Myogenic capacity of muscle progenitor cells from head and limb muscles

Isolation and Characterization of Satellite Cells from Rat Head Branchiomeric Muscles

Fibrosis and defective muscle regeneration can hamper the functional recovery of the soft palate muscles after cleft palate repair. This causes persistent problems in speech, swallowing, and sucking. In vitro culture systems that allow the study of satellite cells (myogenic stem cells) from head muscles are crucial to develop new therapies based on tissue engineering to promote muscle regeneration after surgery. These systems will offer new perspectives for the treatment of cleft palate patients. A protocol for the isolation, culture and differentiation of satellite cells from head muscles is presented. The isolation is based on enzymatic digestion and trituration to release the satellite cells. In addition, this protocol comprises an innovative method using extracellular matrix gel coatings of millimeter size, which requires only low numbers of satellite cells for differentiation assays.

Parathyroid hormone and parathyroid hormone type-1 receptor accelerate myocyte differentiation

The ZHTc6-MyoD embryonic stem cell line expresses the myogenic transcriptional factor MyoD under the control of a tetracycline-inducible promoter. Following induction, most of the ZHTc6-MyoD cells differentiate to myotubes. However, a small fraction does not differentiate, instead forming colonies that retain the potential for myocyte differentiation. In our current study, we found that parathyroid hormone type 1 receptor (PTH1R) expression in colony-forming cells at 13 days after differentiation was higher than that in the undifferentiated ZHTc6-MyoD cells. We also found that PTH1R expression was required for myocyte differentiation, and that parathyroid hormone accelerated the differentiation. Our analysis of human and mouse skeletal muscle tissues showed that most cells expressing PTH1R also expressed Pax7 and CD34, which are biomarkers of satellite cells. Furthermore, we found that parathyroid hormone treatment significantly improved muscle weakness in dystrophin-deficient mdx mice. This is the first report indicating that PTH1R and PTH accelerate myocyte differentiation.

The role of Pitx2 in maintaining the phenotype of myogenic precursor cells in the extraocular muscles

Many differences exist between extraocular muscles (EOM) and non-cranial skeletal muscles. One striking difference is the sparing of EOM in various muscular dystrophies compared to non-cranial skeletal muscles. EOM undergo continuous myonuclear remodeling in normal, uninjured adults, and distinct transcription factors are required for the early determination, development, and maintenance of EOM compared to limb skeletal muscle. Pitx2, a bicoid-like homeobox transcription factor, is required for the development of EOM and the maintenance of characteristic properties of the adult EOM phenotype, but is not required for the development of limb muscle. We hypothesize that these unique properties of EOM contribute to the constitutive differences between EOM and non-craniofacial skeletal muscles. Using flow cytometry, CD34(+)/Sca1(-/)CD45(-/)CD31(-) cells (EECD34 cells) were isolated from extraocular and limb skeletal muscle and in vitro, EOM EECD34 cells proliferated faster than limb muscle EECD34 cells. To further define these myogenic precursor cells from EOM and limb skeletal muscle, they were analyzed for their expression of Pitx2. Western blotting and immunohistochemical data demonstrated that EOM express higher levels of Pitx2 than limb muscle, and 80% of the EECD34 cells expressed Pitx2. siRNA knockdown of Pitx2 expression in EECD34 cells in vitro decreased proliferation rates and impaired the ability of EECD34 cells to fuse into multinucleated myotubes. High levels of Pitx2 were retained in dystrophic and aging mouse EOM and the EOM EECD34 cells compared to limb muscle. The differential expression of Pitx2 between EOM and limb skeletal muscle along with the functional changes in response to lower levels of Pitx2 expression in the myogenic precursor cells suggest a role for Pitx2 in the maintenance of constitutive differences between EOM and limb skeletal muscle that may contribute to the sparing of EOM in muscular dystrophies.

Regenerative strategies for craniofacial disorders

Craniofacial disorders present markedly complicated problems in reconstruction because of the complex interactions of the multiple, simultaneously affected tissues. Regenerative medicine holds promise for new strategies to improve treatment of these disorders. This review addresses current areas of unmet need in craniofacial reconstruction and emphasizes how craniofacial tissues differ from their analogs elsewhere in the body. We present a problem-based approach to illustrate current treatment strategies for various craniofacial disorders, to highlight areas of need, and to suggest regenerative strategies for craniofacial bone, fat, muscle, nerve, and skin. For some tissues, current approaches offer excellent reconstructive solutions using autologous tissue or prosthetic materials. Thus, new “regenerative” approaches would need to offer major advantages in order to be adopted. In other tissues, the unmet need is great, and we suggest the greatest regenerative need is for muscle, skin, and nerve. The advent of composite facial tissue transplantation and the development of regenerative medicine are each likely to add important new paradigms to our treatment of craniofacial disorders.