Dexmedetomidine postconditioning suppresses myocardial ischemia/reperfusion injury by activating the SIRT1/mTOR axis

Xiong Zhang, Yongxing Li, Yong Wang, Yuerong Zhuang, Xiaojie Ren, Kai Yang, Wuhua Ma, Ming Zhong, Xiong Zhang, Yongxing Li, Yong Wang, Yuerong Zhuang, Xiaojie Ren, Kai Yang, Wuhua Ma, Ming Zhong

Abstract

Myocardial ischemia/reperfusion (MI/R) triggers a complicated chain of inflammatory reactions. Dexmedetomidine (Dex) has been reported to be important in myocardial disorders. We evaluated the role of Dex in MI/R injury via the silent information regulator factor 2-related enzyme 1 (SIRT1)/mammalian target of rapamycin (mTOR) signaling pathway. First, Dex was immediately injected into rat models of MI/R injury during reperfusion. After Evans Blue-triphenyl tetrazolium chloride (TTC) and Hematoxylin-Eosin (H-E) staining, MI/R injury was observed. The extracted serum and myocardial tissues were used to detect oxidative stress and the inflammatory response. Western blot analysis was performed to evaluate MI/R autophagy and the levels of proteins associated with the SIRT1/mTOR axis. The effects of the combination of Dex and SIRT1 inhibitor EX527 on MI/R injury and autophagy were evaluated. Finally, the mechanism of Dex was tested, and autophagy levels and the levels of proteins associated with the SIRT1/mTOR signaling pathway were assessed in MI/R rats. The results of the present study suggested that Dex relieved MI/R injury, reduced cardiomyocyte apoptosis, oxidative stress and inflammatory reactions, up-regulated the SIRT1/mTOR axis and decreased overautophagy in MI/R rats. SIRT1 inhibitor EX527 attenuated the protective effects of Dex. Our study demonstrated that Dex alleviated MI/R injury by activating the SIRT1/mTOR axis. This investigation may offer new insight into the treatment of MI/R injury.

Keywords: Dexmedetomidine; EX527; Myocardial ischemia/reperfusion; SIRT1; mTOR.

Conflict of interest statement

The authors declare that there are no competing interests associated with the manuscript.

© 2020 The Author(s).

Figures

Figure 1. Protective functions of Dex in…
Figure 1. Protective functions of Dex in MI/R rats
(A) Representative ECG of MI/R rats. (B) Images of myocardial infarction in rats visualized by TTC staining and analysis of the infarct size, with the white part representing ischemic infarcted myocardium, red representing ischemic noninfarcted myocardium, and blue representing normal myocardium; the percentage of the infarct area relative to the total area analyzed. (C) Representative images of cardiomyocytes stained with HE. (D,E) LDH content and CK-MB content in rat serum. (F) TUNEL-stained myocardial tissues; the TUNEL-positive cells are shown in green. (G) Bcl-2 and cleaved caspase-3 expression detected by Western blot analysis. The data are expressed as the mean ± standard deviation, n=6. One-way ANOVA and Tukey’s multiple comparisons test were applied to determine statistical significance. *P<0.05, compared with the sham group, #P<0.05, compared with the MI/R group.
Figure 2. Effects of Dex on inflammatory…
Figure 2. Effects of Dex on inflammatory responses and oxidative stress in MI/R rats
(A–C), (A) TNF-α, (B) IL-1β and (C) IL-6 contents in serum. (D–G) (D) SOD, (E) CAT, (F) GSH-Px and (G) MDA contents in myocardial tissues. The data are expressed as the mean ± standard deviation, n=6. One-way ANOVA and Tukey’s multiple comparisons test were applied to determine statistical significance. *P<0.05, compared with the sham group, #P<0.05, compared with the MI/R group.
Figure 3. Dex reduces autophagy in MI/R…
Figure 3. Dex reduces autophagy in MI/R rats
Western blot analysis of LC3II/LC3I, p62 and Beclin-1 expression in myocardial tissues. The data are expressed as the mean ± standard deviation, n=6. One-way ANOVA and Tukey’s multiple comparisons test were applied to determine statistical significance. *P<0.05, compared with the sham group, #P<0.05, compared with the MI/R group. Abbreviations: MI/R, myocardial/ischemia reperfusion.
Figure 4. Effects of Dex on SIRT1…
Figure 4. Effects of Dex on SIRT1 and mTOR expression
(A) Representative results of SIRT1 immunohistochemistry in myocardial tissue. (B) SIRT1 expression in nuclei in myocardial tissue detected using Western blot analysis. (C) mTOR expression in myocardial tissue measured by Western blot analysis. The data are expressed as the mean ± standard deviation, n=6. One-way ANOVA and Tukey’s multiple comparisons test were applied to determine statistical significance. *P<0.05, compared with the sham group, #P<0.05, compared with the MI/R group.
Figure 5. Effects of EX527 on autophagy…
Figure 5. Effects of EX527 on autophagy and the SIRT1/mTOR axis in MI/R rats after Dex postconditioning
(A) Representative results of SIRT1 immunohistochemistry in myocardial tissues. (B) SIRT1 expression in nuclei in myocardial tissue detected by Western blot analysis. (C,D) mTOR (C) LC3II/LC3I, p62 and Beclin-1 (D) expression in myocardial tissues measured by Western blot analysis. The data are expressed as the mean ± standard deviation, n=6. The t test was employed to analyze comparisons between two groups. *P<0.05, compared with the MI/R + Dex group.
Figure 6. Effects of EX527 on rats…
Figure 6. Effects of EX527 on rats with MI/R injury after Dex postconditioning
(A) Representative images of myocardial infarction in rats visualized by TTC staining and analysis of the infarct size. (B) Rat cardiomyocytes stained with H-E. (C) Representative images and analysis of TUNEL staining. (D,E) LDH (D) and CK-MB (E) levels in serum. The data are expressed as the mean ± standard deviation, n=6. The t test was employed to analyze comparisons between two groups. *P<0.05, compared with the MI/R + Dex group.

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