Emerging role of adipose tissue hypoxia in obesity and insulin resistance. Int J Obes (Lond). 2009;33:54-66. [PMID: 19050672 DOI: 10.1038/ijo.2008.229]

Pediatric sleep-disordered breathing: New evidence on its development

Sleep-disordered breathing (SDB) in children could be resolved by adenotonsillectomy (T&A). However, incomplete results are often noted post-surgery. Because of this partial resolution, long-term follow-up is needed to monitor for reoccurrence of SDB, which may be diagnosed years later through reoccurrence of complaints or in some cases, through systematic investigations. Children undergoing T&A often have small upper airways. Genetics play a role in the fetal development of the skull, the skull base, and subsequently, the size of the upper airway. In non-syndromic children, specific genetic mutations are often unrecognized early in life and affect the craniofacial growth, altering functions such as suction, mastication, swallowing, and nasal breathing. These developmental and functional changes are associated with the development of SDB. Children without genetic mutations but with impairment of the above said functions also develop SDB. When applied early in life, techniques involved in the reeducation of these functions, such as myofunctional therapy, alter the craniofacial growth and the associated SDB. This occurs as a result of the continuous interaction between cartilages, bones and muscles involved in the growth of the base of the skull and the face. Recently collected data show the impact of the early changes in craniofacial growth patterns and how these changes lead to an impairment of the developmental functions and consequent persistence of SDB. The presence of nasal disuse and mouth breathing are abnormal functions that are easily amenable to treatment. Understanding the dynamics leading to the development of SDB and recognizing factors affecting the craniofacial growth and the resulting functional impairments, allows appropriate treatment planning which may or may not include T&A. Enlargement of lymphoid tissue may actually be a consequence as opposed to a cause of these initial dysfunctions.

Oxygen sensing and metabolic homeostasis

Oxygen-sensing mechanisms have evolved to maintain cell and tissue homeostasis since the ability to sense and respond to changes in oxygen is essential for survival. The primary site of oxygen sensing occurs at the level of the carotid body which in response to hypoxia signals increased ventilation without the need for new protein synthesis. Chronic hypoxia activates cellular sensing mechanisms which lead to protein synthesis designed to alter cellular metabolism so cells can adapt to the low oxygen environment without suffering toxicity. The master regulator of the cellular response is hypoxia-inducible factor (HIF). Activation of this system under condition of hypobaric hypoxia leads to weight loss accompanied by increased basal metabolic rate and suppression of appetite. These effects are dose dependent, gender and genetic specific, and results in adverse effects if the exposure is extreme. Hypoxic adipose tissue may represent a unified cellular mechanism for variety of metabolic disorders, and insulin resistance in patients with metabolic syndrome.

The role of reactive oxygen species in obesity therapeutics

Obesity is a major risk factor for multiple severe health conditions, including cardiovascular diseases, diabetes and cancer. It is often related to an increased risk of morbidity and mortality and, as it can be accompanied by non-fatal health problems, quality of life is seriously reduced due to related conditions including hypertension, sleep apnea, osteoarthritis, respiratory problems and infertility. Evidence suggests that oxidative stress is related to obesity and its complications. In obese patients, there is an increase in levels of reactive oxygen species and nitrogen species and antioxidant defenses are undermined in comparison to normal-weight counterparts. In addition, these parameters inversely correlate with central adiposity. In this review, the authors discuss current concepts concerning the relationship between obesity and oxidative stress and mitochondrial impairment. Potential interventions to improve redox balance are also explored.

Estrogen signaling in metabolic inflammation

There is extensive evidence supporting the interference of inflammatory activation with metabolism. Obesity, mainly visceral obesity, is associated with a low-grade inflammatory state, triggered by metabolic surplus where specialized metabolic cells such as adipocytes activate cellular stress initiating and sustaining the inflammatory program. The increasing prevalence of obesity, resulting in increased cardiometabolic risk and precipitating illness such as cardiovascular disease, type 2 diabetes, fatty liver, cirrhosis, and certain types of cancer, constitutes a good example of this association. The metabolic actions of estrogens have been studied extensively and there is also accumulating evidence that estrogens influence immune processes. However, the connection between these two fields of estrogen actions has been underacknowledged since little attention has been drawn towards the possible action of estrogens on the modulation of metabolism through their anti-inflammatory properties. In the present paper, we summarize knowledge on the modification inflammatory processes by estrogens with impact on metabolism and highlight major research questions on the field. Understanding the regulation of metabolic inflammation by estrogens may provide the basis for the development of therapeutic strategies to the management of metabolic dysfunctions.

15-LOX metabolites and angiogenesis: angiostatic effect of 15(S)-HPETE involves induction of apoptosis in adipose endothelial cells

Inflammation is critical in the dysregulated growth of adipose tissue and associated vascular dysfunctions. 15-Lipoxygenase metabolites, important mediators of inflammation in adipose tissue during obese conditions, may contribute to codependence of inflammation and angiogenesis in adipose tissue. We have already reported the pro-angiogenic effect of 15(S)-HETE in adipose tissue. The present study was designed to understand the effect of 15(S)-HPETE, precursor of 15(S)-HETE, on angiogenesis in adipose tissue. Results showed that 15(S)-HPETE exerts an anti-angiogenic effect in adipose tissue. This was evidenced from decreased endothelial sprouting in adipose tissue explants, inhibition of angiogenic phenotype in adipose endothelial cells, decreased production of CD31 and VEGF in endothelial cells treated with 15(S)-HPETE. Further studies to examine the molecular mechanism of anti-angiogenic effect of 15(S)-HPETE showed that it inhibited cell survival signaling molecule Akt and anti-apoptotic Bcl-2 and also activated caspase-3 in adipose endothelial cells. These observations indicate that 15(S)-HPETE exerts its angiostatic effect in adipose tissue by inducing apoptosis of endothelial cells.

Role of NKG2D in obesity-induced adipose tissue inflammation and insulin resistance

The early events that initiate inflammation in the adipose tissue during obesity are not well defined. It is unclear whether the recruitment of CD8 T cells to the adipose tissue during onset of obesity occurs through antigen-dependent or -independent processes. We have previously shown that interaction between NKG2D (natural-killer group 2, member D) and its ligand Rae-1ε is sufficient to recruit cytotoxic T lymphocytes to the pancreas and induce insulitis. Here, we tested whether NKG2D–NKG2D ligand interaction is also involved in obesity-induced adipose tissue inflammation and insulin resistance. We observed a significant induction of NKG2D ligand expression in the adipose tissue of obese mice, especially during the early stages of obesity. However, mice lacking NKG2D developed similar levels of insulin resistance and adipose tissue inflammation compared to control mice when placed on a high-fat diet. Moreover, overexpression of Rae-1ε in the adipose tissue did not increase immune cell infiltration to the adipose tissue either in the setting of a normal or high-fat diet. These results indicate that, unlike in the pancreas, NKG2D–NKG2D ligand interaction does not play a critical role in obesity-induced inflammation in the adipose tissue.

Six-month intragastric balloon treatment for obesity improves lung function, body composition, and metabolic syndrome

BACKGROUND

The purpose of this study is to establish whether the use of an intragastric balloon (IGB) for 6 months improves lung function, metabolic parameters, and body fat distribution in patients with overweight/obesity and metabolic syndrome (MS).

