Assymetric segregation of damaged proteins
During aging, the collapse in protein quality control leads to the accumulation of damaged and aggregated proteins in the cell. As these protein aggregates affect cellular fitness and determines longevity, these aggregates are considered to be aging factors. Similar to other aging factors, protein aggregates are retained in the mother cell during cell division so that the newly formed daughter cell is free of damage and born with a reset lifespan. Work in our lab have demonstrated that this aggregate retention is an active process that is dependent on the histone deacetylase Sir2, the disaggregase Hsp104 and functions of the polarisome and actin cytoskeleton. We are currently continuing this search for Asymmetry Generating Genes (AGGs) to fully understand the molecular mechanisms behind damage retention and cellular rejuvenation.
Recognition and Degradation of Damaged Proteins by the UPS system
Misfolded and aggregated proteins that can not be rescued and refolded to retrieve its full function will have to be degraded and cleared from the cell. The Ubiquitin Proteasome System (UPS) is the major cellular degradation pathway, where damaged proteins are recognized and labeled with a chain of ubiquitin molecules that targets the protein towards the proteasome for destruction. Our lab is attempting to understand how damaged proteins are recognized, and how this process is regulated by chaperones and other assisting factors.
The role of a metacaspase in survival and protein quality control
In our search for asymmetry generating genes (AGGs), we identified that the establishment of asymmetry is dependent on the simulteneous processes of aggregate retention and aggregate removal. We found that the metacaspase Mca1 is important for aggregate removal, by buffering for Hsp40 functions and aiding proteasomal degradation. We showed that Mca1 serves a beneficial role, in contrast to its previous impoications in regulating yeast apoptosis, and that overexpression of this metacaspase could improve proteastatis and extend lifespan. We are now using a biochemical approach and in vitro applications to try to elucidate the mechanistic functions of Mca1 in protein quality control.
Spatial Quality Control of Misfolded Proteins
During periods of prolonged stress, aggregated proteins coalesce into large inlcusion bodies and are sequestered to one or two distinc locations within the cell; one juxtanuclear or intranuclear site (JUNQ/INQ) and one site in close proximity of the vacuole (IPOD). Spatial sorting of misfolded substrates limits the number of potentially harmful interactions between misfolded proteins and other proteins, and contributes to the asymmetrical retention of damaged proteins during cell division.
We have shown that inclusion formation requires components of the endosomal transport pathway and demonstrated an important role for the vacuole-adaptor protein Vac17 in this spatial control. We have also demonstrated that components of the endocytic trafficking pathway are physically interacting with the protein disaggregase Hsp104. We are currently working on further elucidating the role of the vacuole and vesicle trafficking in the spatial control of aggregated proteins.
ER-Golgi retrograde transport regulating aggregate kinetics
Metabolic Buffering against Proteostatic stress in Aging cells
Different genetic networks which extend lifespan of an organism all converge at regulation of proteostasis network. Thus, it is clear that maintaining a healthy proteome is absolutely essential for a healthy lifespan. Since, availability of nutrients has a great impact on the life span of an organism; we currently intend to find out how changes in intracellular metabolites contribute to the loss of proteostasis capacity of aging cells.
Mechanisms of toxicity for the disease-related Huntington protein
The neurodegenerative disorder Huntington’s disease (HD) is caused by a pathological expansion of a polyglutamine (polyQ) repeat present in the protein huntingtin (Htt). Such polyQ expansion above a critical threshold converts the otherwise soluble wild type Htt into an aggregation-prone mutant version resulting in intracellular aggregates and cellular death of specific neurons. The complete function of the wild type version of Htt is not yet fully known. Using yeast as a model organism we are investigating what genes are required for managing human wild type exon-1 of Htt and to what extent the proline-rich region, flanking the polyQ sequence, is influencing the inherent toxicity of wild type exon-1 of Htt. This may reveal what cellular processes Htt is involved in and possibly identify novel functions of the Htt protein.