TRPV1 Channel Activated by the PGE2/EP4 Pathway Mediates Spinal Hypersensitivity in a Mouse Model of Vertebral Endplate Degeneration

Low back pain (LBP) is the primary cause of disability globally. There is a close relationship between Modic changes or endplate defects and LBP. Endplates undergo ossification and become highly porous during intervertebral disc (IVD) degeneration. In our study, we used a mouse model of vertebral endplate degeneration by lumbar spine instability (LSI) surgery. Safranin O and fast green staining and μCT scan showed that LSI surgery led to endplate ossification and porosity, but the endplates in the sham group were cartilaginous and homogenous. Immunofluorescent staining demonstrated the innervation of calcitonin gene-related peptide- (CGRP-) positive nerve fibers in the porous endplate of LSI mice. Behavior test experiments showed an increased spinal hypersensitivity in LSI mice. Moreover, we found an increased cyclooxygenase 2 (COX2) expression and an elevated prostaglandin E2 (PGE2) concentration in the porous endplate of LSI mice. Immunofluorescent staining showed the colocalization of E-prostanoid 4 (EP4)/transient receptor potential vanilloid 1 (TRPV1) and CGRP in the nerve endings in the endplate and in the dorsal root ganglion (DRG) neurons, and western blotting analysis demonstrated that EP4 and TRPV1 expression significantly increased in the LSI group. Our patch clamp study further showed that LSI surgery significantly enhanced the current density of the TRPV1 channel in small-size DRG neurons. A selective EP4 receptor antagonist, L161982, reduced the spinal hypersensitivity of LSI mice by blocking the PGE2/EP4 pathway. In addition, TRPV1 current and neuronal excitability in DRG neurons were also significantly decreased by L161982 treatment. In summary, the PGE2/EP4 pathway in the porous endplate could activate the TRPV1 channel in DRG neurons to cause spinal hypersensitivity in LSI mice. L161982, a selective EP4 receptor antagonist, could turn down the TRPV1 current and decrease the neuronal excitability of DRG neurons to reduce spinal pain.

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Activation of EP4 receptors contributes to prostaglandin E2-mediated stimulation of renal sensory nerves

AJP Renal Physiology ◽

10.1152/ajprenal.00230.2004 ◽

2004 ◽

Vol 287 (6) ◽

pp. F1269-F1282 ◽

Cited By ~ 36

Author(s):

Ulla C. Kopp ◽

Michael Z. Cicha ◽

Kazuhiro Nakamura ◽

Rolf M. Nüsing ◽

Lori A. Smith ◽

...

Keyword(s):

Receptor Antagonist ◽

Sensory Nerve ◽

Nerve Fibers ◽

Prostaglandin E ◽

Ep4 Receptor ◽

Pelvic Wall ◽

Ep4 Receptor Antagonist ◽

Cox 2 ◽

Ep3 Receptor ◽

Stimulation Of

Induction of cyclooxygenase-2 (COX-2) in the renal pelvic wall increases prostaglandin E2 (PGE2) leading to stimulation of cAMP production, which results in substance P (SP) release and activation of renal mechanosensory nerves. The subtype of PGE receptors involved, EP2 and/or EP4, was studied by immunohistochemistry and renal pelvic administration of agonists and antagonists of EP2 and EP4 receptors. EP4 receptor-like immunoreactivity (LI) was colocalized with calcitonin gene-related peptide (CGRP)-LI in dorsal root ganglia (DRGs) at Th9-L1 and in nerve terminals in the renal pelvic wall. Th9-L1 DRG neurons also contained EP3 receptor-LI and COX-2-LI, each of which was colocalized with CGRP-LI in some neurons. No renal pelvic nerves contained EP3 receptor-LI and only very few nerves COX-2-LI. The EP1/EP2 receptor antagonist AH-6809 (20 μM) had no effect on SP release produced by PGE2 (0.14 μM) from an isolated rat renal pelvic wall preparation. However, the EP4 receptor antagonist L-161,982 (10 μM) blocked the SP release produced by the EP2/EP4 receptor agonist butaprost (10 μM) 12 ± 2 vs. 2 ± 1 and PGE2, 9 ± 1 vs. 1 ± 0 pg/min. The SP release by butaprost and PGE2 was similarly blocked by the EP4 receptor antagonist AH-23848 (30 μM). In anesthetized rats, the afferent renal nerve activity (ARNA) responses to butaprost 700 ± 100 and PGE2·780 ± 100%·s (area under the curve of ARNA vs. time) were unaffected by renal pelvic perfusion with AH-6809. However, 1 μM L-161,982 and 10 μM AH-23848 blocked the ARNA responses to butaprost by 94 ± 5 and 78 ± 10%, respectively, and to PGE2 by 74 ± 16 and 74 ± 11%, respectively. L-161,982 also blocked the ARNA response to increasing renal pelvic pressure 10 mmHg, 85 ± 5%. In conclusion, PGE2 increases renal pelvic release of SP and ARNA by activating EP4 receptors on renal sensory nerve fibers.

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