Untersuchung regulatorischer Proteine des metabolischen Netzwerkes zellulärer Fettspeicherorganellen
Zellbiologie
Zusammenfassung der Projektergebnisse
All eukaryotic cells are able to store metabolic energy as fat in the lipid droplets (LDs) and this process is evolutionary conserved from budding yeast, S. cerevisiae, to human. As pivotal components of the lipid metabolism, LDs provide the supply of metabolites for cellular processes and play a decisive role in obesity and related diseases such as type 2 diabetes (T2D) and nonalcoholic fatty liver disease (NAFLD). Integrated in an all-embracing cellular network, LDs functionally and physically interact with other organelles. By applying a high-throughput flow cytometry genome-wide screen of S. cerevisiae, we were able to identify several candidates (ESCRT, V-ATPase) essential in the interplay between LD and vacuole during growth resumption. Moreover, we showed that Tsc3p, a regulator of serine palmitoyl transferase (SPT) and thus ceramide synthesis in the ER, is an essential regulator of neutral lipid consumption and ultimately LD dynamics. Finally, we showed that the human analog of Tsc3p, the SPT small subunit b (ssSPTb), is able to rescue the growth and LD consumption defect in tsc3Δ cells, suggesting an essential role for ssSPTb in the regulation of LD dynamics in human. Of note, the silencing of ssSPTb in human hepatocytes did not significantly affect the concentration of any diacylglycerol (DAG), ceramide and sphingolipid species as well as the activity of the novel protein kinase C (nPKC) ɛ and the phosphorylation of the insulin receptor kinase domain (IRK). We first hypothesized that the second stimulator of the SPT, the ssSPTa, could compensate for the activity of ssSPTb. However, we did not observe any change in lipid composition of HepG2 cells after treatment with myriocin. Further experiments will therefore unravel the potential interplay between LD and sphingolipid dynamics in mammalian cells.
