The study shows that a specific type of bone‑marrow cell makes IGF‑1, which helps build the outer part of bone in adult female mice. When IGF‑1 was removed from those cells, the mice had weaker cortical bone, but their inner spongy bone and blood‑cell production stayed the same. This points to a local, bone‑specific role for IGF‑1 rather than a whole‑body effect.

Insulin-like growth factor 1 (IGF-1) is an anabolic signal promoting growth, differentiation and function of both embryonic and postnatal tissues. Both endocrine and paracrine functions of IGF-1 have been documented to regulate bone growth and bone marrow hematopoiesis. Local production of IGF-1 from various cell types may contribute differently to the overall bioactivity of IGF-1 in bone, but relevant sources and mechanisms are yet to be fully elucidated. Here we report that the Adipoq⁺ stromal cells are a notable source of IGF-1 in the bone marrow of postnatal mice. Deletion of IGF-1 with Adipoq-Cre diminished endocortical bone formation and cortical bone mass in mature female mice. On the other hand, the trabecular bone parameters or hematopoietic properties were not affected in mutant mice of either sex. The study uncovers a local source of IGF-1 in the bone marrow microenvironment that contributes to bone anabolic regulation in a site-specific manner.