Scientists led by Thomas Braun, Director of the Max Planck Institute for Heart and Lung Research, have discovered by a number of different experimental approaches that mesenchymal stem cells only show a rudimentarily developed potential for transdifferentiation processes. All cases in which functional skeletal muscle cells arose from mesenchymal stem cells were based on the fusion of stem cells with already differentiated muscle cells.
Although, like the researchers from Bad Nauheim show, cultivated mesenchymal stem cells are able to express a number of heart- and skeletal muscle specific genes and undergo some morphologic changes, after they are co-cultured with growth-factor producing feeder cells, finally they did not become entirely functional muscle cells.
Fully-functional muscle cells only developed after the mesenchymal stem cells were cultivated together with skeletal or heart muscle cells. This was indicated by the green fluorescence of muscle cells derived from the fusion with a stem cell which before had been labelled with the green dye. In contrast, no green fluorescing muscle cells became evident when stem and muscle cells were spatially separated by a membrane between both cell types. The researchers conclude that this experiments proofs that cell fusion of mesenchymal stem cells and muscle cell but not their transdifferentiation forms the basis for the regeneration mechanism. Additional experiments were focussing on the molecular mechanism underlying the cell fusion process. In these investigations, so-called "chimeric" mouse embryos were produced from mesenchymal stem cells and several mouse mutants: Obviously, the stem cells are recruiting the IL-4/NFAT signalling pathway which also is involved in the activation