Microglial Activation of GLP-1R Signaling in Neuropathic Pain Promotes Gene Expression Adaption Involved in Inflammatory Responses

Abstract

Background. Neuropathic pain is a common chronic pain, which is related to hypersensitivity to stimulus and greatly affects the quality of life of patients. Maladaptive gene changes and molecular signaling underlie the sensitization of nociceptive pathways. We previously found that the activation of microglial glucagon-like peptide 1 receptor (GLP-1R) could potently relieve formalin-, bone cancer-, peripheral nerve injury-, and diabetes-induced pain hypersensitivity. So far, little is known about how the gene profile changes upon the activation of GLP-1R signaling in the pathophysiology of neuropathic pain. Methods. Spinal nerve ligation (SNL) was performed to induce neuropathic pain in rats. Mechanical allodynia was assessed using von Frey filaments. The expression of IL-10, β-endorphin, and μ-opioid receptor (MOR) was examined by real-time quantitative polymerase chain reaction (qPCR) and whole-cell recording. Measurements of cellular excitability of the substantia gelatinosa (SG) neurons by whole-cell recording were carried out. R packages of differential gene expression analysis based on the negative binomial distribution (DESeq2) and weighted correlation network analysis (WGCNA) were used to analyze differential gene expression and the correlated modules among GLP-1R clusters in neuropathic pain. Results. The GLP-1R agonist, exenatide, has an antiallodynic effect on neuropathic pain, which could be reversed by intrathecal injections of the microglial inhibitor minocycline. Furthermore, differential gene expression analysis (WGCNA) indicated that intrathecal injections of exenatide could reverse the abnormal expression of 591 genes in the spinal dorsal horn induced by nerve injury. WGCNA revealed 58 modules with a close relationship between the microglial GLP-1R pathway and features of nerve injuries, including pain, ligation, paw withdrawal latency (PWL), and anxiety. The brown module was identified as the highest correlated module, and the Kyoto Encyclopedia of Genes and Genomes (KEGG) analysis indicated that inflammatory responses were most correlated with PWL. To further unravel the changes of hyperalgesia-related neuronal electrophysiological activity mediated by microglia GLP-1 receptors, whole-cell recording identified that MOR agonism stimulated a robust outward current in the sham groups compared with the spinal nerve ligation (SNL) groups. This inhibitory effect on the SNL group was more sensitive than that of the sham group after bath application of β-endorphin. Conclusions. Our results further confirmed that the GLP-1R pathway is involved in alleviating pain hypersensitivity mediated by spinal microglia activation, and inflammatory responses were the most correlated pathway associated with PWL changes in response to exenatide treatment. We found that the identification of gene regulation in response to GLP-1R activation is an effective strategy for identifying new therapeutic targets for neuropathic pain. Investigation for the activation of spinal microglial GLP-1R which might ameliorate inflammatory responses through gene expression and structural changes is providing a potential biomarker in pain management.

Store‐operated calcium entry mediates hyperalgesic responses during neuropathy

“…SOCE‐induced Ca 2+ influx, as a critical channel mediating neuronal excitability and sensory responses, also potentiates cellular stabilization by altering glutamate receptors and neurotransmitter production [ 46 ]. The imbalance of glutamatergic and inhibitory transmission is also shown to affect the excitability of spinal cord neurons, cause aberrant receptor expression, and induce underlying molecular changes [ 29 ]. Consistent with the findings of this study, nerve injury has a long‐lasting effect on neurotransmitter release, indicating that alterations in neuroplasticity lead to behavioral sensitization in rats.…”

“…Total spinal mRNA of the enlargement region was extracted using TRIzol. An OD ratio of 1.8–2.1 was used for the following experiments as previously [ 29 ]. A RefertAid First Strand cDNA synthesis kit (Thermo scientific, Waltham, MA, USA) was used to produce cDNA on oligo (dT) magnetic beads.…”

Involvement of Intestinal Enteroendocrine Cells in Neurological and Psychiatric Disorders

“…Further, the GLP1R agonist decreases pain hypersensitivity through decreasing pro-inflammatory factors and increasing microglia anti-inflammatory factors, such as interleukin 10 (IL-10), cluster of differentiation 206 (CD206), interleukin 4 (IL-4), and arginase 1 (Arg1) [ 102 , 104 , 105 , 106 , 107 , 108 ]. New research claimed that the gene regulation in response to GLP1R activation is an effective strategy in new treatments for neuropathic pain, by confirming that the GLP1R pathway is involved in pain hypersensitivity mediated by microglia activation [ 109 ]. Considering the inter-organ communication though nerve and endocrine systems, regulation of GLP1 and its receptor in the intestine and CNS system could synergistically improve neural pain sensitivity.…”

Beneficial Influence of Exendin-4 on Specific Organs and Mechanisms Favourable for the Elderly with Concomitant Obstructive Lung Diseases

“…GLP-1 receptors, whose agonist is Ex-4, are located in many organs of the human body. Their presence has been confirmed in the pancreas, lungs, stomach, small intestine, kidneys, heart, most areas of the brain [ 16 ], and on peripheral nerves, i.e., the vagus nerve [ 17 ], and in the spinal cord [ 18 , 19 , 20 ] ( Figure 1 ). They have not been found in the liver, skeletal muscles, or adipose tissue, i.e., in organs responsible for glucose metabolism in the body [ 21 ].…”