Autophagy is a physiological degradative process key to cell survival during nutrient deprivation, cell differentiation and development. It plays a major role in the turnover of damaged macromolecules and organelles, and it has been involved in the pathogenesis of different cardiovascular diseases. Activation of the adrenergic system is commonly associated with cardiac fibrosis and remodeling, and cardiac fibroblasts are key players in these processes. Whether adrenergic stimulation modulates cardiac fibroblast autophagy remains unexplored. In the present study, we aimed at this question and evaluated the effects of b(2)-adrenergic stimulation upon autophagy. Cultured adult rat cardiac fibroblasts were treated with agonists or antagonists of beta-adrenergic receptors (b-AR), and autophagy was assessed by electron microscopy, GFP-LC3 subcellular distribution, and immunowesternblot of endogenous LC3. The predominant expression of b(2)-ARs was determined and characterized by radioligand binding assays using [(3)H]dihydroalprenolol. Both, isoproterenol and norepinephrine (non-selective b-AR agonists), as well as salbutamol (selective b(2)-AR agonist) increased autophagic flux, and these effects were blocked by propanolol (b-AR antagonist), ICI-118,551 (selective b(2)-AR antagonist), 3-methyladenine but not by atenolol (selective b(1)-AR antagonist). The increase in autophagy was correlated with an enhanced degradation of collagen, and this effect was abrogated by the inhibition of autophagic flux. Overall, our data suggest that b(2)-adrenergic stimulation triggers autophagy in cardiac fibroblasts, and that this response could contribute to reduce the deleterious effects of high adrenergic stimulation upon cardiac fibrosis.

Angiotensin II (Ang II) is an active peptide that controls systolic blood pressure and also exerts long-term effects on cardiovascular tissue structure, including cardiac hypertrophy and fibrosis. 1 Two major receptors exist for Ang II termed type 1 and type 2 receptors (AT 1 R and AT 2 R, respectively). 2 AT 1 R are predominantly coupled to Gq/11 and signal through phospholipases A, C, D, inositol phosphates, calcium channels, and a variety of serine/threonine and tyrosine kinases. Many AT 1 -induced growth responses are mediated by transactivation of growth factor receptors. 2 The signaling pathways of AT 2 R include serine and tyrosine phosphatases, phospholipase A2, nitric oxide, and cyclic guanosine monophosphate. The AT 2 R counteracts several of the growth responses initiated by the AT1 and growth factor receptors. 2 AT 1 R mediates the established actions of Ang II, including vasoconstriction, aldosterone and vasopressin release, renal sodium reabsorption, increased collagen deposition, cell proliferation, and, importantly, cardiomyocyte hypertrophy. 1,2 Meanwhile AT 2 R function is less clear, but current theories support a role in opposing the AT 1 R actions. 3 AT 2 R is highly expressed in the fetus; however, after birth, its expression decreases. 2 Both AT 1 R and AT 2 R are expressed in adult human and rat heart, and they are upregulated in several cardiac pathologies. 4,5 The effects of Ang II in the heart are cell type-specific. Cardiomyocyte function is tightly regulated by Ang II, which acts in promoting cardiac hypertrophy. 6 However, Ang II also triggers apoptosis in neonatal cardiomyocytes. 7,8 Cardiac fibroblasts play a central role in the maintenance and remodeling of extracellular matrix (ECM) in the normal heart and injured heart. 9 Cultured cardiac fibroblasts undergo AT 1 Rdependent proliferation in response to Ang II, 6 and promotes net accumulation of fibrillar collagen and cardiac fibrosis in vivo, and their expression in cardiac fibroblasts far exceeds that in myocytes. 10 AT 2 R have been shown to lead to stimulation, inhibition, or not affect cardiac fibrosis. [11][12][13] Whether the up-regulation of AT 1 R or AT 2 R stimulates Ang II-dependent adult cardiac cell death remains unsolved. To study this problem, we ectopically expressed AT 1 R and AT 2 R in cultured adult cardiac fibroblasts (ACFs) and adult cardiomyocytes (ACMs), and we investigated the effect of Ang II on cardiac cell death and hypertrophy. Our data show that Ang II stimulated AT 1 R-dependent apoptosis in cultured ACFs, The first two authors contributed equally to the work. BackgroundThe angiotensin II (ang II) type 1 (aT 1 R) and type 2 (aT 2 R) receptors are increased in the heart following myocardial infarction and dilated cardiomyopathy, yet their contribution at a cellular level to compensation and/or failure remains controversial.