[Protective effect and mechanism of Zuogui Jiangtang Jieyu Formula on damage to hippocampal synaptic microenvironment in rats with diabetes-related depression based on microglia-neuron crosstalk signal CD300f/TLR4].

Abstract

This study aims to reveal the protective effect and mechanism of Zuogui Jiangtang Jieyu Formula on the damage to hippo-campal synaptic microenvironment in rats with diabetes-related depression(DD) via regulating microglia immune receptor molecule-like family member f(CD300f)/Toll-like receptor 4(TLR4) signal. Firstly, the model of DD rats was established by a two-week high-fat diet+STZ injection+chronic mild and unpredictable stress plus isolation for 28 days. The rats were randomly divided into normal group, model group, CD300f blocker(CLM1, 2 μg·kg~(-1)) group, CD300f agonist(Fcγ, 5 μg·kg~(-1)) group, positive drug(0.18 g·kg~(-1) metformin+1.8 mg·kg~(-1) fluoxetine) group, and high-dose and low-dose(20.52 and 10.26 g·kg~(-1)) Zuogui Jiangtang Jieyu Formula groups. Depression-like behavior of rats was evaluated by open field and forced swimming experiments. The levels of blood glucose and insulin were detected by biochemical analysis. The levels of tumor necrosis factor α(TNF-α), interleukin-1β(IL-1β), indoleamine 2, 3-dioxygenase(IDO), 5-hydroxytryptamine(5-HT), and dopamine(DA) in the hippocampus were detected by enzyme-linked immunosorbent assay. The changes in the synaptic ultrastructure in hippocampal neurons of rats were observed by transmission electron microscopy. The protein expressions of CD300f, TLR4, synaptophysin(SYN), and postsynaptic density protein 95(PSD-95) in microglial cells of the hippocampus were detected by immunofluorescence and Western blot. The results indicated that compared with that in the normal group, the total movement distance in open field experiments was reduced in the model group, and the immobility time in forced swimming experiments increased, with an elevated insulin level in serum, as well as TNF-α, IL-1β, and IDO levels in the hippocampus. The 5-HT and DA levels in the hippocampus were reduced. In addition, the CD300f expression was down-regulated in microglial cells of the hippocampus, and the TLR4 expression was up-regulated. Moreover, the expression of synapse-related proteins SYN and PSD-95 in hippocampal neurons decreased, and the synaptic ultrastructure of hippocampal neurons was significantly damaged. Compared with the model group, the CD300f blocker and agonist aggravated and alleviated the above abnormal changes, respectively. High-dose and low-dose Zuogui Jiangtang Jieyu Formula could significantly improve the above depression-like beha-vior in rats, inhibit the abnormal increase of TNF-α, IL-1β, and IDO and the decrease of 5-HT and DA, effectively increase the expression of CD300f in microglial cells, and decrease the expression of TLR4. They could up-regulate the protein expression of presyna-ptic membrane SYN and postsynaptic membrane PSD-95 in hippocampal neurons and finally improve the damage to the hippocampal synaptic microenvironment. In conclusion, this research confirmed that Zuogui Jiangtang Jieyu Formula effectively alleviated the depression-like behavior and inhibited inflammatory activation of microglial cells in the hippocampus of rats with DD, and the mechanism might be related to the regulation of CD300f/TLR4 signal to alleviate the damage to hippocampal synaptic microenvironment.