The heat shock response in congeneric land snails (Sphincterochila) from different habitats

Heat Shock Response and Heat Shock Proteins: Current Understanding and Future Opportunities in Human Diseases

The heat shock response is an evolutionarily conserved mechanism that protects cells or organisms from the harmful effects of various stressors such as heat, chemicals toxins, UV radiation, and oxidizing agents. The heat shock response triggers the expression of a specific set of genes and proteins known as heat shock genes/proteins or molecular chaperones, including HSP100, HSP90, HSP70, HSP60, and small HSPs. Heat shock proteins (HSPs) play a crucial role in thermotolerance and aiding in protecting cells from harmful insults of stressors. HSPs are involved in essential cellular functions such as protein folding, eliminating misfolded proteins, apoptosis, and modulating cell signaling. The stress response to various environmental insults has been extensively studied in organisms from prokaryotes to higher organisms. The responses of organisms to various environmental stressors rely on the intensity and threshold of the stress stimuli, which vary among organisms and cellular contexts. Studies on heat shock proteins have primarily focused on HSP70, HSP90, HSP60, small HSPs, and ubiquitin, along with their applications in human biology. The current review highlighted a comprehensive mechanism of heat shock response and explores the function of heat shock proteins in stress management, as well as their potential as therapeutic agents and diagnostic markers for various diseases.

Activities of antioxidant enzymes and Hsp levels in response to elevated temperature in land snail species with varied latitudinal distribution

Land snails occupy a variety of habitats, with differing temperature and humidity regimes and exhibit a wide span of adaptations, to withstand abiotic condition changes. The present work's aim was to examine the correlation of habitat's thermal adversity in different Mediterranean type habitats with the land snail's antioxidant and heat shock responses. For this purpose, snails of different species from populations along a north-south axis from the islands and mainland of Greece were exposed to elevated temperature and antioxidant enzyme activities, and Hsp70 and Hsp90 levels were determined in their tissues. The ATP, ADP, and AMP levels and the adenylate energy charge (AEC) were also determined. The comparison of protein levels and enzymatic activities across time intervals revealed significant differences for all factors examined. While the gradation pattern over time for a given factor was similar in all populations the absolute values over time differed. Catalase activity and the Hsp90 protein levels had the higher contribution in separating the different species and populations, followed by the activity of glutathione reductase and Hsp70 protein levels which contributed to a lesser degree. In general, populations from the southern part of their distribution in Greece tend to display a faster increase than northern populations in induction levels of all factors examined. Our data seem to be in line with the concept of preparation for oxidative stress (POS) while the changes in the AEC indicate an early preparation to cover the energy demand for the induction and synthesis of antioxidant enzymes and Hsps.

Seasonal cellular stress phenomena and phenotypic plasticity in land snail Helix lucorum populations from different altitudes

Temperature, a major abiotic environmental factor, regulates various physiological functions in land snails and therefore determines their biogeographical distribution. Thus, species with different distributions may present different thermal tolerance limits. Additionally, the intense reactivation of snail metabolic rate upon arousal from hibernation or estivation may provoke stress. Land snails, Helix lucorum, display a wide altitudinal distribution resulting in populations being exposed to different seasonal temperature variations. The aim of the present study was to investigate the expression of heat shock proteins (Hsps), mitogen activated protein kinases (MAPKs) and proteins that are related to apoptosis (Bcl-2, ubiquitin), that have 'cytoprotective' roles and are also considered to be reliable indicators of stress because of their crucial role in maintaining cellular homeostasis. These proteins were assessed in H. lucorum individuals from two different populations, one at Axios (sea level, 0 m) and the other at Kokkinopilos (Olympus, 1250 m), as well as after mutual population exchanges, in order to find out whether the different responses of these stress-related proteins depend solely on the environmental temperature. The results showed seasonally altered levels in all studied proteins in the hepatopancreas and foot of snails, both among different populations and between the same populations exposed to varying altitudes. However, individuals of the same population in their native habitat or acclimatized to a different habitat showed a relatively similar pattern of expression, supporting the induction of the specific proteins according to the life history of each species.

