Molecular dissection of sphingolipid and sterol homeostasis in yeast

• Applicant: Professor Dr. Florian Fröhlich
• Subject Area: Biochemistry
• Term: from 2015 to 2024
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 282452898

Sphingolipids and sterols are abundant and essential molecules in eukaryotes that have crucial functions as signaling molecules and as membrane components. They are important for many processes, including endocytosis and surface receptor function. Changes in lipid levels are associated with several common pathologies, ranging from obesity to cancer, asthma, and atherosclerosis, and to neurodegenerative diseases and genetic disorders. In the last few years, we and others have made progress towards understanding sphingolipid homeostasis by identifying mechanisms regulating specific steps of sphingolipid metabolism. How the cellular distribution of sphingolipids and sterols between different organelles is maintained, how this influences sphingolipid homeostasis and how cellular physiology is affected remains obscure. During the last funding period we identified and started to decipher the molecular mechanism of sphingolipid and sterol transport that is mediated by the Golgi associated retrograde protein trafficking complex (GARP). We have also identified signaling pathways essential to regulate serine uptake and thus sphingolipid homeostasis utilizing a combination of chemical genetic screening and mass spectrometry based proteomics and phospho-proteomics. Our research has led to two different mechanisms how cells maintain lipid homeostasis and cellular function. These preliminary data will be the basis for this proposal. In the first aim we will biochemically dissect a so far undiscovered membrane contact site that is formed between the Golgi apparatus and mitochondria depending on phosphorylation of the GARP subunit Vps53. This aim will involve the identification of the proteome and structural characterization of the contact site as well as the identification of lipids transported there between the organelles. The second aim focusses on the understanding of the regulation of serine uptake by a process dependent on the TOR complex 1 to maintain sphingolipid homeostasis. In this aim we will study mechanism of TORC1 regulation by serine and/or sphingolipid levels, the mechanism of regulation of the plasma membrane permease Gnp1 towards serine uptake and the cellular response to increased sphingolipid levels. For all aims we will build on our expertise in proteomics and lipidomics that, in the combination, are only available to few groups in the world. We will combine them with classic biochemical and cell biological approaches to develop new tools and aim to understand lipid homeostasis in yeast on a mechanistic as well as on a holistic level. Our findings should also provide a starting point to better understanding and potential treatment strategies for neurodegenerative diseases.

• DFG Programme: Research Grants