Upregulation of CRABP1 in human neuroblastoma cells overproducing the Alzheimer-typical A beta(42) reduces their differentiation potential

Abstract

Background: 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. Owing to varying APP processing, several beta-amyloid peptides (A beta) are generated. In contrast to the form with 40 amino acids (A beta(40)), the variant with 42 amino acids (A beta(42)) is thought to be the pathogenic form triggering the pathological cascade in AD. While total-A beta effects have been studied extensively, little is known about specific genome-wide effects triggered by A beta(42) or A beta(40) derived from their direct precursor C99. Methods: A combined transcriptomics/proteomics analysis was performed to measure the effects of intracellularly generated A beta 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. Results: Here we studied the transcriptomic and proteomic responses to increased or decreased A beta(42) and A beta(40) levels generated in human neuroblastoma cells. Genome-wide expression profiles (Affymetrix) and proteomic approaches were combined to analyze the cellular response to the changed A beta(42)- and A beta(40)-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 A beta(42)/A beta(40) 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 A beta(42)/A beta(40) ratio, whereas a decreased ratio did not result in up-regulation of CRABP1. Conclusion: We conclude that increasing the A beta(42)/A beta(40) 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.