Objective—Synergistic interactions between aldosterone (Aldo) and angiotensin II (Ang II) have been implicated in vascular inflammation, fibrosis, and remodeling. Molecular mechanisms underlying this are unclear. We tested the hypothesis that c-Src activation, through receptor tyrosine kinase transactivation, is critically involved in synergistic interactions between Aldo and Ang II and that it is upstream of promigratory signaling pathways in vascular smooth muscle cells (VSMCs).

Methods and Results—VSMCs from WKY rats were studied. At low concentrations (10^-10 mol/L) Aldo and Ang II alone did not influence c-Src activation, whereas in combination they rapidly increased phosphorylation (P<0.01), an effect blocked by eplerenone (Aldo receptor antagonist) and irbesartan (AT1R blocker). This synergism was attenuated by AG1478 and AG1296 (inhibitors of EGFR and PDGFR, respectively), but not by AG1024 (IGFR inhibitor). Aldo and Ang II costimulation induced c-Src–dependent activation of NAD(P)H oxidase and c-Src–independent activation of ERK1/2 (P<0.05), without effect on ERK5, p38MAPK, or JNK. Aldo/Ang II synergistically activated RhoA/Rho kinase and VSMC migration, effects blocked by PP2, apocynin, and fasudil, inhibitors of c-Src, NADPH oxidase, and Rho kinase, respectively.

Conclusions—Aldo/Ang II synergistically activate c-Src, an immediate signaling response, through EGFR and PDGFR, but not IGFR transactivation. This is associated with activation of redox-regulated RhoA/Rho kinase, which controls VSMC migration. Although Aldo and Ang II interact to stimulate ERK1/2, such effects are c-Src–independent. These findings indicate differential signaling in Aldo-Ang II crosstalk and highlight the importance of c-Src in redox-sensitive RhoA, but not ERK1/2 signaling. Blockade of Aldo/Ang II may be therapeutically useful in vascular remodeling associated with abnormal VSMC migration.