LC-MS Reveals Food-Linked Stress Proteins

Among the various environmental factors that affect how cells respond to stress, how much food an organism gets has not been often studied, even though it likely plays an important role in how much stress an organism can handle.To see how food availability and temperature work together to affect how cells respond to heat stress, the Department of Biological Sciences of California Polytechnic State University (San Luis Obispo, California) and the Department of Marine and Earth Sciences of Florida Gulf Coast University (Fort Myers, Florida) teamed up to study intertidal mussels, exposing the subjects to four different combinations of conditions: either low or high amounts of phytoplankton (their food source, with "low" mimicking natural coastal waters and "high" mimicking the richer conditions found near aquaculture farms), paired with either a milder temperature (20 °C) or a hotter temperature (30 °C) during the daytime, mimicking what the mussels would experience when exposed to air during low tide. The researchers measured changes in proteins within the mussels' gills, both before and after the heat stress, using liquid-chromatography-mass spectrometry (LC-MS) and label-free quantification, which let them identify and measure protein levels without needing to add special labeling chemicals. A paper based on their efforts was published in the Journal of Experimental Biology.¹

What is Known About Cellular Stress Response, and What Gap Does this Study Address?

Scientists studying cellular stress response (CSR) to determine how cells respond to sudden increases in temperature made, in the opinion of the research team, some of the earliest and most important discoveries in the field of molecular biology.^2,3 Since those early discoveries, scientists have found that a cell's stress response involves far more than just the proteins that help fold other proteins correctly. It also includes proteins responsible for breaking down damaged proteins, managing energy production and metabolism, keeping the cell's chemical balance in check, and repairing damaged DNA.^4,5 Early studies comparing different organisms looked at how important this stress response is for animals living in their natural habitats and typical temperature ranges. These studies found that the point at which the stress response kicked in was closely tied to seasonal changes and the animals' ability to adjust to those changes over time. This gave researchers useful clues about how this stress response might help organisms cope with climate change.^6-8 While this research has taught us a lot about how cells respond to stress, one thing that has been largely overlooked is the role that food intake plays, either on its own or combined with temperature, despite other research showing that food levels and diet can significantly affect how well cold-blooded animals handle temperature changes in general.⁹

The researchers behind this study set out to fill that gap by looking at how proteins in intertidal mussels responded after the mussels were raised under different combinations of food and temperature conditions, aiming to understand how these marine animals cope with a constantly changing environment.¹

How Did Food and Temperature Conditions Affect the Protein-Level Heat Stress Response in Mussels?

The researchers found that mussels raised in cooler water with less food showed the strongest response to heat stress, compared to mussels raised under other conditions. These mussels increased their levels of proteins involved in basic sugar and sulfur-related metabolism. The byproducts of this sugar-processing are thought to feed into other important metabolic pathways involving folate and an amino acid called methionine, which also became more active. These pathways likely help the mussels build genetic material, add chemical tags to DNA and proteins (a process called methylation), and process sulfur-containing compounds.¹

These same mussels also ramped up production of proteins that neutralize a harmful compound called hydrogen peroxide, bind up loose iron that can cause cell damage, and maintain levels of glutathione, a molecule that helps protect cells from damage. Additionally, they showed increased activity of proteins that alter how DNA is packaged and control gene activity. This suggests a link between the mussels' metabolic changes and modifications to their genetic material, potentially helping repair DNA damage caused by stress-related molecular byproducts.¹

“Overall,” write the authors of the paper,¹ “our results suggest a food-dependent link between metabolism and epigenetic modifications that we hypothesize may function as an autoregulatory feedback mechanism during the CSR under tidally fluctuating conditions.”

References

1. Fabela, R. F.; May, M. A.; Tomanek, L. Food Dependent Activation of One Carbon Metabolism During Heat Shock in Mytilus californianus. J Exp Biol. 2026, jeb.252105. DOI: 10.1242/jeb.252105
2. Lindquist, S. The Heat-Shock Response. Annu Rev Biochem. 1986, 55, 1151-91. DOI: 10.1146/annurev.bi.55.070186.005443
3. Ritossa, F. A New Puffing Pattern Induced by Temperature Shock and DNP in Drosophila. Experientia 1962,18, 571–573. DOI: 10.1007/BF02172188
4. Kültz, D. Molecular and Evolutionary Basis of the Cellular Stress Response. Annu Rev Physiol. 2005, 67, 225-257. DOI: 10.1146/annurev.physiol.67.040403.10363
5. Somero, G. N.; Lockwood, B. L.; Tomanek, L. Biochemical Adaptation: Response to Environmental Challenges from Life's Origins to the Anthropocene; Sinauer Associates, Inc., 2017.
6. Feder, M. E.; Hofmann, G. E. Heat-Shock Proteins, Molecular Chaperones, and the Stress Response: Evolutionary and Ecological Physiology. Annu Rev Physiol. 1999, 61, 243-282. DOI: 10.1146/annurev.physiol.61.1.243
7. Tomanek, L.; Zuzow, M. J. The Proteomic Response of the Mussel Congeners Mytilus galloprovincialis and M. trossulus to Acute Heat Stress: Implications for Thermal Tolerance Limits and Metabolic Costs of Thermal Stress. J Exp Biol. 2010, 213 (Pt 20), 3559-3574.DOI: 10.1242/jeb.041228
8. Tomanek, L. Variation in the Heat Shock Response and Its Implication for Predicting the Effect of Global Climate Change on Species' Biogeographical Distribution Ranges and Metabolic Costs. J Exp Biol. 2010, ;213 (6), 971-979.DOI: 10.1242/jeb.038034
9. Hardison, E. A.; Eliason, E. J. Diet Effects on Ectotherm Thermal Performance. Biol. Rev Camb Philos Soc.2024, 99 (4), 1537-1555. DOI: 10.1111/brv.13081