By the simplest account, osteoarthritis is the wearing away of articular cartilage, a tissue that has a limitedability to repair itself. As a result, minor damage from load injury or joint inflammation can lead toprogressive matrix degradation. Recent studies found significant increases of degraded matrix in thesynovial fluid of injured joints along with a surge of degradative enzymes, called metalloproteinases (MMPs).Of particular interests are MMP-2 and MMP-9, which are well known for their roles in angiogenesis and formediating cell migration during joint inflammation in addition to degrading cartilage matrix. Studying theroles of MMP-2 and MMP-9 in vivo is complicated, however, due to various degrees of injury, the complianceof soft tissues, and, sometimes, an alteration of joint kinematics. Taking advantage of an injury model, wecan induce defined cartilage injury in a mouse knee without alterating joint kinematics. We propose to testthe hypothesis that elevation of MMP-2 and MMP-9 mediates acute joint inflammation and increasescartilage degeneration after load injury with the following two specific aims: 1) To determine whether injuryinducedcartilage degeneration in MMP-2 or MMP-9 knockout mice is decreased as compared to wildtypes;2) To determine whether injury-induced cartilage degeneration in MMP-9 knockout and wildtype miceincreases with the treatment of recombinant MMP-9 protein. The outcomes will be tested at molecular,cellular, and tissue levels with a focus on matrix degradation and evaluation of joint inflammation bydetermining proteoglycan content/degradation, collagen cleavage, enzyme content (MMP-1, -2, -3, -9, -13;aggrecanases; TIMP-1, -2, -3;), inflammation (IL-1, IL-6, TNF-a, synovial membrane) and proteinaseactivities using FTIR spectroscopy, contrast-enhanced micro-computed tomography, immunohistochemistryand in situ zymography. The functional properties of cartilage will be determined using micro-indentationtests. These outcome measurements will depend heavily on the Analytical Microscopy Core and ImagingCore. This project will also enable us to establish a novel mouse model for future studies of signal pathwaysand molecules related to MMP-2 and MMP-9 and/or important to cartilage degradation, such as MMP-13,aggrecanase, IL-1, and TNF-a. Ultimately, increased understanding of the mechanisms of cartilagedegeneration after injury will enable more specific targeting of therapeutics for osteoarthritis.
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