liver in high-fat-high-fructose diet (HFHF) induced obese mice. EX and IF reduced systematic inflammation, improved glucose and lipid metabolism in liver and muscle, and amino acid metabolism and thermogenesis in adipose tissues. EX exhibited broad regulatory effects on TCA cycle, carbon metabolism, thermogenesis, propanoate-, fatty acid and amino acid metabolism across multiple tissues. IF prominently affected genes involved in mitophagy and autophagy in adipose tissues and core genes involved in butanoate metabolism in liver. DR, however, failed to improve metabolic homeostasis and biological dysfunctions in obese mice. Notably, by exploring potential inter-organ communication, we identified an obesity-resistant-like gene profile that were strongly correlated with HFHF induced metabolic derangements and could predict the degree of weight regain induced by the follow-up HFHF diet. Among them, 12 genes (e.g., Gdf15, Tfrc, Cdv3, Map2k4, and Nqo1) were causally associated with human metabolic traits, i.e., BMI, body fat mass, HbA1C, fasting glucose, and cholesterol. Our findings provide critical groundwork for improved understanding of the impacts of weight-loss interventions on host metabolism. The identified genes predicting weight regain may be considered regulatory targets for improving long-term weight control.

Lipid-associated macrophages reshape BAT cell identity in obesity

Obesity and type 2 diabetes cause a loss in brown adipose tissue (BAT) activity, but the molecular mechanisms that drive BAT cell remodeling remain largely unexplored. Using a multilayered approach, we comprehensively mapped a reorganization in BAT cells. We uncovered a subset of macrophages as lipid-associated macrophages (LAMs), which were massively increased in genetic and dietary model of BAT expansion. LAMs participate in this scenario by capturing extracellular vesicles carrying damaged lipids and mitochondria released from metabolically stressed brown adipocytes. CD36 scavenger receptor drove LAM phenotype, and CD36-deficient LAMs were able to increase brown fat genes in adipocytes. LAMs released transforming growth factor β1 (TGF-β1), which promoted the loss of brown adipocyte identity through aldehyde dehydrogenase 1 family member A1 (Aldh1a1) induction. These findings unfold cell dynamic changes in BAT during obesity and identify LAMs as key responders to tissue metabolic stress and drivers of loss of brown adipocyte identity.

Adiposity, immunity, and inflammation: interrelationships in health and disease: a report from 24th Annual Harvard Nutrition Obesity Symposium, June 2023

The rapidly evolving field of immunometabolism explores how changes in local immune environments may affect key metabolic and cellular processes, including that of adipose tissue. Importantly, these changes may contribute to low-grade systemic inflammation. In turn, chronic low-grade inflammation affecting adipose tissue may exacerbate the outcome of metabolic diseases. Novel advances in our understanding of immunometabolic processes may critically lead to interventions to reduce disease severity and progression. An important example in this regard relates to obesity, which has a multifaceted effect on immunity, activating the proinflammatory pathways such as the inflammasome and disrupting cellular homeostasis. This multifaceted effect of obesity can be investigated through study of downstream conditions using cellular and systemic investigative techniques. To further explore this field, the National Institutes of Health P30 Nutrition Obesity Research Center at Harvard, in partnership with Harvard Medical School, assembled experts to present at its 24th Annual Symposium entitled "Adiposity, Immunity, and Inflammation: Interrelationships in Health and Disease" on 7 June, 2023. This manuscript seeks to synthesize and present key findings from the symposium, highlighting new research and novel disease-specific advances in the field. Better understanding the interaction between metabolism and immunity offers promising preventative and treatment therapies for obesity-related immunometabolic diseases.

The multifaceted life of macrophages in white adipose tissue: Immune shift couples with metabolic switch

White adipose tissue (WAT) is a vital endocrine organ that regulates energy balance and metabolic homeostasis. In addition to fat cells, WAT harbors macrophages with distinct phenotypes that play crucial roles in immunity and metabolism. Nutrient demands cause macrophages to accumulate in WAT niches, where they remodel the microenvironment and produce beneficial or detrimental effects on systemic metabolism. Given the abundance of macrophages in WAT, this review summarizes the heterogeneity of WAT macrophages in physiological and pathological conditions, including their alterations in quantity, phenotypes, characteristics, and functions during WAT growth and development, as well as healthy or unhealthy expansion. We will discuss the interactions of macrophages with other cell partners in WAT including adipose stem cells, adipocytes, and T cells in the context of various microenvironment niches in lean or obese condition. Finally, we highlight how adipose tissue macrophages merge immunity and metabolic changes to govern energy balance for the organism.

T cells in obesity-associated inflammation: The devil is in the details

Obesity presents a significant health challenge, affecting 41% of adults and 19.7% of children in the United States. One of the associated health challenges of obesity is chronic low-grade inflammation. In both mice and humans, T cells in circulation and in the adipose tissue play a pivotal role in obesity-associated inflammation. Changes in the numbers and frequency of specific CD4+ Th subsets and their contribution to inflammation through cytokine production indicate declining metabolic health, that is, insulin resistance and T2D. While some Th subset alterations are consistent between mice and humans with obesity, some changes mainly characterize male mice, whereas female mice often resist obesity and inflammation. However, protection from obesity and inflammation is not observed in human females, who can develop obesity-related T-cell inflammation akin to males. The decline in female sex hormones after menopause is also implicated in promoting obesity and inflammation. Age is a second underappreciated factor for defining and regulating obesity-associated inflammation toward translating basic science findings to the clinic. Weight loss in mice and humans, in parallel with these other factors, does not resolve obesity-associated inflammation. Instead, inflammation persists amid modest changes in CD4+ T cell frequencies, highlighting the need for further research into resolving changes in T-cell function after weight loss. How lingering inflammation after weight loss affecting the common struggle to maintain lower weight is unknown. Semaglutide, a newly popular pharmaceutical used for treating T2D and reversing obesity, holds promise for alleviating obesity-associated health complications, yet its impact on T-cell-mediated inflammation remains unexplored. Further work in this area could significantly contribute to the scientific understanding of the impacts of weight loss and sex/hormones in obesity and obesity-associated metabolic decline.

