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Long-term exposure to PGE2 causes homologous desensitization of receptor-mediated activation of protein kinase A.

Malty RH, Hudmon A, Fehrenbacher JC, Vasko MR - J Neuroinflammation (2016)

Bottom Line: Acute exposure to 1 μM PGE2 augments the capsaicin-evoked release of iCGRP, and this effect is blocked by the PKA inhibitor H-89.Exposing neuronal cultures to 1 μM PGE2 for 12 h to 5 days blocks the ability of PGE2 to activate PKA.Long-term exposure to PGE2 also results in desensitization of the ability of a selective EP4 receptor agonist, L902688 to activate PKA, but does not alter the ability of cholera toxin, forskolin, or a stable analog of prostacyclin to activate PKA.

View Article: PubMed Central - PubMed

Affiliation: Department of Chemistry and Biochemistry, Faculty of Science, University of Regina, Regina, SK, Canada.

ABSTRACT

Background: Acute exposure to prostaglandin E2 (PGE2) activates EP receptors in sensory neurons which triggers the cAMP-dependent protein kinase A (PKA) signaling cascade resulting in enhanced excitability of the neurons. With long-term exposure to PGE2, however, the activation of PKA does not appear to mediate persistent PGE2-induced sensitization. Consequently, we examined whether homologous desensitization of PGE2-mediated PKA activation occurs after long-term exposure of isolated sensory neurons to the eicosanoid.

Methods: Sensory neuronal cultures were harvested from the dorsal root ganglia of adult male Sprague-Dawley rats. The cultures were pretreated with vehicle or PGE2 and used to examine signaling mechanisms mediating acute versus persistent sensitization by exposure to the eicosanoid using enhanced capsaicin-evoked release of immunoreactive calcitonin gene-related peptide (iCGRP) as an endpoint. Neuronal cultures chronically exposed to vehicle or PGE2 also were used to study the ability of the eicosanoid and other agonists to activate PKA and whether long-term exposure to the prostanoid alters expression of EP receptor subtypes.

Results: Acute exposure to 1 μM PGE2 augments the capsaicin-evoked release of iCGRP, and this effect is blocked by the PKA inhibitor H-89. After 5 days of exposure to 1 μM PGE2, administration of the eicosanoid still augments evoked release of iCGRP, but the effect is not attenuated by inhibition of PKA or by inhibition of PI3 kinases. The sensitizing actions of PGE2 after acute and long-term exposure were attenuated by EP2, EP3, and EP4 receptor antagonists, but not by an EP1 antagonist. Exposing neuronal cultures to 1 μM PGE2 for 12 h to 5 days blocks the ability of PGE2 to activate PKA. The offset of the desensitization occurs within 24 h of removal of PGE2 from the cultures. Long-term exposure to PGE2 also results in desensitization of the ability of a selective EP4 receptor agonist, L902688 to activate PKA, but does not alter the ability of cholera toxin, forskolin, or a stable analog of prostacyclin to activate PKA.

Conclusions: Long-term exposure to PGE2 results in homologous desensitization of EP4 receptor activation of PKA, but not to neuronal sensitization suggesting that activation of PKA does not mediate PGE2-induced sensitization after chronic exposure to the eicosanoid.

No MeSH data available.


Related in: MedlinePlus

Acute PGE2-induced sensitization and persistent sensitization after long-term exposure to the eicosanoid are mediated by the same EP receptor subtypes. Each column represents the mean ± SEM of capsaicin-stimulated release of iCGRP as percent of total iCGRP content per well/10 min in cultures maintained in the absence of added NGF and preexposed to vehicle (a) or to 1 μM PGE2 for 5 days (b). After pretreatment, cultures were acutely exposed to vehicle (lightly shaded columns) or to 1 μM PGE2 (dark-shaded columns) for 20 min in the absence or presence of EP receptor antagonists, as indicated. An asterisk indicates a statistically significant difference between capsaicin-stimulated release of iCGRP after vehicle versus after PGE2 using one-way ANOVA followed by Bonferroni’s post hoc test
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Fig4: Acute PGE2-induced sensitization and persistent sensitization after long-term exposure to the eicosanoid are mediated by the same EP receptor subtypes. Each column represents the mean ± SEM of capsaicin-stimulated release of iCGRP as percent of total iCGRP content per well/10 min in cultures maintained in the absence of added NGF and preexposed to vehicle (a) or to 1 μM PGE2 for 5 days (b). After pretreatment, cultures were acutely exposed to vehicle (lightly shaded columns) or to 1 μM PGE2 (dark-shaded columns) for 20 min in the absence or presence of EP receptor antagonists, as indicated. An asterisk indicates a statistically significant difference between capsaicin-stimulated release of iCGRP after vehicle versus after PGE2 using one-way ANOVA followed by Bonferroni’s post hoc test

