Sex hormones regulate metainflammation in diet-induced obesity in mice.

Men have a statistically higher risk of metabolic and cardiovascular disease than premenopausal women, but the mechanisms mediating these differences are elusive. Chronic inflammation during obesity contributes to disease risk and is significantly more robust in males. Prior work demonstrated that compared with obese males, obese females have reduced proinflammatory adipose tissue macrophages (ATMs). Given the paucity of data on how sex hormones contribute to macrophage responses in obesity, we sought to understand the role of sex hormones in promoting obesity-induced myeloid inflammation. We used gonadectomy, estrogen receptor-deficient alpha chimeras, and androgen-insensitive mice to model sex hormone deficiency. These models were evaluated in diet-induced obesity conditions (high-fat diet [HFD]) and in vitro myeloid assays. We found that ovariectomy increased weight gain and adiposity. Ovariectomized females had increased ATMs and bone marrow myeloid colonies compared with sham-gonadectomized females. In addition, castrated males exposed to HFD had improved glucose tolerance, insulin sensitivity, and adiposity with fewer Ly6chi monocytes and bone marrow myeloid colonies compared with sham-gonadectomized males, although local adipose inflammation was enhanced. Similar findings were observed in androgen-insensitive mice; however, these mice had fewer CD11c+ ATMs, implying a developmental role for androgens in myelopoiesis and adipose inflammation. We concluded that gonadectomy results in convergence of metabolic and inflammatory responses to HFD between the sexes, and that myeloid estrogen receptor alpha contributes minimally to diet-induced inflammatory responses, whereas loss of androgen-receptor signaling improves metabolic and inflammatory outcomes. These studies demonstrate that sex hormones play a critical role in sex differences in obesity, metabolic dysfunction, and myeloid inflammation.

TLR4, TRIF, and MyD88 are essential for myelopoiesis and CD11c+ adipose tissue macrophage production in obese mice.

Obesity-induced chronic inflammation is associated with metabolic disease. Results from mouse models utilizing a high-fat diet (HFD) have indicated that an increase in activated macrophages, including CD11c+ adipose tissue macrophages (ATMs), contributes to insulin resistance. Obesity primes myeloid cell production from hematopoietic stem cells (HSCs) and Toll-like receptor 4 (TLR4), and the downstream TIR domain-containing adapter protein-inducing interferon-ß (TRIF)- and MyD88-mediated pathways regulate production of similar myeloid cells after lipopolysaccharide stimulation. However, the role of these pathways in HFD-induced myelopoiesis is unknown. We hypothesized that saturated fatty acids and HFD alter myelopoiesis by activating TLR4 pathways in HSCs, differentially producing pro-inflammatory CD11c+ myeloid cells that contribute to obesity-induced metabolic disease. Results from reciprocal bone marrow transplants (BMTs) with Tlr4-/- and WT mice indicated that TLR4 is required for HFD-induced myelopoiesis and production of CD11c+ ATMs. Experiments with homozygous knockouts of Irakm (encoding a suppressor of MyD88 inactivation) and Trif in competitive BMTs revealed that MyD88 is required for HFD expansion of granulocyte macrophage progenitors and that Trif is required for pregranulocyte macrophage progenitor expansion. A comparison of WT, Tlr4-/-, Myd88-/-, and Trif-/- mice on HFD demonstrated that TLR4 plays a role in the production of CD11c+ ATMs, and both Myd88-/- and Trif-/- mice produced fewer ATMs than WT mice. Moreover, HFD-induced TLR4 activation inhibited macrophage proliferation, leading to greater accumulation of recruited CD11c+ ATMs. Our results indicate that HFD potentiates TLR4 and both its MyD88- and TRIF-mediated downstream pathways within progenitors and adipose tissue and leads to macrophage polarization.

Gender and Sex Differences in Adipose Tissue.

PURPOSE OF REVIEW: As the ongoing epidemic of adult and childhood obesity grows, it puts a greater burden on individuals and the healthcare system due to increased prevalence of obesity-associated diseases. An important area that has gained much attention recently is the sex and gender difference related to obesity and associated complications. Basic science and clinical studies have now improved our understanding of obesity and have discovered adipose tissue biology to be key in metabolism. RECENT FINDINGS: There is evidence related to the sex dichotomy in obesity in a variety of areas including adipocyte function, sex hormone effects, genetics, and metabolic inflammation leading to critical differences in adipose tissue biology. The sex and gender difference in adipose tissue is a factor that should be considered when studying an individuals' risk for obesity and metabolic dysfunction. This understanding is important for strategizing treatment and prevention measures.

The Role of Sex and Sex Hormones in Regulating Obesity-Induced Inflammation.

