Haemocyte apoptosis as a general cellular immune response of the snail, Lymnaea stagnalis, to a toxicant

Abstract

The effects of a xenobiotic on the circulating haemocytes of Lymnaea stagnalis were investigated after short-term (24 h, 96 h) and long-term (504 h) exposure of snails to environmental concentrations. Fomesafen, a pro-oxidant generator led to the activation of the haemocyte apoptotic program by promoting reactive oxygen species (ROS). Cells entering apoptosis underwent a series of events, both on the plasma membrane and in the mitochondria; these events were quantified by flow cytofluorometry. The data showed a loss of mitochondrial transmembrane potential (Deltapsim), which was dose-dependent and time-dependent and related to an increased release of superoxide anions. The phosphatidylserine that was exposed at the outer plasma membrane was not related to the disruption of either ROS or Deltapsim but was strongly correlated with the haemocyte concentration (total haemocyte count). This cascade of apoptotic processes occurred in a dose-independent manner and was not strengthened over time. The increase of circulating haemocytes depended upon the life span of the cells and might have reflected either facilitated cell turn-over or the accompanying presence of haemocytes phagocytosing apoptotic cells.

Apoptosis and its functional significance in molluscs

“…Cell surface exposure of phosphatydylserine is an important hallmark of apoptosis. It is a phylogenetically well conserved process, which was demonstrated in a number of vertebrate species and in a few invertebrates [12][13][14][15]. Integrin-like molecules mediate hemocyte adhesion, which is an initial step in phagocytosis of foreign particles.…”

“…Dashed line represents hypothetical pathway. Abbreviations: R receptor, FADD Fas-associated death domain, Apaf1 apoptotic peptidase activity factor 1, AIF apoptosis inducing factor, ROS reactive oxygen species, GPCR G-protein coupled receptor, AC adenylate cyclase, MAPK mitogen-activated protein kinase, PKA and PKC protein kinases, TRAIL TNF-related apoptosis-inducing ligand, TNF tumor necrosis factor, UV ultra violet, CREB cAMP response element binding protein [12]. Cell surface exposure of phosphatydylserine is an important hallmark of apoptosis.…”

Effect of a toxicant on phagocytosis pathways in the freshwater snail Lymnaea stagnalis

“…Despite an exceptionally high rate of circulating cells being observed in exposed snails (Russo and Madec 2007), a cell population (M3) with a sustained increase in lectin binding appears after long-term incubations (504 h) in controls, in vehicle controls and in fomesafen-treated snails. This can be related to the cell turn-over and/or to the age of snails, whereas no noticeable modification of plasma membrane carbohydrate moieties has been reported in the course of haemocyte maturation (Dikkeboom et al 1988).…”

“…In L. stagnalis, previous studies have shown that, in addition to an impaired phagocytosis , the herbicide fomesafen can trigger apoptosis in haemocytes (Russo and Madec 2007). Thus, in the present study, we have investigated the effects of the herbicide on various haemocyte membrane ligands and on the actin cytoskeleton.…”

“…Haemocytes are the immune competent cells of freshwater snails, some of them being professional phagocytes. In addition to the decrease in phagocytic capabilities, toxicants also trigger a number of other biological effects in the haemocytes, such as increased lysosomal fragility or apoptosis (Russo and Madec 2007). One mechanism that may explain the toxic activity of fomesafen is based on the adverse effects observed on membranes during oxidative stress.…”