Human perivascular adipose tissue dysfunction as a cause of vascular disease: Focus on vascular tone and wall remodeling

Perivascular Adipose Tissue and Uterine Artery Adaptations to Pregnancy

Pregnancy is characterized by longitudinal maternal, physiological adaptations to support the development of a fetus. One of the cardinal maternal adaptations during a healthy pregnancy is a progressive increase in uterine artery blood flow. This facilitates sufficient blood supply for the development of the placenta and the growing fetus. Regional hemodynamic changes in the uterine circulation, such as a vast reduction in uterine artery resistance, are mainly facilitated by changes in uterine artery reactivity and myogenic tone along with remodeling of the uterine arteries. These regional changes in vascular reactivity have been attributed to pregnancy-induced adaptations of cell-to-cell communication mechanisms, with an emphasis on the interaction between endothelial and vascular smooth muscle cells. Perivascular adipose tissue (PVAT) is considered the fourth layer of the vascular wall and contributes to the regulation of vascular reactivity in most vascular beds and most species. This review focuses on mechanisms of uterine artery reactivity and the role of PVAT in pregnancy-induced maternal vascular adaptations, with an emphasis on the uterine circulation.

The emerging roles of irisin in vascular calcification

Vascular calcification is a common accompanying pathological change in many chronic diseases, which is caused by calcium deposition in the blood vessel wall and leads to abnormal blood vessel function. With the progress of medical technology, the diagnosis rate of vascular calcification has explosively increased. However, due to its mechanism's complexity, no effective drug can relieve or even reverse vascular calcification. Irisin is a myogenic cytokine regulating adipose tissue browning, energy metabolism, glucose metabolism, and other physiological processes. Previous studies have shown that irisin could serve as a predictor for vascular calcification, and protect against hypertension, diabetes, chronic kidney disease, and other risk factors for vascular calcification. In terms of mechanism, it improves vascular endothelial dysfunction and phenotypic transformation of vascular smooth muscle cells. All the above evidence suggests that irisin plays a predictive and protective role in vascular calcification. In this review, we summarize the association of irisin to the related risk factors for vascular calcification and mainly explore the role of irisin in vascular calcification.

Adiponectin Resistance in Obesity: Adiponectin Leptin/Insulin Interaction

The adiponectin (APN) levels in obesity are negatively correlated with chronic subclinical inflammation markers. The hypertrophic adipocytes cause obesity-linked insulin resistance and metabolic syndrome. Furthermore, macrophage polarization is a key determinant regulating adiponectin receptor (AdipoR1/R2) expression and differential adiponectin-mediated macrophage inflammatory responses in obese individuals. In addition to decrease in adiponectin concentrations, the decline in AdipoR1/R2 messenger ribonucleic acid (mRNA) expression leads to a decrement in adiponectin binding to cell membrane, and this turns into attenuation in the adiponectin effects. This is defined as APN resistance, and it is linked with insulin resistance in high-fat diet-fed subjects. The insulin-resistant group has a significantly higher leptin-to-APN ratio. The leptin-to-APN ratio is more than twofold higher in obese individuals. An increase in expression of AdipoRs restores insulin sensitivity and β-oxidation of fatty acids via triggering intracellular signal cascades. The ratio of high molecular weight to total APN is defined as the APN sensitivity index (ASI). This index is correlated to insulin sensitivity. Homeostasis model of assessment (HOMA)-APN and HOMA-estimated insulin resistance (HOMA-IR) are the most suitable methods to estimate the metabolic risk in metabolic syndrome. While morbidly obese patients display a significantly higher plasma leptin and soluble (s)E-selectin concentrations, leptin-to-APN ratio, there is a significant negative correlation between leptin-to-APN ratio and sP-selectin in obese patients. When comparing the metabolic dysregulated obese group with the metabolically healthy obese group, postprandial triglyceride clearance, insulin resistance, and leptin resistance are significantly delayed following the oral fat tolerance test in the first group. A neuropeptide, Spexin (SPX), is positively correlated with the quantitative insulin sensitivity check index (QUICKI) and APN. APN resistance together with insulin resistance forms a vicious cycle. Despite normal or high APN levels, an impaired post-receptor signaling due to adaptor protein-containing pleckstrin homology domain, phosphotyrosine-binding domain, and leucine zipper motif 1 (APPL1)/APPL2 may alter APN efficiency and activity. However, APPL2 blocks adiponectin signaling through AdipoR1 and AdipoR2 because of the competitive inhibition of APPL1. APPL1, the intracellular binding partner of AdipoRs, is also an important mediator of adiponectin-dependent insulin sensitization. The elevated adiponectin levels with adiponectin resistance are compensatory responses in the condition of an unusual discordance between insulin resistance and APN unresponsiveness. Hypothalamic recombinant adeno-associated virus (rAAV)-leptin (Lep) gene therapy reduces serum APN levels, and it is a more efficient strategy for long-term weight maintenance.

Endothelial Dysfunction in Obesity and Therapeutic Targets

Parallel to the increasing prevalence of obesity in the world, the mortality from cardiovascular disease has also increased. Low-grade chronic inflammation in obesity disrupts vascular homeostasis, and the dysregulation of adipocyte-derived endocrine and paracrine effects contributes to endothelial dysfunction. Besides the adipose tissue inflammation, decreased nitric oxide (NO)-bioavailability, insulin resistance (IR), and oxidized low-density lipoproteins (oxLDLs) are the main factors contributing to endothelial dysfunction in obesity and the development of cardiorenal metabolic syndrome. While normal healthy perivascular adipose tissue (PVAT) ensures the dilation of blood vessels, obesity-associated PVAT leads to a change in the profile of the released adipo-cytokines, resulting in a decreased vasorelaxing effect. Higher stiffness parameter β, increased oxidative stress, upregulation of pro-inflammatory cytokines, and nicotinamide adenine dinucleotide phosphate (NADP) oxidase in PVAT turn the macrophages into pro-atherogenic phenotypes by oxLDL-induced adipocyte-derived exosome-macrophage crosstalk and contribute to the endothelial dysfunction. In clinical practice, carotid ultrasound, higher leptin levels correlate with irisin over-secretion by human visceral and subcutaneous adipose tissues, and remnant cholesterol (RC) levels predict atherosclerotic disease in obesity. As a novel therapeutic strategy for cardiovascular protection, liraglutide improves vascular dysfunction by modulating a cyclic adenosine monophosphate (cAMP)-independent protein kinase A (PKA)-AMP-activated protein kinase (AMPK) pathway in PVAT in obese individuals. Because the renin-angiotensin-aldosterone system (RAAS) activity, hyperinsulinemia, and the resultant IR play key roles in the progression of cardiovascular disease in obesity, RAAS-targeted therapies contribute to improving endothelial dysfunction. By contrast, arginase reciprocally inhibits NO formation and promotes oxidative stress. Thus, targeting arginase activity as a key mediator in endothelial dysfunction has therapeutic potential in obesity-related vascular comorbidities. Obesity-related endothelial dysfunction plays a pivotal role in the progression of type 2 diabetes (T2D). The peroxisome proliferator-activated receptor gamma (PPARγ) agonist, rosiglitazone (thiazolidinedione), is a popular drug for treating diabetes; however, it leads to increased cardiovascular risk. Selective sodium-glucose co-transporter-2 (SGLT-2) inhibitor empagliflozin (EMPA) significantly improves endothelial dysfunction and mortality occurring through redox-dependent mechanisms. Although endothelial dysfunction and oxidative stress are alleviated by either metformin or EMPA, currently used drugs to treat obesity-related diabetes neither possess the same anti-inflammatory potential nor simultaneously target endothelial cell dysfunction and obesity equally. While therapeutic interventions with glucagon-like peptide-1 (GLP-1) receptor agonist liraglutide or bariatric surgery reverse regenerative cell exhaustion, support vascular repair mechanisms, and improve cardiometabolic risk in individuals with T2D and obesity, the GLP-1 analog exendin-4 attenuates endothelial endoplasmic reticulum stress.

Single-Cell RNA Sequencing of Coronary Perivascular Adipose Tissue From End-Stage Heart Failure Patients Identifies SPP1+ Macrophage Subpopulation as a Target for Alleviating Fibrosis

BACKGROUND

Perivascular adipose tissue (PVAT) is vital for vascular homeostasis, and PVAT dysfunction is associated with increased atherosclerotic plaque burden. But the mechanisms underlining coronary PVAT dysfunction in coronary atherosclerosis remain elusive.

