The effect of the gut microbiome of adult and aging mice on metabolic characteristics

During aging, there is a physiological decline, an increase of morbidity and mortality and a natural change in the gut microbiome. In this study, we investigated the influence of the gut microbiome on different metabolic parameters in adult and aging mice.
Fecal and blood samples from adult (n=42, 100-300 days) and aging (n=32, 550-750 days) mice were collected. 16S rRNA gene sequence analysis was carried out using Qiime2. Mice weight and body composition were measured by using NMR, and insulin and leptin levels in the blood were measured using the Mouse Adipokine Magnetic Bead Panel kit. We then preformed Fecal Microbiota Transplantation (FMT) from adult and aging mice into young germ-free (GF) mice in order to examine the effect of the gut microbiome of adult and aging mice on weight, body composition and insulin and leptin levels. We also monitored food consumption and RQ 10 days after FMT using Metabolic Cages.
We found that adults and aging mice have different microbiomes. We observed a high Firmicutes/Bacteroidetes ratio in aging mice compared to adult mice in addition to several genera that were significantly different between the groups. In the examined metabolic parameters, we observed significantly higher weight and fat mass and lower lean mass in aging mice along with high insulin and leptin levels in the blood. In the FMT mice, the gut microbiome from aging mice caused several metabolic changes in the young transplanted mice. Fat body mass and insulin levels were higher in the mice who received aging feces than mice receiving adult feces. In addition, they consumed more food and had higher metabolic activity (average RQ) compared to mice receiving adult feces.
We conclude that aging mice have a gut microbiota that is associated with obesity, and they also exhibit metabolic parameters related to obesity. In addition, the gut bacterial population itself is sufficient to induce some of the manifestations of obesity.