Dahl SS rats demonstrate enhanced aortic perivascular adipose tissue-mediated buffering of vasoconstriction through activation of NOS in the endothelium

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.

Effects of Long-Term Aerobic Exercise on Perivascular Adipose Tissue Function and Akt/eNOS/NO Pathway in Obese Rats

Background

Perivascular adipose tissue (PVAT) in obesity critically contributes to vascular dysfunction, which might be restored by long-term exercise. Protein kinase B/nitric oxide synthase/nitric oxide (Akt/eNOS/NO) down-regulation within PVAT might be involved in the impaired anti-contractile function of arteries. Therefore, the present study evaluated the effect of long-term aerobic exercise on PVAT function and the potential regulator during this process.

Methods

Male Sprague Dawley rats were divided into normal diet control group (NC), normal diet exercise group (NE), high-fat diet control group (HC), and high-fat diet exercise group (HE) (n = 12 in each group). Upon the establishment of obesity (20 weeks of high-fat diet), exercise program was performed on a treadmill for 17 weeks. After the intervention, circulating biomarkers and PVAT morphology were evaluated. Vascular contraction and relaxation were determined with or without PVAT. Production of NO and the phosphorylations of Akt (Ser473) and eNOS (Ser1177) within PVAT were quantified.

Results

Metabolic abnormalities, systemic inflammation, and circulating adipokines in obesity were significantly restored by long-term aerobic exercise (P < 0.05). The anti-contractile effect of PVAT was significantly enhanced by exercise in obese rats (P < 0.05), which was accompanied by a significant reduction in the PVAT mass and lipid droplet area (P < 0.05). Furthermore, the production of NO was significantly increased, and phosphorylation levels of Akt (Ser473) and eNOS (Ser1177) were also significantly promoted in PVAT by long-term aerobic exercise (P < 0.05).

Conclusion

Long-term aerobic exercise training restored PVAT morphology and anti-contractile function in obese rats, and enhanced the activation of the Akt/eNOS/NO signaling pathway in PVAT.

Administration of recombinant human placental growth factor decreases blood pressure in obese hypertensive pregnant rats

OBJECTIVES

Although epidemiological studies have shown that obesity is associated with increased incidence of hypertension during pregnancy, the mechanisms linking these two comorbidities are not as well studied. Previous investigations detected lower levels of the anti-hypertensive and pregnancy-related factor, placental growth factor (PlGF), in obese hypertensive pregnancies. Therefore, we examined whether obese hypertensive pregnant rats have reduced PlGF and whether increasing its levels by administering recombinant human (rh)PlGF reduces their blood pressure.

METHODS

We utilized a genetic model of obesity characterized to be heavier, hypertensive and fertile, namely rats having heterozygous deficiency of the melanocortin-4 receptor (MC4R-def).

RESULTS

MC4R-def obese rats had lower circulating levels of PlGF than wild-type lean controls at gestational day 19. Also, assessment of the PlGF receptor, Flt-1, in the vasculature showed that its levels were reduced in aorta and kidney glomeruli but increased in small mesenteric arteries. Chronic intraperitoneal administration of rhPlGF from gestational day 13-19 significantly increased circulating PlGF levels in both obese and lean rats, but reduced blood pressure only in the obese pregnant group. The rhPlGF treatment did not alter maternal body and fat masses or circulating levels of the adipokines, leptin and adiponectin. In addition, this treatment did not impact average foetal weights but increased placental weights regardless of obese or lean pregnancy.

CONCLUSION

PlGF is reduced in MC4R-def obese hypertensive pregnant rats, which is similar to findings in obese hypertensive pregnant women, while increasing its levels with exogenous rhPlGF reduces their blood pressure.

Liver circadian clock disruption alters perivascular adipose tissue gene expression and aortic function in mice

