Cardiology, Swiss Cardiovascular Center Bern, Bern University Hospital and University of Bern, Bern, Switzerland.
Cell Tissue Res. 2012 Nov;350(2):361-72. doi: 10.1007/s00441-012-1475-8. Epub 2012 Aug 4.
The clinical use of anthracyclines in cancer therapy is limited by dose-dependent cardiotoxicity that involves cardiomyocyte injury and death. We have tested the hypothesis that anthracyclines affect protein degradation pathways in adult cardiomyocytes. To this aim, we assessed the effects of doxorubicin (Doxo) on apoptosis, autophagy and the proteasome/ubiquitin system in long-term cultured adult rat cardiomyocytes. Accumulation of poly-ubiquitinated proteins, increase of cathepsin-D-positive lysosomes and myofibrillar degradation were observed in Doxo-treated cardiomyocytes. Chymotrypsin-like activity of the proteasome was initially increased and then inhibited by Doxo over a time-course of 48 h. Proteasome 20S proteins were down-regulated by higher doses of Doxo. The expression of MURF-1, an ubiquitin-ligase specifically targeting myofibrillar proteins, was suppressed by Doxo at all concentrations measured. Microtubule-associated protein 1 light chain 3B (LC3)-positive punctae and both LC3-I and -II proteins were induced by Doxo in a dose-dependent manner, as confirmed by using lentiviral expression of green fluorescence protein bound to LC3 and live imaging. The lysosomotropic drug chloroquine led to autophagosome accumulation, which increased with concomitant Doxo treatment indicating enhanced autophagic flux. We conclude that Doxo causes a downregulation of the protein degradation machinery of cardiomyocytes with a resulting accumulation of poly-ubiquitinated proteins and autophagosomes. Although autophagy is initially stimulated as a compensatory response to cytotoxic stress, it is followed by apoptosis and necrosis at higher doses and longer exposure times. This mechanism might contribute to the late cardiotoxicity of anthracyclines by accelerated aging of the postmitotic adult cardiomyocytes and to the susceptibility of the aging heart to anthracycline cancer therapy.
蒽环类抗生素在癌症治疗中的临床应用受到剂量依赖性心脏毒性的限制，这种毒性涉及心肌细胞损伤和死亡。我们已经测试了这样一个假设，即蒽环类抗生素会影响成年心肌细胞中的蛋白降解途径。为此，我们评估了多柔比星（阿霉素）对长期培养的成年大鼠心肌细胞凋亡、自噬和蛋白酶体/泛素系统的影响。在阿霉素处理的心肌细胞中观察到多聚泛素化蛋白的积累、组织蛋白酶 D 阳性溶酶体的增加和肌原纤维降解。在 48 小时的时间过程中，蛋白酶体的糜蛋白酶样活性最初增加，然后被阿霉素抑制。较高剂量的阿霉素下调蛋白酶体 20S 蛋白。阿霉素在所有测量浓度下均抑制泛素连接酶 MURF-1 的表达，该酶特异性靶向肌原纤维蛋白。微管相关蛋白 1 轻链 3B（LC3）阳性斑点以及 LC3-I 和 -II 蛋白均被阿霉素以剂量依赖性方式诱导，这通过使用与 LC3 结合的绿色荧光蛋白的慢病毒表达和实时成像得到证实。溶酶体趋化药物氯喹导致自噬体积累，而阿霉素处理则进一步增加，表明自噬通量增强。我们得出结论，阿霉素导致心肌细胞蛋白降解机制下调，导致多聚泛素化蛋白和自噬体的积累。尽管自噬最初作为对细胞毒性应激的代偿反应而被激活，但在更高剂量和更长暴露时间下，它会被凋亡和坏死所取代。这种机制可能通过加速有丝分裂后成年心肌细胞的衰老以及衰老心脏对蒽环类癌症治疗的敏感性来导致蒽环类药物的迟发性心脏毒性。
