This work was financially support by the grants from Research Grant Council of Hong Kong [17124718 and 17121714], Hong Kong Health and Medical Research Fund [13142651 and 13142641], Collaborative Research Fund of Hong Kong [C7055-14G], and the National Basic Research Program of China [973 Program 2015CB553603].

<ol>
	<li>Furchgott, R. F., Zawadzki, J. V. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=The+obligatory+role+of+endothelial+cells+in+the+relaxation+of+arterial+smooth+muscle+by+acetylcholine.">The obligatory role of endothelial cells in the relaxation of arterial smooth muscle by acetylcholine.</a> Nature. 288 (5789), 373-376 (1980).</li><li>Furchgott, R. F., Vanhoutte, P. M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Endothelium-derived+relaxing+and+contracting+factors.">Endothelium-derived relaxing and contracting factors.</a> The FASEB Journal. 3 (9), 2007-2018 (1989).</li><li>Feletou, M., Kohler, R., Vanhoutte, P. M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Endothelium-derived+vasoactive+factors+and+hypertension:+possible+roles+in+pathogenesis+and+as+treatment+targets.">Endothelium-derived vasoactive factors and hypertension: possible roles in pathogenesis and as treatment targets.</a> Current Hypertension Reports. 12 (4), 267-275 (2010).</li><li>Vanhoutte, P. M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Endothelial+dysfunction:+the+first+step+toward+coronary+arteriosclerosis.">Endothelial dysfunction: the first step toward coronary arteriosclerosis.</a> Circulation Journal. 73 (4), 595-601 (2009).</li><li>Feletou, M., Huang, Y., Vanhoutte, P. M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Endothelium-mediated+control+of+vascular+tone:+COX-1+and+COX-2+products.">Endothelium-mediated control of vascular tone: COX-1 and COX-2 products.</a> British Journal of Pharmacology. 164 (3), 894-912 (2011).</li><li>Harrison, D. G. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Cellular+and+molecular+mechanisms+of+endothelial+cell+dysfunction.">Cellular and molecular mechanisms of endothelial cell dysfunction.</a> Journal of Clinical Investigation. 100 (9), 2153 (1997).</li><li>Vanhoutte, P. M., Shimokawa, H., Tang, E. H., Feletou, M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Endothelial+dysfunction+and+vascular+disease.">Endothelial dysfunction and vascular disease.</a> Acta physiologica. 196 (2), 193-222 (2009).</li><li>Kl&#246;&#223;, S., Bouloumi&#233;, A., M&#252;lsch, A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Aging+and+chronic+hypertension+decrease+expression+of+rat+aortic+soluble+guanylyl+cyclase.">Aging and chronic hypertension decrease expression of rat aortic soluble guanylyl cyclase.</a> Hypertension. 35 (1), 43-47 (2000).</li><li>Csiszar, A., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Aging-induced+phenotypic+changes+and+oxidative+stress+impair+coronary+arteriolar+function.">Aging-induced phenotypic changes and oxidative stress impair coronary arteriolar function.</a> Circulation Research. 90 (11), 1159-1166 (2002).</li><li>Guo, Y., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Endothelial+SIRT1+prevents+age-induced+impairment+of+vasodilator+responses+by+enhancing+the+expression+and+activity+of+soluble+guanylyl+cyclase+in+smooth+muscle+cells.">Endothelial SIRT1 prevents age-induced impairment of vasodilator responses by enhancing the expression and activity of soluble guanylyl cyclase in smooth muscle cells.</a> Cardiovascular Research. , (2018).</li><li>Auch-Schwelk, W., Katusic, Z. S., Vanhoutte, P. M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Nitric+oxide+inactivates+endothelium-derived+contracting+factor+in+the+rat+aorta.">Nitric oxide inactivates endothelium-derived contracting factor in the rat aorta.</a> Hypertension. 19 (5), 442-445 (1992).</li><li>Tang, E. H., Feletou, M., Huang, Y., Man, R. Y., Vanhoutte, P. M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Acetylcholine+and+sodium+nitroprusside+cause+long-term+inhibition+of+EDCF-mediated+contractions.">Acetylcholine and sodium nitroprusside cause long-term inhibition of EDCF-mediated contractions.</a> American Journal of Physiology - Heart and Circulation Physiology. 289 (6), H2434-H2440 (2005).</li><li>Ghiadoni, L., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Endothelial+function+and+common+carotid+artery+wall+thickening+in+patients+with+essential+hypertension.">Endothelial function and common carotid artery wall thickening in patients with essential hypertension.</a> Hypertension. 32 (1), 25-32 (1998).</li><li>Xu, X., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Age-related+Impairment+of+Vascular+Structure+and+Functions.">Age-related Impairment of Vascular Structure and Functions.</a> Aging and Disease. 