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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.

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.

Background Weight loss by surgery or lifestyle changes is strongly recommended for obese individuals to improve metabolic health, but the underlying impairments that persist from a history of obesity remain unclear. Recent investigations demonstrate a persistent inflammatory state with weight loss and bariatric surgery, but the mechanism and impact are not fully understood. Additionally, these studies have not been performed in females although women are the majority of individuals undergoing weight loss interventions. Methods The goal of this study was to determine the sex differences in metabolically induced inflammation after dietary weight loss (WL) or bariatric surgery. Following a 60% high-fat diet (HFD) for 12 weeks, C57Bl/6j mice underwent either a dietary switch to normal chow for WL or vertical sleeve gastrectomy (VSG) and were evaluated 8 weeks after intervention. WL effects on myelopoiesis were further evaluated with bone marrow chimeras. Results Both sexes had a decrease in adiposity and total weight following WL or VSG intervention. With HFD, females had very little inflammation and no further increase with WL, but males had persistent inflammation even after WL despite metabolic improvement. Interestingly, after VSG, myeloid inflammation was increased in the livers of males and to a lesser extent in females. Conclusions These studies demonstrate that regardless of sex, it is critical to assess an individuals’ history of obesity rather than just rely on current weight status in medical decision-making. There are long-lasting effects on tissue inflammation in both sexes especially with surgical weight loss. Dietary change is overall most effective to improve meta-inflammation in obese males on its own or in combination with surgical weight loss.

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.

Adipose tissue derived chronic inflammation is a critical component of obesity induced type II diabetes. Major histocompatibility complex II (MHCII) mediated T cell activation within adipose tissue is one mechanism that contributes to this phenotype. However, the contribution of dendritic cells as professional antigen presenting cells in adipose issue has not previously been explored. Using Itgax(Cre) x MHCII(fl/fl) (M11cKO) mice we observed adipose tissue specific changes in adipose tissue leukocytes. While there was a complete knockout of MHCII in dendritic cells, MHCII was also absent on the majority of macrophages. This resulted in reduction of TCR expression in CD4(+) T cells in obese adipose tissue, and an increase in CD8(+) and CD4(+) CD8(+) double positive T cells with decreased CD4(+) T cells independent of diet type. Increased CD8(+) cells were not observed in the spleen, suggesting adipose tissue T cell regulation is tissue specific. In vitro studies demonstrated more potent antigen presentation function in adipose tissue dendritic cells compared to macrophages. Obese M11cKO mice had decreased CD11c(+) adipose tissue macrophages. Despite the changes of immune cellularity in adipose tissue, M11cKO largely did not change inflammatory gene expression in adipose tissue and did not demonstrate differences in glucose and insulin intolerance. Overall MHCII expression on CD11c(+) cells is important for maintaining CD4(+) and CD8(+) adipose tissue T cells, but these cellular changes fail to alter inflammatory output and systemic metabolism.

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.

Objective In addition to adipocytes, adipose tissue contains large numbers of immune cells. A wide range of evidence links the activity of these cells to regulation of adipocyte and systemic metabolic function. Bariatric surgery improves several aspects of metabolic derangements and at least some of these effects occur in a weight-loss independent manner. We sought to investigate the impact of vertical sleeve gastrectomy (VSG) on adipose immune cell frequencies. Methods We analyzed the frequencies of immune cells within distinct adipose tissue depots in obese mice that had VSG or sham surgery with a portion of the latter group pair-fed such that their body mass was matched to the VSG animals. Results We demonstrate that VSG induced a shift in the epididymal adipose tissue leukocyte profile including increased frequencies of CD11c− macrophages, increased frequencies of T cells (CD4+, CD8+, and CD4−/CD8− T cells all increased), but a significantly decreased frequency of adipose tissue dendritic cells (ATDC) that, despite the continued high fat feeding of the VSG group, dropped below control diet levels. Conclusions These results indicate that VSG induces substantial changes in the immune populations residing in the adipose depots independent of weight loss., Highlights • Sleeve gastrectomy in mice altered the adipose leukocyte populations. • CD11c− macrophages were selectively upregulated independent from weight loss. • All identified T cell populations increased manifold independent from weight loss. • The dendritic cell fraction was decreased below lean control levels with surgery.

