Application of a dye-based mitochondrion-thermometry to determine the receptor downstream of prostaglandin E(2) involved in the regulation of hepatocyte metabolism

Temperature distributions inside a living cell reflect the thermodynamics and functions of cellular components. We used a newly-developed method of mitochondrial thermometry based on Rhodamine B methyl ester, which equilibrates as a thermosensitive mixture of nonfluorescent and fluorescent resonance forms. Prostaglandin E(2) (PGE(2)) is released from hepatic non-parenchymal Kupffer cells and acts as an inflammatory factor to impact various functions of hepatocytes. The activity of PGE(2) on energy mechanism of hepatocytes has not been fully elucidated and in particular, which PGE(2) receptor mediates the functions has been elusive. We identified EP4 as the major receptor of PGE(2) via our mitochondrion-thermometry approach and then substantiated this receptor’s role in hepatic metabolism. We discovered that PGE(2) is able to decrease intracellular temperature of hepatocytes, via increasing some lipogenic genes’ expressions, hampering lipolysis and mitochondrial β-oxidation, reducing intracellular ATP level and elevating cAMP level through EP4 receptor. The redox status of hepatocytes represented by FAD vs FAD + NADH ratio is influenced by PGE(2) in an EP4 receptor-dependent manner. Collectively, these data demonstrate that PGE(2) regulates metabolism of hepatocytes mainly through EP4 receptor.