8 (5), 590-610 (2017).</li><li>Tabit, C. E., Chung, W. B., Hamburg, N. M., Vita, J. A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Endothelial+dysfunction+in+diabetes+mellitus:+Molecular+mechanisms+and+clinical+implications.">Endothelial dysfunction in diabetes mellitus: Molecular mechanisms and clinical implications.</a> Reviews in Endocrine &amp; Metabolic Disorders. 11 (1), 61-74 (2010).</li><li>Tanaka, K., Sata, M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Roles+of+perivascular+adipose+tissue+in+the+pathogenesis+of+atherosclerosis.">Roles of perivascular adipose tissue in the pathogenesis of atherosclerosis.</a> Frontiers in Physiology. 9, 3 (2018).</li><li>Brown, N. K., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Perivascular+adipose+tissue+in+vascular+function+and+disease:+a+review+of+current+research+and+animal+models.">Perivascular adipose tissue in vascular function and disease: a review of current research and animal models.</a> Arteriosclerosis Thrombosis and Vascular Biology. 34 (8), 1621-1630 (2014).</li><li>Lohn, M., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Periadventitial+fat+releases+a+vascular+relaxing+factor.">Periadventitial fat releases a vascular relaxing factor.</a> The FASEB Journal. 16 (9), 1057-1063 (2002).</li><li>G&#225;lvez-Prieto, B., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=A+reduction+in+the+amount+and+anti-contractile+effect+of+periadventitial+mesenteric+adipose+tissue+precedes+hypertension+development+in+spontaneously+hypertensive+rats.">A reduction in the amount and anti-contractile effect of periadventitial mesenteric adipose tissue precedes hypertension development in spontaneously hypertensive rats.</a> Hypertension research. 31 (7), 1415 (2008).</li><li>Gao, Y. J., Lu, C., Su, L. Y., Sharma, A., Lee, R. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Modulation+of+vascular+function+by+perivascular+adipose+tissue:+the+role+of+endothelium+and+hydrogen+peroxide.">Modulation of vascular function by perivascular adipose tissue: the role of endothelium and hydrogen peroxide.</a> British Journal of Pharmacology. 151 (3), 323-331 (2007).</li><li>Gao, Y. -. J., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Perivascular+adipose+tissue+promotes+vasoconstriction:+the+role+of+superoxide+anion.">Perivascular adipose tissue promotes vasoconstriction: the role of superoxide anion.</a> Cardiovascular Research. 71 (2), 363-373 (2006).</li><li>Szasz, T., Webb, R. C. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Perivascular+adipose+tissue:+more+than+just+structural+support.">Perivascular adipose tissue: more than just structural support.</a> Clinical Science (London). 122 (1), 1-12 (2012).</li><li>Ramirez, J. G., O'Malley, E. J., Ho, W. S. V. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Pro-contractile+effects+of+perivascular+fat+in+health+and+disease.">Pro-contractile effects of perivascular fat in health and disease.</a> Brish Journal of Pharmacology. 174 (20), 3482-3495 (2017).</li><li>Hajer, G. R., van Haeften, T. W., Visseren, F. L. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Adipose+tissue+dysfunction+in+obesity,+diabetes,+and+vascular+diseases.">Adipose tissue dysfunction in obesity, diabetes, and vascular diseases.</a> European Heart Journal. 29 (24), 2959-2971 (2008).</li><li>Mulvany, M. J., Halpern, W. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Contractile+properties+of+small+arterial+resistance+vessels+in+spontaneously+hypertensive+and+normotensive+rats.">Contractile properties of small arterial resistance vessels in spontaneously hypertensive and normotensive rats.</a> Circulation Research. 41 (1), 19-26 (1977).</li><li>Mulvany, M. J., Halpern, W. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Mechanical+properties+of+vascular+smooth+muscle+cells+in+situ.">Mechanical properties of vascular smooth muscle cells in situ.</a> Nature. 260 (5552), 617-619 (1976).</li><li>del Campo, L., Ferrer, M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Wire+myography+to+study+vascular+tone+and+vascular+structure+of+isolated+mouse+arteries.">Wire myography to study vascular tone and vascular structure of isolated mouse arteries.</a> Methods in Molecular Biology. 1339, 255-276 (2015).</li><li>Dobrin, P. B. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Influence+of+initial+length+on+length-tension+relationship+of+vascular+smooth+muscle.">Influence of initial length on length-tension relationship of vascular smooth muscle.</a> American Journal of Physiology. 225 (3), 664-670 (1973).</li><li>Xu, C., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Calorie+restriction+prevents+metabolic+aging+caused+by+abnormal+SIRT1+function+in+adipose+tissues.">Calorie restriction prevents metabolic aging caused by abnormal SIRT1 function in adipose tissues.