npg Function of miR-27b in cardiac hypertrophy 524 saline displayed progressive cardiac hypertrophy and interstitial fibrosis, whereas TAC-operated mice treated with antagomir-27b showed significant attenuation of the effects (Figure 7D-7G). Analysis of cardiac function by echocardiography showed that antagomir-27b treatment significantly reversed LV wall thickness and LV mass and normalized fractional shortening (Figure 7H-7J and Supplementary information, Table S3). Discussion In this study, we investigated the physiological func- tions of miR-27b and the molecular mechanisms by which miR-27b induces cardiac hypertrophy. The im- portant novel findings of our study are as follows: (1) miR-27b is upregulated in Smad4-deficient hypertrophic heart; (2) miR-27b is significantly inhibited by TGF- β1 in cardiomyocytes; (3) cardiac overexpression of miR-27b is sufficient to induce cardiac hypertrophy and dysfunction; (4) PPAR-γ, the target gene of miR-27b, is downregulated in miR-27b transgenic mice, and PPAR-γ overexpression could partially rescue the effects caused by miR-27b overexpression; (5) in vivo inhibition of miR-27b attenuates structural and functional deterio- ration in a TAC-induced HF mouse model. Thus, our results provide the first and critical genetic evidences showing that TGF-β-regulated miR-27b plays an impor- tant role in cardiac growth and hypertrophy. Increasing evidences from experimental studies have shown that Smad-mediated responses to TGF-β signaling have cardioprotective effects in cardiac hypertrophy [21]. Cardiomyocyte-specific deletion of Smad4 induces car- diac hypertrophy and HF [6], while transaortic constric- tion leads to a significant increase in cardiac hypertrophy Figure 7 Antagomir-27b attenuated cardiac hypertrophy and dysfunction in a TAC mouse model. (A) Detection of miR-27b expression level in TAC models by real-time PCR. *P < 0.05 relative to control. (B) Detection of miR-27b expression level 3 weeks after treatment with saline or antagomir-27b by real-time PCR. *P < 0.05 and **P < 0.01. (C) PPAR-γ expression level was determined in hearts by western blot (n = 3/condition). (D) Heart weight to body weight or tibia length of mice from sham (n = 11), TAC treated with saline (n = 7) or with antagomir-27b (n = 5). *P < 0.05 and **P < 0.01. (E) Histological analysis of hearts from different groups using masson staining and Laminin immunostaining. Scale bar, upper panel: 2 mm and middle and lower panel: 50 µm. (F) Analysis of ANF, BNP, β-MHC and α-MHC in hearts from different groups by real-time PCR (n = 3/condition). *P < 0.05. (G) Cross-sectional areas were analyzed after laminin immunostaining (n = 400 cells/condition). *P < 0.05 and **P < 0.01. (H-J) LVPWD, FS and LVM were analyzed from TAC mice treated with saline (n = 8) or antagomir-27b (n = 5). *P < 0.05. Cell Research | Vol 22 No 3 | March 2012