Mázala Davi A G, Chen Dapeng, Chin Eva R
Department of Kinesiology, School of Public Health, University of Maryland, College Park, MD, USA.
Department of Kinesiology, College of Health Professions, Towson University, Towson, MD, USA.
J Neuromuscul Dis. 2024;11(2):315-326. doi: 10.3233/JND-230123.
Amyotrophic lateral sclerosis (ALS) is characterized by progressive loss of muscle mass and muscle function. Previous work from our lab demonstrated that skeletal muscles from a mouse model of ALS show elevated intracellular calcium (Ca2+) levels and heightened endoplasmic reticulum (ER) stress.
To investigate whether overexpression of sarcoplasmic reticulum (SR) Ca2+ ATPase 1 (SERCA1) in skeletal muscle would improve intracellular Ca2+ handling, attenuate ER stress, and improve motor function ALS transgenic mice.
B6SJL-Tg (SOD1*G93A)1Gur/J (ALS-Tg) mice were bred with skeletal muscle α-actinin SERCA1 overexpressing mice to generate wild type (WT), SERCA1 overexpression (WT/+SERCA1), ALS-Tg, and SERCA1 overexpressing ALS-Tg (ALS-Tg/+SERCA1) mice. Motor function (grip test) was assessed weekly and skeletal muscles were harvested at 16 weeks of age to evaluate muscle mass, SR-Ca2+ ATPase activity, levels of SERCA1 and ER stress proteins - protein disulfide isomerase (PDI), Grp78/BiP, and C/EBP homologous protein (CHOP). Single muscle fibers were also isolated from the flexor digitorum brevis muscle to assess changes in resting and peak Fura-2 ratios.
ALS-Tg/+SERCA1 mice showed improved motor function, delayed onset of disease, and improved muscle mass compared to ALS-Tg. Further, ALS-Tg/+SERCA1 mice returned levels of SERCA1 protein and SR-Ca2+ ATPase activity back to levels in WT mice. Unexpectedly, SERCA-1 overexpression increased levels of the ER stress maker Grp78/BiP in both WT and ALS-Tg mice, while not altering protein levels of PDI or CHOP. Lastly, single muscle fibers from ALS-Tg/+SERCA1 had similar resting but lower peak Fura-2 levels (at 30 Hz and 100 Hz) compared to ALS-Tg mice.
These data indicate that SERCA1 overexpression attenuates the progressive loss of muscle mass and maintains motor function in ALS-Tg mice while not lowering resting Ca2+ levels or ER stress.
肌萎缩侧索硬化症（ALS）的特征是肌肉质量和肌肉功能逐渐丧失。我们实验室之前的研究表明，ALS小鼠模型的骨骼肌细胞内钙（Ca2+）水平升高，内质网（ER）应激增强。
研究骨骼肌中肌浆网（SR）Ca2+ATP酶1（SERCA1）的过表达是否能改善细胞内Ca2+处理、减轻ER应激并改善ALS转基因小鼠的运动功能。
将B6SJL-Tg（SOD1*G93A）1Gur/J（ALS-Tg）小鼠与骨骼肌α-肌动蛋白SERCA1过表达小鼠杂交，以产生野生型（WT）、SERCA1过表达（WT/+SERCA1）、ALS-Tg和SERCA1过表达的ALS-Tg（ALS-Tg/+SERCA1）小鼠。每周评估运动功能（握力测试），并在16周龄时采集骨骼肌，以评估肌肉质量、SR-Ca2+ATP酶活性、SERCA1水平和ER应激蛋白——蛋白二硫键异构酶（PDI）、葡萄糖调节蛋白78/免疫球蛋白重链结合蛋白（Grp78/BiP）和C/EBP同源蛋白（CHOP）的水平。还从趾短屈肌中分离出单根肌纤维，以评估静息和峰值Fura-2比率的变化。
与ALS-Tg小鼠相比，ALS-Tg/+SERCA1小鼠的运动功能得到改善，疾病发作延迟，肌肉质量增加。此外，ALS-Tg/+SERCA1小鼠的SERCA1蛋白水平和SR-Ca2+ATP酶活性恢复到WT小鼠的水平。出乎意料的是，SERCA-1过表达在WT和ALS-Tg小鼠中均增加了ER应激标志物Grp78/BiP的水平，而未改变PDI或CHOP的蛋白水平。最后，与ALS-Tg小鼠相比，ALS-Tg/+SERCA1的单根肌纤维静息Fura-2水平相似，但峰值Fura-2水平较低（在30Hz和100Hz时）。
这些数据表明，SERCA1过表达可减轻ALS-Tg小鼠肌肉质量的逐渐丧失并维持运动功能，同时不会降低静息Ca2+水平或ER应激。