Remission of type 2 diabetes: position statement of the Italian society of diabetes (SID)

The primary cause of the pandemic scale of type 2 diabetes (T2D) is the excessive and/or abnormal accumulation of adiposity resulting from a chronic positive energy balance. Any form of weight loss dramatically affects the natural history of T2D, favoring prevention, treatment, and even remission in the case of significant weight loss. However, weight regain, which is often accompanied by the recurrence or worsening of obesity complications such as T2D, is an inevitable biological phenomenon that is an integral part of the pathophysiology of obesity. This can occur not only after weight loss, but also during obesity treatment if it is not effective enough to counteract the physiological responses aimed at restoring adiposity to its pre-weight-loss equilibrium state. Over the past few years, many controlled and randomized studies have suggested a superior efficacy of bariatric surgery compared to conventional therapy in terms of weight loss, glycemic control, and rates of T2D remission. Recently, the therapeutic armamentarium in the field of diabetology has been enriched with new antihyperglycemic drugs with considerable efficacy in reducing body weight, which could play a pathogenetic role in the remission of T2D, not through the classical incretin effect, but by improving adipose tissue functions. All these concepts are discussed in this position statement, which aims to deepen the pathogenetic links between obesity and T2D, shift the paradigm from a "simple" interaction between insulin resistance and insulin deficiency, and evaluate the efficacy of different therapeutic interventions to improve T2D management and induce diabetes remission whenever still possible.

The Impact of Weight Cycling on Health and Obesity

Obesity is a systemic and chronic inflammation, which seriously endangers people's health. People tend to diet to control weight, and the short-term effect of dieting in losing weight is significant, but the prognosis is limited. With weight loss and recovery occurring frequently, people focus on weight cycling. The effect of weight cycling on a certain tissue of the body also has different conclusions. Therefore, this article systematically reviews the effects of body weight cycling on the body and finds that multiple weight cycling (1) increased fat deposition in central areas, lean mass decreased in weight loss period, and fat mass increased in weight recovery period, which harms body composition and skeletal muscle mass; (2) enhanced the inflammatory response of adipose tissue, macrophages infiltrated into adipose tissue, and increased the production of pro-inflammatory mediators in adipocytes; (3) blood glucose concentration mutation and hyperinsulinemia caused the increase or decrease in pancreatic β-cell population, which makes β-cell fatigue and leads to β-cell failure; (4) resulted in additional burden on the cardiovascular system because of cardiovascular rick escalation. Physical activity combined with calorie restriction can effectively reduce metabolic disease and chronic inflammation, alleviating the adverse effects of weight cycling on the body.

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

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

Deficiency of the hemoglobin-haptoglobin receptor, CD163, worsens insulin sensitivity in obese male mice

Excessive iron accumulation in metabolic organs such as the adipose tissue, liver, and skeletal muscle is associated with increased diabetes risk. Tissue-resident macrophages serve multiple roles including managing inflammatory tone and regulating parachymal iron homeostasis; thus protecting against metabolic dysfunction upon iron overload. The scavenger receptor CD163 is uniquely present on tissue-resident macrophages, and plays a significant role in iron homeostasis by clearing extracellular hemoglobin-haptoglobin complexes, thereby limiting oxidative damage caused by free hemoglobin in metabolic tissues. We show that the absence of CD163 exacerbates glucose intolerance and insulin resistance in male mice with obesity. Additionally, loss of CD163 reduced the expression of iron regulatory genes (Tfr1, Cisd1, Slc40a1) in adipose tissue macrophages and anti-inflammatory (M2-like) bone marrow-derived macrophages (BMDMs). Further, CD163 deficiency mediated a pro-inflammatory shift and limited hemoglobin scavenging specifically in M2-like BMDMs. To this end, iron buffering was diminished in inguinal white adipose tissue (iWAT) macrophages in vivo, which culminated in iron spillover into adipocytes and CD45+CD11B- non-myeloid immune cells in iWAT. These findings show that CD163 on tissue-resident macrophages is critical for their anti-inflammatory and hemoglobin scavenging roles, and its absence results in impaired systemic insulin action in an obese setting.

How does the ion concentration affect the functions of kinesin BimC

BimC family proteins are bipolar motor proteins belonging to the kinesin superfamily which promote mitosis by crosslinking and sliding apart antiparallel microtubules. Understanding the binding mechanism between the kinesin and the microtubule is crucial for researchers to make advances in the treatment of cancer and other malignancies. Experimental research has shown that the ion concentration affects the function of BimC significantly. But the insights of the ion-dependent function of BimC remain unclear. By combining molecular dynamics (MD) simulations with a series of computational approaches, we studied the electrostatic interactions at the binding interfaces of BimC and the microtubule under different KCl concentrations. We found the electrostatic interaction between BimC and microtubule is stronger at 0 mM KCl compared to 150 mM KCl, which is consistent with experimental conclusions. Furthermore, important salt bridges and residues at the binding interfaces of the complex were identified, which illustrates the details of the BimC-microtubule interactions. Molecular dynamics analyses of salt bridges identified that the important residues on the binding interface of BimC are positively charged, while those residues on the binding interface of the tubulin heterodimer are negatively charged. The finding in this work reveals some important mechanisms of kinesin-microtubule binding, which helps the future drug design for cancer therapy.

Trained immunity: A link between risk factors and cardiovascular disease

Cardiovascular diseases are significant contributors to human mortality, closely associated with inflammation. With the changing living conditions and the extension of human lifespan, greater attention has been directed towards understanding the impact of early, long-term events on the development of cardiovascular events. Lifestyle factors such as stress, unhealthy diet and physical inactivity can increase the risk of cardiovascular diseases. Interestingly, even if the risk factors are addressed later, their influence may persist. Recently, the concept of trained innate immunity (TRIM), defined as sustained alterations in the function of innate immunocyte that promote a more robust response to downstream stimuli, has been proposed to be involved in cardiovascular diseases. It is hypothesized that TRIM may serve as a mediator bridging the impacts of aforementioned risk factors. This review aims to elucidate the role of TRIM in cardiovascular diseases and highlight its significance in uncovering new mechanisms and therapeutic targets.

How does bariatric surgery remodel adipose tissue?