METHODS

This is a longitudinal and interventional study on 40 adults, whose anthropometric, laboratory, and lung function parameters were assessed and who underwent dual-energy X-ray absorptiometry (DXA) before implantation and after removal of IGB.

RESULTS

The total lung capacity (TLC) (p = 0.0001), functional residual capacity (FRC) (p = 0.0001), residual volume (p = 0.0005), and expiratory reserve volume (ERV) (p = 0.0001) were significantly reduced by IGB. The body mass index (BMI) significantly decreased from a median of 39.1 kg/m(2) at the beginning of the study to 34.5 kg/m(2) at the end of the 6-month period (p = 0.0001). At the end of the study, 31 participants (77.5%) no longer met the diagnostic criteria of MS. The percentage of truncal, android, gynoid, and total fat investigated by DXA exhibited significant reductions (p = 0.0001). Significant correlations were found between delta TLC and delta waist circumference (ρ = -0.34; p = 0.03), delta FRC and delta IMC (ρ = -0.39; p = 0.01), delta ERV and delta BMI (ρ = -0.44; p = 0.005), and delta ERV and delta high-density lipoprotein (HDL) (ρ = -0.37; p = 0.02). Significant correlations were also found between delta ERV and delta truncal (ρ = -0.51; p = 0.004), android (ρ = -0.46; p = 0.01), gynoid (ρ = -0.55; p = 0.001), and total fat (ρ = -0.59; p = 0.0005).

CONCLUSIONS

IGB efficiently induced weight loss and promoted the improvement of lung function parameters, with a reduction of the restrictive ventilatory defect. It also promoted improvements of MS and the pattern of body fat distribution.

Moderate exercise training provides modest protection against adipose tissue inflammatory gene expression in response to high-fat feeding

As white adipose tissue (WAT) expands under obesogenic conditions, local WAT hypoxia may contribute to the chronic low-grade inflammation observed in obesity. Aerobic exercise training is beneficial in treating WAT inflammation after obesity is established, but it remains unknown whether exercise training, while on a concomitant high-fat (HF) diet, influences WAT inflammation during the development of obesity. We sought to determine the effects of 4, 8, and 12 weeks of HF feeding and/or moderate intensity treadmill exercise training (EX) on the relationship between inflammatory and hypoxic gene expression within mouse WAT. Male C57Bl6/J mice (n = 113) were randomized into low-fat (LF)/sedentary (SED), LF/EX, HF/SED, or HF/EX groups. The low-fat and high-fat diets contained 10% and 60% energy from fat, respectively. Exercise training consisted of treadmill running 5 days/week at 12 m/min, 8% incline, 40 min/day. Quantitative real-time PCR was used to assess gene expression. HF diet impaired glucose regulation, and upregulated WAT gene expression of inflammation (IL-1β, IL-1ra, TNFα), macrophage recruitment and infiltration (F4/80 and monocyte chemoattractant protein), and M1 (CD11c) and M2 (CD206 and Arginase-1) macrophage polarization markers. Treadmill training resulted in a modest reduction of WAT macrophage and inflammatory gene expression. HF diet had little effect on hypoxia-inducible factor-1α and vascular endothelial growth factor, suggesting that WAT inflammatory gene expression may not be driven by hypoxia within the adipocytes. Treadmill training may provide protection by preventing WAT expansion and macrophage recruitment.

Central fat accumulation associated with metabolic risks beyond total fat in normal BMI Chinese adults

OBJECTIVE

To investigate the association of central fat with metabolic risks in normal BMI Chinese people.

METHODS

Normal BMI subjects (18.5 ≤ BMI < 24, n = 520) aged 18-82 years were included. Blood pressure, triglycerides, high-density lipoprotein cholesterol and fasting plasma glucose were collected as metabolic risk factors. Dual-energy X-ray absorptiometry was used to measure total and central fat. Central fat was indicated as percent trunk fat (%TF) and android/gynoid fat ratio. Multiple adjusted regression models were applied to investigate the association of total and central fat with metabolic risk factors. The assessment values of these fat measures were further compared by receiver-operating characteristic (ROC) curves.

RESULTS

Both total and central fat were correlated with metabolic risk factors. After adjusting for BMI, the significant association of percent body fat (%BF) with metabolic risks diminished, whereas %TF and android/gynoid fat ratio were still correlated. When BMI was replaced with %BF in the models, the results remained unchanged. ROC analysis showed the areas under the curve (AUCs) of total and central fat for at least two metabolic risk factors were comparable in men. However, in women, the AUCs of %TF and android/gynoid fat ratio were significantly greater than those of BMI, %BF and waist circumference.

CONCLUSIONS

Central fat accumulation had a stronger association with metabolic risks than total fat in normal BMI Chinese adults, particularly in women. Central fat had more important implications in assessing 'metabolically obese' individuals among normal BMI subjects.

Markers of endothelial cell dysfunction are increased in human omental adipose tissue from women with pre-existing maternal obesity and gestational diabetes

OBJECTIVE

To determine the effect of maternal obesity and gestational diabetes mellitus (GDM) on the expression and release of genes involved in endothelial cell dysfunction in human placenta and omental adipose tissue.

MATERIALS/METHODS

Human placenta and omental adipose tissue were obtained from non-obese and obese normal glucose tolerant (NGT) women and women with GDM at the time of Caesarean section. Quantitative RT-PCR was performed to determine the level of expression. Tissue explants were performed to determine the release of proteins of interest.

RESULTS

There was no effect of pre-existing maternal obesity or GDM on placental gene expression or secretion of members of the VEGF family members (PLGF and VEGF-A expression and secretion; sFlt-1 release; VEGFR1 and VEGFR2 mRNA expression); FGFR1 mRNA expression, FGF2 mRNA expression and secretion; endoglin mRNA expression and secretion (sEng); and the adhesion molecules ICAM-1 and VCAM-1. On the other hand, in omental adipose tissue, pre-existing maternal obesity and GDM were associated with increased gene expression of PLGF, endoglin and ICAM-1 and increased secretion of PLGF, sFlt-1, FGF2, sEng and sICAM-1. There was, however, no effect of maternal pre-existing obesity and GDM on VEGF-A, VEGFR1, VEGFR2, FGFR1 and VCAM-1 expression or secretion.

CONCLUSIONS

This study demonstrated the presence of abnormal expression and secretion of angiogenic proteins and adhesion molecules in omental adipose tissue, but not placenta, from pregnant women with GDM and pre-existing maternal obesity. Increased angiogenic and adhesion molecules released from adipose tissue may affect angiogenesis, inflammation and or lipid and glucose metabolism in both mum and her offspring.

High-salt intake induced visceral adipose tissue hypoxia and its association with circulating monocyte subsets in humans

OBJECTIVE

To investigate the feasibility of blood oxygen level dependent magnetic resonance imaging (BOLD-MRI) in evaluating human visceral adipose tissue (AT) oxygenation induced by salt loading/depletion and its association with changes in circulating monocyte subsets.

METHODS

A dietary intervention study was performed in 23 healthy volunteers beginning with a 3-day usual diet followed by a 7-day high-salt diet (≥15 g NaCl/day) and a 7-day low-salt diet (≤5 g NaCl/day). BOLD-MRI was used to evaluate oxygenation in perirenal AT.

