A single injection into the muscle – and ageing mice not only live longer but also stay leaner, fitter and mentally more agile. This was reported in June 2026 by a team at the Universitat Autònoma de Barcelona led by Prof. Fàtima Bosch in the journal Molecular Therapy.
What is FGF21?
FGF21 (fibroblast growth factor 21) is a hormone released mainly by the liver during food deprivation. It regulates glucose and fat metabolism, improves insulin sensitivity and is considered one of the messengers through which calorie restriction might exert its life-extending effect. Genetically modified mice that produce high levels of FGF21 throughout their lives are known to live longer but also show side effects such as bone loss.
The approach
The researchers used a harmless virus (adeno-associated virus, AAV) as a gene vector to introduce the FGF21 gene into the leg muscles. The muscle thus becomes a permanent source of the hormone, which acts from there throughout the body. Mice were treated at the age of 13 months – roughly equivalent to middle age in humans – and a small group only at 22 months.
The results
- Lifespan: the median lifespan of male mice rose from 28 to 34 months, an increase of just over 20 per cent according to the study.
- Metabolism: body weight and fat percentage normalised with the same amount of food, and insulin sensitivity and glucose metabolism improved.
- Organs: less scarring (fibrosis) and amyloid deposits in the liver, kidney, heart and muscle; the mitochondria worked better.
- Performance and brain: better coordination, strength and endurance. In the memory test, treated animals aged 27 months performed as well as two-month-old young animals.
- Bone: unlike in mice producing FGF21 throughout life, bone metabolism remained unchanged.
Assessment
The study is among the most impressive gene therapy results in ageing research, but it has clear limitations: the lifespan data come only from male mice; female animals benefited in several areas but were studied less comprehensively. In addition, results from mouse studies cannot be transferred directly to humans.
Study leader Bosch is associated with the company Kriya Therapeutics, which wants to bring the approach into the clinic – initially not against ageing but against the fatty liver disease MASH. For this indication, the FDA has authorised a clinical trial due to start in 2026.
Note: This article is for general information only and does not replace medical advice. The therapy described is experimental and is not approved for use in humans.
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