08 Jan 2025

For nearly a century, scientists have been trying to understand why many animals live longer, healthier lives when they have less to eat. Now, work led by Sheng-Cai Lin, Chen-Song Zhang, and Xianming Deng of Xiamen University in China links the benefits of calorie restriction to a bile acid called lithocholic acid, which works by activating the metabolic master regulator AMP-activated protein kinase. The finding feeds hopes that LCA could help humans fight old age without drastic dieting.

“The discovery of LCA as a metabolic mediator of calorie restriction, and its effects across biochemical, cellular, and organismal levels, is truly striking. Moreover, the mechanistic study elegantly uncovered the molecular pathway underlying LCA-mediated AMPK activation,” wrote Xu Chen at the University of California San Diego.

Liu Cao, Health Sciences Institute, China Medical University, Shenyang, called the work remarkable. “This discovery fills in the gaps in how the body senses metabolic signals caused by calorie restriction and how CR plays a role in delaying aging,” he wrote. Neither he nor Chen were involved in the work (comments below). The findings were published in two papers in the December 18 Nature.

Caloric restriction is widely hailed as a way to extend lifespan in everything from yeast to rodents to monkeys (Kapahi et al., 2017; Jan 2017 news). In people, it appears to improve cardiometabolic health and markers of aging, even when people are not overweight to start with (Flanagan et al., 2020; Belsky et al., 2017; Jan 2009 news). Hints from mouse models of Alzheimer’s disease suggest caloric restriction suppresses production of Aβ and phospho-tau and speeds Aβ clearance from the brain (Halagappa et al., 2007; Zhang et al., 2017). In older people, CR benefits working memory and processing speed but perhaps at the expense of psychomotor speed, namely tasks that rely on good hand-eye coordination, and cognitive flexibility, i.e., the ability to quickly shift attention between tasks (Jan 2009 news; Leclerc et al., 2020; O’Leary et al., 2025).

For most, though, maintaining that kind of diet isn’t realistic.  

“It's almost humanly impossible,” said Lin. “People can't withstand the hardship to starve all the time.” Moreover, he added, caloric restriction exacts a price in terms of lost muscle.

Lin and colleagues hoped to find a metabolite that might reproduce the benefits of caloric restriction without the hunger and muscle loss. They anticipated this would act through AMP-activating protein kinase, because AMPK regulates energy balance by promoting production of ATP and is found throughout the body, including in muscle and brain.

Some drugs can activate AMPK, most prominently metformin, which is approved for diabetes and being trialed in dementia. Less well-known is aldometanib, developed by Lin’s team, which blocks aldolase, an essential glycolysis enzyme (Zhang et al., 2022). 

However, the scientists wanted something natural—a compound that is part of the body’s own youth-preserving armory. To see if one exists, they infused serum from calorie-restricted mice into the bodies of mice on an all-you-can-eat diet. The serum proved as effective as calorie restriction at activating AMPK.

“We knew immediately that we had something big,” said Lin. “It's like the calorie-restricted mice have rejuvenating serum.”

Upping AMPK. In response to calorie restriction, LCA binds TULP3, activating sirtuins and triggering deacetylation of lysines on the V1E1 subunit of the lysosomal V-ATPase. This slows the proton pump, leading to activation of AMPK. Metformin and aldolase inhibitors also activate AMPK. [Courtesy of Qu et al., 2024.]

To figure out which ingredient of the CR serum was responsible, the scientists used mass spectrometry. This yielded more than 200 candidates, which they tested individually. LCA was the only one that stimulated AMPK in mouse embryonic fibroblasts, human embryonic kidney cells, primary hepatocytes, and primary myocytes at the concentrations found in the serum.

An Unexpected Source
Bacteria produce LCA in the small intestine when they break down primary bile acids. Like other bile acids, LCA emulsifies fats to render them digestible. But LCA can be absorbed into the blood like other fatty acids produced by the microbiome, some of which improve the health of the brain (June 2015 news). 

When the scientists added LCA to the drinking water of well-fed mice, it activated AMPK in their skeletal muscles to the same degree seen in calorie-restricted mice. While it didn’t extend their lifespans, it did boost their vigor: Old mice that ingested LCA ran farther on a treadmill and gripped a pressure-sensing bar harder. Their insulin sensitivity and glucose tolerance were better, and their muscles recovered faster after damage.