RESULTS

Salt loading led to a consistent AT hypoxia (increase in the R2* signal, 25.2 ± 0.90 s(-1) vs. baseline 21.5 ± 0.71 s(-1) , P < 0.001) and suppression of circulating renin-angiotensin-aldosterone system (RAAS), as well as an expansion of the CD14++CD16+ monocytes and monocyte pro-inflammatory activation. In salt depletion phase, the hypoxic state of AT and the expanded CD14++CD16+ monocyte pool were regressed to baseline levels, accompanied by a rebound activation of RAAS. Moreover, AT oxygenation level was positively correlated with the CD14++CD16+ monocytes (r = 0.419, P < 0.001).

CONCLUSIONS

This work provides proof-of-principle evidence supporting the feasibility of BOLD-MRI in monitoring visceral AT oxygenation in humans induced by dietary salt loading/depletion. In addition, the CD14++CD16+ monocytes may participate in the pathogenesis of high-salt intake induced AT hypoxia.

Biphasic response of mitochondrial biogenesis to oxidative stress in visceral fat of diet-induced obesity mice

AIMS

Studies in skeletal muscle demonstrate a strong association of mitochondrial dysfunction with insulin resistance (IR). However, there is still a paucity of knowledge regarding the alteration of mitochondria in adipose tissue (AT) in the pathogenesis of IR in obesity. We investigated the mitochondrial biogenesis in visceral fat (VF) and subcutaneous fat (SF) in C57BL/6J mice fed a high-fat high-sucrose diet for 12 months.

RESULTS

Impairment of glucose tolerance and insulin sensitivity developed after 1 month of the diet and was associated with a prompt increase of VF. The VF adipocytes were larger than those in the SF and had increased expressions of HIF-1α and p-NFκB p65. However, the alteration of mitochondrial biogenesis did not occur in the early stage when increased intracellular reactive oxygen species (ROS), mitochondrial oxygen consumption rate, and mitochondrial ROS emerged at the 1st, 2nd and 2nd month, respectively. Until the 6th month, the VF had markedly increased mitochondrial DNA content and expression of PGC-1α, Tfam, ATP5A, and MnSOD. This increase of mitochondrial biogenesis was followed by a generalized decrease at the 12th month and the mitochondrial morphology altered markedly. In the late stage, although mitochondrial ROS decreased, the increased expression of 8-OHdG in VF continued.

INNOVATION AND CONCLUSION

These data suggest that IR and ROS production occur before the biphasic changes of mitochondrial biogenesis in AT, and the VF plays a more crucial role.

Targeting inflammation in the treatment of type 2 diabetes: time to start

The role of inflammation in the pathogenesis of type 2 diabetes and associated complications is now well established. Several conditions that are driven by inflammatory processes are also associated with diabetes, including rheumatoid arthritis, gout, psoriasis and Crohn's disease, and various anti-inflammatory drugs have been approved or are in late stages of development for the treatment of these conditions. This review discusses the rationale for the use of some of these anti-inflammatory treatments in patients with diabetes and what we could expect from their use. Future immunomodulatory treatments may not target a specific disease, but could instead act on a dysfunctional pathway that causes several conditions associated with the metabolic syndrome.

Hyperactivated Signaling Pathways of Chemokine RANTES/CCL5 in Osteopathies of Jawbone in Breast Cancer Patients-Case Report and Research

BACKGROUND

Hollow spaces in the jawbone have been defined as fatty degenerative osteonecrosis of jawbone (FDOJ) and have been linked with a dysregulated immune system. Little is known about the underlying relationship.

OBJECTIVES

Samples of FDOJ were analyzed to assess expression of cytokines which can play a role in the pathogenesis of breast cancer (MaCa).

MATERIAL AND METHODS

Samples of FDOJ extracted from 23 patients with MaCa and 19 healthy control jawbone samples were analyzed for 7 immune messengers.

RESULTS

RANTES was found to be highly overexpressed in disease samples. No change was observed in expression levels of the other immune mediators.

DISCUSSION

This data provides a compelling confirmation that FDOJ produces high levels of RANTES, a cytokine implicated in MaCa and metastasis. Levels detected in FDOJ are five-fold higher than that previously reported for MaCa tissue suggesting its role as a cytokine source in MaCa.

CONCLUSION

We thus hypothesize that FDOJ may serve as an expeditor of MaCa progression, through RANTES production.

Obstructive Sleep Apnea Syndrome (OSAS), metabolic syndrome and mental health in small enterprise workers. feasibility of an Action for Health

Objective

To determine the frequency of obstructive sleep apnea syndrome (OSAS), metabolic syndrome and common mental disorders in the working population of 11 small enterprises and the feasibility of a program of action for health.

Method

The clinical risk of OSAS, the prevalence of metabolic syndrome, and the level of psychological disorders were assessed during routine medical examination at the workplace in 2012. The response to medical advice was assessed in 2013.

Results

12.3% of the workers were suspected of being affected by OSAS. One or more components of metabolic syndrome were present in 24.5% of cases. OSAS in “healthy” workers was significantly associated with the presence of one or more components of metabolic syndrome (OR = 3.83; 95%CI 1.45–10.13) and with a psychological disorders score in the highest quartile (OR = 4.67; 95%CI = 1.72–12.64). Workers with suspected OSAS were reluctant to follow advice about undergoing further tests under the NHS. However, in some cases, confirmation of the OSAS diagnosis and subsequent treatment led to an improvement in metabolic condition.

Conclusion

Although participation in treatment was limited, anecdotal cases support the idea that prevention of obstructive sleep apnea in the workplace might be useful for workers’ health.

Proteasomal degradation of O-GlcNAc transferase elevates hypoxia-induced vascular endothelial inflammatory response†

AIMS

Hypoxia induces vascular inflammation by a mechanism not fully understood. Emerging evidence implicates O-GlcNAc transferase (OGT) in inflammation. This study explored the role of OGT in hypoxia-induced vascular endothelial inflammatory response.

METHODS AND RESULTS

Hypoxia was either induced (1% O2 chamber) or mimicked by exposure to hypoxia-mimetic agents in cultured endothelial cells. Hypoxia increased hypoxia-inducible factor (HIF-1α) and inflammatory response (gene and protein expression of interleukin (IL)-6, IL-8, monocyte chemoattractant protein-1, and E-selectin) but, surprisingly, reduced OGT protein (not mRNA) levels. Hypoxia-mimetic CoCl2 failed to reduce OGT when proteasome inhibitors were present, suggesting proteasome involvement. Indeed, CoCl2 enhanced 26S proteasome functionality evidenced by diminished reporter (Ub(G76V)-GFP) proteins in proteasome reporter cells, likely due to increased chymotrypsin-like activities. Mechanistically, β-TrCP1 mediated OGT degradation, since siRNA ablation of this E3 ubiquitin ligase stabilized OGT. Administration of the oxidative stress inhibitors reversed both proteasome activation and OGT degradation. Furthermore, up-regulation of OGT by stabilization, overexpression, or activation mitigated CoCl2-elicited inflammatory response. These observations were recapitulated in a mouse (C57BL/6J) model mimicking hypoxia, in which lung tissues presented higher levels of HIF-1α, proteasome activity, and inflammatory response, but lower levels of OGT (n = 5/group, hypoxia vs. normoxia, P < 0.05). However, administration of an activator of OGT (glucosamine: 1 mg/g/day, vehicle: saline, ip, 5 days) abolished the up-regulation of proteasome activity and inflammatory response (n = 5/group, the treated vs. untreated hypoxia groups, P < 0.05).

