Skin/muscle incision and retraction regulates the persistent postoperative pain in rats by the Epac1/PKC-βII pathway

Role of EPAC1 in chronic pain

Chronic pain usually lasts over three months and commonly occurs in chronic diseases (cancer, arthritis, and diabetes), injuries (herniated discs, torn ligaments), and many major pain disorders (neuropathic pain, fibromyalgia, chronic headaches). Unfortunately, there is currently a lack of effective treatments to help people with chronic pain to achieve complete relief. Therefore,it is particularly important to understand the mechanism of chronic pain and find new therapeutic targets. The exchange protein directly activated by cyclic adenosine monophosphate(cAMP) (EPAC) has been recognized for its functions in nerve regeneration, stimulating insulin release, controlling vascular pressure, and controlling other metabolic activities. In recent years, many studies have found that the subtype of EPAC, EPAC1 is involved in the regulation of neuroinflammation and plays a crucial role in the regulation of pain, which is expected to become a new therapeutic target for chronic pain. This article reviews the major contributions of EPAC1 in chronic pain.

The peripheral Epac1/p-Cav-1 pathway underlies the disruption of the vascular endothelial barrier following skin/muscle incision and retraction-induced chronic postsurgical pain

Background

Vascular endothelial barrier disruption is pivotal in the development of acute and chronic pain. Here, we demonstrate a previously unidentified molecular mechanism in which activation of the peripheral Epac1/p-Cav-1 pathway accelerated the disruption of the vascular endothelial barrier, thereby promoting chronic postsurgical pain (CPSP).

Methods

We established a rat model of CPSP induced by skin/muscle incision and retraction (SMIR). Pain behaviors were assessed by the mechanical withdrawal threshold (MWT) at different times. Local muscle tissues around the incision were isolated to detect the vascular permeability and the expression of Epac1 and Cav-1. They were assessed by western blot and immunofluorescence staining.

Results

SMIR increased vascular endothelial permeability and the number of macrophages and endothelial cells in the muscle tissues around the incision. The peripheral upregulation of Epac1 was macrophage-derived, whereas that of p-Cav-1 was both macrophage and endothelial cell-derived in the SMIR model. Moreover, the Epac1 agonist 8-pCPT could induce mechanical sensitivity, increase the expression of p-Cav-1, and disrupt vascular endothelial barrier in normal rats. The Epac1 inhibitor CE3F4 attenuated established SMIR-induced mechanical hyperalgesia, the upregulation of p-Cav-1 and vascular endothelial barrier. Finally, we showed that intrathecal injection of Cav-1siRNA relieved SMIR-induced mechanical allodynia, but had no effects of the expression of Epac1.

Conclusions

Collectively, these results revealed a molecular mechanism for modulating CPSP through the peripheral Epac1/Cav-1 pathway. Importantly, targeting Epac1/Cav-1 signaling might be a potential treatment for CPSP.