University of Illinois researchers have identified a protein expressed by human bone marrow stem cells that guides and stimulates the construction of blood vessels.
Jalees Rehman, associate professor of cardiology and pharmacology at the University of Illinois at Chicago College of Medicine and lead author of this paper, said: “Some stem cells actually have multiple jobs.”
As an example, stem cells from bone marrow known as mesenchymal stem cells can form bone, cartilage, or fat, but they also have a secondary role in that they support other cells in bone marrow.
Rehman and others have worked on developing engineered tissues for use in cardiac patients, and they noticed that mesenchymal stem cells were crucial for organizing other cells into functional stem cells.
Workers from Rehman’s laboratory mixed mesenchymal stem cells from human bone marrow with endothelial cells that line the inside of blood vessels. The mesenchymal stem cells elongated and formed a kind of scaffold upon which the endothelial cells adhered and organized to form tubes.
“But without the stem cells, the endothelial cells just sat there,” said Rehman.
When the cell mixtures were implanted into mice, blood vessels formed that were able to support the flow of blood. Then Rehman and his colleagues examined the genes expressed when their stem cells and endothelial cells were combined. They were aided in this venture by two different bone marrow stem cell lines, one of which supported the formation of blood vessels, and the other of which did.
Their microarray experiments showed that the vessel-supporting mesenchymal stem cells expressed high levels of the SLIT3 protein. SLIT3 is a blood vessel-guidance protein that directs blood vessel-making cells to particular places and induces them to make blood vessels. The cell line that do not stimulate blood vessel production made little to no SLIT3.
Rehman commented, “This means that not all stem cells are created alike in terms of their SLIT3 production and their ability to encourage blood vessel formation.”
Rehman continued: “While using a person’s own stem cells for making blood vessels is ideal because it eliminates the problem of immune rejection, it might be a good idea to test a patient’s stem cells to make sure they are good producers of SLIT3. If they aren’t, the engineered vessels may not thrive or even fail to grow.
Mesenchymal stem cells injections are being evaluated in clinical trials to see if their can help grow blood vessels and improve heart function in patients who have suffered heart attacks.
So far, the benefits of stem cell injection have been modest, according to Rehman. Evaluating the gene and protein signatures of stem cells from each patient may allow for a more individualized approach so that every patient receives mesenchymal stem cells that are most likely to promote blood vessel growth and cardiac repair. Such pre-testing might substantially improve the efficacy of stem cell treatments for heart patients.