Osteopontin induces airway remodeling and lung fibroblast activation in a murine model of asthma.
ABSTRACT Airway remodeling is a central feature of asthma; however, the mechanisms underlying its development have not been fully elucidated. We have demonstrated that osteopontin, an inflammatory cytokine and an extracellular matrix glycoprotein with profibrotic properties, is up-regulated in a murine model of allergen-induced airway remodeling. In the present study, we determined whether osteopontin plays a functional role in airway remodeling. Osteopontin (OPN)-deficient (OPN(-/-)) and wild-type mice were sensitized and exposed to inhaled ovalbumin (OVA) or saline for 5 weeks. Collagen production, peribronchial smooth muscle area, mucus-producing cell number, and bronchoalveolar cell counts were assessed. The functional behavior and phenotype of lung fibroblasts from OVA-treated OPN(-/-) and from wild-type mice were studied using ex vivo cultures. OVA-treated OPN(-/-) mice exhibited reduced lung collagen content, smooth muscle area, mucus-producing cells, and inflammatory cell accumulation as compared with wild-type mice. Reduced matrix metalloproteinase-2 activity and expression of transforming growth factor-beta1 and vascular endothelial growth factor were observed in OVA-treated OPN(-/-) mice. Lung fibroblasts from OVA-treated OPN(-/-) mice showed reduced proliferation, migration, collagen deposition, and alpha-smooth muscle actin expression in comparison with OVA-treated wild-type lung fibroblasts. Thus, OPN is key for the development of allergen-induced airway remodeling in mice. In response to allergen, OPN induces the switching of lung fibroblasts to a pro-fibrogenic myofibroblast phenotype.
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ABSTRACT: Osteopontin (OPN), a 41-kDa phosphorylated glycoprotein, has been detected in rat aorta and carotid arteries, and expression of its mRNA in blood vessels is strongly increased in response to vascular injury. To investigate the potential role of OPN in vascular pathophysiology, we studied the effect of rat OPN on aortic smooth muscle cell migration and proliferation in vitro. OPN enhanced the migration of rat smooth muscle cells in a time- and concentration-dependent manner with an EC50 value of 46 +/- 11 nmol/liter (n = 5). The maximal increase in cell migration by OPN was 29-fold over basal levels. OPN-induced smooth muscle cell migration was inhibited in a concentration-dependent manner by the monoclonal antibody F11, which recognizes the rat integrin subunit beta 3. In contrast, polyclonal antiserum recognizing the rat integrin beta 1 subunit did not inhibit smooth muscle cell migration in response to OPN, but did block fibronectin-promoted migration. Moreover, OPN-induced smooth muscle cell migration was dependent on the presence of extracellular divalent cations and was significantly inhibited by anti-OPN antibodies. OPN did not stimulate [3H]thymidine incorporation into cultured smooth muscle cells, indicating that it selectively enhanced migration. In view of the pathological significance of arterial smooth muscle cell migration in the formation of intimal thickening, our results suggest that smooth muscle cell recognition of OPN, probably through the vitronectin receptor, alpha v beta 3, could play a role in the cells' response to vascular injury and especially neointima formation.Experimental Cell Research 11/1994; 214(2):459-64. · 3.56 Impact Factor
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ABSTRACT: Osteopontin is a macrophage adhesive protein that is expressed by renal tubules in tubulointerstitial disease. To investigate the function of OPN, we induced tubulointerstitial disease in OPN null mutant (OPN-/-) and wild-type (OPN+/+) mice by unilateral ureteral ligation. Tissue was analyzed for macrophages (ED-1), types I and IV collagen deposition, TGF-beta expression, and for tubular and interstitial cell apoptosis. Obstructed kidneys from both OPN-/- and OPN+/+ mice developed hydronephrosis, tubular atrophy, interstitial inflammation and fibrosis. OPN was absent in OPN-/- kidneys but was increased in obstructed OPN+/+ kidneys. Macrophage influx, measured by computer-assisted quantitative immunostaining, was less in OPN-/- mice compared to OPN+/+ mice at day 4 (threefold, P < 0.02), day 7 (fivefold, P < 0.02), but not at day 14. Interstitial deposition of types I and IV collagen were also two- to fourfold less in obstructed OPN-/- kidneys (P < 0.02). There was also a reduction of TGF-beta mRNA expression in the interstitium at day 7 (by in situ hybridization) and a near significant 34% reduction in cortical TGF-beta activity (P = 0.06) compared to obstructed OPN+/+ kidneys at day 14. Obstructed kidneys from OPN-/- mice also had more interstitial and tubular apoptotic cells (TUNEL assay) compared to obstructed OPN+/+ mice at all time points. The ability of OPN to act as a cell survival factor was also documented by showing that the apoptosis of serum-starved NRK52E renal epithelial cells was markedly enhanced in the presence of neutralizing anti-OPN antibody. OPN mediates early interstitial macrophage influx and interstitial fibrosis in unilateral ureteral obstruction. OPN may also function as a survival factor for renal tubulointerstitial cells.Kidney International 09/1999; 56(2):571-80. · 7.92 Impact Factor
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ABSTRACT: A chronic inflammatory process is almost invariably associated with tissue damage and healing. Healing results in repair and replacement of dead or damaged cells by viable cells. Repair usually involves 2 distinct processes: regeneration, which is the replacement of injured tissue by parenchymal cells of the same type, and replacement by connective tissue and its eventual maturation into scar tissue. In many instances both processes contribute to the healing response. Chronic inflammatory disease can therefore lead to a wide variety of consequences, from complete or partial restitution of organ structure and function to fibrosis. Asthma is characterized by a chronic inflammatory process of the airways. The ensuing healing process results in structural alterations referred to as a remodeling of the airways. The mechanisms underlying these structural alterations are still largely unknown. They are likely to be heterogeneous, leading-through the highly dynamic process of cell de-differentiation, migration, differentiation, and maturation-to changes in connective tissue deposition and to the altered restitution of airways structure, resulting in mucus gland hyperplasia, neovascularization, fibrosis, and an increase in smooth muscle mass.Journal of Allergy and Clinical Immunology 07/2000; 105(6 Pt 1):1041-53. · 12.05 Impact Factor