Search

Objective Weight regain after weight loss is common, and there is evidence to suggest negative effects on health because of weight cycling. This study sought to investigate the impact of weight regain in formerly obese mice on adipose tissue architecture and stromal cell function. Methods A diet-switch model was employed for obesity induction, weight loss, and weight regain in mice. Flow cytometry quantified adipose tissue leukocytes in adipose tissue. Liver and adipose tissue depots were compared to determine tissue-specific effects of weight cycling. Results Epididymal white adipose tissue of formerly obese mice failed to expand in response to repeat exposure to high-fat diet and retained elevated numbers of macrophages and T cells. Weight regain was associated with disproportionally elevated liver mass, hepatic triglyceride content, serum insulin concentration, and serum transaminase concentration. These effects occurred despite an extended 6-month weight loss cycle and they demonstrate that formerly obese mice maintain durable alterations in their physiological response to weight regain. Conditioned media from epididymal adipose tissue of formerly obese mice inhibited adipogenesis of 3T3-L1 preadipocytes, suggesting a potential mechanism to explain failed epididymal adipose tissue expansion during weight regain. Conclusions Metabolic abnormalities related to defects in adipose tissue expansion and ongoing dysfunction manifest in formerly obese mice during weight regain.

Adipose tissue pathology in obese patients often features impaired adipogenesis, angiogenesis, and chronic low-grade inflammation, all of which are regulated in large part by adipose tissue stromal vascular cells [SVC; i.e., non-adipocyte cells within adipose tissue including preadipocytes, endothelial cells (ECs), and immune cells]. Exercise is known to increase subcutaneous adipose tissue lipolysis, but the impact of exercise on SVCs in adipose tissue has not been explored. The purpose of this study was to assess the effects of a session of exercise on preadipocyte, EC, macrophage, and T cell content in human subcutaneous adipose tissue. We collected abdominal subcutaneous adipose tissue samples from 10 obese adults (BMI 33 ± 3 kg/m2, body fat 41 ± 7%) 12 h after a 60 min acute session of endurance exercise (80 ± 3%HRpeak) vs. no acute exercise session. SVCs were isolated by collagenase digestion and stained for flow cytometry. We found that acute exercise reduced preadipocyte content (38 ± 7 vs. 30 ± 13%SVC; p = 0.04). The reduction was driven by a decrease in CD34hi preadipocytes (18 ± 5 vs. 13 ± 6%SVC; p = 0.002), a subset of preadipocytes that generates high lipolytic rate adipocytes ex vivo. Acute exercise did not alter EC content. Acute exercise also did not change total immune cell, macrophage, or T cell content, and future work should assess the effects of exercise on subpopulations of these cells. We conclude that exercise may rapidly regulate the subcutaneous adipose tissue preadipocyte pool in ways that may help attenuate the high lipolytic rates that are commonly found in obesity.

Obesity-related changes in adipose tissue leukocytes, in particular adipose tissue macrophages (ATMs) and dendritic cells (ATDCs), are implicated in metabolic inflammation, insulin resistance, and altered regulation of adipocyte function. We evaluated stromal cell and white adipose tissue (WAT) expansion dynamics with high fat diet (HFD) feeding for 3–56 days, quantifying ATMs, ATDCs, endothelial cells (ECs), and preadipocytes (PAs) in visceral epididymal WAT and subcutaneous inguinal WAT. To better understand mechanisms of the early response to obesity, we evaluated ATM proliferation and lipid accumulation. ATMs, ATDCs, and ECs increased with rapid WAT expansion, with ATMs derived primarily from a CCR2-independent resident population. WAT expansion stimulated proliferation in resident ATMs and ECs, but not CD11c+ ATMs or ATDCs. ATM proliferation was unperturbed in Csf2- and Rag1-deficient mice with WAT expansion. Additionally, ATM apoptosis decreased with WAT expansion, and proliferation and apoptosis reverted to baseline with weight loss. Adipocytes reached maximal hypertrophy at 28 days of HFD, coinciding with a plateau in resident ATM accumulation and the appearance of lipid-laden CD11c+ ATMs in visceral epididymal WAT. ATM increases were proportional to tissue expansion and adipocyte hypertrophy, supporting adipocyte-mediated regulation of resident ATMs. The appearance of lipid-laden CD11c+ ATMs at peak adipocyte size supports a role in responding to ectopic lipid accumulation within adipose tissue. In contrast, ATDCs increase independently of proliferation and may be derived from circulating precursors. These changes precede and establish the setting in which large-scale adipose tissue infiltration of CD11c+ ATMs, inflammation, and adipose tissue dysfunction contributes to insulin resistance.