Summary An adaptive immune response triggered by obesity is characterized by the activation of adipose tissue CD4 + T cells by unclear mechanisms. We have examined whether interactions between adipose tissue macrophages (ATMs) and CD4 + T cells contribute to adipose tissue metainflammation. Intravital microscopy identifies dynamic antigen-dependent interactions between ATMs and T cells in visceral fat. Mice deficient in major histocompatibility complex class II (MHC II) showed protection from diet-induced obesity. Deletion of MHC II expression in macrophages led to an adipose tissue-specific decrease in the effector/memory CD4 + T cells, attenuation of CD11c + ATM accumulation, and improvement in glucose intolerance by increasing adipose tissue insulin sensitivity. Ablation experiments demonstrated that the maintenance of proliferating conventional T cells is dependent on signals from CD11c + ATMs in obese mice. These studies demonstrate the importance of MHCII-restricted signals from ATMs that regulate adipose tissue T cell maturation and metainflammation.

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.

The molecular mechanisms that direct the development of TCRαβ+CD8αα+ intestinal intraepithelial lymphocytes (IELs) are not thoroughly understood. Here we show that transforming growth factor-β (TGF-β) controls the development of TCRαβ+CD8αα+ IELs. Mice with either a null mutation in the gene encoding TGF-β1 or T cell-specific deletion of TGF-β receptor I lacked TCRαβ+CD8αα+ IELs, whereas mice with transgenic overexpression of TGF-β1 had a larger population of TCRαβ+CD8αα+ IELs. We observed defective development of the TCRαβ+CD8αα+ IEL thymic precursors (CD4⁻CD8⁻TCRαβ+CD5+) in the absence of TGF-β. In addition, we found that TGF-β signaling induced CD8α expression in TCRαβ+CD8αα+ IEL thymic precursors and induced and maintained CD8α expression in peripheral populations of T cells. Our data demonstrate a previously unrecognized role for TGF-β in the development of TCRαβ+CD8αα+ IELs and the expression of CD8α in T cells.

Human γδ T-cell lymphoma is a rare clinicopathologic entity with aggressive course and poor prognosis. The etiology and pathogenesis of γδ T-cell lymphoma is unknown. We show here that mice with deficiency in inhibitory helix-loop-helix protein Id3 (Id3−/−) developed γδ T-cell lymphoma that resembled human γδ T-cell lymphoma. The Id3−/− mice with lymphoma showed splenomegaly, hepatomegaly, and lymphadenopathy with involvement of bone marrow, thymus, kidney, and lungs between 6 and 15 months of age. Phenotypic analysis revealed that lymphomatous cells were cluster of differentiation (CD)3+, γδ T-cell receptor (TCR)+, and αβ TCR−, and expressed CD8+CD4−, CD4+CD8−, or a mixture of the two. Id3−/− γδ T-cell lymphoma used predominantly Vγ1.1, some Vγ3, yet no Vγ2 TCR, and some showed increased levels of the oncogene c-Myc. Strikingly, adoptive transfer of the γδ T-cell lymphoma into syngeneic Rag1−/− mice resulted in aggressive γδ T-cell lymphoma, identical to the Id3−/− donor. Thus, our data demonstrate that Id3 regulates the development of γδ T-cell lymphoma in mice, raising a possibility of Id3 gene mutation in human γδ T-cell lymphoma. Our model will provide a tool for studying the molecular mechanisms and development of human γδ T-cell lymphoma.

The search for effective treatments for obesity and its comorbidities is of prime importance. We previously identified IKK-ε and TBK1 as promising therapeutic targets for the treatment of obesity and associated insulin resistance. Here we show that acute inhibition of IKK-ε and TBK1 with amlexanox treatment increases cAMP levels in subcutaneous adipose depots of obese mice, promoting the synthesis and secretion of the cytokine IL-6 from adipocytes and preadipocytes, but not from macrophages. IL-6, in turn, stimulates the phosphorylation of hepatic Stat3 to suppress expression of genes involved in gluconeogenesis, in the process improving glucose handling in obese mice. Preliminary data in a small cohort of obese patients show a similar association. These data support an important role for a subcutaneous adipose tissue–liver axis in mediating the acute metabolic benefits of amlexanox on glucose metabolism, and point to a new therapeutic pathway for type 2 diabetes., The drug amlexanox is known to improve obesity-related metabolic dysfunction in mice. Here the authors show that this effect is mediated by interleukin-6 secreted from subcutaneous adipocytes, which then inhibits gluconeogenesis in the liver by phosphorylating the hepatic transcription factor Stat3.