The liver plays a central role that influences cardiovascular disease outcomes through regulation of glucose and lipid metabolism. It is recognized that the local liver molecular clock regulates some liver-derived metabolites. However, it is unknown whether the liver clock may impact cardiovascular function. Perivascular adipose tissue (PVAT) is a specialized type of adipose tissue surrounding blood vessels. Importantly, cross talk between the endothelium and PVAT via vasoactive factors is critical for vascular function. Therefore, we designed studies to test the hypothesis that cardiovascular function, including PVAT function, is impaired in mice with liver-specific circadian clock disruption. Bmal1 is a core circadian clock gene, thus studies were undertaken in male hepatocyte-specific Bmal1 knockout (HBK) mice and littermate controls (i.e., flox mice). HBK mice showed significantly elevated plasma levels of β-hydroxybutyrate, nonesterified fatty acids/free fatty acids, triglycerides, and insulin-like growth factor 1 compared with flox mice. Thoracic aorta PVAT in HBK mice had increased mRNA expression of several key regulatory and metabolic genes, Ppargc1a, Pparg, Adipoq, Lpl, and Ucp1, suggesting altered PVAT energy metabolism and thermogenesis. Sensitivity to acetylcholine-induced vasorelaxation was significantly decreased in the aortae of HBK mice with PVAT attached compared with aortae of HBK mice with PVAT removed, however, aortic vasorelaxation in flox mice showed no differences with or without attached PVAT. HBK mice had a significantly lower systolic blood pressure during the inactive period of the day. These new findings establish a novel role of the liver circadian clock in regulating PVAT metabolic gene expression and PVAT-mediated aortic vascular function.

Male and female high-fat diet-fed Dahl SS rats are largely protected from vascular dysfunctions: PVAT contributions reveal sex differences

Vascular dysfunctions are observed in the arteries from hypertensive subjects. The establishment of the Dahl salt-sensitive (SS) male and female rat models to develop a reproducible hypertension with high-fat (HF) diet feeding from weaning allows addressing the question of whether HF diet-associated hypertension results in vascular dysfunction similar to that of essential hypertension in both sexes. We hypothesized that dysfunction of three distinct vascular layers, i.e., endothelial, smooth muscle, and perivascular adipose tissue (PVAT), would be present in the aorta from HF diet-fed versus control diet-fed male and female rats. Dahl SS rats were fed a control (10% kcal of fat) or HF (60%) diet from weaning for 24 wk. Male and female Dahl SS rats became equally hypertensive when placed on a HF diet. For male and female rats, the thoracic aorta exhibited medial hypertrophy in HF diet-induced hypertension versus control, but neither displayed a hyperresponsive contraction to the α-adrenergic agonist phenylephrine nor an endothelial cell dysfunction as measured by acetylcholine-induced relaxation. A beneficial PVAT function, support of stress relaxation, was reduced in the male versus female rats fed a HF diet. PVAT in the aorta of males but not in females retained the anticontractile activity. We conclude that this HF model does not display the same vascular dysfunctions observed in essential hypertension. Moreover, both male and female show significantly different vascular dysfunctions in this HF feeding model.NEW & NOTEWORTHY Although the aorta exhibits medial hypertrophy in response to HF diet-induced hypertension, it did not exhibit hyperresponsive contraction to an α-adrenergic agonist nor endothelial cell dysfunction; this was true for both sexes. Unlike other hypertension models, PVAT around aorta from (male) rats on the HF diet retained significant anticontractile activity. PVAT around aorta of the male on a HF diet was modestly more fibrotic and lost the ability to assist in arterial stress relaxation.

The Local Regulation of Vascular Function: From an Inside-Outside to an Outside-Inside Model

Our understanding of the regulation of vascular function, specifically that of vasomotion, has evolved dramatically over the past few decades. The classic conception of a vascular system solely regulated by circulating hormones and sympathetic innervation gave way to a vision of a local regulation. Initially by the so-called, autacoids like prostacyclin, which represented the first endothelium-derived paracrine regulator of smooth muscle. This was the prelude of the EDRF-nitric oxide age that has occupied vascular scientists for nearly 30 years. Endothelial cells revealed to have the ability to generate numerous mediators besides prostacyclin and nitric oxide (NO). The need to classify these substances led to the coining of the terms: endothelium-derived relaxing, hyperpolarizing and contracting factors, which included various prostaglandins, thromboxane A2, endothelin, as well numerous candidates for the hyperpolarizing factor. The opposite layer of the vascular wall, the adventitia, eventually and for a quite short period of time, enjoyed the attention of some vascular physiologists. Adventitial fibroblasts were recognized as paracrine cells to the smooth muscle because of their ability to produce some substances such as superoxide. Remarkably, this took place before our awareness of the functional potential of another adventitial cell, the adipocyte. Possibly, because the perivascular adipose tissue (PVAT) was systematically removed during the experiments as considered a non-vascular artifact tissue, it took quite long to be considered a major source of paracrine substances. These are now being integrated in the vast pool of mediators synthesized by adipocytes, known as adipokines. They include hormones involved in metabolic regulation, like leptin or adiponectin; classic vascular mediators like NO, angiotensin II or catecholamines; and inflammatory mediators or adipocytokines. The first substance studied was an anti-contractile factor named adipose-derived relaxing factor of uncertain chemical nature but possibly, some of the relaxing mediators mentioned above are behind this factor. This manuscript intends to review the vascular regulation from the point of view of the paracrine control exerted by the cells present in the vascular environment, namely, endothelial, adventitial, adipocyte and vascular stromal cells.

