Intramuscular migration of myoblasts transplanted after muscle pretreatment with metalloproteinases

The effect of pretreatments of host muscles with metalloproteinases (MMPs) or with notexin on the migration of transplanted myoblasts was investigated . Transgenic TnILacZ mice in which the beta-galactosidase gene is under the control of a quail fast skeletal troponin I gene promoter were used as don ors. A polyethylene microtube with four perforations was inserted in the ti bialis anterior (TA) of CD1 mice. Both pretreatment substances and cells we re slowly injected through that microtube. Muscles were pretreated 2 days b efore myoblast injection either with a mixture of collagenase, matrilysin, and notexin or with only collagenase and matrilysin or only notexin. As con trol for our experiments, TnILacZ and C2C12 myoblasts were also injected in TA muscles not pretreated. Comparison of short and long-term myoblast radi al migration was performed using a dye (PKH26) and X-gal staining, respecti vely. The recipient mice were immunosuppressed with FK506. Two days after m yoblast transplantation, the cell movement in muscles pretreated with colla genase, matrilysin, and notexin was slightly greater than in muscles pretre ated only with collagenase and matrilysin but was about twice that observed in muscles treated with notexin alone. Almost no radial migration of TnILa cZ myoblasts was observed in untreated muscles. The C2C12 myoblasts showed a four to fivefold higher migration capacity than TnILacZ myoblasts, At 15 days after TnILacZ myoblast transplantation, the farthest positive beta-gal muscle fibers show a two- to threefold extension of the initial migration observed at 2 days, demonstrating the ability of myoblasts to continue the migration following all pretreatments and even in the untreated muscles. In addition, more muscle fibers expressed the beta-gal reporter gene in muscl es pretreated only with MMPs. Our results clearly demonstrate that muscle p retreatments with MMPs increase myoblast migration and fusion with host mus cle fibers after transplantation and that the C2C12 cell line producing MMP s has a higher migratory capacity.