Metabolic and non-metabolic complications due to obesity are becoming more prevalent, yet our understanding of the mechanisms driving these is not. This is due to individual risk factor variability making it difficult to predict disease outcomes such as diabetes and insulin resistance. Gender is a critical factor in obesity outcomes with women having more adiposity but reduced metabolic complications compared to men. The role of immune system activation during obesity is an emerging field that links adiposity to metabolic syndrome. Furthermore, evidence from animal models suggests that sex differences exist in immune responses and, therefore, could be a possible mechanism leading to sex differences in metabolic disease. While there is still much to learn in the area of sex-differences research, this chapter will review the current knowledge and literature detailing the role of sex and sex hormones on adiposity and metabolically induced inflammation in obesity.

The Influence of Maternal High Fat Diet During Lactation on Offspring Hematopoietic Priming.

Obesity and metabolic diseases are rising among women of reproductive age, increasing offspring metabolic risk. Maternal nutritional interventions during lactation present an opportunity to modify offspring outcomes. We previously demonstrated in mice that adult male offspring have metabolic impairments and increased adipose tissue macrophages (ATM) when dams are fed high fat diet (HFD) during the postnatal lactation window (HFD PN). We sought to understand the effect of HFD during lactation on early-life inflammation. HFD PN offspring were evaluated at postnatal day 16 to 19 for tissue weight and gene expression. Profiling of adipose tissue and bone marrow immune cells was conducted through lipidomics, in vitro myeloid colony forming unit assays, and flow cytometry. HFD PN mice had more visceral gonadal white adipose tissue (GWAT) and subcutaneous fat. Adipose tissue RNA sequencing demonstrated enrichment of inflammation, chemotaxis, and fatty acid metabolism and concordant changes in GWAT lipidomics. Bone marrow (BM) of both HFD PN male and female offspring had increased monocytes (CD45+Ly6G-CD11b+CD115+) and B cells (CD45+Ly6G-CD11b-CD19+). Similarly, serum from HFD PN offspring enhanced in vitro BM myeloid colonies in a toll-like receptor 4-dependent manner. We identified that male HFD PN offspring had increased GWAT pro-inflammatory CD11c+ ATMs (CD45+CD64+). Maternal exposure to HFD alters milk lipids enhancing adiposity and myeloid inflammation even in early life. Future studies are needed to understand the mechanisms driving this pro-inflammatory state of both BM and ATMs, the causes of the sexually dimorphic phenotypes, and the feasibility of intervening in this window to improve metabolic health.

Age-associated adipose tissue inflammation promotes monocyte chemotaxis and enhances atherosclerosis.

Although aging enhances atherosclerosis, we do not know if this occurs via alterations in circulating immune cells, lipid metabolism, vasculature, or adipose tissue. Here, we examined whether aging exerts a direct pro-atherogenic effect on adipose tissue in mice. After demonstrating that aging augmented the inflammatory profile of visceral but not subcutaneous adipose tissue, we transplanted visceral fat from young or aged mice onto the right carotid artery of Ldlr-/- recipients. Aged fat transplants not only increased atherosclerotic plaque size with increased macrophage numbers in the adjacent carotid artery, but also in distal vascular territories, indicating that aging of the adipose tissue enhances atherosclerosis via secreted factors. By depleting macrophages from the visceral fat, we identified that adipose tissue macrophages are major contributors of the secreted factors. To identify these inflammatory factors, we found that aged fat transplants secreted increased levels of the inflammatory mediators TNFα, CXCL2, and CCL2, which synergized to promote monocyte chemotaxis. Importantly, the combined blockade of these inflammatory mediators impeded the ability of aged fat transplants to enhance atherosclerosis. In conclusion, our study reveals that aging enhances atherosclerosis via increased inflammation of visceral fat. Our study suggests that future therapies targeting the visceral fat may reduce atherosclerosis disease burden in the expanding older population.

Monocyte Trafficking and Polarization Contribute to Sex Differences in Meta-Inflammation.

