RESUMO
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.
Assuntos
Autofagia/fisiologia , Colágeno/metabolismo , Fibroblastos/fisiologia , Receptores Adrenérgicos beta 2/fisiologia , Adenina/análogos & derivados , Adenina/farmacologia , Agonistas Adrenérgicos beta/farmacologia , Antagonistas Adrenérgicos beta/farmacologia , Animais , Autofagia/efeitos dos fármacos , Western Blotting , Células Cultivadas , Di-Hidroalprenolol/metabolismo , Relação Dose-Resposta a Droga , Fibroblastos/metabolismo , Fibroblastos/ultraestrutura , Isoproterenol/farmacologia , Masculino , Microscopia Eletrônica de Transmissão , Miocárdio/citologia , Norepinefrina/farmacologia , Propanolaminas/farmacologia , Ensaio Radioligante , Ratos , Ratos Sprague-Dawley , Receptores Adrenérgicos beta 2/metabolismo , TrítioRESUMO
BACKGROUND: The 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. METHODS: We ectopically expressed AT(1)R and AT(2)R in cultured adult rat cardiomyocytes and cardiac fibroblasts to investigate Ang II-mediated cardiomyocyte hypertrophy and cardiac cell viability. RESULTS: In adult rat cardiomyocytes, Ang II did not induce hypertrophy via the AT(1)R, and no effect of Ang II on cell viability was observed following AT(1)R or AT(2)R expression. In adult rat cardiac fibroblasts, Ang II stimulated cell death by apoptosis via the AT(1)R (but not the AT(2)R), which required the presence of extracellular calcium, and induced a rapid dissipation of mitochondrial membrane potential, which was significant from 8 h. CONCLUSIONS: We conclude that Ang II/AT(1)R triggers apoptosis in adult rat cardiac fibroblasts, which is dependent on Ca2+ influx.