[Mechanism of "olfactory three needles" in regulating microglia and promoting remyelination in vascular dementia rats].

OBJECTIVE

To observe the effects of "olfactory three needles" on cognition, learning and memory abilities, as well as hippocampal microglia (MG) phagocytic activity in vascular dementia (VD) rats, and explore the mechanisms of acupuncture in regulating MG activation and improving remyelination, so as to ameliorate VD.

METHODS

Among 38 SD rats meeting experimental requirements, 9 rats were randomly assigned to a sham-operation group, and the remaining rats underwent permanent bilateral common carotid artery ligation to establish VD model. Eighteen successfully modeled rats were randomly divided into a model group and an electroacupuncture (EA) group, with 9 rats in each one. In the EA group, EA was performed at "olfactory three needles" ("Yintang" [GV24] and bilateral "Yingxiang" [LI20]), at disperse-dense wave, the frequency of 2 Hz/15 Hz and the current intensity of 1 mA, for 15 min per intervention, once daily. One course was composed of 7 days, and 2 courses were required, with the interval of 2 days. The novel object recognition test was employed to assess the cognition of rats, and the Morris water maze was adopted to observe learning and memory abilities. Luxol fast blue (LFB) staining was performed to evaluate myelin sheath loss in the hippocampus, the Western blot was used to detect the protein expression of triggering receptor expressed on myeloid cells-2 (TREM2) and proteolipid protein (PLP) in the hippocampus; and the immunofluorescence staining was used to detect the positive expression of PLP, sex determining region Y-box 10 (SOX10), ionized calcium binding adaptor molecule 1 (Iba1) TREM2 and Iba1 lysosome-associated membrane protein 1 (LAMP1) in the hippocampus.

RESULTS

Compared with the sham-operation group, the rats in the model group exhibited the prolonged escape latency on day 3 and 4 (<0.05, <0.01), the increase of the total distance traveling (<0.01) and the decrease of the recognition index (RI) and platform crossing frequency (<0.01). Compared with the model group, the rats in the EA group showed the shortened escape latency on day 3 and 4 (<0.05), the decrease of total distance traveling (<0.01) and the increase of RI and platform crossing frequency (<0.05, <0.01). When compared with the sham-operation group, the rats of the model group presented uneven staining, sparse arrangement of myelin sheath fibers, unclear contours, and prominent vacuole-like changes in the hippocampal CA1 region. When compared with the model group, the EA group showed more dense staining, the increase of myelin sheath fibers with more orderly alignment, and fewer vacuolar changes in the hippocampal CA1 region. Compared with the sham-operation group, the model group exhibited the increase of TREM2 protein expression and the decrease of PLP protein expression in the hippocampus (<0.01), whereas the EA group showed the up-regulation of TREM2 and PLP protein expression when compared with the model group (<0.01, <0.05). The positive expression of the hippocampal PLP, SOX10, and Iba1LAMP1 in the model group was reduced in comparison with the sham-operation group (<0.05, <0.01), and the positive expression of Iba1 TREM2 was elevated (<0.05). In the EA group, the positive expression of PLP, SOX10, Iba1TREM2, and Iba1 LAMP1 was higher compared with that in the model group (<0.05, <0.01).

CONCLUSION

"Olfactory three needles" can improve the learning and memory, and cognitive functions of VD rats, and its mechanism may be associated with the up-regulation of TREM2 and LAMP1 to adjust MG phagocytic activity and intracellular degradation, and promote remyelination.