Obesity is associated with systemic inflammation and immune cell recruitment to metabolic tissues. Sex differences have been observed where male mice challenged with high fat diet (HFD) exhibit greater adipose tissue inflammation than females demonstrating a role for sex hormones in differential inflammatory responses. Circulating monocytes that respond to dietary lipids and chemokines and produce cytokines are the primary source of recruited adipose tissue macrophages (ATMs). In this study, we investigated sexual dimorphism in biological pathways in HFD-fed ATMs from male and female mice by RNA-seq. We also conducted chemotaxis assays to investigate sex differences in the migration of monocytes isolated from bone marrow from male and female mice toward a dietary saturated lipid - palmitate (PA), and a chemokine - monocyte chemoattractant protein 1 (MCP1), factors known to stimulate myeloid cells in obesity. ATM RNA-Seq demonstrated sex differences of both metabolic and inflammatory activation, including pathways for chemokine signaling and leukocyte trans-endothelial migration. In vivo monocyte transfer studies demonstrated that male monocytes traffic to female adipose tissue to generate ATMs more readily. In chemotaxis assays, lean male monocytes migrated in greater numbers than females toward PA and MCP1. With short-term HFD, male and female monocytes migrated similarly, but in chronic HFD, male monocytes showed greater migration than females upon PA and MCP1 stimulation. Studies with monocytes from toll-like receptor 4 knockout mice (Tlr4-/- ) demonstrated that both males and females showed decreased migration than WT in response to PA and MCP1 implying a role for TLR4 in monocyte influx in response to meta-inflammation. Overall, these data demonstrate the role of sexual dimorphism in monocyte recruitment and response to metabolic stimuli that may influence meta-inflammation in obesity.

Age and Sex: Impact on adipose tissue metabolism and inflammation.

Age associated chronic inflammation is a major contributor to diseases with advancing age. Adipose tissue function is at the nexus of processes contributing to age-related metabolic disease and mediating longevity. Hormonal fluctuations in aging potentially regulate age-associated visceral adiposity and metabolic dysfunction. Visceral adiposity in aging is linked to aberrant adipogenesis, insulin resistance, lipotoxicity and altered adipokine secretion. Age-related inflammatory phenomena depict sex differences in macrophage polarization, changes in T and B cell numbers, and types of dendritic cells. Sex differences are also observed in adipose tissue remodeling and cellular senescence suggesting a role for sex steroid hormones in the regulation of the adipose tissue microenvironment. It is crucial to investigate sex differences in aging clinical outcomes to identify and better understand physiology in at-risk individuals. Early interventions aimed at targets involved in adipose tissue adipogenesis, remodeling and inflammation in aging could facilitate a profound impact on health span and overcome age-related functional decline.

Weight Gain, Glucose Tolerance, and the Gut Microbiome of Male C57BL/6J Mice Housed on Corncob or Paper Bedding and Fed Normal or High-Fat Diet.

Understanding how differences in animal husbandry practices affect the reproducibility of research results is critical. We sought to understand how different beddings might influence dietary obesity studies. We compared the effects of paper and corncob bedding on weight gain, metabolism, and gut microbiome (GM) of mice fed a high-fat diet (HFD) or a normal diet (ND) and evaluated effects on fecal and cecal microbiomes collected from these cohorts after euthanasia. Male C57BL/6J mice at 5 wk age were allowed to acclimate to the facility and the assigned bedding for one week before being placed on HFD or remaining on the ND for 12 wk. Fecal pellets and cecal samples were collected and frozen for batched 16S sequencing. Mice had similar body weight, visceral gonadal white adipose tissue (GWAT), subcutaneous inguinal white adipose tissue (IWAT), liver and spleen weights and metabolic changes regardless of the bedding type. Baseline microbiota differences were detected one week after bedding assignment. After 12 wk, the GM showed significant differences depending on both bedding and diet. The effects of the bedding were not significantly different between endpoint fecal and cecal GM, despite the inherent differences in microbiota in fecal and cecal samples. A correlation was detected between diet and the relative abundance of Bacteroidetes and Verrucomicrobia: Akkermansia. In conclusion, this study demonstrates the importance of considering bedding type when performing dietary experiments.

Female adipose tissue has improved adaptability and metabolic health compared to males in aged obesity.

Aging, like obesity, is associated with metabolic and inflammatory alterations within adipose tissue in older individuals. Younger females are protected from adipose inflammation, but older post-menopausal females exhibit exaggerated visceral adiposity correlated with increased disease risk. Obesity accelerates the onset and progression of age-associated diseases, but it is unclear if aging and obesity drive adipose tissue dysfunction in a sexually dimorphic fashion. We investigated adipose tissue metabolism and inflammation in a diet-induced obesity model in young and old mice. We identified age related sex differences in adipose tissue macrophages (ATMs), fibrosis and lipid metabolism in male and female visceral fat depot (GWAT). Although aging normalized body weights between the sexes, females remained protected from proinflammatory ATMs and stimulated lipolysis failed to adversely affect the inflammatory state even with obesity. Older obese males had augmented CD11c+ ATMs and higher insulin levels, while females showed increased visceral adiposity and exaggerated Pparγ, and Pgc1α expression. Obesity in aging demonstrated similar expression of GWAT p53, p16, p21, Timp1 and Tgfß1 in both sexes. Our studies suggest that even with aging, female GWAT shows an attenuated inflammatory response compared to males due to an efficient oxidative metabolism combined with an active tissue remodeling state.