Extracellular matrix in fetal kidney after experimental obstruction

Purpose: We studied the long-term effects of complete unilateral ureteral o bstruction on the extracellular matrix composition of the fetal kidney inte rstitium in neonatal opossums. Materials and Methods: We created complete left ureteral obstruction in 2-w eek-old opossum pups. Sham operated animals served as controls. A total of 12 animals were sacrificed 2, 3 and 5 weeks after obstruction, and the kidn eys were harvested. Resultant tissue sections were prepared for light and e lectron microscopy, and immunohistochemical testing for a-smooth muscle act ion (SMA), fibronectin, laminin and type IV collagen. In situ hybridization was done to determine interstitial collagen type 1. Western blot analysis was performed on single kidney protein extracts for alpha -SMA, fibronectin and laminin. Results: Light microscopy revealed established interstitial fibrosis and tu bular atrophy 2 weeks after obstruction which increased with the duration o f obstruction. Electron microscopy showed an increased number of interstiti al fibroblasts, increased extracellular lucent substance and thin collagen fibrils. The tubular basement membranes were irregular and thickened compar ed with the continuous and even contours in controls. The deposition of a-S MA, fibronectin, collagen types I and type IV were markedly increased in th e interstitium compared with controls and were highest at 5 weeks. Type IV collagen was associated with aberrant peritubular capillaries within the sc arred interstitium. There were no appreciable differences in laminin expres sion in obstructed and sham operated kidneys. Conclusions: Experimental obstruction in opossums alters the cell phenotype , extracellular matrix and microcapillary composition in the fetal kidney i nterstitium. Biosynthetic properties of the interstitial fibroblasts in obs tructed kidneys appear similar to those of undifferentiated mesenchyma befo re the induction of nephrons. We propose that these aberrant extracellular matrices coincident with cytoarchitectural disturbance may form a faulty sc affold that hampers normal kidney development secondary to complete unilate ral ureteral obstruction.