ESPN 51th Annual Meeting

ESPN 2018


 
A Novel nephrotic syndrome Circulating Factor Disease Model based on PAR-1 activation
CARL MAY 1 RICHARD COWARD 1 SARAH HIGGINS 1 GAVIN WELSH 1 MOIN SALEEM 1

1- UNIVERSITY OF BRISTOL, CHILDRENS RENAL UNIT
 
Introduction:

There is strong evidence for the role of a circulating factor in the pathogenesis of idiopathic nephrotic syndrome (iNS). Several candidates have been put forward over the years, however, none have been definitively proved. Work previously published by this group has suggested a role for Protease Activated Receptor 1 (PAR-1) on podocytes, via circulating plasma proteases. Conditionally immortalised podocytes respond to treatment with nephrotic syndrome relapse plasma (and not paired remission plasma) by phosphorylating VASP and increasing motilility. Furthermore, the response can be blocked by knocking down the PAR-1 receptor with siRNA. To definitively establish a direct role for PAR-1 in proteinuria, a transgenic mouse was developed that expressed a podocyte specific constitutively active form of PAR-1. Once activated, it is not sent to the lysosome for degradation, but stays constantly activated. We hypothesise that this replicates over exposure to a circulating protease and hence causes idiopathic nephrotic syndrome.

Material and methods:

Transgenic mice were generated by Genoway (Lyon, France). The transgene was inserted at the Rosa 26 locus. These mice were crossed with Pod-Cre mice for the developmental line and Pod-rtTA Tet-O-Cre mice for the inducible line. Kidneys were harvested and processed for histological staining and EM as indicated

Results:

The developmental PAR-1active mice were born normal, and died consistently between the ages of 39 and 45 days. They demonstrate increasing proteinuria from the age of 14 days.. By day 40 they have significantly higher blood urea and creatinine (mean 70mMol/L, 60μMol/L respectively), suggesting the mice die of renal failure. EM analysis showed a significantly thickened GBM and foot process effacement. Histology demonstrated an initial hypercellualrity within the Bowman’s capsule at 8 days that appear to reduce by 14 days. By 30 days there is clear evidence of fibrosis and by 40 days there is both fibrosis and sclerosis. The inducible PAR-1 Active mice show a similar phenotype although less severe. These mice die around 6 months old. We have also seen increased staining for activated PAR-1 in human iNS, compared to IgAN control biopsies

Conclusions:

This work demonstrates a clear role for the PAR-1 receptor in proteinuria, and strengthens the hypothesis that circulating factor(s) may act via this receptor. Additionally this is a novel model for circulating factor NS, to test novel therapies in vivo.