Abstract 18021: Overexpression of microRNA-221 Cause Heart Failure by Inhibiting Autophagy
Background MicroRNAs serve as crucial intracellular regulators of cardiac function in health and disease, through negatively regulating target gene expression. We have previously identified that miR-221 was significantly up-regulated in pathological cardiac remodeling and promotes hypertrophy of cultured cardiomyocytes. In the present study, we investigated the role of miR-221 in the regulation of cardiac function in vivo.
Methods Transgenic C57Bl/6 mice with cardiac-specific overexpression of miR-221 were generated by using alpha-MHC promoter. Cardiac function was measured with high-resolution echocardiography. Heart weight/body weight (HW/BW) ratio, Masson trichrome staining, qRT-PCR and Western blot were performed on cardiac tissue at 3 months of age.
Results Cardiac function of miR-221 transgenic mice was significantly impaired by 3 months of age compared with their control littermates (LVIDd 5.51 ± 0.14mm vs. 4.05 ± 0.07mm, p<0.001; LVIDs 4.33 ± 0.14mm vs. 2.66 ± 0.09mm, p<0.001; fractional shorting 21.3 ± 2.6% vs. 34.5 ± 1.4%, p<0.001; n=8), accompanied with increased HW/BW ratio (1.6 fold, p<0.01) and up-regulated expression of ANP and BNP (10.2 and 5.3 fold, respectively; p<0.05 for both). Masson trichrome staining showed increased cardiac fibrosis in miR-221 transgenic mice. Both p27 and PTEN are two known downstream targets of miR-221 and reported to positively regulate autophagy through RB-dependent manner and PI3K-AKT-mTOR pathway respectively. This led us hypothesize that the dysregulation of autophagy may be responsible for the miR-221 induced cardiac function impairment. We measured the lipidation of LC3B and phosphorylation of S6 protein, the marker of autophagy and mTOR pathway activation, respectively. In the cardiac tissues of miR-221 transgenic mice, significant reduced conversion from LC3-I to LC3-II and increased phosphorylation of S6 were observed, indicating miR-221 overexpression resulted in autophagy inhibition and mTOR signaling pathway activation.
Conclusion These findings reveal that miR-221 is an important regulator of cardiac function in vivo, maybe through inhibiting autophagy activation. Therefore, modulating miR-221 expression may represent a novel approach for the treatment of heart failure.
- © 2012 by American Heart Association, Inc.