Muñoz-Arellano Ana Joyce, Chen Xin, Molt Andrea, Meza Eugenio, Petranovic Dina
Division of Systems and Synthetic Biology, Department of Biology and Biological Engineering, Chalmers University of Technology, Gothenburg, Sweden.
Novo Nordisk Foundation Center for Biosustainability, Chalmers University of Technology, Gothenburg, Sweden.
Front Mol Neurosci. 2018 Jun 8;11:200. doi: 10.3389/fnmol.2018.00200. eCollection 2018.
The ubiquitin-proteasome system (UPS) is the main pathway responsible for the degradation of misfolded proteins, and its dysregulation has been implicated in several neurodegenerative diseases, including Alzheimer's disease (AD). UBB, a mutant variant of ubiquitin B, was found to accumulate in neurons of AD patients and it has been linked to UPS dysfunction and neuronal death. Using the yeast as a model system, we constitutively expressed UBB to evaluate its effects on proteasome function and cell death, particularly under conditions of chronological aging. We showed that the expression of UBB caused inhibition of the three proteasomal proteolytic activities (caspase-like (β1), trypsin-like (β2) and chymotrypsin-like (β5) activities) in yeast. Interestingly, this inhibition did not alter cell viability of growing cells. Moreover, we showed that cells expressing UBB at lower level displayed an increased capacity to degrade induced misfolded proteins. When we evaluated cells during chronological aging, UBB expression at lower level, prevented cells to accumulate reactive oxygen species (ROS) and avert apoptosis, dramatically increasing yeast life span. Since proteasome inhibition by UBB has previously been shown to induce chaperone expression and thus protect against stress, we evaluated our UBB model under heat shock and oxidative stress. Higher expression of UBB caused thermotolerance in yeast due to induction of chaperones, which occurred to a lesser extent at lower expression level of UBB (where we observed the phenotype of extended life span). Altering UPS capacity by differential expression of UBB protects cells against several stresses during chronological aging. This system can be valuable to study the effects of UBB on misfolded proteins involved in neurodegeneration and aging.
泛素-蛋白酶体系统（UPS）是负责降解错误折叠蛋白的主要途径，其失调与包括阿尔茨海默病（AD）在内的多种神经退行性疾病有关。泛素B的突变变体UBB被发现积聚在AD患者的神经元中，并与UPS功能障碍和神经元死亡有关。我们以酵母作为模型系统，组成型表达UBB以评估其对蛋白酶体功能和细胞死亡的影响，特别是在时序衰老条件下。我们发现UBB的表达导致酵母中三种蛋白酶体蛋白水解活性（半胱天冬酶样（β1）、胰蛋白酶样（β2）和糜蛋白酶样（β5）活性）受到抑制。有趣的是，这种抑制并未改变生长中细胞的活力。此外，我们表明低水平表达UBB的细胞显示出降解诱导产生的错误折叠蛋白的能力增强。当我们在时序衰老过程中评估细胞时，低水平的UBB表达可防止细胞积累活性氧（ROS）并避免细胞凋亡，显著延长酵母寿命。由于先前已证明UBB对蛋白酶体的抑制可诱导伴侣蛋白表达从而抵御应激，我们在热休克和氧化应激条件下评估了我们的UBB模型。UBB的高表达因伴侣蛋白的诱导而使酵母产生耐热性，在UBB低表达水平时这种情况发生的程度较小（此时我们观察到寿命延长的表型）。通过差异表达UBB改变UPS能力可保护细胞在时序衰老过程中抵御多种应激。该系统对于研究UBB对参与神经退行性变和衰老的错误折叠蛋白的影响可能具有重要价值。