</a> Diabetes. 64 (5), 1576-1590 (2015).</li><li>Sheykhzade, M., Nyborg, N. C. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Caliber+dependent+calcitonin+gene-related+peptide-induced+relaxation+in+rat+coronary+arteries:+effect+of+K++on+the+tachyphylaxis.">Caliber dependent calcitonin gene-related peptide-induced relaxation in rat coronary arteries: effect of K+ on the tachyphylaxis.</a> European Journal of Pharmacology. 351 (1), 53-59 (1998).</li><li>Soltis, E. E., Cassis, L. A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Influence+of+perivascular+adipose+tissue+on+rat+aortic+smooth+muscle+responsiveness.">Influence of perivascular adipose tissue on rat aortic smooth muscle responsiveness.</a> Clinical and Experimental Hypertension A. 13 (2), 277-296 (1991).</li><li>Lohn, M., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Periadventitial+fat+releases+a+vascular+relaxing+factor.">Periadventitial fat releases a vascular relaxing factor.</a> FASEB Journal. 16 (9), 1057-1063 (2002).</li><li>Fesus, G., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Adiponectin+is+a+novel+humoral+vasodilator.">Adiponectin is a novel humoral vasodilator.</a> Cardiovascular Research. 75 (4), 719-727 (2007).</li><li>Greenstein, A. S., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Local+inflammation+and+hypoxia+abolish+the+protective+anticontractile+properties+of+perivascular+fat+in+obese+patients.">Local inflammation and hypoxia abolish the protective anticontractile properties of perivascular fat in obese patients.</a> Circulation. 119 (12), 1661-1670 (2009).</li><li>Yudkin, J. S., Eringa, E., Stehouwer, C. D. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term="Vasocrine"+signalling+from+perivascular+fat:+a+mechanism+linking+insulin+resistance+to+vascular+disease.">"Vasocrine" signalling from perivascular fat: a mechanism linking insulin resistance to vascular disease.</a> Lancet. 365 (9473), 1817-1820 (2005).</li><li>Xia, N., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Uncoupling+of+endothelial+nitric+oxide+synthase+in+perivascular+adipose+tissue+of+diet-induced+obese+mice.">Uncoupling of endothelial nitric oxide synthase in perivascular adipose tissue of diet-induced obese mice.</a> Arteriosclerosis Thrombosis and Vascular Biology. 36 (1), 78-85 (2016).</li><li>Xia, N., Forstermann, U., Li, H. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Effects+of+resveratrol+on+eNOS+in+the+endothelium+and+the+perivascular+adipose+tissue.">Effects of resveratrol on eNOS in the endothelium and the perivascular adipose tissue.</a> Annals of the New York Academy of Sciences. 1403 (1), 132-141 (2017).</li><li>Schinzari, F., Tesauro, M., Cardillo, C. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Endothelial+and+perivascular+adipose+tissue+abnormalities+in+obesity-related+vascular+dysfunction:+novel+targets+for+treatment.">Endothelial and perivascular adipose tissue abnormalities in obesity-related vascular dysfunction: novel targets for treatment.</a> Journal of Cardiovascular Pharmacology. 69 (6), 360-368 (2017).</li><li>Liu, J. T., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Lipocalin-2+deficiency+prevents+endothelial+dysfunction+associated+with+dietary+obesity:+role+of+cytochrome+P450+2C+inhibition.">Lipocalin-2 deficiency prevents endothelial dysfunction associated with dietary obesity: role of cytochrome P450 2C inhibition.</a> British Journal of Pharmacology. 165 (2), 520-531 (2012).</li><li>Martinez-Quinones, P., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Hypertension+induced+morphological+and+physiological+changes+in+cells+of+the+arterial+wall.">Hypertension induced morphological and physiological changes in cells of the arterial wall.</a> American Journal of Hypertension. 31 (10), 1067-1078 (2018).</li><li>Outzen, E. M., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Translational+value+of+mechanical+and+vasomotor+properties+of+mouse+isolated+mesenteric+resistance-sized+arteries.">Translational value of mechanical and vasomotor properties of mouse isolated mesenteric resistance-sized arteries.</a> Pharmacology Research and Perspectives. 3 (6), e00200 (2015).</li><li>Sheykhzade, M., Simonsen, A. H., Boonen, H. C., Outzen, E. M., Nyborg, N. C. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Effect+of+ageing+on+the+passive+and+active+tension+and+pharmacodynamic+characteristics+of+rat+coronary+arteries:+age-dependent+increase+in+sensitivity+to+5-HT+and+K+.">Effect of ageing on the passive and active tension and pharmacodynamic characteristics of rat coronary arteries: age-dependent increase in sensitivity to 5-HT and K+.</a> Pharmacology. 90 (3-4), 160-168 (2012).</li></ol>

