ABSTRACT
Intracellular tau accumulation forming neurofibrillary tangles is hallmark pathology of Alzheimer's disease (AD), but how tau accumulation induces synapse impairment is elusive. By overexpressing human full-length wild-type tau (termed hTau) to mimic tau abnormality as seen in the brain of sporadic AD patients, we find that hTau accumulation activates JAK2 to phosphorylate STAT1 (signal transducer and activator of transcription 1) at Tyr701 leading to STAT1 dimerization, nuclear translocation, and its activation. STAT1 activation suppresses expression of N-methyl-D-aspartate receptors (NMDARs) through direct binding to the specific GAS element of GluN1, GluN2A, and GluN2B promoters, while knockdown of STAT1 by AAV-Cre in STAT1flox/flox mice or expressing dominant negative Y701F-STAT1 efficiently rescues hTau-induced suppression of NMDAR expression with amelioration of synaptic functions and memory performance. These findings indicate that hTau accumulation impairs synaptic plasticity through JAK2/STAT1-induced suppression of NMDAR expression, revealing a novel mechanism for hTau-associated synapse and memory deficits.
Subject(s)
Gene Expression Regulation , Memory Disorders/genetics , Memory Disorders/metabolism , Receptors, N-Methyl-D-Aspartate/genetics , STAT1 Transcription Factor/metabolism , tau Proteins/metabolism , Alzheimer Disease/genetics , Alzheimer Disease/metabolism , Alzheimer Disease/psychology , Animals , Disease Models, Animal , Disease Susceptibility , Humans , Janus Kinase 2/metabolism , Memory Disorders/psychology , Mice , Models, Biological , Neuronal Plasticity , Phosphorylation , Promoter Regions, Genetic , Protein Binding , Protein Interaction Domains and Motifs , Protein Transport , Receptors, N-Methyl-D-Aspartate/metabolism , Signal Transduction , tau Proteins/geneticsABSTRACT
A new aporphine, 3-hydroxyhernandonine (1) and a new lignin, 4'-O-demethyl-7-O-methyldehydropodophyllotoxin (2), have been isolated from the root wood of Hernanadia nymphaeifolia, together with thirteen known compounds (3â»15). The structures of these compounds were determined through mass spectrometry (MS) and spectroscopic analyses. The known isolate, 2-O-methyl-7-oxolaetine (3), was first isolated from natural sources. Among the isolated compounds, 3-hydroxyhernandonine (1), 4'-O-demethyl-7-O-methyldehydropodophyllotoxin (2), hernandonine (4), oxohernangerine (5), and oxohernagine (6) displayed inhibition (IC50 values ≤5.72 µg/mL) of superoxide anion production by human neutrophils in response to formyl-l-methionyl-l-leucyl-l-phenylalanine/cytochalasin B (fMLP/CB). In addition, 3-hydroxyhernandonine (1), 4'-O-demethyl-7-O-methyldehydropodophyllotoxin (2), oxohernangerine (5), and oxohernagine (6) suppressed fMLP/CB-induced elastase release with IC50 values ≤5.40 µg/mL.
Subject(s)
Anti-Inflammatory Agents, Non-Steroidal/isolation & purification , Aporphines/isolation & purification , Hernandiaceae/chemistry , Lignans/isolation & purification , Plant Roots/chemistry , Wood/chemistry , Anti-Inflammatory Agents, Non-Steroidal/chemistry , Anti-Inflammatory Agents, Non-Steroidal/pharmacology , Aporphines/chemistry , Aporphines/pharmacology , Chromatography, Liquid , Humans , Lignans/chemistry , Lignans/pharmacology , Molecular Structure , Neutrophils/drug effects , Neutrophils/enzymology , Neutrophils/metabolism , Pancreatic Elastase/metabolism , Spectrum Analysis/methods , Superoxides/metabolismABSTRACT
Hyperphosphorylated tau is the major protein component of neurofibrillary tangles in the brains of patients with Alzheimer's disease (AD). However, the mechanism underlying tau hyperphosphorylation is not fully understood. Here, we demonstrated that exogenously expressed wild-type human tau40 was detectable in the phosphorylated form at multiple AD-associated sites in cytoplasmic and nuclear fractions from HEK293 cells. Among these sites, tau phosphorylated at Thr205 and Ser214 was almost exclusively found in the nuclear fraction at the conditions used in the present study. With the intracellular tau accumulation, the Ca2+ concentration was significantly increased in both cytoplasmic and nuclear fractions. Further studies using site-specific mutagenesis and pharmacological treatment demonstrated that phosphorylation of tau at Thr205 increased nuclear Ca2+ concentration with a simultaneous increase in the phosphorylation of Ca2+/calmodulin-dependent protein kinase IV (CaMKIV) at Ser196. On the other hand, phosphorylation of tau at Ser214 did not significantly change the nuclear Ca2+/CaMKIV signaling. Finally, expressing calmodulin-binding protein-4 that disrupts formation of the Ca2+/calmodulin complex abolished the okadaic acid-induced tau hyperphosphorylation in the nuclear fraction. We conclude that the intracellular accumulation of phosphorylated tau, as detected in the brains of AD patients, can trigger nuclear Ca2+/CaMKIV signaling, which in turn aggravates tau hyperphosphorylation. Our findings provide new insights for tauopathies: hyperphosphorylation of intracellular tau and an increased Ca2+ concentration may induce a self-perpetuating harmful loop to promote neurodegeneration.
