assessment-human-adipose-tissue-microvascular-function-using

Assessment of Human Adipose Tissue Microvascular Function Using Videomicroscopy

While obesity is closely linked to the development of metabolic and cardiovascular disease, little is known about mechanisms that govern these processes. ...

Boston University School of Medicine

The purpose of this study was to determine whether obese individuals with reduced adipose tissue inflammation exhibit a more favorable cardiovascular risk profile.

Reduced adipose tissue inflammation represents an intermediate cardiometabolic phenotype in obesity.

The purpose of this study was to characterize the relationship between adipose tissue phenotype and depot-specific microvascular function in fat.

Arteriolar function in visceral adipose tissue is impaired in human obesity.

Accumulation of macrophages and T cells within crown-like structures (CLS) in subcutaneous adipose tissue predicts disease severity in obesity-related insulin resistance (OIR). Although rodent data suggest the B cell is an important feature of these lesions, B cells have not been described within the human CLS. In order to identify B cells in the human subcutaneous CLS (sCLS) in obese subjects and determine whether the presence of B cells predict insulin resistance, we examined archived samples of subcutaneous and omental fat from 32 obese men and women and related findings to clinical parameters. Using immunohistochemistry, we identified B (CD19(+)) and T cells (CD3 (+)) within the sCLS and perivascular space. The presence and density of B cells (B cells per high-power field (pHPF), T cells pHPF, and B cell:T cell (B:T) ratio) were compared with measures of insulin resistance (homeostasis model assessment (HOMA)) and other variables. In 16 of 32 subjects (50%) CD19(+) B cells were localized within sCLS and were relatively more numerous than T cells. HOMA was not different between subjects with CD19(+) vs. CD19(-) sCLS (5.5 vs. 5.3, P = 0.88). After controlling for diabetes and glycemia (hemoglobin A(1c) (HbA(1c))), the B:T ratio correlated with current metformin treatment (r = 0.89, P = 0.001). These results indicate that in human OIR, B cells are an integral component of organized inflammation in subcutaneous fat, and defining their role will lead to a better understanding of OIR pathogenesis and potentially impact treatment.

B lymphocytes in human subcutaneous adipose crown-like structures.

High fat diet and its induced changes in glucose homeostasis, inflammation and obesity continue to be an epidemic in developed countries. The A2b adenosine receptor (A2bAR) is known to regulate inflammation. We used a diet-induced obesity murine knockout model to investigate the role of this receptor in mediating metabolic homeostasis, and correlated our findings in obese patient samples.

The A2b adenosine receptor modulates glucose homeostasis and obesity.

Abnormal endothelial function promotes atherosclerotic vascular disease in diabetes. Experimental studies indicate that disruption of endothelial insulin signaling, through the activity of protein kinase C-β (PKCβ) and nuclear factor κB, reduces nitric oxide availability. We sought to establish whether similar mechanisms operate in the endothelium in human diabetes mellitus.

Protein kinase C-β contributes to impaired endothelial insulin signaling in humans with diabetes mellitus.

The purpose of this study was to determine whether cyclooxygenase inhibition improves vascular dysfunction of adipose microvessels from obese humans.

Cyclooxygenase inhibition improves endothelial vasomotor dysfunction of visceral adipose arterioles in human obesity.

The aim of this study was to determine whether the effects of weight loss on arterial function are differentially modified by insulin status.

Insulin status and vascular responses to weight loss in obesity.

Experimental studies suggest that visceral adiposity and adipose tissue dysfunction play a central role in obesity-related cardiometabolic complications. Impaired angiogenesis in fat has been implicated in the development of adipose tissue hypoxia, capillary rarefaction, inflammation, and metabolic dysregulation, but pathophysiological mechanisms remain unknown. In this study, we examined the role of a novel antiangiogenic isoform of vascular endothelial growth factor-A (VEGF-A), VEGF-A165b, in human obesity.

Antiangiogenic actions of vascular endothelial growth factor-A165b, an inhibitory isoform of vascular endothelial growth factor-A, in human obesity.

Adipose tissue dysfunction plays a pivotal role in the development of insulin resistance in obese individuals. Cell culture studies and gain-of-function mouse models suggest that canonical Wnt proteins modulate adipose tissue expansion. However, no genetic evidence supports a role for endogenous Wnt proteins in adipose tissue dysfunction, and the role of noncanonical Wnt signaling remains largely unexplored. Here we provide evidence from human, mouse, and cell culture studies showing that Wnt5a-mediated, noncanonical Wnt signaling contributes to obesity-associated metabolic dysfunction by increasing adipose tissue inflammation. Wnt5a expression is significantly upregulated in human visceral fat compared with subcutaneous fat in obese individuals. In obese mice, Wnt5a ablation ameliorates insulin resistance, in parallel with reductions in adipose tissue inflammation. Conversely, Wnt5a overexpression in myeloid cells augments adipose tissue inflammation and leads to greater impairments in glucose homeostasis. Wnt5a ablation or overexpression did not affect fat mass or adipocyte size. Mechanistically, Wnt5a promotes the expression of proinflammatory cytokines by macrophages in a Jun NH2-terminal kinase-dependent manner, leading to defective insulin signaling in adipocytes. Exogenous interleukin-6 administration restores insulin resistance in obese Wnt5a-deficient mice, suggesting a central role for this cytokine in Wnt5a-mediated metabolic dysfunction. Taken together, these results demonstrate that noncanonical Wnt signaling contributes to obesity-induced insulin resistance independent of adipose tissue expansion.

