Short-chain ceramide regulates hepatic methionine adenosyltransferase expression

Area of Science:

• Hepatology
• Molecular Biology
• Cellular Metabolism

Background:

• Methionine metabolism is crucial for hepatic cellular function.
• Methionine adenosyltransferase (MAT) synthesizes S-adenosylmethionine (AdoMet).
• MAT I/III levels are reduced in regenerating rat liver and influenced by cytokines like TNF-alpha and IL-6.

Purpose of the Study:

• To investigate the effect of exogenous cell-permeable ceramide on MAT I/III mRNA levels.
• To explore the association between ceramide and the actions of TNF-alpha and IL-6.
• To understand ceramide's role in modulating hepatic methionine metabolism.

Main Methods:

• Treatment of rat hepatocytes and H35 hepatoma cells with C2-ceramide.
• Administration of TNF-alpha and IL-6 to cell cultures.
• Analysis of MAT I/III mRNA and protein levels.
• Assessment of mRNA half-life and enzyme activity.
• Evaluation of cell viability.

Main Results:

• Exogenous C2-ceramide reduced MAT I/III expression and protein levels in a time-dependent manner.
• IL-6 potentiated ceramide's effect and decreased MAT I/III levels independently.
• TNF-alpha decreased MAT I/III levels and induced endogenous ceramide generation.
• The reduction in MAT I/III mRNA was attributed to transcriptional regulation, not mRNA degradation.
• Decreased MAT I/III mRNA levels correlated with reduced MAT activity.

Conclusions:

• Short-chain ceramide acts as an exogenous agonist to modulate hepatic methionine metabolism.
• Ceramide's effects on methionine metabolism are associated with the actions of cytokines.
• This study reveals a novel mechanism for regulating hepatic methionine metabolism involving ceramide and cytokines.