This lecture delves into the pivotal role of adipose tissue in obesity and its response to weight loss, particularly via bariatric surgery. Adipose tissue, responsible for storing excess energy, undergoes significant changes during obesity, marked by inflammation and fibrosis. Bariatric surgery, serving as a model, allow the exploration of adipose tissue remodeling post-weight loss, inducing metabolic and fibro-inflammatory shifts. Despite successful weight loss, inflammation and fibrosis persist, as evidenced by changes in immune cells, altered cytokine profiles and the accumulation of extracellular matrix (ECM). Unfortunately, these lingering effects impair the normal adipose tissue function. In this context, adipose progenitors, an heterogenous resident population of mesenchymal stromal cells, display functions important to fibrosis development, capable of differentiating into myofibroblasts and contributing to ECM deposition. Particularly, a distinct subpopulation of adipose progenitors with high CD9 expression (CD9high) is associated with fibrosis and insulin resistance in human obesity. The persistence of fibrosis post-weight loss poses challenges, correlating with metabolic dysfunction despite improved glucose tolerance. A comprehensive understanding of the mechanisms driving adipose tissue remodeling and fibrosis post-weight loss is imperative for the development of effective treatments for obesity. The intricate interplay between adipose tissue, inflammation, and fibrosis underscores the necessity for further in-depth research to elucidate these mechanisms and formulate targeted therapies for obesity-related complications.

Functional brain connectivity predictors of prospective substance use initiation and their environmental correlates

Background

Early substance use initiation (SUI) places youth at substantially higher risk for later substance use disorders. Furthermore, adolescence is a critical period for the maturation of brain networks, the pace and magnitude of which are susceptible to environmental influences and may shape risk for SUI.

Methods

We examined whether patterns of functional brain connectivity during rest (rsFC), measured longitudinally in pre-and-early adolescence, can predict future SUI. In an independent sub-sample, we also tested whether these patterns are associated with key environmental factors, specifically neighborhood pollution and socioeconomic dimensions. We utilized data from the Adolescent Brain Cognitive Development (ABCD) Study®. SUI was defined as first-time use of at least one full dose of alcohol, nicotine, cannabis, or other drugs. We created a control group (N = 228) of participants without SUI who were matched with the SUI group (N = 233) on age, sex, race/ethnicity, and parental income and education.

Results

Multivariate analysis showed that whole-brain rsFC prior to SUI during 9-10 and 11-12 years of age successfully differentiated the prospective SUI and control groups. This rsFC signature was expressed more at older ages in both groups, suggesting a pattern of accelerated maturation in the SUI group in the years prior to SUI. In an independent sub-sample (N = 2,854) and adjusted for family socioeconomic factors, expression of this rsFC pattern was associated with higher pollution, but not neighborhood disadvantage.

Conclusion

Brain functional connectivity patterns in early adolescence that are linked to accelerated maturation and environmental exposures can predict future SUI in youth.

Lipid-associated macrophages between aggravation and alleviation of metabolic diseases

Lipid-associated macrophages (LAMs) are phagocytic cells with lipid-handling capacity identified in various metabolic derangements. During disease development, they locate to atherosclerotic plaques, adipose tissue (AT) of individuals with obesity, liver lesions in steatosis and steatohepatitis, and the intestinal lamina propria. LAMs can also emerge in the metabolically demanding microenvironment of certain tumors. In this review, we discuss major questions regarding LAM recruitment, differentiation, and self-renewal, and, ultimately, their acute and chronic functional impact on the development of metabolic diseases. Further studies need to clarify whether and under which circumstances LAMs drive disease progression or resolution and how their phenotype can be modulated to ameliorate metabolic disorders.

Obesity-related T cell dysfunction impairs immunosurveillance and increases cancer risk

Obesity is a well-established risk factor for human cancer, yet the underlying mechanisms remain elusive. Immune dysfunction is commonly associated with obesity but whether compromised immune surveillance contributes to cancer susceptibility in individuals with obesity is unclear. Here we use a mouse model of diet-induced obesity to investigate tumor-infiltrating CD8 + T cell responses in lean, obese, and previously obese hosts that lost weight through either dietary restriction or treatment with semaglutide. While both strategies reduce body mass, only dietary intervention restores T cell function and improves responses to immunotherapy. In mice exposed to a chemical carcinogen, obesity-related immune dysfunction leads to higher incidence of sarcoma development. However, impaired immunoediting in the obese environment enhances tumor immunogenicity, making the malignancies highly sensitive to immunotherapy. These findings offer insight into the complex interplay between obesity, immunity and cancer, and provide explanation for the obesity paradox observed in clinical immunotherapy settings.

Unraveling the complex roles of macrophages in obese adipose tissue: an overview

Macrophages, a heterogeneous population of innate immune cells, exhibit remarkable plasticity and play pivotal roles in coordinating immune responses and maintaining tissue homeostasis within the context of metabolic diseases. The activation of inflammatory macrophages in obese adipose tissue leads to detrimental effects, inducing insulin resistance through increased inflammation, impaired thermogenesis, and adipose tissue fibrosis. Meanwhile, adipose tissue macrophages also play a beneficial role in maintaining adipose tissue homeostasis by regulating angiogenesis, facilitating the clearance of dead adipocytes, and promoting mitochondrial transfer. Exploring the heterogeneity of macrophages in obese adipose tissue is crucial for unraveling the pathogenesis of obesity and holds significant potential for targeted therapeutic interventions. Recently, the dual effects and some potential regulatory mechanisms of macrophages in adipose tissue have been elucidated using single-cell technology. In this review, we present a comprehensive overview of the intricate activation mechanisms and diverse functions of macrophages in adipose tissue during obesity, as well as explore the potential of drug delivery systems targeting macrophages, aiming to enhance the understanding of current regulatory mechanisms that may be potentially targeted for treating obesity or metabolic diseases.

The Effect of Diet Composition on the Post-operative Outcomes of Roux-en-Y Gastric Bypass in Mice

PURPOSE

Roux-en-Y gastric bypass (RYGB) leads to the improvement of many obesity-associated conditions. The degree to which post-operative macronutrient composition contributes to metabolic improvement after RYGB is understudied.

METHODS

A mouse model of RYGB was used to examine the effects of diet on the post-operative outcomes of RYGB. Obese mice underwent either Sham or RYGB surgery and were administered either chow or HFD and then monitored for an additional 8 weeks.