METHODS

We performed single-cell RNA sequencing of the stromal vascular fraction of coronary PVAT from 3 groups of heart transplant recipients with end-stage heart failure, including 3 patients with nonobstructive coronary atherosclerosis, 3 patients with obstructive coronary artery atherosclerosis, and 4 nonatherosclerosis control subjects. Bioinformatics was used to annotate the cellular populations, depict the cellular developmental trajectories and interactions, and explore the differences among 3 groups of coronary PVAT at the cellular and molecular levels. Pathological staining, quantitative real-time polymerase chain reaction, and in vitro studies were performed to validate the key findings.

RESULTS

Ten cell types were identified among 67 936 cells from human coronary PVAT. Several cellular subpopulations, including SPP1+ (secreted phosphoprotein 1) macrophages and profibrotic fibroadipogenic progenitor cells, were accumulated in PVAT surrounding atherosclerotic coronary arteries compared with nonatherosclerosis coronary arteries. The fibrosis percentage was increased in PVAT surrounding atherosclerotic coronary arteries, and it was positively associated with the grade of coronary artery stenosis. Cellular interaction analysis suggested OPN (osteopontin) secreted by SPP1+ macrophages interacted with CD44 (cluster of differentiation 44)/integrin on fibroadipogenic progenitor cells. Strikingly, correlation analyses uncovered that higher level of SPP1 in PVAT correlates with a more severe fibrosis degree and a higher coronary stenosis grade. In vitro studies showed that conditioned medium from atherosclerotic coronary PVAT promoted the migration and proliferation of fibroadipogenic progenitor cells, while such effect was prevented by blocking CD44 or integrin.

CONCLUSIONS

SPP1+ macrophages accumulated in the PVAT surrounding atherosclerotic coronary arteries, and they promoted the migration and proliferation of fibroadipogenic progenitor cells via OPN-CD44/integrin interaction and thus aggravated the fibrosis of coronary PVAT, which was positively correlated to the coronary stenosis burden. Therefore, SPP1+ macrophages in coronary PVAT may participate in the progression of coronary atherosclerosis.

Perivascular Adipose Tissue and Vascular Smooth Muscle Tone: Friends or Foes?

Perivascular adipose tissue (PVAT) is a specialized type of adipose tissue that surrounds most mammalian blood vessels. PVAT is a metabolically active, endocrine organ capable of regulating blood vessel tone, endothelium function, vascular smooth muscle cell growth and proliferation, and contributing critically to cardiovascular disease onset and progression. In the context of vascular tone regulation, under physiological conditions, PVAT exerts a potent anticontractile effect by releasing a plethora of vasoactive substances, including NO, H₂S, H₂O₂, prostacyclin, palmitic acid methyl ester, angiotensin 1-7, adiponectin, leptin, and omentin. However, under certain pathophysiological conditions, PVAT exerts pro-contractile effects by decreasing the production of anticontractile and increasing that of pro-contractile factors, including superoxide anion, angiotensin II, catecholamines, prostaglandins, chemerin, resistin, and visfatin. The present review discusses the regulatory effect of PVAT on vascular tone and the factors involved. In this scenario, dissecting the precise role of PVAT is a prerequisite to the development of PVAT-targeted therapies.

The biological actions of prostanoids in adipose tissue in physiological and pathophysiological conditions

Adipose tissue has been established as an endocrine organ that plays an important role in maintaining metabolic homeostasis. Adipose tissue releases several bioactive molecules called adipokines. Inflammation, dysregulation of adipokine synthesis, and secretion are observed in obesity and related diseases and cause adipose tissue dysfunction. Prostanoids, belonging to the eicosanoid family of lipid mediators, can be synthesized in adipose tissue and play a critical role in adipose tissue biology. In this review, we summarized the current knowledge regarding the interaction of prostanoids with adipokines, the expression of prostanoid receptors, and prostanoid synthase enzymes in adipose tissues in health and disease. Furthermore, the involvement of prostanoids in the physiological function or dysfunction of adipose tissue including inflammation, lipolysis, adipogenesis, thermogenesis, browning of adipocytes, and vascular tone regulation was also discussed by examining studies using pharmacological approaches or genetically modified animals for prostanoid receptors/synthase enzymes. Overall, the present review provides a perspective on the evidence from literature regarding the biological effects of prostanoids in adipose tissue. Among prostanoids, prostaglandin E2 (PGE₂) is prominent in regards to its substantial role in both adipose tissue physiology and pathophysiology. Targeting prostanoids may serve as a potential therapeutic strategy for preventing or treating obesity and related diseases.

Extracellular Matrix in Aging Aorta

The aging population is booming all over the world and arterial aging causes various age-associated pathologies such as cardiovascular diseases (CVDs). The aorta is the largest elastic artery, and transforms pulsatile flow generated by the left ventricle into steady flow to maintain circulation in distal tissues and organs. Age-associated structural and functional changes in the aortic wall such as dilation, tortuousness, stiffening and losing elasticity hamper stable peripheral circulation, lead to tissue and organ dysfunctions in aged people. The extracellular matrix (ECM) is a three-dimensional network of macromolecules produced by resident cells. The composition and organization of key ECM components determine the structure-function relationships of the aorta and therefore maintaining their homeostasis is critical for a healthy performance. Age-associated remodeling of the ECM structural components, including fragmentation of elastic fibers and excessive deposition and crosslinking of collagens, is a hallmark of aging and leads to functional stiffening of the aorta. In this mini review, we discuss age-associated alterations of the ECM in the aortic wall and shed light on how understanding the mechanisms of aortic aging can lead to the development of efficient strategy for aortic pathologies and CVDs.

Urban fine particulate air pollution exposure promotes atherosclerosis in apolipoprotein E-deficient mice by activating perivascular adipose tissue inflammation via the Wnt5a/Ror2 signaling pathway

Urban fine particulate matter (PM_2.5) is a deleterious risk factor in the ambient air and is recognized to exacerbate atherosclerosis. Perivascular adipose tissue (PVAT) secretes a large number of inflammatory cytokines and plays a crucial role in the pathogenic microenvironment of atherogenesis. However, there is a lack of knowledge about the role of PVAT inflammation in the genesis of PM_2.5-related atherosclerosis. The aim of this research was to probe the latent links between PM_2.5 exposure and PVAT inflammation and further discovered the underlying mechanisms of PM_2.5-triggered atherosclerosis pathogenesis. Apolipoprotein E-deficient (ApoE^-/-) mice were exposed to real-world atmospheric PM_2.5 or filtered clean air for three months, the Wnt5a inhibitor Box5 and the Ror2 inhibitor β-Arrestin2 were applied to verify the possible mechanisms. We noticed that the average daily PM_2.5 mass concentration was 84.27 ± 28.84 μg/m³. PM_2.5 inhalation might significantly expedite the deterioration of atherosclerosis, increase the protein and mRNA expressions of MCP-1, IL-6, TNF-α, Wnt5a, and Ror2 in PVAT tissues, upregulate the distributions of IL-6, TNF-α, MCP-1, and leptin in the histological sections of PVAT, promote lipid deposition in the aorta, elevate the plasma levels of leptin, MCP-1, IL-6, TNF-α, LDL-C, TC, and TG, however, decrease the plasma levels of adiponectin and HDL-C, downregulate the distribution of adiponectin. Nevertheless, these effects caused by PM_2.5 exposure were dramatically diminished after the administration of Box5 or β-Arrestin2. This research illuminated that PVAT inflammation was involved in the PM_2.5-induced atherosclerosis process, as well as lipid deposition, which was closely associated with the activation of the Wnt5a/Ror2 signaling pathway.

