Mechanisms and Immunological Roles of Apoptosis in Molluscs

Abstract

Molluscan defense mechanisms are regulated to innate immunity, which is largely dependent on cellular components such as hemocytes possessing phagocytic and bactericidal activities. Among immune responses, apoptosis is an indispensable process because it enables the adequate clearance of damaged, senescent and infected cells without inflammation. Available information related to the molecular mechanisms of apoptosis has been accumulated for many molluscan species during the last decade. Almost all molluscan species live in an environment that changes incessantly according to microorganisms, industrial pollutants, temperature, and salinity. Such environmental factors might directly or indirectly induce apoptosis in molluscan cells. One type of apoptotic agent, reactive oxygen intermediates (ROIs), which are produced by a stress signal or phagocytosis, triggers apoptotic cell death in molluscan hemocytes. Dysfunction of ROI-mediated hemocytic apoptosis putatively causes disease morbidity and/or mortality when molluscan organisms are infected by pathogens. Furthermore, integrins have attracted attention for their unique functions because integrins regulate the phagocytic ability of molluscan hemocytes and induce hemocytic apoptosis. That process might be the result of ROI-generation. In this review, we summarize the roles and molecular mechanisms of apoptosis related to immunological functions of molluscan hemocytes.

The effects of zinc nanooxide on cellular stress responses of the freshwater mussels Unio tumidus are modulated by elevated temperature and organic pollutants

“…Activation of apoptosis is an important mechanism involved in the adaptive responses to stresses (Estévez-Calvar et al, 2013) which also plays an important role in environmental stress responses of mollusks (Terahara and Takahashi, 2008;Sokolova, 2009;Kiss, 2010). Apoptosis is involved in the clearance of damaged cells (Romero et al, 2011).…”

Apoptosis and its functional significance in molluscs

“…1). TNF-a and NF-jB transcription factors are involved in the extrinsic apoptotic signaling pathway in mollusks [26]. In bacterial infections, the expression of TNF-a increases in hemocytes.…”

Hemocytes of the carpet shell clam (Ruditapes decussatus) and the Manila clam (Ruditapes philippinarum): Current knowledge and future prospects

“…This does not, however, diminish the probable importance of oxidative mechanisms in physiological processes of hemocytes in bivalves. For instance, ROS production was shown to be involved in the induction of apoptotic mechanisms in the hemocytes of C. gigas (Terahara and Takahashi, 2008). Furthermore, in vertebrate cells, free radicals are also involved in various physiological processes such as cell signalling, gene expression, regulation of cell growth, reduction of metal ions, and regulation of matrix metalloproteinases or angiogenesis (for reviews, see Dröge, 2002;Bedard and Krause, 2007).…”