RESULTS

After RYGB, reductions to body weight, fat mass, and lean mass were similar regardless of diet. RYGB and HFD were independently detrimental to bone mineral density and plasma vitamin D levels. Independent of surgery, HFD accelerated hematopoietic stem and progenitor cell proliferation and differentiation and exhibited greater myeloid lineage commitment. Independent of diet, systemic iron deficiency was present after RYGB. In both Sham and RYGB groups, HFD increased energy expenditure. RYGB increased fecal energy loss, and HFD after RYGB increased fecal lipid content. RYGB lowered fasting glucose and liver glycogen levels but HFD had an opposing effect. Indices of insulin sensitivity improved independent of diet. HFD impaired improvements to dyslipidemia, NAFLD, and fibrosis.

CONCLUSION

Post-operative diet plays a significant role in determining the degree to which RYGB reverses obesity-induced metabolic abnormalities such as hyperglycemia, dyslipidemia, and NAFLD. Diet composition may be targeted in order to assist in the treatment of post-RYGB bone mineral density loss and vitamin D deficiency as well as to reverse myeloid lineage commitment. HFD after RYGB continues to pose a significant multidimensional health risk.

Vitamin E: An assistant for black soldier fly to reduce cadmium accumulation and toxicity

Cadmium (Cd) is a toxic heavy metal associated with osteoporosis, liver, and kidney disease. The black soldier fly (BSF) Hermetia illucens may be exposed to Cd during the transformation of livestock manure. The BSF has a high tolerance to Cd. In the previous work of the laboratory, we found that vitamin E (VE) may play a role in the tolerance of BSF to Cd exposure. The main findings are as follows: The BSF larvae pretreated with exogenous VE had heavier body weight, lower content and toxicity of Cd under similar Cd exposure. Even in high Cd exposure at the concentrations of 300 and 700 mg/kg, the BSF larvae pretreated with exogenous VE at a concentration of 100 mg/kg still reduced the Cd toxicity to 85.33 % and 84.43 %, respectively. The best-fitting models showed that metallothionein (MT) content, oxidative damage (8-hydroxydeoxyguanosine content, malondialdehyde content), antioxidant power (total antioxidant power, peroxidase activity) had a great influence on content and toxicity of Cd bioaccumulated in the larvae. The degree of oxidative damage was reduced in the larvae with exogenous VE pretreatments. This variation can be explained by their changed MT content and increased antioxidant power because of exogenous VE. These results reveal the roles of VE in insects defense against Cd exposure and provide a new option for the prevention and therapy of damage caused by Cd exposure.

Adipocyte p53 coordinates the response to intermittent fasting by regulating adipose tissue immune cell landscape

In obesity, sustained adipose tissue (AT) inflammation constitutes a cellular memory that limits the effectiveness of weight loss interventions. Yet, the impact of fasting regimens on the regulation of AT immune infiltration is still elusive. Here we show that intermittent fasting (IF) exacerbates the lipid-associated macrophage (LAM) inflammatory phenotype of visceral AT in obese mice. Importantly, this increase in LAM abundance is strongly p53 dependent and partly mediated by p53-driven adipocyte apoptosis. Adipocyte-specific deletion of p53 prevents LAM accumulation during IF, increases the catabolic state of adipocytes, and enhances systemic metabolic flexibility and insulin sensitivity. Finally, in cohorts of obese/diabetic patients, we describe a p53 polymorphism that links to efficacy of a fasting-mimicking diet and that the expression of p53 and TREM2 in AT negatively correlates with maintaining weight loss after bariatric surgery. Overall, our results demonstrate that p53 signalling in adipocytes dictates LAM accumulation in AT under IF and modulates fasting effectiveness in mice and humans.

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.

The effect of leptin on trained innate immunity and on systemic inflammation in subjects with obesity

Leptin is associated with cardiometabolic complications of obesity, such as metabolic syndrome and atherosclerosis. In obese men, the presence of metabolic syndrome is associated with higher circulating leptin and interleukin (IL)-6 concentrations and increased monocyte cytokine production capacity. Here, we investigated the effects of leptin on monocyte function and systemic inflammatory markers in obese individuals. We specifically explored whether leptin can induce long-term changes in innate immune function by inducing innate immune memory (also called trained immunity). We exposed human primary monocytes for 24 h to relevant leptin concentrations in vitro and measured cytokine production. In addition, after removing leptin, we incubated monocytes for 5 d in culture medium, and we restimulated them on day 6 to assess cytokine production capacity, phagocytosis, and foam cell formation. Direct stimulation with leptin did not induce cytokine production, but exposure to 50 ng/mL leptin augmented lipopolysaccharide- and R848-induced tumor necrosis factor α (TNF-α) production after 1 wk. In a separate in vivo study in a cohort of 302 obese subjects (body mass index [BMI] >27 kg/m2, 55 to 81 yr), we measured circulating leptin, inflammatory markers, and cytokine production upon ex vivo stimulation of isolated peripheral blood mononuclear cells. Circulating leptin concentrations positively correlated with circulating IL-1β and IL-6, which was more pronounced in men than in women. Four single nucleotide polymorphisms in the leptin gene influenced circulating IL-6 concentrations in men, suggesting a direct effect of leptin on IL-6. In conclusion, in vitro, leptin does not directly stimulate monocytes to produce cytokines, yet induces long-term monocyte hyperresponsiveness, i.e. trained immunity. In obese subjects, leptin is associated with circulating IL-6 in a sex-dependent manner. The underlying mechanisms of the sex-specific effect of leptin on innate immune cells remain to be further investigated.

Macrophage and T cell networks in adipose tissue

The signals and structure of the tissues in which leukocytes reside critically mould leukocyte function and development and have challenged our fundamental understanding of how to define and categorize tissue-resident immune cells. One specialized tissue niche that has a powerful effect on immune cell function is adipose tissue. The field of adipose tissue leukocyte biology has expanded dramatically and has revealed how tissue niches can shape immune cell function and reshape them in a setting of metabolic stress, such as obesity. Most notably, adipose tissue macrophages and T cells are under intense investigation due to their contributions to adipose tissue in the lean and obese states. Both adipose tissue macrophages and T cells have features associated with the metabolic function of adipose tissue that are distinct from features of macrophages and T cells that are classically characterized in other tissues. This Review provides state-of-the-art understanding of adipose tissue macrophages and T cells and discusses how their unique niche can help us to better understand diversity in leukocyte responses.

