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Dysfunction of growth factor (GF) activities contributes to the decline and death of neurons during aging and in neurodegenerative diseases. In addition, neurons become more resistant to GF signaling with age. Micro (mi)RNAs are posttranscriptional regulators of gene expression that may be crucial to age- and disease-related changes in GF functions. miR-126 is involved in regulating Insulin/IGF-1/PI3K/AKT and ERK signaling and we recently demonstrated a functional role of miR-126 in dopamine neuronal cell survival in models of Parkinson’s disease (PD)-associated toxicity. Here, we show that elevated levels of miR-126 increase neuronal vulnerability to ubiquitous toxicity mediated by staurosporine (STS) or Alzheimer’s disease (AD)-associated amyloid beta 1-42 peptides (Aβ1-42). The neuroprotective factors IGF-1, NGF, BDNF, and soluble amyloid precursor protein α (sAPPα) could diminish but not abrogate the toxic effects of miR-126. In miR-126 overexpressing neurons derived from Tg6799 familial AD model mice, we observed an increase in Aβ1-42 toxicity but, surprisingly, both Aβ1-42 and miR-126 promoted neurite sprouting. Pathway analysis revealed that miR-126 overexpression downregulated elements in the GF/PI3K/AKT and ERK signaling cascades, including AKT, GSK-3β, ERK, their phosphorylation, and the miR-126 targets IRS-1 and PIK3R2. Finally, inhibition of miR-126 was neuroprotective against both STS and Aβ1-42 toxicity. Our data provide evidence for a novel mechanism of regulating GF/PI3K signaling in neurons by miR-126 and suggest that miR-126 may be an important mechanistic link between metabolic dysfunction and neurotoxicity in general, during aging, and in the pathogenesis of specific neurological disorders, including PD and AD.

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BackgroundLittle is known about the relationship between miRNA and mRNA expression in Alzheimer’s disease (AD) at early- or late-symptomatic stages. Sequence-based target prediction algorithms and anti-correlation profiles have been applied to predict miRNA targets using omics data, but this approach often leads to false positive predictions. Here, we applied the joint profiling analysis of mRNA and miRNA expression levels to Tg6799 AD model mice at 4 and 8 months of age using a network topology-based method. We constructed gene regulatory networks and used the PageRank algorithm to predict significant interactions between miRNA and mRNA.ResultsIn total, 8 cluster modules were predicted by the transcriptome data for co-expression networks of AD pathology. In total, 54 miRNAs were identified as being differentially expressed in AD. Among these, 50 significant miRNA-mRNA interactions were predicted by integrating sequence target prediction, expression analysis, and the PageRank algorithm. We identified a set of miRNA-mRNA interactions that were changed in the hippocampus of Tg6799 AD model mice. We determined the expression levels of several candidate genes and miRNA. For functional validation in primary cultured neurons from Tg6799 mice (MT) and littermate (LM) controls, the overexpression of ARRDC3 enhanced PPP1R3C expression. ARRDC3 overexpression showed the tendency to decrease the expression of miR139-5p and miR3470a in both LM and MT primary cells. Pathological environment created by Aβ treatment increased the gene expression of PPP1R3C and Sfpq but did not significantly alter the expression of miR139-5p or miR3470a. Aβ treatment increased the promoter activity of ARRDC3 gene in LM primary cells but not in MT primary cells.ConclusionsOur results demonstrate AD-specific changes in the miRNA regulatory system as well as the relationship between the expression levels of miRNAs and their targets in the hippocampus of Tg6799 mice. These data help further our understanding of the function and mechanism of various miRNAs and their target genes in the molecular pathology of AD.Electronic supplementary materialThe online version of this article (doi:10.1186/1471-2164-15-644) contains supplementary material, which is available to authorized users.

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