Infiltration of pro-inflammatory adipose tissue macrophages (ATMs) is implicated in systemic low-grade inflammation that underlies metabolic health complications in obesity. Exercise training has been linked to reduced adipose tissue and systemic inflammation, but these observations are often confounded by concomitant weight loss. Many metabolic benefits of exercise are a cumulative effect of each bout of exercise, thus the aim of this study was to determine changes in ATMs (using flow cytometry) in response to a single exercise session. We collected subcutaneous abdominal adipose tissue samples from 10 obese (BMI: 33±3kg/m2; fat mass: 41±20kg) and 14 lean (BMI: 23±13kg/m2; fat mass: 16±5kg) adults, 12 hours after exercising for 60 minutes at 70% VO2max (EX); and again 3 days after their most recent exercise session (No-EX). To characterize the cellular response to exercise without the confounding influence of exercise novelty, all subjects were habitual exercisers. The exercise session did not alter total immune cell number (OBESE: 30±7 vs. 31±7; LEAN: 27±9 vs. 28±8% live cells) or total ATM number (OBESE: 3.9±1.7 vs. 4.0±1.6; LEAN: 3.5±1.5 vs. 4.3±1.9% live cells; for No-EX and EX, respectively). However, there was a main effect for exercise to increase the number of CD11c- ATMs (OBESE: 1.3±1.4 vs. 1.5±1.5; LEAN: 1.0±0.6 vs. 2.0±1.6% live cells; P=0.03), indicating the abundance of resident ATMs increased after exercise. Surprisingly, the response to exercise was not different in lean vs. obese subjects. Although the change in resident ATM content after exercise was rather subtle in this cohort of healthy regular exercisers, these are the first single cell data to suggest each session of exercise may induce a phenotypic shift in subcutaneous ATMs. This could be a mechanism contributing to the anti-inflammatory health benefits of exercise. Disclosure A. Ludzki: None. E.M. Krueger: None. T.C. Baldwin: None. N.M. Taylor: None. L.A. Muir: None. C. Lumeng: None. J.F. Horowitz: Research Support; Self; American Diabetes Association. Funding National Institutes of Health (R01DK077966) Canadian Institutes of Health Research (DFS146190)

Obesity causes dramatic proinflammatory changes in the adipose tissue immune environment, but relatively little is known regarding how this inflammation responds to weight loss (WL). To understand the mechanisms by which meta-inflammation resolves during WL, we examined adipose tissue leukocytes in mice after withdrawal of a high-fat diet. After 8 weeks of WL, mice achieved similar weights and glucose tolerance values as age-matched lean controls but showed abnormal insulin tolerance. Despite fat mass normalization, total and CD11c+ adipose tissue macrophage (ATM) content remained elevated in WL mice for up to 6 months and was associated with persistent fibrosis in adipose tissue. ATMs in formerly obese mice demonstrated a proinflammatory profile, including elevated expression of interferon-γ, tumor necrosis factor-α, and interleukin-1β. T-cell–deficient Rag1−/− mice showed a degree of ATM persistence similar to that in WT mice, but with reduced inflammatory gene expression. ATM proliferation was identified as the predominant mechanism by which ATMs are retained in adipose tissue with WL. Our study suggests that WL does not completely resolve obesity-induced ATM activation, which may contribute to the persistent adipose tissue damage and reduced insulin sensitivity observed in formerly obese mice.

Objective The relationship between adipose tissue fibrosis, adipocyte hypertrophy, and preadipocyte hyperplasia in the context of obesity and the correlation of these tissue-based phenomena with systemic metabolic disease are poorly defined. The goal of this study was to clarify the relationship between adipose tissue fibrosis, adipocyte hypertrophy, and preadipocyte hyperplasia in human obesity and determine the correlation of these adipose-tissue based phenomena with diabetes. Methods Visceral and subcutaneous adipose tissues from humans with obesity collected during bariatric surgery were studied with QRTPCR, immunohistochemistry, and flow cytometry for expression of collagens and fibrosis-related proteins, adipocyte size, and preadipocyte frequency. Results were correlated with clinical characteristics including diabetes status. Results Fibrosis was decreased, hypertrophy was increased, and preadipocyte frequency and fibrotic gene expression were decreased in adipose tissues from diabetic subjects compared to non-diabetic subjects. These differences were greater in visceral compared to subcutaneous adipose tissue. Conclusions These data are consistent with the hypothesis that adipose tissue fibrosis in the context of human obesity limits adipocyte hypertrophy and is associated with a reciprocal increase in adipocyte hyperplasia, with beneficial effects on systemic metabolism. These findings suggest adipose tissue fibrosis as a potential target for manipulation of adipocyte metabolism.

