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5.3 Lysosomal Responses and Pathological Reactions to Environmental Stressors
Pathological reactions involving the lysosomal system are often linked to augmented
autophagic sequestration of cellular components; and numerous studies have shown that
many environmental stressors including pollution are capable of inducing cellular autoph-
agy in the cells of social amoebae (slime molds, myxomycetes), aquatic mollusks, and fish
(Köhler et al. 2002; Moore et al. 2004a, 2006a, 2007; Dondero et al. 2006; Einsporn and
Koehler 2008a, b). Protistans, earthworms, aquatic mollusks, and flatfish are now widely
used in monitoring the health of the environment, while fish and mollusks also provide
about 20% of global animal protein consumed by mankind, hence raising issues of food
safety and security of supply (Deutsch et al. 2007).
Autophagy is often considered to be primarily a survival strategy in multicellular organ-
isms, which is initiated by stressors (e.g., restricted nutrients, hyperthermia, hypoxia, and
salinity increase; Klionsky and Emr 2000; Cuervo 2004; Moore et al. 2006a, b, c). However,
recent evidence indicates that autophagy is much more than just a survival process and is,
in fact, intimately involved in cell physiology (Moore et al. 1980, 2006a; Moore 1988, 2004;
Cuervo 2004; Lockshin and Zakeri 2004). Augmented autophagy is apparently controlled by
switching off the mTOR kinase: mTOR signaling is involved in many aspects of cell growth
regulation and has been implicated in some cancers (Asnaghi et al. 2004; Proud 2002; Levine
2005). mTOR kinase is also coupled with a nutrient sensing pathway, and is switched off
by lack of nutrients (see review by Proud 2002). This kinase is evolutionarily conserved in
eukaryotes and has been variously described in yeast, nematodes, mollusks, insects, crus-
taceans, and mammals (Klionsky and Emr 2000; Beaumont et al. 2001; Cammalleri et al.
2003; Levine 2005; Klionsky et al. 2007). The mTOR signaling system is classically switched
off by nutrient deprivation, with resultant up-regulation of autophagy in mammals, which
has been described in mussels and marine and terrestrial snails as well (Moore and Halton
1973, 1977; Bayne et al. 1978, 1979; Moore et al. 1978, 1979, 1985, 1986; Proud 2002; Bergamini
et al. 2003; Cuervo 2004). Hypoxia also switches off the mTOR protein and has previously
been demonstrated to induce autophagy in eukaryotes including mussels (Moore et al.
1979; Proud 2002; Wouters et al. 2005; Hipkiss 2006), as have both increases and decreases in
salinity (Moore and Halton 1973, 1977; Moore et al. 1980, 1985; Pipe and Moore 1985).
Lysosomal and autophagic responses and reactions to environmental stressors have
been widely documented in the scientific literature. As well as being used in a variety of
marine sentinel species, they have also been used in amoebic slime molds and earthworms
for assessing the impacts of soil contamination.
Tests involving lysosomal biomarkers in marine bivalves have been extensively used in
this context, including blue and green mussels and oysters (Moore et al. 2004, 2008). The
flatfish, flounder, and dab, have also been used, particularly in the North Sea (Köhler et al.
1992; Moore et al. 2004a, b, 2008).
5.4 Linking Lysosomal Biomarkers with Other Ecotoxicological Effects
5.4.1 Physiological Relevance of Lysosomal and Autophagic Responses
Physiological responses and pathological reactions to environmental stressors in mollus-
can digestive gland cells (hepatocyte analogues), phagocytic hemocytes (blood cells), and
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