Tier 3 — preclinical

Alpha-ketoglutarate extends Drosophila lifespan by inhibiting mTOR and activating AMPK

Su Y, Wang T, Wu N, Li D, Fan X, Xu Z, Mishra SK, Yang M

Aging (Albany NY) 2019 Volume 11, issue 12, pages 4183–4197

Bibliography

DOI: 10.18632/aging.102045
PubMed: PMID 31242135
PubMed Central: PMC6629006
Funding: This work was supported by Science and Technology Department of Sichuan Province (2019JDTD0009) and the National Natural Science Foundation of China (31771338).
Competing interests: The authors declare no competing financial interests.

Study snapshot

Design	Dose-response dietary supplementation lifespan study with gene expression, energy status, and autophagy analyses
Model	Wild-type Dahomey (wDah) Drosophila melanogaster, female adults, standard 25°C rearing
Sample	100 flies per treatment condition (10 vials × 10 flies) across 9 AKG concentrations; each experiment repeated at least twice
Intervention	Dietary AKG (Sigma K1128) at 0, 0.5, 1, 5, 10, 50, 100, 200, and 1000 μM added to standard 1× sugar/yeast/agar (SYA) medium from young adulthood; 5 μM identified as optimal dose
Duration	Full adult lifespan (~80 days); stress and biochemical assays at day 10
Endpoints	Median and maximum lifespan; Fecundity; Body weight; Vertical climbing (RING assay); Heat/paraquat/H₂O₂/starvation/desiccation stress tolerance; ATP content and ATP/ADP ratio; Gene expression (AMPK, mTOR, autophagy pathway); Phagosome staining (LysoTracker)

What the study showed, in plain terms

Fruit flies share many of the ageing pathways found in humans, which makes them a useful screening model for compounds that might extend healthy lifespan. This study asked whether alpha-ketoglutarate — already shown to extend lifespan in worms — does the same in fruit flies, and if so, through what molecular mechanism.

The researchers fed adult female flies AKG at doses ranging from 0.5 to 1000 μM in standard food. A striking pattern emerged: low doses (1 to 10 μM) extended lifespan by 8 to 15%, but higher doses had no benefit. This "hormetic" dose-response — the compound works at low doses but not high ones — is common among longevity molecules. Five micromolar was optimal.

AKG-fed flies were more heat-resistant, climbed better in old age, and lived longer, but they laid fewer eggs — a trade-off often seen in longevity interventions. AKG did not protect against oxidative stress or starvation.

Molecularly, AKG activated AMPK (an energy-sensing enzyme that promotes cellular clean-up) and suppressed mTOR (a growth-promoting enzyme whose inhibition extends lifespan across species). Cellular ATP levels dropped and autophagy — the process by which cells recycle damaged components — increased. The pattern matches what has been seen in worms, mice, and mammalian cells, confirming that the AKG-mTOR-autophagy axis is a conserved ageing mechanism.

Key findings

Dietary AKG at 5 μM increased median lifespan of wild-type Dahomey female flies by 8.54% and maximum lifespan by ~15% (p < 0.001).
Dose-response was non-monotonic: benefit at 1–10 μM, no benefit at 0.5, 50, 100, 200, or 1000 μM.
Vertical climbing ability at 20, 30, and 40 days was significantly better in AKG-fed flies (p < 0.05 to p < 0.01), indicating preserved neuromuscular function with age.
Heat stress tolerance at 39°C was significantly improved (p = 0.0023), paralleled by increased HSP22 and HSP70 mRNA expression.
Fecundity was reduced at 1 and 5 μM AKG (p = 0.005), consistent with a growth-vs-longevity trade-off.
No protection against paraquat, H₂O₂, starvation, or desiccation, and SOD1 expression was actually decreased — arguing against a classical antioxidant mechanism.
ATP content and ATP/ADP ratio were significantly reduced in AKG-fed flies (p < 0.01), consistent with ATP synthase inhibition and AMPK activation.
AMPKα, upstream kinases PKA and LKB1, and downstream targets Sirt1, FoxO, HNF4, and p300 were upregulated; mTOR pathway components PI3K, TORC, PGC, and SREBP were downregulated.
Autophagy-related genes (Atg1, Atg5, Atg8a, Atg8b) and TFEB (autophagosome regulator) were upregulated; phagosome staining confirmed increased autophagosome formation in fly midguts.

What this study can and cannot tell us

This is an invertebrate study. Drosophila share conserved ageing pathways with humans, but the pharmacokinetics, tissue distribution, and translational dose relationships between fly and human are non-trivial. The 5 μM dietary concentration that maximises fly lifespan cannot be directly translated to a human dose.

Only female flies were tested. Sex differences in AKG response have been reported in earlier fly work (Lylyk 2018 used higher millimolar doses and reported sex-dependent effects), and a female-only study cannot address whether the mechanism generalises.

The optimal AKG concentration (5 μM) is orders of magnitude lower than doses used in prior published fly studies (10–20 mM), which the authors acknowledge but do not fully reconcile. The non-monotonic dose-response also warrants replication.

Gene expression changes were measured by RT-qPCR only; protein-level and functional confirmation of AMPK and mTOR pathway activity would strengthen the mechanistic claim. Direct measurement of AMPK phosphorylation (T172) or S6K phosphorylation (T389) was not reported.

The fecundity reduction is a real trade-off and would need consideration in any translational context, though the reproductive-vs-longevity trade-off is not directly applicable to postmenopausal supplementation in humans.