Apoptosis in long-term denervated rat skeletal muscle

ABSTRACT

Apoptosis occurs in normal tissues and in many pathological conditions, and is regulated by a variety of genes. In this work, we used electron microscopy and the comet assay to study the morphological and biochemical (DNA cleavage) changes associated with apoptosis in long-term denervated rat skeletal muscle. Male Wistar rats were anesthetized with sodium pentobarbital (30 mg/kg, i.p.), and the sciatic nerve was cut at mid-thigh level followed by the excision of a 5-10 mm long segment of the nerve. Rats that were studied more than four months after the operation were re-operated at least every three months. Samples were obtained from red (soleus) and white (extensor digitorum longus, EDL) striated skeletal muscle at different times after denervation. The ultrastructural changes associated with fiber atrophy appeared earlier and were more evident in red than in white muscle. Degenerated fibers frequently contained normal and altered (ghost-like) nuclei, which suggested repair by satellite cells. Apoptotic nuclei were seen in both muscles. There were no differences in the ultrastructural alterations associated with apoptosis in red and white muscles at any stage after denervation. Apoptosis was also confirmed by the comet assay, which showed the presence of many apoptotic cells, but revealed no significant difference between the two muscle types. Overall, these results suggest that the long-term denervation of red and white skeletal muscles causes atrophy and apoptosis, with the latter probably being responsible for the muscle fiber loss after long-term denervation.