Reciprocal organ interactions during heart failure: a position paper from the ESC Working Group on Myocardial Function

Heart failure-either with reduced or preserved ejection fraction (HFrEF/HFpEF)-is a clinical syndrome of multifactorial and gender-dependent aetiology, indicating the insufficiency of the heart to pump blood adequately to maintain blood flow to meet the body's needs. Typical symptoms commonly include shortness of breath, excessive fatigue with impaired exercise capacity, and peripheral oedema, thereby alluding to the fact that heart failure is a syndrome that affects multiple organ systems. Patients suffering from progressed heart failure have a very limited life expectancy, lower than that of numerous cancer types. In this position paper, we provide an overview regarding interactions between the heart and other organ systems, the clinical evidence, underlying mechanisms, potential available or yet-to-establish animal models to study such interactions and finally discuss potential new drug interventions to be developed in the future. Our working group suggests that more experimental research is required to understand the individual molecular mechanisms underlying heart failure and reinforces the urgency for tailored therapeutic interventions that target not only the heart but also other related affected organ systems to effectively treat heart failure as a clinical syndrome that affects and involves multiple organs.

The Role of Obesity-Induced Perivascular Adipose Tissue (PVAT) Dysfunction in Vascular Homeostasis

Perivascular adipose tissue (PVAT) is an additional special type of adipose tissue surrounding blood vessels. Under physiological conditions, PVAT plays a significant role in regulation of vascular tone, intravascular thermoregulation, and vascular smooth muscle cell (VSMC) proliferation. PVAT is responsible for releasing adipocytes-derived relaxing factors (ADRF) and perivascular-derived relaxing factors (PDRF), which have anticontractile properties. Obesity induces increased oxidative stress, an inflammatory state, and hypoxia, which contribute to PVAT dysfunction. The exact mechanism of vascular dysfunction in obesity is still not well clarified; however, there are some pathways such as renin-angiotensin-aldosterone system (RAAS) disorders and PVAT-derived factor dysregulation, which are involved in hypertension and endothelial dysfunction development. Physical activity has a beneficial effect on PVAT function among obese patients by reducing the oxidative stress and inflammatory state. Diet, which is the second most beneficial non-invasive strategy in obesity treatment, may have a positive impact on PVAT-derived factors and may restore the balance in their concentration.

The physiologic and physiopathologic roles of perivascular adipose tissue and its interactions with blood vessels and the renin-angiotensin system

The perivascular adipose tissue (PVAT) refers to an ectopic local deposit of connective tissue that anatomically surrounds most of the blood vessels. While it was initially known only as a structural support for vasculature, the landmark findings of Soltis and Cassis (1991), first demonstrating that PVAT reduces the contractions of norepinephrine in the isolated rat aorta, brought the potential vascular role of PVAT into the limelight. This seminal work implied the potential ability of PVAT to influence vascular responsiveness. Several vasoactive/vasocrine substances influencing vascular homeostasis were successively shown to be released from PVAT that include both adipocyte-derived relaxing and contracting factors. The PVAT is currently recognized as a metabolically active endocrine organ and is eventually considered as the 'protagonist' in vascular homeostasis. It plays prominent defending and opposing roles in vascular function, while the actual vascular influences of PVAT vary with an increase in adiposity. Recent studies have presented compelling evidence implicating the pivotal role of PVAT in the local activation of the renin-angiotensin system (RAS), which substantially impacts vascular physiology and physiopathology. Current findings have advanced our understanding of the role of PVAT in favorably or adversely modulating the vascular function through differential RAS activation. Given that adipocytes also produce major RAS components locally to influence vascular function, this review provides a scientific basis to distinctly understand the key role of PVAT in regulating the autocrine and paracrine functions of vascular RAS components and its potential as an emerging therapeutic target for mitigating cardiovascular complications.

Atorvastatin Attenuates Vascular Remodeling in Mice with Metabolic Syndrome

Fundamento

A síndrome metabólica é caracterizada por um conjunto de comorbidades. Durante a síndrome, observam-se alterações estruturais no sistema cardiovascular, especialmente o remodelamento vascular. Uma das causas predisponentes para essas alterações é a inflamação crônica oriunda de mudanças na estrutura e composição do tecido adiposo perivascular. Atorvastatina é eficaz no tratamento das dislipidemias. No entanto, seus efeitos pleiotrópicos não são totalmente compreendidos. Supõe-se que, durante a síndrome metabólica, ocorre remodelamento vascular e que o tratamento com atorvastatina pode ser capaz de atenuar tal condição.

Objetivos

Avaliar os efeitos do tratamento com atorvastatina sobre o remodelamento vascular em modelo experimental de síndrome metabólica.

Métodos

Camundongos Swiss receberam dieta controle ou dieta hiperglicídica por 18 semanas. Após 14 semanas de dieta, os camundongos foram tratados com veículo ou atorvastatina (20mg/kg) durante 4 semanas. Foram avaliados o perfil nutricional e metabólico por testes bioquímicos; análise estrutural da artéria aorta por histologia e dosagem de citocinas por ensaio imunoenzimático. O nível de significância aceitável para os resultados foi p <0,05.

Resultados

A dieta hiperglicídica promoveu o desenvolvimento de síndrome metabólica. Tal fato culminou no remodelamento hipertrófico do músculo liso vascular e tecido adiposo perivascular. Além disso, houve aumentos das citocinas TNF-α e IL-6 circulantes e no tecido adiposo perivascular. O tratamento com atorvastatina reduziu significativamente os danos metabólicos, o remodelamento vascular e os níveis de citocinas.

Conclusão

Atorvastatina ameniza danos metabólicos associados à síndrome metabólica induzida por dieta hiperglicídica, além de atenuar o remodelamento vascular, sendo esses efeitos associados à redução de citocinas pró-inflamatórias.

Oxidative Stress and Vascular Damage in the Context of Obesity: The Hidden Guest

The vascular system plays a central role in the transport of cells, oxygen and nutrients between different regions of the body, depending on the needs, as well as of metabolic waste products for their elimination. While the structure of different components of the vascular system varies, these structures, especially those of main arteries and arterioles, can be affected by the presence of different cardiovascular risk factors, including obesity. This vascular remodeling is mainly characterized by a thickening of the media layer as a consequence of changes in smooth muscle cells or excessive fibrosis accumulation. These vascular changes associated with obesity can trigger functional alterations, with endothelial dysfunction and vascular stiffness being especially common features of obese vessels. These changes can also lead to impaired tissue perfusion that may affect multiple tissues and organs. In this review, we focus on the role played by perivascular adipose tissue, the activation of the renin-angiotensin-aldosterone system and endoplasmic reticulum stress in the vascular dysfunction associated with obesity. In addition, the participation of oxidative stress in this vascular damage, which can be produced in the perivascular adipose tissue as well as in other components of the vascular wall, is updated.

Perivascular Adipose Tissue Inflammation in Ischemic Heart Disease

OBJECTIVE

There is growing recognition that adipose tissue-derived proatherogenic mediators contribute to obesity-related cardiovascular disease. We sought to characterize regional differences in perivascular adipose tissue (PVAT) phenotype in relation to atherosclerosis susceptibility. Approach and Results: We examined thoracic PVAT samples in 34 subjects (body mass index 32±6 kg/m², age 59±11 years) undergoing valvular, aortic, or coronary artery bypass graft surgeries and performed transcriptomic characterization using whole-genome expression profiling and quantitative polymerase chain reaction analyses. We identified a highly inflamed region of PVAT surrounding the human aortic root in close proximity to coronary takeoff and adjoining epicardial fat. In subjects undergoing coronary artery bypass graft, we found 300 genes significantly upregulated (false discovery rate Q<0.1) in paired samples of PVAT surrounding the aortic root compared with nonatherosclerotic left internal mammary artery. Genes encoding proteins mechanistically implicated in atherogenesis were enriched in aortic PVAT consisting of signaling pathways linked to inflammation, WNT (wingless-related integration site) signaling, matrix remodeling, coagulation, and angiogenesis. Overexpression of several proatherogenic transcripts, including IL1β, CCL2 (MCP-1), and IL6, were confirmed by quantitative polymerase chain reaction and significantly bolstered in coronary artery disease subjects. Angiographic coronary artery disease burden quantified by the Gensini score positively correlated with the expression of inflammatory genes in PVAT. Moreover, periaortic adipose inflammation was markedly higher in obese subjects with striking upregulation (≈8-fold) of IL1β expression compared to nonobese individuals.

CONCLUSIONS

Proatherogenic mediators that originate from dysfunctional PVAT may contribute to vascular disease mechanisms in human vessels. Moreover, PVAT may adopt detrimental properties under obese conditions that play a key role in the pathophysiology of ischemic heart disease. Graphic Abstract: A graphic abstract is available for this article.

