Medizinische Universität Graz Austria/Österreich - Forschungsportal - Medical University of Graz
Gewählte Publikation:
Schuller, M.
Effects of phosphatidylcholine synthesis on LRH1 activity
Humanmedizin; [ Diplomarbeit ] Graz Medical University; 2016. pp.
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- Autor*innen der Med Uni Graz:
- Betreuer*innen:
- Panzitt Katrin
- Wagner Martin
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- Abstract:
- Liver receptor homologue-1 (LRH-1/NR5A2) is a nuclear receptor and transcription factor that can be activated by ligands and is critically involved in the regulation of liver metabolism. Phospholipids have been discovered as potential LRH-1 ligands and activation of LRH-1 by certain phosphatidylcholines (PCs) has been shown to have physiological effects able to ameliorate non-alcoholic fatty liver disease and improve insulin sensitivity. However, a natural ligand or a metabolic pathway producing a LRH-1 ligand has not yet been defined. Since PCs have been described to activate LRH-1 we hypothesized that metabolic pathways producing PCs may generate an endogenous natural LRH-1 ligand. To test our hypothesize we silenced the two metabolic pathways of endogenous PC production, the Kennedy and the PEMT pathway, and studied effects on mRNA expression of LRH-1 target genes invitro in the hepatic cell line HepG2. In addition, we studied LRH-1 dependent gene expression invivo in Pemt knockout mice. Pemt knockout mice showed significantly decreased mRNA expression levels of the classical LRH-1 target genes Cyp8b1, Gck and Gnmt. However, also Lrh-1 mRNA itself was significantly decreased. In human invitro cell line experiments we robustly knocked down the key rate limiting enzyme of the Kennedy pathway, CT¿, and PEMT pathway, PEMT, using siRNA oligonucleotides. In line with the rodent invivo experiments siPEMT in HepG2 cells also showed significant reduction of LRH-1 target genes along with significant decrease in mRNA levels of the nuclear receptor LRH-1 itself. CT¿ knockdown did not have any robust effects on LRH-1 or LRH-1 target genes. Taken together, our experimental evidence suggests that the PEMT pathway, which generates a distinct set of PCs, significantly affects LRH-1 signalling while the Kennedy pathway has only little effect. However, from the experiments performed so far we are unable to differentiate if effects on LRH-1 target genes are caused by reduction of an endogenous ligand - as hypothesized - or rather caused by reduction of LRH-1 itself, or a combination of both. We have also yet not shown if, complementary to PEMT silencing, induction of the PEMT pathway activates LRH-1 signaling. Thus, further studies to answer these questions are warranted. These studies should include overexpression of stable LRH-1, which is unresponsive to gene regulation and gain of function experiments including PEMT overexpression and treatment with PEMT specific PC compounds.