Abstract
BackgroundAlzheimer's disease (AD) is characterized by neurodegeneration and changes in cellular processes, including neurogenesis. Proteolytic processing of the amyloid precursor protein (APP) plays a central role in AD. Owing to varying APP processing, several β-amyloid peptides (Aβ) are generated. In contrast to the form with 40 amino acids (Aβ40), the variant with 42 amino acids (Aβ42) is thought to be the pathogenic form triggering the pathological cascade in AD. While total-Aβ effects have been studied extensively, little is known about specific genome-wide effects triggered by Aβ42 or Aβ40 derived from their direct precursor C99.MethodsA combined transcriptomics/proteomics analysis was performed to measure the effects of intracellularly generated Aβ peptides in human neuroblastoma cells. Data was validated by real-time polymerase chain reaction (real-time PCR) and a functional validation was carried out using RNA interference.ResultsHere we studied the transcriptomic and proteomic responses to increased or decreased Aβ42 and Aβ40 levels generated in human neuroblastoma cells. Genome-wide expression profiles (Affymetrix) and proteomic approaches were combined to analyze the cellular response to the changed Aβ42- and Aβ40-levels. The cells responded to this challenge with significant changes in their expression pattern. We identified several dysregulated genes and proteins, but only the cellular retinoic acid binding protein 1 (CRABP1) was up-regulated exclusively in cells expressing an increased Aβ42/Aβ40 ratio. This consequently reduced all-trans retinoic acid (RA)-induced differentiation, validated by CRABP1 knock down, which led to recovery of the cellular response to RA treatment and cellular sprouting under physiological RA concentrations. Importantly, this effect was specific to the AD typical increase in the Aβ42/Aβ40 ratio, whereas a decreased ratio did not result in up-regulation of CRABP1.ConclusionWe conclude that increasing the Aβ42/Aβ40 ratio up-regulates CRABP1, which in turn reduces the differentiation potential of the human neuroblastoma cell line SH-SY5Y, but increases cell proliferation. This work might contribute to the better understanding of AD neurogenesis, currently a controversial topic.
Highlights
Alzheimer's disease (AD) is characterized by neurodegeneration and changes in cellular processes, including neurogenesis
We conclude that increasing the Aβ42/Aβ40 ratio up-regulates cellular retinoic acid binding protein 1 (CRABP1), which in turn reduces the differentiation potential of the human neuroblastoma cell line SH-SY5Y, but increases cell proliferation
To analyze altered β-amyloid peptides (Aβ) generation in a controlled manner, C-terminal fragment of APP (C99)-overexpression constructs encoding the C-terminal part of amyloid precursor protein (APP) (C99) were used [6,7]
Summary
Alzheimer's disease (AD) is characterized by neurodegeneration and changes in cellular processes, including neurogenesis. Proteolytic processing of the amyloid precursor protein (APP) plays a central role in AD. Amyloid precursor protein (APP), presenilin, presenilin and the apolipoprotein E ε4 allele have been associated with AD [2,3]. These genes are assumed to be responsible for approximately 50% of the genetic background of the disease, suggesting that further susceptibility genes exist. To elucidate the underlying mechanisms, we used a combined transcriptomic-proteomic approach and utilized APP point mutations to modulate the Aβ42/Aβ40 ratio. We identified cellular retinoic acid binding protein 1 (CRABP1) as the exclusive transcript and protein showing strong differential expression as a consequence of an increased Aβ42/Aβ40 ratio. CRABP1 is involved in retinoic acid (RA)-induced differentiation [8,9,10] and is expected to play a crucial role in neurogenesis [11]
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