Mentions: To identify the EP receptor subtypes that contribute to PGE2-induced sensitization, we used the selective EP receptor inhibitors ONO-8711, TG4-155, L798,106, and ONO-AE3-208 to block EP1, EP2, EP3, or EP4 receptor subtypes, respectively. In sensory neuronal cultures that were exposed to vehicle for 5 days, pretreating with 30 or 100 nM of the EP2 receptor antagonist, TG4-155; the EP3 receptor antagonist, L798,106; or the EP4 receptor antagonist, ONO-AE3-208, blocked the PGE2-induced augmentation of capsaicin-stimulated release of iCGRP (Fig. 4a). Exposure to the antagonists in the absence of PGE2 did not alter basal or capsaicin-stimulated release of iCGRP (Fig. 4a). In contrast, pretreating cultures with the EP1 receptor antagonist, ONO-8711, did not attenuate the PGE2-induced increase in capsaicin-stimulated release (Fig. 4a). After 5-day exposure to PGE2, re-exposure to the prostanoid caused sensitization that was completely inhibited by the EP4 receptor antagonist and to a lesser degree by EP2 and EP3 receptor antagonists, but not by the EP1 receptor antagonist (Fig. 4b). Together, these results show that chronic exposure to PGE2 does not change the EP receptor profile that mediates sensitization by the eicosanoid.Fig. 4


Long-term exposure to PGE2 causes homologous desensitization of receptor-mediated activation of protein kinase A.

Malty RH, Hudmon A, Fehrenbacher JC, Vasko MR - J Neuroinflammation (2016)

Acute PGE2-induced sensitization and persistent sensitization after long-term exposure to the eicosanoid are mediated by the same EP receptor subtypes. Each column represents the mean ± SEM of capsaicin-stimulated release of iCGRP as percent of total iCGRP content per well/10 min in cultures maintained in the absence of added NGF and preexposed to vehicle (a) or to 1 μM PGE2 for 5 days (b). After pretreatment, cultures were acutely exposed to vehicle (lightly shaded columns) or to 1 μM PGE2 (dark-shaded columns) for 20 min in the absence or presence of EP receptor antagonists, as indicated. An asterisk indicates a statistically significant difference between capsaicin-stimulated release of iCGRP after vehicle versus after PGE2 using one-way ANOVA followed by Bonferroni’s post hoc test
© Copyright Policy - OpenAccess
Related In: Results  -  Collection

