Osmotic regulation of hepatic choline metabolism. Mus musculus

Betaine critically contributes to the control of hepatocellular hydration and provides protection of the liver from different kinds of stress. This study investigates to what extent hepatocellular hydration changes affect the expression levels of enzymes involved in the metabolism of betaine and related organic osmolytes by using qRT-PCR gene expression studies in rat hepatoma cells as well as metabolic and gene expression profiling in 5,10 - methylene tetrahydrofolate reductase (MTHFR) deficient primary hepatocytes. The results demonstrate a coordinated regulation of betaine degradation and synthesis under anisoosmotic conditions. Expression of betaine degrading enzymes is downregulated by hyperosmolarity and strongly induced by hypoosmolarity. In contrast, synthesis of glycerophosphocholine from phosphoethanolamine and conversion of choline to betaine are both induced by hyperosmolarity but decreased under hypoosmotic conditions. In addition we evaluated the flux of choline and its derivates in liver and plasma of methylene tetrahydrofolate reductase knockout (Mthfr-/-) mice by tandem mass spectrometry. Analyses of system-wide alterations of osmolyte metabolism with microarray studies revealed expression changes similar to those after hypoosmotic exposure in this betaine depletion model. In conclusion, regulation of betaine synthesis and degradation and concomitant changes in intracellular osmolyte concentrations contribute to long-term adaptation to anisoosmotic exposure of the liver. Overall design: Expression of 280 genes were analyzed in wild type and mthr-/- mice (n=7) with spotted oligonucleotides.