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highly effective first-tier standard protective enzymes and antioxidants, as well as second-
tier autophagic antioxidant defensive systems for dealing with oxidative stress (Figure
5.6; Moore et al. 2006c; Moore 2008). The corollary of this is that an ability for rapid up-
regulation of autophagy is a probable necessity for acquisition of tolerance in high stress
environmental scenarios (Moore 2008). Support for this hypothesis comes from the previ-
ously described study of blue mussels from a heavily polluted site in Norway that show
evidence of tolerance, in comparison with less contaminated mussels (Moore et al. 2006c).
Changes in lysosomes have been used as biomarkers of aging in a wide range of organ-
isms including nematodes, fruit flies, mollusks, and mammals (Hole et al. 1992; Cuervo
and Dice 2000; Lockshin and Zakeri 2004). In general, there is a trend for decreasing pro-
teolytic capability with increased age that has been linked with a gradual decline in the
efficiency of the autophagic process (Cuervo and Dice 2000; Ryazonov and Nefsky 2002;
Bergamini et al. 2003). However, Bergamini et al. (2003) have proposed that repeated trig-
gering of the autophagic system by nutrient deprivation or caloric restriction will prevent
the decline in proteolytic capacity and, hence, contribute to increased life span, probably
through the maintenance of more efficient cellular housekeeping. This may parallel the
situation with animals such as mussels that live in an environment where autophagy is
repeatedly switched on and off as discussed above, thus maintaining an effective capacity
for the removal of altered proteins, membranes, and organelles that are damaged by ROS
and hypoxia-induced methylglyoxal (Tavernarakis and Driscoll 2002; Lockshin and Zakeri
2004; Moore et al. 2006c, 2007). Further investigation of the significance of autophagy in
conferring resistance to stress is required, but the possibility raises provocative questions
about the role of ongoing and fluctuating low levels of stress in the evolution of stress
tolerance.
Animals such as marine mussels and periwinkles (e.g., Littorina species) are robust ani-
mals that frequently live in fluctuating environments such as estuaries where they are
subjected to variable nutritional, temperature, and salinity regimes, as well as repeated
air exposure (which results in hypoxia) and reimmersion in seawater (Moore et al. 2006c,
2007). Consequently, this essentially stressful fluctuating environment will tend to trigger
repeated autophagic events, which by effectively removing inappropriately altered pro-
teins and damaged or redundant cellular constituents will result in more efficient cellular
housekeeping and help to minimize the formation of harmful lipofuscin and other aggre-
gates (Kirchin et al. 1992; Klionsky and Emr 2000; Ryazanov and Nefsky 2002; Bergamini
et al. 2003). This more efficient cellular functionality may underpin the ability of mussels
to survive, and often thrive, in environments that are subject to man-made stresses such
as chemical pollution (Moore et al. 2006c, 2007).
5.5.2 Extending Lysosomal Biomarkers to Nonmarine Environments
Given the increasing demands for environmentally sustainable food production, it is
essential to have effective indicators of the health and growth of the prospective food
animals, whether these are farmed (aquaculture) or from the wild, as well as the quality
of their environment. Indicators of animal well-being and potential for growth are pro-
vided by cellular biomarkers of lysosomal and autophagic processes in both mollusks and
fish (Moore 1985; Köhler et al. 2002; Moore et al. 2006a, 2007). Other studies have shown
that lysosomal biomarkers can also be used in protistans, coelenterates, annelid worms,
and crustaceans (Moore and Stebbing 1976; Svendsen and Weeks 1995; Brown et al. 2004;
Svendsen et al. 2004; Dondero et al. 2006; Galloway et al. 2006; Nolde et al. 2006; Sforzini
et al. 2008).
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