Dr Marios Stavridis
Pluripotent cells (embryonic stem cells-ESC and induced pluripotent cells-iPSC) hold great promise for the development of cell replacement therapies, disease models and platforms for the discovery and evaluation of novel pharmaceuticals, as they have the potential to differentiate into any somatic cell type. One of the most important aspects of ESC differentiation remains the study of lineage choice and commitment. On the whole, ESC differentiation is heterogeneous and heterochronous, meaning that different mixtures of cell types are generated at different time points. This is partly due to the starting population of ESCs which often comprises cells at various positions across the bistable state of pluripotency, and partly due to complex signals, feedback and cellular interactions involved in lineage choice. In order for these signals to mediate fate choice, they need to be transduced from the cell surface to the nucleus to co-ordinate changes in gene expression. The Stavridis lab is investigating how pluripotent cells commit to a differentiation fate.
Commonly signal transduction utilises post-translational modifications on proteins which may lead to conformational changes, altered DNA or protein binding, stabilisation, degradation, etc. in a relatively rapid timeframe resulting in transfer and amplification of signals through cellular compartments. Among the post-translational modifications implicated in cellular signalling, phosphorylation is the best studied example; however, there are other modifications with increasingly recognised very important roles in protein control. Glycosylation of serines/threonines with O-linked N-acetylglucosamine on nucleocytoplasmic proteins in higher eukaryotes is an abundant and dynamic intracellular post-translational modification that is essential for metazoan life. Cellular O-GlcNAc levels are a sensitive indicator of metabolism and they are disrupted in metabolic diseases like cancer and diabetes. O-GlcNAcylation has been implicated in a wide range of cellular processes, including transcription, the cell cycle, signal transduction networks and protein folding, and shows interplay with regulatory protein phosphorylation.
Recent work by us and others has identified a key role for O-GlcNAc in the differentiation of embryonic stem cells. In mouse pluripotent stem cells, elevated O-GlcNAc levels impair the exit from a pluripotent state and interfere with repression of many epigenetically regulated genes, resulting in the expression of a gene expression signature associated with a totipotent sub-population. We use mouse embryonic stem cells and human induced pluripotent stem cells to study the mechanism by which O-GlcNAc levels affect the epigenome, cell fate determination and the maintenance of pluripotency.
A separate project investigates embryonic stem cell metabolic activity, its effect on endogenous antioxidant response regulators and how these influence the onset of differentiation. As ESC embark on a differentiation programme, they undergo changes to their metabolism that can affect the production of reactive oxygen species.
We are studying how the metabolic changes that accompany transitions from pluripotency to a stably differentiated fate affect the expression of the master antioxidant response transcription factor Nrf2. Using gain- and loss-of function approaches we study the contribution of this transcription factor to ESC differentiation and the mechanisms by which it influences pluripotency.