Alzheimer-associated neuronal thread protein mediated cell death is linked to impaired insulin signaling

Alzheimer-associated neuronal thread protein, AD7c-NTP, accumulates in cortical neurons and co-localizes with phospho-tau-containing cytoskeletal lesions in brains with AD. Over-expression of AD7c-NTP results in increased neuronal death mediated by apoptosis and mitochondrial dysfunction. Empirical studies demonstrating differential growth factor responses to AD7c-NTP led to us to further investigate the effects of insulin, insulin-like growth factor, type 1 (IGF-1), nerve growth factor (NGF), and platelet-derived growth factor (PDGF) stimulation on neuronal survival mechanisms in relation to AD7c-NTP expression. PNET2 human CNS-derived neuronal cells were stably transfected with a cDNA encoding AD7c-NTP or chloramphenicol acetyl transferase (CAT) whereby gene expression was regulated by an inducible promoter. In cells that expressed AD7c-NTP, insulin or IGF-1 stimulation was associated with reduced viability with increased levels of p53, p21/Waf-1, phospho-JNK, and phospho-tau, and reduced levels of Bcl-2 and phospho-Erk MAPK. In contrast, AD7c-NTP-transfected cells stimulated with NGF or PDGF, and CAT-transfected cells stimulated with any one of the four growth factors remained viable and had low levels of p53, p21/Waf-1, phospho-JNK, and phospho-tau, and abundant Bcl-2 and phospho-Erk expression. The results suggest that reduced survival in neurons that over-express AD7c-NTP may be mediated by impaired insulin/IGF-1 signaling, and that CNS neurons with abundant insulin or IGF-1 receptors may be particularly vulnerable to the adverse effects of AD7c-NTP.