Deciphering the role of dipeptidase 2 (DPEP2) to treat surgical pain

PROJECT SUMMARY: Surgical pain is caused by tissue injury and inflammation. To treat surgical pain, people are given opioids which is leading to secondary health problems after surgery including opioid abuse, dependence, and overdose that is driving the United States opioid epidemic. This is particularly important for older adults as treating pain with opioids also present challenges with age-related changes in drug metabolism in addition to drug-drug interactions due to polypharmacy. Thus, discovering new non-opioid targets and developing non- opioid treatments that are effective in the young and elderly to alleviate surgical pain are urgently needed. For this HEAL R03 proposal, the goal of this research is to further understand the role of dipeptidase 2 (DPEP2) in mediating inflammation leading to surgical pain. In the traditional pro-inflammatory role, DPEP2 converts leukotriene D4 to leukotriene E4 leading to inflammation. However, in a recently discovered anti- inflammatory role, DPEP2 also limits the activation of the canonical NF-B pathway. Here we will leverage new key findings regarding the DPEP2 catalytic site (based upon the crystal structure and functional assays for another DPEP family member) to develop catalytically active and inactive DPEP2 constructs to understand whether DPEP2 limits the activation of the NF-B pathway through a peptidase-dependent or independent mechanism. In order to carry out this work, we will assess how DPEP2 regulates the NF-B pathway by using stable NF-B luciferase reporter cell lines (skin fibroblast NIH-3T3 and macrophage Raw264.7). Further, we will determine whether targeting the cysteinyl leukotriene receptor 1 (CysLTR1) downstream of DPEP2 will limit pain and inflammation after injury using a surgical incision model. To carry out these studies, we developed a rodent paw surgical incision model that increases phosphorylated NF-B 3-fold in addition to a 10-fold increase in NF-B-regulated pro-inflammatory cytokines including IL-6 and IL-1. Taken together, this proposal can advance the field by further understanding the role for DPEP2 in regulating inflammation and whether a non- opioid therapeutic targeting CysLTR1 in the DPEP2 pathway is effective at reducing surgical pain in rodents. Additionally, since the studies performed for this proposal will determine whether DPEP2 limits NF-B activation and production of NF-B-mediated proinflammatory genes, these studies also have a broad importance to aging. This is because inflammation is a hallmark of aging and the cellular senescence- associated secretory phenotype described in aging cells is driven by increases in IL-6 and IL-1; where IL-6 is the major driver of this phenotype. Therefore, understanding further the role of DPEP2 may potentially have broader implications besides treating surgical pain and useful in limiting inflammatory pain for the elderly.