THE TIME-COURSE OF BASIC FIBROBLAST GROWTH-FACTOR EXPRESSION IN CRUSH-INJURED SKELETAL-MUSCLES OF SJL J AND BALB/C MICE/

Staining for basic fibroblast growth factor (bFGF), a potent mitogen, was examined in muscle recovering from a crush injury and compared bet ween two mouse strains with distinctly different capacities for muscle regeneration to determine if bFGF staining and the steps and outcome of repair were related. Immunofluorescence studies on intact and crush ed tibialis anterior muscle were carried out at 0, 1, 3, 6, and 12 h p ostcrush in SJL/J mice, and at 1, 2, 3, 5, 7, and 11 days after injury in both SJL/J and BALB/c mice (n = 2 - 4). Disrupted fibers showed in creased sarcoplasmic staining for bFGF as little as 3-6 h after injury prior to infiltration with intensely fluorescent mononuclear cells (a t 12-24 h). Fiber bFGF was maintained in SJL/J muscles for 2 days, but was lower in most damaged fibers of BALB/c muscles at the same time. Surviving stumps of crushed fibers, once sealed, exhibited sarcoplasmi c extensions, some of which stained intensely for bFGF. These processe s appeared to connect adjacent fiber stumps, and many were noted in as sociation with aligned mononuclear cells (presumptive myoblasts) at th e site of new myotube formation. In representative sections there were more bFGF-positive mononuclear cells present in SJL/J than BALB/c mus cles. Intense bFGF localization marked newly regenerating myotubes in both SJL/J and BALB/c muscles, and such myotubes were more frequent an d larger in SJL/J muscles. More bFGF was present in regenerating muscl es of SJL/J compared with BALB/c mice (with respect to damaged myofibe rs, mononuclear cells, and myotubes) and this correlates with the supe rior new muscle formation seen in SJL/J mice. These studies support th e idea of a positive relation between bFGF in damaged fibers, the bFGF -positive mononuclear cells, and the speed and success of muscle regen eration. (C) 1995 Academic Press, Inc.