Stress protein synthesis and accumulation after traumatic injury of crayfish CNS

Heat shock proteins (chaperones) in fish and shellfish and their potential role in relation to fish health: a review

Heat shock proteins (HSPs), also known as stress proteins and extrinsic chaperones, are a suite of highly conserved proteins of varying molecular weight (c. 16-100 kDa) produced in all cellular organisms when they are exposed to stress. They develop following up-regulation of specific genes, whose transcription is mediated by the interaction of heat shock factors with heat shock elements in gene promoter regions. HSPs function as helper molecules or chaperones for all protein and lipid metabolic activities of the cell, and it is now recognized that the up-regulation in response to stress is universal to all cells and not restricted to heat stress. Thus, other stressors such as anoxia, ischaemia, toxins, protein degradation, hypoxia, acidosis and microbial damage will also lead to their up-regulation. They play a fundamental role in the regulation of normal protein synthesis within the cell. HSP families, such as HSP90 and HSP70, are critical to the folding and assembly of other cellular proteins and are also involved in regulation of kinetic partitioning between folding, translocation and aggregation within the cell. HSPs also have a wider role in relation to the function of the immune system, apoptosis and various facets of the inflammatory process. In aquatic animals, they have been shown to play an important role in health, in relation to the host response to environmental pollutants, to food toxins and in particular in the development of inflammation and the specific and non-specific immune responses to bacterial and viral infections in both finfish and shrimp. With the recent development of non-traumatic methods for enhancing HSP levels in fish and shrimp populations via heat, via provision of exogenous HSPs or by oral or water administration of HSP stimulants, they have also, in addition to the health effects, been demonstrated to be valuable in contributing to reducing trauma and physical stress in relation to husbandry events such as transportation and vaccination.

Feeding Artemia franciscana (Kellogg) larvae with bacterial heat shock protein, protects from Vibrio campbellii infection

Among their numerous physiological effects, heat shock proteins (Hsps) are potent immunomodulators, a characteristic reflecting their potential as therapeutic agents and which led to their application in combating infection. As an example, the up-regulation of endogenous Hsp70 in the branchiopod crustacean Artemia franciscana (Kellogg) is concurrent with shielding against bacterial infection. To better understand this protective mechanism, gnotobiotic Artemia were fed with Escherichia coli treated to over-produce different prokaryotic Hsps. This was shown to increase larval resistance to experimental Vibrio campbellii exposure. Immunoprobing of Western blots showed that the enhanced resistance to V. campbellii correlated with DnaK production in E coli. A definitive role for DnaK was then demonstrated by feeding Artemia larvae with transformed bacteria over-producing only this protein, although other Hsps such as DnaJ and grpE also provided tolerance against Vibrio infection. Feeding of bacteria synthesizing selected Hsps is therefore suggested as an alternative to antibiotic use as a means of enhancing resistance of Artemia larvae to bacterial infection, which may have potential applications in aquaculture.

Impact of natural organic matter (NOM) on freshwater amphipods

Natural organic matter (NOM) isolated from the eutrophic Sanctuary Pond (Point Pelee National Park, Canada) has an adverse impact on amphipod species (Gammarus tigrinus and Chaetogammarus ischnus from Lake Müggelsee, Germany, and Eulimnogammarus cyaneus, from Lake Baikal, Russia). Increases in amphipod mortality, changes in peroxidase activity and increases of heat shock protein (hsp70) expression were observed upon exposure to NOM. The highest resistance to the adverse impact of NOM was observed with the endemic Baikalian amphipod E. cyaneus. However, the mechanisms behind this finding remains obscure. If differences in the sensitivity of the hsp70 antibody may be excluded, different modes of action may be postulated: because the adverse impact of NOM may be caused by reactive oxygen species (ROS) and the NOM itself, the observed differences may be due to the action of ROS alone (with E. cyaneus) and a combination of both adverse modes of action (European species).