Authors have nothing to disclose.

Apart from the endothelial cells, signals derived from PVAT play an important role in the regulation of smooth muscle tone reactivity30. Healthy PVAT releases NO and anti-inflammatory adiponectin to exert an anti-contractile effect on arteries, which is lost under pathological conditions such as obesity and metabolic syndrome31,32. In disease states, PVAT contributes to the development of endothelial dysfunction and other cardiovascular ab...

Dilatations and constrictions of arteries are achieved by relaxations and contractions, respectively, of their vascular smooth muscle cells. Changes in vascular responsiveness of small arteries contribute to the homeostatic regulation of arterial blood pressure by autonomic nerves and hormones present in the blood (e.g., catecholamines, angiotensin II, serotonin, vasopressin). At the local level, the vascular responses of smooth muscle cells are modulated by signals from both the endothelial cells of the intima and the adipose tissue surrounding the arteries (Figure 1).
The endothelium is not only a passive barrier, but also serves as a surface to exchange signals between the blood and the underlying vascular smooth muscle cells. By releasing various vasoactive substances, the endothelium plays a critical role in the local control of vascular tone responses1. For example, in response to acetylcholine, endothelial nitric oxide synthase (eNOS) is activated in the endothelium to produce nitric oxide (NO), which induces relaxation of the underlying vascular smooth muscle by activating soluble guanylyl cyclase (sGC)2. Other vasoactive substances include the products of cyclooxygenases (e.g., prostacyclin and thromboxane A2), lipoxygenase (e.g., 12-hydroxyeicosatetraenoic acids, 12-HETE), and cytochrome P450 monooxygenases (HETEs and epoxyeicosatrienoic acids, EETs), reactive oxygen species (ROS), and vasoactive peptides (e.g., endothelin-1 and angiotensin II), and endothelium-derived hyperpolarizing factors (EDHF)3. A delicate balance between endothelium-derived vasodilators and vasoconstrictors maintain the local vasomotor tone4,5.
Endothelial dysfunction is characterized by the impairment in endothelium-dependent vasodilatation6, a hallmark of vascular aging7. With age, the ability of endothelium to promote vasodilatation is progressively reduced, due largely to a decreased NO bioavailability, as well as the abnormal expression and function of eNOS in the endothelium and sGC in the vascular smooth muscle cells8,9,10. Reduced NO bioavailability potentiates the production of endothelium-dependent vasoconstrictors11,12. In aged arteries, endothelial dysfunction causes hyperplasia in the media, as reflected by the marked increases in wall thickness, number of medial nuclei, which are reminiscent of the arterial thickening in hypertension and atherosclerosis observed in human patients13,14. In addition, pathophysiological conditions such as obesity, diabetes or hypertension accelerate the development of endothelial dysfunction15,16.
Perivascular adipose tissue (PVAT) releases numerous adipokines to regulate vascular structure and function17. The anti-contractile effect of PVAT is mediated by relaxing factors, such as adiponectin, NO, hydrogen peroxide and hydrogen sulphide18,19,20. However, depending on the location and pathophysiological condition, PVAT also can enhance contractile responses&#160;in various arteries21. The pro-contractile substances produced by PVAT include angiotensin-II, leptin, resistin, and ROS22,23.&#160; In most of the studies on isolated blood vessels, PVAT has been considered as a simple structural support for the vasculature and thus removed during the preparation of blood vessel ring segments. Since adipose dysfunction represents an independent risk factor for hypertension and associated cardiovascular complications24, the PVAT surrounding the blood vessels should be considered when investigating the vascular responsiveness of different arteries.
The multi wire myograph systems have been widely used to investigate the vasomotor functions of a variety of blood vessels, including the aorta, mesenteric, renal, femoral, cerebral and coronary arteries25,26. The protocols described herein will use wire myography to evaluate vascular responsiveness in mesenteric arteries isolated from genetically modified mouse models, with a special focus on the modulation by PVAT.

<table>
	<tbody>
		<tr>
			<td>Acetylcholine</td>
			<td>Sigma-Aldrich</td>
			<td>A6625</td>
			<td>Stock concentration: 10-1 M 
			Working concentration: 10-10 to 10-5 M</td>
		</tr>
		<tr>
			<td>L-NAME (N&#969;-nitro-L-arginine methyl ester)</td>
			<td>Sigma-Aldrich</td>
			<td>N5751</td>
			<td>Stock concentration: 3 x 10-2 M 
			Working concentration: 10-4 M</td>
		</tr>
		<tr>
			<td>Phenylephrine</td>
			<td>Sigma-Aldrich</td>
			<td>P6126</td>
			<td>Stock concentration: 10-2 M 
			Working concentration: 10-10 to 10-5 M</td>
		</tr>
		<tr>
			<td>U46619 (9,11-dideoxy-9&#945;,11&#945;methanoepoxy prostaglandin F2&#945;)</td>
			<td>Enzo</td>
			<td>BML-PG023-0001</td>
			<td>Stock concentration: 10-5 M 
			Working concentration: 1-3 x 10-8 M</td>
		</tr>
		<tr>
			<td>Multiwire myograph</td>
			<td>Danish MyoTechnology (DMT)</td>
			<td>620M</td>
			<td></td>
		</tr>
		<tr>
			<td>PowerLab 4/26</td>
			<td>ADInstruments</td>
			<td>ML848</td>
			<td></td>
		</tr>
		<tr>
			<td>Labchart7</td>
			<td>ADInstruments</td>
			<td>-</td>
			<td></td>
		</tr>
		<tr>
			<td>Adipo-SIRT1 wild type mice</td>
			<td>Laboratory Animal Unit, The University of Hong Kong</td>
			<td>CULATR NO.: 4085-16</td>
			<td></td>
		</tr>
		<tr>
			<td>Silicon-coated Petri dishes</td>
			<td>Danish MyoTechnology (DMT)</td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>Tungsten wires</td>
			<td>Danish MyoTechnology (DMT)</td>
			<td>300331</td>
			<td></td>
		</tr>
		<tr>
			<td>Surgical tools</td>
			<td></td>
			<td></td>
			<td></td>
		</tr>
	</tbody>
</table>

assessment of vascular tone responsiveness using isolated mesenteric arteries with a focus on modulation by perivascular adipose tissues

