Regeneration of reinnervated rat soleus muscle is accompanied by fiber transition toward a faster phenotype.
The functional recovery of skeletal muscles after peripheral nerve transection and microsurgical repair is generally incomplete. Several reinnervation abnormalities have been described even after nerve reconstruction surgery. Less is known, however, about the regenerative capacity of reinnervated muscles. Previously, we detected remarkable morphological and motor endplate alterations after inducing muscle necrosis and subsequent regeneration in the reinnervated rat soleus muscle. In the present study, we comparatively analyzed the morphometric properties of different fiber populations, as well as the expression pattern of myosin heavy chain isoforms at both immunohistochemical and mRNA levels in reinnervated versus reinnervated-regenerated muscles. A dramatic slow-to-fast fiber type transition was found in reinnervated soleus, and a further change toward the fast phenotype was observed in reinnervated-regenerated muscles. These findings suggest that the (fast) pattern of reinnervation plays a dominant role in the specification of fiber phenotype during regeneration, which can contribute to the long-lasting functional impairment of the reinnervated muscle. Moreover, because the fast II fibers (and selectively, a certain population of the fast IIB fibers) showed better recovery than did the slow type I fibers, the faster phenotype of the reinnervated-regenerated muscle seems to be actively maintained by selective yet undefined cues.
Mendler
Luca
L
Institute of Biochemistry, Faculty of General Medicine, University of Szeged, Dóm tér 9, 6720 Szeged, Hungary. luca@biochem.szote.u-szeged.hu
Pintér
Sándor
S
Kiricsi
Mónika
M
Baka
Zsuzsanna
Z
Dux
László
L
D000818:Animals; D007150:Immunohistochemistry; D008297:Male; D009045:Motor Endplate; D018656:Muscle Fibers, Fast-Twitch / Q000502:physiology / Q000648:ultrastructure; D018485:Muscle Fibers, Skeletal / Q000502:physiology* / Q000648:ultrastructure; D018657:Muscle Fibers, Slow-Twitch / Q000502:physiology / Q000648:ultrastructure; D018482:Muscle, Skeletal / Q000294:innervation* / Q000502:physiology* / Q000648:ultrastructure; D018995:Myosin Heavy Chains / Q000096:biosynthesis / Q000235:genetics; D009336:Necrosis; D009929:Organ Size; D020033:Protein Isoforms / Q000096:biosynthesis / Q000235:genetics; D012333:RNA, Messenger / Q000096:biosynthesis; D051381:Rats; D017208:Rats, Wistar; D012038:Regeneration; D020133:Reverse Transcriptase Polymerase Chain Reaction
D020033:Protein Isoforms; D012333:RNA, Messenger; D018995:Myosin Heavy Chains