Back to the stem

I am sure you know who Benjamin Button is. But do you know Shinya Yamanaka? Unlike Benjamin Button, Yamanaka is not the protagonist of a movie where he defies ageing and grows younger from old age to childhood. He is a real, flesh-and-blood scientist. A scientist that has won more awards than I could list here without making you close the tab. But to make my point, I’ll mention just one: the 2012 Nobel Prize in Physiology or Medicine in 2012 (which he shared with John Bertrand Gurdon).

What is your point, Juan? What does Benjamin Button have to do with Professor Yamanaka and his Nobel Prize? ― You mentally ask. Yamanaka (along with Gurdon and the many researchers that worked under their guidance or collaborated with them) has come closer than anyone to making the curious case of the case of Benjamin Button a reality. They challenged one of the most fundamentals laws of biology: aging. They showed with their research that mature cells could be reprogrammed into stem cells.

But how this whole rejuvenating mature cells actually work? What the researchers I mentioned earlier discovered in 2006 was that introducing a specific set of genes (known today asYamanaka factors) into differentiated cells could reprogram them back into a pluripotent state. These genes encode transcription factors that play key roles in gene stability, cell self-renewal, and survival.

Their discovery holds great promise for reversing aging by regenerating damaged tissues, replenishing lost cells, and even resetting cellular age. Crazy, I know. But don’t get too excited about the fountain of youth: we are not there yet. Reprogramming cells comes with risks. As previously said, some of the Yamanaka factors play roles in cell survival, so they can potentially increase the risk of tumor formation. And that’s not even considering the unpredictable effects they might have on complex tissues. So, while real-world applications for widespread age reversal remain speculative, this is a big revolution in the field of regenerative medicine. And I have interviewed the perfect person to tell you more about it.

Anna Falk is a molecular biologist specialized in neural stem cells and adult neurogenesis. She did her undergraduate in molecular biology at Umeå University and then her PhD at Karolinska Institutet during the early days of human pluripotent cells and also of adult neurogenesis. After that, she did her postdoc in Cambridge University, working with cell reprogramming. Then she went back to Karolinska to start her new lab in 2012. In parallel, she founded a built-up iPS Core facility (https://ipscore.se), a kind of cell vending machine. Lately, she was recruited in Lund University.

Juan García Ruiz: How would you explain in a simple way what an induced pluripotent cell is?

Anna Falk: It’s a cell that represents a human embryo very early in development, so it can become any kind of cell later on, and that’s why it’s called pluripotent. This pluripotent cell can be induced, for instance, from a somatic cell. Usually skin cells from a little skin biopsy or blood cells from a blood sample are used. The idea is that you can rejuvenate the cell, making them useful for many other functions.

JGR: How far back does your interest in stem cells go?

AF: During my undergraduate, I chose a molecular biology program because I was interested mainly in genes. During the undergraduate, I assisted to a research seminar led by Jonas Frisén, who ended up being my PhD supervisor later. This seminar was about stem cells and it was very inspiring to me, so I think my interest in the field started to emerge at that moment.

JGR: How far in the differentiation can we go from an induced pluripotent cell? Let’s say we obtain neurons from pluripotent stem cells. Can we also manipulate the type of neuron we get?

AF: First, from a somatic stem cell, you get the induced pluripotent cell by using the Yamanaka factors (editor’s note: explained in the introduction). Then there are two different ways of obtaining the cell that you want. Either you add the transcription factors to program the cell in a way that it becomes, for instance, a dopaminergic cell, or you mimic the environment that dopaminergic cells should be in during development, so that the cell is in presence of the necessary elements to become this kind of cell. So yes, it is possible to define cellular identity to a certain extent.

JGR: What’s the idea behind stem cell therapy? Can you give a concrete example of the process?

AF: Let’s say you need cartilage cells in your knee because you are injured. We take a tiny skin biopsy, and then we grow these cells and use the Yamanaka factors to obtain stem cells. At this point the cells are immortal so we can grow them forever and freeze them down to keep them. So at this point we have your induced pluripotent cells. The next step would be to differentiate them into chondrocytes, which are the cells of cartilage tissue. All of this need to be done in very clean conditions, and these are the steps that need to be done in the special stem cell cores. Once you have the chondrocytes you can freeze them and put them in vials and send them to wherever they are needed, and they are ready to be injected into your knee. That’s the future of stem cell therapy.

JGR: And what’s the present?

