Biophysical properties of a tau seed

Hou, Z., Chen, D., Ryder, B.D., and Joachimiak, Ł.A.
Sci Rep 11, 13602 (2021). doi: 10.1038/s41598-021-93093-z

Summary: In this study, we employed several novel and highly sensitive biochemical and biophysical approaches to study how inert tau proteins convert to pathological aggregation-prone “seeds.” Our methods revealed tau conformational changes in a monomer, confirming our 2018 hypothesis that disease inception may be derived from monomeric tau seeds. We found that heparin, an in vitro aggregation inducer, disrupts electrostatic interactions from acidic regions to proline-rich domains. This and other structural findings support our hypothesis that tau’s amyloid motifs are protected by local structures that prevent self-assembly into pathologic seeds. We also suspect that unknown molecular chaperones play a role in preventing aggregation.

Tau strains shape disease

Vaquer-Alicea, J., Diamond, M.I. and Joachimiak, Ł.A.
Acta Neuropathol 2021. doi: 10.1007/s00401-021-02301-7

Summary: This review article looks at the growing evidence from multiple laboratories that tau protein acts as a prion, an infectious protein: in cell culture, unique tau strains propagate indefinitely; in animal studies, inoculation with tau strains causes distinct diseases. In humans, studies of the molecular structure of tau fibrils from patients show an association between tau conformation and pathology, but there is no direct proof yet that infection with any particular tau strain causes a defined disease.

There are more than 25 tauopathies, associated with various symptoms—speech loss, movement disorders, memory loss, etc. But these clinical manifestations correlate poorly to the type of tau fibrils and cell damage seen in tissue samples. The reviewers challenge researchers to develop more accurate diagnostic methods and effective therapies that are based on the underlying pathological protein assemblies instead of clinical symptoms.

The inhibition of cellular toxicity of amyloid-β by dissociated transthyretin

Cao Q, Anderson DH, Liang WY, Chou J, and Saelices L
J Biol Chem 2020; 295, 12015-14024. doi: 10.1074/jbc.RA120.013440

Summary: Transthyretin (TTR), a transport protein for thyroid hormone and Vitamin A, sometimes clumps into toxic fibrils that harm the heart and nerves. Several studies have shown that TTR paradoxically protects against Alzheimer’s disease, which involves the formation of toxic fibrils in the brain. In the present study, we found that the protection of TTR in the brain is somewhat linked to its pathological effect in the heart. We also identified the site of TTR that exert this protection and designed a small peptide that mimics the protective effect. These findings indicate a promising approach for treating or preventing Alzheimer's.

Read the UT Southwestern news release about the study.

Regulatory inter-domain interactions influence Hsp70 recruitment to the DnaJB8 chaperone

Ryder, BD, Matlahov, I, Bali, S, Vaquer-Alicea, J, van der Wel, PCA, Joachimiak, Ł. Nat Commun 2021 12, 946. doi:10.1038/s41467-021-21147-x

Summary: We studied interactions between two co-chaperone proteins—DnaJB8 and Hsp70s—and created a model for how the proteins activate and inactivate. We found that within DnaJB8, the C-terminal domain binds to the J-domain, which prevents the J-domain from binding to and activating Hsp70. We suggest that DnaJB8’s C-terminal domain is an evolutionarily conserved, reversible switch that helps regulate chaperone activation and inactivation in proteostatis.

These findings are significant to our overall work because DnaJB8 belongs to the Hsp40 class of chaperone proteins, which suppress protein aggregation. Future studies will focus on how these and similar chaperones interact with tau protein, which causes Alzheimer’s and similar neurodegenerative diseases when it aggregates in brain tissue.

Read UT Southwestern's news release.

A synthetic heparinoid blocks Tau aggregate cell uptake and amplification

Stopschinski BE, Thomas TL, Nadji S, Darvish E, Fan L, Holmes BB, Modi AR, Finnell JG, Kashmer OM, Estill-Terpack S, Mirbaha H, Luu HS, Diamond MI.
J Biol Chem. 2020 Mar 6;295(10):2974-2983. doi: 10.1074/jbc.RA119.010353.

Summary: We created a synthetic heparin mimic, a pentasaccharide called SN7-13, that binds tau protein with high affinity and blocks cellular uptake of tau aggregates. This heparinoid does not interfere with blood coagulation and shows promise as a base for developing agents to treat tauopathies.

Tau local structure shields an amyloid-forming motif and controls aggregation propensity

Chen D, Drombosky KW, Hou Z, Sari L, Kashmer OM, Ryder BD, Perez VA, Woodard DR, Lin MM, Diamond MI, Joachimiak LA.
Nat Commun. 2019 Jun 7;10(1):2493. doi: 10.1038/s41467-019-10355-1.

Summary: This study demonstrates that disease-causing mutations in tau protein localize near its amyloid motif, where they perturb local secondary structure and drive aggregation. We used a combination of bioinformatics, structural dynamics, and biophysical techniques to identify which conformations of tau prevent or allow pathological aggregation. Research is underway to identify which elements within tau prevent amyloid formation, and determine what features are necessary to stabilize these non-aggregating forms.

Propagation of Protein Aggregation in Neurodegenerative Diseases

Vaquer-Alicea J, Diamond MI.
Annu Rev Biochem. 2019 Jun 20;88:785-810. doi: 10.1146/annurev-biochem-061516-045049.

Summary: This review article discusses the common features of various proteins – tau, β-amyloid, α-synuclein, prion protein, superoxide dismutase 1, and huntingtin – and how they aggregate and spread among cells in neurodegenerative dieaseses. We also lay out strategies to guide future research to create diagnostic tools and therapeutic strategies.

