Coronary Microembolization Induces Cardiomyocyte Apoptosis in Swine by Activating the LOX-1-Dependent Mitochondrial Pathway and Caspase-8-Dependent Pathway.

BACKGROUND: Cardiomyocyte apoptosis by coronary microembolization (CME) contributes to myocardial dysfunction, in which mitochondrial pathway and death receptor pathway are activated. Lectin-like oxidized low-density lipoprotein receptor 1 (LOX-1) is a membrane protein involved in apoptosis. The study aimed to explore the role of LOX-1 in the activation of these 2 major apoptotic pathways. METHODS: Twenty Bama miniature swine were randomized into 4 groups (n = 5 per group). The groups were Sham, CME, LOX-1 small-interfering RNA (siRNA), and control siRNA. Microspheres were injected into the left anterior descending artery of swine to establish CME model. Twelve hours after operation, cardiac function, serum c-troponin I level, microinfarct, and apoptotic index were examined. The levels of LOX-1, Bcl-2, Bax, cytochrome c as well as cleaved caspase 9, -8, and -3 were detected. RESULTS: Myocardial dysfunction, enhanced serum c-troponin I, microinfarct, and apoptosis were induced following CME. Moreover, CME induced increased expression of LOX-1, Bax, cytochrome c, cleaved caspase 9, -8, and -3 as well as decreased Bcl-2 expression levels. The LOX-1 siRNA reversed these effects by CME except cleaved caspase 8 expression, while the control siRNA had no effect. CONCLUSION: Coronary microembolization induces cardiomyocyte apoptosis via the LOX-1-dependent mitochondrial pathway and caspase 8-dependent pathway.

Coronary Microembolization Induces Cardiomyocyte Apoptosis Through the LOX-1-Dependent Endoplasmic Reticulum Stress Pathway Involving JNK/P38 MAPK.

BACKGROUND: Lectin-like oxidized low-density lipoprotein receptor-1 (LOX-1) is a membrane protein associated with apoptosis. Endoplasmic reticulum (ER) stress-induced apoptosis has been determined in several cardiovascular diseases. Mitogen-activated protein kinase (MAPK) signalling is involved in apoptosis. The aim of this study was to investigate whether LOX-1, ER stress, and MAPKs play a role in cardiomyocyte apoptosis after coronary microembolization (CME) and the exact mechanisms involved. METHODS: Thirty swine were randomized into the following groups (n = 5 per group): sham, CME, CME + LOX-1 small-interfering RNA (siRNA), CME + control siRNA, CME + JNK inhibitor, and CME + p38 inhibitor. The CME model was established by injecting microspheres into the left anterior descending (LAD) artery, whereas swine in the sham group received normal saline instead. Twelve hours after the sham operation or CME, cardiac function, serum c-troponin I level, microinfarcts, and apoptotic index were determined. Relative expression levels of LOX-1, ER stress markers (glucose-regulated protein 78 [GRP 78], C/EBP homologous protein [CHOP], and cleaved caspase-12), cleaved caspase-3, c-Jun NH2-terminal protein kinases (JNK), p38, and extracellular signal-related protein kinases (ERK1/2) were measured. RESULTS: CME induced cardiac dysfunction, microinfarction, increased serum c-troponin I levels, and cardiomyocyte apoptosis. Additionally, the expression of LOX-1, ER stress markers, and cleaved caspase-3, and the phosphorylation of JNK, p38, and ERK1/2 were all enhanced. LOX-1 siRNA inhibited these effects except the phosphorylation of ERK1/2. Pretreatment with a JNK inhibitor or a p38 inhibitor attenuated the expression of ER stress markers and apoptosis. CONCLUSIONS: Our results indicated that CME induced cardiomyocyte apoptosis through the LOX-1-dependent ER stress pathway, in which the phosphorylation of JNK and p38 were involved. This might provide a new approach for the prevention and treatment of CME.

Trimetazidine pretreatment inhibits myocardial apoptosis and improves cardiac function in a Swine model of coronary microembolization.

OBJECTIVE: Trimetazidine (TMZ) is a well-known anti-ischemic agent; however, its efficacy and mechanism of cardioprotection on coronary microembolization (CME) are largely unknown. The present study was undertaken to determine whether TMZ pretreatment could attenuate myocardial apoptosis and improve cardiac function in a swine model of CME. METHODS: Fifteen swine were randomly and equally divided into a sham-operated (control) group, CME group and CME plus TMZ (TMZ) group. CME was induced by injecting inert plastic microspheres (42 µm in diameter) into the left anterior descending artery. For the control group, the same dose of normal saline was substituted for the microspheres, and the TMZ group was pretreated with TMZ 30 min before microsphere injection. Cardiac function was assessed by echocardiography, myocardial apoptosis was detected by TUNEL staining, and the expression levels of cleaved caspase-9/3 were measured by Western blot 12 h after operation. RESULTS: Compared to the control group, cardiac function in the CME group was significantly decreased (p < 0.05); however, TMZ pretreatment showed significantly improved cardiac function as compared to the CME group (p < 0.05). The myocardial apoptotic rate and the expression levels of cleaved caspase-9/3 increased remarkably in CME group as compared with the control group (p < 0.001). Again, TMZ pretreatment significantly reduced the apoptotic rate and also the expression levels of cleaved caspase-9/3 (p < 0.001). CONCLUSION: The present study demonstrated that TMZ pretreatment could significantly inhibit CME-induced myocardial apoptosis and improve cardiac function, and that the cardioprotective effect appeared to be mediated by the blockade of the mitochondrial apoptotic pathway. These results emphasize the importance of TMZ pretreatment in the therapy of CME-induced myocardial injury.