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An endocytosis defect as a possible cause of proteinuria in polycystic kidney disease

N Obermüller1, B Kränzlin, W F Blum

  • 1Medical Research Center, Klinikum Mannheim, University of Heidelberg, 68167 Mannheim, Germany.

American Journal of Physiology. Renal Physiology
|February 24, 2001
PubMed

Insights

Proteinuria in autosomal-dominant polycystic kidney disease (ADPKD) models is linked to impaired kidney tubule function. Proximal tubule cysts in (cy/+) rats lose endocytic ability, causing protein and albumin leakage.

Area of Science:

  • Nephrology
  • Molecular Biology
  • Genetics

Background:

  • Autosomal-dominant polycystic kidney disease (ADPKD) is characterized by cyst formation and often presents with proteinuria.
  • The (cy/+) rat is a common animal model used to study ADPKD pathogenesis.

Purpose of the Study:

  • To investigate the occurrence and underlying mechanisms of proteinuria in the (cy/+) rat model of ADPKD.
  • To determine if proximal tubular dysfunction contributes to proteinuria in this model.

Main Methods:

  • Assessed urinary protein excretion and albumin levels in 16-week-old (cy/+) rats.
  • Utilized FITC-labeled dextran to evaluate renal tubular endosomal function in vivo.
  • Employed immunohistochemistry to examine the expression of endocytosis-related proteins (ClC-5, megalin) within cysts.
  • Measured urinary insulin-like growth factor-I (IGF-I) levels.

Main Results:

  • Increased urinary protein and albumin excretion were observed in (cy/+) rats, with patterns suggesting tubular origin.
  • Proximal tubule cyst epithelia demonstrated a loss of endocytic capacity for low-molecular-weight proteins.
  • Expression of ClC-5 and megalin correlated with endocytic function within cysts.
  • Elevated urinary IGF-I levels were detected in (cy/+) rats.

Conclusions:

  • Proteinuria and albuminuria in the (cy/+) rat model of ADPKD result from the loss of the endocytic machinery in proximal tubular cyst epithelia.
  • This impaired endocytosis may influence cyst fluid composition, affecting growth factor and hormone concentrations and potentially modulating cyst development.

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