Nitric oxide and CaMKII: critical steps in the inotropic response to IGF-1

BURGOS JI; YEVES AM; ENNIS IL; VILA-PETROFF MG

Buenos Aires

Congreso; 2016 ISHR World Congress Annual Meeting; 2016

ISHR

Cardiac adaptation to aerobic exercise training includes improvedcardiomyocyte contractility, by a non-yet clarified mechanism in whichnitric oxide (NO) and CaMKII have been implicated. At the cellularlevel, IGF-1 is the main mediator of the adaptive response to exercise.Our purpose was to explore the effect of IGF-1 on mice cardiomyocytecontractility and the underlying signaling pathway.IGF-1 (10nmol/L) increased cardiomyocyte shortening(128.12±4.62%, n=8 vs basal; p˂0.05), effect abrogated by inhibitionof NO production with the non-selective nitric oxide synthase inhibitorL-NAME (2.5 mmol/L; 103.2±3.02%, n=5) or nitroguanidine (NG, 240nmol/L), specific inhibitor for the neuronal isoform(nNOS, 97.4±1.21%,n=5) and by CaMKII inhibition with KN93 (101.50±2.04%, n=6). Inagreement, a significant increase in NO production in response to IGF-1 (133.75±2.17%, n=16) was detected by epifluorescence with DAFFM.Again, this was prevented by L-NAME (110.36±3.20%, n=11)and NG (114.44±1.83%, n=9), confirming the involvement of nNOSbut not altered by KN93 (135.22±1.36%, n=9) suggesting that CaMKIIactivation was downstream NO production. We explored the pathwayinvolved in nNOS activation by measuring AKT phosphorylation. As expected,IGF-1 increased P-AKT (185.90±10.18%, n=3; p˂0.05). SinceNO-dependent CaMKII activation has been proposed, we next determinedCaMKII activity (P-CaMKII) and the phosphorylation of its downstreamtarget Thr17-phospholamban, detecting a significant increase inboth in the presence of IGF-1 (227.19±29.43% and 143.34±5.44%,n=3 respectively) but not when NO production was prevented by NG(126.61±5.48 and 65.76±15.04, n=3 respectively). Interestingly,similar results showing nNOS and CaMKII activation were obtained inthe hypertrophied myocardium of mice subjected to swimmingtraining.In conclusion, our results support a critical role of CaMKII in the positiveinotropic effect of IGF-1. Our findings suggest that IGF-1 throughthe IGF-1R triggers the phosphorylation of AKT which in turn activatesnNOS and increases NO production which would be responsible forCaMKII activation.