Objective Expansion of visceral adipose tissue (VAT) and metabolic inflammation are consequences of obesity and associated with type 2 diabetes (T2DM). Metabolically activated adipose tissue macrophages (ATMs) undergo qualitative and quantitative changes that influence their inflammatory responses. How these cells contribute to insulin resistance (IR) in humans is not well understood. Cholesterol 25-Hydroxylase (CH25H) converts cholesterol into 25-Hydroxycholesterol (25-HC), an oxysterol that modulates immune responses. Using human and murine models, we investigated the role of CH25H in metabolic inflammation. Methods We performed transcriptomic (RNASeq) analysis on the human whole AT biopsies and sorted ATMs from obese non-diabetic (NDM) and obese diabetic (DM) subjects to inquire if CH25H was increased in DM. We challenged mice lacking Ch25h with a high-fat diet (HFD) to characterize their metabolic and immunologic profiling. Ch25h KO mice and human adipose tissue biopsies from NDM and DM subjects were analyzed. LC-MS was conducted to measure 25-HC level in AT. In vitro analysis permitted us to investigate the effect of 25-HC on cytokine expression. Results In our RNASeq analysis of human visceral and subcutaneous biopsies, gene pathways related to inflammation were increased in obese DM vs. non-DM subjects that included CH25H. CH25H was enriched in the stromal vascular fraction of human adipose tissue and highly expressed in CD206+ human ATMs by flow cytometry analysis. We measured the levels of the oxysterols, 25-HC and 7α25diHC, in human visceral adipose tissue samples and showed a correlation between BMI and 25-HC. Using mouse models of diet-induced obesity (DIO), we found that HFD-induced Ch25h expression in eWAT and increased levels of 25-HC in AT. On HFD, Ch25h KO mice became obese but exhibited reduced plasma insulin levels, improved insulin action, and decreased ectopic lipid deposit. Improved insulin sensitivity in Ch25h KO mice was due to attenuation of CD11c+ adipose tissue macrophage infiltration in eWAT. Finally, by testing AT explants, bone marrow-derived macrophages (BMDMs) and SVF cells from Ch25h deficient mice, we observed that 25-HC is required for the expression of pro-inflammatory genes. 25-HC was also able to induce inflammatory genes in preadipocytes. Conclusions Our data suggest a critical role for CH25H/25-HC in the progression of meta-inflammation and insulin resistance in obese humans and mouse models of obesity. In response to obesogenic stimuli, CH25H/25-HC could exert a pro-inflammatory role., HIGHLIGHTS • CH25H upregulation in visceral adipose tissue is associated with diabetes in humans. • ATMs are the primary site of CH25H expression in humans and mice. • DIO in mice activates Ch25h expression and 25-HC production in visceral adipose tissue. • Obese Ch25h KO mice have improved insulin sensitivity due to attenuated adipose tissue inflammation. • In response to inflammatory stimuli, Ch25h/25-HC potentiates myeloid activation.

Women of reproductive age are protected from metabolic disease relative to postmenopausal women and men. Most preclinical rodent studies are skewed toward the use of male mice to study obesity-induced metabolic dysfunction because of a similar protection observed in female mice. How sex differences in obesity-induced inflammatory responses contribute to these observations is unknown. We have compared and contrasted the effects of high fat diet-induced obesity on glucose metabolism and leukocyte activation in multiple depots in male and female C57Bl/6 mice. With both short term and long term high fat diet, male mice demonstrated increased weight gain and CD11c+ adipose tissue macrophage content compared with female mice despite similar degrees of adipocyte hypertrophy. Competitive bone marrow transplant studies demonstrated that obesity induced a preferential contribution of male hematopoietic cells to circulating leukocytes and adipose tissue macrophages compared with female cells independent of the sex of the recipient. Sex differences in macrophage and hematopoietic cell in vitro activation in response to obesogenic cues were observed to explain these results. In summary, this report demonstrates that male and female leukocytes and hematopoietic stem cells have cell-autonomous differences in their response to obesity that contribute to an amplified response in males compared with females. Background: Diet-induced obesity leads to a chronic low grade inflammation with production of activated macrophages associated with systemic sexually dimorphic metabolic dysfunction. Results: Males have enhanced myelopoiesis and a proinflammatory response to obesity compared with females. Conclusion: Sex differences in myelopoiesis result in dimorphic responses to obesity-induced inflammation. Significance: Given differences in inflammatory responses, targeted treatment strategies are probably required for males and females.

