title: p38βMitogen-Activated Protein Kinase Signaling Mediates Exenatide-Stimulated Microglialβ-Endorphin Expression.
abstract: Recent discoveries established that activation of glucagon-like peptide-1 receptors (GLP-1Rs) mediates neuroprotection and antinociception through microglialβ-endorphin expression. This study aimed to explore the underlying signaling mechanisms of microglialβ-endorphin. GLP-1Rs andβ-endorphin were coexpressed in primary cultures of microglia. Treatment with the GLP-1R agonist exenatide concentration-dependently stimulated microglial expression of theβ-endorphin precursor gene proopiomelanocortin (POMC) and peptides, with EC50values of 4.1 and 7.5 nM, respectively. Exenatide also significantly increased intracellular cAMP levels and expression ofp-protein kinase A (PKA),p-p38, andp-cAMP response element binding protein (CREB) in cultured primary microglia. Furthermore, exenatide-induced microglial expression of POMC was completely blocked by reagents that specifically inhibit adenylyl cyclase and activation of PKA, p38, and CREB. In addition, knockdown of p38β(but not p38α) using short interfering RNA (siRNA) eliminated exenatide-induced microglial p38 phosphorylation and POMC expression. In contrast, lipopolysaccharide increased microglial activation of p38, and knockdown of p38α(but not p38β) partially suppressed expression of proinflammatory factors (including tumor necrosis factor-α, interleukin-1β, and interleukin-6). Exenatide-induced phosphorylation of p38 and CREB was also totally blocked by the PKA inhibitor and siRNA/p38β, but not by siRNA/p38αSeven-day intrathecal injections of siRNA/p38β(but not siRNA/p38α) completely blocked exenatide-induced spinal p38 activation,β-endorphin expression, and mechanical antiallodynia in rats with established neuropathy, although siRNA/p38βand siRNA/p38αwere not antiallodynic. To our knowledge, our results are the first to show a causal relationship between the PKA-dependent p38βmitogen-activated protein kinase/CREB signal cascade and GLP-1R agonism-mediated microglialβ-endorphin expression. The differential role of p38αand p38βactivation in inflammation and nociception was also highlighted.
authors.affiliation: King's Laboratory, Shanghai Jiao Tong University School of Pharmacy, Shanghai, China.
authors.forename: Hai-Yun
authors.initials: HY
authors.lastname: Wu
authors.affiliation: King's Laboratory, Shanghai Jiao Tong University School of Pharmacy, Shanghai, China.
authors.forename: Xiao-Fang
authors.initials: XF
authors.lastname: Mao
authors.affiliation: King's Laboratory, Shanghai Jiao Tong University School of Pharmacy, Shanghai, China.
authors.forename: Hui
authors.initials: H
authors.lastname: Fan
authors.affiliation: King's Laboratory, Shanghai Jiao Tong University School of Pharmacy, Shanghai, China yxwang@sjtu.edu.cn.
authors.forename: Yong-Xiang
authors.initials: YX
authors.lastname: Wang
mesh_terms: D000818:Animals; D002478:Cells, Cultured; D000242:Cyclic AMP / Q000378:metabolism; D017362:Cyclic AMP Response Element-Binding Protein / Q000378:metabolism; D017868:Cyclic AMP-Dependent Protein Kinases / Q000378:metabolism; D016207:Cytokines / Q000378:metabolism; D000077270:Exenatide; D000067757:Glucagon-Like Peptide-1 Receptor / Q000378:metabolism; D006930:Hyperalgesia / Q000378:metabolism / Q000473:pathology; D018836:Inflammation Mediators / Q000378:metabolism; D007278:Injections, Spinal; D008070:Lipopolysaccharides; D020935:MAP Kinase Signaling System / Q000187:drug effects; D008297:Male; D017628:Microglia / Q000187:drug effects / Q000378:metabolism*; D008954:Models, Biological; D010455:Peptides / Q000494:pharmacology*; D010766:Phosphorylation / Q000187:drug effects; D011333:Pro-Opiomelanocortin / Q000378:metabolism; D034741:RNA, Small Interfering / Q000378:metabolism; D017208:Rats, Wistar; D014688:Venoms / Q000494:pharmacology*; D001615:beta-Endorphin / Q000378:metabolism*; D048051:p38 Mitogen-Activated Protein Kinases / Q000378:metabolism*
chemical_list: D017362:Cyclic AMP Response Element-Binding Protein; D016207:Cytokines; D000067757:Glucagon-Like Peptide-1 Receptor; D018836:Inflammation Mediators; D008070:Lipopolysaccharides; D010455:Peptides; D034741:RNA, Small Interfering; D014688:Venoms; D001615:beta-Endorphin; D011333:Pro-Opiomelanocortin; D000077270:Exenatide; D000242:Cyclic AMP; D017868:Cyclic AMP-Dependent Protein Kinases; D048051:p38 Mitogen-Activated Protein Kinases