Myocyte apoptosis and Bcl-2 and Bax expression changes in rat atrophic gastrocnemius muscle after denervation

Abstract

Objective To study and analysis changes of apoptosis and expression pattern of Bcl-2 and Bax proteins and their potential role in skeletal muscle denervation atrophy. Methods Gastrocnemius muscle denervation was created in rats. Forty-two female SD rats weighed 200 to 250 g were randomly divided into two groups, 6 for normal control group and 36 for experimental group which were further randomly divided into 6 groups based on different intervals for tissue harvesting. The changes of apoptosis and expression of Bcl-2 and Bax proteins in atrophic gastrocnemius muscles were detected by using Tunel method and immunohistochemical staining at different intervals after denervation. The muscle wet weight ratio and cross-sectional aera of muscle fibers were measured. The ultrastrictiral changes of muscle fiber were also observed. Results There was a rapid decrease and statistically significant difference in the muscle wet weight ratio during the first 4 weeks as well as the time from the 10th week to the 12th week after denervation, but a slow decrease and no statistically significant difference ( P ＞ 0.05) during the time from the 4th week to the 10th week as well as the time from the 12th to the 16th week. Bcl-2 was modestly increased only in the early period after denervation and peaked at the 4th week while Bax was dramatically increased and peaked at the 2nd and 12th week repectively. The Bcl-2/Bax ratio had significantly decreased after denervation and it was smaller than 1 except for the group of 8 week denervation ( 1.065 ± 0.165) and the normal group ( 1.522 ± 0.215). The apoptotic ratio peaked at the 4th and 12th week after denervation and the changes was similar to the apoptosis and over expression of Bax had an important role in regulating inreversible Bax. Conclusion The process of denervation gastrocnemius atrophy has shown four stages. Apoptosis and Bax over expression play an important in atrophy of denervated skeletal muscle. These findings suggest that interventions targeting Bax gene to inhibit its expression may delay skeletal muscle denervation atrophy. Key words: Muscle,skeletal; Muscular atrophy; Apoptosis