Figure 4.

The GM from old mice reduces relative lean mass but not bone mass in young healthy still growing recipient mice compared with the GM from young adult donors.

Cecal microbiota from old or young adult donor mice was transplanted to GF mice of different ages. At the end of the experiment, tibia and humerus were dissected. The tibia were analyzed by high-resolution microCT (µCT) to determine trabecular BV/TV (a) and cortical thickness (b). The humerus was analyzed by three-point bending to measure maximum force (Fmax, c) and the bone quality parameter material stress was calculated (d). Bone marrow cells were harvested from femur and stained for CD4, Foxp3, and CD25 to analyze CD4+ cells (e) and regulatory T cells (Treg, CD4+CD25+Foxp3+, panel f). Body composition was determined at the time of gavage and 5 weeks later using qMR to calculate difference in lean mass percentage (ΔLean%, g). Values are given as the mean ± SEM. Data in panels A-D and G were analyzed by two-way ANOVA to analyze the overall effect of age of donor mice (old vs young adult), age of recipient GF mice, and their interaction followed by Šídák post hoc test to correct for multiple comparisons. Data in panels E and F were analyzed by Student’s t-test followed by Bonferroni correction since samples from the three sub-studies were analyzed on different occasions and cannot be compared due to interassay variation. ***p ≤ 0.001, **p ≤ 0.01, and *p ≤ 0.05.