Abstract 16919: MicroRNA-26b Reduces Sarcomericactin and Disrupts the Sarcomere during Myocyte Hypertrophy
MicroRNA-26b (miR-26b) is downregulated during cardiac hypertrophy. We have previously reported that it inhibits GATA4 and compromises myocyte survival. The objective of this study was to further dissect the role of miR-26b during hypertrophic growth of neonatal myocytes and to verify its targets. We have established that itinhibitsthe expression of GATA4 in a dose dependent manner, with a maximum of 90% inhibition at the higher doses. To determine whether this inhibition was through direct targeting of the 3′ untranslated region (3′UTR), the effect of miR-26b on an exogenous GATA4 or a luciferase gene, both including the3′UTRof GATA4 encompassing the predicted miR-26-targeted site,was assessed in a dose-dependent fashion. This resulted in >80 maximum inhibition of the expression of these genes, suggesting that miR-26b directly targets the 3′UTR of GATA4 and inhibits its translation. Conversely, knockdown of miR-26b enhanced the expression of these genes. To further address the role of miR-26 on the myocytes, we supplied neonatal myocytes,undergoing hypertrophic growth, with exogenous miR-26b. Immunostaining these cells for GATA4 and myosin heavy chain revealed that the cells overexpressing miR-26b not only lacked detectable GATA4 but also exhibited disorganized myofilaments that lacked normal sarcomeric striations. Closer examination of the cells revealedno direct correlation between miR-26b and cell size. Moreover, overexpression of miR-26b did not reduce [3H]leucine incorporation. It should be noted, though, that these effects were measured in the absence of any detectable signs ofcell death. One of the main characteristics of miRNA is that they have the capacity to target multiple genes. In accordance, another predicted target of miR-26b that is a likely candidate to explain these results is sarcomeric alpha skeletal actin (aSkAc), which is upregulated during cardiac hypertrophy. Indeed overexpresion of miR-26b reduced sarcomeric acitn by ∼60%. However, we have not yet determined whether this effect is through direct gene targeting or indirect through GATA4. Thus, the data suggest that downregulation of miR-26b may play a role in the upregulation of aSkAc and GATA4, and regulate sarcomere assembly during cardiac hypertrophy.
- © 2010 by American Heart Association, Inc.