License 1 - License 2
Show All Figures
getmorefigures.php?uid=PMC4940832&req=5

Fig4: Acute PGE2-induced sensitization and persistent sensitization after long-term exposure to the eicosanoid are mediated by the same EP receptor subtypes. Each column represents the mean ± SEM of capsaicin-stimulated release of iCGRP as percent of total iCGRP content per well/10 min in cultures maintained in the absence of added NGF and preexposed to vehicle (a) or to 1 μM PGE2 for 5 days (b). After pretreatment, cultures were acutely exposed to vehicle (lightly shaded columns) or to 1 μM PGE2 (dark-shaded columns) for 20 min in the absence or presence of EP receptor antagonists, as indicated. An asterisk indicates a statistically significant difference between capsaicin-stimulated release of iCGRP after vehicle versus after PGE2 using one-way ANOVA followed by Bonferroni’s post hoc test
Mentions: To identify the EP receptor subtypes that contribute to PGE2-induced sensitization, we used the selective EP receptor inhibitors ONO-8711, TG4-155, L798,106, and ONO-AE3-208 to block EP1, EP2, EP3, or EP4 receptor subtypes, respectively. In sensory neuronal cultures that were exposed to vehicle for 5 days, pretreating with 30 or 100 nM of the EP2 receptor antagonist, TG4-155; the EP3 receptor antagonist, L798,106; or the EP4 receptor antagonist, ONO-AE3-208, blocked the PGE2-induced augmentation of capsaicin-stimulated release of iCGRP (Fig. 4a). Exposure to the antagonists in the absence of PGE2 did not alter basal or capsaicin-stimulated release of iCGRP (Fig. 4a). In contrast, pretreating cultures with the EP1 receptor antagonist, ONO-8711, did not attenuate the PGE2-induced increase in capsaicin-stimulated release (Fig. 4a). After 5-day exposure to PGE2, re-exposure to the prostanoid caused sensitization that was completely inhibited by the EP4 receptor antagonist and to a lesser degree by EP2 and EP3 receptor antagonists, but not by the EP1 receptor antagonist (Fig. 4b). Together, these results show that chronic exposure to PGE2 does not change the EP receptor profile that mediates sensitization by the eicosanoid.Fig. 4

Bottom Line: Acute exposure to 1 μM PGE2 augments the capsaicin-evoked release of iCGRP, and this effect is blocked by the PKA inhibitor H-89.Exposing neuronal cultures to 1 μM PGE2 for 12 h to 5 days blocks the ability of PGE2 to activate PKA.Long-term exposure to PGE2 also results in desensitization of the ability of a selective EP4 receptor agonist, L902688 to activate PKA, but does not alter the ability of cholera toxin, forskolin, or a stable analog of prostacyclin to activate PKA.

View Article: PubMed Central - PubMed

Affiliation: Department of Chemistry and Biochemistry, Faculty of Science, University of Regina, Regina, SK, Canada.

ABSTRACT

Background: Acute exposure to prostaglandin E2 (PGE2) activates EP receptors in sensory neurons which triggers the cAMP-dependent protein kinase A (PKA) signaling cascade resulting in enhanced excitability of the neurons. With long-term exposure to PGE2, however, the activation of PKA does not appear to mediate persistent PGE2-induced sensitization. Consequently, we examined whether homologous desensitization of PGE2-mediated PKA activation occurs after long-term exposure of isolated sensory neurons to the eicosanoid.

Methods: Sensory neuronal cultures were harvested from the dorsal root ganglia of adult male Sprague-Dawley rats. The cultures were pretreated with vehicle or PGE2 and used to examine signaling mechanisms mediating acute versus persistent sensitization by exposure to the eicosanoid using enhanced capsaicin-evoked release of immunoreactive calcitonin gene-related peptide (iCGRP) as an endpoint. Neuronal cultures chronically exposed to vehicle or PGE2 also were used to study the ability of the eicosanoid and other agonists to activate PKA and whether long-term exposure to the prostanoid alters expression of EP receptor subtypes.

Results: Acute exposure to 1 μM PGE2 augments the capsaicin-evoked release of iCGRP, and this effect is blocked by the PKA inhibitor H-89. After 5 days of exposure to 1 μM PGE2, administration of the eicosanoid still augments evoked release of iCGRP, but the effect is not attenuated by inhibition of PKA or by inhibition of PI3 kinases. The sensitizing actions of PGE2 after acute and long-term exposure were attenuated by EP2, EP3, and EP4 receptor antagonists, but not by an EP1 antagonist. Exposing neuronal cultures to 1 μM PGE2 for 12 h to 5 days blocks the ability of PGE2 to activate PKA. The offset of the desensitization occurs within 24 h of removal of PGE2 from the cultures. Long-term exposure to PGE2 also results in desensitization of the ability of a selective EP4 receptor agonist, L902688 to activate PKA, but does not alter the ability of cholera toxin, forskolin, or a stable analog of prostacyclin to activate PKA.

Conclusions: Long-term exposure to PGE2 results in homologous desensitization of EP4 receptor activation of PKA, but not to neuronal sensitization suggesting that activation of PKA does not mediate PGE2-induced sensitization after chronic exposure to the eicosanoid.

No MeSH data available.


Related in: MedlinePlus