ESPN 50th Annual Meeting

ESPN 2017


 
Ubiquitin Carboxyl-Terminal Hydrolase L1 is a Podocyte Target of IgG antibodies in Idiopathic Nephrotic Syndrome
JAMIN AGNES 1 MONTEIRO RENATO 2 DESCHENES GEORGES 1

1- APHP-ROBERT-DEBRE
2- INSERM U1149
 
Introduction:

The efficiency of B cell-depleting treatments highlights the involvement of B cells in INS. This study searched for identifying antibodies (Abs) directed against podocytes in patients with INS.

Material and methods:

The study included 42 patients sampled at various stages of INS, and 38 controls. Fractions of plasma obtained by size exclusion chromatography were tested on cultured podocyte adhesion; 2/ specificities of IgG Abs contained in the plasma fraction of interest were studied through immunoprecipitation of a podocyte lysate then identification of cognate antigens by liquid chromatography-mass spectrometry.

 

Results:

Cultured podocyte detachment was observed with one specific plasma fraction in 16/34 INS relapsing patients, 1/11 INS patients in remission and 0/25 controls. IgG were isolated from this specific plasma fraction in 3 INS relapsing patients (all detaching cultured podocytes), the 3 same INS patients in remission (all not detaching cultured podocytes) and in 3 controls, then used to immunoprecipitate a podocyte lysate. Comparative proteomic analysis allowed selecting 5 proteins according to statistical and biological criteria. Specific Abs were tested and only anti-Ubiquitin Carboxyl-Terminal Hydrolase L1 (UCHL1) IgG led to podocyte detachment. Pre-incubation of either anti-UCHL1 IgG Abs or plasma fractions with recombinant UCHL1 prevented podocyte detachment. Plasma levels of anti-UCHL1 IgG Abs were increased in 18/42 relapsing INS patients over the highest level of 38 controls (median=0.20 AU/µg of total IgG;IQ0.15-0.29;range0.07-0.85). For those 18 patients, the level of anti-UCHL1 IgG Abs in 43 samples available at various stage of the disease was confirmed to be significantly higher in relapse (n=23;median=1.22AU/µg of total IgG;IQ0.92-1.90) compared to remission (n=20;median=0.51;IQ0.33-0.77;p<0.001). In those INS patients, proteinuria correlated with anti-UCHL1 IgG Ab level (n=43,r=0.57,p<0.001).

Conclusions:

1/ UCHL1 is involved in the adhesion of cultured podocytes 2/ UCHL1 is a target of circulating IgG Abs in a subset of relapsing INS patients.