ABSTRACT
First Person is a series of interviews with the first authors of a selection of papers published in Disease Models & Mechanisms, helping researchers promote themselves alongside their papers. Toni Lemmetyinen is first author on ‘ Fibroblast-derived EGF ligand neuregulin 1 induces fetal-like reprogramming of the intestinal epithelium without supporting tumorigenic growth’, published in DMM. Toni is a PhD student in the lab of Saara Ollila at the University of Helsinki, investigating how stromal fibroblasts regulate the intestinal epithelium.
Toni Lemmetyinen
How would you explain the main findings of your paper to non-scientific family and friends?
Stem cells in any given organ give rise to all the specific cell types needed for a fully functional tissue. In rapidly regenerating tissues, the constant need for proliferation must be carefully controlled to prevent cancer formation. Intestinal stem cells are constantly proliferating in response to signals from their environment. For example, the neighbouring epithelial cells stimulate stem cell proliferation by providing an essential growth factor called epidermal growth factor (EGF). However, as there are many other similar growth factors, it is not clear what role the other EGF family members play in the intestine.
In addition to epithelial cells, stromal cells surrounding the intestinal epithelium also contribute to regulation of the intestinal epithelium. For example, stromal fibroblasts guide stem cells to proliferate or to differentiate into mature cells by secretion of different growth factors. In this research, we wanted to study how the EGF family ligands that derive from fibroblasts regulate the intestinal epithelium using special three-dimensional epithelial cell cultures called organoids containing both stem cells and differentiated epithelial cell types.
We found two EGF ligands, epiregulin (EREG) and neuregulin 1 (NRG1), that were fibroblast-derived, and continued to investigate their role in the epithelium. Both of these ligands supported the growth of intestinal organoids, but with NRG1, the organoids grew much bigger, and NRG1 also protected the organoids from irradiation-induced damage. However, we were surprised to note that NRG1 did not support the growth of organoids lacking the tumor suppressor gene Apc, which is commonly mutated in human colorectal cancer (CRC). Interestingly, we also found that high expression of NRG1 in the stroma predicted improved survival in CRC. Thus, we show that NRG1 promotes intestinal cell proliferation without promoting tumorigenic growth. This could mean that activation of NRG1 signaling could help to repair damaged intestine without increasing cancer risk.
“NRG1 has a tumor-suppressive function, and activating this pathway could be safely used to protect the epithelium during radiation therapy and speed up the recovery process of patients.”
What are the potential implications of these results for your field of research?
In this research, we have characterized and provided more information on how fibroblast-derived EREG and NRG1 contribute to the maintenance of the epithelium in homeostasis, injury and tumorigenesis, which can be beneficial for future studies. NRG1 could be used to study what is happening during regeneration as NRG1-treated organoids mimic the growth of regenerative epithelium. This research suggests that NRG1 has a tumor-suppressive function, and activating this pathway could be safely used to protect the epithelium during radiation therapy and speed up the recovery process of patients.
What are the main advantages and drawbacks of the experimental system you have used as it relates to the disease you are investigating?
The intestinal stem cells are constantly proliferating and renewing the epithelium every 3-5 days; therefore, it is a great environment to study stem cell function and development. The rapid renewal of the epithelium allows a great model to study regeneration. We studied the intestinal epithelium in a three-dimensional organoid culture, in which single intestinal stem cells or intestinal crypts are mixed with the Matrigel matrix and form a fully functional epithelium including all intestinal epithelial cell types. Therefore, organoid culture is a great way to study what is happening to the epithelium. With organoids, it is easy to manipulate the growth factors that are given to the epithelium and they offer more opportunities to perform various experiments compared to 2D models. They also allow repetition and performing multiple different experiments at the same time, thus reducing the use of experimental animals. The main drawback of organoid culture is that although it resembles in vivo settings, it still lacks the complex in vivo microenvironment and systemic factors.
NRG1 induces branching and irregular shape of the apical filamentous actin belt in intestinal organoids. Confocal microscopy analysis of apical filamentous actin (F-actin, red) in organoids grown for 48 h in the presence of EGF or NRG1. DNA is shown in blue. Scale bars: 50 µm.
What has surprised you the most while conducting your research?
It was surprising to see how dramatically NRG1 induces the growth of intestinal organoids and the way it caused a bloated appearance and rearrangement of the actin cytoskeleton of the organoids. Although EREG also increased the growth of organoids, it was still very distinct from NRG1-treated organoids and had a more similar gene expression signature than that of EGF-treated organoids. I would have thought that as NRG1 robustly increased the growth of intestinal organoids, it would not appear completely inactive in terms of supporting tumorigenic growth. Another surprising thing was that none of the tested inflammatory factors induced NRG1 expression in fibroblast culture, so the exact mechanism of how NRG1 is recruited to the injury site is still unclear.
What do you think is the most significant challenge impacting your research at this time and how will this be addressed over the next 10 years?
Many of the EGF family ligands are not well characterized in terms of cell specificity. Also, the functions of EGF ligands in inflammation or tumorigenesis and especially their upstream mediators are still quite unclear. The epithelium is constantly renewing and affected by many internal and external signals and, therefore, it is difficult to get a comprehensive understanding of what is happening. What are the stromal factors that induce or reduce tumor growth and what is the mechanism? More knowledge about the contribution of stromal cells to the epithelium is emerging and I think in the next 10 years, we will have a pretty good consensus on the crosstalk between stromal cells and epithelium in different situations.
“We need to share more of our work. A lot of research may not be published because there is no breakthrough finding but it is still valuable information.”
What changes do you think could improve the professional lives of scientists?
There could be even more collaborations between scientists which helps projects to move forward faster and publish findings more easily, as well as more communication between scientists to get better ideas for experimental setups and more transparency in the community. We need to share more of our work. A lot of research may not be published because there is no breakthrough finding but it is still valuable information. The publication process is usually time consuming and there is a big pressure of publishing data and showing outstanding new findings. Making publishing more efficient would certainly improve the lives of scientists. Furthermore, I think we need to share more of our results with the non-scientific community in an easy way to raise awareness of our important job. This will have a positive impact on the scientific community.
What's next for you?
Next, I will be concentrating on another project which will be the last work of my PhD thesis. This project also focuses on stromal-epithelial interactions in the intestine and I'm characterizing a novel signaling pathway that affects the differentiation of epithelial cells.
Toni Lemmetyinen's contact details: University of Helsinki, Helsinki, Finland.
E-mail: toni.lemmetyinen@helsinki.fi
