Effects Of Starvation Time Phases On Autophagy In Cerebral Cortex Of Rats

Objectives The body is in a state of nutrients and energy insufficiency when under starvation. Autophagy is a fundamental biology process, and one of its basic fuctions is to make cells digest their own cytoplasmic components in order to maintain survival during starvation and other forms of stresses. For the whole body there is a complex integral regulation of metabolism in response to starvation, and autophagy itself is also a dynamic process of continuous changing. As nerve center, the brain occupys a special position while the body involves in nutrient withdrawl. Our study is to investigate the effects of starvation time phases on autophagy in cerebral cortex of rats through the point of autophagosomes.Methods One hundred and five healthy male SD rats, aged 3 months, weighing 330~370g, were randomly divided into three groups: control group(group C, n=15), short-term starvation group(group SS, n=45) and long-term starvation group(group LS, n=45); group LS was randomly divided into three subgroups(n=15): starvation one-day subgroup(subgroup S1), two-day subgroup(subgroup S2) and three-day subgroup(subgroup S3), and group LS was randomly divided into three subgroups(n=15): starvation five-day subgroup(subgroup S5), seven-day subgroup(subgroup S7), and nineday subgroup(subgroup S9). During starvation rats were deprived of food but had free access to drinking water. After starvation processing, the pathological changes in cerebral cortex were examined by HE staining, the ultrastructure changes were detected by transmission electron microscopy, and the expression levels of autophagy related genes LC3 and Beclin 1 were determined by Immunohistochemistry(IHC) and Western blot.Results 1 HE staining: the histomorphology structure was intact in group C; compared with group C, no obvious pathological changes were observed in group SS; but there were visible pathological changes on some neuron in group LS, and as starvation is prolonged, the changes were aggravated. 2 Transmission electron microscopy: the neuron ultrastructure was intact in group C; some mitochondria appeared mild edema in group SS; and in group LS, the capillary endothelial cells presented swollen, the basement membrane were broken, and the mitochondria showed different degrees of damage and autophagosomes were found. 3 Immunohistochemistry: compared with group C, in groupSS, there were no significant differences in the expression of LC3 and Beclin 1 in cerebral cortex of rats both in subgroup S1 and subgroup S2(P>0.05), while in subgroup S3 the expression was up-regulated(P<0.05), and in group LS the expression was significantly up-regulated(P<0.01); compared with group SS, the expression of LC3 and Beclin 1 was significantly up-regulated in group LS(P<0.01). Among the subgroups, comparing subgroup S1 with S2, there were no significant differences in the expression of LC3 and Beclin 1(P>0.05); while compared with subgroup S1 and S2, the expression was up-regulated in subgroup S3(P<0.05); and the expression was gradually up-regulated in subgroup S3, S5 and S7(P<0.01); compared with subgroup S7, in subgroup S9 the expresstion of LC3 was up-regulated(P<0.01), but no significant change was found in the expression of Beclin 1(P>0.05). 4 Western blot: compared with group C, in group SS, there were no significant differences in the expression of LC3-Ⅱ and Beclin 1 in cerebral cortex of rats both in subgroup S1 and subgroup S2(P>0.05), while in subgroup S3 the expression was up-regulated(P<0.01), and in group LS the expression was significantly up-regulated(P<0.01); compared with group SS, the expression of LC3-Ⅱ and Beclin 1 was significantly up-regulated in group LS(P<0.01). Among the subgroups, comparing subgroup S1 with S2, there were no significant differences in the expression of LC3-Ⅱ and Beclin 1(P>0.05); while compared with subgroup S1 and S2, the expression was up-regulated in subgroup S3(P<0.01); and the expression was gradually up-regulated in subgroup S3, S5 and S7(P<0.01); compared with subgroup S7, in subgroup S9 the expresstion of LC3-Ⅱ was up-regulated(P<0.01), but no significant change was found in the expression of Beclin 1(P>0.05).Conclusions The autophagy levels in cerebral cortex of rats do not change obviously during short-term starvation(<2 days). As starvation is prolonged, the number of autophagosomes is increased, and for rats under long-term starvation the number of autophagosomes is significantly increased, which may be related to the dysfunction of autophagy.