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Transcriptional Regulation of Carnitine Palmitoyltransferase Synthesis in Riboflavin Deficiency in Rats¹

Paul S. Brady^*, Ya-Xiong Feng and Linda J. Brady^*

^* Department of Food Science and Nutrition, University of Minnesota, St. Paul, MN 55108 Department of Biochemistry, Shanghai Jiao Tong University, Shanghai, People's Republic of China

Riboflavin deficiency leads to depressed mitochondrial fatty acid oxidation rates but increased activity of carnitine palmitoyltransferase (CPT). Starvation leads to increased CPT activity in ad libitum—fed, riboflavin-supplemented rats. The present studies examined the mechanism of the increase in CPT activity in riboflavin deficiency and whether it was additive to that seen in starvation. Rats were divided into three groups initially: riboflavin-sufficient, ad libitum—fed; riboflavin-deficient, ad libitum—fed; and pair-fed. These groups were subdivided after 5 wk into fed and 24- and 48-h starved groups. When riboflavin-deficient rats were starved for 24 or 48 h, there was only a 30–40% increase in hepatic CPT activity, in contrast to the ad libitum—fed, riboflavin-supplemented rats, in which activity increased twofold. CPT activity of pair-fed rats was similar to that of controls in the fed state and did not increase significantly with starvation. CPT translation, mRNA levels and transcription rates correlated with CPT activity, as did immunoreactive CPT. Concurrently, hepatic ketone production and plasma ß-hydroxybutyrate concentration increased during starvation in the control and pair-fed but not in the riboflavin-deficient rats. The results indicate that increased CPT activity in riboflavin deficiency and starvation results at least in part from increased synthesis. Furthermore, the data support previous work suggesting that the block in fatty acid oxidation occurs in the ß-oxidation pathway at the level of acyl-CoA dehydrogenases.

KEY WORDS: • carnitine palmitoyltransferase • transcription • starvation • riboflavin

¹ This work was supported by National Institutes of Health Grant No. DK39285, a grant from the University of Minnesota Graduate School and the University of Minnesota Agricultural Experiment Station. This is paper #15749 from the University of Minnesota Agricultural Experiment Station.

Manuscript received 21 March 1988. Revision accepted 12 May 1988.