Abnormal tau aggregation is implicated in the development of neurodegenerative diseases such as Alzheimer's disease (AD). The presence of tau in the extracellular space and the spread of tau between nerve cells is associated with its toxicity. At present, researchers are trying to treat AD by limiting, blocking or removing extracellular tau.
Objective
To investigate the molecular mechanism underlying the cytotoxicity of extracellular tau oligomers.
Methods
The morphology of tau oligomers was observed by transmission electron microscopy. The neurocytotoxicity of tau oligomers was examined using CCK-8 assay. The localization of tau oligomers in cells was observed by laser confocal microscopy. The influence of tau oligomers on apoptosis was detected by Hoechst 33342/PI double-staining, Annexin V/PI double-staining and flow cytometry. JC-1 staining, DCFH-DA staining and Fluo-4 AM staining were used to evaluate the effect of tau oligomers on mitochondria. Western blot analysis was used to investigate the mechanism underlying the effects of tau oligomers on apoptosis and autophagy.
Results
After treatment with tau oligomers, the viability of SH-SY5Y cells decreased, and a typical apoptotic morphology was observed. Tau oligomers can enter cells, decrease the mitochondrial membrane potential, increase reactive oxygen species levels and drive calcium levels up to disrupt calcium homeostasis. The cytotoxicity of tau oligomers is closely related to the induction of mitochondrial apoptosis and blockade of mitophagy.
Conclusions
This study provides a molecular mechanism for understanding the cytotoxicity of extracellular tau oligomers and provides a therapeutic target for the development of effective treatment strategies for tau-related diseases.
LauterH. On the clinical study and psychopathology of Alzheimer's disease. Demonstration of 203 pathologically-anatomically verified cases. Psychiatr Clin (Basel)1968; 1: 85–108.
2.
ItagakiSMcGeerPLAkiyamaH, et al.Relationship of microglia and astrocytes to amyloid deposits of Alzheimer disease. J Neuroimmunol1989; 24: 173–182.
3.
TerryRDMasliahESalmonDP, et al.Physical basis of cognitive alterations in Alzheimer's disease: synapse loss is the major correlate of cognitive impairment. Ann Neurol1991; 30: 572–580.
Grundke-IqbalIIqbalKTungYC, et al.Abnormal phosphorylation of the microtubule-associated protein tau (tau) in Alzheimer cytoskeletal pathology. Proc Natl Acad Sci U S A1986; 83: 4913–4917.
6.
WangYPMandelkowE. Tau in physiology and pathology. Nat Rev Neurosci2016; 17: 5–21.
7.
ZhangZYHarischandraDSWangRF, et al.TRIM11 Protects against tauopathies and is down-regulated in Alzheimer's disease. Science2023; 381: eadd6696.
8.
MirbahaHHolmesBBSandersDW, et al.Tau trimers are the minimal propagation unit spontaneously internalized to seed intracellular aggregation. J Biol Chem2015; 290: 14893–14903.
9.
TianHLDavidowitzELopezP, et al.Trimeric tau is toxic to human neuronal cells at low nanomolar concentrations. Int J Cell Biol2013; 2013: 260787.
10.
FlachKHilbrichISchiffmannA, et al.Tau oligomers impair artificial membrane integrity and cellular viability. J Biol Chem2012; 287: 43223–43233.
11.
Gómez-RamosADíaz-HernándezMCuadrosR, et al.Extracellular tau is toxic to neuronal cells. FEBS Lett2006; 580: 4842–4850.
12.
SunXHEastmanGShiY, et al.Structural and functional damage to neuronal nuclei caused by extracellular tau oligomers. Alzheimers Dement2024; 20: 1656–1670.
13.
PampuscenkoKMorkunieneRKrasauskasL, et al.Distinct neurotoxic effects of extracellular tau species in primary neuronal-glial cultures. Mol Neurobiol2021; 58: 658–667.
14.
Lasagna-ReevesCACastillo-CarranzaDLSenguptaU, et al.Tau oligomers impair memory and induce synaptic and mitochondrial dysfunction in wild-type mice. Mol Neurodegener2011; 6: 39.
15.
FáMPuzzoDPiacentiniR, et al.Extracellular tau oligomers produce an immediate impairment of LTP and memory. Sci Rep2016; 6: 19393.
16.
HarringtonJSRyterSWPlatakiM, et al.Mitochondria in health, disease, and aging. Physiol Rev2023; 103: 2349–2422.
17.
DragoIDe StefaniDRizzutoR, et al.Mitochondrial Ca2+ uptake contributes to buffering cytoplasmic Ca2+ peaks in cardiomyocytes. Proc Natl Acad Sci U S A2012; 109: 12986–12991.