Noncanonical Wnt signaling promotes obesity-induced adipose tissue inflammation and metabolic dysfunction independent of adipose tissue expansion.

Obesity has emerged as one of the most critical health care problems globally that is associated with the development of insulin resistance, type 2 diabetes mellitus, metabolic dysfunction and cardiovascular disease. Central adiposity with intra-abdominal deposition of visceral fat, in particular, has been closely linked to cardiometabolic consequences of obesity. Increasing epidemiological, clinical and experimental data suggest that both adipose tissue quantity and perturbations in its quality termed "adiposopathy" contribute to mechanisms of cardiometabolic disease. The current review discusses regional differences in adipose tissue characteristics and highlights profound abnormalities in vascular endothelial function and angiogenesis that are manifest within the visceral adipose tissue milieu of obese individuals. Clinical data demonstrate up-regulation of pro-inflammatory and pro-atherosclerotic mediators in dysfunctional adipose tissue that may support pathological vascular changes not only locally in fat but also in multiple organ systems, including coronary and peripheral circulations, potentially contributing to mechanisms of obesity-related cardiovascular disease.

Visceral adiposopathy: a vascular perspective.

Increased visceral adiposity has been closely linked to insulin resistance, endothelial dysfunction, and cardiometabolic disease in obesity, but pathophysiological mechanisms are poorly understood. We sought to investigate mechanisms of vascular insulin resistance by characterizing depot-specific insulin responses and gain evidence that altered functionality of transcription factor forkhead box O-1 (FOXO-1) may play an important role in obesity-related endothelial dysfunction.

Forkhead box O-1 modulation improves endothelial insulin resistance in human obesity.

Dysregulated lipolysis has been implicated in mechanisms of cardiometabolic disease and inflammation in obesity.

Effect of Bariatric Weight Loss on the Adipose Lipolytic Transcriptome in Obese Humans.

Endothelial dysfunction is linked to insulin resistance, inflammatory activation, and increased cardiovascular risk in diabetes mellitus; however, the mechanisms remain incompletely understood. Recent studies have identified proinflammatory signaling of wingless-type family member (Wnt) 5a through c-jun N-terminal kinase (JNK) as a regulator of metabolic dysfunction with potential relevance to vascular function. We sought to gain evidence that increased activation of Wnt5a-JNK signaling contributes to impaired endothelial function in patients with diabetes mellitus.

Endothelial Dysfunction in Human Diabetes Is Mediated by Wnt5a-JNK Signaling.

Endothelial dysfunction contributes to cardiovascular disease in diabetes mellitus. Autophagy is a multistep mechanism for the removal of damaged proteins and organelles from the cell. Under diabetic conditions, inadequate autophagy promotes cellular dysfunction and insulin resistance in non-vascular tissue. We hypothesized that impaired autophagy contributes to endothelial dysfunction in diabetes mellitus.

Restoration of autophagy in endothelial cells from patients with diabetes mellitus improves nitric oxide signaling.

Obesity is associated with the development of vascular insulin resistance; however, pathophysiological mechanisms are poorly understood. We sought to investigate the role of WNT5A-JNK in the regulation of insulin-mediated vasodilator responses in human adipose tissue arterioles prone to endothelial dysfunction. In 43 severely obese (BMI 44±11 kg/m(2)) and five metabolically normal non-obese (BMI 26±2 kg/m(2)) subjects, we isolated arterioles from subcutaneous and visceral fat during planned surgeries. Using videomicroscopy, we examined insulin-mediated, endothelium-dependent vasodilator responses and characterized adipose tissue gene and protein expression using real-time polymerase chain reaction and Western blot analyses. Immunofluorescence was used to quantify endothelial nitric oxide synthase (eNOS) phosphorylation. Insulin-mediated vasodilation was markedly impaired in visceral compared to subcutaneous vessels from obese subjects (p<0.001), but preserved in non-obese individuals. Visceral adiposity was associated with increased JNK activation and elevated expression of WNT5A and its non-canonical receptors, which correlated negatively with insulin signaling. Pharmacological JNK antagonism with SP600125 markedly improved insulin-mediated vasodilation by sixfold (p<0.001), while endothelial cells exposed to recombinant WNT5A developed insulin resistance and impaired eNOS phosphorylation (p<0.05). We observed profound vascular insulin resistance in the visceral adipose tissue arterioles of obese subjects that was associated with up-regulated WNT5A-JNK signaling and impaired endothelial eNOS activation. Pharmacological JNK antagonism markedly improved vascular endothelial function, and may represent a potential therapeutic target in obesity-related vascular disease.

