06 Oct 2024

Scientists are exploring many ways to tackle tau pathology. In the October 17 Cell Chemical Biology, researchers led by Jian-Zhi Wang at the Huazhong University of Science and Technology, Wuhan, China, advocated for a new one. They generated a chimeric protein, D20, that selectively recruits protein phosphatase 1 (PP1) to tau. PP1 then snips off phospho groups at several AD-related sites. In two tauopathy mouse models, peripheral administration of D20 lowered p-tau and total tau in the brain. Chronic dosing with D20 restored synaptic density and memory to normal.

Similar chimeras could be constructed to selectively target other pathologic proteins, the authors noted. “This study introduces a promising strategy for drug discovery,” they wrote.

The authors had previously experimented with using dephosphorylation targeting chimeras (DEPTACs) to bring phosphatases to tau. This strategy avoids the off-target effects of indiscriminately boosting phosphatase activity, or globally suppressing kinases, since these enzymes have many substrates. In initial studies, Wang and colleagues generated a DEPTAC that recruited protein phosphatase 2A to tau, lowering p-tau and t-tau in mice (Zheng et al., 2021). Scientists led by Craig Crews at Yale University, New Haven, Connecticut, have tried a similar approach (Hu et al., 2023).

Chimeric Workhorse. A constructed molecule, D20, consisting of a tau-binding motif (green) linked to a protein phosphatase 1 (PP1) binder (tan), brings these molecules together, allowing the enzyme to snip off phospho groups. [Courtesy of Xiao et al., Cell Chemical Biology.]

However, that first DEPTAC was effective only at a high dose of 200 mM. Joint first authors Yue Xiao and Linyu Wei set out to optimize it, screening a library of different DEPTACs. These molecules have four parts: a tau-binding motif, a linker region, a phosphatase-recruiting site, and finally a membrane-penetrating peptide at the C-terminal end. Experimenting, Xiao and Wei found that recruiting PP1 worked better than PP2A for lowering p-tau. They also improved the linker and membrane-penetrating sequence, and chose a tau-binding motif that was selective for fibrils over monomers. The new construct, D20, consisted of 23 amino acids plus a polyethylene glycol linker (image above).

DEPTAC. Based on PROTACs, or protein-targeting chimeras, D20, a dephosphorylation-targeting chimera, delivers PP1 to tau. The C-terminal tail (gray) helps the construct enter cells. [Courtesy of Xiao et al., Cell Chemical Biology.]

In rat primary neurons, D20 worked, recruiting PP1 to tau. At a dose of 5 μM, it nearly eliminated phosphorylation at several sites within six hours. These included serines 199, 396, and 404, and threonines 181, 205 and 262. In P301L mice, a single dose of 1 mg/kg D20 into the tail vein cut p-tau and t-tau in half after 24 hours.

To test chronic dosing, the authors chose 3xTg mice, which carry the P301L tau variant as well as two amyloid plaque-promoting mutations. Every other day for 20 days, the authors injected D20 into the tail veins of 10-month-old 3xTg mice, which have severe tau pathology. The treatment suppressed p-tau by one-half to three-fourths, while lowering t-tau to the levels in wild-type mice. Dendritic arborization and spine density returned to wild-type levels as well (image above). Neurons stopped dying, and neuronal calcium responses and neurogenesis bounced back to normal.

In keeping with this, the mice performed like wild-types in several behavioral tests. They remembered foot shocks, objects they had seen before, and the location of a hidden platform in the Morris water maze. Importantly, the mice did not show signs of liver, renal, or cardiac toxicity.

At the same time, D20 did not work well in a third tauopathy mouse model, which expresses the neurotoxic N368 tau fragment via an adenovirus. Possibly, this tau fragment interacts differently with D20, the authors suggested. “This highlights the necessity for customized therapeutic strategies when addressing the complexity of tauopathies … a universal approach may not be effective,” the authors noted.—Madolyn Bowman Rogers

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References

Research Models Citations

1. Tau P301L
2. 3xTg

Paper Citations

1. Zheng J, Tian N, Liu F, Zhang Y, Su J, Gao Y, Deng M, Wei L, Ye J, Li H, Wang JZ. A novel dephosphorylation targeting chimera selectively promoting tau removal in tauopathies. Signal Transduct Target Ther. 2021 Jul 14;6(1):269. PubMed.
2. Hu Z, Chen PH, Li W, Douglas T, Hines J, Liu Y, Crews CM. Targeted Dephosphorylation of Tau by Phosphorylation Targeting Chimeras (PhosTACs) as a Therapeutic Modality. J Am Chem Soc. 2023 Feb 8; PubMed.

Further Reading

News

1. Put a RING on It: Targeting Intracellular Tau Aggregates for Destruction 20 Sep 2024
2. p-Tau217 Immunotherapy Alleviates Tangle Pathology in Mice 11 Apr 2024
3. Therapeutic Contenders Target Hard-to-Reach Pockets of Tau 23 Mar 2024
4. Moving Forward: RNA-Targeted Attempts at Taking Down Tau, APP 9 Nov 2023
5. New Arrows Aimed at Tau: Single-Domain Antibody, Peptibody, Vaccine 3 May 2023
6. Paper Alert: Tau Antisense Oligonucleotide BIIB080 Hits Its Target 26 Apr 2023
7. Two New Stabs at Vaccinating People Against Pathologic Tau 10 Dec 2022