18.
CzabotarPELesseneGStrasserA, et al.Control of apoptosis by the Bcl-2 protein family: implications for physiology and therapy. Nat Rev Mol Cell Biol2014; 15: 49–63.
19.
FangEFHouYPalikarasK, et al.Mitophagy inhibits amyloid-β and tau pathology and reverses cognitive deficits in models of Alzheimer's disease. Nat Neurosci2019; 22: 401–412.
20.
SwerdlowRHBurnsJMKhanSM. The Alzheimer's disease mitochondrial cascade hypothesis: progress and perspectives. Biochim Biophys Acta2014; 1842: 1219–1231.
21.
ZhangLTrushinSChristensenTA, et al.Altered brain energetics induces mitochondrial fission arrest in Alzheimer's disease. Sci Rep2016; 6: 18725.
22.
NeumannKFaríasGSlachevskyA, et al.Human platelets tau: a potential peripheral marker for Alzheimer's disease. J Alzheimers Dis2011; 25: 103–109.
23.
ScholzTMandelkowE. Transport and diffusion of Tau protein in neurons. Cell Mol Life Sci2014; 71: 3139–3150.
24.
MaryAEysertFCheclerF, et al.Mitophagy in Alzheimer’s disease: molecular defects and therapeutic approaches. Mol Psychiatry2022; 28: 202–216.
25.
YangKYanYYuA, et al.Mitophagy in neurodegenerative disease pathogenesis. Neural Regen Res2024; 19: 998–1005.
26.
WuYYTengNNLiS. Effects of macromolecular crowding and osmolyte on human tau fibrillation. Int J Biol Macromol2016; 90: 27–36.
27.
ZhengHSunHCaiQ, et al.The enigma of tau protein aggregation: mechanistic insights and future challenges. Int J Mol Sci2024; 25: 4969.
28.
ZhangWFalconBMurzinAG, et al.Heparin-induced tau filaments are polymorphic and differ from those in Alzheimer's and Pick's diseases. Elife2019; 8: e43584.
29.
ChazotteB. Labeling mitochondria with JC-1. Cold Spring Harb Protoc2011; 2011: pdb.prot065490.
30.
KaneMSParisACodronP, et al.Current mechanistic insights into the CCCP-induced cell survival response. Biochem Pharmacol2018; 148: 100–110.
31.
NaseriMHMahdaviMDavoodiJ, et al.Up regulation of Bax and down regulation of Bcl-2 during 3-NC mediated apoptosis in human cancer cells. Cancer Cell Int2015; 15: 55.
32.
LiuSZYaoSJYangH, et al.Autophagy: regulator of cell death. Cell Death Dis2023; 14: 648.
33.
GhavamiSShojaeiSYeganehB, et al.Autophagy and apoptosis dysfunction in neurodegenerative disorders. Prog Neurobiol2014; 112: 24–49.
34.
KhalequeMAKimGHKimDK, et al.HMGB1 Mediated autophagy and apoptosis in human nucleus pulposus cells; chloroquine amplified apoptosis by inhibiting autophagy. Sci Rep2025; 15: 39314.
35.
GanZYCallegariSCobboldSA, et al.Activation mechanism of PINK1. Nature2022; 602: 328–335.
36.
IvankovicDChauKYSchapiraAH, et al.Mitochondrial and lysosomal biogenesis are activated following PINK1/parkin-mediated mitophagy. J Neurochem2016; 136: 388–402.
37.
MaedaSSaharaNSaitoY, et al.Increased levels of granular tau oligomers: an early sign of brain aging and Alzheimer's disease. Neurosci Res2006; 54: 197–201.
38.
Lasagna-ReevesCACastillo-CarranzaDLGuerrero-MuozMJ, et al.Preparation and characterization of neurotoxic tau oligomers. Biochemistry2010; 49: 10039–10041.
39.
ChenLWeiYWangXQ, et al.D-Ribosylated tau forms globular aggregates with high cytotoxicity. Cell Mol Life Sci2009; 66: 2559–2571.
40.
GhagGBhattNCantuDV, et al.Soluble tau aggregates, not large fibrils, are the toxic species that display seeding and cross-seeding behavior. Protein Sci2018; 27: 1901–1909.
41.
TargettICromptonLAConwayME, et al.Differentiation of SH-SY5Y neuroblastoma cells using retinoic acid and BDNF: a model for neuronal and synaptic differentiation in neurodegeneration. In Vitro Cell Dev Biol Anim2024; 60: 1058–1067.
42.
