Physiological Adaptations of Stressed Fish to Polluted Environments: Role of Heat Shock Proteins

Abstract

Fish are subjected to a wide variety of environmental stressors. Stressors affect fish at all life stages and the stress-specific responses that occur at the biochemical and physiological levels affect the overall health and longevity of such animals. In this review, the organ-specific alterations in fish that inhabit polluted environments are addressed in detail. Fish,like other vertebrates, have evolved strategies to counteract stress-mediated effects. Among the key strategies that fish have developed is the induction of HSPs. The primary functions of HSPs are to promote the proper folding or refolding of proteins, to prevent potentially damaging interactions with proteins, and aiding in the disassembly of formations of protein aggregates. Stress, a state of unbalanced tissue oxidation, causes a general disturbance in the cellular antioxidant and redox balance and evokes HSP70 overexpression. Distinct families of HSPs have diverse physiological functions, and their induction, which is regulated at the transcriptional level, is mediated by the activation of heat shock factors. Interestingly, HSPs also interact with a wide variety of signaling molecules that modulate stress-mediated apoptotic effects. Hence, HSP induction is of major importance for maintenance of cell homeostasis. HSP-mediated adaptation processes are regarded as a fundamental protective mechanism that decreases cellular sensitivity to damaging events. Thus, the adaptive expression of HSPs is a protective response that helps combat stress-induced conformational damage to proteins. Additional research is needed to gain further information on the functional significance and role of individual HSPs and to enhance the understanding of the molecular mechanisms by which they act. In addition, field studies are needed to allow comprehensive evaluation of the potential use of HSPs as biomarkers for environmental monitoring. Furthermore, the expression of HSPs in fish fluctuates in response to seasonal variation. Because HSPs serves as a tool for assessing the stressed state of individuals and/or populations, the impact of seasonal influences on constitutive and inducible factors of these proteins should also be elucidated. Such research will lead to a fundamental improvement in the understanding of the functional role of HSPs in response to natural environmental changes and may allow correlation of the action of HSPs at the molecular level with the whole organismal stress response, which, so far, remains unexplained.

Oxidative stress markers in fish (Astyanax sp. and Danio rerio) exposed to urban and agricultural effluents in the Brazilian Pampa biome

“…The main function of these chaperones is to support the proper folding of proteins, thus preventing damage under stress conditions. Disturbances in the cellular redox balance are shown to evoke HSP70 overexpression (Padmini 2010), a chaperone widely used in biomonitoring studies (Iwama et al 2004). …”

Influence of acclimation temperature on the induction of heat-shock protein 70 in the catfish Horabagrus brachysoma (Günther)

“…Thus, HSPs play an important role in the process of acquired thermotolerance (Kregel 2002). Among the stress proteins, the HSP70, which comprise both the constitutive and inducible isoforms, is the most widely studied group (Ekambaram 2010) and is highly conserved across phyla from bacteria to mammals (Schlesinger 1990). They play vital roles in protein metabolism during normal and stressful conditions such as preventing aggregation or improper folding of proteins, membrane translocation, localization of proteins to their appropriate cellular compartment or degradation of misfolded protein (Bukau and Horwich 1998;Kregel 2002).…”

Environmental Pollution and Oxidative Stress in Fish

“…The long-term effect of pollutants, typical for chronically and heavily polluted areas, the enhancement of ROS level and perturbation of antioxidant efficiency often prelude the onset of significant alterations like protein and DNA damage, lipid peroxidation (LPO) and enzyme inhibition (Winston & Di Giulio, 1991). Fish are particularly threatened by aquatic pollution, and the environmental stress they face may help to shape their ecology, evolution, or biological systems (Padmini, 2010).…”

“…Proteins are considered to be important targets of free radical attack in cells (Eustace & Jay 2004;Almroth et al, 2008b; and thus compromise antioxidant defense, cellular function, and survival (Padmini, 2010). Therefore, protein oxidation, often under investigation in proteomic studies, has been recently proposed as a biomarker of oxidative stress (Sheehan, 2006;.…”