Cardiac β3 -adrenoceptors-A role in human pathophysiology?

Received: 20 September 2018 Revised: 11 January 2019 Accepted: 29 January 2019 DOI: 10.1111/bph.14635 Themed Section: Adrenoceptors—New Roles for Old Players BJP REVIEW ARTICLE Cardiac β3‐adrenoceptors—A role in human pathophysiology? Ebru Arioglu‐Inan1 | Gizem Kayki‐Mutlu1 | Martin C. Michel2 1 Department of Pharmacology, Faculty of Pharmacy, Ankara University, Ankara, Turkey 2 As β3‐adrenoceptors were first demonstrated to be expressed in adipose tissue they Department of Pharmacology, Johannes Gutenberg University, Mainz, Germany have received much attention for their metabolic effects in obesity and diabetes. After Correspondence Professor Ebru Arioglu‐Inan, Department of Pharmacology, Faculty of Pharmacy, Ankara University, Tandogan, Ankara 06100, Turkey. Email: focused on its role in cardiac function. While the presence and functional role of Funding information TUBITAK, Grant/Award Number: SBAG‐ 115S564; Ankara University, Grant/Award Number: 15L0237005 16L0237006 and 17L0237002; Deutsche Forschungsgemeinschaft, Grant/Award Numbers: Mi 294/8‐1 and SBAG‐115S564; Astellas the β3‐adrenceptor has been demonstrated to mediate negative inotropic effects in the existence of this subtype had been suggested to be present in the heart, studies β3‐adrenoceptors in the heart has not uniformly been detected, there is a broad consensus that they become up‐regulated in pathological conditions associated with increased sympathetic activity such as heart failure and diabetes. When detected, an inhibitory G protein‐dependent manner through the NO–cGMP–PKG signalling pathway. Whether these negative inotropic effects provide protection from the adverse effects induced by overstimulation of β1/β2‐adrenoceptors or in themselves are potentially harmful is controversial, but ongoing clinical studies in patients with congestive heart failure are testing the hypothesis that β3‐adrenceptor agonism has a beneficial effect. LINKED ARTICLES: This article is part of a themed section on Adrenoceptors— New Roles for Old Players. To view the other articles in this section visit http:// onlinelibrary.wiley.com/doi/10.1111/bph.v176.14/issuetoc 1 | I N T RO D U CT I O N β‐Adrenoceptors are essential regulators of cardiac function (Brodde 2 | E XP R E SSI O N A N D F U N C TI O N OF β3‐ADRENOCEPTORS IN NORMAL HEART & Michel, 1999). Most studies in the heart involved β1‐ and β2‐ The heart is composed of various cell types, including cardiomyocytes, adrenoceptors, and the existence of a third subtype became fibroblasts and smooth muscle cells, and endothelial cells of the established unequivocally with the cloning of the human gene encoding coronary arteries and intramural blood vessels. This means that the β3‐adrenoceptor (Emorine et al., 1989). While originally proposed studies not isolating specific cell types may have underappreciated as a regulator of thermogenesis and lipolysis in rodents (Harms, findings limited to some of these cell types, as they get diluted in Zaagsma, & van der Wal, 1974), β3‐adrenoceptors in the heart have overall cardiac preparations. For instance, β3‐adrenoceptors expressed been widely studied (Gauthier, Langin, & Balligand, 2000; Michel, in specific cell types such as vascular endothelial cells may be Harding, & Bond, 2011), particularly with regard to them as a potential relevant for cardiac function but barely detectable in homogenates target for the treatment of congestive heart failure (Rasmussen, Figtree, Krum, & Bundgaard, 2009). As the role of β3‐adrenoceptors in the of cardiac biopsies. A second major limitation of much of the data available relates to human heart has been questioned (Mo, Michel, Lee, Kaumann, & the limited specificity of the tools being used. For instance, many of Molenaar, 2017), this manuscript discusses the presence and potential the antibodies do not exhibit the promised target specificity when physiological and pathological role of β3‐adrenoceptors in the heart tested under stringent conditions (see Section 2.2). Similar problems with a special focus on the human heart. exist for many of the pharmacological tools. For instance, the fre- Abbreviations: Gi, inhibitory G protein; PTX, pertussis toxin quently used agonist BRL 37,344 has only poor selectivity for β3‐ over 2482 © 2019 The British Pharmacological Society wileyonlinelibrary.com/journal/bph Br J Pharmacol. 2019;176:2482–2495. ARIOGLU‐INAN ET AL. 2483 BJP β2‐adrenoceptors (Cernecka, Sand, & Michel, 2014), and the partial repeatedly been studied in healthy rats, mice, dogs, and humans. β3‐adrenoceptor agonist CGP 12,177 is an antagonist at the Interpretation of the reported data is hampered by several limita- orthotopic site of the β1‐adrenoceptor and an agonist at a hetero- tions. Most importantly, most studies have been based on cardiac topic site (see Section 2.4). Therefore, many investigators have cho- extracts. This gives potential for both false positive and false nega- sen to use differential antagonism by nadolol or propranolol tive findings. False negative findings may occur if the target gene (assumed to block β1‐ and β2‐adrenoceptors) rather than SR 59,230 is expressed only in a small subset of cells that yields an insuffi- (assumed to block all three subtypes). While SR 59,230 is often ciently strong signal to allow robust detection in the overall extract. referred to as β3‐adrenoceptor‐selective, several studies have shown False positive results may result from the presence of cell types that it has comparable affinity for all three subtypes (Baker, 2010; other than cardiomyocytes such as fibroblasts, cells of intra‐cardiac Hoffmann, Leitz, Oberdorf‐Maass, Lohse, & Klotz, 2004; Niclauß, blood vessels and adipose tissue. For example, one of the studies Michel‐Reher, Alewijnse, & Michel, 2006); moreover, it can be a par- demonstrating the presence of β3‐adrenoceptors in human heart also tial agonist for β3‐adrenoceptor‐mediated cAMP formation and a reported a strong signal for UCP‐1 (Krief et al., 1993); as UCP‐1 is a stronger biased agonist for other signalling pathways of this receptor protein typically found in brown adipose tissue, this may indicate (Hutchinson, Sato, Evans, Christopoulos, & Summers, 2005). Addition- contamination with adipose tissue. The potential for false positives ally, agonists may already activate receptors at concentrations consider- becomes more likely if a very sensitive technique is applied (e.g., ably lower than those needed to occupy 50% of them, a phenomenon 30 PCR cycles; Gauthier, Tavernier, Charpentier, Langin, & Le Marec, called receptor reserve, which is particularly prominent in the heart 1996). The use of trabecular strips in place of whole heart extracts (Brown high may reduce this issue but not fully exclude it. More informative concentrations/doses of moderately selective ligands may have are techniques focusing solely on card (...truncated)