Decreased sucrase and lactase activity in iron deficiency is accompanied by reduced gene expression and upregulation of the transcriptional repressor PDX-1

Abstract

West, Adrian R., and Phillip S. Oates. Decreased sucrase and lactase activity in iron deficiency is accompanied by reduced gene expression and upregulation of the transcriptional repressor PDX-1. Am J Physiol Gastrointest Liver Physiol 289: G1108 -G1114, 2005. First published August 4, 2005; doi:10.1152/ajpgi.00195.2005.-Disaccharidases are important digestive enzymes whose activities can be reduced by iron deficiency. We hypothesise that this is due to reduced gene expression, either by impairment to enterocyte differentiation or by iron-sensitive mechanisms that regulate mRNA levels in enterocytes. Iron-deficient Wistar rats were generated by dietary means. The enzyme activities and kinetics of sucrase and lactase were tested as well as the activity of intestinal alkaline phosphatase (IAP)-II because it is unrelated to carbohydrate digestion. mRNA levels of ␤-actin, sucrase, lactase, and the associated transcription factors pancreatic duodenal homeobox (PDX)-1, caudal-related homeobox (CDX)-2, GATA-binding protein (GATA)-4, and hepatocyte nuclear factor (HNF)-1 were measured by real-time PCR. Spatial patterns of protein and gene expression were assessed by immunofluorescence and in situ hybridization, respectively. It was found that iron-deficient rats had significantly lower sucrase (19.5% lower) and lactase (56.8% lower) but not IAP-II activity than control rats. Kinetic properties of both enzymes remained unchanged from controls, suggesting a decrease in the quantity of enzyme present. Sucrase and lactase mRNA levels were reduced by 44.5% and 67.9%, respectively, by iron deficiency, suggesting that enzyme activity is controlled primarily by gene expression. Iron deficiency did not affect the pattern of protein and gene expression along the crypt to villus axis. Expression of PDX-1, a repressor of sucrase and lactase promoters, was 4.5-fold higher in iron deficiency, whereas CDX-2, GATA-4, and HNF-1 levels were not significantly different. These data suggest that decreases in sucrase and lactase activities result from a reduction in gene expression, following from increased levels of the transcriptional repressor PDX-1.anemia; transcription; nutrition; pancreatic duodenal homeobox CARBOHYDRATES are a vitally important dietary component, and disaccharidases are an essential subset of digestive enzymes required for the terminal step of carbohydrate digestion (13). The enzymatic activity of each individual disaccharidase is influenced primarily by the dietary level of their corresponding substrate (2, 12), and, under normal conditions, this level of activity is controlled by the abundance of the mRNA encoding the proteins (12, 34). However, it has been shown on many occasions that dietary iron deficiency can cause a significant decrease in disaccharidase activity (2,4,5,9,16,20,31,38) and that this decrease is reversible by iron supplementation (9,20,38).It is unlikely that iron is directly required for disaccharidase activity (16) or that iron deficiency alters the kinetic properties of sucrase (5). In additio...

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