title: Tissue plasminogen activator contributes to morphine tolerance and induces mechanical allodynia via astrocytic IL-1β and ERK signaling in the spinal cord of mice.
abstract: Accumulating evidence indicates that activation of spinal cord astrocytes contributes importantly to nerve injury and inflammation-induced persistent pain and chronic opioid-induced antinociceptive tolerance. Phosphorylation of extracellular signal-regulated kinase (pERK) and induction of interleukin-1 beta (IL-1β) in spinal astrocytes have been implicated in astrocytes-mediated pain. Tissue plasminogen activator (tPA) is a serine protease that has been extensively used to treat stroke. We examined the potential involvement of tPA in chronic opioid-induced antinociceptive tolerance and activation of spinal astrocytes using tPA knockout (tPA(-/-)) mice and astrocyte cultures. tPA(-/-) mice exhibited unaltered nociceptive pain and morphine-induced acute analgesia. However, the antinociceptive tolerance, induced by chronic morphine (10mg/kg/day, s.c.), is abrogated in tPA(-/-) mice. Chronic morphine induces tPA expression in glial fibrillary acidic protein (GFAP)-expressing spinal cord astrocytes. Chronic morphine also increases IL-1β expression in GFAP-expressing astrocytes, which is abolished in tPA-deficient mice. In cultured astrocytes, morphine treatment increases tPA, IL-1β, and pERK expression, and the increased IL-1β and pERK expression is abolished in tPA-deficient astrocytes. tPA is also sufficient to induce IL-1β and pERK expression in astrocyte cultures. Intrathecal injection of tPA results in up-regulation of GFAP and pERK in spinal astrocytes but not up-regulation of ionized calcium binding adapter molecule 1 in spinal microglia. Finally, intrathecal tPA elicits persistent mechanical allodynia, which is inhibited by the astroglial toxin alpha-amino adipate and the MEK (ERK kinase) inhibitor U0126. Collectively, these data suggest an important role of tPA in regulating astrocytic signaling, pain hypersensitivity, and morphine tolerance.
authors.affiliation: Pain Signaling and Plasticity Laboratory, Department of Anesthesiology, Duke University Medical Center, Durham, NC 27710, USA.
authors.forename: T
authors.initials: T
authors.lastname: Berta
authors.forename: Y-C
authors.initials: YC
authors.lastname: Liu
authors.forename: Z-Z
authors.initials: ZZ
authors.lastname: Xu
authors.forename: R-R
authors.initials: RR
authors.lastname: Ji
mesh_terms: D000818:Animals; D001253:Astrocytes / Q000378:metabolism; D004361:Drug Tolerance / Q000502:physiology; D006930:Hyperalgesia / Q000378:metabolism* / Q000473:pathology; D007278:Injections, Spinal; D053583:Interleukin-1beta / Q000096:biosynthesis*; D020935:MAP Kinase Signaling System / Q000502:physiology; D008297:Male; D051379:Mice; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D009020:Morphine / Q000008:administration & dosage*; D010766:Phosphorylation; D015398:Signal Transduction / Q000502:physiology; D013116:Spinal Cord / Q000378:metabolism*; D010959:Tissue Plasminogen Activator / Q000172:deficiency*
chemical_list: D053583:Interleukin-1beta; D009020:Morphine; D010959:Tissue Plasminogen Activator
keywords: DRGs; ERK; ERK kinase; FBS; GAPDH; GFAP; IBA-1; IL-1β; L-2-AA; LTP; MEK; MMP-2; PWL; WT; acute opioid analgesia; chronic morphine exposure; dorsal root ganglia; extracellular signal-regulated kinase; extracellular signal-regulated kinase (ERK); fetal bovine serum; glial fibrillary acidic protein; glyceraldehyde3-phosphate dehydrogenase; interleukin-1 beta; interleukin-1 beta (IL-1β); ionized calcium binding adapter molecule 1; l-2-Aminoadipic acid; long-term potentiation; matrix metalloprotease-2; pERK; paw withdrawal latency; phosphoERK; protease; tPA; tPA knockout mice; tissue plasminogen activator; wild-type