Beta2-adrenergic receptor regulates cardiac fibroblast autophagy and collagen degradation

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 b2-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 b2-ARs was determined and characterized by radioligand binding assays using [3H]dihydroalprenolol. Both, isoproterenol and norepinephrine (non-selective b-AR agonists), as well as salbutamol (selective b2-AR agonist) increased autophagic flux, and these effects were blocked by propanolol (b-AR antagonist), ICI-118,551 (selective b2-AR antagonist), 3-methyladenine but not by atenolol (selective b1-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 b2-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.