β-hydroxybutyrate is a metabolic regulator of proteostasis in the aged and Alzheimer disease brain

• Published in: Cell chemical biology Vol. 32; no. 1; pp. 174 - 191.e8
• Main Authors: Madhavan, Sidharth S., Roa Diaz, Stephanie, Peralta, Sawyer, Nomura, Mitsunori, King, Christina D., Ceyhan, Kaya E., Lin, Anwen, Bhaumik, Dipa, Foulger, Anna C., Shah, Samah, Blade, Thanh, Gray, Wyatt, Chamoli, Manish, Eap, Brenda, Panda, Oishika, Diaz, Diego, Garcia, Thelma Y., Stubbs, Brianna J., Ulrich, Scott M., Lithgow, Gordon J., Schilling, Birgit, Verdin, Eric, Chaudhuri, Asish R., Newman, John C.
• Format: Journal Article
• Language: English
• Published: United States Elsevier Ltd 16.01.2025
• Subjects: 3-Hydroxybutyric Acid - metabolism; 3-Hydroxybutyric Acid - pharmacology; aging; Aging - metabolism; Alzheimer disease; Alzheimer Disease - metabolism; Alzheimer Disease - pathology; Amyloid beta-Peptides - metabolism; Animals; Brain - metabolism; Brain - pathology; Humans; ketone body; Mice; neurodegenerative disease; proteostasis; Proteostasis - drug effects; neurodegenerative disease; ketone body; aging; proteostasis; Alzheimer disease
• ISSN: 2451-9456; 2451-9456; 2451-9448
• DOI: 10.1016/j.chembiol.2024.11.001

Loss of proteostasis is a hallmark of aging and Alzheimer disease (AD). We identify β-hydroxybutyrate (βHB), a ketone body, as a regulator of protein solubility. βHB primarily provides ATP substrate during periods of reduced glucose availability, and regulates other cellular processes through protein interactions. We demonstrate βHB-induced protein insolubility is not dependent on covalent protein modification, pH, or solute load, and is observable in mouse brain in vivo after delivery of a ketone ester. This mechanism is selective for pathological proteins such as amyloid-β, and exogenous βHB ameliorates pathology in nematode models of amyloid-β aggregation toxicity. We generate libraries of the βHB-induced protein insolublome using mass spectrometry proteomics, and identify common protein domains and upstream regulators. We show enrichment of neurodegeneration-related proteins among βHB targets and the clearance of these targets from mouse brain. These data indicate a metabolically regulated mechanism of proteostasis relevant to aging and AD. [Display omitted] •βHB regulates protein solubility and is selective for a misfolding structural state•βHB-induced insolubility is not dependent on covalent modification, pH, or solute load•Protein targets of βHB include neurodegeneration-related proteins such as amyloid-β•βHB effects are observable in vitro, ex vivo, and in vivo in nematode and mouse models Ketone bodies, small molecules that provide lipid-derived energy to cells during fasting, have been linked to various mechanisms of brain aging and increased healthy longevity in mice, and other fasting metabolism mechanisms have been linked to proteostasis. These data fill an important puzzle piece in the literature on pathogenic protein clearance under varying metabolic states. Here, we provide a direct molecular mechanism for the regulation of misfolded proteins by ketone bodies and related metabolites. While many factors can affect protein solubility in vitro, we showed that this mechanism is robust and reproducibly not dependent on covalent protein modification, pH, or solute load. Importantly, we reproduced the ex vivo effect in vivo, using a ketone ester to indirectly deliver exogenous R-βHB to the mouse brain via hepatic metabolism to R-βHB and physiological transport of R-βHB into the brain without other exogenous biochemical alterations. R-βHB insolubilization targets that we identified ex vivo strongly overlap with targets found in vivo, supporting the similarity of mechanism between the ex vivo and in vivo systems. We validated the physiological relevance of the mechanism by showing rescue in cell-based and C. elegans models of amyloid-β proteotoxicity. Given that proteostatic mechanisms like autophagy are known to be activated by nutrient deprivation, it is unsurprising that evolutionary pressures would encourage the clearance of pathogenic proteins during ketosis to promote cellular health in organisms seeking additional substrate for ATP production. In this situation, ketone bodies are janitors of damaged proteins, chaperoning away molecular waste so organisms can operate at peak molecular fitness. This mechanism can be leveraged for therapeutic development in aging and NDDs, including via pharmacological approaches for which we provide proof of principle with BH-BD. Understanding the molecular mechanisms of metabolism is an essential aspect of the future of accessible therapeutic interventions in aging and NDDs. Madhavan et al. identify and characterize the selective regulation of protein solubility by the ketone body β-hydroxybutyrate (βHB) across a range of models. βHB exposure rescues cell-based and C. elegans models of amyloid-β proteotoxicity, and induces clearance of neurodegeneration-related proteins from aged mouse brain following exogenous ketone supplementation.