Osteoarthritis (OA) is highly prevalent in U.S. military service members and Veterans due to the impact of joint trauma and overuse injury. Its socioeconomic impact is substantial, estimated to approach $60 billion per year, and no disease-modifying treatments exist. The overall goal of the collaborative Program is to develop a treatment for post-traumatic osteoarthritis (PTOA) that will relieve pain and improve function. We hypothesize that PTOA is caused by maladaptive repair responses including activation of the pro-inflammatory pathways of innate immunity that in turn result in pain, loss of function and structural decline. This Program address the hypothesis through two highly-integrated aims: (1) developing innovative non-pharmacologic and intra-articular therapies inhibiting local pain and inflammation, and (2) optimizing mesenchymal stem cell (MSC)-based therapies for reconstruction of the damaged joint. The goal of this proposal is to develop novel therapy to diminish OA-associated pain by reducing inflammation and bone remodeling through inhibition of the receptor CD14. We were the first to discover high levels of CD14 in OA patients, and others subsequently linked CD14 to pain in OA patients. CD14 is a pattern-recognition receptor expressed by monocytes, macrophages and osteoclasts (bone-resorbing myeloid cells), that augments innate immune responses to tissue injury, like that observed in the joint in PTOA. Our group has now demonstrated that genetic deficiency of CD14 reduces pain and bone remodeling after joint injury in mice, and prevents progression of arthritic cartilage damage. We hypothesize that CD14 receptor activation promotes OA pain and pathology by enhancing inflammation and modifying osteoclast activity, and anticipate that CD14 blockade can be developed as a therapeutic option to treat pain and inflammation in OA. We will utilize in vitro techniques, small and large animal models of disease to understand how this receptor can be effectively inhibited to reduce pain, inflammation and joint pathology. Specifically, in Aim 1 we will use two complementary murine models of PTOA to determine how genetic deficiency of CD14 alters patterns of pain, inflammation, and bone remodeling, and modifies osteoclast activity. We will use cell and tissue culture along with imaging to identify the main cellular sources of CD14 in joint tissues. Finally, in Aim 2 we will test whether intra-articular inhibition of CD14 can reduce development of pain and progression of PTOA in murine and porcine models of meniscal injury. This project will establish anti-CD14 therapy as safe and effective in preclinical models of PTOA. As clinically-tested neutralizing anti-CD14 antibodies to interfere with this pathway in humans are available, this will set the stage for translation to future clinical trials of this approach in Veterans and others with OA.