A potential antiapoptotic regulation: The interaction of heat shock protein 70 and apoptosis-inducing factor mitochondrial 1 during heat stress and aestivation in sea cucumber

Comparative proteomic and phosphoproteomic analysis reveals differential heat response mechanism in two congeneric oyster species

High-temperature stress caused by global climate change poses a significant threat to marine ectotherms. This study investigated the role of protein phosphorylation modifications in the molecular regulation network under heat stress in oysters, which are representative intertidal organisms that experience considerable temperature changes. Firstly, the study compared the extent of thermal damage between two congeneric oyster species, the relative heat-tolerant Crassostrea angulata (C. angulata) and heat-sensitive Crassostrea gigas (C. gigas), under sublethal temperature (37 °C) for 12 h, using various physiological and biochemical methods. Subsequently, the comparative proteomic and phosphoproteomic analyses revealed that high-temperature considerably regulated signal transduction, energy metabolism, protein synthesis, cell survival and apoptosis, and cytoskeleton remodeling through phosphorylation modifications of related receptors and kinases. Furthermore, the protein kinase A, mitogen-activated protein kinase 1, tyrosine-protein kinase Src, and serine/threonine kinase AKT, exhibiting differential phosphorylation modification patterns, were identified as hub regulators that may enhance glycolysis and TCA cycle to increase the energy supply, distribute protein synthesis, inhibit Caspase-dependent apoptosis activated by endogenous mitochondrial cytochrome release and maintain cytoskeletal stability, ultimately shaping the higher thermal resistance of C. angulata. This study represents the first investigation of protein phosphorylation dynamics in marine invertebrates under heat stress, reveals the molecular mechanisms underlying the differential thermal responses between two Crassostrea oysters at the phosphorylation level, and provides new insights into understanding phosphorylation-mediated molecular responses in marine organisms during environmental changes and predicting the adaptive potential in the context of global warming.

Aestivation in Nature: Physiological Strategies and Evolutionary Adaptations in Hypometabolic States

Aestivation is considered to be one of the "purest" hypometabolic states in nature, as it involves aerobic dormancy that can be induced and sustained without complex factors. Animals that undergo aestivation to protect themselves from environmental stressors such as high temperatures, droughts, and food shortages. However, this shift in body metabolism presents new challenges for survival, including oxidative stress upon awakening from aestivation, accumulation of toxic metabolites, changes in energy sources, adjustments to immune status, muscle atrophy due to prolonged immobility, and degeneration of internal organs due to prolonged food deprivation. In this review, we summarize the physiological and metabolic strategies, key regulatory factors, and networks utilized by aestivating animals to address the aforementioned components of aestivation. Furthermore, we present a comprehensive overview of the advancements made in aestivation research across major species, including amphibians, fish, reptiles, annelids, mollusks, and echinoderms, categorized according to their respective evolutionary positions. This approach offers a distinct perspective for comparative analysis, facilitating an understanding of the shared traits and unique features of aestivation across different groups of organisms.

Chaperone proteins: universal roles in surviving environmental stress

Chaperone proteins have crucial roles to play in all animal species and are involved in mediating both the folding of newly synthesized peptides into their mature conformation, the refolding of misfolded proteins, and the trafficking of proteins between subcellular compartments. These highly conserved proteins have particularly important roles to play in dealing with disruptions of the proteome as a result of environmental stress since abiotic factors, including temperature, pressure, oxygen, water availability, and pollutants can readily disrupt the conformation and/or function of all types of proteins, e.g., enzymes, transporters, and structural proteins. The current review provides an update on recent advances in understanding the roles and responses of chaperones in aiding animals to deal with environmental stress, offering new information on chaperone action in supporting survival strategies including torpor, hibernation, anaerobiosis, estivation, and cold/freeze tolerance among both vertebrate and invertebrate species.

Gut Microbiota and Metabolites May Play a Crucial Role in Sea Cucumber Apostichopus japonicus Aestivation

