Novel function of platelets in tumor blood vessels found

Date:
June 25, 2020
Source:
Uppsala University
Summary:
Scientists have discovered a hitherto unknown function of blood
platelets in cancer. In mouse models, these platelets have proved
to help preserve the vascular barrier which makes blood-vessel
walls selectively impermeable, thereby reducing the spread of
tumor cells to other parts of the body.



FULL STORY ========================================================================== Scientists at Uppsala University have discovered a hitherto unknown
function of blood platelets in cancer. In mouse models, these platelets
have proved to help preserve the vascular barrier which makes blood-vessel walls selectively impermeable, thereby reducing the spread of tumour
cells to other parts of the body. The study is published in the journal
Cancer Research.


========================================================================== Platelets, or thrombocytes, as they are also termed, are tiny cell
fragments that form in the bone marrow and circulate in the blood. If
we are injured and start bleeding they clump together, sealing off the
wound while also helping the blood to coagulate.

When the platelets are activated -- which occurs not only in wounds but
also in tumours -- the substances known as growth factors contained in
the platelets are released into their immediate surroundings. One is platelet-derived growth factor B (PDGFB).

In the study, the researchers investigated what happens when the PDGFB
in platelets, but not in other cell types, is deleted in individuals
with cancer.

PDGFB from platelets was found to be essential, to attract supporting
cells to the tumour blood vessels. In healthy tissue, on the other hand,
the platelets did not to perform this function. If PDGFB was lacking in platelets, the quantity of circulating tumour cells increased and they
spread to other parts of the body to a much higher degree.

Previous studies have shown that PDGFB from cells of another kind,
endothelial cells that line the inside of blood vessels, is necessary to attract supporting cells to the vessels when they form. According to the
new study, this function in tumours also requires PDGFB from platelets,
which distinguishes them from healthy tissue.

From a medical point of view, it may be advantageous, in some situations,
to reduce platelet activity in order to prevent blood clots, for example.

Moreover, previous research shows that platelets can promote spread of
tumour cells.

"Our data show that platelet activation in cancer is not altogether
harmful.

Instead, the PDGFB released when the platelets are activated can help
to maintain the vascular barrier in tumours, thereby counteracting
the spread of tumour cells. That makes it important for the specific
functions of the various platelet-derived molecules to be taken into consideration when new therapies are developed," says Anna-Karin Olsson,
who leads a research group at the Department of Medical Biochemistry
and Microbiology at Uppsala University.


========================================================================== Story Source: Materials provided by Uppsala_University. Note: Content
may be edited for style and length.


========================================================================== Journal Reference:
1. Yanyu Zhang, Jessica Cedervall, Anahita Hamidi, Melanie Herre, Kati
Viitaniemi, Gabriela D'Amico, Zuoxiu Miao, Ragaseema Valsala
Madhavan Unnithan, Alessandra Vaccaro, Luuk van Hooren, Maria
Georganaki, AAsa Thulin, Qi Qiao, Johanna Andrae, Agneta Siegbahn,
Carl-Henrik Heldin, Kari Alitalo, Christer Betsholtz, Anna Dimberg,
Anna-Karin Olsson.

Platelet-specific PDGFB ablation impairs tumor vessel integrity
and promotes metastasis. Cancer Research, 2020; canres.3533.2019
DOI: 10.1158/0008-5472.CAN-19-3533 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2020/06/200625080937.htm

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