MeCP2 plays an analgesic role in pain transmission through regulating CREB / miR-132 pathway

Abstract

Background: The Methyl CpG binding protein 2 gene (MeCP2 gene) encodes a critical transcriptional repressor and is widely expressed in mammalian neurons. MeCP2 plays a critical role in neuronal differentiation, neural development, and synaptic plasticity. Mutations and duplications of the human MECP2 gene lead to severe neurodevelopmental disorders, such as Rett syndrome and autism. In this study we investigate the role of MeCP2 in the spinal cord and found that MeCP2 plays an important role as an analgesic mediator in pain circuitry.

Findings: Experiments using MeCP2 transgenic mice showed that overexpression of MeCP2 weakens both acute mechanical pain and thermal pain, suggesting an analgesic role of MeCP2 in acute pain transduction. We found that through p-CREB/miR-132 signaling cascade is involved in MeCP2-mediated pain transduction. We also examined the role of MeCP2 in chronic pain formation using spared nerve injury (SNI) model. Strikingly, we found that development of neuropathic pain attenuates in MeCP2 transgenic mice comparing to wild type (WT) mice.

Conclusions: Our study shows that MeCP2 plays an analgesic role in both acute pain transduction and chronic pain formation through regulating CREB-miR-132 pathway. This work provides a potential therapeutic target for neural pathologic pain, and also sheds new lights on the abnormal sensory mechanisms associated with autism spectrum orders.

Figure 1

MeCP2 overexpression attenuates both mechanical and thermal pain sensitivity. A, Comparison of paw withdrawal threshold to mechanical stimulation between WT mice and MeCP2 overexpression mice (OE). 7 mice were tested in each group. B, Comparison of pain sensitivity to thermal stimulation between WT mice and MeCP2 overexpression mice (OE). n = 9 for WT and OE respectively. All values are represented as means ± SEM. *p < 0.05, **p < 0.01, ***p < 0.001.

Figure 2

MeCP2 weakens pain sensitivity through central mechanism. A, The location of MeCP2 expression in DRG and spinal cord dorsal horn (DH). In DRG, all IB4 (red) positive neurons and NF200 (blue) positive neurons have MeCP2 (green) expression (upper panel). All TRPV1 (blue) positive neurons have MeCP2 (green) expression (mid panel). In DH, MeCP2 expressed more intense than other area of spinal cord (lower panel). Representative pictures show single focal plane. Scale bars, 50 μm. B, In DRG, MeCP2 protein level was downregulated after SNI. C, Relative protein levels of MeCP2 expression in DRG. D, In spinal cord, MeCP2 protein level was elevated by 3d to 7d after SNI, and then downregulated. E, Relative protein level of MeCP2 expression in spinal cord. Bars are relative protein level to control without SNI. Error bars are SEM. *p < 0.05 (t test).

Figure 3

The role of MeCP2 in pain suppression. In WT mice, hindpaws after SNI showed significant reduction in withdrawal threshold compared to contralateral hindpaws in mechanical von Frey test. But MeCP2 overexpression mice only had a slight downgrade in paw withdrawal threshold and their withdrawal threshold after SNI shows no diffierence compared with WT contralateral. 9 mice were tested in each group. All values are represented as means ± SEM. *p < 0.05, **p < 0.01, ***p < 0.001.

Figure 4

Change of MeCP2 transcript, miR-132 and p-CREB after SNI. A, MeCP2 transcript did not change significantly after SNI. B, miR-132 was downregulated by 3d to 7d after SNI. RNAs were collected from lumbar spinal cord L4-L6 lysates of WT mice. Levels of MeCP2 transcript and miR-132 were analyzed by qPCR. C, p-CREB(Ser133) was elevated by 3 days after SNI and then fell off. D, Relative protein level of p-CREB expression in spinal cord. Bars are relative protein level to control without SNI. Error bars are SEM. *p < 0.05 , **p < 0.01 (t test).