Shaanxi Key Laboratory for Animal Conservation, College of Life Sciences, Northwest University, Xi'an 710069, China.
Key Laboratory of Resource Biology and Biotechnology in Western China, College of Life Sciences, Northwest University, Ministry of Education, Xi'an 710069, China.
Cells. 2023 Apr 3;12(7):1077. doi: 10.3390/cells12071077.
Disuse atrophy of skeletal muscle is associated with a severe imbalance in cellular Ca homeostasis and marked increase in nuclear apoptosis. Nuclear Ca is involved in the regulation of cellular Ca homeostasis. However, it remains unclear whether nuclear Ca levels change under skeletal muscle disuse conditions, and whether changes in nuclear Ca levels are associated with nuclear apoptosis. In this study, changes in Ca levels, Ca transporters, and regulatory factors in the nucleus of hindlimb unloaded rat soleus muscle were examined to investigate the effects of disuse on nuclear Ca homeostasis and apoptosis. Results showed that, after hindlimb unloading, the nuclear envelope Ca levels ([Ca]) and nucleocytoplasmic Ca levels ([Ca]) increased by 78% ( < 0.01) and 106% ( < 0.01), respectively. The levels of Ca-ATPase type 2 (Ca-ATPase2), Ryanodine receptor 1 (RyR1), Inositol 1,4,5-tetrakisphosphate receptor 1 (IPR1), Cyclic ADP ribose hydrolase (CD38) and Inositol 1,4,5-tetrakisphosphate (IP) increased by 470% ( < 0.001), 94% ( < 0.05), 170% ( < 0.001), 640% ( < 0.001) and 12% ( < 0.05), respectively, and the levels of Na/Ca exchanger 3 (NCX3), Ca/calmodulin dependent protein kinase II (CaMK II) and Protein kinase A (PKA) decreased by 54% ( < 0.001), 33% ( < 0.05) and 5% ( > 0.05), respectively. In addition, DNase X is mainly localized in the myonucleus and its activity is elevated after hindlimb unloading. Overall, our results suggest that enhanced Ca uptake from cytoplasm is involved in the increase in [Ca] after hindlimb unloading. Moreover, the increase in [Ca] is attributed to increased Ca release into nucleocytoplasm and weakened Ca uptake from nucleocytoplasm. DNase X is activated due to elevated [Ca], leading to DNA fragmentation in myonucleus, ultimately initiating myonuclear apoptosis. Nucleocytoplasmic Ca overload may contribute to the increased incidence of myonuclear apoptosis in disused skeletal muscle.
骨骼肌废用性萎缩与细胞内钙稳态严重失衡和核凋亡明显增加有关。核钙参与细胞内钙稳态的调节。然而，目前尚不清楚在骨骼肌废用条件下核钙水平是否发生变化，以及核钙水平的变化是否与核凋亡有关。在这项研究中，检查了后肢去负荷大鼠比目鱼肌细胞核内钙水平、钙转运体和调节因子的变化，以研究废用对核钙稳态和凋亡的影响。结果表明，后肢去负荷后，核包膜钙水平([Ca])和核浆钙水平([Ca])分别增加了 78%(<0.01)和 106%(<0.01)。钙-ATP 酶 2 型(Ca-ATPase2)、Ryanodine 受体 1(RyR1)、肌醇 1,4,5-三磷酸受体 1(IPR1)、环 ADP 核糖水解酶(CD38)和肌醇 1,4,5-三磷酸(IP)的水平分别增加了 470%(<0.001)、94%(<0.05)、170%(<0.001)、640%(<0.001)和 12%(<0.05)，而 Na/Ca 交换器 3(NCX3)、钙/钙调蛋白依赖性蛋白激酶 II(CaMK II)和蛋白激酶 A(PKA)的水平分别降低了 54%(<0.001)、33%(<0.05)和 5%(>0.05)。此外，DNase X 主要定位于肌核，后肢去负荷后其活性升高。总的来说，我们的结果表明，细胞质中钙摄取的增加参与了后肢去负荷后[Ca]的增加。此外，[Ca]的增加归因于核浆中钙释放的增加和核浆中钙摄取的减弱。由于[Ca]升高，DNase X 被激活，导致肌核中 DNA 片段化，最终引发肌核凋亡。核浆钙超载可能导致废用性骨骼肌中肌核凋亡发生率增加。
