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  • Cadmium disorganises the sc...
    Boucherie, Sylviane; Decaens, Catherine; Verbavatz, Jean-Marc; Grosse, Brigitte; Erard, Marie; Merola, Fabienne; Cassio, Doris; Combettes, Laurent

    Biology of the cell, December 2013, Volume: 105, Issue: 12
    Journal Article

    Background Information Hepatocytes, which perform the main functions of the liver, are particularly vulnerable to toxic agents such as cadmium, an environmental pollutant. To identify the molecular targets for cadmium in hepatocytes, we have studied the effects of CdCl2 on the hybrid cell line WIF‐B9 that exhibits stable structural and functional hepatocytic polarity. Results We showed that the toxicity of CdCl2 (1 µM, 24 h) resulted in a reduction in direct intercellular communication (via gap junctions) and in an increase in paracellular permeability (decrease in the sealing of tight junctions). These effects were not related to changes in the expression of the key proteins involved, Cx32 and claudin 2, the first being constitutive of gap junctions and the second of tight junctions in this cell line. Using immunofluorescence experiments, we observed a change in the location of Cx32 and claudin 2: these two proteins were less often found in the tight junction network that closes the bile canaliculi (BC). In control cells, ‘Proximity Ligation Assay’ (PLA Duolink®) has confirmed in situ that molecules of claudin 2 and Cx32 are very close to each other at the BC (probably less than 16 nm). This was no longer the case after treatment with CdCl2. Localisation of occludin and Cx32 relative to each other was not modified by CdCl2, but CdCl2 increased the PLA signal between molecules of JAM‐A and Cx32. Finally, examination of freeze‐fracture replicas obtained from cultures treated with CdCl2 showed the disruption of the network of tight junctions and the depletion or the disintegration of the junctional plaques associated with tight junctions. Conclusions This study demonstrates in situ the changes induced by cadmium on the organisation of cell–cell junctions and points out the importance of the association Cx32/claudin 2 for the maintenance of normal hepatocyte functions. Research Article The organisation of cell–cell junctions is crucial for the maintenance of integrity and functions of the liver parenchyma. In the polarised hepatic cell line WIF‐B9, we showed that cadmium, an environmental pollutant, disturbed the arrangement of gap and tight junction proteins, particularly the association Cx32/claudin 2. Cadmium caused a loss of intercellular communication and altered the tightness of the paracellular barrier. Freeze‐fracture images (left panel) highlighted the damage caused by cadmium to intercellular junctions and PLA (right panel) demonstrated that the association Cx32/Claudin 2 was disrupted by cadmium.