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Introduction Myocardial dysfunction consists of biventricular systolic and diastolic dysfunction, is one of the chief properties of patients with severe sepsis, and continues to be the leading cause of mortality and morbidity in the intensive care unit [[1], [2], [3], [4], [5]]. However, the mechanism involved in myocardial dysfunction is not fully clear, and there is no effective way to prevent and treat this condition. Calpains, a large family of calcium-dependent cysteine proteases, play a critical role in the development of myocardial dysfunction, and specific inhibition of calpain in rats with endotoxic shock attenuates circulatory failure and inflammatory factors, improving myocardial systolic and diastolic dysfunction [[6], [7], [8]]. Activated caspase-3 was also confirmed to be involved in septic heart dysfunction since it directly sheared the myocardial contractile proteins Troponin-T, Troponin-I and Troponin-C [[7], [8], [9], [10], [11]]. We demonstrated that gp91phox-NADPH oxidase-mediated calpain-1 activation induces caspase-3 activation and TNF-α L-741,626 in cardiomyocytes during LPS stimulation [12], and in addition, myocardial calpain induces caspase-3 activation and apoptosis through activation of the Hsp90/Akt pathway in C57BL/6 septic mice [13]. In a recent study, we reported that myocardial calpain activation promoted TNF-α expression in LPS-induced myocardial dysfunction via IκBα/NF-κB signaling [14]. This finding provides evidence that the eNOS/NO pathway may help suppress the degradation of the apoptotic protein molecule Bcl-2 and the release of cytochrome-c by mitochondria to inhibit caspase-3 activation and cell apoptosis [[15], [16], [17]]. These results strongly indicate that the Akt/eNOS/NO pathway might play a potential role in this pathological process.
Materials and methods
Results
Discussion To our knowledge, this is the first study to suggest a direct link between calpain and the subsequent activation of caspase-3 and NF-κB via the Akt/eNOS/NO pathway. These findings make further efforts to explain our previous studies that LPS-induced myocardial calpain activity promoted apoptosis and cardiac dysfunction [[12], [13], [14]]. TNF-α was first discovered as a myocardial inhibitor in patients with sepsis-induced shock [18]. We demonstrated that increased TNF-α in cardiomyocytes directly inhibited myocardial contractile function and that inhibition of TNF-α expression in myocardium could improve cardiac dysfunction in vivo and in vitro in a model of sepsis [12]. Moreover, TNF-α production is aroused by the activation of NF-κB, and inhibition of NF-κB activation could block the expression of TNF-α in myocardium [14]. Subsequently, we demonstrated that calpain activity activates caspase-3 and NF-κB in LPS-treated cardiomyocytes/pulmonary endothelial cells and after inhibition of calpain by drug inhibitors, overexpression of the calpastatin gene in cells or mice blocked the activation of caspase-3 and NF-κB in myocardium and ameliorated the levels of TNF-α, apoptosis, and cardiac dysfunction [[12], [13], [14],19]. It is suggested that the calpain-induced activation of caspase-3 and NF-κB is involved in the pathological process of sepsis-induced cardiac dysfunction. In addition, a previous study reported that TNF-α and IL-1β play a key role in promoting the acute inflammatory response, circulatory failure and septic shock under endotoxin stimulation [18,20].