Activation of TRPV1 receptor facilitates myelin repair following demyelination via the regulation of microglial function.

The transient receptor potential vanilloid 1 (TRPV1) is a non-selective cation channel that is activated by capsaicin (CAP), the main component of chili pepper. Despite studies in several neurological diseases, the role of TRPV1 in demyelinating diseases remains unknown. Herein, we reported that TRPV1 expression was increased within the corpus callosum during demyelination in a cuprizone (CPZ)-induced demyelination mouse model. TRPV1 deficiency exacerbated motor coordinative dysfunction and demyelination in CPZ-treated mice, whereas the TRPV1 agonist CAP improved the behavioral performance and facilitated remyelination. TRPV1 was predominantly expressed in Iba1+ microglia/macrophages in human brain sections of multiple sclerosis patients and mouse corpus callosum under demyelinating conditions. TRPV1 deficiency decreased microglial recruitment to the corpus callosum, with an associated increase in the accumulation of myelin debris. Conversely, the activation of TRPV1 by CAP enhanced the recruitment of microglia to the corpus callosum and potentiated myelin debris clearance. Using real-time live imaging we confirmed an increased phagocytic function of microglia following CAP treatment. In addition, the expression of the scavenger receptor CD36 was increased, and that of the glycolysis regulators Hif1a and Hk2 was decreased. We conclude that TRPV1 is an important regulator of microglial function in the context of demyelination and may serve as a promising therapeutic target for demyelinating diseases such as multiple sclerosis.

[Electroacupuncture promotes regeneration and repair of myelin sheath of corpus callosum in demyelination mice].

OBJECTIVE: To explore the mechanism of electroacupuncture (EA) in accelerating the aggregation of microglia and promoting the remyelination at the location of demyelination. METHODS: C57BL/6 mice were randomly divided into 4 groups: normal, control, model (LPC) and LPC＋EA. The demyelination model was established by microinjection of Lysolecithin (LPC, 1 µL) into the left corpus callosum. EA (2 Hz/15 Hz, 2－4 mA) was applied to "Baihui"(GV20)and "Zhiyang"(GV9)for 30 min，once daily for 3 days, then, once every other day for 18 days. Immuno-fluorescence staining was used to observe the expression of myelin basic protein (MBP) and Axl tyrosine kinase receptor (Axl), Iba1 and numbers of Olig2-positive oligodendrocytes in the corpus callosum. Western blot was employed to detect the expression of MBP in the corpus callosum, and Oil Red O staining was used to observe changes of number of myelin pieces. RESULTS: Following modeling, the expression levels of MBP on day 5 and 10 after modeling were significantly decreased (P<0.05, P<0.01), Iba1 expression and Olig2-positive oligodendrocyte numbers on day 10 apparently increased (P<0.001, P<0.01). On day 21 after modeling, the levels of the above mentioned indexes returned to normal. After EA intervention, the levels of MBP expression on day 5 and 10, Axl, Iba1 protein expression and Olig2-positive oligodendrocyte numbers on day 5 were markedly increased (P<0.001，P<0.01，P<0.05), while Iba1 expression on day 10 was considerably decreased in comparison with the model group (P<0.01)．Oil Red O staining showed that on day 5 after modeling, the number of red lipid droplets were obviously increased in the corpus callosum tissue on the injection side, and apparently reduced in the EA group, suggesting a clearance of the accumulated myelin fragments by EA. CONCLUSION: EA intervention may reduce myelin debris and promote the aggregation of microglial cells and oligodendrocytes to the injured site, accelerate the myelin regeneration and up-regulate the expression of MBP and Axl of corpus callosum in demyelination mice.