Iron handling and gene expression of the divalent metal transporter, DMT1, in the kidney of the anemic Belgrade (b) rat

Background. We have previously shown that the rat kidney reabsorbs metabolically significant amounts of iron and that it expresses the divalent metal transporter 1, DMT1. The Belgrade (b) rat carries a mutation in DMT1 gene, which causes hypochromic, microcytic anemia due to impaired intestinal iron absorption and transport of iron out of the transferrin cycle endosome. In the duodenum of b/b rats, expression of DMT1 mRNA and protein is increased, suggesting a feedback regulation by iron stores. The aim of this study was to investigate iron handling and DMT1 expression in the kidneys of Belgrade rats. Methods. Animals were maintained for 3 weeks on a synthetic diet containing 185 mg/kg iron (FeSO4), after which functional and molecular parameters were analyzed in male heterozygous (+/b) and homozygous (b/b) rats (N = 4 to 6 for each group). Results. Serum iron concentration was significantly higher in b/b compared to +/b rats while urinary iron excretion rates were unchanged in b/b compared to +/b rats. Northern analysis using a rat DMT1 probe showed comparable mRNA levels between +/b and b/b animals. Western analysis and immunofluorescence microscopy performed using a polyclonal antibody against rat DMT1 showed that DMT1-specific immunoreactivity was almost absent in the kidneys of b/b rats compared to that seen in +/b animals. Conclusion. Our results indicate that the G185R mutation of DMT1 causes protein instability in the kidneys of b/b rats. Given that +/b and b/b rats excrete comparable amounts of iron, the lack of DMT1 protein is compensated by an alternative, yet to be identified, mechanism.