CONCLUSIONS

26S proteasome-mediated OGT reduction contributed to hypoxia-induced vascular endothelial inflammatory response. Modulation of OGT may represent a new approach to treat diseases characterized by hypoxic inflammation.

Hypoxia increases serum amyloid A3 (SAA3) in differentiated 3T3-L1 adipocytes

Hypoxia has been implicated as a possible cause of adipose tissue inflammation. Furthermore, the acute phase protein serum amyloid A (SAA) has been associated with the modulation of the adipogenic process, and it is well-known that obese individuals have increased levels of SAA. The effect of hypoxia in the expression and production of SAA was examined in murine 3T3-L1 adipocytes. Hypoxia leads to a substantial increase in SAA3 mRNA and protein level, apparently in a time-dependent manner (threefold in 48 h), in fully differentiated 3T3-L1, followed by reestablishment of gene expression to basal levels after 24 h of reoxygenation. Hypoxia-induced SAA may be one of the key molecules to the development of the inflammatory response in adipose tissue.

Regulation of hepatocyte growth factor expression by NF-κB and PPARγ in adipose tissue

Hepatocyte growth factor (HGF) is expressed as an angiogenic factor in adipose tissue. However, the molecular mechanism of Hgf expression remains largely unknown in the tissue. We addressed the issue by studying Hgf expression in adipocytes and macrophages. Hgf was expressed more in the stromal-vascular fraction than the adipocyte fraction. The expression was fivefold more in macrophages than the stromal-vascular faction and was reduced by 50% after macrophage deletion in adipose tissue. The expression was reduced by differentiation in adipocytes and by tumor necrosis factor-α or lipopolysaccharide treatment in macrophages. The expression was suppressed by nuclear factor (NF)-κB in C57BL/6 mice with NF-κB p65 overexpression under the aP2 gene promoter (aP2-p65 mice) but enhanced by inactivation of NF-κB p65 in mouse embryonic fibroblasts. The Hgf gene promoter was suppressed by p65 overexpression, which blocked peroxisome proliferator-activated receptor-γ (PPARγ) interaction with RNA polymerase II. The p65 activity was abolished by knockdown of histone deacetylase 3. Hgf expression was upregulated by hypoxia in vitro and in vivo. Compared with vascular endothelial growth factor (Vegf), which was predominately expressed in mature adipocytes, Hgf was mainly expressed in nonadipocytes, suggesting that Hgf and Vegf may have different cell sources in adipose tissue. In mechanism, Hgf expression is inhibited by NF-κB through suppression of PPARγ function in the Hgf gene promoter. Both Hgf and Vegf are induced by hypoxia. The study provides a molecular mechanism for the difference of inflammation and hypoxia in the regulation of angiogenic factors.

Circulating sCD36 is associated with unhealthy fat distribution and elevated circulating triglycerides in morbidly obese individuals

Background:

The recently identified circulating sCD36 has been proposed to reflect tissue CD36 expression, and is upregulated in case of obesity, insulin resistance and hepatic steatosis. The aim of this study was to explore the effect of weight loss secondary to bariatric surgery in relation to sCD36 among morbidly obese individuals. Furthermore, we investigated the levels of sCD36 in relation to obesity-related metabolic complications, low-grade inflammation and fat distribution.

Methods:

Twenty morbidly obese individuals (body mass index (BMI) 43.0±5.4 kg m⁻²) with a referral to Roux-en-Y gastric bypass were included. Anthropometric measurements and fasting blood samples were collected at a preoperative baseline visit and 3 months after surgery. sCD36 was measured by an in-house assay, whereas insulin sensitivity and the hepatic fat accumulation were estimated by the homeostasis model assessment (HOMA-%S) and liver fat percentage (LF%), respectively.

Results:

Postoperatively, BMI was reduced by 20% to 34.3±5.2 kg m⁻² (P<0.001). sCD36 was reduced by 31% (P=0.001) and improvements were observed in the amount of fat mass (P<0.001), truncal fat mass (P<0.001), circulating triglycerides (P=0.001), HOMA-%S (P=0.007), LF% (P=0.001) and the inflammatory marker high-sensitive C-reactive protein (P=0.005). sCD36 correlated with triglycerides (ρ=0.523, P=0.001) and truncal fat mass (ρ=0.357, P=0.026), and triglycerides were found to be an independent predictor of sCD36. At baseline, participants with the metabolic syndrome had a higher LF% and higher levels of the inflammatory biomarker YKL-40 (P=0.003 and P=0.014) as well as a tendency towards higher levels of sCD36.

Conclusion:

sCD36 was reduced by weight loss and associated with an unhealthy fat accumulation and circulating triglycerides, which support the proposed role of sCD36 as a biochemical marker of obesity-related metabolic complications and risks.

Effects of exercise training on indicators of adipose tissue angiogenesis and hypoxia in obese rats

OBJECTIVE

To investigate the effects of obesity and exercise training on regional adipose tissue angiogenesis and hypoxia markers in rats.

METHODS

Lean (Fa/Fa) and obese (fa/fa) male Zucker rats at 2 months of age were randomly assigned to a sedentary or an exercise training group (lean sedentary: n=7, lean exercise: n=8, obese sedentary: n=7, obese exercise: n=8). The exercise group walked on a rat treadmill 5 times per week for 8 weeks. Inguinal and epididymal adipose tissue vascular endothelial growth factor A (VEGF-A) and lactate levels were determined.

RESULTS

There were significant effects of obesity in increasing inguinal (P<0.001) and epididymal (P<0.05) adipose tissue VEGF-A, and a significant effect of exercise training in increasing epididymal adipose tissue VEGF-A (P<0.05). There was a significant effect of obesity in increasing inguinal adipose tissue lactate levels (P<0.001). Compared to lean sedentary animals, obese sedentary animals had significantly higher epididymal adipose tissue lactate levels (P<0.001); compared to obese sedentary animals, obese exercise rats had significantly lower epididymal adipose tissue lactate levels (P<0.05).

CONCLUSIONS

Exercise training increased adipose tissue VEGF-A, an important factor of tissue angiogenesis, and lowered adipose tissue lactate, an indicator of adipose tissue hypoxia in obese rats. However, these effects are depot-specific and only observed in intra-abdominal adipose tissue.

Effects of LPS and dietary free fatty acids on MCP-1 in 3T3-L1 adipocytes and macrophages in vitro

BACKGROUND

High levels of free fatty acids (FFA) have been suggested to be one of the underlying mechanisms for adipose tissue (AT) inflammation and dysfunction in obesity. Human AT produces several adipokines including monocyte chemoattractant protein-1 (MCP-1), which are involved in the pathogenesis of obesity-mediated inflammation.

OBJECTIVE

In this study, we investigated the effects of lipopolysaccharide (LPS) and a panel of dietary FFA on MCP-1 gene and protein expression in adipocytes and macrophages. Furthermore, we investigated whether the effect of LPS and FFA were mediated through the toll-like receptor 4 (TLR4).

