Osteoblast/osteocyte-derived interleukin-11 regulates osteogenesis and systemic adipogenesis

Here, the authors identify interleukin-11 as a mediator of bone-adipose crosstalk during mechanical loading of the bone. Interleukin-11 secreted by the bone acts as a hormone to regulate fat metabolism, in addition to having an autocrine-paracrine effect on bone itself. Exercise results in mechanical loading of the bone and stimulates energy expenditure in the adipose tissue. It is therefore likely that the bone secretes factors to communicate with adipose tissue in response to mechanical loading. Interleukin (IL)-11 is known to be expressed in the bone, it is upregulated by mechanical loading, enhances osteogenesis and suppresses adipogenesis. Here, we show that systemic IL-11 deletion (IL-11(-/-)) results in reduced bone mass, suppressed bone formation response to mechanical loading, enhanced expression of Wnt inhibitors, and suppressed Wnt signaling. At the same time, the enhancement of bone resorption by mechanical unloading was unaffected. Unexpectedly, IL-11(-/-) mice have increased systemic adiposity and glucose intolerance. Osteoblast/osteocyte-specific IL-11 deletion in osteocalcin-Cre;IL-11(fl/fl) mice have reduced serum IL-11 levels, blunted bone formation under mechanical loading, and increased systemic adiposity similar to IL-11(-/-) mice. Adipocyte-specific IL-11 deletion in adiponectin-Cre;IL-11(fl/fl) did not exhibit any abnormalities. We demonstrate that osteoblast/osteocyte-derived IL-11 controls both osteogenesis and systemic adiposity in response to mechanical loading, an important insight for our understanding of osteoporosis and metabolic syndromes.