Key Points:
- Feeding old mice gut bacteria from young mice increases their grip strength and muscle cell size.
- The skin of old mice fed gut bacteria from young mice is thicker and retains more moisture.
- Improved muscle and skin gene activation in old mice correlates with gut bacteria called Bacteroidetes.
Some have likened our gut bacteria — the bacteria that live in our gut — to an organ. This “organ” is capable of modulating our immune system and metabolism, as well as other organs like the brain and muscle. However, our gut bacteria change with aging and may contribute to age-related diseases. This has brought scientists to examine how gut bacteria from young mice affect old mice in the hopes of finding rejuvenating species of beneficial gut bacteria.
Now, researchers from Yonsei University in Korea report in Microbiome that gut bacteria from young mice improve the physical fitness of old mice. Kim and colleagues show that feeding old mice gut bacteria from young mice increases their grip strength and muscle cell size. Old mice fed gut bacteria from young mice also have increased skin thickness and moisture. Additionally, specific types of bacteria correlated with improved muscle and skin gene activation, which may underlie the rejuvenating effects of gut bacteria transfer.
Gut Bacteria From Young Mice Rejuvenates Old Mouse Muscle and Skin
Our fecal matter contains bacteria representing the composition of the entirety of our gut bacteria. Kim and colleagues isolated the gut bacteria from the fecal matter of young mice (equivalent to teenage humans) and fed them to old mice (equivalent to 58-year-old humans). The gut bacteria transfer increased the forelimb grip strength and muscle cell size of the old mice, suggesting that gut bacteria from young mice rejuvenates the muscle of old mice.
With aging comes the deterioration of multiple organs. For example, the age-related deterioration of muscle — sarcopenia — is characterized by reduced muscle strength and size. Upon finding that “young” gut bacteria ameliorate aspects of sarcopenia, Kim and colleagues next assessed the largest organ — the skin, which becomes thin and dry as it deteriorates with aging.
The researchers found that the outermost layer of the skin (stratum corneum) became thicker in old mice when fed gut bacteria from young mice. Gut bacteria from young mice also increased moisture retention, which was assessed by measuring skin hydration and water loss (TEWL) with specialized probes. These findings suggest that gut bacteria from young mice rejuvenates the skin of old mice.
By analyzing muscle and skin gene activation from old mice fed “young” gut bacteria, Kim and colleagues were able to correlate specific types of gut bacteria with genetic improvements in these organs. This included a family of bacteria called Bacteroides. In a previous study, Bacteroides were associated with increased survival probability in older adults. Bacteroides belong to the phylum (taxonomic classification) Bacteroidetes. Bacteroidetes may treat irritable bowel syndrome and obesity.
Rejuvenating Our Muscles and Skin with Fiber and Probiotics
Our gut bacteria thrive off the food we eat, so what we eat can change which bacteria grow in our gut. For example, Bacteroides can possibly be increased by consuming more fiber, either through supplementation or foods like beans, berries, and avocados. Gut bacteria also interact in a complex network, with some gut bacteria affecting the growth of others. For example, Bacteroidetes could be increased by supplementing with Lactobacillus probiotics.
While the research is still ongoing and in its early stages, it would seem that a fecal matter transplant, or possibly a proper diet containing adequate levels of fiber and probiotics (which may call for supplementation) can rejuvenate our gut bacteria, an “organ” system that affects our aging body.
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