Unique adipose tissue invariant natural killer T cell subpopulations control adipocyte turnover in mice

Adipose tissue invariant natural killer T (iNKT) cells are a crucial cell type for adipose tissue homeostasis in obese animals. However, heterogeneity of adipose iNKT cells and their function in adipocyte turnover are not thoroughly understood. Here, we investigate transcriptional heterogeneity in adipose iNKT cells and their hierarchy using single-cell RNA sequencing in lean and obese mice. We report that distinct subpopulations of adipose iNKT cells modulate adipose tissue homeostasis through adipocyte death and birth. We identify KLRG1+ iNKT cells as a unique iNKT cell subpopulation in adipose tissue. Adoptive transfer experiments showed that KLRG1+ iNKT cells are selectively generated within adipose tissue microenvironment and differentiate into a CX3CR1+ cytotoxic subpopulation in obese mice. In addition, CX3CR1+ iNKT cells specifically kill enlarged and inflamed adipocytes and recruit macrophages through CCL5. Furthermore, adipose iNKT17 cells have the potential to secrete AREG, and AREG is involved in stimulating adipose stem cell proliferation. Collectively, our data suggest that each adipose iNKT cell subpopulation plays key roles in the control of adipocyte turnover via interaction with adipocytes, adipose stem cells, and macrophages in adipose tissue.

Alterations in the mammary gland and tumor microenvironment of formerly obese mice

BACKGROUND

Obesity is a risk factor for breast cancer, and women with obesity that develop breast cancer have a worsened prognosis. Within the mammary gland, obesity causes chronic, macrophage-driven inflammation and adipose tissue fibrosis. Weight loss is a recommended intervention to resolve obesity, but the impact of weight loss on the mammary gland microenvironment and in tumors has not been well identified.

METHODS

To examine the effects of weight loss following obesity, mice were fed a high-fat diet for 16 weeks to induce obesity, then switched to a low-fat diet for 6 weeks. We examined changes in immune cells, including fibrocytes, which are myeloid lineage cells that have attributes of both macrophages and myofibroblasts, and collagen deposition within the mammary glands of non-tumor-bearing mice and within the tumors of mice that were transplanted with estrogen receptor alpha positive TC2 tumor cells.

RESULTS

In formerly obese mice, we observed reduced numbers of crown-like structures and fibrocytes in mammary glands, while collagen deposition was not resolved with weight loss. Following transplant of TC2 tumor cells into the mammary glands of lean, obese, and formerly obese mice, diminished collagen deposition and cancer-associated fibroblasts were observed in tumors from formerly obese mice compared to obese mice. Within tumors of obese mice, increased myeloid-derived suppressor cells and diminished CD8+ T cells were identified, while the microenvironment of tumors of formerly obese mice were more similar to tumors from lean mice. When TC2 tumor cells were mixed with CD11b+CD34+ myeloid progenitor cells, which are the cells of origin for fibrocytes, and transplanted into mammary glands of lean and obese mice, collagen deposition within the tumors of both lean and obese was significantly greater than when tumor cells were mixed with CD11b+CD34- monocytes or total CD45+ immune cells.

CONCLUSIONS

Overall, these studies demonstrate that weight loss resolved some of the microenvironmental conditions within the mammary gland that may contribute to tumor progression. Additionally, fibrocytes may contribute to early collagen deposition in mammary tumors of obese mice leading to the growth of desmoplastic tumors.

Adipose cDC1s contribute to obesity-associated inflammation through STING-dependent IL-12 production

Obesity is associated with chronic low-grade white adipose tissue (WAT) inflammation that can contribute to the development of insulin resistance in mammals. Previous studies have identified interleukin (IL)-12 as a critical upstream regulator of WAT inflammation and metabolic dysfunction during obesity. However, the cell types and mechanisms that initiate WAT IL-12 production remain unclear. Here we show that conventional type 1 dendritic cells (cDC1s) are the cellular source of WAT IL-12 during obesity through analysis of mouse and human WAT single-cell transcriptomic datasets, IL-12 reporter mice and IL-12p70 protein levels by enzyme-linked immunosorbent assay. We demonstrate that cDC1s contribute to obesity-associated inflammation by increasing group 1 innate lymphocyte interferon-γ production and inflammatory macrophage accumulation. Inducible depletion of cDC1s increased WAT insulin sensitivity and systemic glucose tolerance during diet-induced obesity. Mechanistically, endocytosis of apoptotic bodies containing self-DNA by WAT cDC1s drives stimulator of interferon genes (STING)-dependent IL-12 production. Together, these results suggest that WAT cDC1s act as critical regulators of adipose tissue inflammation and metabolic dysfunction during obesity.

Lifestyle and host determinants of antitumor immunity and cancer health disparities

Lifestyle factors exert profound effects on host physiology and immunology. Disparities in cancer outcomes persist as a complex and multifaceted challenge, necessitating a comprehensive understanding of the interplay between host environment and antitumor immune responses. Determinants of health - such as obesity, diet, exercise, stress, or sleep disruption - have the potential for modification, yet some exert long-lasting effects and may challenge the notion of complete reversibility. Herein we review intersectional considerations of lifestyle immunity and the impact on tumor immunology and disparities in cancer outcomes, with a focus on obesity.

Metaflammation in obesity and its therapeutic targeting

Obesity-associated inflammation is a systemic process that affects all metabolic organs. Prominent among these is adipose tissue, where cells of the innate and adaptive immune system are markedly changed in obesity, implicating these cells in a range of processes linking immune memory to metabolic regulation. Furthermore, weight loss and weight cycling have unexpected effects on adipose tissue immune populations. Here, we review the current literature on the roles of various immune cells in lean and obese adipose tissue. Within this context, we discuss pharmacological and nonpharmacological approaches to obesity treatment and their impact on systemic inflammation.