APPLICATION OF QUERCETIN FOR CORRECTION OF THE IMPAIRMENT OF THE FUNCTIONAL STATE OF THE ENDOTHELIUS OF VESSELS (CLINICAL AND EXPERIMENTAL STUDY)

OBJECTIVE

in the experiment, to investigate the effect of Quercetin on the NO-dependent reactions of isolated vessels involving endothelium and perivascular adipose tissue (PVAT) after a single X-ray irradiation of rats at a sublethal dose. In a clinical study, to investigate the effect of long-term use of Quercetin on the functional state of themicrovascular endothelium in the elderly patients with metabolic syndrome (MS).

MATERIAL AND METHODS

Experimental studies were performed on vascular fragments obtained from adult male rats(7-8 months) of the control group, in animals exposed to a single R-irradiation at a dose of 7 Gy and animals irradiated in the same dose, which received Quercetin orally for 14 days three times a week based on 10 mg/kg bodyweight. Fragments of the thoracic aorta (TA) and mesenteric artery (MA) were cleaned of perivascular adipose tissue (PVAT-) or left uncleaned (PVAT+), and then were cut into rings (up to 2 mm). The amplitude of the contractionof the rings TA and MA under the influence of phenylephrine (PE, 3 x 10-6 M), the amplitude of the contraction of therings TA and MA in the presence of a competitive blocker of NO-synthase methyl ester of N-nitro-L-arginine(L-NAME, 10-5 M), the amplitude of relaxation of the rings TA and MA in the presence of N-acetylcysteine (NAC, 10-4 M)were measured. The clinical study examined 110 patients with MS criteria in accordance with ATP III (2001).Patients in the main group for 3 months received Quercetin from the same manufacturer, 80 mg three times a day,patients in the control group received placebo.

RESULTS

Single R-irradiation disrupts the regulation of the contractile function of TA and MA, which is evidenced bychanges in the contractile reactions of isolated fragments of these vessels as a response to the action of vasoactivecompounds. Course use of Quercetin in irradiated rats leads to the normalization of contractile and dilatory vascular responses due to partial correction of NO metabolism in the endothelium and PVAT. For the majority of patients(69 %) who received Quercetin, a post-occlusive hyperemia test showed a statistically significant increase of maximal volumetric velocity of the skin blood flow rate and duration of the recovery period to the baseline, which indicates about improvement of vasomotor vascular endothelial function.

CONCLUSIONS

Course use of Quercetin improves the functional state of the microvascular endothelium among theelderly people with MS, normalizes contractile and dilatory vascular responses in irradiated rats due to partial correction of NO metabolism in the endothelium and PVAT.

PVAT targets VSMCs to regulate vascular remodelling: angel or demon

Vascular remodelling refers to abnormal changes in the structure and function of blood vessel walls caused by injury, and is the main pathological basis of cardiovascular diseases such as atherosclerosis, hypertension, and pulmonary hypertension. Among them, the neointimal hyperplasia caused by abnormal proliferation of vascular smooth muscle cells (VSMCs) plays a key role in the pathogenesis of vascular remodelling. Perivascular adipose tissue (PVAT) can release vasoactive substances to target VSMCs and regulate the pathological process of vascular remodelling. Specifically, PVAT can promote the conversion of VSMCs phenotype from contraction to synthesis by secreting visfatin, leptin, and resistin, and participate in the development of vascular remodelling-related diseases. Conversely, it can also inhibit the growth of VSMCs by secreting adiponectin and omentin to prevent neointimal hyperplasia and alleviate vascular remodelling. Therefore, exploring and developing new drugs or other treatments that facilitate the beneficial effects of PVAT on VSMCs is a potential strategy for prevention or treatment of vascular remodelling-related cardiovascular diseases.

Ecklonia Cava Extract Attenuates Endothelial Cell Dysfunction by Modulation of Inflammation and Brown Adipocyte Function in Perivascular Fat Tissue

It is well known that perivascular fat tissue (PVAT) dysfunction can induce endothelial cell (EC) dysfunction, an event which is related with various cardiovascular diseases. In this study, we evaluated whether Ecklonia cava extract (ECE) and pyrogallol-phloroglucinol-6,6-bieckol (PPB), one component of ECE, could attenuate EC dysfunction by modulating diet-induced PVAT dysfunction mediated by inflammation and ER stress. A high fat diet (HFD) led to an increase in the number and size of white adipocytes in PVAT; PPB and ECE attenuated those increases. Additionally, ECE and PPB attenuated: (i) an increase in the number of M1 macrophages and the expression level of monocyte chemoattractant protein-1 (MCP-1), both of which are related to increases in macrophage infiltration and induction of inflammation in PVAT, and (ii) the expression of pro-inflammatory cytokines (e.g., tumor necrosis factor-α (TNF-α) and interleukin (IL)-6, chemerin) in PVAT which led to vasoconstriction. Furthermore, ECE and PPB: (i) enhanced the expression of adiponectin and IL-10 which had anti-inflammatory and vasodilator effects, (ii) decreased HFD-induced endoplasmic reticulum (ER) stress and (iii) attenuated the ER stress mediated reduction in sirtuin type 1 (Sirt1) and peroxisome proliferator-activated receptor γ (PPARγ) expression. Protective effects against decreased Sirt1 and PPARγ expression led to the restoration of uncoupling protein -1 (UCP-1) expression and the browning process in PVAT. PPB or ECE attenuated endothelial dysfunction by enhancing the pAMPK-PI3K-peNOS pathway and reducing the expression of endothelin-1 (ET-1). In conclusion, PPB and ECE attenuated PVAT dysfunction and subsequent endothelial dysfunction by: (i) decreasing inflammation and ER stress, and (ii) modulating brown adipocyte function.

The Influence of Photoperiod on the Action of Exogenous Leptin on Gene Expression of Proinflammatory Cytokines and Their Receptors in the Thoracic Perivascular Adipose Tissue (PVAT) in Ewes

Leptin resistance is either a condition induced by human obesity or a natural phenomenon associated with seasonality in ruminants. In the cardiovascular system, the leptin resistance state presence is a complex issue. Moreover, the perivascular adipose tissue (PVAT) appears to be crucial as a source of proinflammatory cytokines and as a site of interaction for leptin contributing to endothelium dysfunction and atherosclerosis progression. So the aim of this study was to examine the influence of the photoperiod on the action of exogenous leptin on gene expression of selected proinflammatory cytokines and their receptors in thoracic PVAT of ewe with or without prior lipopolysaccharide (LPS) stimulation. The experiment was conducted on 48 adult, female ewes divided into 4 group (n = 6 in each): control, with LPS intravenous (iv.) injection (400 ng/kg of BW), with leptin iv. injection (20 μg/kg BW), and with LPS and 30-minute-later leptin injection, during short-day (SD) and long-day (LD) seasons. Three hours after LPS/control treatment, animals were euthanized to collect the PVAT adherent to the aorta wall. The leptin injection enhanced IL1B gene expression only in the LD season; however, in both seasons leptin injection intensified LPS-induced increase in IL1B gene expression. IL1R2 gene expression was increased by leptin injection only in the SD season. Neither IL6 nor its receptor and signal transducer gene expressions were influenced by leptin administration. Leptin injection increased TNFA gene expression regardless of photoperiodic conditions. Only in the SD season did leptin treatment increase the gene expression of both TNFα receptors. To conclude, leptin may modulate the inflammatory reaction progress in PVAT. In ewe, the sensitivity of PVAT on leptin action is dependent upon the photoperiodic condition with stronger effects stated in the SD season.

In vitro tissue-engineered adipose constructs for modeling disease

BACKGROUND

Adipose tissue is a vital tissue in mammals that functions to insulate our bodies, regulate our internal thermostat, protect our organs, store energy (and burn energy, in the case of beige and brown fat), and provide endocrine signals to other organs in the body. Tissue engineering of adipose and other soft tissues may prove essential for people who have lost this tissue from trauma or disease.

MAIN TEXT

In this review, we discuss the applications of tissue-engineered adipose tissue specifically for disease modeling applications. We provide a basic background to adipose depots and describe three-dimensional (3D) in vitro adipose models for obesity, diabetes, and cancer research applications.

