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Metformin promotes microglial cells to facilitate myelin debris clearance and accelerate nerve repairment after spinal cord injury

Abstract

Spinal cord injury (SCI) is one kind of severe trauma for central nervous system. Myelin debris clearance and axon regeneration are essential for nerve regeneration after SCI. Metformin, a glucose-lowering drug, has been demonstrated to promote the locomotor functional recovery after SCI. In this study, we investigated the role and molecular mechanism of metformin on myelin preservation in a rat SCI model. SCI was induced in rats by compression at T9 level using a vascular clip. We showed that administration of metformin (50 mg·kg−1·d−1, ip) for 28 days significantly improved locomotor function in SCI rats. Metformin also ameliorated SCI-induced neuronal apoptosis and promoted axon regeneration in the spinal cord. Using co-immunofluorescence of IBa-1 and MBP, and luxol fasting blue (LFB) staining, we demonstrated that metformin promoted the transformation of M1 to M2 phenotype polarization of microglial cells, then greatly facilitated myelin debris clearance and protected the myelin in SCI rats. Furthermore, metformin ameliorated SCI-induced blockade of autophagic flux in the spinal cord, and enhanced the fusion of autophagosome and lysosome by inhibiting the AMPK-mTOR signaling pathway. Moreover, metformin significantly attenuated inflammatory responses in the spinal cord. In LPS-treated BV2 cells, pretreatment with metformin (2 mM) significantly enhanced autophagy level, suppressed inflammation and cell apoptosis. The protective effects were blocked in the presence of an autophagy inhibitor 3-methyladenine (3-MA, 5 mM), suggesting that the effect of metformin on autophagy in microglial cells is essential for the myelin preservation during nerve recovery. This study reveals a novel therapeutic effect of metformin in SCI recovery by regulating the activation of microglial cells and enhancing its autophagy level.

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Fig. 1: Experimental protocol of Met treatment for SCI rats and BV2 cells.
Fig. 2: Metformin improves locomotor functional recovery after SCI.
Fig. 3: Metformin relieves neuronal apoptosis following SCI.
Fig. 4: Metformin promotes axon regeneration after SCI.
Fig. 5: Metformin enhances microglial cells to phagocytose myelin debris.
Fig. 6: Metformin ameliorates SCI-induced blockade of autophagic flux in microglial cells.
Fig. 7: Metformin ameliorates inflammatory level in spinal cord following SCI.
Fig. 8: 3-MA treatment reverses the protective effect of metformin on BV2 cells.
Fig. 9: Metformin promotes microglial cells to facilitate myelin debris clearance and accelerate nerve repairment after SCI.

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Acknowledgements

This study was partially supported by National Natural Science Foundation of China (81801233 to YQW, 81802251 to KX), Zhejiang Provincial Natural Science Foundation (LQ18H090011 to YQW and LQ18H150003 to KX), Research Unit of Research and Clinical Translation of Cell Growth Factors and Diseases, Chinese Academy of Medical Science (2019RU010), and Graduate Student Innovation Foundation of Wenzhou University (316202001029).

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YQW, JX (Jun Xiong) and ZLH performed research and wrote the manuscript. YY, BNW, JYX, MW, SSZ, SFC, JXZ and KX performed researched. HYZ participated in data analyses and manuscript writing. JX (Jian Xiao) conceived the project, designed the experiments, and wrote the manuscript. All authors have approved the final version of the manuscript.

Corresponding authors

Correspondence to Hong-yu Zhang or Jian Xiao.

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The authors declare no competing interests.

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Wu, Yq., Xiong, J., He, Zl. et al. Metformin promotes microglial cells to facilitate myelin debris clearance and accelerate nerve repairment after spinal cord injury. Acta Pharmacol Sin (2021). https://doi.org/10.1038/s41401-021-00759-5

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Keywords

  • spinal cord injury
  • metformin
  • microglial cells
  • autophagy
  • nerve regeneration
  • 3-methyladenine

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