ABSTRACT
Mucosal pentraxin (Mptx), identified in rats, is a short pentraxin of unknown function. Other subfamily members are Serum amyloid P component (SAP), C-reactive protein (CRP) and Jeltraxin. Rat Mptx mRNA is predominantly expressed in colon and in vivo is strongly (30-fold) regulated by dietary heme and calcium, modulators of colon cancer risk. This renders Mptx a potential nutrient sensitive biomarker of gut health. To support a role as biomarker, we examined whether the pentraxin protein structure is conserved, whether Mptx protein is nutrient-sensitively expressed and whether Mptx is expressed in mouse and human. Sequence comparison and 3D modelling showed that rat Mptx is highly homologous to the other pentraxins. The calcium-binding site and subunit interaction sites are highly conserved, while a loop deletion and charged residues contribute to a distinctive "top" face of the pentamer. In accordance with mRNA expression, Mptx protein is strongly down-regulated in rat colon mucosa in response to high dietary heme intake. Mptx mRNA is expressed in rat and mouse colon, but not in human colon. A stop codon at the beginning of human exon two indicates loss of function, which may be related to differences in intestinal cell turnover between man and rodents.
ABSTRACT
Consumption of red meat is associated with increased colon cancer risk. Our previous work indicated that this association might be due to the heme content of red meat. In rat studies, dietary heme increased colonic cytotoxicity and epithelial cell turnover, carcinogenesis biomarkers. Here we apply DNA microarray technology to examine effects of heme on colonic gene expression. A rat colon-specific microarray was constructed and hybridized in duplicate to RNA extracts from colon scrapings of rats fed diets with or without heme (n=6-7). We were able to reproducibly identify changes in colonic mRNA abundance in response to heme. Most striking was a >10-fold down-regulation of a single rat gene, an unprecedented gene-modulating effect of a dietary component. Based on homology, the novel gene encodes a pentraxin, the first identified in colon. Pentraxins are postulated to be involved in dealing with dying cells. Quantitative PCR confirmed the strong heme-induced down-regulation of this gene, which we named mucosal pentraxin (Mptx). Overall, our data support the efficacy of cDNA array expression profiling to investigate effects of specific nutrients in an in vivo system and may provide an approach to establishing markers for diet-induced stress of mammalian colonic mucosa.
