The effects of cold stress on Mytilus species in the natural environment

Does temperature influence on biomarker responses to copper exposure? The invasive bivalve Limnoperna fortunei (Dunker 1857) as a model

Biomarkers are useful tools for assessing the early warning effects of pollutants. However, their responses can be influenced by confounding factors. In this study, we investigated the influence of temperature on multiple biomarkers in the invasive freshwater bivalve Limnoperna fortunei exposed to copper (Cu). The mussels were exposed to low and high environmental Cu concentrations at two temperatures (15 °C and 25 °C). After 96 h, the oxidative stress, neurotoxicity, and metabolic parameters were assessed. Our results showed that temperature is a key factor influencing biomarker responses in mussels, with higher glutathione S-transferase activity and lower energy reserves at cold temperature. In addition, the effects of Cu were greater at the highest concentration at 15 °C (increased lipid peroxidation and cholinesterase activity). Overall, these findings suggest that cold stress increases the susceptibility of L. fortunei to metal effects and highlight the importance of including temperature in toxicity testing and biomonitoring. In addition, using the invasive bivalve L. fortunei as a model could prove valuable in its role as a sentinel species for other organisms.

Influence of temperature changes on oxidative stress and antioxidant defense system in the bay scallop, Argopecten irradians

In this study, we aimed to understand the effects of changes in temperature on biochemical and molecular responses associated with the antioxidant defense system in the bay scallop, Argopecten irradians. We measured the contents of H2O2 and malondialdehyde (MDA), as well as the activities of antioxidant enzymes (e.g., glutathione S-transferase [GST], superoxide dismutase [SOD], and catalase [CAT]), and the regulation of stress-related genes (e.g., GST, SOD, CAT, and heat shock protein 70 [HSP70]). In addition, total antioxidant capacity (TAC) was examined in scallops exposed to different temperatures. A. irradians showed high levels of H2O2 and MDA in response to acute thermal stress (48 and 72 h of exposure). Temperature changes also led to a significant increase in antioxidant enzyme activity and mRNA expression levels in A. irradians. Interestingly, the TAC increased in response to acute thermal stress (28 °C) for up to 12 h and decreased thereafter. The oxidative stress induced by high temperatures could not be alleviated by an increase in levels of antioxidant enzymes, such as GST, SOD, and CAT, resulting in high levels of H2O2 and MDA and low levels of TAC. In addition, significant changes (P < 0.05) in HSP70 levels were observed in response to changes in temperature, suggesting that HSP70 played an important role in the heat tolerance of A. irradians. In conclusion, A. irradians exhibits a greater degree of oxidative stress responses in high-temperature environments than that in low-temperature environments. Overall, these findings indicate that temperature changes lead to oxidative stress, resulting in cellular damage and activation of the antioxidant defense system in bay scallops. Further experiments are required to elucidate other antioxidants and fully understand the redox system in A. irradians.

Biomarker responsiveness in Norwegian Sea mussels, Mytilus edulis, exposed at low temperatures to aqueous fractions of crude oil alone and combined with dispersant

Biological effects of aqueous fractions of a crude oil, alone or in combination with dispersant, were investigated in mussels, Mytilus edulis, exposed at three temperatures (5, 10 and 15 °C). Polycyclic aromatic hydrocarbons (PAHs) tissue concentrations were determined, together with genotoxicity, oxidative stress and general stress biomarkers and the Integrated Biological Response (IBR) index. The bioaccumulation of individual PAHs varied depending on the exposure temperature, with relevant bioaccumulation of phenantrene and fluoranthene at 5 °C and heavier (e.g. 5-rings) PAHs at 15 °C. The values and response profiles of each particular biomarker varied with exposure time, concentration of the oil aqueous fraction and dispersant addition, as well as with exposure temperature. Indeed, PAH bioaccumulation and biomarker responsiveness exhibited specific recognizable patterns in mussels exposed at low temperatures. Thus, genotoxicity was recorded early and transient at 5 °C and delayed but unremitting at 10-15 °C. Catalase activity presented a temperature-dependent response profile similar to the genotoxicity biomarker; however, glutathione-S-transferase responsiveness was more intricate. Lysosomal membrane stability in digestive cells decreased more markedly at 5 °C than at higher temperatures and the histological appearance of the digestive gland tissue was temperature-specific, which was interpreted as the combined effects of PAH toxicity and cold stress. It can be concluded that the profile and level of the biological effects are definitely different at low temperatures naturally occurring in the Arctic/Subarctic region (e.g. 5 °C) than at higher temperatures closer to the thermal optimum of this species (10-15 °C).

