Perivascular adipose tissue (PVAT) is fat perfectly situated to influence vascular tone. In this proposal, we provide substantial evidence for the expression and novel contractile function of a peptide that is typically discussed as being produced within visceral white adipose tissue (WAT) and the liver, but never associated with PVAT. Chemerin (tazarotene induced gene, TIG2;RARRES2) is a biomarker for adiposity. Circulating chemerin levels associate strongly with BMI, and chemerin levels are reduced with reduction of weight and fat. Importantly, disruption of the primary receptor for chemerin, ChemR23 (G protein coupled receptor), is associated with reduced adiposity and body mass in mice;the role of chemerin in blood pressure is not known. Chemerin is best known for activation of inflammatory cells, and regulation of adipocyte differentiation and production of pro-inflammatory cytokines (IL-1beta, TNF-alpha, IL-6) in the adipocyte. We have discovered the production and expression of chemerin in PVAT, the ability of chemerin to stimulate blood vessel contraction in a ChemR23-dependent manner, and that suppression of chemerin gene expression reduces blood pressure, novel and here-to undescribed actions of chemerin. Importantly, chemerin- induced contraction is significantly amplified with loss of the endothelial cell, inhibition of nitric oxide synthase or by prior contraction to an agonist. In other words, chemerin also has important cardiovascular effects in non-obese conditions. Our overall hypothesis is that chemerin is a functional connector of fat (including PVAT) and blood pressure and thus unites obesity and hypertension, so commonly comorbid. Our primary model is the rat, in which we have significant versatility in models of hypertension (deoxycorticosterone acetate, NOS-inhibited) and obesity (high fat fed). We focus on the mesenteric vasculature, because the splanchnic circulation controls a considerable portion of cardiac output and is the site at which significant fat is deposited in obesity. We will also use human mesenteric arteries to test whether the vascular chemerin axis exists and is relevant to human health/disease. A range of experimental techniques (gene, tissue and whole animal) allows us to study two Aims.
In Aim 1, we test the hypothesis that Chemerin induces ChemR23 receptor-dependent contraction and is amplified by dysfunctional endothelium.
This aim i s dedicated to understanding the vascular mechanism(s) of chemerin-induced contraction in arteries, as well as contributions of chemerin to agonist-induced contraction. This is paired with a second aim, dedicated to testing the physiological relevance of the chemerin axis.
In Aim 2, we test whether antagonism of the ChemR23 receptor, or knockdown of chemerin gene by new antisense oligodeoxynucleotides, will reduce endpoints of the obese or hypertensive phenotype, including elevated blood pressure. Such a finding would argue that endogenous chemerin plays a role in vascular tone and blood pressure. Our findings place chemerin as a critical regulator of arterial tone, poised to be a bridge between obesity and hypertension.
Obesity in and of itself damages health, but it is the comorbity and predisposition of obese individuals to develop cardiovascular diseases such as hypertension, diabetes and stroke that is so damaging. Endogenous sources of the peptide chemerin are the white fat, the liver, and, as we will show, fat deposited outside of blood vessels. Our work points to chemerin, which contracts blood vessels, as a substance that connects the presence of fat to arterial function and blood pressure, with blockade of chemerin function a real therapeutic possibility for a disease escaping our control.