Experimental simulation of environmental warming selects against pigmented morphs of land snails

In terrestrial snails, thermal selection acts on shell coloration. However, the biological relevance of small differences in the intensity of shell pigmentation and the associated thermodynamic, physiological, and evolutionary consequences for snail diversity within the course of environmental warming are still insufficiently understood. To relate temperature-driven internal heating, protein and membrane integrity impairment, escape behavior, place of residence selection, water loss, and mortality, we used experimentally warmed open-top chambers and field observations with a total of >11,000 naturally or experimentally colored individuals of the highly polymorphic species Theba pisana (O.F. MÜller, 1774). We show that solar radiation in their natural Mediterranean habitat in Southern France poses intensifying thermal stress on increasingly pigmented snails that cannot be compensated for by behavioral responses. Individuals of all morphs acted neither jointly nor actively competed in climbing behavior, but acted similarly regardless of neighbor pigmentation intensity. Consequently, dark morphs progressively suffered from high internal temperatures, oxidative stress, and a breakdown of the chaperone system. Concomitant with increasing water loss, mortality increased with more intense pigmentation under simulated global warming conditions. In parallel with an increase in mean ambient temperature of 1.34°C over the past 30 years, the mortality rate of pigmented individuals in the field is, currently, about 50% higher than that of white morphs. A further increase of 1.12°C, as experimentally simulated in our study, would elevate this rate by another 26%. For 34 T. pisana populations from locations that are up to 2.7°C warmer than our experimental site, we show that both the frequency of pigmented morphs and overall pigmentation intensity decrease with an increase in average summer temperatures. We therefore predict a continuing strong decline in the frequency of pigmented morphs and a decrease in overall pigmentation intensity with ongoing global change in areas with strong solar radiation.

Snails in the sun: Strategies of terrestrial gastropods to cope with hot and dry conditions

Terrestrial gastropods do not only inhabit humid and cool environments but also habitat in which hot and dry conditions prevail. Snail species that are able to cope with such climatic conditions are thus expected to having developed multifaceted strategies and mechanisms to ensure their survival and reproduction under heat and desiccation stress. This review paper aims to provide an integrative overview of the numerous adaptation strategies terrestrial snails have evolved to persist in hot and dry environments as well as their mutual interconnections and feedbacks, but also to outline research gaps and questions that remained unanswered. We extracted relevant information from more than 140 publications in order to show how biochemical, cellular, physiological, morphological, ecological, thermodynamic, and evolutionary parameters contribute to provide an overall picture of this classical example in stress ecology. These mechanisms range from behavioral and metabolic adaptations, including estivation, to the induction of chaperones and antioxidant enzymes, mucocyte and digestive gland cell responses and the modification and frequency of morphological features, particularly shell pigmentation. In this context, thermodynamic constraints call for processes of complex adaptation at varying levels of biological organization that are mutually interwoven. We were able to assemble extensive, mostly narrowly focused information from the literature into a web of network parameters, showing that future work on this subject requires multicausal thinking to account for the complexity of relationships involved in snails' adaptation to insolation, heat, and drought.

Cadmium in vivo exposure alters stress response and endocrine-related genes in the freshwater snail Physa acuta. New biomarker genes in a new model organism

The freshwater snail Physa acuta is a sensitive organism to xenobiotics that is appropriate for toxicity testing. Cadmium (Cd) is a heavy metal with known toxic effects on several organisms, which include endocrine disruption and activation of the cellular stress responses. There is scarce genomic information on P. acuta; hence, in this work, we identify several genes related to the hormonal system, the stress response and the detoxification system to evaluate the effects of Cd. The transcriptional activity of the endocrine-related genes oestrogen receptor (ER), oestrogen-related receptor (ERR), and retinoid X receptor (RXR), the heat shock proteins genes hsp70 and hsp90 and a metallothionein (MT) gene was analysed in P. acuta exposed to Cd. In addition, the hsp70 and hsp90 genes were also evaluated after heat shock treatment. Real-time reverse transcriptase-polymerase chain reaction (qRT-PCR) analysis showed that Cd presence induced a significant increase in the mRNA levels of ER, ERR and RXR, suggesting a putative mode of action that could explain the endocrine disruptor activity of this heavy metal at the molecular level on Gastropoda. Moreover, the hsp70 gene was upregulated after 24-h Cd treatment, but the hsp90 gene expression was not affected. In contrast, the hsp70 and hsp90 genes were strongly upregulated during heat shock response. Finally, the MT gene expression showed a non-significant variability after Cd exposure. In conclusion, this study provides, for the first time, information about the effects of Cd on the endocrine system of Gastropoda at the molecular level and offers new putative biomarker genes that could be useful in ecotoxicological studies, risk assessment and bioremediation.