Genome-wide map of proximity linkage to renin proximal promoter in rat

A challenge to understanding enhancer-gene relationships is that enhancers are not always sequentially close to the gene they regulate. Physical proximity mapping through sequencing can provide an unbiased view of the chromatin close to the proximal promoter of the renin gene ( Ren). Our objective was to determine genomic regions that physically interact with the renin proximal promoter, using two different genetic backgrounds, the Dahl salt sensitive and normotensive SS-13BN, which have been shown to have different regulation of plasma renin in vivo. The chromatin conformation capture method with sequencing focused at the Ren proximal promoter in rat-derived cardiac endothelial cells was used. Cells were fixed, chromatin close to the Ren promoter was captured, and fragments were sequenced. The clustering of mapped reads produced a genome-wide map of chromatin in contact with the Ren promoter. The largest number of contacts was found on chromosome 13, the chromosome with Ren, and contacts were found on all other chromosomes except chromosome X. These contacts were significantly enriched with genes positively correlated with Ren expression and with mapped quantitative trait loci associated with blood pressure, cardiovascular, and renal phenotypes. The results were reproducible in an independent biological replicate. The findings reported here represent the first map between a critical cardiovascular gene and physical interacting loci throughout the genome and will provide the basis for several new directions of research.

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.

Brown Adipose Tissue Regulates Small Artery Function Through NADPH Oxidase 4–Derived Hydrogen Peroxide and Redox-Sensitive Protein Kinase G-1α

Objective—

Biomedical interest in brown adipose tissue (BAT) has increased since the discovery of functionally active BAT in adult humans. Although white adipose tissue (WAT) influences vascular function, vascular effects of BAT are elusive. Thus, we investigated the regulatory role and putative vasoprotective effects of BAT, focusing on hydrogen peroxide, nicotinamide adenine dinucleotide phosphate oxidase 4 (Nox4), and redox-sensitive signaling.

Approach and Results—

Vascular reactivity was assessed in wild-type and Nox4-knockout mice (Nox4 −/− ) by wire myography in the absence and presence of perivascular adipose tissue of different phenotypes from various adipose depots: (1) mixed WAT/BAT (inguinal adipose tissue) and (2) WAT (epididymal visceral fat) and BAT (intrascapular fat). In wild-type mice, epididymal visceral fat and perivascular adipose tissue increased EC 50 to noradrenaline without affecting maximum contraction. BAT increased EC 50 and significantly decreased maximum contraction, which were prevented by a hydrogen peroxide scavenger (polyethylene glycated catalase) and a specific cyclic GMP–dependent protein kinase G type-1α inhibitor (DT-3), but not by inhibition of endothelial nitric oxide synthase or guanylate cyclase. BAT induced dimerization of cyclic GMP–dependent protein kinase G type-1α and reduced phosphorylation of myosin light chain phosphatase subunit 1 and myosin light chain 20. BAT from Nox4-knockout mice displayed reduced hydrogen peroxide levels and no anticontractile effects. Perivascular adipose tissue from β 3 agonist–treated mice displayed browned perivascular adipose tissue and an increased anticontractile effect.

Conclusions—

We identify a novel vasoprotective action of BAT through an anticontractile effect that is mechanistically different to WAT. Specifically, BAT, via Nox4-derived hydrogen peroxide, induces cyclic GMP–dependent protein kinase G type-1α activation, resulting in reduced vascular contractility. BAT may constitute an interesting therapeutic target to restore vascular function and prevent vascular complications in cardiovascular diseases.

Increased mitochondrial ROS generation mediates the loss of the anti-contractile effects of perivascular adipose tissue in high-fat diet obese mice

BACKGROUND AND PURPOSE

Obesity is associated with structural and functional changes in perivascular adipose tissue (PVAT), favouring release of reactive oxygen species (ROS), vasoconstrictor and proinflammatory factors. The cytokine TNF-α induces vascular dysfunction and is produced by PVAT. We tested the hypothesis that obesity-associated PVAT dysfunction was mediated by augmented mitochondrial ROS (mROS) generation due to increased TNF-α production in this tissue.