Proteostasis in ice: the role of heat shock proteins and ubiquitin in the freeze tolerance of the intertidal mussel, Mytilus trossulus

The bay mussel, Mytilus trossulus, is an animal that can survive extracellular ice formation. Depending on air and ocean temperatures, freeze tolerant intertidal organisms, like M. trossulus, may freeze and thaw many times during the winter. Freezing can cause protein denaturation, leading to an induction of the heat shock response with expression of chaperone proteins like the 70 kDa heat shock protein (HSP70), and an increase in ubiquitin-conjugated proteins. There has been little work on the mechanisms of freeze tolerance in intertidal species, limiting our understanding of this survival strategy. Additionally, this limited research has focused solely on the effects of single freezing events, but the act of repeatedly crossing the freezing threshold may present novel physiological or biochemical stressors that have yet to be discovered. Mytilus are important ecosystem engineers and provide habitat for other intertidal species, thus understanding their physiology under thermal extremes is important for preserving shoreline health. We predicted that repeated freeze exposures would increase mortality, upregulate HSP70 expression, and increase ubiquitin conjugates in mussels, relative to single, prolonged freeze exposures. Mytilus trossulus from Vancouver, Canada were repeatedly frozen for a combination of 1 × 8 h, 2 × 4 h, or 4 × 2 h. We then compared mortality, HSP70 expression, and the quantity of ubiquitin-conjugated proteins across experimental groups. We found a single 8-h freeze caused significantly more mortality than repeated freeze-thaw cycles. We also found that HSP70 and ubiquitinated protein was upregulated exclusively after freeze-thaw cycles, suggesting that freeze-thaw cycles offer a period of damage repair between freezes. This indicates that freeze-thaw cycles, which happen naturally in the intertidal, are crucial for M. trossulus survival in sub-zero temperatures.

Variations of Supercooling Capacity in Intertidal Gastropods

Winter low-temperature confines species distribution. Intertidal gastropods are distributed from tropical to polar zones, facing variable intensities and durations of low temperatures. They usually set their supercooling points (SCPs) at high subzero temperatures to stimulate freezing. However, the variations in SCP in intertidal gastropods at intraspecific and interspecific levels remain poorly understood. Here, we measured the body size, cooling rate, and SCP of nine intertidal gastropod species in China. These species were distributed in high or middle intertidal zone with different geographic distributions. The average SCPs (-4.27~-7.10 °C) and the coefficients of variation of SCP (22.6%~45.9%) were high in all species. At the intraspecific level, the supercooling capacity was positively correlated with the cooling rate. Interspecifically, the supercooling capacity was closely related to the cooling rate, and also to the species' geographical distribution. Northern high-shore species showed lower SCPs, while southern high-shore species had higher SCPs. There was no difference in SCP between widespread high- and mid-shore species. Our results indicated that the supercooling capability is potentially an adaptative response to the local winter temperatures, and the cooling rate is a factor in determining the difference in SCP at the intraspecific and interspecific levels.

Genome-wide sequencing identifies a thermal-tolerance related synonymous mutation in the mussel, Mytilisepta virgata

The roles of synonymous mutations for adapting to stressful thermal environments are of fundamental biological and ecological interests but poorly understood. To study whether synonymous mutations influence thermal adaptation at specific microhabitats, a genome-wide genotype-phenotype association analysis is carried out in the black mussels Mytilisepta virgata. A synonymous mutation of Ubiquitin-specific Peptidase 15 (MvUSP15) is significantly associated with the physiological upper thermal limit. The individuals carrying GG genotype (the G-type) at the mutant locus possess significantly lower heat tolerance compared to the individuals carrying GA and AA genotypes (the A-type). When heated to sublethal temperature, the G-type exhibit higher inter-individual variations in MvUSP15 expression, especially for the mussels on the sun-exposed microhabitats. Taken together, a synonymous mutation in MvUSP15 can affect the gene expression profile and interact with microhabitat heterogeneity to influence thermal resistance. This integrative study sheds light on the ecological importance of adaptive synonymous mutations as an underappreciated genetic buffer against heat stress and emphasizes the importance of integrative studies at a microhabitat scale for evaluating and predicting the impacts of climate change.

