RESEARCH ARTICLE Cytosolic calcium regulates cytoplasmic accumulation of TDP-43 through Calpain-A and Importin a3 Jeong Hyang Park1,2†, Chang Geon Chung1,2†, Sung Soon Park1,2, Davin Lee1,2, Kyung Min Kim1,3, Yeonjin Jeong1,2, Eun Seon Kim1,4, Jae Ho Cho1,2, Yu-Mi Jeon4, C-K James Shen5, Hyung-Jun Kim4, Daehee Hwang3*, Sung Bae Lee1,2,4* 1Department of Brain & Cognitive Sciences, DGIST, Daegu, Republic of Korea; 2Protein dynamics-based proteotoxicity control laboratory, Basic research lab, DGIST, Daegu, Republic of Korea; 3School of Biological Sciences, Seoul National University, Seoul, Republic of Korea; 4Dementia research group, Korea Brain Research Institute (KBRI), Daegu, Republic of Korea; 5Taipei Medical University/ Institute of Molecular Biology, Academia Sinica, Taipei, Taiwan Abstract Cytoplasmic accumulation of TDP-43 in motor neurons is the most prominent pathological feature in amyotrophic lateral sclerosis (ALS). A feedback cycle between nucleocytoplasmic transport (NCT) defect and TDP-43 aggregation was shown to contribute to accumulation of TDP-43 in the cytoplasm. However, little is known about cellular factors that can control the activity of NCT, thereby affecting TDP-43 accumulation in the cytoplasm. Here, we identified via FRAP and optogenetics cytosolic calcium as a key cellular factor controlling NCT of TDP-43. Dynamic and reversible changes in TDP-43 localization were observed in Drosophila sensory neurons during development. Genetic and immunohistochemical analyses identified the *For correspondence: cytosolic calcium-Calpain-A-Importin a3 pathway as a regulatory mechanism underlying NCT of
[email protected] (DH); TDP-43. In C9orf72 ALS fly models, upregulation of the pathway activity by increasing cytosolic
[email protected] (SBL) calcium reduced cytoplasmic accumulation of TDP-43 and mitigated behavioral defects.