Understanding stem and progenitor cell fate
Dr Kevin Chalut at Cambridge Stem Cell Institute, working on the CellFateTech project, is developing pioneering tools, including a substrate that enables stem cells and progenitor cells to proliferate in cultures outside of the body. The research could have profound implications for cellular programming. The
regenerative qualities of stem cells and progenitor cells harbour the potential to create new healthy tissues and even de-age cells. Research by CellFateTech is attempting to understand the dynamics of stem cells and progenitor cells, which possess the ability to ‘decide’ how they develop. The ‘decisions’ are made from responding to chemical signals and mechanical signals from their environment. CellFateTech approached the problem in two ways by investigating the signals cells make and by trying to replicate the most suitable micro-environment for the cells to influence their decision making process. “Knowing what the cells are doing in an embryo is important because they are making choices between maintaining a pool of progenitor cells and giving rise to new tissue for embryonic development. It is a very coordinated process and we don’t understand how it works. We would like to understand because some of the same mechanisms that give rise to a developing fetus also help us maintain healthy tissue,” said Dr Kevin Chalut.
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The secrets of fate choice The processes by which the dynamics of cells choose their eventual form and fate are complex and coordinated, yet remain largely a mystery, to the intrigue of scientists around the world. Unlocking those secrets of how a cell makes the choice can lead to enormous benefits for a great many healthcare applications; for repairing damaged tissue, curing life threatening diseases and regrowing organs. Dr Kevin Chalut and the CellFateTech team are working the problem and have published papers on their findings in journals like Nature. Stem and Progenitor cells coordinate their development continuously through our lifespans all around our bodies as the driver for our survival and growth, which is why cell fate decision making has sustained as such an important, fundamental scientific mystery to crack. “Progenitor cells in our body have a purpose to maintain themselves whilst having the capacity to give rise to more specialised cells or differentiating cells,” explains Chalut. “For example, stem cells in your skin divide and replenish themselves
but they also give rise to new skin. Our skin turns over approximately every 30 days. This process is supported by the stem cells that are there. There is this choice that has to be made by these cells. They need to ensure that they maintain, for your entire lifespan, a stem cell population. However, at the same time they need to make sure they produce the cells needed for your organs and tissues. There is a sequence of decisions they make and we are developing ways to probe at the exact time they are making one of these decisions, at the level of the genetic network, to ask what these cells are doing.” The process of monitoring how cells choose their fate is very challenging. To assess the decisions a population of cells will make, next generation sequencing (NGS) determines what genes are being expressed, and that informs about the decisions being made. However, in a petri-dish they do not do this in a synchronised fashion. One cell might make a choice hours ahead of another cell and it becomes apparent there is not a consistent pattern in the way they make these decisions. At a population-level the dynamics are ‘washed out’, as Chalut puts it.
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CellFateTech Biotechnology for investigating cell fate choice
Project Objectives
The project laboratory primarily investigates how the mechanical microenvironment regulates fate decisions, and exactly how cells process information during that fate choice. The ultimate goal of his laboratory is to apply their physics-based techniques to understand how organisms develop, and also how to use stem cells for therapeutic use.
Project Funding
ERC H2020-EU.1.1. - EXCELLENT SCIENCE European Research Council (ERC) € 1 876 618
Contact Details
The research team looked into single cells but there are problems in monitoring for results here, too. “If you do next generation single cell sequencing, there is a lot of noise involved in that process and trying to pick out the interesting noise that we care about is an immense challenge. You can put a fluorescent reporter on the cell to show how a cell did one thing to another thing, but to do that you make a choice about what decision you care about, so you are not looking holistically at the process. Instead, you are choosing to follow the one aspect you put that reporter on. In a sense you are saying you have chosen the decision you care about.”