Selenium Deficiency Activates Heat Shock Protein Expression in Chicken Spleen and Thymus

Heat shock proteins (Hsps) are protective proteins present in nearly all species; they are used as biomarkers of various stress conditions in humans, animals, and birds. Selenium (Se) deficiency, which can depress the production of Hsps, can cause chicken tissue injuries. To investigate Hsp production, mRNA, and protein levels in Se-deficient chicken spleens and thymuses, a total of 180 1-day-old sea blue white laying hens (90 chickens/group) were harvested in two groups (the control group and the Se-deficient group) in 15, 25, 35, 45, and 55 days, respectively. The results showed that mRNA levels of Hsp27, Hsp40, Hsp60, Hsp70, and Hsp90 were significantly increased in the spleens and thymuses of the Se-deficient group compared to the control group. Further protein levels of Hsp60, Hsp70, and Hsp90 were also significantly increased in the spleen and thymus of the Se-deficient group compared to the control group. Meanwhile, the spleen expression ratio of Hsp40 mRNA level and Hsp70 protein level were higher in the Se-deficient group than other proteins. In the thymus, the Hsp90 mRNA level and Hsp60 protein expression level were the highest level in the Se-deficient group among other proteins. Based on these results, we concluded that Se deficiency could induce a protective stress response in chicken by means of promoting the mRNA and protein expression of Hsps, thus easing the effects of Se deficiency to some extent.

Geographic variation in thermal tolerance and strategies of heat shock protein expression in the land snail Theba pisana in relation to genetic structure

Land snails are exposed to conditions of high ambient temperature and low humidity, and their survival depends on a suite of morphological, behavioral, physiological, and molecular adaptations to the specific microhabitat. We tested in six populations of the land snail Theba pisana whether adaptations to different habitats affect their ability to cope with thermal stress and their strategies of heat shock protein (HSP) expression. Levels of Hsp70 and Hsp90 in the foot tissue were measured in field-collected snails and after acclimation to laboratory conditions. Snails were also exposed to various temperatures (32 up to 54 °C) for 2 h and HSP messenger RNA (mRNA) levels were measured in the foot tissue and survival was determined. To test whether the physiological and molecular data are related to genetic parameters, we analyzed T. pisana populations using partial sequences of nuclear and mitochondrial DNA ribosomal RNA genes. We show that populations collected from warmer habitats were more thermotolerant and had higher constitutive levels of Hsp70 isoforms in the foot tissue. Quantitative real-time polymerase chain reaction (PCR) analysis indicated that hsp70 and hsp90 mRNA levels increased significantly in response to thermal stress, although the increase in hsp70 mRNA was larger compared to hsp90 and its induction continued up to higher temperatures. Generally, warm-adapted populations had higher temperatures of maximal induction of hsp70 mRNA synthesis and higher upper thermal limits to HSP mRNA synthesis. Our study suggests that Hsp70 in the foot tissue of T. pisana snails may have important roles in determining stress resistance, while Hsp90 is more likely implicated in signal transduction processes that are activated by stress. In the phylogenetic analysis, T. pisana haplotypes were principally divided into two major clades largely corresponding to the physiological ability to withstand stress, thus pointing to genetically fixed tolerance.

Natural variation in resistance to desiccation and heat shock protein expression in the land snail Theba pisana along a climatic gradient

Land snails frequently encounter desiccating conditions, and their survival depends on a suite of morphological, physiological, and molecular adaptations to the specific microhabitat. Strategies of survival can be determined by integrating information from various levels of biological organization. In this study, we used a combination of physiological parameters related to water economy and molecular factors (stress protein expression) to investigate the strategies of survival adopted by seven populations of the Mediterranean-type land snail Theba pisana from different habitats. We analyzed water compartmentalization during aestivation and used experimental desiccation to compare desiccation resistance. We also measured the endogenous levels of heat shock proteins (HSPs) Hsp72, Hsp74, and Hsp90 under nonstress conditions and analyzed the HSP response to desiccation in two populations that differed mostly in their resistance to desiccation. We revealed significant intraspecific differences in resistance to desiccation that seem to be determined by the speed of recruitment of the water-preserving mechanisms. The ability to cope with desiccating conditions was correlated with habitat temperature but not with the rainfall gradient, implying that in the coastal region, temperature is likely to have a major impact on desiccation resistance rather than precipitation. Also, higher desiccation resistance was correlated with higher constitutive levels of Hsp74 in the foot tissue. HSPs were upregulated during desiccation, but the response was delayed and was milder in the most resistant population compared to the most susceptible one. Our study suggests that T. pisana populations from warmer habitats were more resistant to desiccation and developed distinct strategies of HSP expression for survival, namely, the maintenance of high constitutive levels of Hsp70 together with a delayed and limited response to stress.

