HETEROGENEITY AMONG MUSCLE PRECURSOR CELLS IN ADULT SKELETAL-MUSCLES WITH DIFFERING REGENERATIVE CAPACITIES

Skeletal muscle has a remarkable capacity to regenerate after injury, although studies of muscle regeneration have heretofore been limited a lmost exclusively to limb musculature, Muscle precursor cells in skele tal muscle are responsible for the repair of damaged muscle. Heterogen eity exists in the growth and differentiation properties of muscle pre cursor cell (myoblast) populations throughout limb development but whe ther the muscle precursor cells differ among adult skeletal muscles is unknown. Such heterogeneity among myoblasts in the adult may give ris e to skeletal muscles with different regenerative capacities, Here we compare the regenerative response of a masticatory muscle, the massete r, to that of limb muscles, After exogenous trauma (freeze or crush in juries), masseter muscle regenerated much less effectively than limb m uscle. In limb muscle, normal architecture was restored 12 days after injury, whereas in masseter muscle, minimal regeneration occurred duri ng the same time period. Indeed, at late time points, masseter muscles exhibited increased fibrous connective tissue in the region of damage , evidence of ineffective muscle regeneration. Similarly, in response to endogenous muscle injury due to a muscular dystrophy, widespread ev idence of impaired regeneration was present in masseter muscle but not in limb muscle. To explore the cellular basis of these different rege nerative capacities, we analyzed the myoblast populations of limb and masseter muscles both in vivo and in vitro, From in vivo analyses, the number of myoblasts in regenerating muscle was less in masseter compa red with limb muscle. Assessment of population growth in vitro indicat ed that masseter myoblasts grow more slowly than limb myoblasts under identical conditions. We conclude that the impaired regeneration in ma sseter muscles is due to differences in the intrinsic myoblast populat ions compared to limb muscles. (C) 1998 Wiley-Liss, Inc.