G.P.5.05 Transient overexpression of the Rho family exchange factor GEFT stimulates myogenic differentiation of inclusion-body myositis (IBM) mesoangioblasts

Mesoangioblasts are a new class of adult stem cells of mesoderm origin, potentially useful for the treatment of primitive myopathies of different etiology. We recently isolated human mesoangioblasts from patients with idiopathic inflammatory myopathies (dermatomyositis, DM, polymyositis, PM and inclusion-body myositis, IBM), and showed that these stem cells can be extensively expanded in vitro to obtain a number of mesoangioblasts suitable for intra-arterial delivery to an adult patient. In addition, we demonstrated that mesoangioblasts obtained from IBM patients have a defective differentiation in skeletal muscle and this block can be corrected in vitro by transient MyoD overexpression. In order to clarify the myogenic defect of IBM mesoangioblasts we investigated, the expression and the regulation of proteins such as the Rho family exchange factor GEFT which is transcriptionally upregulated during myogenic differentiation. Furthermore GEFT gene transfer induces a powerful promotion of skeletal muscle regeneration in vivo activating the Rho-signalling cascade. By western blot analysis we observed that IBM mesoangioblasts express significantly lower levels of GEFT protein compared to controls and DM cells. Since GEFT expression in multipotent cell lines, promotes myogenic cell fate decision of progenitor mesenchymal cells, we then performed GEFT gene transfer experiments in IBM mesoangioblasts by using a pCMV-Tag 2B expression vector containing the human GEFT cDNA sequence. We demonstrated that transient transfection of GEFT was capable of stimulating myogenic differentiation of IBM mesoangioblasts both in vitro and in vivo. In conclusion, the presence of GEFT protein, known as a powerful enhancer of myogenesis and a modulator of mesenchimal multipotent cells fate decision, seems to correlate with the myogenic potential of mesoangioblasts and its overexpression in vitro and in vivo might specifically induce IBM mesoangioblasts myogenic differentiation. Our data suggest that GEFT plays an important role in mesoangioblasts differentiation and it might represent a selective target for pharmacological stimulation with molecules known to induce its up-regulation.