DE-NOVO GLOMERULAR OSTEOPONTIN EXPRESSION IN RAT CRESCENTIC GLOMERULONEPHRITIS

Osteopontin (OPN) is a secreted acidic glycoprotein that has potent mo nocyte chemoattractant and adhesive properties. Up-regulation of tubul ar OPN expression is thought to promote interstitial macrophage infilt ration in experimental nephritis; however, the role of OPN in glomerul ar lesions, particularly crescent formation, is unknown. The present s tudy used Northern blotting, in situ hybridization and immunohistochem istry to examine OPN expression in a rat model of accelerated anti-GEM glomerulonephritis. Osteopontin mRNA and protein is expressed by some parietal epithelial cells, thick ascending limbs of Henle and medulla ry tubules and collecting ducts in normal rat kidney. De novo OPN mRNA and protein expression was evident in glomerular visceral and parieta l epithelial cells in anti-GEM glomerulonephritis. Glomerular OPN expr ession preceded and correlated with macrophage infiltration in the dev elopment of hypercellularity, focal and segmental lesions and, notably , crescent formation. There was marked up-regulation of OPN expression by tubular epithelial cells that also preceded and correlated with in terstitial macrophage (r = 0.93, P = 0.001) and T-cell infiltration (r = 0.85, P < 0.001). Both glomerular and tubular OPN expression correl ated significantly with proteinuria (P < 0.001) and a reduction in cre atinine clearance (P < 0.01). In addition, double immunohistochemistry showed co-expression of osteopontin and one of its ligands, CD44, in intrinsic renal cells. CD44 and OPN expression by parietal epithelial cells was evident in crescent formation, while virtually all OPN-posit ive tubules expressed CD44. Infiltrating macrophages and T-cells were CD44-positive, but only a small proportion of T-cells and few macropha ges showed OPN expression. Interestingly, strong OPN mRNA and protein expression was seen in macrophage multinucleated giant cells. In summa ry, this study suggests that OPN promotes macrophage and T-cell infilt ration in the development of renal lesions in rat anti-GEM glomerulone phritis, including glomerular crescent and multinucleated giant cell f ormation.