CONCLUSIONS

The approaches to engineering 3D adipose models are diverse in terms of scaffold type (hydrogel-based, silk-based and scaffold-free), species of origin (H. sapiens and M. musculus) and cell types used, which allows researchers to choose a model that best fits their application, whether it is optimization of adipocyte differentiation or studying the interaction of adipocytes and other cell types like endothelial cells. In vitro 3D adipose tissue models support discoveries into the mechanisms of adipose-related diseases and thus support the development of novel anti-cancer or anti-obesity/diabetes therapies.

Rab27a Regulates Human Perivascular Adipose Progenitor Cell Differentiation

PURPOSE

Perivascular adipose tissue (PVAT) surrounds blood vessels and regulates vascular tone through paracrine secretion of cytokines. During conditions promoting cardiometabolic dysfunction, such as obesity, cytokine secretion is altered towards a proinflammatory and proatherogenic profile. Despite the clinical implications for cardiovascular disease, studies addressing the biology of human PVAT remain limited. We are interested in characterizing the resident adipose progenitor cells (APCs) because of their potential role in PVAT expansion during obesity. We also focused on proteins regulating paracrine interactions, including the small GTPase Rab27a, which regulates protein trafficking and secretion.

METHODS

PVAT from the ascending aorta was collected from patients with severe cardiovascular disease undergoing coronary artery bypass grafting (CABG). Freshly-isolated PVAT was digested and APC expanded in culture for characterizing progenitor markers, evaluating adipogenic potential and assessing the function(s) of Rab27a.

RESULTS

Using flow cytometry, RT-PCR, and immunoblot, we characterized APC from human PVAT as negative for CD45 and CD31 and expressing CD73, CD105, and CD140A. These APCs differentiate into multilocular, UCP1-producing adipocytes in vitro. Rab27a was detected in interstitial cells of human PVAT in vivo and along F-actin tracks of PVAT-APC in vitro. Knockdown of Rab27a using siRNA in PVAT-APC prior to induction resulted in a marked reduction in lipid accumulation and reduced expression of adipogenic differentiation markers.

CONCLUSIONS

PVAT-APC from CABG donors express common adipocyte progenitor markers and differentiate into UCP1-containing adipocytes. Rab27a has an endogenous role in promoting the maturation of adipocytes from human PVAT-derived APC.

Perivascular Adipose Tissue: the Sixth Man of the Cardiovascular System

Perivascular adipose tissue (PVAT) refers to the local aggregate of adipose tissue surrounding the vascular tree, exhibiting phenotypes from white to brown and beige adipocytes. Although PVAT has long been regarded as simply a structural unit providing mechanical support to vasculature, it is now gaining reputation as an integral endocrine/paracrine component, in addition to the well-established modulator endothelium, in regulating vascular tone. Since the discovery of anti-contractile effect of PVAT in 1991, the use of multiple rodent models of reduced amounts of PVAT has revealed its regulatory role in vascular remodeling and cardiovascular implications, including atherosclerosis. PVAT does not only release PVAT-derived relaxing factors (PVRFs) to activate multiple subsets of endothelial and vascular smooth muscle potassium channels and anti-inflammatory signals in the vasculature, but it does also provide an interface for neuron-adipocyte interactions in the vascular wall to regulate arterial vascular tone. In this review, we outline our current understanding towards PVAT and attempt to provide hints about future studies that can sharpen the therapeutic potential of PVAT against cardiovascular diseases and their complications.

Alogliptin improves endothelial function by promoting autophagy in perivascular adipose tissue of obese mice through a GLP-1-dependent mechanism

OBJECTIVE

Perivascular adipose tissue (PVAT) regulates vascular function in a paracrine manner and the vasodilatory effect of PVAT on vessels is completely abolished in obesity. In addition, autophagy is required for maintaining biological function of PVAT and has been shown to be inhibited in obesity. The aim of this study was to explore whether alogliptin improves endothelial function by promoting autophagy in PVAT in obese mice.

METHODS

C57BL/6 mice were maintained on high fat diet with or without alogliptin intervention for 3 months. Vasorelaxation function of thoracic aorta with or without PVAT was determined. Autophagy related protein level of p62 and LC3B, along with phosphorylated mTOR (p-mTOR) were evaluated. In addition, the effects of alogliptin on autophagy were also investigated in cultured adipocytes.

RESULTS

The presence of PVAT significantly impaired endothelium-dependent vasodilation in obese mice and alogliptin intervention corrected this defect. Autophagy in PVAT was decreased in obese mice and alogliptin intervention activated autophagy. Activating autophagy in PVAT improved endothelium-dependent vasodilation while blocking it in PVAT impaired vasodilation function. Further, addition of glucagon-like peptide-1 (GLP-1) but not alogliptin alone activated autophagy. Moreover, GLP-1 and alogliptin co-treatment did not show additive effect on activating autophagy.

CONCLUSIONS

These results revealed that promoting autophagy in PVAT improved endothelial function in response to alogliptin intervention. Additionally, the beneficial effect of alogliptin intervention on PVAT was GLP-1 dependent.

Depletion of dendritic cells in perivascular adipose tissue improves arterial relaxation responses in type 2 diabetic mice

BACKGROUND

Accumulation of multiple subtypes of immune cells in perivascular adipose tissue (PVAT) has been proposed to cause vascular inflammation and dysfunction in type 2 diabetes (T2DM). This study was designed to investigate specific roles for dendritic cells in PVAT in the development of vascular inflammation and impaired PVAT-mediated vasorelaxation in T2DM.

METHODS AND RESULTS

Studies were performed using db/db mice (model of T2DM) and their Db heterozygote (DbHET), lean and normoglycemic controls. Dendritic cell depletion was performed by cross-breeding DbHet with Flt3l-/- (null for ligand for FMS-kinase tyrosine kinase) mice. Using PCR, it was found that the majority of dendritic cells (CD11c+) were located in PVAT rather than the vascular wall. Flow cytometry similarly showed greater dendritic cell accumulation in adipose tissue from db/db mice than DbHET controls. Adipose tissue from db/db mice displayed increased mRNA levels of proinflammatory cytokines TNF-α and IL-6 and decreased mRNA levels of the anti-inflammatory mediator adiponectin, compared to DbHET mice. Depletion of dendritic cells in dbFlt3l-/dbFlt3l- (confirmed by flow cytometry) reduced TNF-α and IL-6 mRNA levels in diabetic adipose tissue without influencing adiponection expression. Moreover, in mesenteric arteries, dendritic cell depletion improved the ability of PVAT to augment acetylcholine-induced vasorelaxation and anti-contractile activity.

CONCLUSIONS

In a murine model of T2DM, dendritic cells accumulated predominantly in PVAT, as opposed to the vessel wall, per se. Accumulation of dendritic cells in PVAT was associated with overproduction of pro-inflammatory cytokines, which contributed to an impaired ability of PVAT to augment vasorelaxation and exert anti-contractile activity in T2DM.

Micro-environment and intracellular metabolism modulation of adipose tissue macrophage polarization in relation to chronic inflammatory diseases

The accumulation and pro-inflammatory polarization of immune cells, mainly macrophages, in adipose tissue (AT) are considered crucial factors for obesity-induced chronic inflammatory diseases. In this review, we highlighted the role of adipose tissue macrophage (ATM) polarization on AT function in the obese state and the effect of the micro-environment and intracellular metabolism on the dynamic switch of ATMs into their pro-inflammatory or anti-inflammatory phenotypes, which may have distinct influences on obesity-related chronic inflammatory diseases. Obesity-associated metabolic dysfunctions, including those of glucose, fatty acid, cholesterol, and other nutrient substrates such as vitamin D and iron in AT, promote the pro-inflammatory polarization of ATMs and AT inflammation via regulating the interaction between ATMs and adipocytes and intracellular metabolic pathways, including glycolysis, fatty acid oxidation, and reverse cholesterol transportation. Focusing on the regulation of ATM metabolism will provide a novel target for the treatment of obesity-related chronic inflammatory diseases, including insulin resistance, cardiovascular diseases, and cancers.

