Qin Tingting, Yuan Ziqiao, Yu Jiayu, Fu Xinxin, Deng Xueyang, Fu Qiang, Ma Zhanqiang, Ma Shiping
Department of Pharmacology of Chinese Materia Medica, China Pharmaceutical University, Nanjing, China.
Jiangsu Key Laboratory of Drug Screening, China Pharmaceutical University, Nanjing, China.
Clin Transl Med. 2020 Dec;10(8):e243. doi: 10.1002/ctm2.243.
Neural stem/progenitor cells (NPCs) are multipotent stem cells in the central nervous system. Damage to NPCs has been demonstrated to cause adverse effects on neurogenesis and to contribute to neurological diseases. Our previous research suggested that saikosaponin-d (SSd), a cytostatic drug belonging to the bioactive triterpenoid saponins, exhibited neurotoxicity by inhibiting hippocampal neurogenesis, but the underlying mechanism remained elusive. This study was performed to clarify the role of SSd in cognitive function and the mechanism by which SSd induced damage to hippocampal neurogenesis and NPCs. Our results indicated that SSd caused hippocampus-dependent cognitive deficits and inhibited hippocampal neurogenesis by reducing the numbers of newborn neurons in mice. RNA sequencing analysis revealed that SSd-induced neurotoxicity in the hippocampus involved neurotrophin receptor-interacting MAGE (NRAGE)/neurotrophin receptor interacting factor (NRIF)/p75 -associated cell death executor (NADE) cell signaling activated by the p75 neurotrophin receptor (p75 ). Mechanistic studies showed that a short hairpin RNA targeting p75 intracellular domain reversed SSd-increased NRAGE/NRIF/NADE signaling and the c-Jun N-terminal kinase/caspase apoptotic pathway, subsequently contributing to the survival of NPCs, as well as cell proliferation and differentiation. The addition of recombinant brain-derived neurotrophic factor (BDNF) ameliorated the SSd-induced inhibition of BDNF/Tyrosine kinase receptor B (TrkB) neurotrophic signaling, but did not affect SSd-activated pro-BDNF/p75 signaling. Moreover, the SSd-induced elevation of cytosolic Ca concentration was responsible for damage to NPCs. The extracellular Ca chelator ethylene glycol-bis(2-aminoethylether)-N,N,N',N'-tetraacetic acid (EGTA), rather than the intracellular Ca chelator 1,2-bis(2-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid tetrakis(acetoxymethyl ester) (BAPTA/AM), attenuated SSd-induced cytosolic Ca dysfunction and SSd-disordered TrkB/p75 signaling. Overall, this study demonstrated a new mechanism for the neurotoxic effect of SSd, which has emerging implications for pharmacological research of SSd and provides a better understanding of neurotoxicity induced by cytostatic drugs.
神经干细胞/祖细胞（NPCs）是中枢神经系统中的多能干细胞。已证实NPCs受损会对神经发生产生不利影响，并导致神经疾病。我们之前的研究表明，柴胡皂苷d（SSd）是一种属于生物活性三萜皂苷的细胞生长抑制剂，通过抑制海马神经发生表现出神经毒性，但其潜在机制仍不清楚。进行本研究以阐明SSd在认知功能中的作用以及SSd诱导海马神经发生和NPCs损伤的机制。我们的结果表明，SSd导致小鼠出现海马依赖性认知缺陷，并通过减少新生神经元数量抑制海马神经发生。RNA测序分析显示，SSd在海马中诱导的神经毒性涉及由p75神经营养因子受体（p75）激活的神经营养因子受体相互作用MAGE（NRAGE）/神经营养因子受体相互作用因子（NRIF）/p75相关细胞死亡执行器（NADE）细胞信号通路。机制研究表明，靶向p75细胞内结构域的短发夹RNA可逆转SSd增加的NRAGE/NRIF/NADE信号通路和c-Jun N末端激酶/半胱天冬酶凋亡途径，随后有助于NPCs的存活以及细胞增殖和分化。添加重组脑源性神经营养因子（BDNF）可改善SSd诱导的BDNF/酪氨酸激酶受体B（TrkB）神经营养信号抑制，但不影响SSd激活的前体BDNF/p75信号通路。此外，SSd诱导的胞质Ca浓度升高是NPCs损伤的原因。细胞外Ca螯合剂乙二醇双（2-氨基乙醚）-N，N，N'，N'-四乙酸（EGTA），而不是细胞内Ca螯合剂1,2-双（2-氨基苯氧基）乙烷-N，N，N'，N'-四乙酸四（乙酰氧基甲基酯）（BAPTA/AM），减轻了SSd诱导的胞质Ca功能障碍和SSd紊乱的TrkB/p75信号通路。总体而言，本研究证明了SSd神经毒性作用的新机制，这对SSd的药理研究具有新的意义，并有助于更好地理解细胞生长抑制剂诱导的神经毒性。
