P4-142: Characterization and mapping of iron compounds in a huntington’s disease transgenic mouse model

Abstract

Abnormal accumulations of metals, protein aggregation, and oxidative stress are uniting features in neurodegenerative conditions, such as Alzheimer's (AD), Huntington's (HD) and Parkinson's (PD) diseases. At present, little is understood about the mechanisms behind these abnormalities and the role of metals in HD pathogenesis remains a mystery. Here we describe a novel method for the detection and identification of anomalous iron compounds and related metals in mammalian brain tissue using x–ray fluorescence (XRF) methods. The potential for high–resolution iron mapping using microfocused x–ray beams has direct application to investigations of the location and structural form of metal compounds associated with human neurodegenerative disorders – a problem which has vexed researchers for 50 years. (i) To develop techniques for investigating iron in brain tissue using synchrotron x–ray fluorescence methods; (ii) to characterize iron compounds in situ allowing for direct correlation with the disease pathology at cellular resolution; (iii) to use immunohistochemistry to evaluate regional changes in tissue. Synchrotron x–ray analysis, light and transmission electron microscopy were employed to examine brain tissue of transgenic model of HD and control animals. The synchrotron findings were supported by a SQUID magnetometry study. Using the XRF we have shown the iron oxide deposits in the basal ganglia of the HD transgenic mice. A variety of iron oxides were found to be present, including normal ferritin iron, and some deposits of magnetite which contain both Fe3+ and Fe2+, a finding that has not been reported previously in the literature. The presence of magnetite was supported by the SQUID magnetometry data. An increasing microglial reaction which paralleled the iron accumulation in R6/2 brain tissue was found in some samples, though neither neuronal death nor atrophy was observed. Together, these observations provide a preliminary indication that alterations in iron deposition occur prior to pronounced neuronal cell death in the model of HD. In view of the neuronal damage caused by iron–catalyzed free radical formation, these alterations are likely to contribute to the vulnerability of striatal neurons. Therefore, early–onset iron deposition may be relevant to the pathogenesis of the disease.