Molecular Neurotoxicology and Cell Integrity Laboratory, Systems Toxicology and Health Risk Assessment Group, CSIR-Indian Institute of Toxicology Research (CSIR-IITR), Vishvigyan Bhavan, 31, Mahatma Gandhi Marg, Lucknow, 226001, Uttar Pradesh (U.P.), India.
Academy of Scientific and Innovative Research (AcSIR), Ghaziabad, 201002, India.
Mol Neurobiol. 2023 Jun;60(6):3277-3298. doi: 10.1007/s12035-023-03249-3. Epub 2023 Feb 25.
The ubiquitin-proteasome system (UPS) controls protein homeostasis to maintain cell functionality and survival. Neurogenesis relies on proteasome function, and a defective proteasome system during brain development leads to neurological disorders. An endocrine-disrupting xenoestrogen bisphenol-A (BPA) used in plastic products adversely affects human health and causes neurotoxicity. Previously, we reported that BPA reduces neural stem cells (NSCs) proliferation and differentiation, impairs myelination and mitochondrial protein import, and causes excessive mitochondrial fragmentation leading to cognitive impairments in rats. Herein, we examined the effect(s) of prenatal BPA exposure on UPS functions during NSCs proliferation and differentiation in the hippocampus. Rats were orally treated with 40 µg/kg body weight BPA during day 6 gestation to day 21 postnatal. BPA significantly reduced proteasome activity in a cellular extract of NSCs. Immunocytochemistry exhibited a significant reduction of 20S proteasome/Nestin and PSMB5/Nestin cells in NSCs culture. BPA decreased 20S/Tuj1 and PSMB5/Tuj1 cells, indicating disrupted UPS during neuronal differentiation. BPA reduced the expression of UPS genes, 20S, and PSMB5 protein levels and proteasome activity in the hippocampus. It significantly reduced overall protein synthesis by the loss of Nissl substances in the hippocampus. Pharmacological activation of UPS by a bioactive triterpenoid 18α-glycyrrhetinic acid (18α GA) caused increased proteasome activities, significantly increased neurosphere size and number, and enhanced NSCs proliferation in BPA exposed culture, while proteasome inhibition by MG132 further aggravates BPA-mediated effects. In silico studies demonstrated that BPA strongly binds to catalytic sites of UPS genes (PSMB5, TRIM11, Parkin, and PSMD4) which may result in UPS inactivation. These results suggest that BPA significantly reduces NSCs proliferation by impairing UPS, and UPS activation by 18α GA could suppress BPA-mediated neurotoxicity and exerts neuroprotection.
泛素-蛋白酶体系统（UPS）控制着蛋白质的动态平衡，以维持细胞的功能和存活。神经发生依赖于蛋白酶体的功能，而大脑发育过程中蛋白酶体系统的缺陷会导致神经紊乱。一种用于塑料制品的内分泌干扰性外源性雌激素双酚 A（BPA）对人类健康有害，并导致神经毒性。之前，我们报道过 BPA 会减少神经干细胞（NSCs）的增殖和分化，损害髓鞘形成和线粒体蛋白的输入，并导致线粒体过度碎片化，从而导致大鼠的认知障碍。在此，我们研究了产前 BPA 暴露对 NSCs 增殖和分化过程中 UPS 功能的影响。大鼠在妊娠第 6 天至产后第 21 天每天经口给予 40µg/kg 体重的 BPA。BPA 显著降低了 NSCs 细胞提取物中的蛋白酶体活性。免疫细胞化学显示 NSCs 培养物中 20S 蛋白酶体/Nestin 和 PSMB5/Nestin 细胞显著减少。BPA 减少了 20S/Tuj1 和 PSMB5/Tuj1 细胞，表明 UPS 在神经元分化过程中被破坏。BPA 降低了 UPS 基因、20S 和 PSMB5 蛋白水平以及海马体中的蛋白酶体活性。它通过减少海马体中的尼氏物质显著降低了整体蛋白质合成。生物活性三萜 18α-甘草次酸（18α GA）通过激活 UPS，导致蛋白酶体活性增加，神经球的大小和数量显著增加，并增强了 BPA 暴露培养物中的 NSCs 增殖，而蛋白酶体抑制剂 MG132 进一步加重了 BPA 介导的作用。计算机模拟研究表明，BPA 强烈结合 UPS 基因（PSMB5、TRIM11、Parkin 和 PSMD4）的催化位点，这可能导致 UPS 失活。这些结果表明，BPA 通过损害 UPS 显著减少 NSCs 的增殖，而 18α GA 通过激活 UPS 可以抑制 BPA 介导的神经毒性并发挥神经保护作用。
