Experiment Studies On Effects Of Starvation On Myocardium Autophagy Of Rats

Objectives The body is in the state of inefficiency of nutrients and energy during total starvation condition. Autophagy is an important biological phenomenon that generally exists in eukaryotic cells and involved widely in various physiological and pathological processes. One of its main functions is to degrade cytoplasm components and recycle the degradation products, in order to maintain the cellular homeostasis. Our study intends to investigate the effects of starvation on the changes of myocardium autophagy of rats, to explore the mechanism of starvation stress on autophagy phenomenon.Methods 105 healthy male SD rats, aged 3 months, weighing 330~370g, were randomly divided into two groups: control group(group C, n=15) and starvation model group(group S, n=90). And group S was randomly divided into six subgroups(n=15): starvation one-day subgroup(subgroup S1), starvation two-day subgroup(subgroup S2) and starvation three-day subgroup(subgroup S3), starvation five-day subgroup(subgroup S5), starvation seven-day subgroup(subgroup S7), and starvation nine-day subgroup(subgroup S9). During starvation no food was supplied but water was freely provided. After starvation, the myocardial tissue for ultrastructural observation was fixed by 2% paraformaldehyde-2.5% glutaraldehyde phosphate buffer and was detected by transmission electron microscope. The other myocardial tissue was fixed by 4% paraformaldehyde phosphate buffer and detected by HE staining. The expression of autophagy related genes LC3 and Beclin 1 was detected by Immunohistochemistry and Western blot.Results 1 HE staining: the histomorphology was normal in group C; compared with group C, the myocardial tissue showed different degrees of injury in group S, and as the time extension of starvation, pathological changes aggravated. 2 Transmission electron microscopy: the myocardial cell ultrastructure was normal in group C; the mitochondria showed different degrees of injury in group S, and the pathological changes were gradually aggravated with phagophone and autophagosome structure appeared as the prolonging of starvation. 3 Immunohistochemistry: compared with group C, the expressions of LC3 and Beclin in myocardium of rats were upregulated in all subgroups of group S with statistical significances(P<0.05 or P<0.01); there were also statistically different in expression of LC3 and Beclin 1 among the subgroups(P<0.05 or P<0.01). The expression of LC3 and Beclin 1 continuously increased in subgroup S1 and S2, peaked in S2, and then decreased gradually; the expression of LC3 and Beclin 1 raised again in subgroup S7 and S9. 4 Western blot: compared with group C, the expressions of LC3 and Beclin in myocardium of rats were upregulated in all subgroups of group S with statistical significances(P<0.05 or P<0.01); the expressions of LC3 and Beclin 1 were also statistically different among the subgroups,(P<0.05 or P<0.01). The expressions of LC3 and Beclin 1 increased continuously in subgroup S1 and S2, peaked in subgroup S2, then decreased gradually and raised again afterword in subgroup S7 and S9.Conclusions The expression of LC3 and Beclin 1 is upregulated in myocardium tissue of rats under starvation. The peak levels of the expression of LC3 and Beclin 1 were found in the 2nd day of starvation, with the autophagic activity enhanced. As the prolonging of starvation, the expression of LC3 and Beclin 1 upregulates again with significant increase of the number of autophagosomes in rat myocardium.