Transcription errors occur in all living cells; however, it is unknown how these errors affect cellular health. To answer this question, we monitor yeast cells that are genetically engineered to display error-prone transcription. We discover that these cells suffer from a profound loss in proteostasis, which sensitizes them to the expression of genes that are associated with protein-folding diseases in humans; thus, transcription errors represent a new molecular mechanism by which cells can acquire disease phenotypes. We further find that the error rate of transcription increases as cells age, suggesting that transcription errors affect proteostasis particularly in aging cells. Accordingly, transcription errors accelerate the aggregation of a peptide that is implicated in Alzheimer's disease, and shorten the lifespan of cells. These experiments reveal a previously unappreciated role for transcriptional fidelity in cellular health and aging.

Alzheimer’s disease is the leading cause of dementia in the elderly. Pathologically it is characterized by the presence of amyloid plaques and neuronal loss within the brain tissue of affected individuals. It is now widely hypothesised that fibrillar structures represent an inert structure. Biophysical and toxicity assays attempting to characterize the formation of both the fibrillar and the intermediate oligomeric structures of Aβ typically involves preparing samples which are largely monomeric; the most common method by which this is achieved is to use the fluorinated organic solvent 1,1,1,3,3,3-hexafluoro-2-propanol (HFIP). Recent evidence has suggested that this method is not 100% effective in producing an aggregate free solution. We show, using dynamic light scattering, size exclusion chromatography and small angle X-ray scattering that this is indeed the case, with HFIP pretreated Aβ peptide solutions displaying an increased proportion of oligomeric and aggregated material and an increased propensity to aggregate. Furthermore we show that an alternative technique, involving treatment with strong alkali results in a much more homogenous solution that is largely monomeric. These techniques for solubilising and controlling the oligomeric state of Aβ are valuable starting points for future biophysical and toxicity assays.

An unexpected finding is that the structure of PNMT provides independent evidence of both backward evolution and fold recruitment in the evolution of a complex enzyme from a simple fold. The proposed evolutionary pathway implies that adrenaline, the product of PNMT catalysis, is a relative newcomer in the catecholamine family. The PNMT structure reported here enables the design of potent and selective inhibitors with which to characterize the role of adrenaline in the CNS. Such chemical probes could potentially be useful as novel therapeutics.

Latrepirdine (Dimebon™), an anti-histamine, has shown some benefits in trials of neurodegenerative diseases characterized by accumulation of aggregated or misfolded protein such as Alzheimer’s disease (AD) and has been shown to promote the removal of α-synuclein protein aggregates in vivo. An important pathway for removal of aggregated or misfolded proteins is the autophagy-lysosomal pathway, which has been implicated in AD pathogenesis, and enhancing this pathway has been shown to have therapeutic potential in AD and other proteinopathies. Here we use a yeast model Saccharomyces cerevisiae, to investigate whether latrepirdine can enhance autophagy and reduce levels of Aβ42 aggregates. Latrepirdine was shown to up-regulate yeast vacuolar (lysosomal) activity and promote transport of the autophagic marker (Atg8) to the vacuole. Using an in vitro GFP tagged Aβ yeast expression system, we investigated whether latrepirdine-enhanced autophagy was associated with a reduction in levels of intracellular GFP-Aβ42. GFP-Aβ42 was localized into punctate patterns compared to the diffuse cytosolic pattern of GFP and the GFP-Aβ42 (19:34), which does not aggregate. In the autophagy deficient mutant (Atg8Δ), GFP-Aβ42 showed a more diffuse cytosolic localization, reflecting the inability of this mutant to sequester GFP-Aβ42. Similar to rapamycin, we observed that latrepirdine significantly reduced GFP-Aβ42 in wild-type compared to the Atg8Δ mutant. Further, latrepirdine treatment attenuated Aβ42-induced toxicity in wild-type cells but not in the Atg8Δ mutant. Together, our findings provide evidence for a novel mechanism of action for latrepirdine in inducing autophagy and reducing intracellular levels of GFP-Aβ42.

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