Human mesodermal induced pluripotent stem cell derived progenitors can successfully engraft into the skeletal muscle and hearts of dystrophic mice, researchers from Northwestern University have shown. The work shows the potential to regenerate lost muscle mass in muscular dystrophy.

Muscular dystrophy is a genetic disease characterized by the progressive loss of both skeletal and cardiac muscle mass. While there is no cure, physical therapy or medication can offer relief for symptoms, and recent advancements in induced pluripotent stem cells (iPSCs) have pointed to the possibility of future muscle regeneration therapies.

Past studies have shown that mouse-derived mesodermal iPSC-derived progenitor (MiP) stem cells can spur muscle regeneration in mice, with the unprecedented advantage of regenerating both heart and muscle tissue with the same stem cell type.

However, the viability of human–based cells to perform similarly had been largely untested.

Regenerative Potential

To investigate if human stem cells can effectively regenerate lost muscle tissue, the Northwestern University Medicine scientists injected human MiP cells into mouse models, finding increased heart volume and improved muscle structure compared to controls with untreated muscle degeneration. When they later introduced a drug to down-regulate the MiPs, the beneficial effects were reversed, bolstering the evidence that human MiPs have regenerative potential.

[caption id=“attachment_93955” align=“aligncenter” width=“680”]Human MiPs engraft and are able to functionally regenerate dystrophic muscles Human MiPs engraft and are able to functionally regenerate dystrophic muscles.
(a, b) Four weeks after delivery, immunostaining shows that fibroblast- and MAB-MiPs engraft and express hDYS to a similar extent in the heart, but differently in the hindlimb muscles (gastrocnemius).
(c) Tetanic force of EDL muscles and treadmill assay showed that skeletal muscle performance was increased in fibroblast-MiP-treated vs untreated mice, and increased in MAB-MiP- vs fibroblast-MiP-treated mice.
(d) Functional assessment of the heart, by means of fractional shortening quantitation, shows comparable amelioration in both MiP-treated cohorts, but not after induced MiP death.
(e) Bungarotoxin-based staining of NMJs throughout whole EDL and soleus muscles (n = 3/cohort) reveals that dystrophic mice (sham) present highly fragmented NMJs, while MiP-engrafted fibers present NMJs with a morphology siilar to WT fibers.
(f) Masson’s trichromic staining of hindlimb (quadriceps) muscles of recipient mice.
Credit: Giorgia Giacomazzi et al. CC-BY[/caption]

In addition, the study also explored ways to improve these stem cells' ability to differentiate into both skeletal and cardiac muscle.

“While we can make stem cells differentiate into cardiac cells, making them differentiate into muscle cells has not been as easy,"

said co-author Elizabeth McNally, MD, Ph.D., the Elizabeth J. Ward Professor of Genetic Medicine and professor of Medicine in the Division of Cardiology and of Biochemistry and Molecular Genetics.

MicroRNA Cocktails

One possible solution is to use MiP cells created from skeletal muscle mesoangioblasts (MAB). The study also showed that these MAB-MiPs created more skeletal muscle cells when compared to MiPs derived from fibroblasts, a type of connective tissue cell. On the other hand, the capacity to generate cardiac muscle cells appeared comparable between the two.

However, treating fibroblast MiPs with microRNA cocktails showed even more promise, greatly improving the skeletal muscle differentiation of fibroblast MiPs, bringing them on par with MAB-MiPs.

In the future, these microRNA treatments could even be used to mobilize existing stem cells in addition to any newly injected cells, compounding the benefits of muscle regeneration therapy, according to the study.

“One of the most innovative aspects of this study is the identification of actionable molecules—the microRNA cocktails—to improve the innate efficiency of functional amelioration that human MiPs can impart on dystrophic muscle. The next step will be to capitalize on these discoveries by improving safety and bringing this novel therapeutic option closer to clinical standards,"

said Mattia Quattrocelli, Ph.D., a postdoctoral fellow in McNally’s lab, and one of the study’s co-senior authors.

McNally and Quattrocelli intend to continue exploring microRNA modulation and the use of MiPs in muscle regeneration, hopefully moving on to larger animal models as a proof-of-concept on the road to eventual patient therapy.

Giorgia Giacomazzi, Bryan Holvoet, Sander Trenson, Ellen Caluwé, Bojana Kravic, Hanne Grosemans, Álvaro Cortés-Calabuig, Christophe M. Deroose, Danny Huylebroeck, Said Hashemolhosseini, Stefan Janssens, Elizabeth McNally, Mattia Quattrocelli & Maurilio Sampaolesi MicroRNAs promote skeletal muscle differentiation of mesodermal iPSC-derived progenitors Nature Communications 8, Article number: 1249 (2017) doi:10.1038/s41467-017-01359-w

Top Image: MiPs inducing regeneration of both heart and muscle tissue (green), and subsequent destruction of regenerated tissue when the MiPs are turned off by the molecule AP20187. Credit: Northwestern University

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