The stem cells found in the umbilical cord’s blood and in its walls, tissues that can be stored for future therapeutic needs, have different genetic profiles.
This discovery was made by the teams of Mayana Zatz, from the Human Genome Studies Center of the University of São Paulo (USP), and of Sergio Verjovski-Almeida, from the Institute of Chemistry of the same university, and it may affect the medical use of such cells, should it be proven that the genetic differences reflect a reduction in the cells’ versatility.
“The function of each gene depends on the context, such as, for instance, all the genes that operate at the same time,” explains Verjovski, an expert in the use of the technique called microarrays to study genes as a set. The microarrays study he developed included coding genes, which carry the code for making protein, and non-coding genes that play a key role in regulating DNA functioning. Mariane Secco and Eder Zucconi, PhD candidates in Mayana’s lab, and Yuri Moreira, from Verjovski’s group, examined 40 thousand genes (10 thousand of which of the coding kind), looking for what is common and what is different between the mesenchymal stem cells extracted from umbilical cord blood and from the cord itself.
They collected paired tissues from 65 newborns; from each, they extracted the mesenchymal stem cells from both the blood and the cord itself. “We need another 60 newborns to achieve a sufficient number of blood samples, because the blood is very poor in mesenchymal stem cells,” Mariane warns. The paired samples make it quite clear that the sort of tissue from which the stem cells are drawn is the most important factor for determining the activity of the genes. “Cells of the same origin – blood, for instance – from different individuals had a more similar genetic profile than the cells of the same person but from different tissues,” she explains.
“The 30 genes most expressed in the blood and the 30 most expressed in the walls of the cord are completely different,” Verjovski sums up. These differences lie in the protein coding genes rather than in the regulatory ones and might, perhaps, indicate that these cells had already started to define the sort of tissue that they were going to generate. In the cells drawn from the blood, the genes connected with making bone cells and immune cells are more active. On the other hand, in the umbilical cord wall cells, the most active genes are those responsible for producing neurons and blood vessels.
This does not necessarily mean that the destiny of these cells has already been defined. “Might the cord cells have greater potential for turning into neurons?” questions Mariane. She has already started conducting tests to find out how these cells behave in living organisms. However, she is sure of one thing: this finding buries the hypothesis that cells found in the blood came from the walls of the cord, leaking into the blood vessels by accident. “The cells are not the same,” she concludes.
The group from the Human Genome Studies Center (one of the Cepids – Centers of Research, Innovation and Dissemination – supported by FAPESP) had already shown, in 2008, that in the cord there are far more stem cells than in the blood of that region. Their most recent work, which has been accepted for publication in Stem Cells Reviews and Reports, reinforces what Mayana had been suggesting previously: if one wants to store a source of stem cells for future use, it should be the entire umbilical cord, blood and all. She is critical of the standard procedure used by specialized banks, which consists of storing the blood and discarding the rest.
SECCO, M. et al. Gene expression profile of mesenchymal stem cells from paired umbilical cord units: cord is different from blood. Stem Cells Reviews and Reports. 2009.