GuidiMMuiños-GimenoMKagerbauerB, et al.Overexpression of miR-128 specifically inhibits the truncated isoform of NTRK3 and upregulates BCL2 in SH-SY5Y neuroblastoma cells. BMC Mol Biol2010; 11: 95.
43.
SiddiquiMAFarshoriNNAl-OqailMM, et al.Neuroprotective effects of withania somnifera on 4-hydroxynonenal induced cell death in human neuroblastoma SH-SY5Y cells through ROS inhibition and apoptotic mitochondrial pathway. Neurochem Res2021; 46: 171–182.
44.
TozihiMNourazarianAYousefiH, et al.Methylglyoxal-induced neuronal dysfunction: linking diabetes to Alzheimer's disease through cytoskeletal disruption. Eur J Pharmacol2025; 998: 177526.
45.
NaseriNNWangHGuoJ, et al.The complexity of tau in Alzheimer's disease. Neurosci Lett2019; 705: 183–194.
46.
EvansLDWassmerTFraserG, et al.Extracellular monomeric and aggregated tau efficiently enter human neurons through overlapping but distinct pathways. Cell Rep2018; 22: 3612–3624.
47.
WuJWHermanMLiuL, et al.Small misfolded tau species are internalized via bulk endocytosis and anterogradely and retrogradely transported in neurons. J Biol Chem2013; 288: 1856–1870.
48.
LiangJCaoRXWangXJ, et al.Mitochondrial PKM2 regulates oxidative stress-induced apoptosis by stabilizing Bcl-2. Cell Res2017; 27: 329–351.
49.
KerkhofsMBittremieuxMMorcianoG, et al.Emerging molecular mechanisms in chemotherapy: ca2+ signaling at the mitochondria-associated endoplasmic reticulum membranes. Cell Death Dis2018; 9: 334–348.
50.
AndersonMWMossJJSzalaiR, et al.Mathematical modeling highlights the complex role of AKT in TRAIL-induced apoptosis of colorectal carcinoma cells. iScience2019; 12: 182–193.
51.
HaoXDChenZLQuML, et al.Decreased integrity, content, and increased transcript level of mitochondrial DNA are associated with keratoconus. PLoS One2016; 11: e0165580.
52.
ValenzuelaRCosta-BesadaMAIglesias-GonzalezJ, et al.Mitochondrial angiotensin receptors in dopaminergic neurons. Role in cell protection and aging-related vulnerability to neurodegeneration. Cell Death Dis2016; 7: e2427.
53.
SchanneFAKaneABYoungEE, et al.Calcium dependence of toxic cell death: a final common pathway. Science1979; 206: 700–702.
54.
CenteMFilipcikPMandakovaS, et al.Expression of a truncated human tau protein induces aqueous-phase free radicals in a rat model of tauopathy: implications for targeted antioxidative therapy. J Alzheimers Dis2009; 17: 913–920.
55.
ShiHZhaoY. Astaxanthin inhibits apoptosis in a cell model of tauopathy by attenuating endoplasmic reticulum stress and unfolded protein response. Eur J Pharmacol2024; 983: 176962.
56.
EsterasNKundelFAmodeoGF, et al.Insoluble tau aggregates induce neuronal death through modification of membrane ion conductance, activation of voltage-gated calcium channels and NADPH oxidase. FEBS J2021; 288: 127–141.
SettembreCFraldiAMedinaDL, et al.Signals from the lysosome: a control centre for cellular clearance and energy metabolism. Nat Rev Mol Cell Biol2013; 14: 283–296.
59.
TranSFairlieWDLeeEF. Beclin1: protein structure, function and regulation. Cells2021; 10: 1522.
60.
RomanovJWalczakMIbiricuI, et al.Mechanism and functions of membrane binding by the Atg5-Atg12/Atg16 complex during autophagosome formation. EMBO J2012; 31: 4304–4317.
61.
KaufmannABeierVFranquelimHG, et al.Molecular mechanism of autophagic membrane-scaffold assembly and disassembly. Cell2014; 156: 469–481.
62.
MukhopadhyayRVenkatadriRKatsnelsonJ, et al.Digitoxin suppresses human cytomegalovirus replication via Na+, K+/ATPase α1 subunit-dependent AMP-activated protein kinase and autophagy activation. J Virol2018; 92: e01861–17.
63.
LouGFPalikarasKLautrupS, et al.Mitophagy and neuroprotection. Trends Mol Med2020; 26: 8–20.
64.
PiccaAFaitgJAuwerxJ, et al.Mitophagy in human health, ageing and disease. Nat Metab2023; 5: 2047–2061.
65.
ZhangLJDaiLLiDY. Mitophagy in neurological disorders. J Neuroinflammation2021; 18: 297.
