Urinary Podocyte Loss Is Increased in Patients with Fabry Disease and Correlates with Clinical Severity of Fabry Nephropathy

Abstract

Chronic kidney disease is a major complication of Fabry disease. Podocytes accumulate globotriaosylceramide inclusions more than other kidney cell types in Fabry patients. Podocyte injury occurs early in age, and is progressive. Since injured podocytes detach into the urine (podocyturia), we hypothesized that podocyturia would increase in Fabry patients and correlate with clinical severity of Fabry nephropathy. Urine specimens from 39 Fabry patients and 24 healthy subjects were evaluated for podocyturia. Most of the Fabry patients and many healthy subjects had podocyturia. The number of podocytes per gram of urine creatinine (UPodo/g Cr) was 3.6 fold greater in Fabry patients (3,741 ± 2796; p = 0.001) than healthy subjects (1,040 ± 972). Fabry patients with normoalbuminuria and normoproteinuria had over 2-fold greater UPodo/g Cr than healthy subjects (p = 0.048). UPodo/gCr was inversely related to eGFR in male patients (r = -0.69, p = 0.003). UPodo/gCr was directly related to urine protein creatinine ratio (r = 0.33; p = 0.04) in all Fabry patients. These studies confirm increased podocyturia in Fabry disease, even when proteinuria and albuminuria are absent. Podocyturia correlates with clinical severity of Fabry nephropathy, and potentially may be of prognostic value.

Conflict of interest statement

This study was supported by an investigator-initiated research grant to BN from Genzyme (a Sanofi company). BN is a recipient of investigator initiated Genzyme research grants, a consultant to Genzyme and has received speaker's honoraria and travel support from Genzyme. He is also a member of the Medical Advisory Board of Amicus and performs kidney biopsy studies for Amicus. MM is a member of the Genzyme sponsored North American Fabry Registry Advisory Board, a recipient of investigator initiated Genzyme research grants, a consultant to Genzyme for clinical trial design, and a speaker at Genzyme educational meetings. He is also a consultant to and performs kidney biopsy studies for Amicus and a grant reviewer for Shire. DW is consultant to Genzyme, Protalix, Actelion, and Amicus. ELW has received honoraria for lectures and participates in the National Fabry Registry Advisory Board sponsored by Genzyme. RS is on the Genzyme board of advisors for Fabry disease. BF, SS, JP, JJ, and PH did not have any relevant financial disclosure. These interests have been reviewed and managed according to the conflict of interest policies of authors' affiliated institutions.

Figures

Fig 1. Urine cells on cytospin slides stained for podocalyxin (PCX, red), claudin-1 (CL1, green), and Dapi (blue).

(A-D) A Faby podocyte which is PCX+/CL1- and shows characteristic vacuolated cytoplasm. (E-H) A urine cells which is PCX+/CL1+ consistent with a parietal epithelial cell (PEC) phenotype. (I-L) An apoptotic podocyte (PCX+/CL1-) in the urine from a Fabry patient with shrunken cytoplasm and small nucleus (arrow) compared to its adjacent cells. (M-P) A podocyte (PCX+/CL1-) in the urine from a healthy subject does not show vacuolated cytoplasm.

Fig 2. Urine cells on cytospin stained for podocalyxin (PCX, red), Dapi (blue), and TUNEL (green).

Two podocytes (PCX+) with apoptotic nuclei (white arrows in B-D) are also positive for TUNEL (white arrows in C-D), confirming apoptosis. The yellow arrow (B-D) shows a non-podocyte cell (PCX-) that is TUNEL+ (C-D).

Fig 3

(A) Comparison of podocyturia in healthy subjects and Fabry patients. Fabry patients had significantly more urine podocytes (p = 0.001) per g creatinine (UPodo/g Cr). * There was a weak trend (p<0.1) for greater UPodo/g Cr in male Fabry patients compared to females. UPodo/g Cr was not different between male and female healthy subjects. (B) Comparison of urine apoptotic podocyturia in healthy subjects and Fabry patients. Fabry patients had significantly more apoptotic UPodo/g Cr than healthy subjects (p = 0.005). Apoptotic UPodo/g Cr were not different between males and females either in Fabry patients or in healthy subjects.

Fig 4. Relationships between podocyturia and renal function in patients with Fabry disease by gender.

(A and B) Urine podocytes per g creatinine (UPodo/g Cr) vs. estimated GFR (eGFR) in males (A) and females (B). (C and D) UPodo/g Cr vs. urine protein creatinine ratio (UPCR) in males (C) and females (D). (E and F) UPodo/g Cr vs. urine albumin creatinine ratio (UACR) in males (E) and females (F). ns = statistically not significant.