Amyloid precursor protein subtypes and secretases implicated in Alzheimer's disease.
To date there is no definite understanding to suggest a clear causative route in the events which lead to the neurodegenerative disorder Alzheimer disease (AD) however several proteins have been implicated.Eight proteins that have been implicated in AD have been mapped across seven regions of non-human primate brain tissue from a Macaca fascicularis in this study: APP[770]; APP[751]; APP[695]; ADAM 9, 10 and 17 as alpha-secretases; BACE 1 as beta-secretase and PS1 as gamma-secretase.The APP[695] isoform was found to have the highest levels in the frontal and temporal regions. However, the APP[751] isoform was found to be at the highest level, with very low levels of APP[695] in the soluble fractions of the hippocampus and hypothalamus.Membrane associated levels of alpha-secretases were found to be highest in frontal, temporal, cerebellar, hypothalamus, basal ganglia and hippocampus.The distribution of BACE 1 was found to be low in the frontal and temporal regions in comparison to all the other regions sampled where levels exceeded the levels in the frontal region by over three times. The distribution of gamma-secretase across the regions showed an even distribution with the exception of the hippocampus which had an almost double level in comparison to the other areas sampled. With a relatively high level of the gamma-secretase and gamma-secretase and a concomitant very high level of the APP[kpi] containing subtype APP[751] this would tend to indicate a different sensitivity in the hippocampus and hypothalamus compared to the other regions sampled. The conclusion that may be drawn from these findings is that since the hippocampus and hypothalamus are two of the earliest regions to be affected in AD altered processing of the subtype APP[751] may indicate a regional sensitivity.The culture of NT2/D1 clonal cells with retinoic acid results in the appearance of post-mitotic human neuronal cells.The APP isoforms and secretases present in the brain regions of the Macaca fascicularis have been observed in the NT2 cells as they have been cultured with retinoic acid to obtain the NT2-N neuron-like cells. NT2 cells cultured without retinoic acid produced the sAPP[kpi] subtype in contrast to the cells cultured in the presence of retinoic acid where APP[695] is the predominant subtype.The three secretases of interest in AD were expressed in the NT2 cells and the NT2-N cells similar to the expression in Macaca fascicularis brain tissue. The most notable difference between the brain tissue and NT2/NT2-N cells was to be seen in the expression of BACE 1 as beta-secretase. In the NT2/NT2-N cells BACE 1 appears to be expressed as a stable and high molecular weight form not seen in the Macaca fascicularis brain tissue. The gamma-secretase expression in NT2/NT2-N cells represented by immuno-blotting with an antibody raised against Presenilinl reflected the position seen in the brain tissue.The secretases and APP subtypes in the NT2-N cells most closely reflect the expression found in the hippocampus and hypothalamus of the Macaca fascicularis brain tissue and therefore are a good cellular model for AD.
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Sheffield Hallam University (United Kingdom).