Obesity phenotypes: depot-differences in adipose tissue and their clinical implications

Obesity, defined as excess fat mass, increases risks for multiple chronic diseases, such as type 2 diabetes, cardiovascular disease, and several types of cancer. Beyond adiposity per se, the pattern of fat distribution, android or truncal as compared to gynoid or peripheral, has a profound influence on systemic metabolism and hence risk for obesity complications. Not only factors as genetics, environment, gender, and age account for the apparent compartmentalization of white adipose tissue (WAT) in the body. Indeed, the heterogeneity among different anatomical depots also appears to stem from their intrinsic diversity, including cellular developmental origin, proliferative capacity, glucose and lipid metabolism, insulin sensitivity, cytokine pattern, thermogenic ability, and vascularization. Under the obese condition, these depot-specific differences translate into specific WAT distribution patterns, giving rise to different cardiometabolic consequences. This review summarizes the clinical and mechanistic evidence for the depot-specific differences and the phenotypic characteristics of different WAT depots that link their depot-specific biology to obesity-specific complications.

Distinct adipocyte progenitor cells are associated with regional phenotypes of perivascular aortic fat in mice

Objective

Perivascular adipose tissue depots around the aorta are regionally distinct and have specific functional properties. Thoracic aorta perivascular adipose tissue (tPVAT) expresses higher levels of thermogenic genes and lower levels of inflammatory genes than abdominal aorta perivascular adipose tissue (aPVAT). It is not known whether this distinction is due to the in-vivo functional environment or to cell-autonomous traits that persist outside the in-vivo setting. In this study, we asked whether the progenitor cells in tPVAT and aPVAT have cell-autonomous traits that lead to formation of regionally distinct PVAT.

Methods

We performed microarray analysis of thoracic and abdominal peri-aortic adipose tissues of C57Bl/6J mice to define gene expression profile of each depot. To derive adipocyte progenitor cells, C57Bl/6J mice were sacrificed and thoracic and abdominal aorta fragments were embedded in Matrigel and cultured under pro-angiogenic conditions. Adipogenesis was induced using the Ppar-γ agonist rosiglitazone, a thiazolidinedione (TZD). TZD-induced adipocyte populations were analyzed using immunofluorescence and qRT-PCR.

Results

Microarray analysis showed that tPVAT expressed higher levels of transcription factors related brown adipose tissue development compared to aPVAT. Classic brown adipose tissue (BAT) genes such as Ucp-1, Prdm16, Dio2, Slc27a displayed a concordant trend of higher level expression in tPVAT, while white adipose tissue (WAT) genes such as Hoxc8, Nnat, Sncg, and Mest were expressed at a higher level in aPVAT. The adipokines resistin and retinol binding protein 4 were also higher in aPVAT. Furthermore, adipocyte progenitors from abdominal and thoracic aortic rings responded to TZD with expression of canonical adipocyte genes Acrp30, Plin1, and Glut4. Adipocytes differentiated from thoracic aorta progenitors displayed markedly higher induction of Ucp-1 and Cidea.

Conclusions

Thoracic aorta PVAT expresses higher levels of brown adipocyte transcription factors than aPVAT. Precursor cells from the thoracic aorta give rise to adipocytes that express significantly higher levels of Ucp-1 and Cidea ex vivo, suggesting that progenitor cells in tPVAT and aPVAT have cell-autonomous properties that dictate adipocyte phenotype.

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Brown fat transcription factors are differentially expressed PVAT.

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Thoracic PVAT progenitors give rise to more thermogenic adipocytes.

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PVAT progenitors have cell-autonomous properties that dictate adipocyte phenotype.

Communication Is Key: Mechanisms of Intercellular Signaling in Vasodilation

Thirty years ago, Robert F. Furchgott concluded that nitric oxide, a compound traditionally known to be a toxic component of fuel exhaust, is in fact released from the endothelium, and in a paracrine fashion, induces relaxation of underlying vascular smooth muscle resulting in vasodilation. This discovery has helped pave the way for a more thorough understanding of vascular intercellular and intracellular communication that supports the process of regulating regional perfusion to match the local tissue oxygen demand. Vasoregulation is controlled not only by endothelial release of a diverse class of vasoactive compounds such as nitric oxide, arachidonic acid metabolites, and reactive oxygen species, but also by physical forces on the vascular wall and through electrotonic conduction through gap junctions. Although the endothelium is a critical source of vasoactive compounds, paracrine mediators can also be released from surrounding parenchyma such as perivascular fat, myocardium, and cells in the arterial adventitia to exert either local or remote vasomotor effects. The focus of this review will highlight the various means by which intercellular communication contributes to mechanisms of vasodilation. Paracrine signaling and parenchymal influences will be reviewed as well as regional vessel communication through gap junctions, connexons, and myoendothelial feedback. More recent modes of communication such as vesicular and microRNA signaling will also be discussed.

Antiobesity and Anti-Inflammatory Effects of Orally Administered Bonito Extracts on Mice Fed a High-Fat Diet

Background

The condensed fermentative extract of bonito (BoE), skipjack tuna (Katsuwonus pelamis), has claimed its health conditioning effects against lifestyle-related diseases such as hypertension and type 2 diabetes.

Methods

We evaluated the antiobesity and anti-inflammatory effects of BoE on mice fed a high-fat diet (HFD). Mice (9 weeks of age) were maintained for 11 weeks on HFD with or without BoE (50 mg or 500 mg/kg).

Results

Compared with untreated mice, BoE50 or BoE500 mice achieved maximum weight reductions of 7.4% (males) and 11.4% (females), and visceral fat in male BoE500 mice was more decreased among all mice (P = 0.00459). Furthermore, an antiobesity gene uncoupling protein-1 was significantly induced in the visceral fat tissues of male BoE500 (P = 0.0110) and female BoE50 and BoE500 mice (P = 0.0110 and P = 0.0110, resp.). Finally, we detected reduced amount of granulocyte-colony stimulating factor (P = 0.0250) in the sera of female BoE50 and interleukin- (IL-) 5 (P = 0.0120), IL-6 (P = 0.0118), and IL-13 (P = 0.0243) in female BoE500 mice.

Conclusion

The antiobesity and anti-inflammatory effects of BoE were demonstrated with our examination system and any toxic adverse effects were not observed in mice during the 3-month investigation.

Endothelial function and gene expression in perivascular adipose tissue from internal mammary arteries of obese patients with coronary artery disease

BACKGROUND AND AIMS

Obesity is a risk factor for endothelial dysfunction and atherosclerosis. However, perivascular adipose tissue can release adipokines and other unknown adipose-derived relaxing factors. Therefore, we investigated the impact of obesity on vascular function and expression of genes in perivascular adipose tissue from internal mammary arteries of patients with coronary artery disease undergoing coronary artery bypass grafting.

METHODS

The vessel function was compared between groups of patients with a body-mass index (BMI) between 25 and 30 kg/m². The groups did not differ in age, gender (males), and ejection fraction. Vascular segments of internal mammary arteries were examined in a Mulvany myograph. Following preconstriction with noradrenaline, dose-response curves were assessed for relaxation with acetylcholine and sodium nitroprusside.

RESULTS

Maximum contraction in response to potassium and noradrenaline was increased in obese patients with a BMI >30 kg/m². EC50 of endothelium-dependent relaxation was impaired in patients with a BMI above 25, but below 30 kg/m². Sodium nitroprusside-mediated maximal relaxation was not different between study groups. Integrin alpha X chain (ITGAX/CD11c) and macrophage mannose receptor (MRC1/CD206) expression was reduced in perivascular adipose tissue of patients with a BMI above 30 kg/m², while adiponectin (ADPQ) expression was increased in the same tissue.

CONCLUSION

Our data suggest a partially reduced endothelial function in internal mammary arteries of adipose patients with a BMI between 25 and 30 kg/m² undergoing coronary artery bypass grafting surgery. Increased adiponectin expression in perivascular tissue might contribute to maintenance of endothelial function in obese patients with a BMI above 30 kg/m².

Pro-contractile effects of perivascular fat in health and disease

Perivascular adipose tissue (PVAT) is now recognized as an active player in vascular homeostasis. The expansion of PVAT in obesity and its possible role in vascular dysfunction have attracted much interest. In terms of the regulation of vascular tone and blood pressure, PVAT has been shown to release vasoactive mediators, for instance, angiotensin peptides, reactive oxygen species, chemokines and cytokines. The secretory profile of PVAT is altered by obesity, hypertension and other cardiovascular diseases, leading to an imbalance between its pro-contractile and anti-contractile effects. PVAT adipocytes represent an important source of the mediators, but infiltrating immune cells may become more important under conditions of hypoxia and inflammation. This review describes recent advances in the effects of PVAT on the regulation of vascular tone, highlighting the evidence for a pro-contractile action in health and disease. The role of the endothelium, vascular smooth muscle, immune cells and probably perivascular nerves in PVAT function is also discussed.

