In vitro study of apoptosis in mussel (Perna canaliculus) haemocytes induced by lipopolysaccharide

Abstract

Apoptosis or programmed cell death is a fundamental process essential for an organism's development and homeostasis in the immune system of both vertebrates and invertebrates. However, little is known about apoptotic processes in marine bivalves which require further investigation to elucidate mechanisms and identify molecular effectors of cell death pathways. In this study, we characterized cellular and molecular mechanisms of apoptosis induced by lipopolysaccharide (LPS) in New Zealand Greenshell™ mussel (Perna canaliculus) haemocytes. Mussel haemocyte samples were exposed to different LPS concentrations (0, 50 and 100 μg ml−1) and incubated at 19 °C for 3 h prior to assessment of various cell health parameters via flow cytometry assays and GC/MS-based metabolomic analyses. Flow cytometry results showed slightly higher, but non-significant differences in production of reactive oxygen species between LPS-exposed and control (no LPS) samples. However, percentages of apoptotic cells determined via depolarization of the mitochondrial membrane potential and caspase-3/7 activity in LPS-exposed samples were significantly higher than in control samples, providing mechanistic information regarding initiation and progression of the apoptotic cascade. The metabolite profile of LPS-exposed haemocytes showed elevated levels of 11 metabolites compared to that of the control. These metabolites may be involved in protein and lipid degradation as a consequence of apoptosis and other immune or physiological responses. This study demonstrates that LPS could trigger apoptosis in mussel haemocytes and provides insights into apoptotic processes in mussel haemocytes. Such knowledge could be useful for understanding the immune responses of farmed bivalves to waterborne pathogens and identification of molecular biomarkers for disease management in aquaculture.