In fetal heart, stem cells known as cardiovascular progenitor cell (CPC) differentiates into smooth muscle cells for blood vessels, blood vessel wall cells, and heart muscle cells. Making CPCs from stem cells has proven to be rather difficult because CPCs do not express any known surface molecules that distinguishes them from other cell types. Therefore, if you want to differentiate pluripotent stem cells into CPCs, determining that you have made CPCs is very difficult.
This problem has been addressed by an international research team led by a team from Stuttgart, Germany who have discovered cell surface molecules that allow the identification and isolation of CPCs. With this knowledge, it will be possible to derive CPCs from induced pluripotent stem cells, which can be implanted into damaged hearts, differentiate into heart-specific cell types and integrate into the heart.
Heart attacks are the most frequent cause of death in the developed world. The cause of a heart attack is usually a clogged coronary vessel, which prevents sufficient blood flow through the heart and kills off heart tissue as a result of ischemia. There are some 17 million people who die from cardiovascular disease each.
Heart muscle cells (cardiomyocytes) do not have the ability to regenerate sufficiently after a heart attack. A heart attack causes a huge loss of cells and further impairs blood supply through the heart. This causes the heart to deteriorate further. To fix the heart, new heart muscle cells are required to replace to dead ones.
This now seems to be a distinct possibility. A research team led by Dr. Katja Schenke-Layland from the Frauhofer Institute for Interfacial engineering and Biotechnology IGD in Stuttgart, in collaboration with Dr. Ali Nasar from the University of California and Dr. Robb MacLean from the University of Washington in Seattle have used cultured CPCs to make heart muscle cells.
To identify CPCs, two proteins of the surfaces of CPCs were identified; a receptor called Flt1 and another called Flt4. By exploiting these two surface proteins, scientists can identify and isolate CPCs from a culture of differentiating pluripotent stem cells. To exploit this new finding, these groups, made induced pluripotent stem cells (iPSCs) from a mouse strain that expressed a green fluorescent protein. They then used skin cells from these mice to make iPSCs.
Japanese stem cell researcher Shinya Yamanaka won the Nobel Prize this year for the discovery of iPSCs. To make iPSCs, adult cells are genetically engineered with four different genes and these genes de-differentiate the adult cells to a pluripotent stem cells state.
The iPSCs made from the green fluorescent mice were then differentiated into CPCs. They were able to isolate and identify CPCs by means of capturing all the cells that made Flt1 and Flt4.
According to Schenke-Layland, “Using our newly established cell surface markers, we could detect and isolate the Flt1- and Flt4-positive CPCs in culture. When we cultured the isolated mouse CPCs then in vitro, they actually developed – as well as the embryonic stem cell-derived progenitor cells – into endothelial cells, smooth muscle cells and more interestingly into functional heart muscle cells.”
To determine if these iPSC-derived CPCs could integrate into a living heart, they injected them into the hearts of living mice. 28 days later, the noticed that the injected hearts were loaded with green fluorescent cells that had differentiated into beating heart muscle that were fully integrated into the heart muscle tissue of the heart.
The next step is to determine if these CPCs can help heal a heart after a heart attack. Bone marrow-derived stem cells have been used to help heal the hearts of heart attack patients, and to date, these stem cells are safe, but only seem to help most people just little, even though they seem to help some patients more than others. However, iPSC-derived CPCs could potentially heal the heart to a greater degree.
According to Schenke-Layland, “We are currently focusing on research with human iPS cells. If we can show that cardiovascular progenitor cells can be derived from human iPS cells that have the ability to mature into functional heart muscle, we will have discovered a truly therapeutic solution for heart attack patients.”
See “Characterization and Therapeutic Potential of INduced Pluripotent Stem Cell-Derived Cardiovascular Progenitor Cells;” Ali Nasar et al: PLoS ONE, 2012; 7 (10): e45603 DOI: 10.1371/journal.pone.0045603.