LCA also amped up AMPK in nematodes and fruit flies. These animals lived longer and coped better with oxidative stress, which the researchers induced using FeSO4 and H2O2.

Intriguingly, LCA also increased glucagon-like peptide 1 levels in mice. Some scientists have suggested that GLP-1 receptor agonists such as semaglutide might slow aging (e.g., Ortiz and de Freitas, 2024). Seeing GLP-1 appear in this context adds support to such claims, said Marc Tatar of Brown University in Providence, Rhode Island, who was not involved in the work.

In their companion paper, the Chinese scientists teased out the mechanism behind LCA. They report that it works through the lysosomal AMPK-activating pathway, which amps up AMPK in response to low cellular glucose. The signaling pathway relies on the vacuolar H+-ATPase (V-ATPase), which keeps the lysosome acidic. Lysosomal dysfunction has emerged as a major player in neurodegeneration (Dec 2024 news; Dec 2024 news).

By knocking out, or mutating, various components of this pathway in mouse embryonic fibroblasts, the scientists traced the effects of LCA to three lysine residues on V-ATPase. Deacetylating those residues inhibits the proton pump. This in turn leads to a signaling cascade that flips AMPK to its active state, the authors report.

LCA triggers this process by riling sirtuins, a family of seven proteins involved in the anti-aging effects of calorie restriction (Jul 2008 news; Sep 2013 news). All seven sirtuins deacetylated V-ATPase in response to LCA, with sirtuin 1 doing so most strongly.

Alas, there was still a missing link between LCA and sirtuins. To try to find it, the scientists ran pull-down assays from mouse fibroblast lysates, which netted 1,655 proteins that appear to associate with SIRT1. Co-immunoprecipitation narrowed the list to 157 candidates, each of which the scientists tested by knocking them down in the fibroblasts. This revealed a single winner: Tubby-like protein 3.

TULP3 bound to all seven sirtuins. And it bound LCA. Without it, LCA was unable to activate AMPK. When the scientists knocked down TULP3 analogues in nematodes and fruit flies, LCA no longer extended their lives.

“The work is incredibly comprehensive,” said Tatar. “I think this will break open a whole new branch of research based on gut microbiome byproducts and aging.” Whether LCA can be used as a longevity drug needs to be validated in clinical trials, noted Cao. “At the same time, the analysis of the life-prolonging mechanism of LCA also provides a new theory and target for the development of such drugs,” he wrote.—Nala Rogers

Nala Rogers is a freelance science writer based in Silver Spring, Maryland.

Comments

1. • Xu Chen
     University of California, San Diego
   • Posted: 08 Jan 2025

   These two studies by Qi et al. from Dr. Sheng-Cai Lin's group revealed a fundamental mechanism by which lithocholic acid mediates the pro-longevity effects of caloric restriction through the activation of AMPK, a key metabolic regulator. The discovery of LCA as a metabolic mediator of CR, and its effects across biochemical, cellular, and organismal levels, is truly striking. Moreover, the mechanistic study elegantly uncovered the molecular pathway underlying LCA-mediated AMPK activation: LCA binds to its receptor, TULP3, which activates sirtuins. These, in turn, inhibit vacuolar H⁺-ATPase on lysosomes, leading to AMPK activation. This novel signaling axis highlights the complex interplay between the deacetylation and phosphorylation of AMPK in response to glucose and nutrient-sensing signals.

   Given AMPK’s well-established role in regulating glucose and lipid metabolism in the brain, these findings offer exciting new insights into neural health and disease. Alzheimer's disease in particular is associated with impaired glucose utilization and disrupted lipid metabolism, contributing to neuronal metabolic dysfunction and neuroinflammation. Both AMPK and sirtuins have been reported to directly and indirectly impact neuronal health, with both pathways linked to lysosomal function. Future investigations into the LCA-TULP3–sirtuin–v-ATPase–AMPK signaling pathway in neurons and glial cells during aging and neurological disorders could uncover new mechanistic insights into health and disease, while also informing potential translational strategies.