Altered vascular tone responsiveness to pathophysiological stimuli contributes to the development of a wide range of cardiovascular and metabolic diseases. Endothelial dysfunction represents a major culprit for the reduced vasodilatation and enhanced vasoconstriction of arteries. Adipose (fat) tissues surrounding the arteries play important roles in the regulation of endothelium-dependent relaxation and/or contraction of the vascular smooth muscle cells. The cross-talks between the endothelium and perivascular adipose tissues can be assessed ex vivo using mounted blood vessels by a wire myography system. However, optimal settings should be established for arteries derived from animals of different species, ages, genetic backgrounds and/or pathophysiological conditions.

Examination of the length/tension relationships to obtain the normalization factor k 
The amount of stretch applied to a vessel segment influences the extent of the actin-myosin interaction and hence the maximal active force developed. Thus, for every type of blood vessel, determining the amount of stretch needed for maximal active force is required for proper myography studies. Here, normalization of t...

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Assessment of Vascular Tone Responsiveness using Isolated Mesenteric Arteries with a Focus on Modulation by Perivascular Adipose Tissues

The protocol describes the use of wire myography to evaluate the transmural isometric tension of mesenteric arteries isolated from mice, with special consideration of the modulation by factors released from endothelial cells and perivascular adipose tissues.

Altered vascular tone responsiveness to pathophysiological stimuli contributes to the development of a wide range of cardiovascular and metabolic ...

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9.7K Views.  University of Hong Kong. The protocol describes the use of wire myography to evaluate the transmural isometric tension of mesenteric arteries isolated from mice, with special consideration of the modulation by factors released from endothelial cells and perivascular adipose tissues.

Video: Assessment of Vascular Tone Responsiveness using Isolated Mesenteric Arteries with a Focus on Modulation by Perivascular Adipose Tissues

Genetic Studies of Human DNA Repair Proteins Using Yeast as a Model System 

Understanding the roles of human DNA repair proteins in genetic pathways is a formidable challenge to many researchers. Genetic studies in mammalian systems have been limited due to the lack of readily available tools including defined mutant genetic cell lines, regulatory expression systems, and appropriate selectable markers. To circumvent these difficulties, model genetic systems in lower eukaryotes have become an attractive choice for the study of functionally conserved DNA repair proteins and pathways. We have developed a model yeast system to study the poorly defined genetic functions of the Werner syndrome helicase-nuclease (WRN) in nucleic acid metabolism. Cellular phenotypes associated with defined genetic mutant backgrounds can be investigated to clarify the cellular and molecular functions of WRN through its catalytic activities and protein interactions. The human WRN gene and associated variants, cloned into DNA plasmids for expression in yeast, can be placed under the control of a regulatory plasmid element. The expression construct can then be transformed into the appropriate yeast mutant background, and genetic function assayed by a variety of methodologies. Using this approach, we determined that WRN, like its related RecQ family members BLM and Sgs1, operates in a Top3-dependent pathway that is likely to be important for genomic stability. This is described in our recent publication [1] at <a href="http://www.impactaging.com">www.impactaging.com</a>. Detailed methods of specific assays for genetic complementation studies in yeast are provided in this paper.

Genetic Studies of Human DNA Repair Proteins Using Yeast as a Model System

Genetic studies in yeast can be employed to investigate the molecular and cellular functions of human genes in cellular DNA metabolism. Methods are described for the genetic characterization of the human WRN gene product defective in the premature aging disorder Werner syndrome in functionally conserved pathways using yeast as a tractable model system.

Understanding the roles of human DNA repair proteins in genetic pathways is a formidable challenge to many researchers.  Genetic studies in mammalian ...

Right Hemihepatectomy by Suprahilar Intrahepatic Transection of the Right Hemipedicle using a Vascular Stapler

Successful hepatic resection requires profound anatomical knowledge and delicate surgical technique. Hemihepatectomies are mostly performed after preparing the extrahepatic hilar structures within the hepatoduodenal ligament, even in benign tumours or liver metastasis.1-5. Regional extrahepatic lymphadenectomy is an oncological standard in hilar cholangiocarcinoma, intrahepatic cholangio-cellular carcinoma and hepatocellular carcinoma, whereas lymph node metastases in the hepatic hilus in patients with liver metastasis are rarely occult. Major disadvantages of these procedures are the complex preparation of the hilus with the risk of injuring contralateral structures and the possibility of bleeding from portal vein side-branches or impaired perfusion of bile ducts. We developed a technique of right hemihepatectomy or resection of the left lateral segments with intrahepatic transection of the pedicle that leaves the hepatoduodenal ligament completely untouched. 6 However, if intraoperative visualization or palpation of the ligament is suspicious for tumor infiltration or lymph node metastasis, the hilus should be explored and a lymphadenectomy performed.