EXPERIMENTAL APPROACH

C57Bl/6J and TNF-α receptor-deficient mice received control or high fat diet (HFD) for 18 weeks. We used pharmacological tools to determine the participation of mROS in PVAT dysfunction. Superoxide anion (O₂^.- ) and H₂ O₂ were assayed in PVAT and aortic rings were used to assess vascular function.

KEY RESULTS

Aortae from HFD-fed obese mice displayed increased contractions to phenylephrine and loss of PVAT anti-contractile effect. Inactivation of O₂^.- , dismutation of mitochondria-derived H₂ O₂ , uncoupling of oxidative phosphorylation and Rho kinase inhibition, decreased phenylephrine-induced contractions in aortae with PVAT from HFD-fed mice. O₂^.- and H₂ O₂ were increased in PVAT from HFD-fed mice. Mitochondrial respiration analysis revealed decreased O₂ consumption rates in PVAT from HFD-fed mice. TNF-α inhibition reduced H₂ O₂ levels in PVAT from HFD-fed mice. PVAT dysfunction, i.e. increased contraction to phenylephrine in PVAT-intact aortae, was not observed in HFD-obese mice lacking TNF-α receptors. Generation of H₂ O₂ was prevented in PVAT from TNF-α receptor deficient obese mice.

CONCLUSION AND IMPLICATIONS

TNF-α-induced mitochondrial oxidative stress is a key and novel mechanism involved in obesity-associated PVAT dysfunction. These findings elucidate molecular mechanisms whereby oxidative stress in PVAT could affect vascular function.

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.

New actions of an old friend: perivascular adipose tissue's adrenergic mechanisms

The revolutionary discovery in 1991 by Soltis and Cassis that perivascular adipose tissue (PVAT) has an anti-contractile effect changed how we think about the vasculature. Most experiments on vascular pharmacology begin by removing the fat surrounding vessels. Thus, PVAT was thought to have a minor role in vascular function and its presence was just for structural support. The need to rethink PVAT's role was precipitated by observations that obesity carries a high cardiovascular risk and PVAT dysfunction is associated with obesity. PVAT is a vascular-adipose organ that has intimate connections with the nervous and immune system. A complex world of physiology resides in PVAT, including the presence of an 'adrenergic system' that is able to release, take up and metabolize noradrenaline. Adipocytes, stromal vascular cells and nerves within PVAT contain components that make up this adrenergic system. Some of the great strides in PVAT research came from studying adipose tissue as a whole. Adipose tissue has many roles and participates in regulating energy balance, energy stores, inflammation and thermoregulation. However, PVAT is dissimilar from non-PVAT adipose tissues. PVAT is intimately connected with the vasculature, which is what makes its role in body homeostasis unique. The adrenergic system within PVAT may be an integral link connecting the effects of obesity with the vascular dysfunction observed in obesity-associated hypertension, a condition in which the sympathetic nervous system has a significant role. This review will explore what is known about the adrenergic system in adipose tissue and PVAT, plus the translational importance of these findings.

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.

The paracrine control of vascular motion. A historical perspective

During the last quarter of the past century, the leading role the endocrine and nervous systems had on the regulation of vasomotion, shifted towards a more paracrine-based regulation. This begun with the recognition of endothelial cells as active players of vascular control, when the vessel's intimal layer was identified as the main source of prostacyclin and was followed by the discovery of an endothelium-derived smooth muscle cell relaxing factor (EDRF). The new position acquired by endothelial cells prompted the discovery of other endothelium-derived regulatory products: vasoconstrictors, generally known as EDCFs, endothelin, and other vasodilators with hyperpolarizing properties (EDHFs). While this research was taking place, a quest for the discovery of the nature of EDRF carried back to a research line commenced a decade earlier: the recently found intracellular messenger cGMP and nitrovasodilators. Both were smooth muscle relaxants and appeared to interact in a hormonal fashion. Prejudice against an unconventional gaseous molecule delayed the acceptance that EDRF was nitric oxide (NO). When this happened, a new era of research that exceeded the vascular field commenced. The discovery of the pathway for NO synthesis from L-arginine involved the clever assembling of numerous unrelated observations of different areas of knowledge. The last ten years of research on the paracrine regulation of the vascular wall has shifted to perivascular fat (PVAT), which is beginning to be regarded as the fourth layer of the vascular wall. Starting with the discovery of an adipose-derived relaxing substance (ADRF), the role that different adipokines have on the paracrine control of vasomotion is now filling the research activity of many vascular pharmacology labs, and surprising interactions between the endothelium, PVAT and smooth muscle are being unveiled.