Zebrafish can regenerate heart tissue after injury, according to research by a MDC team led by Jan Philipp Junker and Daniela Panakov.
If a person has a heart attack and is not treated in time, heart muscle cells (cardiomyocytes) are damaged due to lack of oxygen and begin to die. Scar tissue grows, and because we can’t make new cardiomyocytes, the heart can’t pump as efficiently as it should. However, in lower vertebrates, such as the zebrafish, which can regenerate organs, including the heart, things are radically different.
“We wanted to find out how this little fish does this and whether we can learn from it,” says Professor Jan Philipp Junker, head of the Quantitative Developmental Biology Laboratory at the Berlin Institute for Medical Systems Biology (BIMSB), which is part of the Center for Molecular Medicine. Max Delbrück of the Helmholtz Association (MDC) in Berlin.
The researchers modeled myocardial infarction damage in zebrafish hearts with the help of Dr. Daniela Panakova, who heads MDC’s Laboratory of Electrochemical Signaling in Development and Disease. They followed cardiomyocyte regeneration by analyzing single cells and cell lineage trees. Their results were recently published in Genetics of nature.
Human hearts stop without regeneration
The researchers exposed a one-millimeter zebrafish heart to a cold needle for a few seconds while they observed it under a microscope. Any tissue touched by the needle dies. As in those who have suffered a heart attack, this leads to an inflammatory response, accompanied by fibroblast scarring.
“Surprisingly, the immediate response to trauma is very similar. But while in humans the process stops there, in fish it continues. They form new cardiomyocytes that are able to contract,” says Junker.
“We wanted to identify the signals that come from other cells and promote regeneration,” he continues. Junker’s team used single-cell genomics to search for cells in the damaged heart that are absent in the healthy zebrafish heart.
Researchers have discovered three new types of fibroblasts that are instantly activated. Despite their similar appearance to other fibroblasts, these activated cells have the ability to read many additional genes involved in the formation of proteins such as connective tissue factors such as collagen 12.
Fibroblasts signal regeneration
In humans, fibrosis, also known as scarring, is thought to be an obstacle to cardiac regeneration. Once activated, however, fibroblasts appear to be critical to the process. When Panakova used a genetic technique to turn off collagen 12-expressing fibroblasts in zebrafish, it became clear how important they were. Result: No regeneration. Junker believes that fibroblasts are responsible for signaling repair: “After all, they are generated right at the site of damage,” he says.
To determine the source of these activated fibroblasts, Junker’s team created cell lineage trees using a technique called LINNAEUS, which his lab developed in 2018. LINNAEUS works with genetic scars that collectively act as a barcode of each cell’s origin.
“We create this barcode using CRISPR-Cas9 genetic scissors. If two cells have the same barcode sequence after an injury, it means they are linked,” Junker explains.
The researchers identified two sources of transiently activated fibroblasts: the outer layer of the heart (epicardium) and the inner layer (endocardium). Cells producing collagen 12 were found exclusively in the epicardium.
Different disciplines worked closely on the research
Several MDC researchers collaborated throughout the study, from the fish experiments to the genetic analysis to the bioinformatic interpretation of the results.
“For me, the most exciting thing was to see how well our disciplines complement each other and how we can test the results of bioinformatics in a live animal,” says Sarah Lelek, lead author of the study and responsible for the animal. tests. “It was a big project that allowed all of us to contribute our experience. I think that’s why the research is so comprehensive and so useful to so many researchers.”
Dr. Bastian Spaniard, also lead author, agrees: “Because we had very different areas of expertise, we often had to explain our experiments and analyzes to each other. Cardiac regeneration is a complex process influenced by many different factors. The experiments provided a huge amount of data. It was very difficult to filter out the correct biological signals from them.”
It is still unclear whether heart-damaged mammals such as humans and mice lack the necessary signals or the ability to read the signals. If the signals are missing, eventually drugs can be developed to mimic them. But, Juncker says, finding a way to mimic the interpretation of the signal would be much more difficult.
Fibroblasts also help form new blood vessels
Now the researchers want to take a closer look at the genes that transiently activated fibroblasts read in particular. They know that many of the genes in question are important for releasing proteins into the surrounding space. And this may include factors that also affect cardiomyocytes. And initial evidence suggests that activated fibroblasts not only promote cardiac regeneration; they also help form new blood vessels that supply the heart with oxygen.
Reference: “Origin and function of activated fibroblast states during zebrafish heart regeneration” Bo Hu, Sara Lelek, Bastian Spainard, Hadil El-Sammak, Mariana Guedes Simoins, Janita Mincheva, Hanane Ali, Ronnie Schaefer, Alexander M. Meyer, Fabian Theiss, Didier Y. R. Stanier, Daniela Panakova and Jan Philippe Juncker, 21 July 2022. Genetics of nature.