A lack of commensal microbiota influences the male reproductive tract intergenerationally in mice

The microbiome encompasses the array of microorganisms inhabiting various niches in the body and is necessary for numerous physiological processes, including normal metabolism and a functioning immune system. Not only does the absence of a microbiome in mice impact the exposed animals but also inherited phenotypes in successive generations of progeny, suggesting that the absence of a microbiome impacts the germline and gametes. Indeed, recent research has identified a role of the gut microbiome in contributing to male fertility, in both healthy and disease states. While this link is beginning to be established, the impact of the microbiome on the male reproductive tract remains understudied. Here, we utilized a germ-free mouse model to examine the influence of the absence of microbes on the male reproductive tract. In contrast to mice with an established microbiome, germ-free mice display decreased testicular weight and the prevalence of an epididymitis-like inflammation phenotype. These histopathological changes are accompanied by transcriptomic dysregulation in the reproductive tract of germ-free mice, particularly in the cauda epididymis. Moreover, such transcriptomic changes are transmitted to the next generation with high correlation of gene expression in the cauda epididymis between germ-free mice and their conventionalized (microbiome-restored) male offspring, when compared to control mice. Ultimately, our findings identify the reproductive sequalae of males without a functional microbiome and additionally in their conventionalized offspring, suggesting that the paternal microbiota is an underappreciated contributor to male reproductive function. Overall design: To investigate the influence of microbiota on the male reproductive tract we collected testis from specific pathogen free control mice (SPF) and germ-free mice (GF) (n = 3-4) and caput and cauda epididymis tissue from SPF, GF and male offspring from GF x SPF parents for RNA-seq. We also investigated the role of T and B cells in directing gene expression changes by performing RNA-seq on caput and cauda epididymal tissue from Rag2 knockout male mice.