The constant increase in temperatures under global warming has led to a prolonged aestivation period for Apostichopus japonicus, resulting in considerable losses in production and economic benefits. However, the specific mechanism of aestivation has not been fully elucidated. In this study, we first tried to illustrate the biological mechanisms of aestivation from the perspective of the gut microbiota and metabolites. Significant differences were found in the gut microbiota of aestivating adult A. japonicus (AAJSD group) compared with nonaestivating adult A. japonicus (AAJRT group) and young A. japonicus (YAJRT and YAJSD groups) based on 16S rRNA gene high-throughput sequencing analysis. The abundances of Desulfobacterota, Myxococcota, Bdellovibrionota, and Firmicutes (4 phyla) in the AAJSD group significantly increased. Moreover, the levels of Pseudoalteromonas, Fusibacter, Labilibacter, Litorilituus, Flammeovirga, Polaribacter, Ferrimonas, PB19, and Blfdi19 genera were significantly higher in the AAJSD group than in the other three groups. Further analysis of the LDA effect size showed that species with significant variation in abundance in the AAJSD group, including the phylum Firmicutes and the genera Litorilituus, Fusibacter, and Abilibacter, might be important biomarkers for aestivating adult A. japonicus. In addition, the results of metabolomics analysis showed that there were three distinct metabolic pathways, namely biosynthesis of secondary metabolites, tryptophan metabolism, and sesquiterpenoid and triterpenoid biosynthesis in the AAJSD group compared with the other three groups. Notably, 5-hydroxytryptophan was significantly upregulated in the AAJSD group in the tryptophan metabolism pathway. Moreover, the genera Labilibacter, Litorilituus, Ferrimonas, Flammeovirga, Blfdi19, Fusibacter, Pseudoalteromonas, and PB19 with high abundance in the gut of aestivating adult A. japonicus were positively correlated with the metabolite 5-HTP. These findings suggest that there may be potential biological associations among the gut microbiota, metabolites, and aestivation in A. japonicus. This work may provide a new perspective for further understanding the aestivation mechanism of A. japonicus.

Apoptosis-Inducing Factor 2 (AIF-2) Mediates a Caspase-Independent Apoptotic Pathway in the Tropical Sea Cucumber (Holothuria leucospilota)

Apoptosis, also known as programmed cell death, is a biological process that is critical for embryonic development, organic differentiation, and tissue homeostasis of organisms. As an essential mitochondrial flavoprotein, the apoptosis-inducing factor (AIF) can directly mediate the caspase-independent mitochondrial apoptotic pathway. In this study, we identified and characterized a novel AIF-2 (HlAIF-2) from the tropical sea cucumber Holothuria leucospilota. HlAIF-2 contains a conserved Pyr_redox_2 domain and a putative C-terminal nuclear localization sequence (NLS) but lacks an N-terminal mitochondrial localization sequence (MLS). In addition, both NADH- and FAD-binding domains for oxidoreductase function are conserved in HlAIF-2. HlAIF-2 mRNA was ubiquitously detected in all tissues and increased significantly during larval development. The transcript expression of HlAIF-2 was significantly upregulated after treatment with CdCl₂, but not the pathogen-associated molecular patterns (PAMPs) in primary coelomocytes. In HEK293T cells, HlAIF-2 protein was located in the cytoplasm and nucleus, and tended to transfer into the nucleus by CdCl₂ incubation. Moreover, there was an overexpression of HlAIF-2-induced apoptosis in HEK293T cells. As a whole, this study provides the first evidence for heavy metal-induced apoptosis mediated by AIF-2 in sea cucumbers, and it may contribute to increasing the basic knowledge of the caspase-independent apoptotic pathway in ancient echinoderm species.

MiR-200-3p Is Potentially Involved in Cell Cycle Arrest by Regulating Cyclin A during Aestivation in Apostichopus japonicus

The sea cucumber (Apostichopus japonicus) has become a good model organism for studying environmentally induced aestivation in marine invertebrates. We hypothesized that mechanisms that arrest energy-expensive cell cycle activity would contribute significantly to establishing the hypometabolic state during aestivation. Cyclin A is a core and particularly interesting cell cycle regulator that functions in both the S phase and in mitosis. In the present study, negative relationships between miR-200-3p and AjCA expressions were detected at both the transcriptional and the translational levels during aestivation in A. japonicus. Dual-luciferase reporter assays confirmed the targeted location of the miR-200-3p binding site within the AjCA gene transcript. Furthermore, gain- and loss-of-function experiments were conducted in vivo with sea cucumbers to verify the interaction between miR-200-3p and AjCA in intestine tissue by qRT-PCR and Western blotting. The results show that the overexpression of miR-200-3p mimics suppressed AjCA transcript levels and translated protein production, whereas transfection with a miR-200-3p inhibitor enhanced both AjCA mRNA and AjCA protein in A. japonicus intestine. Our findings suggested a potential mechanism that reversibly arrests cell cycle progression during aestivation, which may center on miR-200-3p inhibitory control over the translation of cyclin A mRNA transcripts.