AdipoRon Regulates Neuropathic Pain Through The AdipoR1/AMPK Pathway In Microglia

ObjectivesNeuropathic pain(NeuP)is a pain caused by a lesion or disease of the somatosensory nervous system.The persistence of this disease affects the patient’s quality of life and places additional burdens on the patient’s family and society.Therefore,it is necessary to explore the pathological mechanism of NeuP and find effective therapeutic methods.Microglia-associated neuroinflammation plays a crucial role in the initiation and development of NeuP.Therefore,targeting microglia to modulate neuroinflammation may be a feasible therapeutic strategy for NeuP.AdipoRon is an analog of adiponectin,which can activate the adiponectin receptors(AdipoRs)and exhibit anti-inflammatory property in various diseases.However,the effect of AdipoRon on NeuP has not been investigated.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 AdipoRl/AMPK pathway is involved in the regulation of inflammation.And therapies targeting this pathway are beneficial for a variety of diseases.But,it is still unknown whether AdipoRon can exert beneficial effects on NeuP by regulating the AdipoR1/AMPK pathway.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.MethodsIn vivo,the spared nerve injury(SNI)model was established to induce NeuP.The mice were divided into four groups:Sham,SNI,SNI+Vehicle and SNI+AdipoRon.Using the Von Frey test to detect the effect of AdipoRon on mechanical paw withdrawal threshold.The effects of AdipoRon on the expression of AdipoR1,AMPK,p-AMPK and TNF-α in the ipsilateral spinal cord were detected by Western Blot.The effects of AdipoRon on the number of spinal microglia were observed by immunofluorescence.In vitro,the use of lipopolysaccharide(LPS)to induce inflammatory response in BV2 cells.The BV2 cells were divided into Naive group,LPS group and LPS+AdipoRon group.The effect of AdipoRon on cell proliferation was detected by CCK8.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.ResultsIn vivo,the expression of TNF-α and the number of microglia in the ipsilateral spinal cord of mice were significantly increased after SNI.In addition,in the ipsilateral spinal cord of SNI mice,the expression of AdipoRl was compensatively increased and the expression of p-AMPK was decreased.After intraperitoneal injection of AdipoRon,the mechanical pain threshold of SNI mice was up-regulated,while the expression of TNF-α and the number of microglia were decreased in the ipsilateral spinal cord.In addition,AdipoRon decreased the expression of AdipoR1 and increased the expression of p-AMPK in the ipsilateral spinal cord.In vitro,the expression of TNF-α was increased in LPS-treated BV2 cells.Meanwhile,the expression of CD32,a marker of pro-inflammatory phenotype,was up-regulated,and the expression of CD206,a marker of anti-inflammatory phenotype,was down-regulated.AdipoRon inhibited BV2 cell proliferation and reversed LPS-induced TNF-α expression and polarization imbalance.Furthermore,AdipoRon abrogated the LPS-induced increase in AdipoRl expression and decrease in p-AMPK expression in BV2 cells.ConclusionsAdipoRon alleviates NeuP by regulating the proliferation and polarization of spinal microglia through the AdipoRl/AMPK pathway to inhibit the expression of TNF-α.