MAPT/Tau accumulation represses autophagy flux by disrupting IST1-regulated ESCRT-III complex formation: a vicious cycle in Alzheimer neurodegeneration.

Macroautophagy/autophagy deficit induces intracellular MAPT/tau accumulation, the hallmark pathology in Alzheimer disease (AD) and other tauopathies; however, the reverse role of MAPT accumulation in autophagy and neurodegeneration is not clear. Here, we found that overexpression of human wild-type full-length MAPT, which models MAPT pathologies as seen in sporadic AD patients, induced autophagy deficits via repression of autophagosome-lysosome fusion leading to significantly increased LC3 (microtubule-associated protein 1 light chain 3)-II and SQSTM1/p62 (sequestosome 1) protein levels with autophagosome accumulation. At the molecular level, intracellular MAPT aggregation inhibited expression of IST1 (IST1 factor associated with ESCRT-III), a positive modulator for the formation of ESCRT (the Endosomal Sorting Complex Required for Transport) complex that is required for autophagosome-lysosome fusion. Upregulating IST1 in human MAPT transgenic mice attenuated autophagy deficit with reduced MAPT aggregation and ameliorated synaptic plasticity and cognitive functions, while downregulating IST1 per se induced autophagy deficit with impaired synapse and cognitive function in naïve mice. IST1 can facilitate association of CHMP2B (charged multivesicular body protein 2B) and CHMP4B/SNF7-2 to form ESCRT-III complex, while lack of IST1 impeded the complex formation. Finally, we demonstrate that MAPT accumulation suppresses IST1 transcription with the mechanisms involving the ANP32A-regulated mask of histone acetylation. Our findings suggest that the AD-like MAPT accumulation can repress autophagosome-lysosome fusion by deregulating ANP32A-INHAT-IST1-ESCRT-III pathway, which also reveals a vicious cycle of MAPT accumulation and autophagy deficit in the chronic course of AD neurodegeneration.Abbreviations: AAV: adeno-associated virus; Aß: ß-amyloid; aCSF: artificial cerebrospinal fluid; AD: Alzheimer disease; ANP32A: acidic nuclear phosphoprotein 32 family member A; ATG: autophagy related; AVs: autophagic vacuoles; CEBPB: CCAAT enhancer binding protein beta; CHMP: charged multivesicular body protein; DMEM: Dulbecco's modified eagle's medium; EBSS: Earle's balanced salt solution; EGFR: epidermal growth factor receptor; ESCRT: endosomal sorting complex required for transport; fEPSPs: field excitatory postsynaptic potentials; GAPDH: glyceraldehyde-3-phosphate dehydrogenase; GSK3B: glycogen synthase kinase 3 beta; HAT: histone acetyl transferase; HDAC: histone deacetylase; INHAT: inhibitor of histone acetyl transferase; IST1: IST1 factor associated with ESCRT-III; LAMP2: lysosomal associated membrane protein 2; LTP: long-term potentiation; MAP1LC3: microtubule associated protein 1 light chain 3; MAPT/tau: microtubule associated protein tau; MVB: multivesicular bodies; MWM: Morris water maze; PBS: phosphate-buffered saline solution; RAB7: member RAS oncogene family; SNAREs: soluble N-ethylmaleimide-sensitive factor attachment protein receptors; SQSTM1/p62: sequestosome 1.

Tau accumulation triggers STAT1-dependent memory deficits by suppressing NMDA receptor expression.

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.