Mosaic PKHD1 in Polycystic Kidneys Caused Aberrant Protein Expression in the Mitochondria and Lysosomes

Chengxian Xu,Lingxiao Tong,Jianhua Mao,Huijun Shen,Pingping Jiang,Zhihong Lu,Qing Ye,Jie Xu,Yuchen Zhang,Chenxi Yang,Enyin Lai,Jingjing Wang

doi:10.3389/fmed.2021.743150

Abstract

Autosomal recessive polycystic kidney disease (ARPKD) is a severe renal cystic disease caused mainly by the polycystic kidney and hepatic disease 1 (PKHD1). However, the genetic cause, pathologic features, and mechanism of action of ARPKD are not well known. Here, we identified a family with ARPKD. Two siblings harbored biallelic variants in PKHD1 (c.7205G>A, c.7973T>A). We determined that the “de novo” variant, c.7205G>A, arose from the mosaicism of the father and had a 7.4% level. Pathologic characterization, using biopsy analysis, was evidenced with predominant cystic dilation in proximal tubules, slight ectasia of collecting ducts, defective ciliogenesis, and impaired cell-cell junctions in renal tubules and collecting ducts. Exosome proteomics in the urine from patients with ARPKD were markedly different from those of controls, with the most significant alterations occurring in mitochondrial and lysosomal proteins. Expression of the proteins of OXPHOS was downregulated sharply, in parallel with upregulated expression of the proteins involved in glycolysis in patients with ARPKD. Several lysosomal proteins associated with renal lesions were more abundant in the exosome of the patient than in controls. Moreover, the lysosomal enzyme sulfamidase, which is produced by the SGSH gene, was abrupt uniquely in the exosome of the patient. Consistently, swollen mitochondria and abundant lysosomes were visualized in the mutant tubular epithelial cells of patients with mutant PKHD1. Collectively, these findings provide new insights on the pathophysiology of the polycystic kidney due to PKHD1 deficiency. PKHD1 mosaicism should be considered in genetic testing of ARPKD patients.

Highlights

Autosomal recessive polycystic kidney disease (ARPKD) is a rare and severe renal cystic disease caused by homozygous or compound heterozygous variants of polycystic kidney and hepatic disease 1 (PKHD1) or DAZ interacting zinc finger protein 1 like (DZIP1L) [1, 2]
We present a rare case of ARPKD due to compound heterozygous PKHD1 variants, of which one “de novo” variant was originally from the mosaicism of the father
The “adherence junction” pathway is destroyed in vitro in null-PKHD1 cells [14], so we explored the features of cell-cell junctions using the junctional markers E-cadherin and zonula occludens (ZO)-1

Summary

Introduction

Autosomal recessive polycystic kidney disease (ARPKD) is a rare and severe renal cystic disease caused by homozygous or compound heterozygous variants of polycystic kidney and hepatic disease 1 (PKHD1) or DAZ interacting zinc finger protein 1 like (DZIP1L) [1, 2]. Mosaic PKHD1 in Polycystic Kidney is postulated to result in dedifferentiation of cells, excessive secretion of fluid, and proliferation of tubular epithelia causing renal cysts [3]. The use of a large membrane spanning protein, fibrocystin/polyductin (FPC), is challenging for exploring the pathogenesis of PKHD1 variants in ARPKD. We present a rare case of ARPKD due to compound heterozygous PKHD1 variants, of which one “de novo” variant was originally from the mosaicism of the father. Proteomic analysis and immunohistochemical (IHC) analyses of exosomes revealed significant alternative profiling of mitochondrial and lysosomal proteins in patients with ARPKD and an abrupt increase in expression of lysosomal N-sulfoglucosamine sulfohydrolase (SGSH) in both urinary exosomes and renal biopsies

Results

Discussion

Conclusion