Age-related Iron Transport Proteins Expression In Rat Proximal Small Intestine

Iron (Fe) is essential for DNA synthesis, oxygen transport and the ability of aerobic oxidation and the production of ATP of life. Unlike many other nutrients, the iron should be tightly regulated at the point of absorption, because the body lacks a defined mechanism for the active excretion of iron. Intestinal iron absorption and its regulation have been focused for many decades. However, only in the past few years with the discovery of a number of key molecules involved in intestinal iron transport like DMT1, FPN1, HP, and hepcidin, we have begun to understand the process of the molecular mechanisms of intestine iron transport. There are different reports of the change of iron status and stores in different ages due to different methods and animal models were performed. However, the sequential study of variation of iron status with aging and its mechanism have not been identified. With aging, there is close relationship between iron overload and age-related proteinopathies like HH etc. However, the molecular mechanism of age-related iron overload is still unknown. In this study, we examined age-related changes of iron status and expressions of iron transport proteins in duodenum of male SD rats in order to illustrate the relationship between aging and iron metabolism.150 male SD rats were randomly divided into 5 groups: 1week group, 3week group, 12week group, 44week group, and 88week group. The serum iron (SI), serum unsaturated iron-binding capacity (UIBC), total iron-binding capacity (TIBC), serum transferrin, transferrin saturation (TS), Hematocrit, Hb and RBC were identified. The non-heam iron of heart, liver, spleen, kidney, gastrocnemius and bone marrow were also measureed. The expression of DMT1, FPN1, and HP of different ages in duodenum were detected by RT-PCR and Western-blot. Iron levels of duodenum mucosa were detected by Graphite Furnace Atomic Absorption Spectrometry. The expression of hepcidin mRNA in liver was examined by RT-PCR.The results were as follows:1. Hematocrit, Hb and RBC showed age-related increase from 1w to 12w and then stabilized at this level. Serum iron status was firstly increased, and then decreased with age. 3w showed the highest iron content and 88w was the lowest. The expression of serum transferrin and UIBC showed no significant different before 44w, it was then significantly decreased at age 88w.2. Non-heam iron distribution of different tissues showed significant decrease at age 3w and then increased thereafter with aging, especially in liver, spleen, heart and kidney. Non-heam iron in gastrocnemius was age-related decreased from 1w to 12w, after12w it was stabilized at a certain level. We also found that iron contents of duodenum mucosa was firstly decreased at age 3w, and then increased with aging, which was detected by Graphite Furnace Atomic Absorption Spectrometry.3. The expression of DMT1(-IRE) showed age-related decline from 1w to 12w and then stabilized to age of 88 w. DMT1(+IRE) expression was up-regulated from 1w to 3w but down-regulated from 3w to 88 w. FPN1 showed the highest expression in 3w, but no difference was found among five periods of age. There was also no significant change in HP expression.4. The analysis of Hepcidin mRNA expression showed decline at age 3w first and then age-related increase.Conclusion:1. Our results indicate that in this animal model, aging was associated with significant decline in serum iron status but severe iron accumulation in other kinds of tissue.This accumulation may play a role in morbility of many diseases.2. Decreased DMT1 but not FPN1 in both mRNA and protein level with aging in the duodenum. This result indicated that duodenum epithelium iron uptake was decreased while iron release showed no significant change with aging.3. The DMT1 and FPN1 expression may be regulated by both hepcidin on the translatable level and the interaction of iron regulatory proteins (IRP) and IRE on the DMT1 and FPN1 mRNA on the transcriptional level.4. The analysis of Hepcidin mRNA expression showed decline at age 3w first and then age-related increase. The result revealed that hepcidin could modulate the duodenal iron absorption, and further regulate the body iron metabolism with aging. Hepatic iron stores may play a part in the regulation of hepcidin expression.