# IGF-1 from bone marrow Adipoq-lineage cells stimulates endocortical bone formation in mature female mice

## TL;DR

A specific type of bone marrow cell produces IGF-1, which helps build cortical bone in adult female mice.

## Contribution

Identifies Adipoq+ stromal cells as a local source of IGF-1 that specifically supports endocortical bone formation in mature females.

## Key findings

- IGF-1 from Adipoq+ cells in bone marrow promotes endocortical bone formation in mature female mice.
- Deleting IGF-1 in these cells reduces cortical bone mass without affecting trabecular bone or hematopoiesis.
- The effect is sex-specific and site-specific, with no impact on male mice or other bone parameters.

## Abstract

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 BM 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 BM 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 BM microenvironment that contributes to bone anabolic regulation in a site-specific manner.