Enhancement of regeneration by addition of exogenous myoblasts

Mass and functional capacity of autologous transplanted extensor digitorum longus muscles of adult SCID mice that received 7 × 10⁶ myoblasts [stably transfected to express β-gal (nuclear localizing) under the control of a muscle specific promoter/enhancer] 1 days post-transplantation were evaluated and compared to similarly transplanted muscles that received: 1) no further treatment, 2) sham injection of vehicle without myoblasts. Twelve weeks after transplantation, myofibers containing donor nuclei could be identified in muscle subjected to myoblast injection by assaying for β-gal with X-gal solution. Judging from the decreased size and poor functional performance, sham injection provided a second trauma to the regenerating muscle from which it failed to fully recover. In comparison to the sham operated muscles, the myoblast injected muscles weighed 62% more, had 50% more myofibers, and had 82% more cross-sectional area at the muscles' widest girths. Their absolute twitch and tetanic tensions were approximately 3 times that of the sham injected muscles, and their specific twitch and tetanic tensions were 71% and 51% greater, respectively. In many parameters the regenerating muscles subjected to myoblast transfer equaled or exceed those of muscles that were transplanted only (received only 1 trauma). They weighed significantly more, and contained more myofibers. Absolute twitch and tetanic tensions were 73% and 65% greater, respectively, than muscles subjected to transplantation only, and specific twitch tension of the muscles receiving myoblasts were 50% greater than the transplant only group.