Membrane contact sites and proteostasis during aging

Ageing of a cell or an organism can be described as a progressive decline of essential cellular functions and a reduction of intercellular communication processes. One vital function that substantially impacts cellular health and well-being is protein homeostasis, which is a fine-tuned and coordinated balance between production, maintenance and degradation of proteins. If this process is inhibited or if its activity is dropping with increasing age, dysfunctional proteins that cannot fulfill their cellular functions start to accumulate and inhibit other important processes as well, further amplifying the deterioration of cellular health with increasing age. Another essential function of a cell that also decreases with age is intercellular communication. While cells use different compartments, called organelles, to fulfill incompatible biochemical reactions, these subsystems have to communicate with each other, which is partially mediated via direct contact established by specialized proteins. In this research project, we propose an age-dependent crosstalk between cellular protein homeostasis and the communication route via direct contact between two organelles, mitochondria and the vacuole. This contact between mitochondria, a compartment responsible for energy production, and the vacuole, an organelle often denoted as trash bin of a cell, has been already shown to influence cellular decay over time. In our work, we utilize the bakers yeast, a simple model organism widely used to study cellular fundamentals due to its high analogy to mammalian cells, and aim to elucidate the interplay between mitochondria-vacuole contacts and protein homeostasis during ageing. Our goal is to identify and characterize the molecular mechanisms of this crosstalk, and to analyse its impact on cellular health and lifespan. Using an interdisciplinary approach with experimental techniques ranging from cell biology and biochemistry to bioinformatics and structural biology, we will gain novel insights into multi-layered and highly complex cellular events that critically influence ageing and age-associated diseases upon dysregulation.

The overarching goal of our project was to understand protein homeostasis, a delicate balance in the cell that often decides between health and disease, and the influence of communication inside a cell over ageing. This research led to several significant research outcomes: 1. This study mainly investigates how cells maintain protein balance as they age. We discovered that a protein called Hsp104 moves to the nucleus of yeast cells to help maintain a functional protein set. This is important because it gives us new insights into how Hsp104 helps maintain protein balance and its additional roles as cells age. 2. We also identified a protein called Snd3 as a key player in the formation of contacts between the nucleus and the vacuole in cells, two important compartments. These contacts are crucial for communication between different parts of the cell. Our findings provide a new model for how metabolism controls these contact sites. 3. We also showed that so-called nuclear envelope budding, a process where the nuclear envelope forms small outgrowths, is common across many different species, from early single-celled organisms to humans. We also found that this process happens more often when cells are under stress, suggesting a link to protein quality control. 4. We finally explored the challenges of folding newly made proteins in mitochondria. We found that certain a big, highly conserved protein complex, called prohibitin, determines the fate of these new proteins. This gives us new insights into how these processes work for proteins made in the mitochondria, which are key parts of the cell's energy conversion system. Overall, our research has significantly advanced our understanding of how cells maintain protein balance, particularly as they age. This work has laid a solid foundation for future research in this field. We believe that studying proteostasis factors over ageing will indeed be a promising and highly rewarding path.