Single cell RNA-sequencing suggests a novel lipid associated mast cell population following weight cycling

Our recent study showed weight cycled mice have increased adipose mast cells compared to obese mice by single cell RNA-sequencing. Here, we aimed to confirm and elucidate these changes. Further analysis of our dataset showed that our initial mast cell cluster could subcluster into two unique populations: one with very high expression of classical mast cell markers and another with elevated lipid handling and antigen presentation genes. This new mast cell cluster accounted for most of the mast cells in the weight cycled group although it was not possible to detect the different populations by new studies with flow cytometry or Toluidine blue staining in mice, possibly due to a downregulation in classical mast cell genes. Interestingly, a pilot study in humans did suggest the existence of two mast cell populations in subcutaneous adipose tissue from obese women that appear similar to the murine populations detected by sequencing; one of which was significantly correlated with weight variance. Together, these data suggest that weight cycling may induce a unique population of mast cells similar to lipid associated macrophages. Future studies will focus on isolation of these cells to better determine their lineage, differentiation, and functional roles.

Trained immunity in diabetes and hyperlipidemia: Emerging opportunities to target cardiovascular complications and design new therapies

Some metabolic diseases, such as diabetes and hyperlipidemia, are associated with a state of inflammation, which adversely affects cardiovascular health. Emerging evidence suggests that long-term hyperactivation of innate immune cells and their bone marrow progenitors, termed trained immunity, functions to accelerate atherosclerosis and its complications in cardiometabolic diseases. This review will focus on how trained immunity is established, particularly through metabolic and epigenetic reprogramming, to cause persistent and deleterious changes in immune cell function, even after the original stimulus has been corrected or removed. Understanding the mechanisms driving maladaptive trained immunity and its fundamental contribution to cardiovascular disease might enable the development of novel disease-modifying therapeutics for the reduction in cardiovascular risk in diabetes, hyperlipidemia, and related cardiometabolic states.

Obesity-induced and weight-loss-induced physiological factors affecting weight regain

Weight regain after successful weight loss resulting from lifestyle interventions is a major challenge in the management of overweight and obesity. Knowledge of the causal mechanisms for weight regain can help researchers and clinicians to find effective strategies to tackle weight regain and reduce obesity-associated metabolic and cardiovascular complications. This Review summarizes the current understanding of a number of potential physiological mechanisms underlying weight regain after weight loss, including: the role of adipose tissue immune cells; hormonal and neuronal factors affecting hunger, satiety and reward; resting energy expenditure and adaptive thermogenesis; and lipid metabolism (lipolysis and lipid oxidation). We describe and discuss obesity-associated changes in these mechanisms, their persistence during weight loss and weight regain and their association with weight regain. Interventions to prevent or limit weight regain based on these factors, such as diet, exercise, pharmacotherapy and biomedical strategies, and current knowledge on the effectiveness of these interventions are also reviewed.

Immune profiling of murine cardiac leukocytes identifies triggering receptor expressed on myeloid cells 2 as a novel mediator of hypertensive heart failure

AIMS

Heart failure with preserved ejection fraction (HFpEF) is characterized by diastolic dysfunction, microvascular dysfunction, and myocardial fibrosis with recent evidence implicating the immune system in orchestrating cardiac remodelling.

METHODS AND RESULTS

Here, we show the mouse model of deoxycorticosterone acetate (DOCA)-salt hypertension induces key elements of HFpEF, including diastolic dysfunction, exercise intolerance, and pulmonary congestion in the setting of preserved ejection fraction. A modified single-cell sequencing approach, cellular indexing of transcriptomes and epitopes by sequencing, of cardiac immune cells reveals an altered abundance and transcriptional signature in multiple cell types, most notably cardiac macrophages. The DOCA-salt model results in differential expression of several known and novel genes in cardiac macrophages, including up-regulation of Trem2, which has been recently implicated in obesity and atherosclerosis. The role of Trem2 in hypertensive heart failure, however, is unknown. We found that mice with genetic deletion of Trem2 exhibit increased cardiac hypertrophy, diastolic dysfunction, renal injury, and decreased cardiac capillary density after DOCA-salt treatment compared to wild-type controls. Moreover, Trem2-deficient macrophages have impaired expression of pro-angiogenic gene programmes and increased expression of pro-inflammatory cytokines. Furthermore, we found that plasma levels of soluble TREM2 are elevated in DOCA-salt treated mice and humans with heart failure.

CONCLUSIONS

Together, our data provide an atlas of immunological alterations that can lead to improved diagnostic and therapeutic strategies for HFpEF. We provide our dataset in an easy to explore and freely accessible web application making it a useful resource for the community. Finally, our results suggest a novel cardioprotective role for Trem2 in hypertensive heart failure.

A lipid-associated macrophage lineage rewires the spatial landscape of adipose tissue in early obesity

Adipose tissue macrophage (ATM) infiltration is associated with adipose tissue dysfunction and insulin resistance in mice and humans. Recent single-cell data highlight increased ATM heterogeneity in obesity but do not provide a spatial context for ATM phenotype dynamics. We integrated single-cell RNA-Seq, spatial transcriptomics, and imaging of murine adipose tissue in a time course study of diet-induced obesity. Overall, proinflammatory immune cells were predominant in early obesity, whereas nonresident antiinflammatory ATMs predominated in chronic obesity. A subset of these antiinflammatory ATMs were transcriptomically intermediate between monocytes and mature lipid-associated macrophages (LAMs) and were consistent with a LAM precursor (pre-LAM). Pre-LAMs were spatially associated with early obesity crown-like structures (CLSs), which indicate adipose tissue dysfunction. Spatial data showed colocalization of ligand-receptor transcripts related to lipid signaling among monocytes, pre-LAMs, and LAMs, including Apoe, Lrp1, Lpl, and App. Pre-LAM expression of these ligands in early obesity suggested signaling to LAMs in the CLS microenvironment. Our results refine understanding of ATM diversity and provide insight into the dynamics of the LAM lineage during development of metabolic disease.

Western-style diet in the presence of elevated circulating testosterone induces adipocyte hypertrophy without proinflammatory responses in rhesus macaques

PROBLEM

Anovulatory infertility is commonly associated with hyperandrogenemia (elevated testosterone, T), insulin resistance, obesity, and white adipose tissue (WAT) dysfunction associated with adipocyte hypertrophy. However, whether hyperandrogenemia and adipocyte hypertrophy per se induce a proinflammatory response is unknown.

