GLEPP1 receptor tyrosine phosphatase (Ptpro) in rat PAN nephrosis. A marker of acute podocyte injury.

Glomerular epithelial protein 1 (GLEPP1) is a podocyte receptor membrane protein tyrosine phosphatase located on the apical cell membrane of visceral glomerular epithelial cell and foot processes. This receptor plays a role in regulating the structure and function of podocyte foot process. To better understand the utility of GLEPP1 as a marker of glomerular injury, the amount and distribution of GLEPP1 protein and mRNA were examined by immunohistochemistry, Western blot and RNase protection assay in a model of podocyte injury in the rat. Puromycin aminonucleoside nephrosis was induced by single intraperitoneal injection of puromycin aminonucleoside (PAN, 20 mg/100g BW). Tissues were analyzed at 0, 5, 7, 11, 21, 45, 80 and 126 days after PAN injection so as to include both the acute phase of proteinuria associated with foot process effacement (days 5-11) and the chronic phase of proteinuria associated with glomerulosclerosis (days 45-126). At day 5, GLEPP1 protein and mRNA were reduced from the normal range (265.2 +/- 79.6 x 10(6) moles/glomerulus and 100%) to 15% of normal (41.8 +/- 4.8 x 10(6) moles/glomerulus, p < 0.005). This occurred in association with an increase in urinary protein content from 1.8 +/- 1 to 99.0 +/- 61 mg/day (p < 0.001). In contrast, podocalyxin did not change significantly at this time. By day 11, GLEPP1 protein and mRNA had begun to return towards baseline. By day 45-126, at a time when glomerular scarring was present, GLEPP1 was absent from glomerulosclerotic areas although the total glomerular content of GLEPP1 was not different from normal. We conclude that GLEPP1 expression, unlike podocalyxin, reflects podocyte injury induced by PAN. GLEPP1 expression may be a useful marker of podocyte injury.