METHODS

3T3-L1 adipocytes and THP-1 macrophages were incubated for 24 h with the following FFA: monounsaturated fatty acid (oleic acid), saturated fatty acid (palmitic acid) and trans fatty acid (elaidic acid; 500 μM) with and without LPS (2 ng ml(-1)), and MCP-1 and TLR4 mRNA expression and MCP-1 protein secretion was determined.

RESULTS

The results showed that LPS significantly increased MCP-1 and TLR4 expression and MCP-1 secretion in 3T3-L1 adipocytes, and that the MCP-1 expression was blocked by a TLR4 inhibitor (CLI095). The effects of the various FFA on MCP-1 mRNA expression and protein secretion in the adipocytes showed no significant changes either alone or in combination with LPS. In macrophages, palmitic acid increased MCP-1 mRNA expression by 1.8-fold (P<0.05), but oleic acid and elaidic acid had no effects.

CONCLUSIONS

In conclusion, in 3T3-L1 adipocyte, the TLR4-agonist, LPS, stimulates the proinflammatory chemokine MCP-1. The different classes of FFA did not induce MCP-1 mRNA expression or protein secretion in the adipocytes, but the saturated FFA, palmitic acid, induced MCP-1 mRNA expression in macrophages, possibly because of the higher expression level of TLR4 in the macrophages than the adipocytes. Our results indicate that FFA may induce AT inflammation through proinflammatory stimulation of macrophages.

Unique transcriptomic signature of omental adipose tissue in Ossabaw swine: a model of childhood obesity

To better understand the impact of childhood obesity on intra-abdominal adipose tissue phenotype, a complete transcriptomic analysis using deep RNA-sequencing (RNA-seq) was performed on omental adipose tissue (OMAT) obtained from lean and Western diet-induced obese juvenile Ossabaw swine. Obese animals had 88% greater body mass, 49% greater body fat content, and a 60% increase in OMAT adipocyte area (all P < 0.05) compared with lean pigs. RNA-seq revealed a 37% increase in the total transcript number in the OMAT of obese pigs. Ingenuity Pathway Analysis showed transcripts in obese OMAT were primarily enriched in the following categories: 1) development, 2) cellular function and maintenance, and 3) connective tissue development and function, while transcripts associated with RNA posttranslational modification, lipid metabolism, and small molecule biochemistry were reduced. DAVID and Gene Ontology analyses showed that many of the classically recognized gene pathways associated with adipose tissue dysfunction in obese adults including hypoxia, inflammation, angiogenesis were not altered in OMAT in our model. The current study indicates that obesity in juvenile Ossabaw swine is characterized by increases in overall OMAT transcript number and provides novel data describing early transcriptomic alterations that occur in response to excess caloric intake in visceral adipose tissue in a pig model of childhood obesity.

IL-6 regulates adipose deposition and homeostasis in lymphedema

Lymphedema (LE) is a morbid disease characterized by chronic limb swelling and adipose deposition. Although it is clear that lymphatic injury is necessary for this pathology, the mechanisms that underlie lymphedema remain unknown. IL-6 is a known regulator of adipose homeostasis in obesity and has been shown to be increased in primary and secondary models of lymphedema. Therefore, the purpose of this study was to determine the role of IL-6 in adipose deposition in lymphedema. The expression of IL-6 was analyzed in clinical tissue specimens and serum from patients with or without LE, as well as in two mouse models of lymphatic injury. In addition, we analyzed IL-6 expression/adipose deposition in mice deficient in CD4(+) cells (CD4KO) or IL-6 expression (IL-6KO) or mice treated with a small molecule inhibitor of IL-6 or CD4 depleting antibodies to determine how IL-6 expression is regulated and the effect of changes in IL-6 expression on adipose deposition after lymphatic injury. Patients with LE and mice treated with lymphatic excision of the tail had significantly elevated tissue and serum expression of IL-6 and its downstream mediator. The expression of IL-6 was associated with adipose deposition and CD4(+) inflammation and was markedly decreased in CD4KO mice. Loss of IL-6 function resulted in significantly increased adipose deposition after tail lymphatic injury. Our findings suggest that IL-6 is increased as a result of adipose deposition and CD4(+) cell inflammation in lymphedema. In addition, our study suggests that IL-6 expression in lymphedema acts to limit adipose accumulation.

Negative regulation of Hif1a expression and TH17 differentiation by the hypoxia-regulated microRNA miR-210

MicroRNA-210 (miR-210) is a signature microRNA of hypoxia. We found robust increase (>100-fold) of miR-210 abundance in activated T cells, especially in the T_H17 lineage. Hypoxia synergized with T cell receptor (TCR)–CD28 stimulation to accelerate and increase the magnitude of Mir210 expression. Mir210 was directly regulated by HIF-1α, a key regulator of T_H17 polarization. Surprisingly, Hif1a was identified as a miR-210-target, suggesting negative-feedback by miR-210 to inhibit HIF-1α protein expression. Deletion of Mir210 promoted T_H17 differentiation under conditions with limited oxygen. In experimental colitis, miR-210 reduced Hif1a transcript abundance, reduced the proportion of cells producing inflammatory cytokines and controlled disease severity. Our study identifies miR-210 as an important regulator of T cell differentiation in hypoxia, which can limit immunopathology.

Obesity and surgical wound healing: a current review

Objective. The correlation between obesity and deficient wound healing has long been established. This review examines the current literature on the mechanisms involved in obesity-related perioperative morbidity. Methods. A literature search was performed using Medline, PubMed, Cochrane Library, and Internet searches. Keywords used include obesity, wound healing, adipose healing, and bariatric and surgical complications. Results. Substantial evidence exists demonstrating that obesity is associated with a number of postoperative complications. Specifically in relation to wound healing, explanations include inherent anatomic features of adipose tissue, vascular insufficiencies, cellular and composition modifications, oxidative stress, alterations in immune mediators, and nutritional deficiencies. Most recently, advances made in the field of gene array have allowed researchers to determine a few plausible alterations and deficiencies in obese individuals that contribute to their increased risk of morbidity and mortality, especially wound complications. Conclusion. While the literature discusses how obesity may negatively affect health on various of medical fronts, there is yet to be a comprehensive study detailing all the mechanisms involved in obesity-related morbidities in their entirety. Improved knowledge and understanding of obesity-induced physiological, cellular, molecular, and chemical changes will facilitate better assessments of surgical risks and outcomes and create efficient treatment protocols for improved patient care of the obese patient population.

Translational medicine as a new clinical tool and application which improves metabolic diseases: perspectives from 2012 Sino-American symposium on clinical and translational medicine

Because of the economic growth and changes in lifestyle, metabolic diseases have become a major public health problem, which impose heavy economic burdens on individuals, families and health systems. However, its precise mediators and mechanisms remain to be fully understood. Clinical translational medicine (CTM) is an emerging area comprising multidisciplinary research from basic science to medical applications and as a new tool to improve human health by reducing disease incidence, morbidity and mortality. It can bridge knowledge of metabolic diseases processes, gained by in vitro and experimental animal models, with the disease pathways found in humans, further to identify their susceptibility genes and enable patients to achieve personalized medicament treatment. Thus, we have the reasons to believe that CTM will play even more roles in the development of new diagnostics, therapies, healthcare, and policies and the Sino-American Symposium on Clinical and Translational Medicine (SAS-CTM) will become a more and more important platform for exchanging ideas on clinical and translational research and entails a close collaboration among hospital, academia and industry.

