A small-molecule stabilizer of the calpastatin-calpain-2 complex restores mitochondrial function and mitigates neurodegeneration.

Overview

1. Department of Physiology and Biophysics, Case Western Reserve University School of Medicine, Cleveland, OH 44106, USA
2. Center for Mitochondrial Research and Therapeutics, Case Western Reserve University School of Medicine, Cleveland, OH 44106, USA
3. Proteomics Center, Case Western Reserve University School of Medicine, Cleveland, OH 44106, USA
4. Department of Genetics and Genome Sciences, Case Western Reserve University School of Medicine, Cleveland, OH 44106, USA

Abstract

Mitochondrial dysfunction and dysregulated proteolysis drive Huntington’s disease (HD), tauopathy, and related neurodegenerative disorders. Calpain-2, a Ca2+-activated protease restrained by calpastatin (CAST), is pathologically overactivated, yet no therapies directly target this axis. We identify A36, a brain-penetrant small molecule derived from CHIR99021 that selectively stabilizes the CAST–calpain-2 complex without inhibiting GSK3. A36 acts as a protein-protein interaction stabilizer, enhancing CAST–calpain-2 binding, preventing CAST degradation, and thereby limiting calpain-2 activation and mitochondrial damage. In patients with HD induced pluripotent stem cell–derived neurons and mutant mouse striatal neurons, A36 normalized mitochondrial morphology and membrane potential, reduced oxidative stress, and improved survival. In vivo, A36 displayed favorable pharmacokinetics and central nervous system exposure; treatment reduced striatal neurodegeneration, mutant huntingtin aggregation, and motor deficits in HD R6/2 mice, and lowered phosphorylated tau, neuroinflammation, and cognitive decline in tauopathy PS19 mice. These findings establish pharmacological stabilization of CAST–calpain-2 as a therapeutic strategy and position A36 as a mechanism-selective modulator with broad neurodegenerative disease potential.

Reproduced under the paper's license (CC BY), from the paper cited above.

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Data

Datasets cited

• figshare:30660461, at figshare; found in “Data, code, and materials availability:”
• zenodo:17797021, at Zenodo; found in “Data, code, and materials availability:”

Data, code, and materials availability

All data and code needed to evaluate and reproduce the results in the paper are present in the paper and/or the Supplementary Materials. Data are available at Zenodo (https://doi.org/10.5281/zenodo.17797021). The DARTS proteomic dataset is available at Figshare (https://doi.org/10.6084/m9.figshare.30660461). CHIR99021 is commercially available from MedChemExpress (catalog no.: HY-10182) (https://medchemexpress.com/laduviglusib-gmp.html?gad_source=1&gad_campaignid=23203642493&gbraid=0AAAAApdGtXkZwNddJLjkqU03MWAJs8JYq&gclid=Cj0KCQiAubrJBhCbARIsAHIdxD-zLWFbB2Oom5MkzLyAPTHaqW7a8kDKIjBxxk3Zztg4GU4YqO19rLYaAmN7EALw_wcB). All analog compounds were synthesized by WuXi AppTec. The synthesis procedures are fully provided in the supporting information 1 with the Supplementary Materials. All analog compounds are stored in X.Q.’s laboratory. The analog compounds can be provided by X.Q. pending scientific review. Requests for the analog compounds should be submitted to: .

Reproduced under the paper's license (CC BY), from the paper cited above.

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Version 1, 30 September 2026: the first record

Recorded: type, language, journal, volume, issue, pages, dates, 6 authors, 12 MeSH terms, 3 funders, 74 references.

Cite

This paper

Hu, D., Sun, X., Shang, Y., Lundberg, K., Adams, D. J., & Qi, X. (2026). A small-molecule stabilizer of the calpastatin-calpain-2 complex restores mitochondrial function and mitigates neurodegeneration. Science advances, 12(13), eaeb1174. https://doi.org/10.1126/sciadv.aeb1174

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