An ex vivo gene therapy approach to treat muscular dystrophy using inducible pluripotent stem cells.

Duchenne muscular dystrophy is a progressive and incurable neuromuscular disease caused by genetic and biochemical defects of the dystrophin-glycoprotein complex. Here we show the regenerative potential of myogenic progenitors derived from corrected dystrophic induced pluripotent stem cells generated from fibroblasts of mice lacking both dystrophin and utrophin. We correct the phenotype of dystrophic induced pluripotent stem cells using a Sleeping Beauty transposon system carrying the micro-utrophin gene, differentiate these cells into skeletal muscle progenitors and transplant them back into dystrophic mice. Engrafted muscles displayed large numbers of micro-utrophin-positive myofibers, with biochemically restored dystrophin-glycoprotein complex and improved contractile strength. The transplanted cells seed the satellite cell compartment, responded properly to injury and exhibit neuromuscular synapses. We also detect muscle engraftment after systemic delivery of these corrected progenitors. These results represent an important advance towards the future treatment of muscular dystrophies using genetically corrected autologous induced pluripotent stem cells.

A critical role for endoglin in the emergence of blood during embryonic development.

Much remains unknown about the signals that induce early mesoderm to initiate hematopoietic differentiation. Here, we show that endoglin (Eng), a receptor for the TGFß superfamily, identifies all cells with hematopoietic fate in the early embryo. These arise in an Eng(+)Flk1(+) mesodermal precursor population at embryonic day 7.5 (E7.5), a cell fraction also endowed with endothelial potential. In Eng-knockout embryos, hematopoietic colony activity and numbers of CD71(+)Ter119(+) erythroid progenitors were severely reduced. This coincided with severely reduced expression of embryonic globin and key bone morphogenic protein (BMP) target genes, including the hematopoietic regulators Scl, Gata1, Gata2, and Msx-1. To interrogate molecular pathways active in the earliest hematopoietic progenitors, we applied transcriptional profiling to sorted cells from E7.5 embryos. Eng(+)Flk-1(+) progenitors coexpressed TGFß and BMP receptors and target genes. Furthermore, Eng(+)Flk-1(+) cells presented high levels of phospho-SMAD1/5, indicating active TGFß and/or BMP signaling. Remarkably, under hematopoietic serum-free culture conditions, hematopoietic outgrowth of Eng-expressing cells was dependent on the TGFß superfamily ligands BMP4, BMP2, or TGF-ß1. These data demonstrate that the E(+)F(+) fraction at E7.5 represents mesodermal cells competent to respond to TGFß1, BMP4, or BMP2, shaping their hematopoietic development, and that Eng acts as a critical regulator in this process by modulating TGF/BMP signaling.