Cysteine Sulfinic Acid Decarboxylase mRNA Abundance Decreases in Rats Fed a High-Protein Diet

Abstract

The partitioning of cysteine metabolism between sulfate and taurine biosynthetic pathways may be regulated in part by the activity of cysteine sulfinic acid decarboxylase (CSAD). CSAD activity is repressed by high-protein feeding, and we have previously reported that changes in CSAD activity are correlated with changes in CSAD protein. We conducted experiments to determine the relative expression of CSAD mRNA in rats fed 18 or 60% casein diets. In rats fed a 60% casein diet for 1 wk, hepatic CSAD activity and CSAD protein were 16 and 36%, respectively, of the values measured in rats fed the 18% casein diet. CSAD mRNA abundance in rats fed the 60% casein diet was 14% of the CSAD mRNA abundance in rats fed an 18% casein diet. The time course of the change in CSAD activity and mRNA abundance was examined in rats fed 18 or 60% casein diets for 48 h. Within 6 h of switching rats to a 60% casein diet, CSAD activity was decreased by 20% and after 48 h, activity was decreased 47% compared to activity measured at baseline. CSAD mRNA abundance was decreased 54% within 12 h of feeding rats a high-protein diet and remained depressed at 48 h. In a parallel group of rats fed the 18% casein diet, CSAD activity and CSAD mRNA were not significantly different from baseline values at 48 h. The decreased expression of CSAD mRNA in rats fed a high-protein diet is consistent with decreases in both CSAD enzyme activity and CSAD protein. Our results suggest dietary protein may regulate CSAD at the level of mRNA.