A newly developed ELISA showing the effect of environmental stress on levels of hsp86 in Cherax quadricarinatus and Penaeus monodon

The induction of hsps by stress in Cherax quadricarinatus and Penaeus monodon was investigated using SDS-PAGE, Western blotting and ELISA techniques. Western blotting showed the presence of an immuno-reactive protein to mouse alpha-human hsp70 IgG1 monoclonal antibody at a mass of 86 kDa (hsp86) in pleopod samples but was not sensitive enough to detect differences in response to stress. An enzyme-linked immunosorbent assay (ELISA) was developed using this antibody for the detection of hsp86 in the pleopods of C. quadricarinatus and P. monodon. Using this assay, significantly higher levels of hsp86 were detected in hyperthermally stressed C. quadricarinatus (21 to 70 g) and P. monodon (14 to 32 g) and hypoosmotically stressed P. monodon (14 to 32 g). Male C. quadricarinatus and P. monodon were thermally stressed with an increase in temperature from 24 to 33 degrees C for a period of 2 h then a recovery period of 6 h. SDS-PAGE gels of thermally stressed C. quadricarinatus and P. monodon samples revealed an increase in protein band intensity at 97 kDa (C. quadricarinatus) and 43 and 35 kDa in P. monodon. A 25 kDa mass protein was induced in C. quadricarinatus when thermally stressed. P. monodon were osmotically stressed with a decrease from 31 to 15 ppt for 2 h with a recovery of 6 h. SDS-PAGE gels revealed increased intensity of bands at 35 and 43 kDa and a 100 kDa band was induced demonstrating a wide range response of protein profile to stress in these species. SDS-PAGE gels of both species investigated also revealed an apparent reduction in band intensity of the haemocyanin subunits in stressed samples. The ELISA described here constitutes the first quantitative assay for the detection of a hsp in crustaceans and the following investigations are believed to be the first to describe the response of hsps to stress in C. quadricarinatus and P. monodon. In doing so, they provide a sound basis for future studies of the role of hsps in physiological functions in commercially cultured crustaceans.

Heat-shock proteins in axoplasm: high constitutive levels and transfer of inducible isoforms from glia

To characterize heat-shock proteins (HSPs) of the 70-kDa family in the crayfish medial giant axon (MGA), we analyzed axoplasmic proteins separately from proteins of the glial sheath. Several different molecular weight isoforms of constitutive HSP 70s that were detected on immunoblots were approximately 1-3% of the total protein in the axoplasm of MGAs. To investigate inducible HSPs, MGAs were heat shocked in vitro or in vivo, then the axon was bathed in radiolabeled amino acid for 4 hours. After either heat-shock treatment, protein synthesis in the glial sheath was decreased compared with that of control axons, and newly synthesized proteins of 72 kDa, 84 kDa, and 87 kDa appeared in both the axoplasm and the sheath. Because these radiolabeled proteins were present in MGAs only after heat-shock treatments, we interpreted the newly synthesized proteins of 72 kDa, 84 kDa, and 87 kDa to be inducible HSPs. Furthermore, the 72-kDa radiolabeled band in heat-shocked axoplasm and glial sheath samples comigrated with a band possessing HSP 70 immunoreactivity. The amount of heat-induced proteins in axoplasm samples was greater after a 2-hour heat shock than after a 1-hour heat shock. These data indicate that MGA axoplasm contains relatively high levels of constitutive HSP 70s and that, after heat shock, MGA axoplasm obtains inducible HSPs of 72 kDa, 84 kDa, and 87 kDa from the glial sheath. These constitutive and inducible HSPs may help MGAs maintain essential structures and functions following acute heat shock.

