The Interference Mechanism Of Iron-overload In Biological Rhythm And Blood System

As an important metal element of human life, iron was an essential component of hemoglobin, myohemoglobin and cytochromes, and played a critical role in growth and development. Iron was commonly absorbed from food and water, and was lost through sweat, urine and the gastrointestinal tract. In human, the absorption of iron was more than the eduction of iron. Consequently, iron was found to accumulate with aging. Iron-overload was frequently accompanied by sleep disorders, which were similar to the elderly. Sleep was also correlated with biological rhythms. The relationship between the expression of circadian clock genes and excessive accumulation of iron with age was unclear. We used knockout mice to study this relationship.Comparative analysis of transcription of six clock genes Clock, Bmal1, Per1, Per2, Cry1 and Cry2 between 8 weeks and 64 weeks old mice, the results showed that only Per2 decreased by 40% in the liver of 64 weeks old mice and the expression of other clock genes did not be weakened. Increased 50% liver iron content was observed in 64 weeks old mice. Compared with mice fed with a normal diet, the liver iron content of mice fed the high-iron diets increased 10-fold. The transcription of clock gene in the liver of mice fed the high-iron diets had a similar pattern with 64 weeks old mice. The level of Per2 decreased 60% and other clock genes were not impaired in the mice fed the high-iron diets. Iron-overload models by injecting iron dextran also showed that iron-overload impaired Per2 expression in dose dependent and time dependent manners. In vitro experiments, FeSO4 suppressed the expression of Per2 in NIH3T3 cells. These results indicated that the accumulation of iron from food suppressed the expression of clock gene Per2.Per2 deficiency leads to impaired platelet function and decreased platelet counts. Compared with WT mice, the tail bleeding time of Per2-null mice increased 1-fold. Per2-null platelets were compromised in their ability to aggregate and secretion, consistent with a marked reduction in the number of dense and a-granules. The Per2-null mice had nearly 50% platelet counts in peripheral blood. Megakaryocytes from Per2-null mice showed no significant variation in number but increased in ploidy. Ultrastructural examination of Per2-null megakaryocytes revealed many vacuoles in demarcation membranes and reduction in platelet granules. Megakaryocytes from Per2-null bone marrow decreased the rate of proplatelet formation and impaired apoptosis. Per2-null mice showed increased both in Tpo in livers and its receptors C-mpl in bone marrow. Enhanced Tpo/ C-mpl expression in Per2-null mice may be due to low platelet level. The megakaryocytes from Per 2-null mice showed decreased P53 expression, consequently increased Bcl-xl and Bcl-2 level. The clock gene Per2 modulating the apoptosis of megakaryocytes was required for platelet formation and function. These results were consistent with low platelet count in elders.Per2 defeciency lead to increased susceptibility to acute stress in the erythrocytes. Per2-null RBCs were significantly increased susceptibility to acute stresses, displaying high mortality rate and severely anemia on phenylhydrazine, osmotic and H2O2-induced damages. In addition, Per2-null erythrocytes showed an increased methemoglobin formation after incubation with H2O2. These resulted in reduced oxygen consumption, low SaO2, an increase in the serum and spleen iron. As a compensatory action, reticulocyte counts increased in these mutant mice. MCV and RDW increased in Per2-null mice. Morphologically abnormal cells were elevated in the Per2-null RBCs. HPLC analysis revealed that the ATP levels of RBCs markedly reduced in Per2-null mice compared to wild type mice. An obvious increase in membrane ATPase activities were observed in Per2-null RBCs; and enhancement of Atp1a1 mRNA expression were detected in bone marrow cells. These results demonstrated that clock gene Per2 played a role in response to acute stress by influencing ATPase-regulated ATP level in the erythrocytes. These observations were consistent with increased susceptibility of aging individual RBCs to acute stress.These findings indicated that iron absorbed from daily food intake accumulated in the body with age and impaired Per2 expression, affecting biological clock and blood system. We suggested that iron supplementation should be carefully in adult.