Abstract 17620: Paracrine Actions of the Intracellular Second Messenger cAMP Secreted From Cardiac Myocytes
Acute stimulation of cardiac β-adrenergic receptors and the resultant modulation of cyclic adenosine monophosphate (cAMP) signalling are crucial to increase cardiac function under stress. Yet, continuous stimulation causes myocardial remodelling and cardiac disease. And therefore, a number of intracellular mechanisms exist that limit the extent of intracellular cAMP concentration. Here, we report quantitative secretion and paracrine activity of cAMP from cardiomyocytes, constituting an extracellular mechanism that regulates cardiac cAMP signalling.
To investigate whether cAMP has an extracellular signalling function in the heart, we infused adrenergically stimulated mice with cAMP and tested for cardiac function and morphology. Interestingly, we found that treatment with cAMP reduced the prohypertrophic and profibrotic effects of adrenergic stimulation. Since ABCC4 is expressed in CM, we hypothesized that cardiac cells are both a source of cAMP and sensitive to exogenous cAMP. To test this, we employed a fluorescence resonance energy transfer (FRET)-based sensor (Epac2-cAMPs) to directly assay for the formation of cAMP in CM and cardiac fibroblasts (CF). We found that ecto-cAMP blocked the βAR-mediated increase in intracellular cAMP in CM and that this was through the activation of A1 adenosine receptors. In contrast, application of extracellular cAMP onto CF induced an increase in intracellular cAMP levels through A2 adenosine receptors. We then asked whether cAMP exported from CM affected cAMP formation in CF. For this, CF from β1β2-AR-/- mice, which had been infected with an Epac2-cAMPs-expressing adenovirus were incubated with conditioned medium (coM) from isoproterenol-treated CM. CoM from Iso-treated CMs led to a significant increase of intracellular cAMP in CF, compared to control-coM or CoM from Iso-treated Abcc4-/- CMs (FRET ratio: control-coM: 1.9±0.6, Iso-coM: 4.66±0.6, Iso-coM from Abcc4-/- CMs: 1.22±0.2, p<0.05).
In conclusion, these data assign secreted cAMP a potent regulatory role in the heart. Our study demonstrates that β-adrenergic stimulation causes cardiomyocytes to secrete cAMP as a source of adenosine, which then signals to cardiac fibroblasts and to vicinal cardiomyocytes.
- © 2013 by American Heart Association, Inc.