Bcl-2/Bax protein expression in heart, slow-twitch and fast-twitch muscles in young rats growing under chronic hypoxia conditions.
We have studied the magnitude of apoptosis in heart, slow-twitch skeletal muscle (soleus) and fast-twitch skeletal muscle (gastrocnemius) of rats exposed to 3 weeks in vivo chronic hypoxia. Apoptosis was evaluated biochemically by DNA laddering and by TUNEL and annexin V-staining. The expression of Bax and Bcl-2 proteins was determined by immunohistochemistry and Western blotting. Western blot analysis revealed only a slight difference in Bax expression among the different tissues under normoxic and hypoxic conditions; therefore we can consider that Bax protein is constitutively expressed in muscle tissues. However a singular pattern of Bcl-2 expression was observed among the different tissues under normoxic conditions. Bcl-2 protein was more expressed in fast-twitch glycolytic muscles than in slow-twitch or oxidative muscles with a highest value found in gastrocnemius (4926 +/- 280 AU), followed by soleus (2138 +/- 200 AU) and a very low expression was displayed in the heart muscle (543 +/- 50 AU). After exposure to hypoxia for 21 days (10% O2), Bcl-2 protein expression markedly increased, (44%) in gastrocnemius, (323%) in soleus and (1178%) in heart, with significant differences (p < 0.05 student t-test), reaching a similar threshold of expression in both types of muscles. Furthermore, no sign of apoptosis was detected by TUNEL assay, annexin V-binding assay or DNA electrophoresis analysis. The latter suggested some indiscriminate fragmentations of DNA without apoptosis. In conclusion, we postulate that these protein modifications could represent a adaptative mechanism allowing a better protection against the lack of oxygen in oxidative muscles by preventing apoptosis.
Riva
C
C
Fondamental and Applied Bioenergetics Laboratory, Joseph Fourier University, Grenoble, France. catherine.riva-lavieille@ujf-grenoble.fr
Chevrier
C
C
Pasqual
N
N
Saks
V
V
Rossi
A
A
D000818:Animals; D017209:Apoptosis; D015153:Blotting, Western; D002467:Cell Nucleus / Q000378:metabolism; D053938:DNA Fragmentation; D000860:Hypoxia; D007150:Immunohistochemistry; D020287:In Situ Nick-End Labeling; D008297:Male; D018656:Muscle Fibers, Fast-Twitch / Q000378:metabolism*; D018657:Muscle Fibers, Slow-Twitch / Q000378:metabolism*; D018482:Muscle, Skeletal / Q000378:metabolism; D009206:Myocardium / Q000378:metabolism*; D011518:Proto-Oncogene Proteins / Q000096:biosynthesis*; D019253:Proto-Oncogene Proteins c-bcl-2 / Q000096:biosynthesis*; D051381:Rats; D017208:Rats, Wistar; D013997:Time Factors; D014018:Tissue Distribution; D051028:bcl-2-Associated X Protein
C494828:Bax protein, rat; D011518:Proto-Oncogene Proteins; D019253:Proto-Oncogene Proteins c-bcl-2; D051028:bcl-2-Associated X Protein