AdipoRon engages microglia to analgesia through the AdipoR1-AMPK pathway in SNI mice

Background: Microglia-associated neuroinflammation plays a crucial role in the initiation and development of neuropathic pain (NeuP). AdipoRon is an analog of adiponectin, which can activate the adiponectin receptors and exhibit anti-inflammatory property in various diseases. Adenosine monophosphate-activated protein kinase (AMPK) is the main downstream target of adiponectin receptor 1 (AdipoR1). Activation of AdipoR1 promotes the conversion of AMPK to phosphorylated AMPK (p-AMPK). The AdipoR1/AMPK pathway is involved in the regulation of inflammation. And therapies targeting this pathway are beneficial for a variety of diseases. This study aimed to investigate whether AdipoRon could alleviate NeuP by inhibiting the expression of microglia-derived tumor necrosis factor-alpha (TNF-α) through the AdipoR1/AMPK pathway. Methods: : In vivo, the spared nerve injury (SNI) model was established in mice to simulate NeuP. Using the Von Frey test to detect the effect of AdipoRon on mechanical paw withdrawal threshold. Western Blot was performed to detected the effects of AdipoRon on the expression of AdipoR1, AMPK, p-AMPK and TNF-α. Immunofluorescence was performed to observed the effects of AdipoRon on spinal microglia. In vitro, using lipopolysaccharide (LPS) to induce inflammatory responses in BV2 cells. The effect of AdipoRon on cell proliferation was detected by CCK-8. Using qPCR to examined the effects of AdipoRon on the expression of TNF-α and polarization markers in LPS-treated BV2 cells. And the effect of AdipoRon on the AdipoR1/AMPK pathway was confirmed by Western Blot. Results: : Intraperitoneal injection of AdipoRon alleviated mechanical pain in SNI mice. Moreover, the application of AdipoRon reduced expression of TNF-α and the number of activated microglia in the ipsilateral spinal cord. Then, AdipoRon decreased the protein level of AdipoR1 and increased the protein level of p-AMPK in the ipsilateral spinal cord. In vitro, AdipoRon inhibited BV2 cell proliferation and reversed LPS-induced TNF-α expression and polarization imbalance. Furthermore, AdipoRon abrogated the LPS-induced increase in AdipoR1 expression and decrease in p-AMPK expression in BV2 cells. Conclusions: : Our results suggest that AdipoRon alleviates NeuP by inhibiting the expression of microglia-derived TNF-α through the AdipoR1/AMPK pathway.