Phenotypic Changes of Intermediate Filament Proteins during Degeneration and Regeneration of Rat Leg Muscles following Sciatic Nerve Injury

Kim, Byeong Hwan; Yoo, Ki Soo; Sohn, Sung Keun

Abstract

PURPOSE
The intermediate filament proteins, desmin and vimentin, are specific components of the cytoskeleton of striated muscle fibers and of mononuclear cells of mesenchymal origin including myoblasts, respectively. Desmin has also been found in presumptive myoblasts of mammals. The aim of this experiment was attempted to observe the phenotypic changes of intermediate filaments in skeletal muscle fibers during early stages of sciatic nerve crushing injury.
MATERIALS AND METHODS
The sciatic nerves of rats were surgically crushed by hemostat and serial cryosections of soleus and extensor digitorum longus(EDL) muscles were prepared at 2, 4, 6, 8, 10, 15, 20 and 27 days after nerve injury. Serial cryosections were immunolabelled with desmin, vimentin and laminin and were histochemically reacted with NADH-TR.
RESULTS
1) Firstly, desmin positive fibers were appeared in fast-twitch type C fibers of both muscles at 6 days after nerve crushing, but were not reacted for vimentin. 2) Co-expressions of desmin and vimentin were firstly detected in fast-twitch type A fibers of EDL muscles at 8 days after nerve injury. In soleus muscles, co-expressions of desmin and vimentin were firstly seen in slow-twitch type B fibers at 10 days after nerve injury. Many atrophic fibers, that contained several central nuclei like myotubes and co-expressed desmin and vimentin, were appeared in EDL muscles at 10 days after nerve injury. Although whole regions of fibers were regenerated in EDL muscles, only peripheral regions of fibers were regenerated in soleus muscles at 15 days after nerve injury. Many atrophic fibers, co-expressed of desmin and vimentin, were appeared in EDL muscles at 20 days after nerve injury. These whole fibers represented various degrees of regenerating stages. Most of mature fibers containing several central nuclei, only expressed vimentin slightly, were seen in soleus muscles at 20 days after nerve injury. Most fibers of both muscles were matured at 27 days after nerve injury, but some fibers in EDL muscles were still in processing of degeneration and regeneration. No expressions of desmin and vimentin indicated that muscle fibers were almostly matured in soleus muscles at 27 days after nerve injury. 3) Targetoid or target fibers which informed reinnervation, were appeared firstly in soleus muscles at 20 days and were seen in both muscles at 27 days after nerve injury. All targetoid and target fibers were type B fibers.
CONCLUSION
Desmin was revealed in processes of degeneration and regeneration and vimentin was appealed in regeneration process. At the same time, positive immunoreactivity of desmin and vimentin showed specific differences in degree of degeneration and regeneration according to different muscles and muscle fibers.