A vascular piece in the puzzle of adipose tissue dysfunction: mechanisms and consequences

In the last years, several studies unravelled many aspects of adipose tissue pathophysiology in metabolic diseases. Some studies suggested hypoxia as one of such aspects, despite the exact mechanisms and pathophysiological significance is still partially unknown. Adipose tissue was shown to be hypoxic in obesity, mainly resulting from adipocyte hypertrophy, leading to increased activation of inflammatory pathways. In animal and cell models, hypoxia-induced inflammation was shown to lead to endocrine alterations and dysmetabolism. However, recent evidences suggest that instead of a simple low oxygenation theory, adipose tissue microvasculature may be regulated by a series of factors, including vasoactive factors like angiotensin II, angiogenesis and glycation, among others. This review summarizes the current knowledge about the role of these factors in the regulation of adipose tissue irrigation and the functional consequences of adipose tissue microvascular dysfunction.

DISORDER OF INTERCELLULAR CORRELATIONS IN PATHOGENESIS OF FATTY TISSUE INFLAMMATION IN METABOLIC SYNDROME

Due to the fact that nowadays mechanisms of syntropy of pathological conditions and nosological units, united within the metabolic syndrome, remain unclear, the scientific review attempts to summarize data on the role of fatty tissue inflammation in pathogenesis of this symptom complex. The results of recent major foreign studies on evaluation of pro-inflammatory activity of adipocytes and macrophages of the fatty tissue, as well as the data on peculiarities of their interactions in abdominal obesity, which is the main component of the metabolic syndrome, were analyzed. Studing pathogenesis of fatty tissue inflammation from the perspective of evaluation of disorders in cell cooperation will allow to more deeply understand cellular and molecular mechanisms of this process as well as open new avenues for developing new pathogenetically justified approaches to metabolic syndrome treatment.

Adipocytokines in relation to cardiovascular disease

Adipose tissue can be considered as a huge gland producing paracrine and endocrine hormones, the adipo(cyto)kines. There is growing evidence that these adipo(cyto)kines may link obesity to cardiovascular diseases. The excessive adipocyte hypertrophy in obesity induces hypoxia in adipose tissue. This leads to adiposopathy, the process that converts "healthy" adipose tissue to "sick" adipose tissue. This is accompanied by a change in profile of adipo(cyto)kines released, with less production of the "healthy" adipo(cyto)kines such as adiponectin and omentin and more release of the "unhealthy" adipo(cyto)kines, ultimately leading to the development of cardiovascular diseases. The present review provides a concise and general overview of the actual concepts of the role of adipo(cyto)kines in endothelial dysfunction, hypertension, atherosclerosis and heart diseases. The knowledge of these concepts may lead to new tools to improve health in the next generations.

Interplay of pro- and anti-inflammatory cytokines to determine lipid accretion in adipocytes

OBJECTIVE

Obesity is associated with an increase in various pro-inflammatory and anti-inflammatory cytokines, but the interplay of these cytokines is incompletely understood. We conducted experiments to test a broader hypothesis that a dynamic interplay of pro-inflammatory and anti-inflammatory cytokines controls lipid storage in adipocytes.

DESIGN

Three experiments were designed to test the overall hypothesis that proinflammatory cytokine (for example, tumor necrosis factor-α (TNF-α) inhibits anti-inflammatory cytokine (for example, adiponectin) activity in an attempt to limit excess lipid accumulation in adipocytes.

RESULTS

Experiment one showed that in pro-inflammatory animal models (ap2-P65, ob/ob and high-fat diet-induced obese mice), the increase in TNF-α expression was associated with a decrease in adiponectin expression. Experiment two showed that in 3T3-L1 adipocytes, TNF-α significantly reduced lipid accumulation and glucose uptake induced by adiponectin, and increased lipolysis. Experiment three showed that in 3T3-L1 adipocytes, TNF-α reduced mRNA and protein expression of adiponectin. Adiponectin gene transcription and mRNA stability were both reduced by TNF-α. The expression of peroxisome proliferator-activated receptor gamma, an activator of adiponectin gene promoter, was reduced by TNF-α. The inhibitory activity of TNF-α was blocked by the chemical inhibitors of NF-κB and super suppressor IκBα.

CONCLUSIONS

TNF-α opposes the action of adiponectin in the regulation of lipid metabolism, and inhibits adiponectin expression at transcriptional and post-transcriptional levels. The results suggest that pro-inflammatory cytokine inhibit anti-inflammatory cytokine in adipocytes to reduce lipid storage. This suggests a potential role of anti-inflammatory cytokines in the control of adipose tissue expansion.

15(S)-HETE-induced angiogenesis in adipose tissue is mediated through activation of PI3K/Akt/mTOR signaling pathway

Chronic low-grade inflammation underlies obesity and associated metabolic dysfunctions. Lipoxygenase pathways are activated in adipose tissue during obese conditions. Since adipogenesis is associated with angiogenesis, the present study was designed to examine the role of 15-lipoxygenase metabolite, 15(S)-hydroxyeicosatetraenoic acid [15(S)-HETE] on angiogenesis in adipose tissue. Results showed that 15(S)-HETE induced sprouting in fat pad stromovascular tissues, induced morphological changes relevant to angiogenesis in endothelial cells derived from adipose tissue, upregulated the production of CD31, upregulated the gene level expression and production of vascular endothelial growth factor (VEGF), indicating the pro-angiogenic effect of 15(S)-HETE. LY294002, an inhibitor of PI3K-Akt pathway, and rapamycin, inhibitor of mammalian target of rapamycin (mTOR), significantly reversed the effect of 15(S)-HETE. 15(S)-HETE also induced activation of Akt and mTOR. These observations suggest that 15(S)-HETE stimulates angiogenesis in adipose tissue through activation of PI3K/Akt/mTOR signaling.

Adipose tissue immunity and cancer

Inflammation and altered immune response are important components of obesity and contribute greatly to the promotion of obesity-related metabolic complications, especially cancer development. Adipose tissue expansion is associated with increased infiltration of various types of immune cells from both the innate and adaptive immune systems. Thus, adipocytes and infiltrating immune cells secrete pro-inflammatory adipokines and cytokines providing a microenvironment favorable for tumor growth. Accumulation of B and T cells in adipose tissue precedes macrophage infiltration causing a chronic low-grade inflammation. Phenotypic switching toward M1 macrophages and Th1 T cells constitutes an important mechanism described in the obese state correlating with increased tumor growth risk. Other possible synergic mechanisms causing a dysfunctional adipose tissue include fatty acid-induced inflammation, oxidative stress, endoplasmic reticulum stress, and hypoxia. Recent investigations have started to unravel the intricacy of the cross-talk between tumor cell/immune cell/adipocyte. In this sense, future therapies should take into account the combination of anti-inflammatory approaches that target the tumor microenvironment with more sophisticated and selective anti-tumoral drugs.