Shifting focus to the microenvironment Not a great deal is known about mechanical signalling in stem cells. However, using substrates with a mechanical environment that can be manipulated makes it possible to create
different levels of stiffness to influence cell behaviour – this is essentially tricking the cell so it responds and adapts to the substrate in ways it would in natural environments. The stiffness of the substrate is an important factor, and we will reveal why, further in this article. A useful innovation created by the CellFateTech project was the cell stretching device. Using CAD software, the team at CellFateTech designed this specialist ‘cell stretcher’ that could be printed from fully biocompatible plastic on 3D printers. It has the ability to stretch cell substrates to create specific, reproducible forces on cells and tissues. Different versions were optimised for various purposes such as live cell imaging, immunofluorescence stainings and molecular biology assays. Indeed, CellFateTech gained traction in their results when they scrutinised the microenvironment of most stem cells, the extra cellular matrix (ECM), its mechanics, and how that coordinates cell fate choices. The
ECM is essentially what is called a hydrogel – a polymerised network, that is mostly made up of water. There are many hydrogels already in existence to culture stem cells, so this was not a standing start in terms of innovating a solution, but the team needed something more appropriate and unique in design. “The most gains for our research were in getting the mechanical microenvironment right because putting these cells onto plastic or a glass dish is physiologically illsuited. When we initially tried with existing hydrogels, they did not work well for stem cells for soft tissues like brain and liver cells. That seemed to be because the cells would not stay attached, over the long term, to these hydrogels. Hydrogels are functionally inert, so you have to functionalise them and that functionalisation just didn’t seem to be robust enough from what was available. So, we invented this different kind of hydrogel called StemBond. It is a different chemistry and with this different
One of the goals of CellFateTech was to deliver a system that could apply controlled mechanical cues to cells. Thus, they developed a 3D-printed cell stretcher, which can controllably and precisely stretch an elastic substrate functionalized especially for stem cells. With this stretcher, cells can be stretched over any time programme, and biological assays can be performed subsequently to see how the cells changed.
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EU Research
chemistry we can give robust attachments with the stem cells for the long term. And this has been quite transformative. Now we can really study the effects that the mechanical microenvironment has on culturing stem cells.”
The mechanics of aging Tissue regeneration deteriorates when you age. A clear example of this is when the population of central nervous system multipotent stem cells, also known as oligodendrocyte progenitor cells (OPC), are less able to regenerate. The OPC environment stiffens with age and this mechanical change causes loss of function of OPCs. By creating synthetic scaffolds to appear like
in a soft environment even though it was stiff. “This is the kind of result we can achieve for getting the mechanics right for stem cells. Another example of working with these gels, is for liver regeneration. One of the aspects of liver regeneration that is problematic, is that if you want to do stem cell transplants or stem cell therapy then it’s difficult to get the regenerative cells of the liver to be cultured outside of the body – proliferating, able to differentiate etc. It is hard to get proper function. With the test subject of a mouse, we have been able to take those regenerative liver cells and culture them on our hydrogels outside of the body, maintaining a pool of healthy functioning regenerative cells over several passages. It’s exciting because to my knowledge no one had
We took the oligodendrocyte progenitor cells (OPCs) and put them on our soft hydrogels and they were able to function just like in a neonatal animal. That was a striking result because we didn’t need anything else, we just needed to put them in the right mechanical microenvironment and they essentially de-aged. the stiffness and environment of young tissue, the mechanical signalling changes and the differentiation rates of OPCs increase. Tissue stiffness, the researchers revealed, is a regulator of aging in OPCs – showing how progenitor cells change with age. “We took the OPCs and put them on our soft hydrogels and they were able to function just like in a neonatal animal. That was a striking result because we didn’t need anything else. We just needed to put them in the right mechanical microenvironment and they essentially de-aged. In a sense, we were able to fool these cells with genetic intervention. We depleted a gene called Piezo1 and fooled cells to act as if they were
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ever done that before on such simple substrates, only controlling the mechanics, and this is what I would consider a next important frontier for our work. I should add we have not done this with a human yet, so that is one of the first things we will be doing next in the laboratory. The brain and liver are two examples of tissues where we have been able to produce healthy functioning progenitor cell populations outside the body and maintain them, which could have huge implications for cell therapy.” It is not an understatement to say that the research from the CellFateTech project could have a significant influence on regenerative therapies, as well as for understanding the aging process at a cellular level.
Dr Kevin Chalut, Project Coordinator Principal Investigator in the Cambridge Stem Cell Institute Cavendish Laboratory University of Cambridge JJ Thomson Avenue Cambridge CB3 0HE T: +44 (0)1223 337256 E: kc370@cam.ac.uk W: https://www.phy.cam.ac.uk/directory/chalutk
https://www.nature.com/articles/s41586-019-1484-9
Dr Kevin Chalut
Dr Kevin Chalut is a biophysicist with a PhD in Physics from Duke University. He is currently a group leader at the Wellcome Trust-Medical Research Council Stem Cell Institute in Cambridge. His work focuses on using the tools and concepts of physics to study cell fate choice in stem cells and developing organisms.
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