WNT5A-JNK regulation of vascular insulin resistance in human obesity.

Experimental studies have suggested that Wingless-related integration site 5A (WNT5A) is a proinflammatory secreted protein that is associated with metabolic dysfunction in obesity. Impaired angiogenesis in fat depots has been implicated in the development of adipose tissue capillary rarefaction, hypoxia, inflammation, and metabolic dysfunction. We have recently demonstrated that impaired adipose tissue angiogenesis is associated with overexpression of antiangiogenic factor VEGF-A165b in human fat and the systemic circulation. In the present study, we postulated that upregulation of WNT5A is associated with angiogenic dysfunction and examined its role in regulating VEGF-A165b expression in human obesity. We biopsied subcutaneous and visceral adipose tissue from 38 obese individuals (body mass index: 44 ± 7 kg/m(2), age: 37 ± 11 yr) during planned bariatric surgery and characterized depot-specific protein expression of VEGF-A165b and WNT5A using Western blot analysis. In both subcutaneous and visceral fat, VEGF-A165b expression correlated strongly with WNT5A protein (r = 0.9, P < 0.001). In subcutaneous adipose tissue where angiogenic capacity is greater than in the visceral depot, exogenous human recombinant WNT5A increased VEGF-A165b expression in both whole adipose tissue and isolated vascular endothelial cell fractions (P < 0.01 and P < 0.05, respectively). This was associated with markedly blunted angiogenic capillary sprout formation in human fat pad explants. Moreover, recombinant WNT5A increased secretion of soluble fms-like tyrosine kinase-1, a negative regulator of angiogenesis, in the sprout media (P < 0.01). Both VEGF-A165b-neutralizing antibody and secreted frizzled-related protein 5, which acts as a decoy receptor for WNT5A, significantly improved capillary sprout formation and reduced soluble fms-like tyrosine kinase-1 production (P < 0.05). We demonstrated a significant regulatory nexus between WNT5A and antiangiogenic VEGF-A165b in the adipose tissue of obese subjects that was linked to angiogenic dysfunction. Elevated WNT5A expression in obesity may function as a negative regulator of angiogenesis.NEW & NOTEWORTHY Wingless-related integration site 5a (WNT5A) negatively regulates adipose tissue angiogenesis via VEGF-A165b in human obesity.

Article	Year
Reduced adipose tissue inflammation represents an intermediate cardiometabolic phenotype in obesity. Journal of the American College of Cardiology\| PubMed ID: 21737012	2011
Arteriolar function in visceral adipose tissue is impaired in human obesity. Arteriosclerosis, thrombosis, and vascular biology\| PubMed ID: 22095978	2012
B lymphocytes in human subcutaneous adipose crown-like structures. Obesity (Silver Spring, Md.)\| PubMed ID: 22395812	2012
The A2b adenosine receptor modulates glucose homeostasis and obesity. PloS one\| PubMed ID: 22848385	2012
Protein kinase C-β contributes to impaired endothelial insulin signaling in humans with diabetes mellitus. Circulation\| PubMed ID: 23204109	2013
Cyclooxygenase inhibition improves endothelial vasomotor dysfunction of visceral adipose arterioles in human obesity. Obesity (Silver Spring, Md.)\| PubMed ID: 23640904	2013
Insulin status and vascular responses to weight loss in obesity. Journal of the American College of Cardiology\| PubMed ID: 23978693	2013
Antiangiogenic actions of vascular endothelial growth factor-A165b, an inhibitory isoform of vascular endothelial growth factor-A, in human obesity. Circulation\| PubMed ID: 25116954	2014
Noncanonical Wnt signaling promotes obesity-induced adipose tissue inflammation and metabolic dysfunction independent of adipose tissue expansion. Diabetes\| PubMed ID: 25352637	2015
Visceral adiposopathy: a vascular perspective. Hormone molecular biology and clinical investigation\| PubMed ID: 25781557	2015
Forkhead box O-1 modulation improves endothelial insulin resistance in human obesity. Arteriosclerosis, thrombosis, and vascular biology\| PubMed ID: 25908760	2015
Effect of Bariatric Weight Loss on the Adipose Lipolytic Transcriptome in Obese Humans. Mediators of inflammation\| PubMed ID: 26663986	2015
Endothelial Dysfunction in Human Diabetes Is Mediated by Wnt5a-JNK Signaling. Arteriosclerosis, thrombosis, and vascular biology\| PubMed ID: 26800561	2016
Restoration of autophagy in endothelial cells from patients with diabetes mellitus improves nitric oxide signaling. Atherosclerosis\| PubMed ID: 26926601	2016
WNT5A-JNK regulation of vascular insulin resistance in human obesity. Vascular medicine (London, England)\| PubMed ID: 27688298	2016
WNT5A regulates adipose tissue angiogenesis via antiangiogenic VEGF-A165b in obese humans. American journal of physiology. Heart and circulatory physiology\| PubMed ID: 28411232	2017

Melissa G. Farb

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