Total joint replacement using metal and polymeric materials has provided dramatic relief of pain and improvement of function for millions of patients with end-stage arthritis. More than 600,000 total hip and knee replacements are performed annually worldwide at an enormous economic impact. Despite the success of joint replacements, aseptic loosening, frequently associated with periprosthetic osteolysis, and focal osteolysis in the absence of loosening, jeopardizes the long-term function of both cemented and cementless total joint replacements. This proposal will study biomaterial-induced responses of osteoblasts. Our hypothesis is that phagocytosed but non-degradable particulate biomaterials (prosthetic wear debris) launch a catastrophic process in vivo by activating a number of cells (macrophages, fibroblasts, osteoclasts and osteoblasts), and these activated cells together create a unique pathological condition at the interface of bone and prothesis. We propose to investigate this hypothesis by studying altered cellular functions at the molecular level which may trigger, maintain and/or contribute to osteolysis. In particular, we will focus on particulate biomaterial-induced cellular responses in osteoblasts, since these cells, in addition to osteoclasts, may play direct and central roles in periprosthetic osteolysis and aseptic loosening of total joint arthroplasties. Phagocytosis is a natural cell function and it seems to be an attractive hypothesis that there is a common and early intracellular signaling pathway, which triggers the """"""""ultimate"""""""" cell response to non-degradable phagocytosed particulates. The long term goal of this proposal is to define the signal transduction mechanisms by which phagocytosed particulates alter gene expressed in osteoblasts. To address this goal we will (i) identify the specific transcription factors induced by Titianium (Ti) particles, a prototype of particulate wear debris, (ii) define the signaling events that activate these transcription factors, and (iii) identify the genes affected by these transcription factors. In preliminary data, we demonstrate that phagocytosed Ti particulates activate the transcription factor NF-kappa B in an osteoblast cell line (MG-63). NF-kappa B is a key transcription factor in activating gene expression in immune and non-immune cells. We hypothesize that Ti particulate activation of NF-kappa B leads to the induction of proinflammatory cytokines, such as TNFalpha, IL-beta, and IL-6, which in turn contribute to osteolysis. There is currently no information on the regulation and function of NF-kappa B in human osteoblasts. To gain a better understanding of the mechanisms by which phagocytosed particulates activate gene expression in these cells, we will focus on the mechanisms by with TI particles activate the transcription factor NF-kappa B and the NF-kappa B dependent gene expression.
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