Millions of cells die every day in our body, either because of a natural replacement or because they are defective. This death occurs in a controlled way by a process known as apoptosis, which allows defective cells to be recognized by other cells that are responsible for eliminating them. Its elimination occurs through the ingestion and destruction of dead cells, a mechanism known as phagocytosis. If dead cells are not properly removed, the tissue is inflamed, leading to many different inflammatory pathologies. Although this process has been studied in cell cultures, little is known about how cells phagocyte others within tissues.
A research led by researcher Esteban Hoijman, from the Institute of Molecular Biology of Barcelona of the CSIC and IDIBELL, and Ivan K. H. Poon, from La Trobe University (Australia), has managed to reveal details hitherto unknown of this process. To do this, they have analyzed phagocytosis within living tissues, both in zebrafish embryos and in the mouse thyme (where some cells of the immune system are formed).
A size problem
During phagocytosis, the cell to be destroyed is surrounded and engulfed by neighbouring cells. One of the problems that these cells have to ingest others is their size, since both are of similar size. Therefore, to properly eliminate dead cells, they must be broken into smaller pieces. “Until now we thought that the same defective cell broke itself into fragments during apoptosis, in a process of self-destruction,” explains Esteban Hoijman, CSIC-IDIBELL researcher. “However, we have seen that this is not necessarily the case, but that it is the neighbouring cells that break them before ingesting them.”
“In this work we have discovered that the cells that phagocyte “chew” those that are going to ingest, that is, they break them in smaller parts to facilitate their ingestion. This process is similar to what happens in our mouths when chewing food, but at the microscopic level”.
To do this, the researcher continues to explain, the cells that phagocyte use extensions that arise from their surface and are able to exert forces on the “food”, in this case dead cells. These extensions are used both to phagocyte (ingest) and to break, as if it were a mouth.
Understand and improve phagocytosis
This work allows to better understand the processes of apoptosis and phagocytosis, both essential mechanisms for the normal functioning of the adult organism, as well as embryonic development. It is known, Hoijman clarifies, that many diseases related to inflammatory processes in the intestine, lung, and joints, such as colitis, respiratory allergies, and arthritis, involve poor removal of cells that accumulate in tissues. Moreover, the deregulation of apoptotic processes can lead to other diseases such as cancer and neurodegeneration, as the researchers explain in their work.
“This finding helps us better understand how the body eliminates cells that are no longer useful, opens the door to new research to improve phagocytosis and, in the future, could help design drugs that improve this capacity,” concludes Hoijman.
The Bellvitge Biomedical Research Institute (IDIBELL) is a research center established in 2004 specialized in cancer, neuroscience, translational medicine, and regenerative medicine. It counts on a team of more than 1.500 professionals who, from 73 research groups, publish more than 1.400 scientific articles per year. IDIBELL is participated by the Bellvitge University Hospital and the Viladecans Hospital of the Catalan Institute of Health, the Catalan Institute of Oncology, the University of Barcelona, and the City Council of L’Hospitalet de Llobregat.
IDIBELL is a member of the Campus of International Excellence of the University of Barcelona HUBc and is part of the CERCA institution of the Generalitat de Catalunya. In 2009 it became one of the first five Spanish research centers accredited as a health research institute by the Carlos III Health Institute. In addition, it is part of the “HR Excellence in Research” program of the European Union and is a member of EATRIS and REGIC. Since 2018, IDIBELL has been an Accredited Center of the AECC Scientific Foundation (FCAECC).