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/phosphatidylinositol-3-kinase (PI3K)/AKT and extracellular signal-regulated kinase (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, nerve growth factor (NGF), brain-derived neurotrophic factor (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.
Keywords: Aβ; Growth factors; MiR-126; Neuroprotection; Neurotoxicity; PI3K/AKT signaling.