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One of responses to increased blood pressure is cardiac hypertrophy through increased size of ventricular myocardial cells leading to increased thickness of the ventricular walls. Cardiac hypertrophy allows the heart to handle the increased stress caused by elevated blood pressure but is also a risk factor associated with heart disease. Cardiac hypertrophy results from cross-talk between G-protein coupled receptor signaling and the EGF receptor pathway. Several GPCR ligands are known to stimulate cardiac hypertrophy, including factors that regulate blood pressure such as angiotensin II and endothelin-1. These factors stimulate phospholipase C through Gq activation, and the production of 1P3 and diacylglycerol second messengers. PKC-delta is activated by DAG and interacts with the metalloproteinase ADAM12. ADAM12 cleaves the membrane-bound HB-EGF to release soluble EGF ligand that activates EGF receptor in myocardial cells. EGF receptor activation downstream through small G proteins and the MAP kinase pathway ultimately leads to cardiac hypertrophy. Signals by GPCR ligands such as angiotensin II result in transcriptional translation of immediate early genes like fos and other genes involved in long-term remodeling of heart tissue and the physiological response to stress in the heart such as the atrial natriuretic factor. Factors such as the AKT kinase, reactive oxygen species (ROS) and NE-kB also are involved in signaling that leads to hypertrophy, although their role is not yet clear. Blocking this pathway at various steps may prevent heart disease through the prevention of cardiac hypertrophy, but may also have other consequences. (This definition may be outdated - see the DesignNote.)
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