Unravelling the pathogenesis of cystic kidney diseases

Altered primate glomerular development due to in utero urinary tract obstruction

BACKGROUND

In utero urinary tract obstruction is an important cause of newborn and childhood renal failure. Ureteric obstruction during active nephrogenesis results in cystic renal dysplasia; the earlier and longer the obstruction the more severe the histopathological changes of dysplasia. We have reported on a non-human primate model of non-surgical in utero fetal ureteric obstruction that accurately reflects the human equivalent of obstructive renal dysplasia. A striking feature of this model is the effect of obstruction on normal glomerular development and podocyte survival.

METHODS

To study the effect of urinary obstruction on glomerular development, kidneys were studied from fetuses undergoing unilateral ureteric obstruction by ultrasound guided injection of alginate beads as early as 75 days gestation (term gestation = 165 +/- 10 days). These kidneys displayed all the features of human obstructive cystic dysplasia, had reduced weights, and significant deficiencies in terminal ureteric duct branching.

RESULTS

A combination of histochemistry, histomorphometry, and immunocytochemistry was used to demonstrate deficient cortical ureteric duct development and branching, reduced glomerular number, and altered glomerular basement membrane formation with in utero urinary tract obstruction.

CONCLUSIONS

These data suggest that urinary tract obstruction during active nephrogenesis results in a defect in ureteric duct branching morphogenesis, and altered vascularization of the glomerulus with consequent podocyte dropout and decreased glomerular number. These abnormalities reflect human renal dysplasia, which is associated with compromised postnatal renal function and, thus, should be predictive of postnatal outcome.

The sea urchin sperm receptor for egg jelly is a modular protein with extensive homology to the human polycystic kidney disease protein, PKD1

During fertilization, the sea urchin sperm acrosome reaction (AR), an ion channel-regulated event, is triggered by glycoproteins in egg jelly (EJ). A 210-kD sperm membrane glycoprotein is the receptor for EJ (REJ). This conclusion is based on the following data: purified REJ binds species specifically to EJ dotted onto nitrocellulose, an mAb to REJ induces the sperm AR, antibody induction is blocked by purified REJ, and purified REJ absorbs the AR-inducing activity of EJ. Overlapping fragments of REJ cDNA were cloned (total length, 5,596 bp). The sequence was confirmed by microsequencing six peptides of mature REJ and by Western blotting with antibody to a synthetic peptide designed from the sequence. Complete deglycosylation of REJ followed by Western blotting yielded a size estimate in agreement with that of the mature amino acid sequence. REJ is modular in design; it contains one EGF module and two C-type lectin carbohydrate-recognition modules. Most importantly, it contains a novel module, herein named the REJ module (700 residues), which shares extensive homology with the human polycystic kidney disease protein (PKD1). Mutations in PKD1 cause autosomal dominant polycystic kidney disease, one of the most frequent genetic disease of humans. The lesion in cellular physiology resulting from mutations in the PKD1 protein remains unknown. The homology between REJ modules of the sea urchin REJ and human PKD1 suggests that PKD1 could be involved in ionic regulation.