Molecular and cellular effects induced by hexavalent chromium in Mediterranean mussels

The present study evaluated the effects of Cr(VI) in digestive gland of the Mediterranean mussel (Mytilus galloprovincialis) exposed for 1 week to the metal at 1, 10, and 50 ng/L. Tissue accumulation of Cr and lysosomal biomarkers were measured. Moreover, a low-density DNA microarray was used to identify early molecular markers of metal exposure. A concentration-dependent increase in tissue Cr concentrations was observed in both digestive gland and remaining soft tissues. A reduction of lysosomal membrane stability was detected in digestive gland at 10 and 50 ng/L of Cr(VI), indicating a loss of cell functional integrity. The expression of mRNAs encoding 13 genes involved in metal resistance (mt10, mt20), molecular chaperoning (hsp70), immune response (mytlB, mytcA and lys), transcriptional (histones h1, h2-a and h4), and antioxidant/detoxification (cat, mrp2, mvp) processes were significantly altered already at the lowest Cr(VI) concentration, where the effects at the histological level were nonsignificant. Altogether, data point out that depending on the exposure concentration Cr(VI) may cause or not oxidative stress altering the efficiency of the antioxidant system in counteracting the effects of Cr as a redox-active metal. Moreover, changes of mRNA expression profiles induced by Cr(VI) concentrations as low as 1-50 ng/L were related to altered immunomodulation, DNA stability, and stress response pathways previously proven to be affected by the metal. The molecular targets presently identified may drive the development of new biomarkers for Cr exposure or help their interpretation.