Heat induces multiomic and phenotypic stress propagation in zebrafish embryos

The molecular signature of heat stress in sweat reveals non-invasive biomarker candidates for health monitoring

Heat stress is a significant public health challenge that leads to an increased risk of serious health deterioration, injuries, and loss of economic productivity. While the gold standard for monitoring heat stress continues to remain with population-based measurements, a straight-forward person-centered approach is lacking. Sweat can supply a wealth of molecular information, ranging from protein levels to levels of metabolites; it is thus a promising monitoring biofluid. A thorough investigation of sweat's molecular signature during heat stress is called for. We conducted a cross-over study on healthy participants with personalized heat-stress visits to investigate heat stress's proteomic and molecular signatures in sweat. Through mass-spectrometry analysis, we identified multiple candidate biomarkers ranging from amino acids to microbiome metabolites and proteins. To the best of our knowledge, these biomarker candidates represent the first successful approach to metabolically differentiate between various heat stressors thereby enabling their acute monitoring. While these biomarker candidates need further investigation to confirm their clinical value, many have already been identified as directly associated with heat stress in animals and plants. Once further investigated, next-generation wearable devices for person-centered, on-skin sweat-analysing platforms could be developed that would transform health management during exposure to heat stress.

Social context prevents heat hormetic effects against mutagens during fish development

Since stress can be transmitted to congeners via social metabolites, it is paramount to understand how the social context of abiotic stress influences aquatic organisms' responses to global changes. Here, we integrated the transcriptomic and phenotypic responses of zebrafish embryos to a UV damage/repair assay following scenarios of heat stress, its social context and their combination. Heat stress preceding UV exposure had a hormetic effect through the cellular stress response and DNA repair, rescuing and/or protecting embryos from UV damage. However, experiencing heat stress within a social context negated this molecular hormetic effect and lowered larval fitness. We discuss the molecular basis of interindividual chemical transmission within animal groups as another layer of complexity to organisms' responses to environmental stressors.

Simulated Heat Waves Affect Cell Fate and Fitness in the Social Amoeba Dictyostelium discoideum

The effects of heatwaves at organism and population levels have been widely investigated; however, little is known about how they affect the development of cell populations and the fitness of the resulting organism. Disruptions caused by heatwaves are especially critical during early developmental stages in organisms lacking parental developmental protection or care. Here we use the social amoeba Dictyostelium discoideum, a soil microbe with a life cycle that transitions between single-cell and multicellular stages. D. discoideum thrives optimally at 22 °C and elevated temperatures impair (27 °C) or completely arrest (30 °C) growth, development, and spore yield. We established a simulated heatwave model in which vegetative cells were exposed to 27 °C for 3 days and studied the effects on the expression of early and cell type specific developmental genes using real-time quantitative PCR. A single heatwave severely impaired the expression of cyclic AMP-dependent early developmental gene markers (carA, acaA, pkaR, gtaC, tgrC1, and csaA) as well as that of prespore markers (cotB and spiA), while the expression of the prestalk marker ecmA was less affected. When mixed with heat-stressed cells, reporter cells expressing β-galactosidase grown at 22 °C preferentially occupy the spore mass of the fruiting body. Chimera assays of wild-type and reporter cells grown at optimal temperature or subjected to a heatwave confirmed a decreased fitness (contribution to chimeric fruiting bodies). We conclude that exposure of unprotected organisms at the single cell stage to a single heatwave has the potential to negatively impact their ability to cope with environmental extremes.

Polystyrene nanoplastics impact the bioenergetics of developing zebrafish and limit molecular and physiological adaptive responses to acute temperature stress

Plastic pollution is a growing environmental concern due to its ubiquitous impact on aquatic ecosystems. Nanoplastics can be generated from the breakdown of plastic waste and interact with organisms at the cellular level, potentially disrupting cellular physiology. We investigated the effects of 44 nm polystyrene nanoparticles (44 nm NanoPS) on the development and physiology of zebrafish (Danio rerio) in the presence of sublethal heat stress (32 °C vs control, 28 °C). We hypothesized that the simultaneous exposure to nanoplastics and rising temperatures seriously threaten developing fish. This combination could create a critical imbalance: rising temperatures may lead to heightened energy demands, while nanoplastic exposure reduces energy production, threatening animal survival. As expected, 32 °C increased markers associated with animal metabolism and developmental timing, such as growth, hatching, heart rate, and feeding. Changes in apoptosis dynamics, oxygen consumption rates, and a decrease in mitochondrial content were detected as adaptive processes to temperature. 44 nm NanoPS alone did not alter development but decreased mitochondrial efficiency in ATP production and increased apoptosis in the heart. Surprisingly, exposure to 44 nm NanoPS at 32 °C did not cause major implications to survival, developmental success, or morphology. Still, 44 nm NanoPS mitigated the temperature-driven change in heart rate, increased oxidative stress, and decreased the coupling efficiency of the less abundant and highly active mitochondria under heat stress. We highlight the interplay between temperature and nanoplastics exposure and suggest that the combined impact of nanoplastics and temperature stress results in a scenario where physiological adaptations are strained, potentially leading to compromised development. This research underscores the need for further investigation into the metabolic costs of plastic pollution, particularly in the context of global warming, to better understand its long-term implications for aquatic life.

Responses of animals and plants to physiological doses of ethanol: a molecular messenger of hypoxia?

Our viewpoint is that ethanol could act as a molecular messenger in animal and plant organisms under conditions of hypoxia or other stresses and could elicit physiological responses to such conditions. There is evidence that both animal and plant organisms have endogenous levels of ethanol, but reports on the changes induced by this alcohol at physiological levels are sparse. Studies have shown that ethanol has different effects on cell metabolism at low and high concentrations, resembling a hormetic response. Further studies have addressed the potential cellular and molecular mechanisms used by organisms to sense changes in physiological concentrations of ethanol. This article summarizes the possible mechanisms by which ethanol may be sensed, particularly at the cell membrane level. Our analysis shows that current knowledge on this subject is limited. More research is required on the effects of ethanol at very low doses, in plants and animals at both molecular and physiological levels. We believe that further research on this topic could lead to new discoveries in physiology and may even help us understand metabolic adjustments related to climate change. As temperatures rise more frequently, dissolved oxygen levels drop, leading to hypoxic conditions and consequently, an increase in cellular ethanol levels.