Aseptic loosening around total hip and knee arthroplasty is linked to plasma microRNA

Abstract

Total hip and knee joint replacement have revolutionised the way we treat end-stage degenerative joint diseases. However, aseptic loosening is still a major cause of prosthesis failure, leading to revision surgery. The pathophysiology of aseptic loosening begins with debris particles being generated as the implants wear over time. These microparticles cause osteolysis around the prosthesis, which begins to weaken the bony architecture over time, thus leading to loosening of the implant. However, this theory alone does not explain why certain patients have significant amounts of prosthesis wear, but very little osteolysis, whereas other patients have minimal prosthesis wear and significant osteolysis and aseptic loosening. Perhaps there is an underlying genetic predisposition that is regulated by pathways that places certain patients at a greater risk of osteolysis and aseptic loosening. One other possible explanation we must acknowledge could be an undetected infection, however this topic is beyond the scope of this thesis. MicroRNAs (miRNA) are well known for their ability to regulate gene expression in humans. They are present in all tissues and can be readily detectable in the blood stream and other bodily fluids contained within exosomes. Their use as biomarkers and master gene regulators have been documented widely in other fields of medicine and science, but very little research has been conducted on their role in orthopaedic surgery and arthroplasty. We hypothesise that there are differences in miRNA expression plasma of patients with aseptic loosening compared to control patients, and that these differences can be linked to bone metabolism leading to osteolysis and aseptic loosening. Our study investigated the potential regulatory roles miRNA have in the development of osteolysis and aseptic loosening around hip and knee arthroplasty. Firstly, a retrospective case-control study was conducted to identify clinical risk factors for aseptic loosening. Then a prospective case-control study was conducted to recruit patients undergoing revision surgery for aseptic loosening compared to control patients. Samples of bone, tissue and blood were collected for RNA-sequencing. RNA-sequencing was conducted on bone, tissue and plasma samples to identify differentially expressed RNA and miRNA genes related to bone metabolism and osteolysis. Matching was done using online databases do identify miRNA-mRNA target-expression pairs to understand regulatory mechanisms by which miRNA can regulate bone metabolism. Gene-expression and pathway analyses were performed to identify regulatory pathways of miRNA in the development of osteolysis and aseptic loosening. Western blotting was done on bone and tissue samples to validate our findings. Our sequencing results revealed several miRNA which were differentially expressed in the plasma of patients with aseptic loosening compared to controls. These miRNA all had several mRNA targets in the periprosthetic bone and tissue around the prosthesis. The potential pathways by which these regulate bone resorption are the Wnt and JAK-STAT pathways. Protein expression analyses confirm differences in protein expression are detectable at the molecular level in osteolytic bone samples. This is the first study to our knowledge investigating the role of circulating miRNA in patients with aseptic loosening around hip and knee replacements. These findings help us understand the pathophysiology of osteolysis and aseptic loosening. It adds to the growing body of knowledge of miRNA and may serve as a base for further research investigating the potential role as a biomarker or therapeutic target in the future. Show more