Dermal fibroblasts participate in the formation of new muscle fibres when implanted into regenerating normal mouse muscle

Both in vitro and in vivo studies have described the conversion of fibrobla sts to myogenesis when in the presence of dysfunctional myogenic cells. Myo genic conversion of fibroblasts subjected to a normal, as opposed to a dise ased muscle environment has only been reported in vitro. The primary aim of this work was to determine if fibroblasts can convert to a myogenic lineag e and contribute to new fibre formation when implanted into the regeneratin g muscle of a normal mouse. Dermal fibroblasts were prepared from neonatal mouse skin and labelled prior to implantation with the fluorescent nuclear marker 4',6-diamidino-2-phenylindole (DAPI). Cells were implanted into musc les of host mice that had been subjected to either cold/crush or minced mus cle injury. Some host muscles were x-irradiated to deplete the muscle of en dogenous muscle precursor cells. Muscles were removed at 3 wk postimplantat ion and analysed both histologically and for the presence of DAPI labelled nuclei. Fibres containing DAPI labelled central nuclei indicated that the i mplanted cells had participated in the regenerative process. Mouse dermal f ibroblasts therefore do contribute to muscle fibre formation in regeneratin g normal mouse muscle but the extent of their contribution is dependent on the nature of the trauma induced in the host muscle. The study also showed that regeneration was more successful in muscles which had not been irradia ted, which is contrary to the previous studies where dermal fibroblasts wer e introduced into myopathic mouse muscle.