The Role of Inflammation and Antibiotics in the Development of Post-Traumatic Osteoarthritis in Mice

Osteoarthritis (OA) is a painful and debilitating disease. There is no treatment for OA other than an expensive full joint replacement surgery that requires an extensive recovery period. Approximately 50% of people who suffer a severe articular injury will develop a form of OA as early as 8 years after injury, which is a secondary form of OA called post-traumatic osteoarthritis (PTOA). PTOA develops from a severe joint injury, like an anterior cruciate ligament (ACL) tear. I want to identify external factors that could be contributing to either a resolution or a progression to the disease. It has been suggested that the progression towards PTOA is led by a continuous activation of inflammatory pathways, which led to questions about which factors affecting the body prior to injury could be changing the PTOA phenotype. The normal gut microbiome aids in immunoregulation by continuously activating an inflammatory cascade helping naïve immune cells mature. However, if there is a bacterial infection, there will be an increase in the levels of inflammation and an increase in mature immune cells to fight the infection. I want to account for patients who are suffering from systemic inflammation after acute bacterial related inflammation. In addition, knowing that in 2015 the CDC reported 269 million antibiotic prescriptions, I want to account for people treated for bacterial infections. Specifically, long term antibiotic treatment will affect PTOA outcome. I will induce inflammation and disrupt the gut microbiome prior to injury separately and later together to study the PTOA phenotype. I will use a non-invasive injury model which will temporarily displace the tibia and produce an ACL rupture. Last, in order to account for different PTOA susceptibilities, I will use three mice models of both sexes that vary from resistant to PTOA to highly susceptible. The contribution of this research will give a better understanding of the role of inflammation and the gut microbiome in the initial inflammation stage and the PTOA outcome after articular injury. Osteoarthritis (OA) is a disease characterized by the progressive degradation of articular cartilage. The treatment for OA is limited to stabilization of the joint, pain management, and ultimately full joint replacement surgery. The primary form of OA is caused by normal wear and tear or genetics. Post-traumatic osteoarthritis (PTOA) is the secondary form of OA develops in ~50% of people severe articular injury like a tibial plateau fracture, a meniscal tear, or an anterior cruciate ligament (ACL) rupture. PTOA can take as little as 8 years and up to 20 years to develop. It has been suggested that elevated levels of inflammation after injury could increase the risk of developing PTOA and the severity. We wanted to use bacterial related inflammation, given how common E. coli and other bacterial infections are today. We aim to look at how residual effects from a sudden increase in inflammation could affect injury outcome. Lipopolysaccharides (LPS) are microbial associated molecular patterns (MAMPS) released by gram-negative bacteria to activate toll-like receptors (TLR), specifically TLR4. LPS is released normally by the gut microbiome, and acts as a transcription factor for immune cell maturation. During a gram-negative bacteria infection there is an increase in LPS. LPS spikes in the short-term cause a fever and pain. Long term increases in circulating LPS cause persistent elevated levels of inflammatory chemokines and cytokines, as well as lower bone volume and a larger spleen. This project examines how a spike in MAMPs induced inflammation days prior to injury will increase the severity of PTOA. This will allow us to provide new insight that could help personalize medicine and create therapeutic treatments specifically for people more vulnerable.In contrast, we wanted to examine how removing part of the MAMP activation by using chronic antibiotic treatment could change the injury progression. There are over 270 million prescriptions of antibiotics each year in the United States, and it is important to know how this would affect it PTOA outcome. There is conflicting data as to how the gut microbiome affects bone, seeming to be dependent on age, housing type, and treatment. We will be using ampicillin and neomycin, which target mainly gram-negative bacteria for six weeks prior to injury. Antibiotic treatment will end the day of injury and we will examine the joints six weeks later. We found that the bone phenotype is worsen by antibiotic treatment while the cartilage staining is stronger on antibiotic treated joints. Last, we did a combination of antibiotic treatment an LPS induced inflammation. We found that it restores the phenotype closet to VEH