Morphological, physiological and behavioral responses of an intertidal snail, Acanthina monodon (Pallas), to projected ocean acidification and cooling water conditions in upwelling ecosystems

Ocean acidification (OA) is expected to rise towards the end of the 21st century altering the life history traits in marine organisms. Upwelling systems will not escape OA, but unlike other areas of the ocean, cooling effects are expected to intensify in these systems. Regardless, studies evaluating the combined effects of OA and cooling remain scarce. We addressed this gap using a mesocosm system, where we exposed juveniles of the intertidal muricid snail Acanthina monodon to current and projected pCO₂ (500 vs. 1500 ppm) and temperature (15 vs. 10 °C) from the southeast Pacific upwelling system. After 9 weeks of experimental exposure to those conditions, we conducted three estimations of growth (wet weight, shell length and shell peristomal length), in addition to measuring calcification, metabolic and feeding rates and the ability of these organisms to return to the normal upright position after being overturned (self-righting). Growth, feeding and calcification rates increased in projected cooling conditions (10 °C) but were unaffected by pCO₂ or the interaction between pCO₂ and temperature. Instead, metabolic rates were driven by pCO₂, but a significant interaction with temperature suggests that in cooler conditions, metabolic rates will increase when associated with high pCO₂ levels. Snail self-righting times were not affected across treatments. These results suggest that colder temperatures projected for this area would drive this species growth, feeding and calcification, and consequently, some of its population biology and productivity. However, the snails may need to compensate for the increase in metabolic rates under the effects of ocean acidification. Although A. monodon ability to adjust to individual or combined stressors will likely account for some of the changes described here, our results point to a complex dynamic to take place in intertidal habitats associated with upwelling systems.

Development of alternative and sustainable methodologies in laboratory research on sea urchin gametes

The aim of the present work is to develop a laboratory-scaled methodology for an on-demand supply of semen from the sea urchin Paracentrotus lividus. Firstly, sea urchin specimens were acclimatized to the long-term rearing in a recirculating aquaculture system and gonad maturation was obtained under controlled conditions. Semen samples were then collected from mature sea urchins and cryopreserved. Finally, post-thawing motility was evaluated, to verify whether the cryopreserved semen had maintained enough viability to be used in laboratory activities. The post-thawing motility parameters remained quite unchanged for up to 60 min after activation; moreover, the semen even retained the ability of motility activation for 60 min after thawing. This motility pattern makes the use of cryopreserved semen a feasible option in spermiotoxicity bioassays. The preliminary ecotoxicity test, carried out using motility parameters as endpoints, showed sensitivity levels to cadmium falling in the same order of magnitude as those recorded for fresh sea urchin semen and for cryopreserved sea bream semen. . Therefore, semen samples produced and stored according to the developed methodology described in this paper, can be considered a promising and sustainable alternative to those collected from mature sea urchins harvested in the field.

Beclin1 haploinsufficiency rescues low ambient temperature-induced cardiac remodeling and contractile dysfunction through inhibition of ferroptosis and mitochondrial injury

OBJECTIVE

Cold exposure provokes cardiac remodeling and cardiac dysfunction. Autophagy participates in cold stress-induced cardiovascular dysfunction. This study was designed to examine the impact of Beclin1 haploinsufficiency (BECN^+/-) in cold stress-induced cardiac geometric and contractile responses.

METHODS AND MATERIALS

Wild-type (WT) and BECN^+/- mice were assigned to normal or cold exposure (4 °C) environment for 4 weeks prior to evaluation of cardiac geometry, contractile and mitochondrial properties. Autophagy, apoptosis and ferroptosis were evaluated.

RESULTS

Our data revealed that cold stress triggered cardiac remodeling, compromised myocardial contractile capacity including ejection fraction, fractional shortening, peak shortening and maximal velocity of shortening/relengthening, duration of shortening and relengthening, intracellular Ca²⁺ release, intracellular Ca²⁺ decay, mitochondrial ultrastructural disarray, superoxide production, unchecked autophagy, apoptosis and ferroptosis, the effects of which were negated by Beclin1 haploinsufficiency. Circulating levels of corticosterone were elevated in both WT and BECN^+/- mice. Treatment of corticosterone synthesis inhibitor metyrapone or ferroptosis inhibitor liproxstatins-1 rescued cold stress-induced cardiac dysfunction and mitochondrial injury. In vitro study noted that corticosterone challenge compromised cardiomyocyte function, provoked lipid peroxidation and mitochondrial injury, the effects of which were nullified by Beclin1 haploinsufficiency, inhibitors of lipoxygenase, ferroptosis and autophagy. In addition, ferroptosis inducer erastin abrogated Beclin1 deficiency-offered cardioprotection.

CONCLUSION

These data suggest that Beclin1 haploinsufficiency protects against cold exposure-induced cardiac dysfunction possibly through corticosterone- and ferroptosis-mediated mechanisms.