Silencing of the epidermal growth factor receptor (EGFR) blunts the slow force response to myocardial stretch.

BREA MS, DÍAZ RG, MORGAN PE, CALDIZ CI, PÉREZ NG

Congreso; XXII Wolrd Congress International Society for Heart Research; 2016

Myocardial stretch induces a biphasic force increase:A first phase due to the Frank-Starling mechanism, followed by a slower onecalled slow force response (SFR). The SFR is due to a complex autocrinemechanism that appears to involve Angiotensin II (AII)-triggered EGFR transactivation and the consequentgeneration/release of reactive oxygen species (ROS) leading to Na+/H+exchanger (NHE1) activation. In order to conclusively prove the role of theEGFR in the SFR, we developed a lentivirus carrying a siRNA against EGFR(siEGFR), and injected it into the rat cardiac left ventricular wall (n=8). Ascramble (SCR) sequence was used as control (n=9). After 4 weeks, EGFR proteinexpression showed a 48±15%reduction insiEGFR-injected hearts comparedto SCR (100±6%, P<0.05). Isolatedrat papillary muscles from both groups were then stretched from 92 to 98% ofLmax. The SFR was 131±2% of initial rapid phase in SCR (P<0.05 vs. rapidphase) and was blunted in siEGFR-expressing muscles (102±1%, P<0.05 vs.SCR). Basal myocardial oxidative stress estimated by T-BARS was not affected bythe reduction in EGFR expression: (in nmol/gr tissue) 1.29±0.09 siEGFR vs.1.38±0.06 SCR. However, AII or EGF-mediated ROS production (assessed by lucigeninmethod in cardiac tissue slices) was significantly reduced in siEGFR-injected hearts: AII (1nM) from 226±27 SCR to 113±9 siEGFR(P<0.05); EGF (0,1ug/ml) from 175±19 to 102±7 (P<0.05) respectively.Finally, we studied the EGFR silencing effect over the reported AII-dependent NHE1activity by measuring pHi (BCECF, papillary muscles) in bicarbonate-freemedium. 1nM AII significantly increased pHi by 0.18±0.06 units in theSCR group (P<0.05), effect that was completely blunted in the siEGFR one (-0.12±0.03).Taken together, we can conclude that EGFR activation after stretch is crucialfor the development of the SFR, effect that would result from preventingROS-mediated NHE1 activation