Translocator Protein (TSPO) Alleviates Neuropathic Pain by Activating Spinal Autophagy and Nuclear SIRT1/PGC-1α Signaling in a Rat L5 SNL Model

Can Hao &ast;, Bingjie Ma &ast;, Nan Gao, Tian Jin, Xiaoming Liu Pain Management Center, Shanghai Xinhua Hospital, School of Medicine, Shanghai Jiaotong University, Shanghai, 210092, People’s Republic of China&ast;These authors contributed equally to this workCorrespondence: Xiaoming Liu, Pain Management Center, Shanghai Xinhua Hospital, School of Medicine, Shanghai Jiaotong University, 1665# Kongjiang Road, Shanghai, 210092, People’s Republic of China, Tel +86-17721213706, Fax +86-21-25078707, Email brightlxm@gmail.comPurpose: Recent studies showed promotion of astrocyte autophagy in the spinal cord would provide analgesic effects. Silent information regulator T1 (SIRT1) and α subunit of peroxisome proliferator-activated receptor-γ coactivator-1 (PGC-1α) are two master regulators of endogenous antioxidant defense and mitochondrial biogenesis. They play vital roles in both autophagy and neuropathic pain (NP). Our previous study showed that TSPO agonist Ro5-4864 elicited potent analgesic effects against NP, but the mechanisms remain unclear. This study aims to investigate the effects of TSPO agonist Ro5-4864 on autophagy and nuclear SIRT1/PGC-1α signaling in spinal dorsal horn.Methods: A rat model of L5 spinal nerve ligation (SNL) was adopted. Rats were randomly assigned to the Sham group, the SNL group, the Ro (TSPO agonist Ro5-4864) group and the Ro+3-MA group. The behavior assessments were conducted at baseline, on Day 1, 3, 7 and 14 after SNL. The autophagy-related proteins (ATG7, Beclin1, LC3, and P62) in spinal dorsal horn were assayed and the nuclear SIRT1/PGC-1α and downstream factors were analyzed.Results: Ro5-4864 alleviated the mechanical allodynia induced by SNL (P < 0.01 vs the SNL group), which could be totally abrogated by autophagy inhibitor 3-MA (P < 0.01 vs the Ro group). SNL induced elevated ATG7 (P < 0.01), Beclin1 (P < 0.01) and LC3-II/LC3-I (P < 0.01) contents and P62 accumulation (P < 0.01) on Day 7 and Day 14, which suggested an autophagy flux impairment. Ro5-4864 augmented ATG7 (P < 0.01), Beclin1 (P < 0.01) and LC3-II/LC3-I (P < 0.05) with decreased P62 (P < 0.01), which indicated a more fluent autophagic process. These effects were also totally abrogated by 3-MA (P < 0.01). Furthermore, Ro5-4864 activated the spinal nuclear SIRT1/PGC-1α signaling pathway.Conclusion: TSPO improved both autophagy impairment and mitochondrial biogenesis, which may provide a new strategy for the treatment of NP.Keywords: translocator protein, TSPO, neuropathic pain, autophagy, silent information regulator T1, SIRT1, α subunit of peroxisome proliferator-activated receptor-γ coactivator-1, PGC-1&#x03B1