Abstract 14271: Microrna765 Impairs Cardiomyocyte Contractility by Targeting Protein Phosphatase 1 Inhibitor-1
Previous studies have shown that the reduction in protein phosphatase 1 inhibitor-1 (I-1) expression may play a role in the pathogenesis of heart disease by impairing sarcoplasmic reticulum (SR) Ca2+ cycling and consequently suppressing cardiac contractility. However, the underlying molecular mechanism contributing to the I-1 downregulation remains to be elucidated. Computational prediction indicates that microRNA765 (miR765) may serve as a candidate to regulate I-1 expression at the mRNA level. In the present study, we investigated whether microRNA-765 can regulate I-1 expression and subsequently affect cardiomyocyte contractility, by adenoviral infection of adult rat ventricular cardiomyocytes with microRNA-765 or non-translated nucleotide sequence (miRcontrol). Real-time PCR analysis indicated that I-1 mRNA expression was decreased by ∼20% in the miR765 cells, compared with the miRcontrol group. Under resting conditions, rates of shortening (+dL/dt), relengthening (−dL/dt) and fraction shortening (FS%), were decreased by 25%, 31% and 26%, respectively, in miR765 cardiomyocytes compared with miRcontrol cells. Although isoproterenol elicited a positive inotropic effect, +dL/dt, -dL/dt and FS% in the miR765 group remained depressed by 30%, 41% and 19% respectively, compared with the miRcontrol group. Coincidently, western blot analysis indicated that the phosphorylation of phospholamban (PLN) at serine16 (S16) and threonine 17 (T17), as well as phosphorylation of ryanodine receptor (RyR) at 2815, were significantly reduced in the miR765 group under basal conditions and remained depressed even in the presence of isoproterenol. Thus, miR765 can down-regulate I-1 expression and reduce cardiomyocyte contractility by decreasing the phosphorylation of both PLN and RyR, suggesting miR765 may play a role in the pathogenesis of heart failure.
- © 2010 by American Heart Association, Inc.