New avenue for combating deterioration in blood stem cells

In 2014, Méndez participated in an international study led by researchers from the University of California San Francisco (USA), published in Nature, in which they discovered the cellular mechanism responsible for the deterioration with aging of the stem cells that generate red blood cells, platelets and white blood cells that make up the immune system. Now, CNIO researchers have managed to replicate this new phenomenon in mouse embryos.

To do so, in these embryos, they reduced the levels of the MCM3 gene, one of the components of the MCM complex responsible for separating the two strands of the DNA double helix during replication. DNA replication is an essential process by which, when a cell is about to divide, it makes an exact copy of its genome, so that each of these copies will be passed along to its two future daughter cells. The cells need to maintain high levels of MCM during the DNA copying process; otherwise a phenomenon known as replication stress takes place, which can cause irreversible damage to the genome.

"When we reduce the levels of the MCM3 gene in the entire organism, we observe that replication stress especially affects the stem cells that give rise to the other blood cells and, in particular, the red blood cell precursors," explains Méndez. "In adult organisms, the production and maturation of red blood cells takes place in the bone marrow, but during embryonic development it occurs mainly in the fetal liver. In animals with MCM3 deficiency, the stem cells of the fetal liver are deteriorated and the embryos develop a severe form of anemia that prevents them from being born. We could say that replication stress turns fetal stem cells, which should be in perfect working order, into very old cells. We have verified this finding in transplantation experiments, where fetal cells with replication stress were unable to adequately reconstitute the blood system in the recipient animals."

The researchers managed to prevent embryonic lethality by increasing the levels of another gene, CHK1. "CHK1 is one of the genes responsible for protecting cells from replication stress. It supervises DNA replication: when something goes wrong, CHK1 slows down or halts cell division until the problem has been resolved." The mice subjected to replication stress due to the loss of MCM3, but with higher levels of CHK1, showed less pronounced anemia, with 4 of every 10 embryos developing normally and completing their gestation.

According to the authors of the study, "an interesting implication of this work is that the type of anemia caused by replication stress is very similar to the aplastic anemia that arises as a complication in patients receiving chemotherapy or radiation therapy, precisely because these treatments introduce massive damage in the DNA of proliferating cells. A path to be explored in future studies will be to extend these results to novel therapies against this anemia, while also contributing to mitigating the effects of aging on blood stem cells."