| Background:Iron is an essential component of many proteins that are involved in important cellular processes like oxygen transport, mitochondrial respiration, and DNA synthesis. In the brain, iron is vital for the synthesis of myelin-proteins and fatty acids in oligodendrocytes, and for the synthesis of neurotransmitters in neurons. Misbalance in iron homeostasis can be devastating, thus it must be regulated stringently. Excessive free iron is involved in the Fenton reaction, which catalyzes the conversion of hydrogen peroxide to highly reactive hydroxyl radical that damages DNA, proteins, and lipids. Over the decades, various studies have suggested that there is an association between accumulation of iron and neurodegenerative disorders such as Alzheimer’s disease (AD) and Parkinson’s disease (PD). Aging remains the most compelling and prominent risk factor for the development AD and PD and has suggested that it might be related to iron accumulation with ageing. However, until now, it is still unclear why and how iron is abnormally increased in these brain areas and the mechanisms involved in brain iron homeostasis are unknown. There is also lacking of systemic research to clarify the relationship between aging, iron accumulation and neurodegenerative diseases.Objective:To systematically investigate the relationship between age, brain iron metabolism disorders and PD/AD. Twenty-seven normal SD rats were divided into three groups in this study based on their age, including a young group (3months old, n=9), an adult group (11months old, n=9) and an aged group (24months old, n=9). Four PD/AD related regions were selected, including cortex, hippocampus, striatum and substantia nigra.Methods:In the first part, the iron content and distribution in selected regions of the young, adult and aged rat brain were investigated by graphite furnace atomic absorption spectrophotometer (GFAAS) and DAB-intensified Perl’s histochemical staining respectively. In the second part, the expression level and distribution of iron-related proteins in selected regions of the young, adult and aged rat brain were tested by western blot, immunohistochemisty. In the third part, the expression level and distribution of AD related proteins in cortex and hippocampus of young, adult and aged rats were tested by immunohistochemistry, and the expression level and distribution of PD related proteins in SN of rats at different ages were tested by double immunofluorescence staining.Results:In the first part, we found that iron content was significantly increased in hippocampus and striatum with age. Iron staining shows that the positive staining intensity of iron was low in all four regions of young rat brain, and gradually increased in adult and aged rats. The predominant cell type containing iron in cortex is neuron, whilst in the other three regions it is oligodendrocyte. Moreover, microglia or astrocyte also can be seen in hippocampus and striatum. In the second part, we found (1) The expression level of Ferritin was increased in all four regions with age, and its distribution pattern is same as iron level.(2) The expression level of DMT1+/-was significantly increased first and then decreased with age in hippocampus and striatum; there is no significant difference for DMT1-between young and adult group, but increased in aged group in substantia nigra.(3) TfR.1protein level decreased significantly in hippocampus, striatum and SN as the rats aged.(4) Cp protein level was significantly increased in striatum and SN with age.(5) The change of Fpnl expression level was only observed in striatum, which was decreased in aged rats.(6) The expression le^el of hepcidin was significantly increased in all four regions with age. In the third part, we found that age has a significant effect on these protein expression levels. The expression level of Aβ and PHF-Tau was increased in cortex and hippocampus with age, and the predominant cell type containing them is neuron, α-synuclein and TH were co-localized in neurons of SN and a-synuclein expression level was increased significantly with age, while the TH protein level decreased dramatically. Moreover, the TH-positive cells loss in SN of aged rats was observed. Conclusion:the results of the present study demonstrated that the effect of age on the iron accumulation level and distribution, as well as the expression levels of iron-related proteins in different brain regions are significant. This suggests that the iron-related proteins play important roles in iron level regulation during the aging process. Moreover, our data shows that age is a critical factor involved in development of AD and PD by changing the expression level of proteins, which are closely associated with these two neurodegenerative diseases. Furthermore, these proteins and iron accumulation was found in the same cell type or the same regions, suggesting that the increasing iron accumulation level with age probably plays an important role in these processes. By studying the content and distribution of iron and iron-related proteins in different regions during the aging process, we should be able to increase our understanding of the mechanisms involved iron homeostasis in the brain, and further enhance our knowledge of the role of increasing iron level in the development of age-related neurodegenerative disorders and develop new therapeutic strategies. |
PDF Full Text Request