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Browsing by Subject "nutrient sensing"

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  • Kuitunen, Essi (2019)
    Glutamine, the conditionally essential amino acid, is a major carbon and nitrogen carrier required for a range of cell functions, such as protein synthesis and maintaining redox balance. While healthy cells adjust their activities in response to glutamine availability, tumor cells display deregulated glutamine uptake and metabolism allowing quick proliferation and survival in cellular stress conditions. Hence, further knowledge of the glutamine sensing network is of interest. Utilizing Drosophila melanogaster, the roles of formerly identified glutamine sensing regulator candidates, Forkhead box O (FoxO), Super sex combs (Sxc), Spalt major (Salm) and Spalt-related (Salr), were explored. Drosophila is an efficient model organism for analyzing gene regulatory mechanisms, with its simple genome but conserved genes and metabolic pathways. Loss-of function and gain-of-function mutants of the candidates were cultured with/without glutamine, and their physiological response and gene expression changes were analyzed. The results show the glutamine intolerant phenotype of FoxO and Sxc deficiency, not dependent on altered food intake levels of larvae. However, glutamine intolerance of Salr and Salm deficiency was not observed. Moreover, we aimed to gain further insight to the roles of FoxO and Sxc in glutamine metabolism. Since amino acid catabolism produces ammonia, and glutamine metabolism plays a vital role in ammonia detoxification, we performed a pH-based measurement of foxo and sxc mutant larvae hemolymph on food with/without glutamine. However, we could not associate FoxO or Sxc with regulation of glutamine-derived ammonia clearance. In addition, we explored FoxO downstream regulator candidates. Putative promoter areas of Paics, Uro, Sesn, salr, Prat2 and Gdh were cloned into reporter vectors and the luciferase activity was analyzed under the expression of foxo. The results indicate that FoxO is a regulator of all of the 6 genes. Next we could utilize the here constructed plasmids to see whether the FoxO-mediated regulation is affected by altered glutamine levels in cell culture.
  • Kari, Moisio (2023)
    Animals regulate their metabolism dynamically as a response to changes in nutritional landscape. Intestine is emerging as a key regulator of systemic metabolism. It possesses secretory enteroendocrine cells (EECs), which have a central role in intestinal nutrient sensing and signaling. However, how the number and function of EECs is regulated in response to nutrients remains poorly understood. Previous work in Hietakangas lab has shown that a transcriptional cofactor, C-terminal binding protein (CtBP), regulates the number of EECs in response to sugar feeding and loss of CtBP function in EECs causes sugar intolerance in Drosophila. CtBP’s transcriptional activity is modulated through homodimerization, which is controlled by redox coenzyme NAD+/NADH, whose levels are dependent on sugar metabolism. Therefore, I hypothesise that CtBP is a sugar- and redox-responsive regulator of EEC function. In this thesis, I aimed to understand how CtBP is regulated and what are its downstream effectors. My results show that the formation of CtBP homodimers is responsive to dietary sugars and cellular redox state. In addition, I observed that CtBP heterodimerizes with EEC fate determining transcription factor Prospero. Functional analysis of CtBP downstream effector genes shows significant overlap with those of Prospero. In conclusion, CtBP is a sugar- and redox-responsive cellular regulator of EEC function, which acts in cooperation with Prospero.