Lack of APOL1 in proximal tubules of normal human kidneys and proteinuric APOL1 transgenic mouse kidneys.

Natalya A Blessing,Zhenzhen Wu,Sethu M Madhavan,John R Sedor,Myung K Shin,John F O’Toole,Michelle Chen,Jonathan W Choy,Maarten Hoek,Leslie A Bruggeman

doi:10.1371/journal.pone.0253197

Abstract

The mechanism of pathogenesis associated with APOL1 polymorphisms and risk for non-diabetic chronic kidney disease (CKD) is not fully understood. Prior studies have minimized a causal role for the circulating APOL1 protein, thus efforts to understand kidney pathogenesis have focused on APOL1 expressed in renal cells. Of the kidney cells reported to express APOL1, the proximal tubule expression patterns are inconsistent in published reports, and whether APOL1 is synthesized by the proximal tubule or possibly APOL1 protein in the blood is filtered and reabsorbed by the proximal tubule remains unclear. Using both protein and mRNA in situ methods, the kidney expression pattern of APOL1 was examined in normal human and APOL1 bacterial artificial chromosome transgenic mice with and without proteinuria. APOL1 protein and mRNA was detected in podocytes and endothelial cells, but not in tubular epithelia. In the setting of proteinuria, plasma APOL1 protein did not appear to be filtered or reabsorbed by the proximal tubule. A side-by-side examination of commercial antibodies used in prior studies suggest the original reports of APOL1 in proximal tubules likely reflects antibody non-specificity. As such, APOL1 expression in podocytes and endothelia should remain the focus for mechanistic studies in the APOL1-mediated kidney diseases.

Highlights

Polymorphisms in the APOL1 gene contribute significant risk for several forms of non-diabetic chronic kidney disease (CKD) [1,2,3]
Lipoproteins and other components of HDLs can be filtered [16], and in the setting of proteinuria, larger molecular weight proteins normally restricted by the filtration barrier may appear in filtrate. It is unclear whether APOL1 or APOL1-containing complexes may be filtered in the setting of proteinuria. We examined both APOL1 gene and protein expression in human kidney tissue and kidneys from humanized transgenic mouse models that recreate native human APOL1 expression
APOL1 transgenic mouse models were made proteinuric by intercrossing with a model of HIV-associated nephropathy (HIVAN), a CKD strongly associated with carriage of APOL1 risk alleles, to determine if proteinuria would change the appearance of APOL1 protein in tubular epithelial

Summary

Introduction

Polymorphisms in the APOL1 gene contribute significant risk for several forms of non-diabetic chronic kidney disease (CKD) [1,2,3]. Merck and Company provided support in the form of salaries and laboratory resources for authors (JWC, MC, MKS, MH), but did not have any additional role in the study design, data collection and analysis, decision to publish, or preparation of the manuscript. Maze Therapeutics provided support in the form of salary for the author (MH) but did not have any additional role in the study design, data collection and analysis, decision to publish, or preparation of the manuscript. We examined both APOL1 gene and protein expression in human kidney tissue and kidneys from humanized transgenic mouse models that recreate native human APOL1 expression For these studies we validated commercial anti-APOL1 antibodies for specificity which may have contributed to prior discrepancies on kidney expression patterns. APOL1 transgenic mouse models were made proteinuric by intercrossing with a model of HIV-associated nephropathy (HIVAN), a CKD strongly associated with carriage of APOL1 risk alleles, to determine if proteinuria would change the appearance of APOL1 protein in tubular epithelial

Materials and methods

Results

Discussion