Angiogenesis and vascular functions in modulation of obesity, adipose metabolism, and insulin sensitivity

White and brown adipose tissues are hypervascularized and the adipose vasculature displays phenotypic and functional plasticity to coordinate with metabolic demands of adipocytes. Blood vessels not only supply nutrients and oxygen to nourish adipocytes, they also serve as a cellular reservoir to provide adipose precursor and stem cells that control adipose tissue mass and function. Multiple signaling molecules modulate the complex interplay between the vascular system and the adipocytes. Understanding fundamental mechanisms by which angiogenesis and vasculatures modulate adipocyte functions may provide new therapeutic options for treatment of obesity and metabolic disorders by targeting the adipose vasculature.

Chronic intermittent hypoxia induces atherosclerosis via activation of adipose angiopoietin-like 4

RATIONALE

Obstructive sleep apnea is a risk factor for dyslipidemia and atherosclerosis, which have been attributed to chronic intermittent hypoxia (CIH). Intermittent hypoxia inhibits a key enzyme of lipoprotein clearance, lipoprotein lipase, and up-regulates a lipoprotein lipase inhibitor, angiopoietin-like 4 (Angptl4), in adipose tissue. The effects and mechanisms of Angptl4 up-regulation in sleep apnea are unknown.

OBJECTIVES

To examine whether CIH induces dyslipidemia and atherosclerosis by increasing adipose Angptl4 via hypoxia-inducible factor-1 (HIF-1).

METHODS

ApoE(-/-) mice were exposed to intermittent hypoxia or air for 4 weeks while being treated with Angptl4-neutralizing antibody or vehicle.

MEASUREMENTS AND MAIN RESULTS

In vehicle-treated mice, hypoxia increased adipose Angptl4 levels, inhibited adipose lipoprotein lipase, increased fasting levels of plasma triglycerides and very low density lipoprotein cholesterol, and increased the size of atherosclerotic plaques. The effects of CIH were abolished by the antibody. Hypoxia-induced increases in plasma fasting triglycerides and adipose Angptl4 were not observed in mice with germline heterozygosity for a HIF-1α knockout allele. Transgenic overexpression of HIF-1α in adipose tissue led to dyslipidemia and increased levels of adipose Angptl4. In cultured adipocytes, constitutive expression of HIF-1α increased Angptl4 levels, which was abolished by siRNA. Finally, in obese patients undergoing bariatric surgery, the severity of nocturnal hypoxemia predicted Angptl4 levels in subcutaneous adipose tissue.

CONCLUSIONS

HIF-1-mediated increase in adipose Angptl4 and the ensuing lipoprotein lipase inactivation may contribute to atherosclerosis in patients with sleep apnea.

Proteomics analysis of human obesity reveals the epigenetic factor HDAC4 as a potential target for obesity

Sedentary lifestyle and excessive energy intake are prominent contributors to obesity; a major risk factors for the development of insulin resistance, type 2 diabetes and cardiovascular diseases. Elucidating the molecular mechanisms underlying these chronic conditions is of relevant importance as it might lead to the identification of novel anti-obesity targets. The purpose of the current study is to investigate differentially expressed proteins between lean and obese subjects through a shot-gun quantitative proteomics approach using peripheral blood mononuclear cells (PBMCs) extracts as well as potential modulation of those proteins by physical exercise. Using this approach, a total of 47 proteins showed at least 1.5 fold change between lean and obese subjects. In obese, the proteomic profiling before and after 3 months of physical exercise showed differential expression of 38 proteins. Thrombospondin 1 (TSP1) was among the proteins that were upregulated in obese subjects and then decreased by physical exercise. Conversely, the histone deacetylase 4 (HDAC4) was downregulated in obese subjects and then induced by physical exercise. The proteomic data was further validated by qRT-PCR, Western blot and immunohistochemistry in both PBMCs and adipose tissue. We also showed that HDAC4 levels correlated positively with maximum oxygen consumption (VO2 Max) but negatively with body mass index, percent body fat, and the inflammatory chemokine RANTES. In functional assays, our data indicated that ectopic expression of HDAC4 significantly impaired TNF-α-dependent activation of NF-κB, establishing thus a link between HDAC4 and regulation of the immune system. Together, the expression pattern of HDAC4 in obese subjects before and after physical exercise, its correlation with various physical, clinical and metabolic parameters along with its inhibitory effect on NF-κB are suggestive of a protective role of HDAC4 against obesity. HDAC4 could therefore represent a potential therapeutic target for the control and management of obesity and presumably insulin resistance.

Effects of exercise training on chronic inflammation in obesity : current evidence and potential mechanisms

Chronic, systemic inflammation is an independent risk factor for several major clinical diseases. In obesity, circulating levels of inflammatory markers are elevated, possibly due to increased production of pro-inflammatory cytokines from several tissues/cells, including macrophages within adipose tissue, vascular endothelial cells and peripheral blood mononuclear cells. Recent evidence supports that adipose tissue hypoxia may be an important mechanism through which enlarged adipose tissue elicits local tissue inflammation and further contributes to systemic inflammation. Current evidence supports that exercise training, such as aerobic and resistance exercise, reduces chronic inflammation, especially in obese individuals with high levels of inflammatory biomarkers undergoing a longer-term intervention. Several studies have reported that this effect is independent of the exercise-induced weight loss. There are several mechanisms through which exercise training reduces chronic inflammation, including its effect on muscle tissue to generate muscle-derived, anti-inflammatory 'myokine', its effect on adipose tissue to improve hypoxia and reduce local adipose tissue inflammation, its effect on endothelial cells to reduce leukocyte adhesion and cytokine production systemically, and its effect on the immune system to lower the number of pro-inflammatory cells and reduce pro-inflammatory cytokine production per cell. Of these potential mechanisms, the effect of exercise training on adipose tissue oxygenation is worth further investigation, as it is very likely that exercise training stimulates adipose tissue angiogenesis and increases blood flow, thereby reducing hypoxia and the associated chronic inflammation in adipose tissue of obese individuals.

Hexosamine biosynthesis is a possible mechanism underlying hypoxia's effects on lipid metabolism in human adipocytes

INTRODUCTION

Hypoxia regulates adipocyte metabolism. Hexosamine biosynthesis is implicated in murine 3T3L1 adipocyte differentiation and is a possible underlying mechanism for hypoxia's effects on adipocyte metabolism.

METHODS

Lipid metabolism was studied in human visceral and subcutaneous adipocytes in in vitro hypoxic culture with adipophilic staining, glycerol release, and palmitate oxidation assays. Gene expression and hexosamine biosynthesis activation was studied with QRTPCR, immunofluorescence microscopy, and Western blotting.

RESULTS

Hypoxia inhibits lipogenesis and induces basal lipolysis in visceral and subcutaneous human adipocytes. Hypoxia induces fatty acid oxidation in visceral adipocytes but had no effect on fatty acid oxidation in subcutaneous adipocytes. Hypoxia inhibits hexosamine biosynthesis in adipocytes. Inhibition of hexosamine biosynthesis with azaserine attenuates lipogenesis and induces lipolysis in adipocytes in normoxic conditions, while promotion of hexosamine biosynthesis with glucosamine in hypoxic conditions slightly increases lipogenesis.

CONCLUSIONS

Hypoxia's net effect on human adipocyte lipid metabolism would be expected to impair adipocyte buffering capacity and contribute to systemic lipotoxicity. Our data suggest that hypoxia may mediate its effects on lipogenesis and lipolysis through inhibition of hexosamine biosynthesis. Hexosamine biosynthesis represents a target for manipulation of adipocyte metabolism.

