AMPK Activator Compound 991 Extends Lifespan Across Three Species
Direct AMPK activation with compound 991 lengthens lifespan in yeast, worms, and flies — and triggers pro-longevity protein changes in mice.
Summary
Metformin is often studied as an anti-aging drug, but it activates the cellular energy sensor AMPK only indirectly and also acts through mitochondria and gut bacteria. Researchers tested compound 991, which binds AMPK directly, in fission yeast, roundworms and fruit flies. It activated AMPK in all three and extended lifespan in each. In flies it also lowered body fat without changing food intake or egg laying. In yeast and worms missing AMPK, 991 did not extend life, which points to AMPK as the mechanism. Higher doses shortened lifespan, so dose matters. In mice, three weeks of treatment produced a liver protein pattern consistent with AMPK activation and pro-longevity biology. Lifespan studies in mammals have not yet been done.
Detailed Summary
AMPK is an evolutionarily conserved cellular energy sensor, and its activation has been linked to longevity in model organisms. Most drug studies rely on indirect activators such as metformin, which also acts on mitochondria and lysosomes and, in worms and flies, extends lifespan partly through the microbiota. That makes it hard to say what AMPK itself contributes. This study asks whether direct, pharmacological AMPK activation can extend lifespan across species.
The authors used 991, a small molecule that binds the allosteric drug and metabolite (ADaM) site between the AMPK α and β subunits. Structural modeling showed that this pocket, including a key β-subunit serine, is conserved from humans to flies, worms and yeast. In kinase assays, 991 dose-dependently activated fly AMPK purified from S2R+ cells (5 μM, p=9.57×10⁻⁴) and protected it from phosphatase-driven dephosphorylation. In fly cells, 5 μM 991 was highly potent (p=9.51×10⁻¹¹), whereas metformin needed 5 mM (p=0.0150) and phenformin 1 mM.
In vivo, 991 given in a chemically defined fly diet activated AMPK dose-dependently from 5 to 500 μM, but not in standard yeast-based food, which highlights bioavailability issues. It also raised phospho-AMPK in worms (p=0.0061) and fission yeast (p=0.0295). Physiologically, 991 lowered whole-body triglycerides in flies (25 μM, p=5.47×10⁻⁴) without changing glycogen, feeding rate or fecundity. Worms showed reduced BODIPY lipid staining (n=228 control vs 271 treated, p=6.61×10⁻⁷).
Lifespan was extended in all three organisms. In female flies (~150 per condition) the effect was strong at 10 μM (p=4.67×10⁻¹¹) and weaker at 100 μM (p=0.0017). Chronological lifespan in S. pombe increased at 10 μM (p=1.18×10⁻³). In worms (~110 per condition), lifespan rose on both BW25113 (p=2.95×10⁻⁷) and OP50 bacteria (p=1.57×10⁻⁵). 991 did not noticeably affect bacterial growth, which suggests a direct action on the host, unlike metformin.
Several controls support AMPK specificity. 991 did not extend lifespan in aak-2 AMPK-null worms (p=0.2697 and 0.1027) and shortened lifespan in ssp2-null yeast (p=1.77×10⁻³), though the authors note these mutants are generally stress-sensitive. Higher doses shortened lifespan in wild-type animals, so dosing must be tuned. In male mice (n=3 per group), three weeks of 3.5 mg/kg intravenous 991 in PLGA nanoparticles produced a liver proteomic signature of ATP biosynthesis, mTOR inhibition and mitochondrial biogenesis, with survival-related terms most enriched.
The authors argue that second-generation direct activators (MK-8722, PF-739, BI-9774, PXL-770) share this binding site and have better bioavailability, so mammalian lifespan trials are warranted. Caveats are substantial: mouse data are a small proteomic snapshot without survival or healthspan measures, fly AMPK-null controls were impossible, and downstream mechanisms remain unresolved.
Key Findings
- In fly cells, 5 μM 991 activated AMPK (p=9.51×10⁻¹¹), while metformin needed 5 mM (p=0.0150) and phenformin 1 mM (p=2.32×10⁻⁸)
- In female flies (~150 per condition), 10 μM 991 extended lifespan (log-rank p=4.67×10⁻¹¹), and 100 μM also did (p=0.0017)
- In worms (~110 per condition), 991 extended lifespan on both BW25113 (p=2.95×10⁻⁷) and OP50 bacteria (p=1.57×10⁻⁵)
- 10 μM 991 extended chronological lifespan of fission yeast (p=1.18×10⁻³)
- AMPK-null worms (aak-2) showed no lifespan extension (p=0.2697 and 0.1027), and AMPK-null yeast (ssp2) had shortened lifespan (p=1.77×10⁻³)
- In flies, 991 lowered whole-body triglycerides (25 μM, p=5.47×10⁻⁴) without changing feeding, glycogen or fecundity; worms showed reduced lipid staining (p=6.61×10⁻⁷)
- In male mice (n=3 per group), 3 weeks of nanoparticle-delivered 991 produced a liver proteome signature of mTOR inhibition and enhanced mitochondrial biogenesis
Methodology
The study combined structural homology modeling, in vitro kinase assays on immunoprecipitated Drosophila AMPK, and in vivo lifespan assays in S. pombe (chronological lifespan, n=3 biological replicates), C. elegans (~90-110 worms per condition, two bacterial diets) and Drosophila (~150 females per condition, defined medium). Specificity was tested with AMPKα-null yeast (ssp2) and worms (aak-2). Mouse work used 10-18 week old male C57BL/6J and D2-mdx mice given IV 991-loaded PLGA nanoparticles (3.5 mg/kg, 3 weeks) followed by unbiased liver proteomics (n=3 per group). Statistics were one-way ANOVA, t-tests and log-rank tests.
Study Limitations
Mammalian evidence is limited to a three-week proteomic snapshot in three male mice per group, with no survival or healthspan outcomes, and 991 requires nanoparticle delivery in mice. Fly AMPK-null controls were not possible, and the mutant yeast and worms are stress-sensitive, so the downstream mechanism of lifespan extension remains unresolved. Higher doses shortened lifespan, so the therapeutic window is narrow. A conflict-of-interest statement was not included in the supplied text.
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