This video describes a right hemihepatectomy with intrahepatic transection of the right hemipedicle leaving the hepatoduodenal ligament completely untouched.

Successful hepatic resection requires profound anatomical knowledge and delicate surgical technique. Hemihepatectomies are mostly performed after ...

The ex vivo Isolated Skeletal Microvessel Preparation for Investigation of Vascular Reactivity

The isolated microvessel preparation is an ex vivo preparation that allows for examination of the different contributions of factors that control vessel diameter, and thus, perfusion resistance1-5. This is a classic experimental preparation that was, in large measure, initially described by Uchida et al.15 several decades ago. This initial description provided the basis for the techniques that was extensively modified and enhanced, primarily in the laboratory of Dr. Brian Duling at the University of Virginia6-8, and we present a current approach in the following pages. This preparation will specifically refer to the gracilis arteriole in a rat as the microvessel of choice, but the basic preparation can readily be applied to vessels isolated from nearly any other tissue or organ across species9-13. Mechanical (i.e., dimensional) changes in the isolated microvessels can easily be evaluated in response to a broad array of physiological (e.g., hypoxia, intravascular pressure, or shear) or pharmacological challenges, and can provide insight into mechanistic elements comprising integrated responses in an intact, although ex vivo, tissue. The significance of this method is that it allows for facile manipulation of the influences on the integrated regulation of microvessel diameter, while also allowing for the control of many of the contributions from other sources, including intravascular pressure (myogenic), autonomic innervation, hemodynamic (e.g., shear stress), endothelial dependent or independent stimuli, hormonal, and parenchymal influences, to provide a partial list. Under appropriate experimental conditions and with appropriate goals, this can serve as an advantage over in vivo or in situ tissue/organ preparations, which do not readily allow for the facile control of broader systemic variables. 
The major limitation of this preparation is essentially the consequence of its strengths. By definition, the behavior of these vessels is being studied under conditions where many of the most significant contributors to the regulation of vascular resistance have been removed, including neural, humoral, metabolic, etc. As such, the investigator is cautioned to avoid over-interpretation and extrapolation of the data that are collected utilizing this preparation. The other significant area of concern with regard to this preparation is that it can be very easy to damage cellular components such as the endothelial lining or the vascular smooth muscle, such that variable source of error can be introduced. It is strongly recommended that the individual investigator utilize appropriate measurements to ensure the quality of the preparation, both at the initiation of the experiment and periodically throughout the course of a protocol.

The ex vivo Isolated Skeletal Microvessel Preparation for Investigation of Vascular Reactivity

An ex vivo preparation is described for isolation of the largest gracilis muscle resistance arterioles for interrogation of both vascular responses to vasoactive stimuli and the assessment of basic structural properties via passive wall mechanics.

The isolated  microvessel preparation is an ex vivo preparation that allows for examination of the different contributions of  factors that control vessel ...

Monitoring Endoplasmic Reticulum Calcium Homeostasis Using a Gaussia Luciferase SERCaMP

The endoplasmic reticulum (ER) contains the highest level of intracellular calcium, with concentrations approximately 5,000-fold greater than cytoplasmic levels. Tight control over ER calcium is imperative for protein folding, modification and trafficking. Perturbations to ER calcium can result in the activation of the unfolded protein response, a three-prong ER stress response mechanism, and contribute to pathogenesis in a variety of diseases. The ability to monitor ER calcium alterations during disease onset and progression is important in principle, yet challenging in practice. Currently available methods for monitoring ER calcium, such as calcium-dependent fluorescent dyes and proteins, have provided insight into ER calcium dynamics in cells, however these tools are not well suited for in vivo studies. Our lab has demonstrated that a modification to the carboxy-terminus of Gaussia luciferase confers secretion of the reporter in response to ER calcium depletion. The methods for using a luciferase based, secreted ER calcium monitoring protein (SERCaMP) for in vitro and in vivo applications are described herein. This video highlights hepatic injections, pharmacological manipulation of GLuc-SERCaMP, blood collection and processing, and assay parameters for longitudinal monitoring of ER calcium.

Monitoring Endoplasmic Reticulum Calcium Homeostasis Using a Gaussia Luciferase SERCaMP

Endoplasmic reticulum calcium homeostasis is disrupted in diverse pathologies. A secreted ER calcium monitoring protein (SERCaMP) reporter can be used to detect disruptions in the ER calcium store. This protocol describes the use of a Gaussia luciferase SERCaMP to examine ER calcium homeostasis in vitro and in vivo.

