The renin-angiotensin system (RAS) is an endocrine system that provides a powerful mechanism for blood pressure control and electrolyte homeostasis. The RAS is composed of two main arms: the vasoconstrictor axis, with the angiotensin-converting enzyme (ACE)/angiotensin (Ang) II/AT1 receptor (AT1R), and the counterregulatory axis, with angiotensin-converting enzyme 2 (ACE2)/Ang-(1–7)/Mas receptor. Ang-(1–7) effects often oppose the AngII effects and fulfill important roles for an organism by providing vasodilatory, antifibrotic, cardioprotective, antihypertrophic, antithrombotic, and antioxidant activities [1].

Alamandine is a newly described RAS peptide. It is formed by the action of a decarboxylase on Ang-(1–7) or by the catalytic action of ACE2 on alatensin Ang-A (Ala1-AngII). Alamandine (Ala-Arg-Val-Tyr-Ile-His-Pro) and Ang-(1–7) (Asp-Arg-Val-Tyr-Ile-His-Pro) share high similarities in terms of their structures, and the difference is the presence of alanine in the place of aspartic acid at the amino terminus [2]. In addition to the structure, some effects of alamandine and Ang-(1–7) are similar; for example, (i) alamandine treatment produces a long-lasting effect of lowering blood pressure in hypertensive rats, and (ii) alamandine decreases the deposition of collagen I, III and fibronectin in isoproterenol-treated rats [2]. (iii) The microinjection of alamandine in brain areas related to blood pressure control, such as in the caudal ventrolateral medulla and in the rostral ventrolateral medulla of rats, generates depressor and pressor effects on blood pressure, respectively [2,3]. Moreover, (iv) alamandine exhibits a vasodilatory effect on the aortic rings of rats and mice. Despite the similarities, the effects of alamandine are mediated by a different receptor, Mas-related G protein-coupled receptor D (MrgD) [2].

The localization of RAS components is important in determining the local effects of each peptide. All RAS components, including the MrgD receptor, are expressed in a wide variety of tissues, including white and brown adipose tissues [4], [5], [6], [7], [8], [9]. Although the effects of alamandine on metabolism have not yet been elucidated, it has been known for a long time that the RAS exerts an important influence on metabolism. AngII is well known as a peptide that mediates the metabolic and vascular consequences of obesity. The overactivity of AngII, through AT1R, triggers a vicious cycle that reinforces obesity symptoms, e.g., dyslipidemia and glucose intolerance [10], [11], [12], [13]. On the other hand, Ang-(1–7) represents a protective peptide for metabolism, improving glycemic, thermogenic, and adiposity parameters in obese animals [14], [15], [16], [17].

Adipose tissues are closely associated with obesity. White adipose tissue (WAT) is a large endocrine organ and the main site of lipid storage. Brown adipose tissue (BAT) is responsible for adaptive thermogenesis and has great anti-obesity potential [18]. Although obesity is a multifactorial disease, the energy source of obesity is the imbalance between energy intake and energy expenditure. BAT activity increases energy expenditure by utilizing lipids and glucose to generate heat. This ability makes BAT a promising target against obesity [19], [20], [21], [22].

In addition to adrenergic stimulation, BAT can also be activated by other systems, for example, by the RAS. ACE2/Ang-(1-7)/Mas signaling is closely associated with adipose tissue browning and increased thermogenic activity. In high-lipid diet-induced obesity, treatment with ACE2 increased O2 consumption, improved insulin and glucose signaling, increased BAT mass, and increased thermogenic activity [23], and treatment with Ang-(1–7) induced significant improvement in glucose levels and thermogenesis. In these animals, increased expression of UCP1, beta-adrenergic receptor, PKA, AMPK and PRDM16 was observed [24]. Ang-(1–7) through Mas increases thermogenic activity by converting white adipocytes into beige thermogenic active adipocytes [17].

Based on these multiple effects of RAS components on adipose tissue, we hypothesize that alamandine may also exert metabolic actions by mediating effects through different signaling pathways. Therefore, we evaluated the consequences of the genetic deletion of the alamandine receptor MrgD on the metabolism of mice and BAT function.