May 15, 2009

Heart Must Beat for Embryonic Blood Cell Growth

A recent study reveals evidence that blood cells of an embryo grow only under conditions of pressure by a beating heart, Reuters reported. 

The results make clear why an embryo's heart begins palpitating in the first weeks of conception, and additionally facilitates support for new stem cell-based treatments for numerous blood disorders including leukemia. 

Dr. George Daley of Harvard Medical School and Children's Hospital Boston said, "In learning how the heartbeat stimulates formation of embryos, we've taken a leap forward in understanding how to direct blood formation from embryonic stem cells in the petri dish." His study can be viewed in the journal Nature. 

Daley's colleague and counterpart in this study, Guillermo Garcia-Cardena of Brigham and Women's Hospital in Boston said, "These observations reveal an unexpected role for biomechanical forces in embryonic development."

Stem cells function as the body's master cells, offering a renewable supply of brain, bone, muscle, blood and other cells. 

During the first days of conception, an embryo consists completely of these cells, each of which is the building blocks of all the cells and tissues in the body. 

By studying how the stress of friction and the flow of fluid influenced the development of blood cells from the stem cells of embryonic mice, Daley's team was able to prove that these forces encourage blood formation.  Additionally, the production of colonies of cells multiply, as do particular kinds of blood cells. 

In mouse embryos having a mutation that prohibited the forming heart from beating, less of these so-called progenitor blood cell colonies could be identified. 

Another team of researchers, directed by Dr. Leonard Zon of Harvard and Children's Hospital Boston, studied the consequences of the embryonic heartbeat in zebrafish. 

Because the zebrafish embryo is transparent, Zon's team was able to catch a good view of what was really occurring inside.
"We were looking in real aortas in real vertebrate embryos to see the actual stem cells," Zon said in a statement.

Levels of nitric oxide, which is instrumental in blood vessel development, amplify when blood is coursing, findings reveal in an article published by the journal Cell. 

Blood-forming stem cells termed hematopoietic progenitor cells, existed in smaller quantities in the mutant embryos with no heart beat or circulation. 

Nitric oxide, the team believes, could serve as some sort of indicator to begin the process of blood stem cell production.

"This finding connects the change in blood flow with the production of new blood cells," Zon asserted.

The results of the study may generate new methods to persuade iPS cells, which closely resemble embryonic cells, into developing blood-forming cells that could support leukemia patients while awaiting bone marrow transplants, he said. 


On The Net:

journal Nature

Harvard Medical School