METHOD OF STUDY

Young adult female rhesus macaques were exposed to an obesogenic Western-style diet (WSD) in the presence of elevated circulating testosterone (T+WSD) or a low-fat control diet with no exogenous T. Immune cells residing in visceral omental white adipose tissue (OM-WAT), corpus luteum and the contralateral ovary, endometrium, lymph nodes, bone marrow, and peripheral blood mononuclear cells were characterized by flow cytometry during the luteal phase of the reproductive cycle.

RESULTS

Following one year of treatment, T+WSD animals became more insulin-resistant and exhibited increased body fat and adipocyte hypertrophy compared to controls. T+WSD treatment did not induce macrophage polarization toward a proinflammatory phenotype in the tissues examined. Additionally, T+WSD treatment did not affect TNFα production by bone marrow macrophages in response to toll-like receptor agonists. While the major lymphoid subsets were not significantly affected by T+WSD treatment, we observed a significant reduction in the frequency of effector memory CD8+ T-cells (Tem) in OM-WAT, but not in other tissues. Notably, OM-WAT Tem frequencies were negatively correlated with insulin resistance as assessed by the Homeostatic Model Assessment for Insulin Resistance (HOMA-IR).

CONCLUSION

This study shows that short-term T+WSD treatment induces weight gain, insulin resistance, and adipocyte hypertrophy, but does not have a significant effect on systemic and tissue-resident proinflammatory markers, suggesting that adipocyte hypertrophy and mild hyperandrogenemia alone are not sufficient to induce a proinflammatory response.

Deletion of complement factor 5 amplifies glucose intolerance in obese male but not female mice

Complement factor 5 of the innate immune system generates C5a and C5b ligands, which initiate inflammatory and cell lysis events, respectively. C5 activation has been linked with obesity-associated metabolic disorders; however, whether it has a causative role is unclear. We generated a C5 null (C5-/-) mouse using CRISPR-Cas9 gene editing to determine whether loss of C5 improves obesity-linked metabolic dysfunction. Generation of a new mouse model was prompted in part by the observation of off-target gene mutations in commercially available C5-/- lines. Male and female wild-type (WT), heterozygous (Het), and C5-/- mice were fed low-fat diet (LFD) or high-fat diet (HFD) for 22 wk. Body weight gain did not differ between genotypes on LFD or HFD. In lean animals, male C5-/- mice had similar glucose tolerance compared with WT controls; however, in obese conditions, glucose tolerance was worsened in C5-/- compared with controls. In contrast, female mice did not exhibit differences in glucose tolerance between genotypes under either dietary paradigm. Fasting insulin was not different between genotypes, whereas diet-induced obese male C5-/- mice had lower fed insulin concentrations compared with WT controls. No differences in adipose tissue inflammation or adipocyte size were identified between groups. Similarly, susceptibility to fatty liver and hepatic inflammation was similar between WT and C5-/- mice. However, the systemic cytokine response to acute endotoxin exposure was decreased in C5-/- mice. Together, these data suggest that loss of C5 worsens glucose tolerance in obese male but not female mice. Additional work is required to pinpoint the mechanisms by which loss of C5 amplifies glucose intolerance in obesity.NEW & NOTEWORTHY We generated a new mouse model of complement factor 5 deficiency. This work was prompted by a need for improved transgenic mouse lines of C5, due to off-target gene mutations. We find that loss of C5 worsens glucose tolerance in a sex-dependent manner. Though the mechanisms evoking glucose intolerance are not clear, we are confident this model will be useful in interrogating complement activation in obesity-associated diseases.

Peripheral and central macrophages in obesity

Obesity is associated with chronic, low-grade inflammation. Excessive nutrient intake causes adipose tissue expansion, which may in turn cause cellular stress that triggers infiltration of pro-inflammatory immune cells from the circulation as well as activation of cells that are residing in the adipose tissue. In particular, the adipose tissue macrophages (ATMs) are important in the pathogenesis of obesity. A pro-inflammatory activation is also found in other organs which are important for energy metabolism, such as the liver, muscle and the pancreas, which may stimulate the development of obesity-related co-morbidities, including insulin resistance, type 2 diabetes (T2D), cardiovascular disease (CVD) and non-alcoholic fatty liver disease (NAFLD). Interestingly, it is now clear that obesity-induced pro-inflammatory signaling also occurs in the central nervous system (CNS), and that pro-inflammatory activation of immune cells in the brain may be involved in appetite dysregulation and metabolic disturbances in obesity. More recently, it has become evident that microglia, the resident macrophages of the CNS that drive neuroinflammation, may also be activated in obesity and can be relevant for regulation of hypothalamic feeding circuits. In this review, we focus on the action of peripheral and central macrophages and their potential roles in metabolic disease, and how macrophages interact with other immune cells to promote inflammation during obesity.

Obesity accelerates age defects in B cells, and weight loss improves B cell function

BACKGROUND

We have previously shown that obesity accelerates age-associated defects in B cell function and antibody production leading to decreased secretion of protective antibodies and increased autoimmunity. We wanted to evaluate if obese adults enrolled in a voluntary weight reduction program had higher protective and lower autoimmune antibody responses similar to those observed in lean adults.

METHODS

Experiments were performed using blood isolated from an established cohort of female lean adult and elderly individuals, as well as from the blood of female adults with obesity, before and after a voluntary weight reduction program in which their Body Mass Index (BMI) was reduced 10-34% in 12 months. All participants were vaccinated with the Trivalent Inactivated Influenza vaccine. Serum samples were evaluated for the presence of pro-inflammatory cytokines and adipokines, vaccine-specific antibodies and autoimmune antibodies. We evaluated the composition of the B cell pool by flow cytometry, the expression of RNA for class switch transcription factors and pro-inflammatory markers by qPCR, the in vitro secretion of pro- and anti-inflammatory cytokines and their capacity to induce pro-inflammatory T cells.

RESULTS

Obesity, similar to aging, induced increased serum levels of pro-inflammatory cytokines and autoimmune antibodies, while vaccine-specific antibodies were reduced. In agreement with the serum results, the B cell pool of obese adults and elderly individuals was enriched in pro-inflammatory B cell subsets and was characterized by higher expression of markers associated with cell senescence, higher levels of T-bet, the transcription factor for autoimmune antibodies and lower levels of E47, the transcription factor associated with protective responses to the influenza vaccine. B cells from obese adults and elderly individuals were also able to secrete inflammatory cytokines and support the generation of inflammatory T cells. All these pro-inflammatory characteristics of B cells from obese individuals were significantly attenuated, but not completely reversed, by weight loss.