Fat-resident Tregs: an emerging guard protecting from obesity-associated metabolic disorders

Obesity, a chronic, low-grade inflammatory disease, is associated with alterations of multiple immune-cell components in the visceral adipose tissue (VAT), in which CD4(+) Foxp3(+) regulatory T cells (Tregs) have been suggested to be a critical regulator. This review focuses on the current understanding of VAT-resident Tregs (VAT Tregs) and their intriguing roles in modulating fat tissue inflammation and obesity-associated metabolic disorders. The potential mechanisms for the regulation of VAT Tregs in lean vs. obese individuals are also discussed. Accumulating evidence reveals that the modulation of VAT Tregs may offer a potential novel strategy for treating obesity-related metabolic disorders, such as insulin resistance and type 2 diabetes.

Hypoxia, energy balance and obesity: from pathophysiological mechanisms to new treatment strategies

High altitude exposure is often accompanied by weight loss. Postulated mechanisms are a reduction of nutritional energy intake, a reduction of intestinal energy uptake from impaired intestinal function and increased energy expenditure. Beyond the field of altitude, there are good reasons for renewed interest in the relationship between hypoxia and energy balance. The increasing prevalence of obesity and associated comorbidities represent a major health concern. Obesity is frequently associated with sleep disorders leading to intermittent systemic hypoxia with deleterious cardiovascular and metabolic consequences. Hypoxic regions may be present within hypertrophic white adipose tissue leading to chronic systemic inflammation. Among the increasing number of people commuting to altitude for work or leisure, obesity is a risk factor for acute mountain sickness. Paradoxically, exposure to intermittent hypoxia might be considered as a means to lose body mass and to improve metabolic risk factors. Daytime exposure to intermittent hypoxia has been used to treat hypertension in former Soviet Union countries and is now being experimented elsewhere. Such intermittent hypoxic exposure at rest or during exercise may lead to improvement in body composition and health status with improved exercise tolerance, metabolism and systemic arterial pressure. Future research should confirm whether hypoxic training could be a new treatment strategy for weight loss and comorbidities in obese subjects and elucidate the underlying mechanisms and signalling pathways.

Chemokine Expression in Inflamed Adipose Tissue Is Mainly Mediated by NF-κB

Immune cell infiltration of expanding adipose tissue during obesity and its role in insulin resistance has been described and involves chemokines. However, studies so far have focused on a single chemokine or its receptor (especially CCL2 and CCL5) whereas redundant functions of chemokines have been described. The objective of this work was to explore the expression of chemokines in inflamed adipose tissue in obesity. Human and mouse adipocytes were analyzed for expression of chemokines in response to inflammatory signal (TNF-α) using microarrays and gene set enrichment analysis. Gene expression was verified by qRT-PCR. Chemokine protein was determined in culture medium with ELISA. Chemokine expression was investigated in human subcutaneous adipose tissue biopsies and mechanism of chemokine expression was investigated using chemical inhibitors and cellular and animal transgenic models. Chemokine encoding genes were the most responsive genes in TNF-α treated human and mouse adipocytes. mRNA and protein of 34 chemokine genes were induced in a dose-dependent manner in the culture system. Furthermore, expression of those chemokines was elevated in human obese adipose tissue. Finally, chemokine expression was reduced by NF-κB inactivation and elevated by NF-κB activation. Our data indicate that besides CCL2 and CCL5, numerous other chemokines such as CCL19 are expressed by adipocytes under obesity-associated chronic inflammation. Their expression is regulated predominantly by NF-κB. Those chemokines could be involved in the initiation of infiltration of leukocytes into obese adipose tissue.

Hypoxia and hypoxia-inducible factors as regulators of T cell development, differentiation, and function

Oxygen is a molecule that is central to cellular respiration and viability, yet there are multiple physiologic and pathological contexts in which cells experience conditions of insufficient oxygen availability, a state known as hypoxia. Given the metabolic challenges of a low oxygen environment, hypoxia elicits a range of adaptive responses at the cellular, tissue, and systemic level to promote continued survival and function. Within this context, T lymphocytes are a highly migratory cell type of the adaptive immune system that frequently encounters a wide range of oxygen tensions in both health and disease. It is now clear that oxygen availability regulates T cell differentiation and function, a response orchestrated in large part by the hypoxia-inducible factor transcription factors. Here, we discuss the physiologic scope of hypoxia and hypoxic signaling, the contribution of these pathways in regulating T cell biology, and current gaps in our understanding. Finally, we discuss how emerging therapies that modulate the hypoxic response may offer new modalities to alter T cell function and the outcome of acute and chronic pathologies.

Obstructive sleep apnea: a cardiometabolic risk in obesity and the metabolic syndrome

Obstructive sleep apnea (OSA) is an underdiagnosed condition characterized by recurrent episodes of obstruction of the upper airway leading to sleep fragmentation and intermittent hypoxia during sleep. Obesity predisposes to OSA, and the prevalence of OSA is increasing worldwide because of the ongoing epidemic of obesity. Recent evidence has shown that surrogate markers of cardiovascular risk, including sympathetic activation, systemic inflammation, and endothelial dysfunction, are significantly increased in obese patients with OSA versus those without OSA, suggesting that OSA is not simply an epiphenomenon of obesity. Moreover, findings from animal models and patients with OSA show that intermittent hypoxia exacerbates the metabolic dysfunction of obesity, augmenting insulin resistance and nonalcoholic fatty liver disease. In patients with the metabolic syndrome, the prevalence of moderate to severe OSA is very high (∼60%). In this population, OSA is independently associated with increased glucose and triglyceride levels as well as markers of inflammation, arterial stiffness, and atherosclerosis. A recent randomized, controlled, crossover study showed that effective treatment of OSA with continuous positive airway pressure for 3 months significantly reduced several components of the metabolic syndrome, including blood pressure, triglyceride levels, and visceral fat. Finally, several cohort studies have consistently shown that OSA is associated with increased cardiovascular mortality, independent of obesity. Taken together, these results support the concept that OSA exacerbates the cardiometabolic risk attributed to obesity and the metabolic syndrome. Recognition and treatment of OSA may decrease the cardiovascular risk in obese patients.

Inflammation in obesity and diabetes: islet dysfunction and therapeutic opportunity

The role of the immune system is to restore functionality in response to stress. Increasing evidence shows that this function is not limited to insults by infection or injury and plays a role in response to overnutrition. Initially, this metabolic activation of the immune system is a physiological response, but it may become deleterious with time. Therefore, therapeutic interventions should aim at modulating the immune system rather than simply damping it. In this article, we describe the physiology and pathology of the immune system during obesity and diabetes with a focus on islet inflammation, the IL-1β pathway, and clinical translation.

The role of chronic inflammation in obesity-associated cancers

There is a strong relationship between metabolism and immunity, which can become deleterious under conditions of metabolic stress. Obesity, considered a chronic inflammatory disease, is one example of this link. Chronic inflammation is increasingly being recognized as an etiology in several cancers, particularly those of epithelial origin, and therefore a potential link between obesity and cancer. In this review, the connection between the different factors that can lead to the chronic inflammatory state in the obese individual, as well as their effect in tumorigenesis, is addressed. Furthermore, the association between obesity, inflammation, and esophageal, liver, colon, postmenopausal breast, and endometrial cancers is discussed.