Different Expression Levels of Human Mutant Ubiquitin B+1 (UBB+1) Can Modify Chronological Lifespan or Stress Resistance of Saccharomyces cerevisiae

Abstract

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+1, 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 Saccharomyces cerevisiae as a model system, we constitutively expressed UBB+1 to evaluate its effects on proteasome function and cell death, particularly under conditions of chronological aging. We showed that the expression of UBB+1 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+1 at lower level displayed an increased capacity to degrade induced misfolded proteins. When we evaluated cells during chronological aging, UBB+1 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+1 has previously been shown to induce chaperone expression and thus protect against stress, we evaluated our UBB+1 model under heat shock and oxidative stress. Higher expression of UBB+1 caused thermotolerance in yeast due to induction of chaperones, which occurred to a lesser extent at lower expression level of UBB+1 (where we observed the phenotype of extended life span). Altering UPS capacity by differential expression of UBB+1 protects cells against several stresses during chronological aging. This system can be valuable to study the effects of UBB+1 on misfolded proteins involved in neurodegeneration and aging.

FMN reduces Amyloid-β toxicity in yeast by regulating redox status and cellular metabolism

“…Quantitative real-Time PCR (qPCR) analysis. qPCR was performed as previously described 90 . Aβ42 and control strains were grown in Delft medium supplemented with 100 mg L −1 histidine and 100 mg L −1 uracil.…”

Exploiting Post-mitotic Yeast Cultures to Model Neurodegeneration

“… Munoz-Arellano et al (2018) have also recently studied the consequences of the expression of the loss-of-function ubiquitin variant UBB +1 in yeast using the CLS model. This UBB +1 variant, found to be neurotoxic in high levels, specifically accumulate and co-aggregate with the tangles and plaques of AD, as well as in HD and some other diseases of protein misfolding, while, in non-diseased cells the UBB +1 variant is degraded albeit inefficiently.…”

“…UBB +1 has a high affinity for the proteasome and thus can make it inefficient to degrading other ubiquitinated moieties. To examine the effects of UBB +1 on aging cell health, Munoz-Arellano et al (2018) expressed UBB +1 both at low and high levels. Whereas high expression of UBB +1 had no effect on yeast CLS, low UBB +1 levels greatly extended CLS, through a mechanism that included reduction of ROS levels and attenuation of apoptosis markers compared to control and high UBB +1 expressing cells.…”

“…Whereas high expression of UBB +1 had no effect on yeast CLS, low UBB +1 levels greatly extended CLS, through a mechanism that included reduction of ROS levels and attenuation of apoptosis markers compared to control and high UBB +1 expressing cells. Altering the ubiquitin–proteasome system capacity by low UBB +1 expression was also found to protect cells against the adverse effects of protein misfolding induced through amino acid analogs ( Munoz-Arellano et al, 2018 ). Further exploitation of this UBB +1 yeast model might help to identify additional factors that together with UBB +1 may contribute to the neurotoxic proteinotaphy disease initiation and/or progression.…”

The Dose-Dependent Pleiotropic Effects of the UBB+1 Ubiquitin Mutant

“…Recent findings highlight the positive effects associated with UBB +1 expression. For example, UBB +1 synthesis reduces amyloid-β-(Aβ-) related toxicity (Verheijen et al, 2018), and in yeast, a low level of UBB +1 expression prevents reactive oxygen species (ROS) accumulation and limits apoptosis, consequently increasing cellular life span (Muñoz-Arellano et al, 2018). Here, we discuss at least some of the many faces of UBB +1 in proteostasis maintenance.…”