The influence of blood glucose fluctuation on hippocampal tau protein phosphorylation of diabetic rats

Objective To investigate the influence of blood glucose fluctuation on ser202 phosphorylation sites of tau protein(p-Tau) in hippocampus of diabetic rats; to explore the possible mechanism of blood glucose fluctuation impacting on tau protein hyperphosphorylation. Methods Healthy male Sprague Dawley rats were randomly divided into normal control group (NC group) and diabetes group. After diabetic rats model was established, all the diabetic rats were randomly divided into diabetic continuous hyperglycemia group (DC group) and diabetic blood glucose fluctuant group (DF group). Rats in DF group were given glucose solution intraperitoneal injection twice at regular time everyday. 30 minutes after each intraperitoneal injection, insulin subcutaneously injections were given. Rats in the NC group and DC groups were given the same volume of saline subcutaneous injection. Specimens were collected in 8 weeks, the levels of p-Tau and total tau in rat hippocampus were detected by immunohistochemical staining and Western blotting. The immunoreactive positive products were analyzed by image analysis system. Glycogen synthase kinase-3β(GSK-3β) mRNA was detected by realtime PCR. Results (1) Blood glucose fluctuation of rats in DC and DF group were greater than NC group. And the mean blood glucose, standard deviation of mean blood glucose (SDBG), and large amplitude of glycemic excursion (LAGE) levels were increased significantly compared to NC group, the difference has statistical significance (all P 0.05). (2) Compared with NC group, the hippocampal p-Tau level of DC group and DF group were increased (P<0.05); Compared with DC group, the hippocampal p-Tau expression of DF group was increased (P<0.05). Compared with DC group, a higher hippocampal GSK-3β mRNA level was found in DF group (P<0.05). Conclusions On the basis of diabetes animal model, giving glucose solution intraperitoneal injection and insulin subcutaneously injection 30 minutes later twice at regular time everyday could establish experimental model of diabetic blood glucose fluctuation. Blood glucose fluctuation may aggravate the diabetic rats hippocampal p-Tau. The possible mechanism seems to be an up regulation of the GSK-3β. (Chin J Endocrinol Metab, 2017, 33: 776-780) Key words: Blood glucose fluctuation; Diabetes mellitus; Hippocampus; Tau protein phosphorylation