Erythropoiesis, EPO, macrophages, and bone.

The regulation of erythropoiesis in the bone marrow microenvironment is a carefully orchestrated process that is dependent upon both systemic and local cues. Systemic erythropoietin (EPO) production by renal interstitial cells plays a critical role in maintaining erythropoietic homeostasis. In addition, there is increasing clinical and preclinical data linking changes in EPO and erythropoiesis to altered skeletal homeostasis, suggesting a functional relationship between the regulation of erythropoiesis and bone homeostasis. As key local components of the bone marrow microenvironment and erythropoietic niche, macrophage subsets play important roles in both processes. In this review, we summarize our current understanding of the cellular and molecular mechanisms that may facilitate the coordinated regulation of erythropoiesis and bone homeostasis.