Cardiac hypertrophy and consequent contractile dysfunction continue to burden Western society. Cardiomyocyte cyclic AMP (cAMP) and calcium are driving forces behind cardiomyocyte contraction. Distortion of their balance may induce HF, but specific therapies aiming at restoring physiological cAMP/calcium signaling are lacking.
We recently identified microRNA-139 (miR-139) to be downregulated in failing human hearts. MiR-139 resides in the phosphodiesterase gene PDE2A and is predicted to target several phosphodiesterase messengers. In view of the central role of phosphodiesterases in controlling cardiac cAMP and calcium signaling, we hypothesized that miR-139 may affect HF progression by fine-tuning cAMP and calcium balances.
Adeno-associated virus serotype 9 (AAV9), either empty control or expressing pre-miR-139, was administered to male C57Bl/6J mice. After allowing transgene expression for 3 weeks, mice were subjected to sham treatment or 4 weeks of pressure overload by subcutaneous Angiotensin II infusion (AngII, 2,5 mg/(kg·d). MiR-139 overexpression mildly aggravated HF development upon AngII with echocardiographically measured fractional shortening decreasing by 24±7% in AAV9-control AngII and by 46±5% in AAV9-pre-miR-139 AngII (n>11/group; p=0.14). In AAV9-control mice, AngII infusion led to concentric hypertrophy with an increased relative wall thickness (RWT) of 35±6%, whereas mice overexpressing miR-139 showed a rather eccentric form of hypertrophy with an increased RWT of 14±7% (p<0.05). The fraction of unphosphorylated cardiac troponin I (cTnI), a substrate of the cAMP dependent protein kinase A (PKA), tended to increase upon AngII infusion only in mice overexpressing miR-139 (n=4/group; p=0.11), indicating a reduced relaxation rate due to increased calcium sensitivity, a feature commonly observed in HF. Complimentary to these data, in vivo knockdown of mir-139 by cholesterol-tagged antagomiRs (20mg/kg) on three consecutive days before start of AngII infusion dampened the development of pressure overload-induced cardiac hypertrophy (increase in HW/TL: ctrl: 48±10%, n=4; antagomiR: 25±7%, n=7; p=0.16).
In conclusion, cardiac downregulation of miR-139 upon pressure overload is a protective response to preserve cardiac function. AAV9-mediated overexpression of miR-139 promotes cardiac dilation and predisposes to HF. Upcoming experiments will aim at defining the molecular mechanism by which miR-139/phosphodiesterase signaling affects cardiac pathophysiology.