Hypoxia-Mimicking Mediated Macrophage-Elimination of Erythrocytes Promotes Bone Regeneration via Regulating Integrin α<sub>v</sub>β<sub>3</sub>/Fe<sup>2+</sup>-Glycolysis-Inflammation.

Abstract

Erythrocytes are the dominant component of a blood clot in terms of volume and number. However, longstanding compacted erythrocytes in blood clots form a physical barrier and make fibrin mesh more anti-fibrinolytic, thus impeding infiltration of mesenchymal stem cells. The necrosis or lysis of erythrocytes that are not removed timely can also lead to the release of pro-inflammatory toxic metabolites, interfering with bone regeneration. Proper bio-elimination of erythrocytes is essential for an undisturbed bone regeneration process. Here, hypoxia-mimicking is applied to enhance macrophage-elimination of erythrocytes. The effect of macrophage-elimination of erythrocytes on the macrophage intracellular reaction, bone regenerative microenvironment, and bone regeneration outcome is investigated. Results show that the hypoxia-mimicking agent dimethyloxalylglycine successfully enhances erythrophagocytosis by macrophages in a dose-dependent manner primarily by up-regulating the expression of integrin α_vβ₃. Increased phagocytosed erythrocytes then regulate macrophage intracellular Fe²⁺-glycolysis-inflammation, creating an improved bone regenerative microenvironment characterized by loose fibrin meshes with down-regulated local inflammatory responses in vivo, thus effectively promoting early osteogenesis and ultimate bone generation. Modulating macrophage-elimination of erythrocytes can be a promising strategy for eradicating erythrocyte-caused bone regeneration hindrance and offers a new direction for advanced biomaterial development focusing on the bio-elimination of erythrocytes.