Predictors of weight loss responses are not well-defined. We hypothesized that adipose tissue phenotypic features related to remodeling would be associated with bariatric surgery weight loss responses. Visceral and subcutaneous adipose tissues collected from patients during bariatric surgery were studied with flow cytometry, immunohistochemistry, and QRTPCR, and results correlated with weight loss outcomes. Age, male sex, and a diagnosis of type 2 diabetes were associated with less weight loss. Adipocyte size was increased and preadipocyte frequency was decreased in visceral adipose tissue from diabetic subjects. Decreased adipose tissue preadipocyte frequency was associated with less weight loss in women but not men. These data suggest that phenotypic features of adipose tissue remodeling may predict responses to weight loss interventions.

Adipocytes differentiated from preadipocytes provide a valuable model for the study of human adipocyte metabolism. We describe methods for isolation of human stromal vascular cells, expansion of preadipocytes, differentiation into mature adipocytes, and in vitro metabolic interrogation of adipocytes.

Dynamic changes of adipose tissue leukocytes, including adipose tissue macrophage (ATM) and adipose tissue dendritic cells (ATDCs), contribute to obesity-induced inflammation and metabolic disease. However, clear discrimination between ATDC and ATM in adipose tissue has limited progress in the field of immunometabolism. In this study, we use CD64 to distinguish ATM and ATDC, and investigated the temporal and functional changes in these myeloid populations during obesity. Flow cytometry and immunostaining demonstrated that the definition of ATM as F4/80+CD11b+ cells overlaps with other leukocytes and that CD45+CD64+ is specific for ATM. The expression of core dendritic cell genes was enriched in CD11c+CD64− cells (ATDC), whereas core macrophage genes were enriched in CD45+CD64+ cells (ATM). CD11c+CD64− ATDCs expressed MHC class II and costimulatory receptors, and had similar capacity to stimulate CD4+ T cell proliferation as ATMs. ATDCs were predominantly CD11b+ conventional dendritic cells and made up the bulk of CD11c+ cells in adipose tissue with moderate high-fat diet exposure. Mixed chimeric experiments with Ccr2−/− mice demonstrated that high-fat diet–induced ATM accumulation from monocytes was dependent on CCR2, whereas ATDC accumulation was less CCR2 dependent. ATDC accumulation during obesity was attenuated in Ccr7−/− mice and was associated with decreased adipose tissue inflammation and insulin resistance. CD45+CD64+ ATM and CD45+CD64−CD11c+ ATDCs were identified in human obese adipose tissue and ATDCs were increased in s.c. adipose tissue compared with omental adipose tissue. These results support a revised strategy for unambiguous delineation of ATM and ATDC, and suggest that ATDCs are independent contributors to adipose tissue inflammation during obesity.

Context: The role of the extracellular matrix (ECM) in regulating adipocyte metabolism in the context of metabolic disease is poorly defined. Objective: The objective of this study was to define the metabolic phenotype of adipocytes associated with human diabetes (DM) and the role of the ECM in regulating adipocyte metabolism. Design: Adipose tissues from obese patients were studied in standard 2-dimensional (2D) cell culture and an in vitro model of decellularized adipose tissue ECM repopulated with human adipocytes, and results were correlated with DM status. Setting: This study was conducted at the Academic University Medical Center and Veteran’s Administration Hospital. Patients: Seventy patients with morbid obesity undergoing bariatric surgery were included in the study. Interventions: Visceral and subcutaneous adipose tissues were collected at the time of bariatric surgery. Outcome measures: This study used metabolic assays for glucose uptake, lipolysis, and lipogenesis in adipocytes in 2D cell culture and 3-dimensional ECM culture. Results: Adipocytes from subjects with DM manifest decreased glucose uptake and decreased lipolysis in 2D culture. ECM supports differentiation of mature adipocytes and recapitulates DM-specific differences in adipocyte metabolism observed in 2D culture. ECM from subjects without DM partially rescues glucose uptake and lipolytic defects in adipocytes from subjects with DM, whereas ECM from subjects with DM impairs glucose uptake in adipocytes from subjects without DM. Conclusions: DM is associated with adipocyte metabolic dysfunction. The ECM regulates adipocyte metabolism. Nondiabetic ECM rescues metabolic dysfunction in DM adipocytes, whereas DM ECM imparts features of metabolic dysfunction to nondiabetic adipocytes. These findings suggest the ECM as a target for manipulating adipose tissue metabolism., An in vitro model of adipose tissue extracellular matrix repopulated with adipocytes was used to demonstrate that the extracellular matrix regulates adipocyte metabolism in a disease-specific manner.