Intraspecific variation in cellular and biochemical heat response strategies of Mediterranean Xeropicta derbentina [Pulmonata, Hygromiidae]

Dry and hot environments challenge the survival of terrestrial snails. To minimize overheating and desiccation, physiological and biochemical adaptations are of high importance for these animals. In the present study, seven populations of the Mediterranean land snail species Xeropicta derbentina were sampled from their natural habitat in order to investigate the intraspecific variation of cellular and biochemical mechanisms, which are assigned to contribute to heat resistance. Furthermore, we tested whether genetic parameters are correlated with these physiological heat stress response patterns. Specimens of each population were individually exposed to elevated temperatures (25 to 52°C) for 8 h in the laboratory. After exposure, the health condition of the snails' hepatopancreas was examined by means of qualitative description and semi-quantitative assessment of histopathological effects. In addition, the heat-shock protein 70 level (Hsp70) was determined. Generally, calcium cells of the hepatopancreas were more heat resistant than digestive cells - this phenomenon was associated with elevated Hsp70 levels at 40°C.We observed considerable variation in the snails' heat response strategy: Individuals from three populations invested much energy in producing a highly elevated Hsp70 level, whereas three other populations invested energy in moderate stress protein levels - both strategies were in association with cellular functionality. Furthermore, one population kept cellular condition stable despite a low Hsp70 level until 40°C exposure, whereas prominent cellular reactions were observed above this thermal limit. Genetic diversity (mitochondrial cytochrome c oxidase subunit I gene) within populations was low. Nevertheless, when using genetic indices as explanatory variables in a multivariate regression tree (MRT) analysis, population structure explained mean differences in cellular and biochemical heat stress responses, especially in the group exposed to 40°C. Our study showed that, even in similar habitats within a close range, populations of the same species use different stress response strategies that all rendered survival possible.

Daily and seasonal changes in heat exposure and the Hsp70 level of individuals from a field population of Xeropicta derbentina (Krynicki 1836) (Pulmonata, Hygromiidae) in Southern France

The Mediterranean land snail Xeropicta derbentina forms huge populations in Southern France. In order to characterize heat exposure and the induction of the 70-kD heat shock protein (Hsp70) response system during the life cycle of this snail, a selected population from the Vaucluse area, Provence, was investigated encompassing the issues of morphological life cycle parameters (shell size and colouration), the daily courses of heat exposure at different heights above the ground, of shell temperature, and that of the individual Hsp70 levels. The study covered all four seasons of the year 2011. Snails were found to be annual, reaching their final size in August. The shell colouration pattern showed high variation in juveniles (spring) with a strong tendency towards becoming uniformly white at old age in autumn. In all seasons, ambient air temperature decreased with increasing distance from the ground surface during daytime while remaining constantly low in the night. Overall, the Hsp70 level of individuals followed the ambient temperature during diurnal and seasonal variations. Correlation analysis revealed a positive association of individual shell temperature and Hsp70 level for the most part of the life cycle of the snails until late summer, whereas a negative correlation was found for aged animals indicating senescence effects on the capacity of the stress response system.

Heat shock proteins and survival strategies in congeneric land snails (Sphincterochila) from different habitats

Polmunate land snails are subject to stress conditions in their terrestrial habitat, and depend on a range of behavioural, physiological and biochemical adaptations for coping with problems of maintaining water, ionic and thermal balance. The involvement of the heat shock protein (HSP) machinery in land snails was demonstrated following short-term experimental aestivation and heat stress, suggesting that land snails use HSPs as part of their survival strategy. As climatic variation was found to be associated with HSP expression, we tested whether adaptation of land snails to different habitats affects HSP expression in two closely related Sphincterochila snail species, a desert species Sphincterochila zonata and a Mediterranean-type species Sphincterochila cariosa. Our study suggests that Sphincterochila species use HSPs as part of their survival strategy following desiccation and heat stress, and as part of the natural annual cycle of activity and aestivation. Our studies also indicate that adaptation to different habitats results in the development of distinct strategies of HSP expression in response to stress, namely the reduced expression of HSPs in the desert-inhabiting species. We suggest that these different strategies reflect the difference in heat and aridity encountered in the natural habitats, and that the desert species S. zonata relies on mechanisms and adaptations other than HSP induction thus avoiding the fitness consequences of continuous HSP upregulation.