AF: I can give you the example of a patient in the US that has been cured from type I diabetes. Douglas Melton is big in making pancreatic beta cells. So this patient doesn’t have to take anymore insulin. So it’s already occurring in some places, and there are some trials going on in Europe. The whole field is a big on a balance. We still need to get good human results to be able to continue to get money into this.

JGR: What are the limits of these kinds of strategy of obtaining differentiated cells? Let’s take neurons as an example.

AF: Some neurons have not been of interest for the scientific society, so we might not be able to get them. I took dopamine neuron as an example because they have been of interest for a long time because of its relationship with Parkinson’s disease. Another problem is the ageing. The pluripotent cells that we use are like an embryo cell that is just a few days old, so they are very young neurons. If you compare them with mature neurons from an adult human, for instance, you can see that they are not exactly the same partly because of this. And then there is the problem of the physiological environment. Sometimes neurons need to be in contact with other cells, especially with astrocytes, to mature and to do its proper functions. That is why we work a lot with 3D structures like brain organoids. It’s important to consider having more than just one layer of neurons because that’s not reality. However, for some types of therapies the strategy is to have just one type of neuron, so actually this aspect really depends on the final goal of the cells.

JGR: What are the main advantages of doing research with induced pluripotent cells compared to other approaches to deal with a biological question?

AF: It’s possible to create cellular models in the lab, especially similar to human tissue that would not be accessible otherwise. We can model neuropsychiatric and neurodevelopmental disorder and mimic these person’s brains to study them. We can mimic for instance how the brain of a person with a certain disease develops, and then we compare to a healthy brain model and see if there’s something in the course of development that was not right. That’s one of the advantages. But you can also create a great amount of cells for therapy, for instance you can develop unlimited dopamine neurons for cell replacement, or insulin-producing cells for diabetes patients.

JGR: What is neurogenesis and how do you study with induced pluripotent cells?

AF: Neurogenesis is the process of creating neurons. There is neurogenesis during development, when the pluripotent cells have the potential to become any cell, but they undergo different steps that make them differentiate into neurons. So the first step is the production of the neural progenitor, the neural stem cell, and then there is a big expansion of these neural progenitors because those are the ones that are going to build up the whole brain in terms of neurons. It is very important that this whole process goes right. But sometimes there are some failures. The causes of the failures are sometimes genetic and sometimes environmental, like toxins or stress. So how do we study all this? You know for example that neurons should migrate into the right of the cortex. Then you can take neurons from a patient in which you observe that the neurons are not migrating correctly. So then you can do all kind of experiments to see what might be causing this problem. Or you can observe that some neurons are not maturing as they should, and you can then study their signaling with electrophysiology approaches. Sometimes what you observe is a difference in the kinetics: some neurons are differentiating faster or slower when compared to the cells of a healthy control. Or yet you can see that the fate choice of the neural stem cell of a patient is making less neurons than a healthy control, and you can then study why this is occurring.

JGR: What are the main discoveries made in your team?

AF: We have found that in early stages of neurogenesis, when the neural stem cells are supposed to differentiate, you can already detect some phenotypes that were believed to appear much later in development. In other words, we have found that it’s not that the neurons of neurodevelopmental disorder patients developed normally and started going wrong later, but actually they were already not functioning as they should early in their development. This is also the case for mental disorders such as schizophrenia: you can have be diagnosed at 28 years old, but it doesn’t mean that the problem started there. Maybe the development seemed functional because it didn’t reach a threshold to be noticeable, and they almost did it as a healthy control but not exactly like that, and then the issues continued developing later on until the first visible manifestations started to emerge.

JGR: What are the black boxes in this field of study?

AF: We don’t know perfectly how to do iPS cultures in a way that the cells are very standardized. It’s still a discussion in the field and because certain iPS cells are better suited to develop a certain kind of cell than other iPS cells. And yet, both iPS come from healthy people with a functional brain, so it’s very strange. So I would say the black box lays there, in the complete standardization of the iPS cultures with no epigenetic traces.

JGR: How do you envision the evolution of the field from now to 2050?

AF: I think we will use stem cells for curing diseases where cells have died or have been injured. We are definitely going to do replacement therapies in human with cells coming from iPS cells.

JGR: What is the most science-fiction experiment that you would do if you could?

AF: Well, the organoids are like mini brains floating around a dish. But in these conditions they lack vessels, they lack immune system, etc. So the science fiction experiment would be to really create mini brains but with all the other tissues that are actually in the brain. But that comes with ethical considerations. What about if these mini brains start thinking?

JGR: Do you have a message you would like to share with the readers?

AF: Go for what is fun! Don’t think too much about what other people are doing, just follow the joy.