Dysregulated Autophagy Contributes to Podocyte Damage in Fabry’s Disease

Max C Liebau,Claudia Weitbrecht,Valerie Bartels,Katja Höpker,Susanne Brodesser,Fabian Braun,Moin A Saleem,Roman-Ulrich Müller,Bernhard Schermer,Thomas Benzing,Markus Cybulla,Christine E Kurschat,Christos Chatziantoniou

doi:10.1371/journal.pone.0063506

Abstract

Fabry’s disease results from an inborn error of glycosphingolipid metabolism that is due to deficiency of the lysosomal hydrolase α-galactosidase A. This X-linked defect results in the accumulation of enzyme substrates with terminally α-glycosidically bound galactose, mainly the neutral glycosphingolipid Globotriaosylceramide (Gb3) in various tissues, including the kidneys. Although end-stage renal disease is one of the most common causes of death in hemizygous males with Fabry’s disease, the pathophysiology leading to proteinuria, hematuria, hypertension, and kidney failure is not well understood. Histological studies suggest that the accumulation of Gb3 in podocytes plays an important role in the pathogenesis of glomerular damage. However, due to the lack of appropriate animal or cellular models, podocyte damage in Fabry’s disease could not be directly studied yet. As murine models are insufficient, a human model is needed. Here, we developed a human podocyte model of Fabry’s disease by combining RNA interference technology with lentiviral transduction of human podocytes. Knockdown of α-galactosidase A expression resulted in diminished enzymatic activity and slowly progressive accumulation of intracellular Gb3. Interestingly, these changes were accompanied by an increase in autophagosomes as indicated by an increased abundance of LC3-II and a loss of mTOR kinase activity, a negative regulator of the autophagic machinery. These data suggest that dysregulated autophagy in α-galactosidase A-deficient podocytes may be the result of deficient mTOR kinase activity. This finding links the lysosomal enzymatic defect in Fabry’s disease to deregulated autophagy pathways and provides a promising new direction for further studies on the pathomechanism of glomerular injury in Fabry patients.

Highlights

Fabry’s disease is a lysosomal storage disorder resulting from an inborn error of glycosphingolipid metabolism [1]
While recent clinical work has convincingly addressed the value and efficiency of a-galactosidase A (a-Gal A) enzyme replacement therapy [9,10,11,12], the underlying pathophysiology leading to the development of renal functional impairment in Fabry patients remains obscure
Multiple studies have confirmed that podocyte damage results in development of proteinuria, focal and segmental glomerulosclerosis (FSGS) and end-stage renal disease (ESRD)

Summary

Introduction

Fabry’s disease is a lysosomal storage disorder resulting from an inborn error of glycosphingolipid metabolism [1]. In Fabry’s disease a mutation in the gene encoding a-galactosidase A (a-Gal A) on the X chromosome (GLA gene) leads to deficiency or impaired function of this lysosomal enzyme. This defect results in a reduced degradation of substrates with terminally a-glycosidically bound galactose (mostly Globotriaosylceramide Gb3) and the subsequent accumulation of these metabolic products in lysosomes of virtually all cells of the human body. As Fabry’s disease is an X-linked disorder hemizygous males are more frequently and more severely affected than females. Some females are not affected at all, even at higher age, and other females have a full-blown Fabry phenotype

Methods

Results

Conclusion