CONCLUSIONS

Although the results from our small observational study show that obesity-induced dysfunctional B cell responses, similar to those occurring during aging, are ameliorated in some but not all obese individuals after weight loss, the effects of body weight loss on mechanistic pathways are largely missing and deserve further investigation.

Alterations in the Mammary Gland and Tumor Microenvironment of Formerly Obese Mice

Obesity is a risk factor for breast cancer, and women with obesity that develop breast cancer have a worsened prognosis. Within the mammary gland, obesity causes chronic, macrophage-driven inflammation and adipose tissue fibrosis. To examine the impact of weight loss on the mammary microenvironment, mice were fed high-fat diet to induce obesity, then switched to a low-fat diet. In formerly obese mice, we observed reduced numbers of crown-like structures and fibrocytes in mammary glands, while collagen deposition was not resolved with weight loss. Following transplant of TC2 tumor cells into the mammary glands of lean, obese, and formerly obese mice, diminished collagen deposition and cancer-associated fibroblasts were observed in tumors from formerly obese mice compared to obese mice. When TC2 tumor cells were mixed with CD11b+CD34+ myeloid progenitor cells, collagen deposition within the tumors was significantly greater compared to when tumor cells were mixed with CD11b+CD34- monocytes, suggesting that fibrocytes contribute to early collagen deposition in mammary tumors of obese mice. Overall, these studies show that weight loss resolved some of the microenvironmental conditions within the mammary gland that may contribute to tumor progression.

Regulation of systemic metabolism by tissue-resident immune cell circuits

Recent studies have demonstrated that tissue homeostasis and metabolic function are dependent on distinct tissue-resident immune cells that form functional cell circuits with structural cells. Within these cell circuits, immune cells integrate cues from dietary contents and commensal microbes in addition to endocrine and neuronal signals present in the tissue microenvironment to regulate structural cell metabolism. These tissue-resident immune circuits can become dysregulated during inflammation and dietary overnutrition, contributing to metabolic diseases. Here, we review the evidence describing key cellular networks within and between the liver, gastrointestinal tract, and adipose tissue that control systemic metabolism and how these cell circuits become dysregulated during certain metabolic diseases. We also identify open questions in the field that have the potential to enhance our understanding of metabolic health and disease.

Post-Effects of Time-Restricted Feeding against Adipose Tissue Inflammation and Insulin Resistance in Obese Mice

Time-restricted feeding (TRF) has been shown to improve the disordered metabolic and immunologic functions associated with obesity, however little is known about its post-effects after the cessation of TRF practice. In the current study, we determined how long the effects of TRF persist, and whether the effects are tissue-dependent. There were four groups of mice in this study: overweight and obese mice were randomized into (1) TRF group (TRF for 6 weeks), (2) post-TRF group (TRF for 4 weeks and later ad libitum), (3) continuous ad libitum of high-fat diet (HFD-AL), and (4) the lean control-fed low-fat diet ad libitum. Blood, liver, and adipose tissues were collected to measure the metabolic, inflammatory, and immune cell parameters. The results showed that TRF withdrawal quickly led to increased body weight/adiposity and reversed fasting blood glucose. However, fasting insulin and insulin resistance index HOMA-IR remained lower in the post-TRF than in the HFD-AL group. In addition, TRF-induced reduction in blood monocytes waned in the post-TRF group, but the TRF effects on mRNA levels of proinflammatory immune cells (macrophages Adgre1 and Itgax) and cytokine (Tnf) in adipose tissue remained lower in the post-TRF group than in the HFD-AL group. Furthermore, the TRF group was protected from the down-regulation of Pparg mRNA expression in adipose tissue, which was also observed in the post-TRF group to a lesser extent. The post-TRF animals displayed liver mass similar to those in the TRF group, but the TRF effects on the mRNA of inflammation markers in the liver vanished completely. Together, these results indicate that, although the lasting effects of TRF may differ by tissues and genes, the impact of TRF on adipose tissue inflammation and immune cell infiltration could last a couple of weeks, which may, in part, contribute to the maintenance of insulin sensitivity even after the cessation of TRF.

Circadian mechanisms in adipose tissue bioenergetics and plasticity

The circadian clock plays an essential role in coordinating feeding and metabolic rhythms with the light/dark cycle. Disruption of clocks is associated with increased adiposity and metabolic disorders, whereas aligning feeding time with cell-autonomous rhythms in metabolism improves health. Here, we provide a comprehensive overview of recent literature in adipose tissue biology as well as our understanding of molecular mechanisms underlying the circadian regulation of transcription, metabolism, and inflammation in adipose tissue. We highlight recent efforts to uncover the mechanistic links between clocks and adipocyte metabolism, as well as its application to dietary and behavioral interventions to improve health and mitigate obesity.

Obesity and Fibrosis: Setting the Stage for Breast Cancer

Obesity is a rising health concern and is linked to a worsened breast cancer prognosis. Tumor desmoplasia, which is characterized by elevated numbers of cancer-associated fibroblasts and the deposition of fibrillar collagens within the stroma, may contribute to the aggressive clinical behavior of breast cancer in obesity. A major component of the breast is adipose tissue, and fibrotic changes in adipose tissue due to obesity may contribute to breast cancer development and the biology of the resulting tumors. Adipose tissue fibrosis is a consequence of obesity that has multiple sources. Adipocytes and adipose-derived stromal cells secrete extracellular matrix composed of collagen family members and matricellular proteins that are altered by obesity. Adipose tissue also becomes a site of chronic, macrophage-driven inflammation. Macrophages exist as a diverse population within obese adipose tissue and mediate the development of fibrosis through the secretion of growth factors and matricellular proteins and interactions with other stromal cells. While weight loss is recommended to resolve obesity, the long-term effects of weight loss on adipose tissue fibrosis and inflammation within breast tissue are less clear. Increased fibrosis within breast tissue may increase the risk for tumor development as well as promote characteristics associated with tumor aggressiveness.