Abstract 334: Cyclic GMP-dependent Protein Kinase Iα Dependent Regulator of G-protein Signaling 2 Activation Is Required for Early Cardiac Compensation to Pressure-overload
In response to pressure-overload, the heart initially develops adaptive hypertrophy with enhanced contractility, but later decompensates with chamber dilation. Such maladaptation can be induced by activation of Gαq-coupled signaling, whereas enhancing cyclic GMP-dependent protein kinase I-α (PKGI-α) by phosphodiesterase 5A inhibition (PDE5A-I) ameliorates pressure-overload pathobiology. A potential coupler of both pathways is RGS2 (regulator of G-protein signaling 2), which is activated by PKGI-α to suppress Gαq-stimulation in vascular smooth muscle cells. Here we tested this signaling in hearts exposed to pressure-overload by transverse aortic constriction (TAC). RGS2 is up-regulated in the particulate fraction of control heart lysate within 48 hours of TAC. Unlike controls, RGS2−/− hearts display no early compensation to TAC, developing accelerated dilation and severe hypertrophy within 1week, with high mortality (Table⇓). Downstream signaling of Gαq stimulation including ERK1/2, CaM kinase II and calcineurin is markedly activated or up-regulated in RGS2−/− -TAC versus RGS2+/+ -TAC. In normal myocytes, RGS2 displays weak diffuse subcellular localization by confocal immunofluorescent histochemistry, whereas PKGI-α has a striated banding pattern. Stimulation of Gαq (angiotensin II, 1μM; endothelin 1, 0.5μM) induces translocation of both RGS2 and PKGI-α to the sarcolemmal membrane, which is dependent on PKG activation. Similar translocation is observed in 48hours-TAC myocytes, but it declines by 1 week. Concomitant PDE5A-I (oral sildenafil; 200mg/kg/day) sustains PKGI-α and RGS2 at the membrane in RGS2+/+ -TAC 1week, ameliorating hypertrophy, whereas PDE5A-I has no effect on RGS2−/− -TAC 1week (Table⇓). Thus RGS2 is an essential regulator of early compensation to pressure-overload, is regulated by PKGI-α activation, and also plays a key mechanistic role in the anti-hypertrophic effects from PDE5A inhibitors.