LINKED ARTICLES

This article is part of a themed section on Molecular Mechanisms Regulating Perivascular Adipose Tissue - Potential Pharmacological Targets? To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v174.20/issuetoc.

Time-Dependent Differences in the Influence of Perivascular Adipose Tissue on Vasomotor Functions in Metabolic Syndrome

BACKGROUND

Metabolic syndrome (MetS) facilitates the development of cardiovascular disease due to atherosclerosis, which is accelerated by defects of the vascular endothelium. Vascular dysfunction in response to nitric oxide (NO) occurs in the mesenteric arteries of an animal model of MetS, SHRSP.Z-Lepr^fa/IzmDmcr (SHRSP.ZF) rats. Vascular responses to vasodilators are affected by perivascular adipose tissue (PVAT) that surrounds the outsides of arteries. In this study, we assessed the role of PVAT in vascular dysfunction observed in SHRSP.ZF.

METHODS

To determine the effects of PVAT on vasodilators in SHRSP.ZF and control Wistar-Kyoto (WKY) rats, we used organ bath bioassay techniques to assay acetylcholine and nitroprusside-induced relaxations of isolated mesenteric arterial ring preparations with PVAT intact or removed.

RESULTS

A PVAT-mediated enhancement of relaxations induced by acetylcholine and nitroprusside occurred in SHRSP.ZF at 20 weeks of age, but not at 10 and 30 weeks, and did not occur in WKY. Furthermore, the enhancing effects of PVAT from SHRSP.ZF at 20 weeks could not be substituted by replacement with PVAT from either WKY or 30-week-old SHRSP.ZF, was inhibited by NO synthase inhibitor, and abolished by removal of the arteries' endothelium. Cyclic guanosine monophosphate (cGMP) accumulation elicited by nitroprusside was higher in SHRSP.ZF arteries with PVAT than arteries without PVAT at 20 weeks, but the enhancement of cGMP accumulation did not occur at 30 weeks.

CONCLUSIONS

PVAT may regulate arterial tone by releasing diffusible vasorelaxing factor(s), which, through endothelium-derived NO production, compensates for impaired vasodilations at early stages of MetS.

Prostanoids in the pathophysiology of human coronary artery

Coronary artery disease is one of the leading causes of death in wordwide. There is growing evidence that prostanoids are involved in the physiology and pathophysiology of the human coronary artery by controlling vascular tone, remodelling of the vascular wall or angiogenesis. In this review, the production of prostanoids and the expression of prostanoid receptors in human coronary artery in health or disease are described. In addition, the interactions between sex hormones and prostanoids, their participations in the development of coronary artery diseases have been addressed. Globally, most of the studies performed in human coronary artery preparations have shown that prostacyclin (PGI₂) has beneficial effects by inducing vasodilatation and promoting angiogenesis while reverse effects are confirmed by thromboxane A₂ (TxA₂). More studies are needed to determine the roles of the other prostanoids (PGE₂, PGD₂ and PGF_2α) in vascular functions of the human coronary artery. Finally, in addition to the in vitro data about the human coronary artery, myocardial infarction induced by cyclooxygenase-2 (COX-2) inhibitor and the protective effects of aspirin after coronary artery bypass surgery suggest that prostanoids are key mediators in coronary homeostasis.

Beyond obesity – thermogenic adipocytes and cardiometabolic health

The global prevalence of obesity and related cardiometabolic disease continues to increase through the 21st century. Whilst multi-factorial, obesity is ultimately caused by chronic caloric excess. However, despite numerous interventions focussing on reducing caloric intake these either fail or only elicit short-term changes in body mass. There is now a focus on increasing energy expenditure instead which has stemmed from the recent ‘re-discovery’ of cold-activated brown adipose tissue (BAT) in adult humans and inducible ‘beige’ adipocytes. Through the unique mitochondrial uncoupling protein 1 (UCP1), these thermogenic adipocytes are capable of combusting large amounts of chemical energy as heat and in animal models can prevent obesity and cardiometabolic disease. At present, human data does not point to a role for thermogenic adipocytes in regulating body weight or fat mass but points to a pivotal role in regulating metabolic health by improving insulin resistance as well as glucose and lipid homeostasis. This review will therefore focus on the metabolic benefits of BAT activation and the mechanisms and signalling pathways by which these could occur including improvements in insulin signalling in peripheral tissues, systemic lipid and cholesterol metabolism and cardiac and vascular function.

Endothelial Dysfunction in Obesity

Chronic inflammatory state in obesity causes dysregulation of the endocrine and paracrine actions of adipocyte-derived factors, which disrupt vascular homeostasis and contribute to endothelial vasodilator dysfunction and subsequent hypertension. While normal healthy perivascular adipose tissue (PVAT) ensures the dilation of blood vessels, obesity-associated PVAT leads to a change in profile of the released adipo-cytokines, resulting in a decreased vasorelaxing effect. Adipose tissue inflammation, nitric oxide (NO)-bioavailability, insulin resistance and oxidized low-density lipoprotein (oxLDL) are main participating factors in endothelial dysfunction of obesity. In this chapter, disruption of inter-endothelial junctions between endothelial cells, significant increase in the production of reactive oxygen species (ROS), inflammation mediators, which are originated from inflamed endothelial cells, the balance between NO synthesis and ROS , insulin signaling and NO production, and decrease in L-arginine/endogenous asymmetric dimethyl-L-arginine (ADMA) ratio are discussed in connection with endothelial dysfunction in obesity.

Adiponectin-Resistance in Obesity

The decrease in adiponectin levels are negatively correlated with chronic subclinical inflammation markers in obesity. The hypertrophic adipocytes cause obesity-linked insulin resistance and metabolic syndrome. Furthermore, macrophage polarization is a key determinant regulating adiponectin receptor (AdipoR1/R2) expression and differential adiponectin-mediated macrophage inflammatory responses in obese individuals. In addition to decrease in adiponectin concentrations, the decline in AdipoR1/R2 mRNA expression leads to a decrement in adiponectin binding to cell membrane, and this turns into attenuation in the adiponectin effects. Within the receptor complex, adaptor protein-containing pleckstrin homology domain, phosphotyrosine-binding domain, and leucine zipper motif 1 (APPL1) is the intracellular binding partner of AdipoR1 and AdipoR2. The expression levels of APPL1 or APPL2 lead to an altered adiponectin activity. Despite normal or high adiponectin levels, an impaired post receptor signaling due to APPL1/APPL2 may alter adiponectin efficiency and activity. However, APPL2 blocks adiponectin signaling through AdipoR1 and AdipoR2 by competitive inhibition of APPL1. APPL1 is also an important mediator of adiponectin dependent insulin sensitization. In this context, adiponectin resistance is associated with insulin resistance and is thought to be partly due to the down-regulation of the AdipoRs in high-fat diet fed subjects. Actually, adiponectin resistance occurs very rapidly after saturated fatty acid feeding, this metabolic disturbance is not due to a decrease in AdipoR1 protein content. Intra-abdominal adipose tissue-AdipoR2 expression is reduced in obesity, whereas AdipoR1 expression is not changed. Adiponectin resistance together with insulin resistance forms a vicious cycle. The elevated adiponectin levels with adiponectin resistance is a compensatory response in the condition of an unusual discordance between insulin resistance and adiponectin unresponsiveness.Additionally, different mechanisms are involved in vascular adiponectin resistance at different stages of obesity. Nevertheless, diet-induced hyperlipidemia is the leading cause of vascular adiponectin resistance. Leptin/adiponectin imbalance may also be an important marker of the elevated risk of developing abdominal obesity-associated cardiovascular diseases.

