Human amniotic fluid-derived stem cells (AFSC) have a demonstrated ability to differentiate into several different adult cell types, and they also fail to form tumors in laboratory animals.
A previous study of AFSCs showed that if these stem cells were grown in culture with heart muscle cells from newly born rats, the AFSCs began to express heart-specific genes. While the AFSCs did not become full-fledged heart muscle cells, they began to differentiate in that direction.
Yang Gao and others in the laboratory of Jeffrey G. Jacot at Rice University tried this same experiment with human heart cells. They used a specific set of cell culture conditions that prevent the AFSCs from fusing with the heart cells, because the fusion of two cells can deceive researchers into thinking that the stem cells have actually become heart cells when in fact they have not.
Jacot and his coworkers discovered that when human AFSC made contact with human heart cells, they began to express proteins normally found in heart muscle that help them contract. One of these proteins, cardiac troponin T (cTnT), was definitely expressed in human AFSCs, even though this protein is rather specific to heart muscle cells. cTnT is also one of the proteins released into the bloodstream after a heart attack. Further investigation uncovered absolutely no evidence of cell fusion. Thus when AFSCs touch human heart cells, they begin to make some heart-specific proteins.
Jacot and his group did an additional experiment. They tried culturing the human AFSCs on one side of the porous membrane and human heart cells on the other side. These conditions allow minimal contact between cells, but still exposes them the anything the cells might be secreting. Under these culture conditions, human AFSCs still showed a statistically significant increase in cTnT expression compared to culture conditions that without contact between the two cell types. However, human AFSCs grown in the present of human heart cells still did not express the calcium modulating proteins that are so important for regulating heart muscle contraction. Additionally, the cells and did not have functional or morphological characteristics of mature heart muscle cells.
These data suggest that contact between heart cells and human AFSCs is a necessary but not sufficient condition to drive AFSCs to differentiate into heart cells. However, touching heart cells gets AFSCs part of the way. Maybe further research will provide other cues that will push these remarkable cells the rest of the way.