Diurnal variations in methionine content and expression of certain genes involved in DNA methylation reaction in pigs

Whether methionine content and its metabolites in liver and skeletal muscle show diurnal rhythmicity remains unknown. In the present study, we investigated the diurnal rhythms in methionine and S-adenosylmethionine (SAM) in plasma, liver, and longissimus thoracis muscle, as well as in enzymes involved in methionine-related transmethylation reaction using pigs maintained in a 12-h photoperiod. The results showed that concentration of methionine and SAM, as well as mRNA expression of methionine adenosyltransferase (MAT1A), DNA methyltranferase (DNMT3A and DNMT3B) in liver showed diurnal rhythmicity. Comparison with typical circadian clock genes revealed a similarity between the diurnal patterns of MAT1A and cryptochrome circadian clock 1 (CRY1) expression, whereas the daily patterns of MAT2A, DNMT3A, and DNMT3B expression were reversely related to the expression patterns of Timeless. These results imply that much attention should be paid to rhythms of methionine metabolism and methylation activity in the pathogenesis of diseases, such as cancer and metabolic syndrome.