The endoplasmic reticulum (ER) contains the highest level of intracellular calcium, with concentrations approximately 5,000-fold greater than cytoplasmic ...

Using Digital Image Correlation to Characterize Local Strains on Vascular Tissue Specimens

Characterization of the mechanical behavior of biological and engineered soft tissues is a central component of fundamental biomedical research and product development. Stress-strain relationships are typically obtained from mechanical testing data to enable comparative assessment among samples and in some cases identification of constitutive mechanical properties. However, errors may be introduced through the use of average strain measures, as significant heterogeneity in the strain field may result from geometrical non-uniformity of the sample and stress concentrations induced by mounting/gripping of soft tissues within the test system. When strain field heterogeneity is significant, accurate assessment of the sample mechanical response requires measurement of local strains. This study demonstrates a novel biomechanical testing protocol for calculating local surface strains using a mechanical testing device coupled with a high resolution camera and a digital image correlation technique. A series of sample surface images are acquired and then analyzed to quantify the local surface strain of a vascular tissue specimen subjected to ramped uniaxial loading. This approach can improve accuracy in experimental vascular biomechanics and has potential for broader use among other native soft tissues, engineered soft tissues, and soft hydrogel/polymeric materials. In the video, we demonstrate how to set up the system components and perform a complete experiment on native vascular tissue.

We describe the use of digital image correlation to characterize the local surface strain field on vascular tissue samples subjected to uniaxial tensile testing. These measurements facilitate precise quantification of the sample mechanical response and the generation of constitutive stress-strain relations.

Characterization of the mechanical behavior of biological and engineered soft tissues is a central component of fundamental biomedical research and ...

Analysis of Cell Suspensions Isolated from Solid Tissues by Spectral Flow Cytometry

Flow cytometry has been used for the past 40 years to define and analyze the phenotype of lymphoid and other hematopoietic cells. Initially restricted to the analysis of a few fluorochromes, currently there are dozens of different fluorescent dyes, and up to 14-18 different dyes can be combined at a time. However, several limitations still impair the analytical capabilities. Because of the multiplicity of fluorescent probes, data analysis has become increasingly complex due to the need of large, multi-parametric compensation matrices. Moreover, mutant mouse models carrying fluorescent proteins to detect and trace specific cell types in different tissues have become available, so the analysis (by flow cytometry) of auto-fluorescent cell suspensions obtained from solid organs is required. Spectral flow cytometry, which distinguishes the shapes of emission spectra along a wide range of continuous wavelengths, addresses some of these problems. The data is analyzed with an algorithm that replaces compensation matrices and treats auto-fluorescence as an independent parameter. Thus, spectral flow cytometry should be capable of discriminating fluorochromes with similar emission peaks and can provide a multi-parametric analysis without compensation requirements.
This protocol describes the spectral flow cytometry analysis, allowing for a 21-parameter (19 fluorescent probes) characterization and the management of an auto-fluorescent signal, providing high resolution in minor population detection. The results presented here show that spectral flow cytometry presents advantages in the analysis of cell populations from tissues difficult to characterize in conventional flow cytometry, such as the heart and the intestine. Spectral flow cytometry thus demonstrates the multi-parametric analytical capacity of high-performing conventional flow cytometry without the requirement for compensation and enables auto-fluorescence management.

This article describes spectral cytometry, a new approach in flow cytometry that uses the shapes of emission spectra to distinguish fluorochromes. An algorithm replaces compensations and can treat auto-fluorescence as an independent parameter. This new approach allows for the proper analysis of cells isolated from solid organs.

Flow cytometry has been used for the past 40 years to define and analyze the phenotype of lymphoid and other hematopoietic cells. Initially restricted to ...

Measuring Endoreduplication by Flow Cytometry of Isolated Tuber Protoplasts

Endoreduplication, the replication of a cell's nuclear genome without subsequent cytokinesis, yields cells with increased DNA content and is associated with specialization, development and increase in cellular size. In plants, endoreduplication seems to facilitate the growth and expansion of certain tissues and organs. Among them is the tuber of potato (Solanum tuberosum), which undergoes considerable cellular expansion in fulfilling its function of carbohydrate storage. Thus, endoreduplication may play an important role in how tubers are able to accommodate this abundance of carbon. However, the cellular debris resulting from crude nuclear isolation methods of tubers, methods that can be used effectively with leaves, precludes the estimation of the tuber endoreduplication index (EI). This article presents a technique for assessing tuber endoreduplication through the isolation of protoplasts while demonstrating representative results obtained from different genotypes and compartmentalized tuber tissues. The major limitations of the protocol are the time and reagent costs required for sample preparation as well as relatively short lifespan of samples after lysis of protoplasts. While the protocol is sensitive to technical variation, it represents an improvement over traditional methods of nuclear isolation from these large specialized cells. Possibilities for improvements to the protocol such as recycling enzyme, the use of fixatives, and other alterations are proposed.

