Fat Droplets Help Yeast Cells Cope with Low Oxygen Stress

Jenn Hoskins
13th June, 2024

Fat Droplets Help Yeast Cells Cope with Low Oxygen Stress

Image Source: Natural Science News, 2024

Key Findings

  • The study from the Slovak Academy of Sciences explored how yeast cells manage sterol accumulation under low oxygen conditions
  • Yeast cells import animal cholesterol and plant sitosterol more efficiently than their native ergosterol under hypoxic stress
  • Lipid droplets are essential for storing these non-native sterols and preventing their toxic effects on cell membranes
Research from the Slovak Academy of Sciences has provided new insights into the role of lipid droplets (LDs) and sterol esterification in the regulation of sterol accumulation in the yeast Saccharomyces cerevisiae under hypoxic (low oxygen) conditions[1]. This study sheds light on how different sterol structures influence yeast growth and membrane properties, adding to our understanding of sterol metabolism and its implications for cellular health. Sterols are a class of lipids that play essential roles in cell membrane structure and function. In yeasts, ergosterol is the primary sterol, while in animals and plants, cholesterol and sitosterol are more common, respectively. The study found that under hypoxic stress, S. cerevisiae imports animal cholesterol and plant sitosterol more efficiently than its native ergosterol. This efficient import is coupled with high esterification (a process where sterols are converted into ester forms) and their relocation to lipid droplets. Lipid droplets are cellular organelles that store neutral lipids, such as sterol esters and triglycerides. The study demonstrated that LDs are crucial for managing the accumulation of non-yeast sterols in cell membranes. When yeast cells were grown anaerobically (without oxygen) in media supplemented with cholesterol or sitosterol but lacked the ability to form LDs, they exhibited a prolonged lag phase before starting to grow. In contrast, normal growth was observed in media containing ergosterol or plant stigmasterol, suggesting that LDs are essential for handling the influx of non-native sterols. Further experiments with a yeast strain lacking the HEM1 gene (hem1∆), which mimics anaerobic conditions, showed that neither cholesterol nor sitosterol supported growth in the absence of LDs. This finding underscores the importance of LDs in protecting cells from the toxic effects of non-native sterols by sequestering them away from cell membranes. The incorporation of non-ergosterol sterols into cell membranes was found to alter key membrane characteristics, including membrane potential, permeability, tolerance to osmotic stress, and the formation of membrane domains. These changes can impact cell viability and function, highlighting the protective role of LDs in maintaining membrane integrity under stress conditions. This study aligns with previous research that has explored the role of ABC transporters in sterol metabolism. For instance, mutations in the ABCG5 and ABCG8 transporters in mice lead to the accumulation of plant sterols in tissues, causing severe health issues, including liver abnormalities and cardiac lesions[2][3]. These findings suggest that the exclusion of certain sterols from the body is a protective mechanism to prevent toxicity. Moreover, the study's findings on sterol import in yeast under hypoxic conditions resonate with earlier research on sterol import in fungal species. It has been shown that S. cerevisiae imports sterols under low oxygen levels, while pathogenic fungi like Candida glabrata and Candida albicans can import sterols under both aerobic and anaerobic conditions[4]. This research further elucidates the conditions under which yeast cells import and utilize exogenous sterols, emphasizing the role of LDs in this process. In conclusion, the research from the Slovak Academy of Sciences highlights the critical role of lipid droplets and sterol esterification in regulating sterol accumulation in yeast membranes under hypoxic stress. By sequestering non-native sterols in LDs, yeast cells can mitigate the potential toxic effects on membrane properties, ensuring cellular health and viability. These findings contribute to our broader understanding of sterol metabolism and its implications for cellular function and stress response.

GeneticsBiochemMycology

References

Main Study

1) Lipid droplets control the negative effect of non-yeast sterols in membranes of Saccharomyces cerevisiae under hypoxic stress.

Published 10th June, 2024

https://doi.org/10.1016/j.bbalip.2024.159523

Related Studies

2) Phytosterol feeding causes toxicity in ABCG5/G8 knockout mice.

https://doi.org/10.1016/j.ajpath.2012.12.014

3) Selective sterol accumulation in ABCG5/ABCG8-deficient mice.

Journal: Journal of lipid research, Issue: Vol 45, Issue 2, Feb 2004

4) Comparison of sterol import under aerobic and anaerobic conditions in three fungal species, Candida albicans, Candida glabrata, and Saccharomyces cerevisiae.

https://doi.org/10.1128/EC.00345-12


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