BAG3 and Hsc70 interact with actin capping protein CapZ to maintain myofibrillar integrity under mechanical stress.
BAG3 and Hsc70 interact with actin capping protein CapZ to maintain myofibrillar integrity under mechanical stress.
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DOI：
10.1161/circresaha.110.225649
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发表时间：
2010-11-12
影响因子：
20.1
通讯作者：
Takayama S
中科院分区：
文献类型：
--
作者：
Hishiya A;Kitazawa T;Takayama S
Bag3基因的纯合子中断或基因突变是Bcl-2相关基因家族蛋白(Bag)的成员，可导致以肌原纤维和Z盘中断为特征的心肌病和肌纤维肌病。然而，详细的发病机制尚不完全清楚。Bag3−/−小鼠的肌肉退化程度在不同的肌肉组之间存在差异，肌肉使用最多的肌肉以加速的速度退化。使用依赖的肌肉退化提示BAG3在机械应力下支持Z盘和肌原纤维之间的细胞骨架连接中起作用。在机械应力下维持肌原纤维结构的机制尚不清楚。本研究的目的是阐明BAG3介导的机械应力下肌肉维持的详细分子机制。为探讨bag3基因敲除是否导致机械应激所致的肌原纤维结构紊乱的问题，采用新生大鼠心肌细胞和shRNA介导的bag3基因敲除系统进行了体外机械拉伸实验。正如预期的那样，机械拉伸迅速破坏了bag3基因敲除的心肌细胞中的肌原纤维结构。Bag3通过肌动蛋白封端蛋白Capzβ1调节F-肌动蛋白的结构稳定性，促进Capzβ1与Hsc70的结合。Bag3促进Capzβ1分布到合适的位置，而Bag3的功能障碍导致Capz泛素-蛋白酶体介导的降解。通过过表达CAPZβ2来抑制CAPZβ1的功能增加了机械应激下肌原纤维的脆弱性和断裂。另一方面，CAPZβ1的过表达抑制了机械应力下Bag3基因敲除细胞的肌原纤维断裂。结果，从Bag3−/−小鼠分离的心肌出现了肌纤维变性，并在咖啡因收缩后失去了收缩活性。这些结果表明，BAG3和Hsc70在稳定肌原纤维结构和抑制机械应激下的肌原纤维变性方面发挥了新的作用。这些蛋白质可能是进一步研究的目标，以确定肌原纤维肌病或其他退行性疾病的治疗方法。
A homozygous disruption or genetic mutation of the bag3 gene, a member of the Bcl-2-associated athanogene (BAG) family proteins, causes cardiomyopathy and myofibrillar myopathy that is characterized by myofibril and Z-disc disruption. However, the detailed disease mechanism is not yet fully understood. bag3−/− mice exhibit differences in the extent of muscle degeneration between muscle groups with muscles experiencing the most usage degenerating at an accelerated rate. Usage-dependent muscle degeneration suggests a role for BAG3 in supporting cytoskeletal connections between the Z-disc and myofibrils under mechanical stress. The mechanism by which myofibrillar structure is maintained under mechanical stress remains unclear. The purpose of the study is to clarify the detailed molecular mechanism of BAG3-mediated muscle maintenance under mechanical stress. To address the question of whether bag3 gene knockdown induces myofibrillar disorganization caused by mechanical stress, in vitro mechanical stretch experiments using rat neonatal cardiomyocytes and an shRNA-mediated gene knockdown system of the bag3 gene were performed. As expected, mechanical stretch rapidly disrupts myofibril structures in bag3 knockdown cardiomyocytes. BAG3 regulates the structural stability of F-actin through the actin capping protein, CapZβ1, by promoting association between Hsc70 and CapZβ1. BAG3 facilitates the distribution of CapZβ1 to the proper location, and dysfunction of BAG3 induces CapZ ubiquitin-proteasome-mediated degradation. Inhibition of CapZβ1 function by overexpressing CapZβ2 increased myofibril vulnerability and fragmentation under mechanical stress. On the other hand, overexpression of CapZβ1 inhibits myofibrillar disruption in bag3 knockdown cells under mechanical stress. As a result, heart muscle isolated from bag3−/− mice exhibited myofibrillar degeneration, and lost contractile activity after caffeine contraction. These results suggest novel roles for BAG3 and Hsc70 in stabilizing myofibril structure and inhibiting myofibrillar degeneration in response to mechanical stress. These proteins are possible targets for further research to identify therapies for myofibrillar myopathy or other degenerative diseases.