Study on the Mechanism of Zuogui Jiangtang Jieyu Decoction Improving Hippocampal Mitochondrial Dynamics in Diabetic Rats with Depression by Regulating AMPK/MFF/DRP1 Signaling

OBJECTIVE  To explore the mechanism of Zuogui Jiangtang Jieyu decoction on the mitochondrial dynamics of hippocampal neurons in diabetic rats with depression.

METHODS  The male SD rats were fed with high-fat diet for 4 weeks, and then injected with streptozotocin through tail vein. According to the level of fasting blood glucose, diabetic rats were definited. Then they were subjected to 28 d of chronic mild unpredictable stress to establish the model of diabetes complicated with depression. The model rats were randomly divided into model group, AMPK inhibitor group, Zuogui Jiangtang Jieyu decoction high and low dose groups. The equal number of healthy SD rats were set as the normal group. After 4 weeks of drug intervention, fasting blood glucose levels were measured by blood glucose test strips, the forced swimming test was used to assess the animals' depressive-like behavior, and the Morris water maze was employed to evaluate the animals' learning and memory abilities. Hippocampal neurons and intracellular mitochondrial morphology were detected by Nissl staining and electron microscopy. The level of ATP and mitochondrial respiratory chain complex I–V were detected by colorimetric methods. Mitochondrial dynamics related proteins MFN1, MFN2 and DRP1 were detected by immunofluorescence. The expression of AMPKα, MFN2, MFF_ser173, and DRP1 were detected by Western blotting.

RESULTS  Compared with the normal group, the model group rats showed significant hyperglycemic and depressive behavior. The content of mitochondrial respiratory chain complexes I–V and energy product ATP in the hippocampus of rats were significantly decreased, and the expression of MFN1 and MFN2 were decreased. The expression of AMPKα, MFF_ser173, and DRP1 were significantly increased. Compared with the model group, AMPK inhibitors significantly reduced the expression of AMPKα, MFF_ser173 and DRP1. The mitochondrial oxidative phosphorylation function were improved, and the content of ATP was increased. But there was no significant effect on MFN1 and MFN2. Zuogui Jiangtang Jieyu decoction significantly reduced the peripheral blood glucose of diabetic rats with depression. The depression like behavior and cognitive function were improved. The morphology of hippocampus mitochondria were improved. The contents of neuronal mitochondrial respiratory chain complexes I-V and ATP were increased. The expression of MFN1 and MFN2 were increased and the expression of AMPKα, MFF_ser173, DRP1 were reduced.

CONCLUSION  Zuogui Jiangtang Jieyu decoction can inhibit neuronal mitochondrial division by regulating AMPK/MFF/DRP1 signaling, improve mitochondrial dynamics, increase the oxidative phosphorylation levels and energy metabolism.