PPARα activation alleviates damage to the cytoskeleton during acute myocardial ischemia/reperfusion in rats

Abstract

The cytoskeleton serves an important role in maintaining cellular morphology and function, and it is a substrate of calpain during myocardial ischemia/reperfusion (I/R) injury (MIRI). Calpain may be activated by endoplasmic reticulum (ER) stress during MIRI. The activation of peroxisome proliferator‑activated receptor α (PPARα) may inhibit ischemia/reperfusion damage by regulating stress reactions. The present study aimed to determine whether the activation of PPARα protects against MIRI‑induced cytoskeletal degradation, and investigated the underlying mechanism involved. Wistar rats were pretreated with or without fenofibrate and subjected to left anterior descending coronary artery ligation for 45 min, followed by 120 min of reperfusion. Calpain activity and the expression of PPARα, desmin and ER stress parameters were evaluated. Electrocardiography was performed and cardiac function was evaluated. The ultrastructure was observed under transmission electron microscopy. I/R significantly induced damage to the cytoskeleton in cardiomyocytes and cardiac dysfunction, all of which were improved by PPARα activation. In addition, I/R increased ER stress and calpain activity, which were significantly decreased in fenofibrate‑pretreated rat heart tissue. The results suggested that PPARα activation may exert a protective effect against I/R in the myocardium, at least in part via ER stress inhibition. Suppression of ER stress may be an effective therapeutic target for protecting the I/R myocardium.

Keywords: PPARα; cytoskeleton; desmin; acute MIRI; endoplasmic reticulum stress; calpain.

Figure 1.

Representative ECG results. (A) A normal ECG was observed in the normal and sham group. (B) QRS wave amplitude increased, (C) the ST segment was elevated and (D) reperfusion arrhythmia occurred following arterial ligation in the I/R and fenofibrate+I/R groups. The black triangle indicates the QRS wave and the black arrow indicates the ST segment. ECG, electrocardiogram; I/R, ischemia/reperfusion.

Figure 2.

Effect of FF on cardiac function in rats with acute I/R. Echocardiograms of rats in the (A) normal group, (B) Sham group, (C) I/R group and (D) FF+I/R group. (E) The LVEF of rats in each group. (F) The LVDd of rats in each group. Data are presented as the mean ± standard error (n=8). *P<0.05 vs. sham group; ^#P<0.05 vs. I/R group. I/R, ischemia/reperfusion; FF, pretreatment with fenofibrate; EF, ejection fraction; LVDd, left ventricular end-diastolic diameter; LVEF, left ventricular ejection fraction.

Figure 3.

Influence of FF on the ultrastructure of myocardial tissues of rats with acute I/R. Representative electron micrographs of cardiomyocytes of rats in each group (n=4 rats/group). The black triangle indicates the endoplasmic reticulum, the arrow indicates the Z line and the M indicates mitochondria. (A) Normal group. (B) Sham group. (C) I/R group. (D) FF+I/R group. Scale bar=2 µm. I/R, ischemia/reperfusion; FF, pretreatment with fenofibrate.

Figure 4.

PPARα activation decreases degradation of desmin caused by acute myocardial I/R injury. Expression levels of the desmin protein were detected by western blotting. A representative image is presented. Data are presented as the mean ± standard error (n=8). ***P<0.001 vs. sham group; ^##P<0.01 vs. I/R group. I/R, ischemia/reperfusion; FF, pretreatment with fenofibrate; PPARα, peroxisome proliferator-activated receptor α.

Figure 5.

Effect of FF on the expression of PPARα protein in the myocardial tissue of rats with acute I/R. The expression levels of the PPARα protein were detected by western blotting. A representative image is presented. Data are presented as the mean ± standard error (n=8). ***P<0.001 vs. sham group. ^###P<0.001 vs. I/R group. I/R, ischemia/reperfusion; FF, pretreatment with fenofibrate; PPARα, peroxisome proliferator-activated receptor α.

Figure 6.

Effect of FF on calpain activity in the myocardium of rats with acute I/R. ***P<0.001 vs. sham group. ^###P<0.001 vs. I/R group. I/R, ischemia/reperfusion; FF, pretreatment with fenofibrate.

Figure 7.

PPARα activation relieves GRP78 overexpression in the myocardium of rats with acute I/R. Expression levels of GRP78 (A) mRNA and (B) protein were detected by reverse transcription-quantitative polymerase chain reaction and western blotting, respectively. Data are presented as the mean ± standard error (n=8). ***P<0.001 vs. sham group. ^###P<0.01 vs. I/R group. PPARα, peroxisome proliferator-activated receptor α; I/R, ischemia/reperfusion; FF, pretreatment with fenofibrate; GRP78, glucose-regulated protein-78.

Figure 8.

Association between the expression levels of GRP78 and desmin in the myocardium of each group (n=8). (A) Normal group; (B) sham group; (C) I/R group; (D) FF+I/R group. I/R, ischemia/reperfusion; FF, pretreatment with fenofibrate; GRP78, glucose-regulated protein-78.