   View all comments by Xu Chen

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References

News Citations

1. Consensus Reached: Dieting Monkeys Survive Longer 27 Jan 2017
2. Research Brief: Eat Less to Remember More 30 Jan 2009
3. To Be Hale and Hearty, Brain Microglia Need a Healthy Gut 5 Jun 2015
4. Sans Presenilin-2, Lysosomes Struggle. Synapses, Memory Circuits Erode 20 Dec 2024
5. Receptors and Broken Lysosomes Explain Risk from APOE Variants 3 Dec 2024
6. SIRT1, Resveratrol and More: Moving Closer to Anti-aging Elixir? 8 Jul 2008
7. Brain-Specific Sirtuin Expression Delays Aging in Mice 6 Sep 2013

Therapeutics Citations

1. Metformin

Paper Citations

1. Kapahi P, Kaeberlein M, Hansen M. Dietary restriction and lifespan: Lessons from invertebrate models. Ageing Res Rev. 2017 Oct;39:3-14. Epub 2016 Dec 19 PubMed.
2. Flanagan EW, Most J, Mey JT, Redman LM. Calorie Restriction and Aging in Humans. Annu Rev Nutr. 2020 Sep 23;40:105-133. Epub 2020 Jun 19 PubMed.
3. Belsky DW, Huffman KM, Pieper CF, Shalev I, Kraus WE. Change in the Rate of Biological Aging in Response to Caloric Restriction: CALERIE Biobank Analysis. J Gerontol A Biol Sci Med Sci. 2017 Dec 12;73(1):4-10. PubMed.
4. Halagappa VK, Guo Z, Pearson M, Matsuoka Y, Cutler RG, Laferla FM, Mattson MP. Intermittent fasting and caloric restriction ameliorate age-related behavioral deficits in the triple-transgenic mouse model of Alzheimer's disease. Neurobiol Dis. 2007 Apr;26(1):212-20. PubMed.
5. Zhang J, Zhan Z, Li X, Xing A, Jiang C, Chen Y, Shi W, An L. Intermittent Fasting Protects against Alzheimer's Disease Possible through Restoring Aquaporin-4 Polarity. Front Mol Neurosci. 2017;10:395. Epub 2017 Nov 29 PubMed.
6. Leclerc E, Trevizol AP, Grigolon RB, Subramaniapillai M, McIntyre RS, Brietzke E, Mansur RB. The effect of caloric restriction on working memory in healthy non-obese adults. CNS Spectr. 2020 Feb;25(1):2-8. PubMed.
7. O'Leary J, Georgeaux-Healy C, Serpell L. The impact of continuous calorie restriction and fasting on cognition in adults without eating disorders. Nutr Rev. 2025 Jan 1;83(1):146-159. PubMed.
8. Zhang CS, Li M, Wang Y, Li X, Zong Y, Long S, Zhang M, Feng JW, Wei X, Liu YH, Zhang B, Wu J, Zhang C, Lian W, Ma T, Tian X, Qu Q, Yu Y, Xiong J, Liu DT, Wu Z, Zhu M, Xie C, Wu Y, Xu Z, Yang C, Chen J, Huang G, He Q, Huang X, Zhang L, Sun X, Liu Q, Ghafoor A, Gui F, Zheng K, Wang W, Wang ZC, Yu Y, Zhao Q, Lin SY, Wang ZX, Piao HL, Deng X, Lin SC. The aldolase inhibitor aldometanib mimics glucose starvation to activate lysosomal AMPK. Nat Metab. 2022 Oct;4(10):1369-1401. Epub 2022 Oct 10 PubMed.
9. Ortiz GU, de Freitas EC. Semaglutide as a possible therapy for healthy aging: Targeting the hallmarks of aging. Ageing Res Rev. 2024 Dec;102:102582. Epub 2024 Nov 14 PubMed.

Further Reading

News

1. Paper Alert: Caloric Restriction Improves Human Health Parameters 6 Apr 2006
2. Research Brief: Eat Less to Remember More 30 Jan 2009
3. The Picture of Health? Aging Better—On Fewer Calories 10 Jul 2009
4. SIRT1, Resveratrol and More: Moving Closer to Anti-aging Elixir? 8 Jul 2008
5. SIRT1 Activator Prevents Metabolic Disorders in Mice 12 Nov 2008