Role of functional polymorphisms of NRAMP1 gene for the development of Crohn's disease.
BACKGROUND
Crohn's disease (CD) is characterized by chronic activation of macrophages. Natural resistance-associated macrophage protein 1 (NRAMP1) gene exerts many pleiotropic effects on macrophage functions. Hence, NRAMP1 may be also involved in the resistance to intracellular pathogens, and this effector of the innate immunity might be involved in CD pathogenesis. Polymorphic alleles at the NRAMP1 locus have been previously associated with susceptibility both to the putative infectious agents and to autoimmune disorders. Based on these indications, in the present study we investigate its candidacy as a genetic determinant for CD in a Greek population in an association-based study, comparing frequencies of 274 CD patients to these of 200 healthy control subjects.


METHODS
The 5'(GT)n promoter polymorphism and 9 either single nucleotide (SNPs) or insertion/deletion type polymorphisms were genotyped across the NRAMP1 gene. Reverse-transcriptase polymerase chain reaction (RT-PCR) and immunohistochemistry were performed in order to investigate the NRAMP1 mRNA levels in RNA isolated from biopsies of CD patients as well as protein expression in tissues.


RESULTS
Three NRAMP1 polymorphisms [5'(GT)n, D543N, and INT4G/C] were significantly associated with CD. Consistent with previous autoimmune disease studies, allele 3 at the functional 5'(GT)n promoter region repeat polymorphism, was significantly associated with CD when compared to healthy controls (odds ratio 1.50; 95% confidence interval [CI]: 1.16-1.95; P = 0.002). Interestingly, we observed that CD patients homozygous for allele 3 expressed higher NRAMP1 mRNA levels compared to carriers of allele 2. Furthermore, the protein levels of allele 3 carriers in tissues were also elevated compared to those of allele 2 carriers. Based on these data we can speculate that overrepresentation of allele 3 in CD patients could lead to hyperactivation of bowel-wall macrophages that are chronically exposed to lipopolysaccharide and this could subsequently cause the autoimmune-like phenotype characteristic of CD.


CONCLUSIONS
Collectively, our data indicate that genetic polymorphisms of NRAMP1 might be associated with susceptibility to CD.
Gazouli
Maria
M
Department of Biology, School of Medicine, University of Athens, Greece. mgazouli@med.uoa.gr
Atsaves
Vassilios
V
Mantzaris
Gerassimos
G
Economou
Michalis
M
Nasioulas
George
G
Evangelou
Konstantinos
K
Archimandritis
Athanassios J
AJ
Anagnou
Nicholas P
NP
D000328:Adult; D016022:Case-Control Studies; D027682:Cation Transport Proteins / Q000235:genetics*; D003424:Crohn Disease / Q000235:genetics*; D005260:Female; D005787:Gene Frequency; D020022:Genetic Predisposition to Disease; D005838:Genotype; D006801:Humans; D007150:Immunohistochemistry; D008262:Macrophage Activation / Q000235:genetics*; D008297:Male; D011110:Polymorphism, Genetic; D011401:Promoter Regions, Genetic / Q000235:genetics; D020133:Reverse Transcriptase Polymerase Chain Reaction; D000099173:Natural Resistance-associated Macrophage Protein 1
D027682:Cation Transport Proteins; D000099173:Natural Resistance-associated Macrophage Protein 1