Identification and characterization of PDGFRα+ mesenchymal progenitors in human skeletal muscle.

Fatty and fibrous connective tissue formation is a hallmark of diseased skeletal muscle and deteriorates muscle function. We previously identified non-myogenic mesenchymal progenitors that contribute to adipogenesis and fibrogenesis in mouse skeletal muscle. In this study, we report the identification and characterization of a human counterpart to these progenitors. By using PDGFRα as a specific marker, mesenchymal progenitors can be identified in the interstitium and isolated from human skeletal muscle. PDGFRα(+) cells represent a cell population distinct from CD56(+) myogenic cells, and adipogenic and fibrogenic potentials were highly enriched in the PDGFRα(+) population. Activation of PDGFRα stimulates proliferation of PDGFRα(+) cells through PI3K-Akt and MEK2-MAPK signaling pathways, and aberrant accumulation of PDGFRα(+) cells was conspicuous in muscles of patients with both genetic and non-genetic muscle diseases. Our results revealed the pathological relevance of PDGFRα(+) mesenchymal progenitors to human muscle diseases and provide a basis for developing therapeutic strategy to treat muscle diseases.

Centering osteotomy for treatment of posterior shoulder dislocation in obstetrical palsy.

BACKGROUND: The main objective of this study is to describe a new surgical technique that, through a gleno-humeral approach, reduces the incongruent joint while a humeral head centering osteotomy achieves shoulder stabilization. A humeral medial derotational osteotomy is performed associated with the articular reduction. PATIENTS AND METHODS: Fourteen patients with obstetrical palsy presenting a posterior humeral head dislocation were submitted to a centering osteotomy procedure. Our study included patients with: (1) more than 1.5 years postoperative follow-up, (2) presence of humeral head posterior dislocation. The exclusion criteria were the following: (1) patients with total flaccid paralysis, (2) low paralysis and (3) any kind of active infection at the time of the procedure. RESULTS: Before treatment, in all patients, the shoulder joint was posteriorly dislocated and in internal rotation. All patients went on to have successful healing at the osteotomy site. In all cases, an improvement in the functional Mallet scale was observed. In all patients, except one, the posterior dislocation was corrected. In two cases, a second surgery (external derotation osteotomy) was performed to improve the upper extremity's position. CONCLUSIONS: Articular congruency, after posterior dislocations of the humeral head, is achieved by humeral head centering osteotomy in patients with obstetrical palsy late deformities and also improves function. LEVEL OF EVIDENCE: Level IV; case series.

CDK4 and cyclin D1 allow human myogenic cells to recapture growth property without compromising differentiation potential.

In vitro culture systems of human myogenic cells contribute greatly to elucidation of the molecular mechanisms underlying terminal myogenic differentiation and symptoms of neuromuscular diseases. However, human myogenic cells have limited ability to proliferate in culture. We have established an improved immortalization protocol for human myogenic cells derived from healthy and diseased muscles; constitutive expression of mutated cyclin-dependent kinase 4, cyclin D1 and telomerase immortalized human myogenic cells. Normal diploid chromosomes were preserved after immortalization. The immortalized human myogenic cells divided as rapidly as primary human myogenic cells during the early passages, and underwent myogenic, osteogenic and adipogenic differentiation under appropriate culture conditions. The immortalized cells contributed to muscle differentiation upon xenotransplantation to immunodeficient mice under conditions of regeneration following muscle injury. We also succeeded in immortalizing cryopreserved human myogenic cells derived from Leigh disease patients following primary culture. Forced expression of the three genes shortened their cell cycle to < 30 h, which is similar to the doubling time of primary cultured human myogenic cells during early passages. The immortalization protocol described here allowed human myogenic cells to recapture high proliferation activity without compromising their differentiation potential and normal diploidy.