Enhancing lysosomal biogenesis and autophagic flux by activating the transcription factor EB protects against cadmium-induced neurotoxicity

Huifeng Pi,Zhengping Yu,Li Tian,Min Li,Zhiqi Yang,Zhou Zhou

doi:10.1038/srep43466

Abstract

Cadmium (Cd), a highly ubiquitous heavy metal, is a well-known inducer of neurotoxicity. However, the mechanism underlying cadmium-induced neurotoxicity remains unclear. In this study, we found that Cd inhibits autophagosome-lysosome fusion and impairs lysosomal function by reducing the levels of lysosomal-associated membrane proteins, inhibiting lysosomal proteolysis and altering lysosomal pH, contributing to defects in autophagic clearance and subsequently leading to nerve cell death. In addition, Cd decreases transcription factor EB (TFEB) expression at both the mRNA and protein levels. Furthermore, Cd induces the nuclear translocation of TFEB and TFEB target-gene expression, associated with compromised lysosomal function or a compensatory effect after the impairment of the autophagic flux. Notably, restoration of the levels of lysosomal-associated membrane protein, lysosomal proteolysis, lysosomal pH and autophagic flux through Tfeb overexpression protects against Cd-induced neurotoxicity, and this protective effect is incompletely dependent on TFEB nuclear translocation. Moreover, gene transfer of the master autophagy regulator TFEB results in the clearance of toxic proteins and the correction of Cd-induced neurotoxicity in vivo. Our study is the first to demonstrate that Cd disrupts lysosomal function and autophagic flux and manipulation of TFEB signalling may be a therapeutic approach for antagonizing Cd-induced neurotoxicity.

Highlights

Cadmium (Cd) is a widespread non-biodegradable industrial and environmental pollutant that can be greatly concentrated in the food chain[1]
Based on our data from LysoSensor Green DND-189 staining, Cd increased the pH of acidic compartments. These results suggest that Cd impairs lysosomal function by reducing the levels of lysosomal-associated membrane proteins, inhibiting lysosomal proteolysis and altering lysosomal pH in Neuro-2a cells
We first demonstrate that (i) Cd blocks autophagic flux via the inhibition of autophagosome-lysosome fusion and the disruption of lysosomal function; (ii) Cd decreases transcription factor EB (TFEB) expression but induces nuclear translocation of endogenous TFEB and TFEB-target gene expression, associated with compromised lysosomal function or a compensatory effect after the impairment of the autophagic flux; (iii) TFEB plays a critical role in enhancing autophagic flux and cytoprotection against Cd injury, and this protective effect is independent, at least in part, of its role as a nuclear transcription factor

Summary

Introduction

Cadmium (Cd) is a widespread non-biodegradable industrial and environmental pollutant that can be greatly concentrated in the food chain[1]. Autophagy is an evolutionarily conserved membrane process that results in the transportation of cellular contents to lysosomes for degradation. TFEB controls the transcription of target genes that are closely related to lysosomal structure and function, including hydrolases, lysosomal membrane proteins and the V-ATPase complex[8]. In vivo TFEB overexpression increased autophagic flux and lysosomal function in neurodegenerative disorders[9,10,11,12]. We characterized the effect of TFEB overexpression on lysosomal and autophagic accumulation in Cd-induced neurotoxicity. TFEB expression markedly increased the levels of lysosomal membrane protein, preserved lysosomal protease activity, maintained the lysosomal pH level and restored cell viability. TFEB overexpression alleviated autophagic pathology by promoting autophagosome-lysosome fusion and the removal of autolysosomes. The modulation of TFEB activity holds promise for the development of better therapy for this devastating disorder

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