Contribution of Maladaptive Adipose Tissue Expansion to Development of Cardiovascular Disease

The overweight and obesity epidemic has led to an increase in the metabolic syndrome and associated cardiovascular disease (CVD). These abnormalities include insulin resistance, type 2 diabetes mellitus, vascular stiffness, hypertension, stroke, and coronary heart disease. Visceral white adipocyte tissue (WAT) expansion and associated fibrosis/stiffness of WAT promote insulin resistance and CVD through increases in proinflammatory adipokines, oxidative stress, activation of renin-angiotensin-aldosterone system, dysregulation of adipocyte apoptosis and autophagy, dysfunctional immune modulation, and adverse changes in the gut microbiome. The expansion of WAT is partly determined by activation of peroxisome proliferator-activated receptor gamma and mammalian target of rapamycin/ribosomal S6 kinase signaling pathways. Further, the chronic activation of these signaling pathways may not only induce adipocyte hypertrophy and fibrosis, but also contribute to systemic inflammation, and impairment of insulin metabolic signaling in fat, liver, and skeletal muscle tissue. Therefore, the interplay of adipocyte dysfunction, maladaptive immune and inflammatory responses, and associated metabolic disorders often coexist leading to systemic low-grade inflammation and insulin resistance that are associated with increased CVD in obese individuals. © 2017 American Physiological Society. Compr Physiol 7:253-262, 2017.

The role of perivascular adipose tissue in obesity-induced vascular dysfunction

Under physiological conditions, perivascular adipose tissue (PVAT) attenuates agonist‐induced vasoconstriction by releasing vasoactive molecules including hydrogen peroxide, angiotensin 1–7, adiponectin, methyl palmitate, hydrogen sulfide, NO and leptin. This anticontractile effect of PVAT is lost under conditions of obesity. The central mechanism underlying this PVAT dysfunction in obesity is likely to be an ‘obesity triad’ (consisting of PVAT hypoxia, inflammation and oxidative stress) that leads to the impairment of PVAT‐derived vasoregulators. The production of hydrogen sulfide, NO and adiponectin by PVAT is reduced in obesity, whereas the vasodilator response to leptin is impaired (vascular leptin resistance). Strikingly, the vasodilator response to acetylcholine is reduced only in PVAT‐containing, but not in PVAT‐free thoracic aorta isolated from diet‐induced obese mice, indicating a unique role for PVAT in obesity‐induced vascular dysfunction. Furthermore, PVAT dysfunction has also been observed in small arteries isolated from the gluteal/visceral fat biopsy samples of obese individuals. Therefore, PVAT may represent a new therapeutic target for vascular complications in obesity. A number of approaches are currently being tested under experimental conditions. Potential therapeutic strategies improving PVAT function include body weight reduction, enhancing PVAT hydrogen sulfide release (e.g. rosiglitazone, atorvastatin and cannabinoid CB₁ receptor agonists) and NO production (e.g. arginase inhibitors), inhibition of the renin–angiotensin–aldosterone system, inhibition of inflammation with melatonin or cytokine antagonists, activators of AMP‐activated kinase (e.g. metformin, resveratrol and diosgenin) and adiponectin releasers or expression enhancers.

Linked Articles

This article is part of a themed section on Molecular Mechanisms Regulating Perivascular Adipose Tissue – Potential Pharmacological Targets? To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v174.20/issuetoc

'Browning' the cardiac and peri-vascular adipose tissues to modulate cardiovascular risk

Excess visceral adiposity, in particular that located adjacent to the heart and coronary arteries is associated with increased cardiovascular risk. In the pathophysiological state, dysfunctional adipose tissue secretes an array of factors modulating vascular function and driving atherogenesis. Conversely, brown and beige adipose tissues utilise glucose and lipids to generate heat and are associated with improved cardiometabolic health. The cardiac and thoracic perivascular adipose tissues are now understood to be composed of brown adipose tissue in the healthy state and undergo a brown-to-white transition i.e. during obesity which may be a driving factor of cardiovascular disease. In this review we discuss the risks of excess cardiac and vascular adiposity and potential mechanisms by which restoring the brown phenotype i.e. “re-browning” could potentially be achieved in clinically relevant populations.

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Epicardial, paracardial and thoracic perivascular adipose tissues resemble BAT at birth.

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Despite ‘whitening’ in early life these depots remain metabolically active and potentially thermogenic into adulthood.

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Obesity induces further ‘whitening’ and inflammation in these depots likely driving the atherogenesis.

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Maintaining or inducing the brown phenotype in these depots could prevent atherosclerotic disease.

Differential Role of Adipose Tissues in Obesity and Related Metabolic and Vascular Complications

This review focuses on the contribution of white, brown, and perivascular adipose tissues to the pathophysiology of obesity and its associated metabolic and vascular complications. Weight gain in obesity generates excess of fat, usually visceral fat, and activates the inflammatory response in the adipocytes and then in other tissues such as liver. Therefore, low systemic inflammation responsible for insulin resistance contributes to atherosclerotic process. Furthermore, an inverse relationship between body mass index and brown adipose tissue activity has been described. For these reasons, in recent years, in order to combat obesity and its related complications, as a complement to conventional treatments, a new insight is focusing on the role of the thermogenic function of brown and perivascular adipose tissues as a promising therapy in humans. These lines of knowledge are focused on the design of new drugs, or other approaches, in order to increase the mass and/or activity of brown adipose tissue or the browning process of beige cells from white adipose tissue. These new treatments may contribute not only to reduce obesity but also to prevent highly prevalent complications such as type 2 diabetes and other vascular alterations, such as hypertension or atherosclerosis.

Severe Brown Fat Lipoatrophy Aggravates Atherosclerotic Process in Male Mice

Obesity is one of the major risk factors for the development of cardiovascular diseases and is characterized by abnormal accumulation of adipose tissue, including perivascular adipose tissue (PVAT). However, brown adipose tissue (BAT) activation reduces visceral adiposity. To demonstrate that severe brown fat lipoatrophy might accelerate atherosclerotic process, we generated a new mouse model without insulin receptor (IR) in BAT and without apolipoprotein (Apo)E (BAT-specific IR knockout [BATIRKO];ApoE(-/-) mice) and assessed vascular and metabolic alterations associated to obesity. In addition, we analyzed the contribution of the adipose organ to vascular inflammation. Brown fat lipoatrophy induces visceral adiposity, mainly in gonadal depot (gonadal white adipose tissue [gWAT]), severe glucose intolerance, high postprandial glucose levels, and a severe defect in acute insulin secretion. BATIRKO;ApoE(-/-) mice showed greater hypertriglyceridemia than the obtained in ApoE(-/-) and hypercholesterolemia similar to ApoE(-/-) mice. BATIRKO;ApoE(-/-) mice, in addition to primary insulin resistance in BAT, also showed a significant decrease in insulin signaling in liver, gWAT, heart, aorta artery, and thoracic PVAT. More importantly, our results suggest that severe brown fat lipoatrophy aggravates the atherosclerotic process, characterized by a significant increase of lipid depots, atherosclerotic coverage, lesion size and complexity, increased macrophage infiltration, and proinflammatory markers expression. Finally, an increase of TNF-α and leptin as well as a decrease of adiponectin by BAT, gWAT, and thoracic PVAT might also be responsible of vascular damage. Our results suggest that severe brown lipoatrophy aggravates atherosclerotic process. Thus, BAT activation might protect against obesity and its associated metabolic alterations.

Overweight status is associated with extensive signs of microvascular dysfunction and cardiovascular risk

The aim of this present study was to investigate if overweight individuals exhibit signs of vascular dysfunction associated with a high risk for cardiovascular disease (CVD). One hundred lean and 100 overweight participants were recruited for the present study. Retinal microvascular function was assessed using the Dynamic Retinal Vessel Analyser (DVA), and systemic macrovascular function by means of flow-mediated dilation (FMD). Investigations also included body composition, carotid intimal-media thickness (c-IMT), ambulatory blood pressure monitoring (BP), fasting plasma glucose, triglycerides (TG), cholesterol levels (HDL-C and LDL-C), and plasma von Willebrand factor (vWF). Overweight individuals presented with higher right and left c-IMT (p = 0.005 and p = 0.002, respectively), average 24-h BP values (all p < 0.001), plasma glucose (p = 0.008), TG (p = 0.003), TG: HDL-C ratio (p = 0.010), and vWF levels (p = 0.004). Moreover, overweight individuals showed lower retinal arterial microvascular dilation (p = 0.039) and baseline-corrected flicker (bFR) responses (p = 0.022), as well as, prolonged dilation reaction time (RT, p = 0.047). These observations emphasise the importance of vascular screening and consideration of preventive interventions to decrease vascular risk in all individuals with adiposity above normal range.