NMR STUDIES OF TRANSGENIC MOUSE MODELS OF HUNTINGTONS DISEASE & ALS

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This project entails measurement of metabolite levels (both 'H and "C) in brain extracts of transgenic mice that are models for amyotrophic lateral sclerosis (ALS) and Huntington's disease (HD). These metabolite levels are then used to complement in vivo determination of many of the same chemicals using MRS. Our goal is to determine if there are defects in TCA cycle metabolism and neuronal-glial cycling in these mice. Elevated glutamate levels have often been implicated in ALS and profound decreases in NAA are often seen in HD. We study the mice longitudinally using in vivo MRS (4.7T at MGH) and then take extracts of brains at various time intervals for study using in vitro NMR spectroscopy at 500 MHz at the Magnet Laboratory. From these extracts, we determine the absolute concentrations of metabolites using 1D and 2D proton spectroscopy. We also utilize direct and indirect observe carbon-13 spectroscopy to determine fractional enrichements of TCA cycle metabolites from mice infused with labeled glucose prior to sacrifice. These are also compared to the in vivo dynamic carbon-13 spectroscopy obtained in localized brain regions. The NMR data is then correlated with HPLC measurements of some of the same compounds to ascertain the accuracy of the results and to provide absolute quantification of the metabolite levels. In addition, we have performed histochemistry and histology on the same animals to determine the correlation of the biochemical defects with other neuropathological changes. The results we have obtained so far indicate a profound disturbance of NAA metabolism in the neurons of the HD animals in spite of the fact that histology shows very little neuronal loss. In addition, there is a profound imbalance in glutamate-glutamine cycling in these mice. The NAA disturbance progresses exponentially over time. In the ALS mice, in contrast, we have found very small changes in NAA metabolism while finding large increases in glutamate. These results clearly indicate that NMR spectroscopy has the potential to yield valuable insight intoi the basic biochemical etiology of these diseases.