BBB Seminar: Catherine Merry

Sugar-coated webs to drive stem cell differentiation
  
Catherine Merry
Stem Cell Glycobiology Group, Materials Science Centre, University of Manchester, UK

Glycosaminoglycans (GAGs) are essential cofactors for many of the signalling molecules which regulate stem cell expansion and differentiation. Whereas many groups are investigating the protein components of these signalling complexes, the carbohydrate fraction is less well understood and therefore remains an under-appreciated factor in the design of stem cell expansion strategies or methods to direct differentiation. Several key issues need to be addressed before pluripotent human stem cells (either of embryonic origin or derived by reprogramming human adult somatic cells) can fulfil their potential for therapy and the improved understanding of disease. Foremost amongst these is the development of defined cell culture systems for the high-efficiency differentiation of stem cells to the target cell type. These systems must be scalable, fully-defined and xeno-free.

Our work^{1, 2}, and that of others, has improved the understanding of specific GAG epitopes in mouse ES cells and has demonstrated that selected GAG saccharides can be used to influence specific signalling pathways during neural³ and mesodermal⁴ differentiation. Importantly we were also able to show that the sulphation pattern and size of saccharides required for neural differentiation were distinct from those required to drive the formation of alternative cell fates such as haematopoiesis. This suggests that GAG saccharides could be used in addition to, or possibly in place of, protein additives in differentiation protocols designed to optimise the generation of therapeutically relevant neural cell types from stem cells.

Recent improvements in the chemoenzymatic production of xeno-free structurally-defined GAG oligosaccharides allow, for the first time, the use of these compounds in the determination of specific sulphation pattern requirements for the control of cell signalling. Importantly, these compounds can also be generated on a scale and at a level of purity acceptable for inclusion in GMP stem cell differentiation protocols. We are combining this work with ongoing studies into the design of artificial cell environments where we have optimized three-dimensional scaffolds, generated by electrospinning or by the formation of hydrogels, for the culture of ES cells⁵. By permeating these scaffolds with defined GAG oligosaccharides, we intend to control the mechanical environment of the cells (via the scaffold architecture) as well as their biological signalling environment (using the oligosaccharides). We predict that this will allow us to control ES cell pluripotency and differentiation in a three-dimensional setting, allowing the generation of differentiated cell types for use in drug discovery/testing or in therapeutics.

References:

1. Johnson, Merry et al. Stem Cells. 2007 25(8):1913-23
2. Baldwin, Merry et al. Stem Cells. 2008 26(12):3108-18
3. Holley, Merry et al. Journal of Biological Chemistry. 2011 286(8):6241-52
4. Pickford, Merry et al. Stem Cells. 2011 29(4):629-40
5. Meade, Merry et al. Journal of Biological Chemistry. 2013 288(8):5530-5538

Host: Marion Kusche-Gullberg , Department of Biomedicine