The protocol described herein is a method for measuring endoreduplication within tubers of potato (Solanum tuberosum). It includes plasmolysis and protoplast extraction steps to decrease the noise and debris in downstream flow cytometric analysis.

Endoreduplication, the replication of a cell's nuclear genome without subsequent cytokinesis, yields cells with increased DNA content and is associated ...

Implantation of Electrospun Vascular Grafts with Optimized Structure in a Rat Model

Here, we present a protocol to fabricate macroporous PCL vascular graft and describe an evaluation protocol by using a rat model of abdominal aorta replacement. The electrospun vascular grafts often possess relatively small pores, which limit cell infiltration into the grafts and hinder the regeneration and remodeling of the neo-arteries. In this study, PCL vascular grafts with thicker fibers (5 - 6 &#181;m) and larger pores (~30 &#181;m) were fabricated by using a modified processing technique. The long-term performance of the graft was evaluated by implantation in a rat abdominal aorta model. Ultrasound analysis showed that the grafts remained patent without aneurysm or stenosis occurring even after 12 months of implantation. Macroporous structure improved the cell ingrowth and thus promoted tissue regenerated at 3 months. More importantly, there was no sign of adverse remodeling, such as calcification within the graft wall after 12 months. Therefore, electrospun PCL vascular grafts with modified macroporous processing hold potential to be an artery substitute for long-term implantation.

Here, we present a modified electrospinning method to fabricate PCL vascular grafts with thick fibers and large pores, and describe a protocol to evaluate the in vivo performance in a rat model of abdominal aorta replacement.

Here, we present a protocol to fabricate macroporous PCL vascular graft and describe an evaluation protocol by using a rat model of abdominal aorta ...

Retinal Cryo-sections, Whole-Mounts, and Hypotonic Isolated Vasculature Preparations for Immunohistochemical Visualization of Microvascular Pericytes

Retinal pericytes play an important role in many diseases of the eye. Immunohistochemical staining techniques of retinal vessels and microvascular pericytes are central to ophthalmological research. It is vital to choose an appropriate method of visualizing the microvascular pericytes. We describe retinal microvascular pericyte immunohistochemical staining in cryo-sections, whole-mounts, and hypotonic isolated vasculature using antibodies for platelet-derived growth factor receptor &#946; (PDGFR&#946;) and nerve/glial antigen 2 (NG2). This allows us to highlight advantages and shortcomings of each of the three tissue preparations for the visualization of the retinal microvascular pericytes. Cryo-sections provide transsectional visualization of all retinal layers but contain only a few occasional transverse cuts of the microvasculature. Whole-mount provides an overview of the entire retinal vasculature, but visualization of the microvasculature can be troublesome. Hypotonic isolation provides a method to visualize the entire retinal vasculature by the removal of neuronal cells, but this makes the tissue very fragile.

We demonstrate three different tissue preparation techniques for immunohistochemical visualization of rat retinal microvascular pericytes, i.e., cryo-sections, whole-mounts, and hypotonic isolation of the vascular network.

Retinal pericytes play an important role in many diseases of the eye. Immunohistochemical staining techniques of retinal vessels and microvascular ...

Differentiation Capacity of Human Aortic Perivascular Adipose Progenitor Cells

Adipose tissue is a rich source of multi-potent mesenchymal stem cells (MSC) capable of differentiating into osteogenic, adipogenic, and chondrogenic lineages. Adipogenic differentiation of progenitor cells is a major mechanism driving adipose tissue expansion and dysfunction in response to obesity. Understanding changes to perivascular adipose tissue (PVAT) is thus clinically relevant in metabolic disease. However, previous studies have been predominately performed in the mouse and other animal models. This protocol uses human thoracic PVAT samples collected from patients undergoing coronary artery bypass graft surgery. Adipose tissue from the ascending aorta was collected and used for explantation of the stromal vascular fraction. We previously confirmed the presence of adipose progenitor cells in human PVAT with the capacity to differentiate into lipid-containing adipocytes. In this study, we further analyzed the differentiation potential of cells from the stromal vascular fraction, presumably containing multi-potent progenitor cells. We compared PVAT-derived cells to human bone marrow MSC for differentiation into adipogenic, osteogenic, and chondrogenic lineages. Following 14 days of differentiation, specific stains were utilized to detect lipid accumulation in adipocytes (Oil red O), calcific deposits in osteogenic cells (Alizarin Red), or glycosaminoglycans and collagen in chondrogenic cells (Masson&#8217;s Trichrome). While bone marrow MSC efficiently differentiated into all three lineages, PVAT-derived cells had adipogenic and chondrogenic potential, but lacked robust osteogenic potential.

The goal of this protocol is to test the ability of progenitor cells derived from human perivascular adipose tissue to differentiate into multiple cell lineages. Differentiation was compared to mesenchymal stem cells derived from human bone marrow, which is known to differentiate into adipocyte, osteocyte, and chondrocyte lineages.

Adipose tissue is a rich source of multi-potent mesenchymal stem cells (MSC) capable of differentiating into osteogenic, adipogenic, and chondrogenic ...