Stem cells are already being used in combating previously untreatable diseases. Nevertheless, stem cells are not delivering their full potential because the production of specific cell types from stem cells cannot yet be managed. Researchers have now discovered the signals that determine the fate of immature cells in the pancreas. The research shows that they are very mobile and that their destiny is strongly influenced by their immediate environment. This breakthrough will facilitate the manufacturing of pancreatic islet cells for combating type 1 diabetes.
We are rapidly approaching the era for safe mass production of specialized neuronal cell types and insulin-producing beta cells. It will then be possible to test whether transplanting such cells will enable paralysed people to walk again or people with type 1 diabetes to restart their own production of insulin. Until now, the engineering of the specialized cells from pluripotent stem cells has largely been based on empirical knowledge of what works. Results published in the prominent journal Nature by a Danish-led research project represent a major leap forward.
“We have now been able to map the signal that determines whether pancreatic progenitor cells will become endocrine, such as insulin-producing beta cells or duct cells. The cells are analogous to pinballs, whose ultimate score is based on the sum of pin encounters. They are constantly moving around within the developing pancreas, leading to frequent environmental changes. We show that the exposure to specific extracellular matrix components determines the ultimate destiny of the cells,” explains Henrik Semb, Professor and Executive Director, Novo Nordisk Foundation Center for Stem Cell Biology, DanStem, University of Copenhagen.
The matrix determines the destiny
Progenitor cells are similar to stem cells since they can both self-renew and differentiate into mature cell types. However, their self-renewal capacity is generally limited compared with that of stem cells. The dynamic behaviour of progenitors during organ formation makes them difficult to study. By seeding individual human stem cell–derived progenitors on micropatterned glass slides, the researchers could study how each progenitor, without the influence of neighbouring cells, reacts to its surroundings.
“This enabled us to discover something very surprising. Our investigation revealed that interactions with different extracellular matrix components change the mechanical force state within the progenitor. These forces result from interactions between the extracellular matrix, which is outside the cell, and the actin cytoskeleton, which is within the cell.”
Pancreatic endocrine cells include all hormone-producing cells, such as insulin-producing beta cells and glucagon-producing alpha cells, within the islet of Langerhans, whereas the duct cells are epithelial cells that line the ducts of the pancreas.
“The experiments show that exposure to the extracellular matrix laminin instructs the progenitor cells towards an endocrine fate by reducing mechanical forces within the cells. Whereas exposure to fibronectin results in a duct fate because of increased mechanical forces.”
Mechanism facilitates exploitation
To exploit their discovery, the researchers had to understand the signalling pathway. They showed that components in the extracellular matrix trigger a signal into the cell via an integrin receptor, resulting in changes in mechanical forces transmitted through the actin cytoskeleton. The yes-associated protein (YAP) then senses these forces to turn on and off specific genes.
“This cascade determines the ultimate fate of the progenitor cell. Perhaps the most astonishing achievement is that our data answer an enigma that has puzzled the field for decades. How some progenitors mature into duct cells, whereas others become endocrine cells via Notch signals.”
The researcher show that the seemingly stochastic regulation of Notch function is in fact mediated by the progenitor’s encounters with extracellular matrix interactions via the force-sensing gene regulator protein YAP. They were even able to validate the physiological relevance in vivo during pancreas development.
“We can now replace significant numbers of empirically derived substances, whose mode of action in current state-of-the-art differentiation protocols is largely unknown, with small molecule inhibitors that target specific components of the newly identified mechanosignalling pathway.”
With this new strategy, insulin-producing beta cells can now be more cost-effectively and robustly produced from human pluripotent stem cells for future treatments against diabetes.
“Our discovery breaks new ground because it explains how multipotent progenitor cells mature into different cell types during organ formation. It also gives us the tools to recreate the processes in the laboratory, to more precisely engineer cells that are lost or damaged in severe diseases, such as type 1 diabetes and neurodegenerative diseases, for future cell replacement therapies.”
”Mechanosignaling via integrins directs pancreatic progenitor fate decisions” has been published in Nature. Henrik Semb, Professor and Executive Director, Novo Nordisk Foundation Center for Stem Cell Biology, DanStem, University of Copenhagen, and head of Institute of Translational Stem Cell Research at Helmholtz Zentrum München is last author. Drs. Anant Mamidi, Assistant Professor, DanStem and Christy Prawiro DanStem share first authorship, and the work is the result of a collaboration with Professor Palle Serup's group, DanStem.. The Novo Nordisk Foundation has awarded grants of almost DKK 700 million (€92 million) to the Center for research between 2010 and 2018.