Cadmium affects autophagy in the human intestinal cells Caco-2 through ROS-mediated ERK activation.

Myriam Mireault,Yong Xiao,Benoît Barbeau,Catherine Jumarie

doi:10.1007/s10565-021-09655-4

Myriam Mireault, Yong Xiao + Show 2 more

Open Access

https://doi.org/10.1007/s10565-021-09655-4

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Abstract

Cadmium is a toxic metal that enters the food chain. Following oral ingestion, the intestinal epithelium has the capacity to accumulate high levels of this metal. We have previously shown that Cd induces ERK1/2 activation in differentiated but not proliferative human enterocytic-like Caco-2 cells. As autophagy is a dynamic process that plays a critical role in intestinal mucosa, we aimed the present study 1) to investigate the role of p-ERK1/2 in constitutive autophagy in proliferative Caco-2 cells and 2) to investigate whether Cd-induced activation of ERK1/2 modifies autophagic activity in postconfluent Caco-2 cell monolayers. Western blot analyses of ERK1/2 and autophagic markers (LC3, SQSTM1), and cellular staining with acridine orange showed that ERK1/2 and autophagic activities both decreased with time in culture. GFP-LC3 fluorescence was also associated with proliferative cells and the presence of a constitutive ERK1/2-dependent autophagic flux was demonstrated in proliferative but not in postconfluent cells. In the latter condition, serum and glucose deprivation triggered autophagy via a transient phosphorylation of ERK1/2, whereas Cd-modified autophagy via a ROS-dependent sustained activation of ERK1/2. Basal autophagy flux in proliferative cells and Cd-induced increases in autophagic markers in postconfluent cells both involved p-ERK1/2. Whether Cd blocks autophagic flux in older cell cultures remains to be clarified but our data suggest dual effects. Our results prompt further studies investigating the consequences that Cd-induced ERK1/2 activation and the related effect on autophagy may have on the intestinal cells, which may accumulate and trap high levels of Cd under some nutritional conditions.

Highlights

Cadmium is a widespread highly toxic metal classified as a type I carcinogen responsible for renal dysfunction, osteoporosis, immunosuppression and hepatotoxicity
We used acridine orange (AO) to address the extent of ongoing autophagy through detection of autolysosomes
This correlation was demonstrated in regions with cell aggregates: central regions were devoid of red AO fluorescence, while at the periphery, where proliferation takes place, red staining was evident (Fig. 1C)

Summary

Introduction

Cadmium is a widespread highly toxic metal classified as a type I carcinogen responsible for renal dysfunction, osteoporosis, immunosuppression and hepatotoxicity. Cadmium enters the food chain and, except for workers in mining industry and cigarette smokers, chronic oral absorption of contaminated food products represents the main exposure source for the general population (Andersen et al 2004; Rani et al 2014). The gut epithelium represents the first protective barrier against Cd toxicity. The intestinal epithelium represents one of the first target tissue of the ingested Cd. Intestinal toxicity of Cd includes disruption of intercellular junctions, paracellular leakage and inflammation (for review see Tinkov et al 2018). Redox signaling is involved in the regulation of biochemical processes. ROS are probably involved in many cellular response following exposure to Cd. Cadmium may modify signaling cascades, including the extracellular signal-regulated kinases (ERK1/2), c-JUN N-terminal kinase (JNK) and p38 kinase in various cell types (Thévenod and Lee 2013)

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