title: Insulin-induced neurite-like process outgrowth: acceleration of tau protein synthesis via a phosphoinositide 3-kinase~mammalian target of rapamycin pathway.
abstract: Both insulin and tau, promoting neuronal differentiation (neurite outgrowth, neuronal polarity, and myelination) and cell survival, are associated with neurodegenerative disease (e.g., Alzheimer's disease). The aim of this study was to explore relation between insulin-induced activation of insulin signal and expression of tau protein on neurite-like process outgrowth in adrenal chromaffin cells. Primary cultured bovine adrenal chromaffin cells were incubated with insulin to determine whether stimulant of insulin signal could affect tau expression and neurite-like process outgrowth. Chronic treatment with insulin (⩾6h) led neurite-like process outgrowth as well as increased tau protein level by ∼99% in a concentration (EC(50) 5.5nM)- and time-dependent manner, without changing Ser(396)-phosphorylated tau level. The insulin-induced increase of tau protein level was abolished by LY294002 [an inhibitor of phosphoinositide 3-kinase (PI3K)] and rapamycin [an inhibitor of mammalian target of rapamycin (mTOR)], but not by PD98059 and U0126 [two inhibitors of mitogen-activated protein kinase/extracellular signal-regulated kinase (MEK)]. Additionally, insulin-induced increase of tau was blocked by cyclohexamide (an inhibitor of protein synthesis), but not by actinomycin D (an inhibitor of gene transcription). Pulse-label followed by polyacrylamide gel electrophoresis revealed that insulin accelerated tau protein synthesis rate (t(1/2)) from 2.6 to 1.9h. Insulin did not change tau mRNA level. Taken together, these results suggest that insulin-induced activation of PI3K∼mTOR pathway up-regulated tau protein via acceleration of protein synthesis, on which insulin promoted neurite-like process outgrowth.
authors.affiliation: Department of Pharmacology, Miyazaki Medical College, University of Miyazaki, Miyazaki, Japan. tnemoto@fc.miyazaki-u.ac.jp
authors.forename: Takayuki
authors.initials: T
authors.lastname: Nemoto
authors.forename: Toshihiko
authors.initials: T
authors.lastname: Yanagita
authors.forename: Shinya
authors.initials: S
authors.lastname: Satoh
authors.forename: Toyoaki
authors.initials: T
authors.lastname: Maruta
authors.forename: Tasuku
authors.initials: T
authors.lastname: Kanai
authors.forename: Manabu
authors.initials: M
authors.lastname: Murakami
authors.forename: Akihiko
authors.initials: A
authors.lastname: Wada
mesh_terms: D000818:Animals; D002417:Cattle; D049108:Cell Enlargement / Q000187:drug effects; D007328:Insulin / Q000494:pharmacology*; D009434:Neural Pathways / Q000187:drug effects / Q000201:enzymology / Q000502:physiology; D016501:Neurites / Q000187:drug effects / Q000201:enzymology / Q000502:physiology*; D055495:Neurogenesis / Q000187:drug effects / Q000502:physiology*; D019869:Phosphatidylinositol 3-Kinases / Q000502:physiology*; D061251:Primary Cell Culture; D058570:TOR Serine-Threonine Kinases / Q000037:antagonists & inhibitors / Q000235:genetics / Q000502:physiology*; D015854:Up-Regulation / Q000187:drug effects / Q000502:physiology*; D016875:tau Proteins / Q000096:biosynthesis* / Q000378:metabolism
chemical_list: D007328:Insulin; D019869:Phosphatidylinositol 3-Kinases; D058570:TOR Serine-Threonine Kinases; D016875:tau Proteins