Distinct Roles of Estrogen Receptor-α and β in the Modulation of Vascular Inducible Nitric-Oxide Synthase in Diabetes

Abstract

Estrogen is known to affect vascular function and diabetes development, but the relative contribution of estrogen receptor (ER) isoforms is unclear. The aim of this study was to determine how individual ER isoforms modulate inflammatory enzymes in the vascular wall of control and streptozotocin (STZ)-injected rodents. Primary cultures of rat aortic smooth muscle cells (SMCs) were stimulated with inflammatory agents in the presence or absence of increasing concentrations of the ER␣ and ER␤-selective agonists 4,4Ј,4ЈЈ-(4-propyl-[1H]-pyrazole-1,3,5-triyl)trisphenol (PPT) and diarylpropionitrile (DPN), respectively. The production of inducible nitric-oxide synthase (iNOS), a classical indicator of vascular inflammation, was significantly reduced by PPT in control but not diabetic SMCs, whereas it was further enhanced by DPN treatment in both groups. This distinct action profile was not related to changes in ER transcriptional activity. However, extracellular signal-regulated kinase 1/2 signaling was activated by DPN but not by PPT in cytokine-treated SMCs. In cultured aortic rings from both normoglycemic and STZ-diabetic mice, pharmacological activation of ER␣ attenuated cytokine-driven iNOS induction by 30 to 50%. Vascular iNOS levels were decreased consistently when adding 1 nM 17␤-estradiol to aortic tissues from ER␤-but not ER␣-knockout mice. These findings suggest a possible role for ER␣-selective ligands in reducing vascular inflammatory responses under normo-and hyperglycemic conditions. Recent large-scale clinical trials found a significantly lower incidence of diabetes in postmenopausal women on hormone replacement therapy despite no improvement in vascular outcomes (Kanaya et al., 2003; Margolis et al., 2004). The mechanisms accounting for this outcome, however, are largely unknown, although estrogen is increasingly recognized as an important regulator of glucose homeostasis Le May et al., 2006). Because the endogenous hormone binds to its receptors with identical affinity, the metabolic effects of individual estrogen receptor (ER) isoforms, ER␣ and ER␤, are hard to differentiate and appear to be tissue-and speciesspecific. In accordance, there is little information as to how ER␣ and ER␤ affect the course and timeline of diabetic vascular dysfunction, which ultimately results in macrovascular complications of clinical relevance. We previously demonstrated that anti-inflammatory activity of estrogen is impaired in vascular smooth muscle cells (SMCs) from streptozotocin (STZ)-diabetic rats, which display ER␤ overexpression with respect to normoglycemic controls (Maggi et al., 2003). The biological significance of ER␤ overexpression in vascular cells from diabetic rats is unclear. There have been concerns that ER␤-selective agonists may be diabetogenic , whereas they are effective anti-inflammatory agents in selected in vivo models of inflammation (Harris, 2007).Inducible nitric-oxide synthase (iNOS) is a well established marker of vascular inflammation (Bardell and MacLeod, 2001;Nagareddy et al., 200...

17β‐estradiol reduces Cav1.2 channel abundance and attenuates Ca2+‐dependent contractions in coronary arteries

“…Because Ca v 1.2 channels are the predominant pathway for voltage-dependent Ca 2+ influx in ASMCs of the coronary circulation (Bowles et al 1998a), decreasing their expression in the plasma membrane of ASMCs will increase arterial diameter and promote coronary blood flow. We used 1 nmol/L 17bE to correlate with previous in vitro studies that used 1 nmol/L 17bE as a near "physiological" E2 concentration to evaluate its effect on the vascular mechanics of arteries (Keung et al 2005(Keung et al , 2011Cignarella et al 2009;Lekontseva et al 2011). Therefore, we did not attempt to use a definite plasma 17bE concentration from cycling sows or premenopausal women (A) (B) Figure 7.…”

Obesity, insulin resistance and diabetes: sex differences and role of oestrogen receptors

“…In both healthy and diabetic mice lacking ERb, 17b-oestradiol reduced inflammatory nitric oxide synthase expression in the aorta. This inhibitory effect was absent in ERa-knockout animals (Cignarella et al 2009) indicating that the protective effects of oestrogens on inflammatory responses in the vessel wall are mediated by ERa (Cignarella et al 2009). In summary, these studies not only indicate an important role of ERa in the regulation of insulin sensitivity but also point to an inhibitory effect of ERb on ERa-dependent actions (Matthews & Gustafsson 2003).…”

Influence of a High-Fat Diet on Cardiac iNOS in Female Rats

“…Furthermore, ERα-selective agonist 4,4',4″-(4-propyl-[1H]-pyrazole-1,3,5-triyl) trisphenol (PPT) significantly reduces cytokine induced iNOS protein expression in aortic smooth muscle cells [93]. However, in conditions that are affecting the level of endogenous oestrogen, such as obesity, T2DM or advancing atherosclerosis, there is loss of ERα expression in the vasculature, which is similar to the results from our study, and there is consequentially loss vasculoprotection in response to exogenous oestrogen [91].…”