Research progress on the effects of macrophage‑derived exosomes on muscle factors IGF‑1 and FGF‑2 mediating musculoskeletal crosstalk molecular signaling pathway on bone metabolism (Review).

Musculoskeletal crosstalk is essential for maintaining the balance of bone metabolism, with macrophage‑derived exosomes emerging as key regulators of this process. Exosomes, small extracellular vesicles secreted by cells, carry a variety of bioactive molecules; proteins, lipids, mRNAs and miRNAs and facilitate intercellular communication by transferring these cargos to recipient cells. Specifically, macrophage‑derived exosomes mediate muscle‑bone interactions by transferring key regulators such as insulin‑like growth factor‑1 (IGF‑1) and fibroblast growth factor‑2 (FGF‑2), thereby playing a pivotal role in bone metabolic homeostasis. Macrophages are classified into pro‑inflammatory M1 and anti‑inflammatory M2 phenotypes, each performing distinct functions in immune responses. Exosomes from M1 macrophages typically carry pro‑inflammatory factors that can activate osteoclastic bone resorption, disrupting bone metabolism in pathological conditions. By contrast, exosomes from M2 macrophages often contain anti‑inflammatory factors that promote tissue repair and bone formation. In the context of bone metabolism, exosomes from M1 and M2 macrophages modulate muscle‑bone signaling by delivering regulators that influence the expression of IGF‑1 and FGF‑2, affecting osteoblast proliferation, differentiation, and mineralization. M1 macrophage‑derived exosomes activate signaling pathways such as NF‑κB and MAPK through the transfer of pro‑inflammatory cargo, thereby enhancing bone resorption. By contrast, exosomes from M2 macrophages can suppress pro‑inflammatory signaling while activating pathways like TGF‑β and PI3K/Akt, promoting bone synthesis and repair. As critical myokines, IGF‑1 and FGF‑2 not only support muscle growth, repair, and maintenance but also directly influence bone remodeling through musculoskeletal crosstalk.