Critical role for Epac1 in inflammatory pain controlled by GRK2-mediated phosphorylation of Epac1

Abstract

cAMP signaling plays a key role in regulating pain sensitivity. Here, we uncover a previously unidentified molecular mechanism in which direct phosphorylation of the exchange protein directly activated by cAMP 1 (EPAC1) by G protein kinase 2 (GRK2) suppresses Epac1-to-Rap1 signaling, thereby inhibiting persistent inflammatory pain. Epac1 −/− mice are protected against inflammatory hyperalgesia in the complete Freund's adjuvant (CFA) model. Moreover, the Epac-specific inhibitor ESI-09 inhibits established CFA-induced mechanical hyperalgesia without affecting normal mechanical sensitivity. At the mechanistic level, CFA increased activity of the Epac target Rap1 in dorsal root ganglia of WT, but not of Epac1 −/− , mice. Using sensory neuronspecific overexpression of GRK2 or its kinase-dead mutant in vivo, we demonstrate that GRK2 inhibits CFA-induced hyperalgesia in a kinase activity-dependent manner. In vitro, GRK2 inhibits Epac1-to-Rap1 signaling by phosphorylation of Epac1 at Ser-108 in the Disheveled/Egl-10/pleckstrin domain. This phosphorylation event inhibits agonist-induced translocation of Epac1 to the plasma membrane, thereby reducing Rap1 activation. Finally, we show that GRK2 inhibits Epac1-mediated sensitization of the mechanosensor Piezo2 and that Piezo2 contributes to inflammatory mechanical hyperalgesia. Collectively, these findings identify a key role of Epac1 in chronic inflammatory pain and a molecular mechanism for controlling Epac1 activity and chronic pain through phosphorylation of Epac1 at Ser-108. Importantly, using the Epac inhibitor ESI-09, we validate Epac1 as a potential therapeutic target for chronic pain.

Peripheral afferents and spinal inhibitory system in dynamic and static mechanical allodynia

“…These results may seem to contradict the findings that inhibiting A-fibers in mice by Piezo2 downregulation (initiated 1 day post-CFA) significantly alleviated the inflammatory static mechanical allodynia ≥4 days post-CFA [49]. However, Piezo2 downregulation initiated 3 days before CFA injection did not prevent static mechanical allodynia 1 day post-CFA [47; 49]. Collectively, it appears that TRPA1-expressing afferents mediate mouse inflammatory static mechanical allodynia early after the inflammation develops (≤3 days post-CFA), whereas A-fibers do so later (≥4 days post-CFA).…”

“…Instead, in CFA-injected mice, targeting TRPA1-expressing nociceptors before or 2–3 days after the inflammation prevented or alleviated the allodynia [15; 28]. These results may seem to contradict the findings that inhibiting A-fibers in mice by Piezo2 downregulation (initiated 1 day post-CFA) significantly alleviated the inflammatory static mechanical allodynia ≥4 days post-CFA [49]. However, Piezo2 downregulation initiated 3 days before CFA injection did not prevent static mechanical allodynia 1 day post-CFA [47; 49].…”

Adrenergic signaling in heart failure and cardiovascular aging

“…Both up-regulated and reduced levels of GRK2 may affect cellular functioning. Alterations in GRK2 activity and expression have been described in numerous diseases, including myocardial infarction [21], Alzheimer’s disease [22], rheumatoid arthritis [23], multiple sclerosis [24], inflammatory pain [25, 26], opioid addiction [26], thyroid gland disorders [27], pituitary adenomas [28], ovarian cancer [29], and cystic fibrosis [30]. …”

Inhibition of Epac1 suppresses mitochondrial fission and reduces neointima formation induced by vascular injury

“…Activation of Epac1 by cAMP further triggers down-stream RAS superfamily small GTPases, Rap1 and Rap2, which are critical for a wide variety of biological functions, ranging from cytoskeleton organization and intracellular trafficking to cell adhesion and junction789. Studies based on genetic Epac1 knockout mice have demonstrated that Epac1 contributes to leptin resistance1011, rickettsial infection12, chronic pain1314, stress induced phospholamban phosphorylation in cardiomyocytes15, Treg-mediated immune-suppression16, and cardiomyocyte hypertrophy17. However, the physiological roles of Epac1 in VSMC function and neointima formation remain controversial181920212223.…”