16S rRNA is a gene that varies in sequence distinctively by microbial species, and thus can be cheaply sequenced to catalog the contents of the gut microbiome for a given individual, determining the composition of specific species and their prevalence. Given this capability, researchers have determined that the distribution of microbial populations alters with age in ways that are harmful to health, such as via loss of beneficial metabolite production or increased inflammation. Further, researchers are increasingly correlating specific features of the gut microbiome to specific age-related conditions.
All of this is groundwork for a near future in which the gut microbiome can be tailored to a specific composition of populations to produce a desired outcome. Lasting rejuvenation of the composition of the gut microbiome, reversing age-related changes, is possible today via fecal microbiota transplantation using a young donor. It is possible in principle (though not yet reduced to practice) to achieve other forms of long-lasting adjustment of the composition of the microbiome by culturing and delivering a specific mix of microbes. Present approaches to oral delivery of probiotics do not achieve this goal, however.
Today's open access paper is an example of present research into correlations between gut microbiome composition and aspects of aging, here the focus is on progressive loss of bone density and muscle mass. The interesting question is the degree to which gut microbiome composition is causative versus being a consequence of other factors that drive osteoporosis and sarcopenia, such as age-related immune dysfunction or the reduced intake of protein and calories typical of older people.
The role of the gut microbiome in the development of osteoporosis and sarcopenia has received increased interest given its promising potential in improving musculoskeletal health. The gut microbiome is commonly assessed in the stool and comprises a collection of microorganisms from the digestive tract that impact human physiology through different biological processes. Previous research has indicated that the community of commensal microbes residing in the gut may represent a potentially modifiable factor contributing to muscle and skeletal health. For instance, the gut microbiome can affect the inflammatory environment through effects on the T-cell landscape, which influences osteoclastogenesis and bone loss in mice, and through the production of complex polysaccharides (e.g., short chain fatty acids (SCFA)). The gut microbiota also interacts with important diet components associated with musculoskeletal health such as vitamin K, vitamin D, and calcium. Moreover, the gut microbiota can modulate lipopolysaccharide (LPS) production and various metabolites that directly or indirectly (i.e., through the brain and liver) affect host skeletal muscle metabolism potentially playing a role in sarcopenia etiology.
We leveraged information from two large population-based cohorts, the Rotterdam Study (mean age 62.7 ± 5.6 years; n=1,249) and the Framingham Heart Study (mean age 55.2 ± 9.1 years; n=1,227). For individuals included in this study, gut microbiome 16S rRNA sequencing, musculoskeletal phenotyping, lifestyle and socioeconomic data, and medication records were available. Using 16S rRNA sequencing data we investigated the association between the human gut microbiome (alpha diversity, genera, and predicted functional pathways) and appendicular lean mass (ALM), femoral neck bone mineral density (FN-BMD), and trabecular bone score (TBS) using multilinear regression models controlling for multiple confounders, and performed a joint analysis from both cohorts. Sex-stratified analyses were also conducted.
The gut microbiome alpha diversity was not associated with either tested phenotype after accounting for multiple-testing. In the joint analysis, lower abundance of Oscillibacter, Anaerotruncus, Eisenbergiella, and higher abundance of Agathobacter were associated with higher ALM. Lower abundance of Anaerotruncus, Hungatella, and Clostridiales bacterium DTU089 was associated with higher ALM only in females. Moreover, the biotin biosynthesis II pathway was positively associated with ALM in females while no associations were observed in males. We did not observe any robust association of bone traits with gut microbiome features. Overall, our study suggests that the gut microbiome is linked to muscle aging in middle-aged and older adults. However, larger sample sizes are still needed to underpin the specific microbiome features involved.
View the full article at FightAging
