Broadly altered expression of the mRNA isoforms of FE65, a facilitator of beta amyloidogenesis, in Alzheimer cerebellum and other brain regions

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Abstract
FE65 is a key “adapter” protein that links a multiprotein complex to an intracellular domain of β-amyloid precursor protein (βPP). Its overexpression modulates the trafficking of βPP and facilitates the generation of β-amyloid (Aβ). FE65 is predominantly expressed in brain tissues. An exon 9-inclusive isoform is exclusively expressed in neurons, and an exon 9-exclusive isoform is only expressed in non-neuronal cells. We quantitated the two isoforms in middle temporal cortex, middle frontal cortex, cerebellar cortex and caudate nucleus of 17 Alzheimer disease (AD) patients, 12 normal controls and 9 non-AD neurodegenerative disease controls by reverse transcription-competitive polymerase chain reaction (RT-cPCR). Expression of the two isoforms was significantly and differentially altered, with a 30–57% decrease in levels of the neuronal form (P < 0.05–0.002) and a 73–135% increase in levels of non-neuronal form (P < 0.02–0.001), in the temporal and frontal cortex of AD brains. These alterations presumably reflect advanced neurodegenerative processes of these regions. Surprisingly, expression of both isoforms was significantly up-regulated by 42–66% in the cerebellar cortex and caudate nucleus of AD brains when compared to normal brains (P < 0.05–0.005). Diffuse Aβ-positive plaques were observed in the cerebellum of these AD subjects but not in the normal controls. Selective up-regulation of only the FE65 neuronal isoform was seen in the cerebellar cortex in association with other neurodegenerative diseases (largely Parkinson's disease). Because FE65 modulates trafficking of βPP toward the production of Aβ, the up-regulation of FE65 in AD cerebellum may be relevant to the genesis of diffuse plaques. Thus, early biochemical alterations in AD, not complicated by advanced pathology, may be beneficially investigated in the less-affected regions of the brain, such as the cerebellum. J. Neurosci. Res. 60:73–86, 2000