Parkinson's disease and multiple system atrophy have distinct α-synuclein seed characteristics

Yamasaki TR, Holmes BB, Furman JL, Dhavale DD, Su BW, Song ES, Cairns NJ, Kotzbauer PT, Diamond MI.
J Biol Chem. 2019 Jan 18;294(3):1045-1058. doi: 10.1074/jbc.RA118.004471.

Summary: We found that alpha-synuclein from patients with Parkinson’s disease (PD) and multiple system atrophy (MSA) had different seeding properties – both soluble and insoluble fractions of extracts from MSA patients supported seeding, while only insoluble fractions from PD patients did. Then, using biosensor cells developed at CAND, we found that the different extracts led to different types of cellular inclusions. These findings are consistent with the idea that distinct strains of alpha-synuclein lead to PD and to MSA, and offer possible directions for diagnosing synucleinopathies.

Tau monomer encodes strains

Sharma AM, Thomas TL, Woodard DR, Kashmer OM, Diamond MI.
Elife. 2018 Dec 11;7:e37813. doi: 10.7554/eLife.37813.

Summary: This study expanded on previous work, in which we found that tau monomer adopts two conformational states: Mi, which is inert, and Ms, which forms seeds that lead to aggregation. We found that Ms occurs in several forms with distinct biochemical characteristics and shapes. When inoculated into mouse brains, these sub-strains triggered unique pathologies; this finding opens a possible route for diagnosis and personalized treatment for tauopathies.

Inert and seed-competent tau monomers suggest structural origins of aggregation

Mirbaha H, Chen D, Morazova OA, Ruff KM, Sharma AM, Liu X, Goodarzi M, Pappu RV, Colby DW, Mirzaei H, Joachimiak LA, Diamond MI.

Elife. 2018 Jul 10;7. pii: e36584. doi: 10.7554/eLife.36584.

Summary: We purified and characterized a conformation of tau monomer that serves as a “seed” that drives aggregation. Using cross-linking mass spectrometry (XL-MS), we found that the aggregation-prone form of tau exposes a part of itself that is normally folded inside. This exposed portion causes it to stick to other tau proteins, enabling the formation of tangles that kill neurons. This finding reveals a discrete point that we call the "Big Bang" of Alzheimer's disease – the first molecular change that leads to neurodegeneration.

Read the UT Southwestern news release on this study.

Tau seeding activity begins in the transentorhinal/entorhinal regions and anticipates phospho-tau pathology in Alzheimer's disease and PART

Kaufman SK, Del Tredici K, Thomas TL, Braak H, Diamond MI.
Acta Neuropathol. 2018 Jul;136(1):57-67. doi: 10.1007/s00401-018-1855-6.

Summary: Using samples from a mouse model of Alzheimer’s disease and from human patients with Alzheimer’s, we found that the earliest stages of tau aggregation—known as seeding—occurs in the transentorhinal and entorhinal cortices. Our study ruled out the locus coeruleus (LC) as an early location for seeding, even though the LC is one of the brain structures where phospho-tau appears. This finding indicates that quantifying tau aggregation may supplement classical histopathology in classifying cases of Alzheimer’s disease and other age-related tauopathies.

Specific glycosaminoglycan chain length and sulfation patterns are required for cell uptake of tau versus α-synuclein and β-amyloid aggregates

Stopschinski BE, Holmes BB, Miller GM, Manon VA, Vaquer-Alicea J, Prueitt WL, Hsieh-Wilson LC, Diamond MI.
J Biol Chem. 2018 Jul 6;293(27):10826-10840. doi: 10.1074/jbc.RA117.000378.

Summary: We studied the binding mechanics of various glycosaminoglycans (GAGs) with aggregates of tau, alpha-synuclein, and beta-amyloid. These binding interactions mediate cell uptake and are potential targets for therapeutic intervention. We found that tau aggregates required a precise GAG architecture with sulfate moieties at particular locations, while binding of alpha-synuclein or beta-amyloid was less stringent. Using a genetic candidate screen of a GAG synthesis pathway, we identified several sulfotransferases that play a role in tau and alpha-synuclein uptake.

Tau Prion Strains Dictate Patterns of Cell Pathology, Progression Rate, and Regional Vulnerability In Vivo

Kaufman SK, Sanders DW, Thomas TL, Ruchinskas AJ, Vaquer-Alicea J, Sharma AM, Miller TM, Diamond MI.
Neuron. 2016 Nov 23;92(4):796-812. doi: 10.1016/j.neuron.2016.09.055. Epub 2016 Oct 27.

Summary: We characterized 18 structurally discrete “strains” of tau, which form distinct patterns in cells. In mouse brain, the strains created different patterns of tangles, and spread within the brain at different rates along neural networks. We propose that tau strains can explain the variety of pathologies seen in human neurodegenerative diseases, and can help predict and treat the course of the diseases.

FRET and Flow Cytometry Assays to Measure Proteopathic Seeding Activity in Biological Samples

Furman JL, Diamond MI.
Methods Mol Biol. 2017;1523:349-359.

Summary: We combined monoclonal cell culture with FRET microscopy (fluorescence resonance energy transfer) and flow cytometry into a novel lab technique that can sensitively and precisely measure early tau aggregation. We engineered a “biosensor” kidney cell line that produces tau protein tagged with fluorescent markers; upon aggregation, the protein produces a measurable light signal. This assay has become a key tool in our subsequent research.