Cadmium stress stimulates tissue turnover in Helix pomatia: increasing cell proliferation from metal tolerance to exhaustion in molluscan midgut gland

• Published in: Cell and tissue research 2010-07, Vol.341 (1), p.159-171
• Main Authors: Hödl, Elisabeth, Felder, Edward, Chabicovsky, Monika, Dallinger, Reinhard
• Format: Article
• Language: English
• Subjects: Adaptation, Physiological - drug effects; Analysis; Animal Structures - cytology; Animal Structures - drug effects; Animal Structures - metabolism; Animal Structures - ultrastructure; Animals; Biomedical and Life Sciences; Biomedicine; Cadmium; Cadmium - metabolism; Cadmium - toxicity; Cell growth; Cell Proliferation - drug effects; Digestive System - cytology; Digestive System - drug effects; Digestive System - metabolism; Digestive System - ultrastructure; Gastropoda; Health aspects; Heavy metal; Helix (Snails) - cytology; Helix (Snails) - drug effects; Helix (Snails) - ultrastructure; Helix pomatia; Helix pomatia (Mollusca); hepatopancreas; Human Genetics; Intracellular Space - drug effects; Intracellular Space - metabolism; Molecular Medicine; Mollusca; Mollusks; Oxidative stress; Proteomics; Regular Article; RNA; stress tolerance; Stress, Physiological - drug effects; Toxic effect; Toxicity
• ISSN: 0302-766X; 1432-0878
• DOI: 10.1007/s00441-010-0980-x

In terrestrial pulmonate snails, cadmium (Cd) uptake leads to the induction of a Cd-specific metallothionein isoform (Cd-MT) that protects against adverse interactions of this toxic metal ion. Increasing concentrations of Cd cause increased individual mortality possibly linked to pathological alterations in the snail midgut gland. Histological, immuno-histochemical, and electron-microscopic methods in combination with tissue metal analyses and quantification of MT induction parameters were applied to the midgut gland of Cd-exposed Roman snails (Helix pomatia). Conspicuous concentration-dependent alterations occurred in this organ, including the metal-induced increase of Cd-MT concentration and manifestation of Cd-MT mRNA precipitations in all midgut gland cell types. The most evident alteration was an increase of cellular turnover reflected by enhanced cell proliferation. Intensified vesiculation of endoplasmic reticulum was noted in basophilic cells and an increasing formation of lipofuscin granules in excretory cells. At the highest Cd concentrations, mitochondrial membranes were disrupted in basophilic cells, and lipofuscin granules were released from excretory cells into the midgut gland tubular system. Some of these alterations (e.g., increased cell proliferation rate, vesiculation of endoplasmic reticulum) detected at low Cd concentrations were interpreted as adaptive response processes enhancing the tolerance of exposed individuals to metal stress. Cellular alterations at higher Cd concentrations (e.g., mitochondrial structural damage) clearly represented ongoing irreversible cellular disruption. Combined evaluation of cellular biomarkers and MT saturation levels indicated that the transition from stress resistance to depletion of resistance capacity occurred above a threshold of 0.8 µmol Cd/g dry weight in the midgut gland of H. pomatia. At these Cd concentrations, Cd-MT was saturated with Cd²⁺ ions, whereas at the cellular level, structural alterations turned into pathological deterioration.