Contribution of PI 3-kinase isoforms to angiotensin II- and α-adrenoceptor-mediated signalling pathways in cardiomyocytes
This work was published before the author joined Aga Khan University.
Abstract
Objective
Angiotensin II stimulation increases the formation of reactive oxygen species (ROS), the phosphorylation of p38 mitogen-activated protein kinase (MAPK), and the expression of transforming growth factor beta (TGFβ) in adult cardiomyocytes. The aim of this study was to determine the involvement of PI 3-kinase and to specify the participation of different isoforms in the angiotensin II-induced formation of ROS in comparison to the hypertrophic pathway triggered by α-adrenoceptor stimulation.
Methods
Freshly isolated myocytes were used to examine formation of ROS via H2DCF fluorescence. p38 MAPK phosphorylation, p70S6-kinase phosphorylation, PI 3-kinase, and TGFβ expression were measured by Western blotting. Sense and antisense oligonucleotides were used to down-regulate diverse PI 3-kinase isoforms. Hypertrophy was measured by 14C-phenylalanine incorporation and cell volume.
Results
Inhibition of PI 3-kinase by Ly294002 or wortmannin, two inhibitors, decreased formation of ROS, phosphorylation of p38 MAPK, and TGFβ expression. Down-regulation of the p110β isoform by antisense oligonucleotides inhibited the angiotensin II-induced signalling pathway but not the α-adrenoceptor-mediated hypertrophic growth of cardiomyocytes. In contrast, down-regulation of the p110α isoform decreased the α-adrenoceptor-mediated hypertrophic growth of cardiomyocytes but did not affect the angiotensin II-mediated signalling pathway.
Conclusion
Thus, our study identifies an involvement of PI 3-kinase in the angiotensin II-induced formation of ROS and provides a biochemical basis for ligand-specific responses for angiotensin II and α-adrenoceptor stimulation as relates to hypertrophy.