Mechanical loading of articular cartilage is essential for normal homeostasis and is also believed to play a role in the onset and progression of joint disease. However, the sequence of biomechanical and biochemical events involved in the transduction of mechanical stress to a cellular response in cartilage are not fully understood and have been the subject of numerous recent investigations. Prostaglandin E2 (PGE2) is an important inflammatory mediator that has been implicated in mechanotransduction in different cell types such as endothelial cells, osteocytes and osteoblasts. Mechanical stress can also induce the release of anabolic growth factors such as transforming growth factor beta (TGFbeta) and insulin like growth factor (IGF1) from osteoblasts and fibroblasts. In cartilage, PGE2 increases collagen synthesis via an autocrine loop involving IGF1 and increases aggrecan and DNA synthesis. PGE2 is regulated by the enzyme cyclooxygenase2 (COX2). Clinically, COX2 inhibitors are rapidly replacing the non-specific non-steroidal anti-inflammatory drugs in the treatment for arthritis and sports injuries. The role of the cyclooxygenase pathway in mechanotransduction of chondrocytes is not fully understood. Our primary hypothesis is that mechanical stress regulates chondrocyte proteoglycan metabolism through a COX2 dependent pathway. In this study, we propose three specific aims.
In Specific Aim 1, physiological levels of intermittent compression will be applied to cartilage explants, and the role of COX2 and PGE2 in regulating proteoglycan synthesis and breakdown determined using selective inhibitors to COX2 and COX 1. Selective inhibitors to PKA, PKC and PTK will be added to determine the pathways involved. The PGE receptor subtypes involved will be determined using selective agonists and antagonists to the receptors.
In Specific Aim 2, we will determine the interplay of PGE, and COX2 with nitric oxide, an inflammatory mediator associated with arthritis which is also upregulated by mechanical stress.
In Specific Aim 3, we shall examine the effect of mechanical stress on the catabolic effects of IL 1 on matrix synthesis. The effects of addition of COX2 or NOS2 inhibitors during compression in the presence of IL 1 will be determined and related to matrix synthesis. Levels of IGF1 and TGFbeta will be determined. Completion of the aims of this study will provide a better understanding of the role of mechanical stress in the physiology and pathophysiology of articular cartilage. The findings will have significant implications in the development of pharmaceutical or biophysical interventions for the treatment of arthritis.
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