Dr. Lindquist’s Lab, using yeast, has taken an innovative approach to study and develop treatments for synucleinopathies, which are diseases that exhibit the toxic buildup of α−synuclein protein. These diseases include Parkinson’s Disease and dementia with Lewy bodies, which have increased in prevalence as our population ages. The use of yeast as a model to look at the underlying genetics of the pathology has several benefits: 1) The biological processes involving α−synuclein are evolutionary conserved from yeast all the way to humans 2) The ability to do whole genome unbiased screens in a simple organism with a uniform genetic and epigenetic population 3) The lack of confounding factors such as different cell types and cell to cell connections 4) The ability to test many small molecules quickly and determine their mechanism of action. To be clear, Dr. Lindquist is not claiming to be modeling human disease, but rather using the genetic and molecular tools in yeast to more quickly and effectively bring treatments back into human neural models.
The Lindquist lab has recently published a paper in Science (Tardiff et al., 2013) that uses yeast to investigate the genetic underpinnings of synucleinopathies. The authors first used an unbiased screen, a method that does not attempt to target a particular pathway or protein but rather looks at cellular level readouts such as cell death or cell growth to find molecules that are cyto-protective in yeast. The authors then figured out the mechanisms of action using the powerful genetic tools of yeast. The drug of focus here was NAB2, which had been previously shown to prevent α−synuclein toxicity in other models. Because NAB2 in yeast slows growth, this phenotype was used to screen for mutants that were unaffected by the drug. This screen implicated 12 closely related genes. Subsequently after knocking these genes out one at a time, Rsp5 (NEDD4 in human) was deemed the target for NAB2. The drug was then tested in yeast expressing human α−synuclein, which demonstrated NAB2 could rescue α−synuclein expressing yeast, but could not rescue a Rsp5 mutant yeast strain from α−synuclein toxicity. Thus the authors confirmed Rsp5 as the target of NAB2 (see figure 1). The Lindquist lab further highlighted the cellular mechanisms that this approach uncovered. The α−synuclein protein over expression seems to disrupt normal vesicle trafficking, while NAB2 through Rsp5 rebalances the trafficking system. This mechanistic understanding gives the authors a new genetic node to target drug therapies towards.
Figure 1: Schematic showing the use of yeast genetic tools to uncover the mechanism of action and cellular targets for the drug NAB2 A) The node of genes which interact with NAB2 B) NAB2 native function in WT cells is linked to Rsp5 C) NAB2 blocks α−synuclein toxicity with WT Rsp5 but not in Rsp5 mutant cells thus specifically implicating Rsp5 as a target of NAB2
The power of this system is demonstrated in a second paper from the Lindquist group (Chung et al., 2013), which takes the information learned in yeast and applies it to human cell lines from PD (Parkinson’s disease) patients. Using stem cell technology which allows researchers to take somatic cells from patients and re-differentiate them into neurons, the Lindquist group used the induced pluripotent stem cells (ipSc) to test drugs and corroborate mechanisms found in yeast. These ipSc contained specific mutations to α−synuclein, which could then be corrected using CRISPR in sister cell lines. Thus each cell line used had its own specific control with only the one gene of interest mutated. The α−synuclein mutant PD cell line and the edited control line could then be compared. This method picked up on two interesting facets of α−synuclein toxicity, which had previously been seen in the yeast: 1) nitrosative stress caused by increasing nitration and 2) increased accumulation of proteins normally degraded by ERAD (ER-acssociated protein degradation). This confirmed that the yeast model of α−synuclein toxicity was legitimate and that these mechanisms were conserved from yeast to human. Finally, the authors were able to test NAB2, the drug previously tested in yeast, in the ipSc. The Lindquist Lab found that α−synuclein toxicity was prevented. Thus “closing the loop” between the two model systems and confirming their drug discovery methodology.
The Lindquist lab’s work is needless to say extremely pertinent to our ability to better discover drugs for treatment of neurodegenerative diseases. Combining model systems and using yeast allows for a potentially more effective and hopefully faster way to get small molecules into the clinic. So as you continue to shovel copious amounts of pizza and swill your beer watching the forthcoming Super Bowl, appreciate the little yeast that make everything so tasty, and could be helping us understand and treat α−synuclein related diseases.
Marc Marino is a first year Neurosciences student currently rotating with Dr. Richard Daneman. He spends his spare time yelling at sports on his TV or reading/watching science fiction, and is currently looking forward to enjoying a yeast brewed beverage.
Tardiff, D. F., Khurana, V., Chung, C. Y., & Lindquist, S. (2014). From yeast to patient neurons and back again: Powerful new discovery platforms. Movement Disorders, 29(10), 1231-1240. doi: 10.1002/mds.25989
Tardiff DF, Jui NT, Khurana V, et al. Yeast reveal a “druggable”Rsp5/Nedd4 network that ameliorates alpha-synuclein toxicity in neurons. Science 2013;342:979-983
Chung CY, Khurana V, Auluck PK, et al. Identification and rescue of alpha-synuclein toxicity in Parkinson patient-derived neurons. Science 2013;342:983-987.