Emerging evidence suggests a significant role of gut microbiome in bone health. Aging is well recognized as a crucial factor influencing the gut microbiome. In this study, we investigated whether age-dependent microbial change contributes to age-related bone loss in CB6F1 mice. The bone phenotype of 24-month-old germ-free (GF) mice was indistinguishable compared to their littermates colonized by fecal transplant at 1-month-old. Moreover, bone loss from 3 to 24-month-old was comparable between GF and specific pathogen-free (SPF) mice. Thus, GF mice were not protected from age-related bone loss. 16S rRNA gene sequencing of fecal samples from 3-month and 24-month-old SPF males indicated an age-dependent microbial shift with an alteration in energy and nutrient metabolism potential. An integrative analysis of 16S predicted metagenome function and LC-MS fecal metabolome revealed an enrichment of protein and amino acid biosynthesis pathways in aged mice. Microbial S-adenosyl methionine metabolism was increased in the aged mice, which has previously been associated with the host aging process. Collectively, aging caused microbial taxonomic and functional alteration in mice. To demonstrate the functional importance of young and old microbiome to bone, we colonized GF mice with fecal microbiome from 3-month or 24-month-old SPF donor mice for 1 and 8 months. The effect of microbial colonization on bone phenotypes was independent of the microbiome donors’ age. In conclusion, our study indicates age-related bone loss occurs independent of gut microbiome.

新出现的证据表明，肠道微生物组在骨骼健康中起着重要作用。衰老是公认的影响肠道微生物组的关键因素。在这项研究中，我们调查了年龄依赖性微生物变化是否会导致 CB6F1 小鼠与年龄相关的骨质流失。与在 1 个月大时通过粪便移植定植的同窝小鼠相比，24 个月大的无菌 （GF） 小鼠的骨骼表型难以区分。此外，GF 和无特异性病原体 （SPF） 小鼠从 3 到 24 个月大的骨质流失相当。因此，GF 小鼠没有受到与年龄相关的骨质流失的保护。来自 3 个月和 24 个月大的 SPF 雄性粪便样本的 16S rRNA 基因测序表明，微生物发生年龄依赖性转变，能量和营养代谢潜力发生变化。对 16S 预测的宏基因组功能和 LC-MS 粪便代谢组的综合分析显示，老年小鼠中蛋白质和氨基酸生物合成途径的富集。老年小鼠的微生物 S-腺苷甲硫氨酸代谢增加，这以前与宿主衰老过程有关。总的来说，衰老导致了小鼠的微生物分类学和功能改变。为了证明年轻和老年微生物组对骨骼的功能重要性，我们用 3 个月或 24 个月大的 SPF 供体小鼠的粪便微生物组定植了 GF 小鼠 1 个月和 8 个月。微生物定植对骨表型的影响与微生物组供体的年龄无关。总之，我们的研究表明，与年龄相关的骨质流失的发生与肠道微生物组无关。