Intermedin 1-53 Ameliorates Atrial Fibrosis and Reduces Inducibility of Atrial Fibrillation via TGF-β1/pSmad3 and Nox4 Pathway in a Rat Model of Heart Failure

Figure 1. Effects of IMD1-53 treatment on cardiac contractile function and LAD after MI surgery. (A) Representative examples of M-mode echocardiogram of three groups. (B) Bar graphs indicate the LAD. IMD1-53 decreased LAD after MI. (C) Bar graphs indicate the LVEF. IMD1-53 improved LVEF after MI. (D) Bar graphs indicate the LVFS. IMD1-53 improved LVFE after MI. Data in bar graphs are means ± SD, n = 10. LVEF, left-ventricular ejection fraction; LVFS, left-ventricular fraction shortening; LAD, left-atrial diameter; MI, myocardial infarction; IMD1-53, intermedin 1-53. ** p < 0.01.

Figure 2. Characteristics of cardiac electrophysiology in rats. (A) Electrocardiogram of SR and AF. Right-atrial electrograms (HRA1-2 and HRA3-4) demonstrate rapid irregular atrial activations with varying electrogram morphology. Note that different atrial electrical activation patterns were recorded from the high right atrium (HRA1-2) and lower right atrium (RA3-4) during sinus rhythm and atrial fibrillation in rats. (B) Changes of AERP in rats. IMD1-53 improved AERP after the MI operation. (C) Bar graphs indicate the AF inducibility. IMD1-53 inhibited AF inducibility compared to the MI group. (D) Bar graphs indicate the AF duration. IMD1-53 decreased AF episode duration. Data in bar graphs are means ± SD, except the bar graph of figure (D), which presents the median and IQR (25–75%), n = 10. AF, atrial fibrillation. HRA, high right atrium; RA, right atrium. ** p < 0.01.

Figure 3. Effects of IMD-1-53 treatment on atrial fibrosis after MI surgery. (A) Representative photomicrographs of left-atrial histologic slides (Masson trichrome stain) from one rat in each group are shown at the top. The blue arrow indicates fibrosis. Scale bar = 200 μm. (B) Values are presented as means ± SD. IMD1-53 reduced fibrosis area. n = 10. MI, myocardial infarction. ** p < 0.01, n.s., no significance.

Figure 4. mRNA and protein expression of collagen I and collagen III in the left atria of rats. (A) mRNA expression of collagen I. IMD1-53 decreased collagen I after MI. (B) mRNA expression of collagen III. IMD1-53 decreased collagen III after MI. (C) Western blot of collagen I and collagen III. (D) Bar graphs indicate Western blot analysis for the protein expression of collagen I. IMD1-53 decreased the protein level of collagen I in the left atrium. (E) Bar graphs indicate Western blot analysis for the protein expression of collagen III. IMD1-53 decreased the protein level of collagen III in the left atrium. Data in bar graphs are means ± SD, n = 10. * p < 0.05, ** p < 0.01. n.s., no significance.

Figure 5. mRNA and protein expression of TGF-β1, α-SMA, Nox4, and Smad3 in the left atria of rats. (A) mRNA expression of TGF-β1 in rat’s left atrium. IMD1-53 reduced TGF-β1 after MI. (B) mRNA expression of α-SMA in rat’s left atrium. IMD1-53 reduced α-SMA after MI. (C) mRNA expression of Nox4 in rat’s left atrium. IMD1-53 reduced Nox4 after MI. (D–G) Western blot analysis for the protein expression of TGF-β1, α-SMA, and Nox4. IMD1-53 decreased each of these indices. (H,I) Representative Smad3 protein expression and phosphorylation level of Smad3 measured by Western blot in left atrium. IMD1-53 reduced the phosphorylation of Smad3 after MI. Data in the bar graphs are means ± SD, n = 10. * p < 0.05, ** p < 0.01. n.s., no significance.

Figure 6. TGF-β1-induced Nox4 expression is inhibited by IMD via TGF-β1/ALK5-dependent pathway. (A) Representative Nox4 protein expression measured by Western blot in atrial fibroblast. (B) Densitometric quantifications of band intensities from Western blot for Nox4/GAPDH in atrial fibroblast. Data in bar graphs are means ± SD, n = 10. * p < 0.05 versus the control group, # p < 0.05 versus the TGF-β1 group, † p < 0.05 versus the TGF-β1 + IMD group.