Angiotensin II receptors subtypes mediate diverse gene expression profile in adult hypertrophic cardiomyocytes

1. Although the systemic and cardiac renin-angiotensin systems are known to be activated in the setting of pressure overload, the actions and signalling mechanisms of angiotensin (Ang) II via AT₁ and AT₂ receptors in hypertrophic cardiomyocytes (CM) remain largely unclear. 2. Hypertrophic CM were prepared from rats with aortic banding for 8 weeks, cultured and then treated as follows: (i) 1 μmol/L AngII for 24 h; (ii) 10 μmol/L losartan (an AT₁ receptor antagonist) for 1 h followed by 1 μmol/L AngII for 24 h; and (iii) 10 μmol/L PD123319 (an AT₂ receptor antagonist) for 1 h followed by 1 μmol/L AngII for 24 h. Changes in the expression of genes following stimulation of AT₁ and AT ₂ receptors specific to G-protein-coupled receptor (GPCR) signalling pathways were tested using GEArray (Superarray, Bethesda, MD, USA). The effects of AngII, acting via AT₁ and AT₂ receptors, on the expression of tumour necrosis factor (TNF)-α, interleukin (IL)-1β and IL-6 were confirmed by reverse transcription-polymerase chain reaction and radioimmunoassay. 3. The genes regulated via stimulation of AT₁ receptors were mainly restricted to the signalling pathways including cAMP/protein kinase (PK) A, Ca²⁺, PKC, protein tyrosine kinase, mitogen-activated protein kinases, phosphatidylinositol 3-kinase and nuclear factor-κB. In addition to these pathways related to activation of AT ₁ receptors, four additional signalling pathways were found to be associated with stimulation of AT₂ receptors, including phospholipase C, nitric oxide/cGMP, Rho and Janus kinase/signal transducer and activator of transcription. Blockade of AT₂ receptors decreased the mRNA and protein expression of TNF-α and IL-1β, whereas blockade of AT ₁ receptors had no such effect. 4. In conclusion, in hypertrophic CM, AngII leads to distinct signalling responses mediated by AT₁ and AT₂ receptors. Stimulation of AT₂ receptors appears to have a greater influence on GPCR-signalling than stimulation of AT₁ receptors. Angiotensin II enhances the synthesis and secretion of TNF-α and IL-1β in hypertrophic CM, which is mediated by AT₂, but not AT₁, receptors.