Obesity is associated with an activated macrophage phenotype in multiple tissues that contributes to tissue inflammation and metabolic disease. To evaluate the mechanisms by which obesity potentiates myeloid activation, we evaluated the hypothesis that obesity activates myeloid cell production from bone marrow progenitors to potentiate inflammatory responses in metabolic tissues. High fat diet-induced obesity generated both quantitative increases in myeloid progenitors as well as a potentiation of inflammation in macrophages derived from these progenitors. In vivo, hematopoietic stem cells from obese mice demonstrated the sustained capacity to preferentially generate inflammatory CD11c(+) adipose tissue macrophages after serial bone marrow transplantation. We identified that hematopoietic MyD88 was important for the accumulation of CD11c(+) adipose tissue macrophage accumulation by regulating the generation of myeloid progenitors from HSCs. These findings demonstrate that obesity and metabolic signals potentiate leukocyte production and that dietary priming of hematopoietic progenitors contributes to adipose tissue inflammation.

Poly (ADP-ribose) polymerase-1 (PARP-1) is a nuclear enzyme and transcription factor that is involved in inflammatory response, but its role in T cell response remains largely unknown. We show here that PARP-1 regulates the suppressive function of CD4(+)CD25(+)Foxp3(+) regulatory T cells (Tregs). Specifically, Tregs in mice with a null mutation of the PARP-1 gene (PARP-1(-/-)) showed significantly stronger suppressive activity than did wild-type Tregs in culture. We elucidate that this enhanced suppressive function is attributed to sustained higher expression of Foxp3 and CD25 in PARP-1(-/-) Tregs. Furthermore, in PARP-1(-/-) Tregs, Foxp3 protein shows substantially higher levels of binding to the conserved non-coding DNA sequence 2 (CNS2) at the foxp3 gene, a region important in maintaining Foxp3 gene expression in Tregs. Thus, our data reveal a role for PARP-1 in controlling the function of Tregs through modulation of the stable expression of Foxp3.

Obesity causes dramatic changes to the adipose tissue immune environment including the recruitment and activation of macrophages. The inflammatory polarization of these cells is thought to play a critical role in the severity of insulin resistance associated with obesity. Weight loss can improve insulin resistance, but little is known concerning the effects of weight loss on immune activity in adipose. Diet switch from a 60% high-fat diet to 13% normal-fat diet was used to induce weight loss in diet-induced obese C57Bl/6 mice. Adipose tissue structural changes were evaluated by histology. Leukocyte populations were analyzed by flow cytometry, including sorting and comparing cytokine expression of adipose tissue macrophages before and after weight loss. Weight loss improved glucose tolerance and reduced serum insulin. However, extensive adipose fibrosis developed during weight loss and was associated with macrophage accumulation. Analysis of adipose macrophages after weight loss showed they retained an inflammatory gene expression profile similar to those found during obesity. These macrophages were derived primarily from older cells present during obesity. These macrophages were maintained though high proliferation and low apoptosis. The data indicate that inflammatory activation of adipose macrophages is not sufficient for whole body metabolic dysfunction, but the retained macrophages may promote adipose tissue fibrosis while impacting adipocyte health and function.

Induction of Foxp3 gene expression and acquisition of regulatory T cell fate is, understandably, a highly controlled process and one which many investigators want to illuminate. In studying the regulation of Foxp3 gene expression, several conserved non-coding regions have been identified and the role of various transcription factors at these sites has been explored. What emerges is that many factors, some positive, some negative, interact to collectively drive Foxp3 gene expression and then maintain its expression in Foxp3(+) regulatory T cells. TCR signaling is imperative for Foxp3 gene expression and TGF-β is a key cytokine for initiating Foxp3 gene expression in naive T cells. But other signaling pathways are also known to play a role in properly orchestrating Foxp3 gene expression and regulatory T cell expansion. Here we review the recent progress in understanding the complex molecular events that drive Foxp3 gene expression and allow functional regulatory T cells to develop.

The molecular mechanisms that direct transcription of the gene encoding the transcription factor Foxp3 in CD4(+) T cells remain ill-defined. We show here that deletion of the DNA-binding inhibitor Id3 resulted in the defective generation of Foxp3(+) regulatory T cells (T(reg) cells). We identify two transforming growth factor-β1 (TGF-β1)-dependent mechanisms that were vital for activation of Foxp3 transcription and were defective in Id3(-/-) CD4(+) T cells. Enhanced binding of the transcription factor E2A to the Foxp3 promoter promoted Foxp3 transcription. Id3 was required for relief of inhibition by the transcription factor GATA-3 at the Foxp3 promoter. Furthermore, Id3(-/-) T cells showed greater differentiation into the T(H)17 subset of helper T cells in vitro and in a mouse asthma model. Therefore, a network of factors acts in a TGF-β-dependent manner to control Foxp3 expression and inhibit the development of T(H)17 cells.