Glutamine cycle enzymes in the crayfish giant nerve fiber: implications for axon-to-glia signaling

Two of the key enzymes involved in glutamate metabolism, glutaminase and glutamine synthetase, were quantitatively localized to axons and glia of the crayfish giant nerve fiber by immunocytochemistry and electron microscopy of antibody-linked gold microspheres. In Western blots, rabbit antisera for glutamine synthetase and glutaminase specifically recognized crayfish polypeptides corresponding approximately in size to subunits of purified mammalian brain enzymes. Glutamine synthetase immunoreactivity was found to be 11 times greater in the adaxonal glial cells than in the axon. Glutaminase immunoreactivity was found in somewhat greater concentration (2.5:1) in glia as compared to axoplasm. Glutamate immunoreactivity also was evaluated and found to be present in high concentration in both glia and axons, as might be expected for an important substrate of cellular metabolism. Using radiolabeled substrates it was demonstrated that glutamine and glutamate were interconverted by the native enzymes in the intact crayfish giant nerve fiber and that the formation of glutamine from glutamate occurred in the axoplasm-free nerve fiber, the cellular component of which is primarily periaxonal glia. The results of this investigation provide immunocytochemical and metabolic evidence consistent with an intercellular glutamine cycle that modulates the concentration of periaxonal glutamate and glutamine in a manner similar to that described for perisynaptic regions of the vertebrate central nervous system. These findings further corroborate previous electrophysiological evidence that glutamate serves as the axon-to-glial cell neurochemical signal that activates glial cell mechanisms responsible for periaxonal ion homeostasis.

70-kDa heat shock protein expression in cultured rat astrocytes after hypoxia: regulatory effect of almitrine

Induction of heat shock proteins (Hsps), especially the 70-kDa family, is well observed in nervous tissues in response to various stressful conditions. By using rat astrocytes in primary culture, the expression of the inducible (Hsp70) and the constitutive (Hsc70) 70-kDa Hsps immunoreactivity of cells exposed to hypoxic conditions has been investigated. We observed that exposure of astroglial cells to an hypoxic-normoxic sequence induces a significant decrease of Hsc70 immunoreactivity. The presence of the heat inducible stress protein Hsp70 is never observed in hypoxic cells nor in control. Hsc 70 lowering is associated with ultrastructural alterations characterized by mitochondria swelling, formation of vacuoles and accumulation of dense material in the cell cytoplasm. The effects of addition of almitrine to the culture medium before and during hypoxia on Hsps immunoreactivity have been examined. The presence of the drug prevents the decrease of Hsc70 immunoreactivity induced by hypoxia. Furthermore, some ultrastructural improvement is observed in astroglial cells treated with almitrine suggesting some protecting role of Hsc70 on cell damage induced by hypoxia.

Whole intact tissue electrophoresis of nerve proteins

We describe a rapid and simple method for analyzing proteins along the length of a nerve tissue using sodium dodecylsulfate-polyacrylamide gel electrophoresis (SDS-PAGE). A long length of nerve tissue is placed on a slab gel, layered with SDS-buffer, and electrophoresed. In this whole-intact-tissue procedure, the in situ differences in location and/or concentration of protein along the length of a nerve tissue are not disturbed by homogenization and dilution prior to electrophoresis.

Stress proteins in aquatic organisms: an environmental perspective

The cellular stress response protects organisms from damage resulting from exposure to a wide variety of stressors, including elevated temperatures, ultraviolet (UV) light, trace metals, and xenobiotics. The stress response entails the rapid synthesis of a suite of proteins referred to as stress proteins, or heat-shock proteins, upon exposure to adverse environmental conditions. These proteins are highly conserved and have been found in organisms as diverse as bacteria, molluscs, and humans. In this review, we discuss the stress response in aquatic organisms from an environmental perspective. Our current understanding of the cellular functions of stress proteins is examined within the context of their role in repair and protection from environmentally induced damage, acquired tolerance, and environmental adaptation. The tissue specificity of the response and its significance relative to target organ toxicity also are addressed. In addition, the usefulness of using the stress response as a diagnostic in environmental toxicology is evaluated. From the studies discussed in this review, it is apparent that stress proteins are involved in organismal adaptation to both natural and anthropogenic environmental stress, and that further research using this focus will make important contributions to both environmental physiology and ecotoxicology.