Time-coordinated prevalence of extracellular HGF, FGF2 and TGF-β3 in crush-injured skeletal muscle

Successful regeneration and remodeling of neuromuscular junctions are critical for restoring functional capacities and properties of skeletal muscle after damage, and axon-guidance molecules may be involved in the signaling that regulates such restoration. Recently, we found that early-differentiated satellite cells up-regulate a secreted neural chemorepellent Sema3A upon in vivo muscle-crush injury. The study also revealed that Sema3A expression is up-regulated in primary satellite-cell cultures in response to hepatocyte growth factor (HGF) and basic fibroblast growth factor (FGF2) and is prevented by transforming growth factor (TGF)-β2, 3. In order to verify the physiological significance of this regulation in vitro, the present study was designed to estimate the time-course of extracellular HGF, FGF2 and TGF-β3 concentrations after crush-injury of Gastrocnemius muscle in the rat lower hind-limb, using a combination of a non-homogenization/non-spin extraction of extracellular wound fluids and enhanced chemiluminescence-Western blotting analyses. Results clearly demonstrated that active HGF and FGF2 are prevalent in 2-8days post-crush, whereas active TGF-β3 increases after 12days, providing a better understanding of the time-coordinated levels of HGF, FGF2 and TGF-β3 that drive regulation of Sema3A expression during regenerative intramuscular moto-neuritogenesis.