There are more than 30 different types of muscular dystrophy, but not one of them is curable. Stem cell therapy, especially using induced pluripotent stem (iPS) cells, may hold the most promise. iPS cells circumvent the ethical constraints associated with embryonic stem (ES) cells and, because they are derived from the patient's own cells, reduce the possibility of tissue rejection. Another advantage of iPS cells is their expansion potential. No one, however, has been able to produce a sufficient supply of transplantable satellite cells– muscle stem cells– without severely and permanently injuring a donor's muscle tissue.
In 2012, a research team led by Rita Perlingeiro, Ph.D., of the Lillehei Heart Institute, University of Minnesota, Minneapolis, achieved that elusive goal. Perlingeiro and her team produced large quantities of human myogenic precursors and transplanted them into NSG-mdx4Cv mice, a new model of Duchenne muscular dystrophy (DMD). They produced this model by crossing the B6Ros.Cg-Dmdmdx-4Cv/J (mdx4Cv, 002378) and NOD.Cg-Prkdcscid Il2rgtm1Wjl/SzJ (NSG, 005557) strains. In this dystrophic mouse model, the human precursor cells engraft, seed the satellite compartment and produce abundant human-derived, dystrophin-positive, strong and persistent myofibers. The study suggests that it is possible to treat DMD with functional skeletal myogenic progenitors derived from human iPS (hiPS) cells (Darabi et al. 2012).
The promise of hiPS cell therapy needs to be carefully evaluated in model organisms. Before the Perlingeiro study, there was little evidence that hiPS cells could treat diseases in mice. Perlingeiro and her colleagues used the PAX7 gene, which controls muscle differentiation, to convert one human ES (hES) and two hiPS cell lines into myogenic progenitors. These cells can then differentiate into multinucleated myotubes that express the high levels of MyoD, myogenin, dystrophin and myosin heavy chain characteristic of mature skeletal muscle cells. hES- and hiPS-derived progenitors exhibit similar surface marker expression profiles, including MHC class I molecules. This promising finding suggests that the stem cell-derived myotubes would not elicit a natural killer (NK) cell-mediated immune response that would impair a transplant.
The Perlingeiro team next transplanted either hES- or hiPS-derived myogenic progenitors into injured tibialis anterior (TA) muscles of NSG mice. These mice are severely immunodeficient and can accept grafts of human myogenic progenitors because they lack B, T, and NK cells. Two months post transplantation, whether injected with hES- or hiPS-derived myogenic progenitors, the injured TA muscles of the NSG mice exhibit comparable levels of human-derived myofiber engraftment and human dystrophin expression. Significant engraftment was still evident 11 months post transplantation.
Having shown that the human myogenic progenitors can regenerate muscle in an immunodeficient mouse, the Perlingeiro lab investigated their therapeutic potential by transplanting them into the new NSG-mdx4Cv model mentioned above. Like the NSG mouse (005557), this new model lacks B, T, and NK cells; like the mdx-4Cv DMD model (002378), it harbors the X-linked muscular dystrophy 4 mutation, which inactivates the Dmd gene. The researchers found that transplantation of either hES- or hiPS-derived myogenic progenitors in the TA muscles of these mice results in significant human myofiber engraftment and improvement in muscle function. They also found that both hES- and hiPS-derived myogenic progenitors seed the satellite cell compartments of injured TA muscles in these mice.
In summary, Perlingeiro and her colleagues used a cellular reprogramming strategy to generate large quantities of skeletal muscle progenitors. Whether hES- or hiPS-derived, these progenitors exhibit virtually identical properties: they engraft long-term, contribute to the satellite cell pool, regenerate muscle, restore dystrophin expression and improve muscle function in the NSG-mdx4Cv mouse model. These findings represented an important step in making the concept of therapeutic iPS cell therapy a reality.
If you'd like to use the immunocompromised NSG-mdx4Cv mouse in your research, JAX® Services can produce it for you.