New Findings: Hindlimb Unloading Causes Nucleocytoplasmic Ca2+ Overload and DNA Damage in Skeletal Muscle

Huajian Yang; Huiping Wang; Fangyang Pan; Yuxi Guo; Liqi Cao; Wenjing Yan; Yunfang Gao

doi:10.3390/cells12071077

New Findings: Hindlimb Unloading Causes Nucleocytoplasmic Ca²⁺ Overload and DNA Damage in Skeletal Muscle

Cells. 2023 Apr 3;12(7):1077. doi: 10.3390/cells12071077.

Authors

Huajian Yang^{1

2}, Huiping Wang^{1

2}, Fangyang Pan^{1

2}, Yuxi Guo^{1

2}, Liqi Cao^{1

2}, Wenjing Yan^{1

2}, Yunfang Gao^{1

2}

Affiliations

¹ Shaanxi Key Laboratory for Animal Conservation, College of Life Sciences, Northwest University, Xi'an 710069, China.
² Key Laboratory of Resource Biology and Biotechnology in Western China, College of Life Sciences, Northwest University, Ministry of Education, Xi'an 710069, China.

Abstract

Disuse atrophy of skeletal muscle is associated with a severe imbalance in cellular Ca²⁺ homeostasis and marked increase in nuclear apoptosis. Nuclear Ca²⁺ is involved in the regulation of cellular Ca²⁺ homeostasis. However, it remains unclear whether nuclear Ca²⁺ levels change under skeletal muscle disuse conditions, and whether changes in nuclear Ca²⁺ levels are associated with nuclear apoptosis. In this study, changes in Ca²⁺ levels, Ca²⁺ transporters, and regulatory factors in the nucleus of hindlimb unloaded rat soleus muscle were examined to investigate the effects of disuse on nuclear Ca²⁺ homeostasis and apoptosis. Results showed that, after hindlimb unloading, the nuclear envelope Ca²⁺ levels ([Ca²⁺]_NE) and nucleocytoplasmic Ca²⁺ levels ([Ca²⁺]_NC) increased by 78% (p < 0.01) and 106% (p < 0.01), respectively. The levels of Ca²⁺-ATPase type 2 (Ca²⁺-ATPase2), Ryanodine receptor 1 (RyR1), Inositol 1,4,5-tetrakisphosphate receptor 1 (IP₃R1), Cyclic ADP ribose hydrolase (CD38) and Inositol 1,4,5-tetrakisphosphate (IP₃) increased by 470% (p < 0.001), 94% (p < 0.05), 170% (p < 0.001), 640% (p < 0.001) and 12% (p < 0.05), respectively, and the levels of Na⁺/Ca²⁺ exchanger 3 (NCX3), Ca²⁺/calmodulin dependent protein kinase II (CaMK II) and Protein kinase A (PKA) decreased by 54% (p < 0.001), 33% (p < 0.05) and 5% (p > 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 Ca²⁺ uptake from cytoplasm is involved in the increase in [Ca²⁺]_NE after hindlimb unloading. Moreover, the increase in [Ca²⁺]_NC is attributed to increased Ca²⁺ release into nucleocytoplasm and weakened Ca²⁺ uptake from nucleocytoplasm. DNase X is activated due to elevated [Ca²⁺]_NC, leading to DNA fragmentation in myonucleus, ultimately initiating myonuclear apoptosis. Nucleocytoplasmic Ca²⁺ overload may contribute to the increased incidence of myonuclear apoptosis in disused skeletal muscle.

Keywords: hindlimb unloading; nuclear Ca2+ regulation; nuclear apoptosis; skeletal muscle.

Publication types

Research Support, Non-U.S. Gov't

MeSH terms

Animals
DNA Damage
Deoxyribonucleases / metabolism
Hindlimb Suspension* / physiology
Muscle, Skeletal / metabolism
Muscular Atrophy* / pathology
Rats

Substances

Deoxyribonucleases

Grants and funding

This study was supported by the Natural Science Foundation of Shaanxi Province, China (No. 2022JM-109), and the National Natural Science Foundation of China (No. 32070442).