Laboratory of Cell Biochemistry, Department of Biological Science, Graduate School of Science and Engineering, Iwate University, 4-3-5 Ueda, Morioka, Iwate 020-8551, Japan.
Department of Stress Response Science, Center for Advanced Medical Research, Hirosaki University Graduate School of Medicine, 5 Zaifuchou, Hirosaki, Aomori 036-8562, Japan.
Biochim Biophys Acta Mol Cell Res. 2021 Apr;1868(5):118989. doi: 10.1016/j.bbamcr.2021.118989. Epub 2021 Feb 16.
Calpain, a Ca-dependent cysteine protease, plays a significant role in gene expression, signal transduction, and apoptosis. Mutations in human calpain-5 cause autosomal dominant neovascular inflammatory vitreoretinopathy and the inhibition of calpain-5 activity may constitute an effective therapeutic strategy for this condition. Although calpain-5 is ubiquitously expressed in mammalian tissues and was recently found to be present in the mitochondria as well as in the cytosol, its physiological function and enzymological properties require further elucidation. The objective of the current study was to determine the characteristics of mitochondrial calpain-5 in porcine retinas, human HeLa cells, and C57BL/6J mice using subcellular fractionation. We found that mitochondrial calpain-5 was proteolyzed/autolyzed at low Ca concentrations in mitochondria isolated from porcine retinas and by thapsigargin-induced endoplasmic reticulum (ER) stress in HeLa cells. Further, mitochondrial calpain-5, as opposed to cytosolic calpain-5, was activated during the early stages of ER stress in C57BL/6J mice. These results showed that mitochondrial calpain-5 was activated at low Ca concentrations in vitro and in response to ER stress in vivo. The present study provides new insights into a novel calpain system in the mitochondria that includes stress responses during the early phases of ER stress. Further, activation of mitochondrial calpain-5 by treatment using low-molecular-weight compounds may have therapeutic potential for diseases related to ER stress, including neurodegenerative diseases, metabolic syndromes, diabetes, and cancer.
钙蛋白酶（Calpain）是一种依赖 Ca 的半胱氨酸蛋白酶，在基因表达、信号转导和细胞凋亡中发挥重要作用。人类钙蛋白酶-5 的突变会导致常染色体显性新生血管性炎症性玻璃体视网膜病变，而抑制钙蛋白酶-5 的活性可能成为治疗这种疾病的有效策略。尽管钙蛋白酶-5 在哺乳动物组织中广泛表达，并且最近在细胞质和线粒体中都有发现，但它的生理功能和酶学特性仍需要进一步阐明。本研究的目的是通过亚细胞分级分离，确定猪视网膜、人 HeLa 细胞和 C57BL/6J 小鼠中线粒体钙蛋白酶-5 的特征。我们发现，猪视网膜线粒体中分离的线粒体钙蛋白酶-5 在低 Ca 浓度下被蛋白水解/自水解，而 HeLa 细胞中的内质网（ER）应激则由 thapsigargin 诱导。此外，与细胞质钙蛋白酶-5 相反，C57BL/6J 小鼠 ER 应激的早期阶段会激活线粒体钙蛋白酶-5。这些结果表明，线粒体钙蛋白酶-5在体外低 Ca 浓度下和体内 ER 应激时被激活。本研究为包括 ER 应激早期阶段在内的线粒体中新型钙蛋白酶系统提供了新的见解。此外，通过使用低分子量化合物处理激活线粒体钙蛋白酶-5，可能为与 ER 应激相关的疾病（包括神经退行性疾病、代谢综合征、糖尿病和癌症）提供治疗潜力。
