Short term triiodo-L-thyronine treatment inhibits cardiac myocyte apoptosis in border area after myocardial infarction in rats

Abstract

Thyroid hormone (TH) levels decline after a myocardial infarction (MI). Treatment with TH has been shown to improve left ventricular (LV) function in MI and other cardiovascular diseases, but the mechanisms are not clear. We have previously shown that TH can prevent myocyte apoptosis via Akt signaling in cultured neonatal rat cardiomyocytes. In this study, the effects of triiodo-L-thyronine (T3) on LV function and myocyte apoptosis after MI was examined in rats. After surgery, MI rats were treated with T3 for 3 days. Compared with sham-operated rats, MI rats showed significantly increased LV chamber dimension during systole and decreased LV function. T3 treatment increased LV +/-dP/dt but did not change LV chamber dimensions. MI rats also showed significantly increased myocyte apoptosis in the border area as assessed by DNA laddering and TUNEL assay. T3 treatment decreased the amount of DNA laddering, and reduced TUNEL positive myocytes in the border area, which was associated with phosphorylation of Akt at serine 473. These results suggest that T3 can protect myocytes against ischemia-induced apoptosis, which may be mediated by Akt signaling.

Figure 1

Transverse myocardial section, hematoxylin and eosin staining. (A) Left ventricle and septum. (B) Enlarged image (×10) of the boxed area in A. The infarcted area (In, short arrows), border area (Bo, long arrows), and septum (Se) are illustrated as indicated.

Figure 2

Myocyte apoptosis in border area was attenuated by T3 treatment. (A) T3 reduced DNA fragmentation significantly in cardiomyocytes in border area. Semi-quantitative PCR amplification of GAPDH gene showed that equal amount of genomic DNA were used for the DNA laddering assay. (B) T3 markedly reduced TUNEL positive cardiomyocytes (arrows). Results are mean (SD) with n=4 rats per group. *P ≤ 0.05 vs. MI group; two-tailed Student’s t-test.

Figure 3

Figure 3A. Border area. Representative Western blot and densitometry for total Akt, phospho-Akt (S473) and Akt2 expressions. Results are mean (SD) with n=4 rats per group. *P ≤ 0.05 vs. MI group. ^‡P ≤ 0.01 vs. Sham operated group; ANOVA with Student-Newman-Keuls’ Multiple Comparison Test. Figure 3B. Septal area. Representative Western blot and densitometry for total Akt, phospho-Akt (S473) and Akt2 expression. Results are mean (SD) with n=4 rats per group. ^†P ≤ 0.05 vs. Sham operated group; ANOVA with Student-Newman-Keuls’ Multiple Comparison Test.

Figure 3

Figure 3A. Border area. Representative Western blot and densitometry for total Akt, phospho-Akt (S473) and Akt2 expressions. Results are mean (SD) with n=4 rats per group. *P ≤ 0.05 vs. MI group. ^‡P ≤ 0.01 vs. Sham operated group; ANOVA with Student-Newman-Keuls’ Multiple Comparison Test. Figure 3B. Septal area. Representative Western blot and densitometry for total Akt, phospho-Akt (S473) and Akt2 expression. Results are mean (SD) with n=4 rats per group. ^†P ≤ 0.05 vs. Sham operated group; ANOVA with Student-Newman-Keuls’ Multiple Comparison Test.