What is strange about the fact that organs and tissues do not fall apart – after all, their cells are connected to each other and to the intercellular substance by special molecular attachments? But cells age, fail and die. The number of dying cells may not be a dozen, or a hundred, or even a thousand: for example, more than ten billion cells of the intestinal epithelium die in the intestine per day. Of course, they are replaced by new ones born from stem cells. But imagine these ten billion – how is it that holes do not appear in the intestinal epithelium?
Staff Pasteur Institute write to Developmental Cellthat the whole point here is how exactly the cells die. The researchers experimented with Drosophila epithelial cells, and found that the ERK signaling pathway is activated for a while in the neighbors of the dying cell. Any signaling pathway is a chain of receptors and enzymes that receive signals from the external environment and transmit to one or another recipient inside the cell.
The ERK signaling pathway is named after the central enzyme, ERK kinase – extracellular signal-regulated kinase, or kinase regulated by extracellular signals. Kinases are enzymes that attach phosphoric acid residues to other proteins and thereby change their activity. The signal through the ERK pathway reaches the cell nucleus, where it activates the genes for survival. A dying cell makes its neighbors live – maybe they would have died after it, but the included ERK signaling pathway does not allow them.
In other words, cells in the epithelium cannot die immediately in a large group, together with their neighbors and neighbors. There will always be survivors around the dead cell, and thanks to them, the tissue remains intact. If you turn off the ERK signaling pathway, then the cells will begin to die along with their neighbors – this will not always happen, but quite often, and so often that the epithelium really begins to spread.
Does such a mechanism work in human tissues too? Researchers from the University of Bern in another article also published in Developmental Cell, write that the same thing happens in human epithelial cells: the ERK signaling pathway prevents them from dying in monolithic heaps. That is, the mechanism that orders the death of failed cells is actually very ancient, as long as it works in such distant species as flies and humans. On the other hand, animals at the dawn of their evolution had to think about how to maintain the integrity of their own tissues with the constant death and renewal of cells; the ERK signaling pathway seems to be an extremely successful tool here.
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