Rheumatoid arthritis is one of the most critical diseases that impair the quality of life of patients, but its pathogenesis has not yet been fully understood. Osteopontin (OPN) is an extracellular matrix protein containing Arg-Gly-Asp (RGD) sequence, which interacts with ␣v␤3 integrins, promotes cell attachment, and cell migration and is expressed in both synovial cells and chondrocytes in rheumatoid arthritis; however, its functional relationship to arthritis has not been known. Therefore, we investigated the roles of OPN in the pathogenesis of inflammatory process in a rheumatoid arthritis model induced by a mixture of anti-type II collagen mAbs and lipopolysaccharide (mAbs͞LPS). mAbs͞LPS injection induced OPN expression in synovia as well as cartilage, and this expression was associated with joint swelling, destruction of the surface structures of the joint based on scanning electron microscopy, and loss of toluidine blue-positive proteoglycan content in the articular cartilage in wild-type mice. In contrast, OPN deficiency prevented the mice from such surface destruction, loss of proteoglycan in the articular joint cartilage, and swelling of the joints even when the mice were subjected to mAbs͞ LPS injection. Furthermore, mAbs͞LPS injection in wild-type mice enhanced the levels of CD31-positive vessels in synovia and terminal deoxynucleotidyltransferase-mediated UTP end labeling-positive chondrocytes in the articular cartilage, whereas such angiogenesis as well as chondrocyte apoptosis was suppressed significantly in OPNdeficient mice. These results indicated that OPN plays a critical role in the destruction of joint cartilage in the rheumatoid arthritis model in mice via promotion of angiogenesis and induction of chondrocyte apoptosis.

ABSTRACT1-10 tM ATP stimulated H+ uptake and slowed the release of H+ in the dark in chloroplasts illuminated at pH values at which photophosphorylation can occur, but not at pH 6.5. This ATP stimulation of H + uptake was abolished by an antiserum to the chloroplast coupling factor and was reduced by the energy transfer inhibitors phlorizin and Dio-9. ATP synthesis after illumination was also enhanced by ATP. Electron flow from water to methyl viologen was inhibited by the same low concentrations of ATP.ADP also increased the extent of H+ uptake in chloroplasts, even in the presence of arsenate and MgCI2. In the presence of hexokinase and glucose, as well as arsenate and Mig ++, ADP inhibited H + uptake. The failure of previous investigators to observe a direct inhibition of H+ uptake by phosphorylation was probably caused by a masking of the inhibition by the stimulation of H + uptake by ATP. Furthermore, the stimulation of H+ uptake by ATP provides an explanation for its inhibition of electron flow.Although there is little doubt that the energy stored in gradients of H+ concentration across chloroplast membranes may be used to drive the synthesis of ATP (1), the relationship between light-dependent H+ uptake (2) and photophosphorylation is not clear. In general, H+ uptake in chloroplasts has properties remarkably similar to those predicted by the chemiosmotic theory of Mitchell (3). H+ uptake is sensitive to uncouplers of photophosphorylation (2) and generates rather large transmembrane gradients in H+ concentration (4,5).If the H+ gradient were the driving force for phosphorylation, or if ATP synthesis and H+ uptake are driven by a common intermediate, phosphorylation should decrease the extent of H+ uptake. The accumulation of either NH4+ (6) or of ethylamine (5) in spinach chloroplasts, which is a reflection of H+ uptake, is inhibited by phosphorylation. In contrast, H+ uptake in lettuce chloroplasts was found by Karlish and Avron (7) tional change may reduce the permeability of the membranes to H+. These observations help to explain the results of Karlish and Avron (7) and why ADP and ATP inhibit electron transport (9).

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