Reconstitution of the host holobiont acutely increases bone growth of the gnotobiotic rat

The effect of microbiota on skeletal growth in adolescence has not been studied. Here, we present for the first time, an accelerated longitudinal and radial bone growth in response to short-term exposure of young germ-free rats to newly established gut microbiota. Seven-week-old germ-free male rats were colonized with microbiota through co-housing with conventional rats of the same sex and age. Changes in bone mass and structure were analyzed 10 days following the onset of colonization and revealed unprecedented acceleration of bone accrual, increased bone tissue mineral density, improved proliferation and hypertrophy of growth plate chondrocytes, and bone lengthening. The observed changes in bone status were paralleled with a dramatic increase in cecal concentration of short-chain fatty acids and increased hepatic Igf-1 expression implicating an involvement of the somatotropic axis. Our studies demonstrate that gut microbiota can deliver powerful signals to the skeleton and accelerate bone expansion resembling adolescent growth spurt.