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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 not mediated by activation of PI3 kinases. 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 for 5 days (left panel) or to 1 μM PGE2 for 5 days (right panel). After long-term exposure, 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 LY294002, 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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Fig8: Acute PGE2-induced sensitization and persistent sensitization after long-term exposure to the eicosanoid are not mediated by activation of PI3 kinases. 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 for 5 days (left panel) or to 1 μM PGE2 for 5 days (right panel). After long-term exposure, 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 LY294002, 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: The data presented above show that both acute and persistent sensitization of sensory neurons by PGE2 are mediated by activation of the same EP receptor subtypes but that sensitization after chronic exposure to PGE2 is not dependent on activation of PKA. Since previous work has shown that binding of PGE2 to EP4 receptors activates phosphoinositide 3-kinase (PI3K) signaling under different conditions [44] and that inhibiting PI3 kinases attenuates inflammatory pain behaviors [45, 46], we examined whether a pan inhibitor of PI3 kinases would attenuate acute or persistent PGE2-induced sensitization. In sensory neuronal cultures treated with vehicle for 5 days, exposing neuronal cultures to 1 or 3 μM LY294002 prior to and throughout exposure to capsaicin did not attenuate the ability of 1 μM PGE2 to augment stimulated iCGRP release (Fig. 8). In a similar manner, when sensory neurons were treated with 1 μM PGE2 for 5 days, then re-exposed to PGE2 neither 1 nor 3 μM LY294002 significantly altered the eicosanoid-induced increase in capsaicin-stimulated release of iCGRP.Fig. 8


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 not mediated by activation of PI3 kinases. 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 for 5 days (left panel) or to 1 μM PGE2 for 5 days (right panel). After long-term exposure, 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 LY294002, 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

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Show All Figures
getmorefigures.php?uid=PMC4940832&req=5

Fig8: Acute PGE2-induced sensitization and persistent sensitization after long-term exposure to the eicosanoid are not mediated by activation of PI3 kinases. 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 for 5 days (left panel) or to 1 μM PGE2 for 5 days (right panel). After long-term exposure, 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 LY294002, 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: The data presented above show that both acute and persistent sensitization of sensory neurons by PGE2 are mediated by activation of the same EP receptor subtypes but that sensitization after chronic exposure to PGE2 is not dependent on activation of PKA. Since previous work has shown that binding of PGE2 to EP4 receptors activates phosphoinositide 3-kinase (PI3K) signaling under different conditions [44] and that inhibiting PI3 kinases attenuates inflammatory pain behaviors [45, 46], we examined whether a pan inhibitor of PI3 kinases would attenuate acute or persistent PGE2-induced sensitization. In sensory neuronal cultures treated with vehicle for 5 days, exposing neuronal cultures to 1 or 3 μM LY294002 prior to and throughout exposure to capsaicin did not attenuate the ability of 1 μM PGE2 to augment stimulated iCGRP release (Fig. 8). In a similar manner, when sensory neurons were treated with 1 μM PGE2 for 5 days, then re-exposed to PGE2 neither 1 nor 3 μM LY294002 significantly altered the eicosanoid-induced increase in capsaicin-stimulated release of iCGRP.Fig. 8

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