IADR Abstract Archives
Defective Efferocytosis (Apoptotic Cell Clearance) Leads to Osteopenia in Mice
Objectives: Osteal macrophages positively impact skeletal homeostasis via mechanisms as yet unclear. The process of apoptotic cell clearance, termed efferocytosis, is a macrophage driven resolving process that declines with age and is associated with autoimmune disease, but little is known of its role in bone. Milk fat globule-EGF factor 8 (MFG-E8) facilitates efferocytosis. The purpose of this study was to investigate MFG-E8 mediated age-related bone loss.
Methods: Bone marrow macrophage (BMM)-mediated efferocytosis of apoptotic cells from MFG-E8 mutant (KO) and wildtype (WT) C57BL/6 mice was assessed via flow cytometry and live-cell imaging. Primary osteoblast and osteoclast cultures were used to assess mineralization and resorption. Skeletal phenotypes were analyzed at 6 and 22wks. KO and WT mice were administered anabolic PTH (iPTH) (50µg/kg/d) or vehicle to assess therapeutic potential. Mice were assessed for skeletal phenotypes, including micro-CT, serum biomarkers, static, and dynamic histomorphometry.
Results: MFG-E8KO BMMs displayed significantly decreased efferocytosis vs WT. KO and WT osteoblasts and osteoclasts displayed similar differentiation, mineralization and resorption. Although similar parameters of trabecular and cortical bone were found in MFG-E8KO and WT mice at 6 wks, 22wk old KO mice displayed significantly reduced trabecular and cortical bone and reduced serum TRAcP5b compared to WT. Interestingly, KO mice treated with iPTH showed a robust anabolic response in trabecular bone volume (+122%), exceeding the anabolic response in iPTH-treated WT mice (+48%).
Conclusions: These data suggest that MFG-E8-mediated apoptotic cell clearance plays an important role in age-related bone loss. The strong anabolic response in KO vs. WT demonstrates that iPTH therapy may be more effective in models of age-related bone loss and/or inflammatory states. These data give us insight into the role of MFG-E8-mediated efferocytosis in aging, provide a new model of age-associated bone loss, and suggest anabolic PTH may be a valuable therapeutic approach for autoimmune associated skeletal disease.
Methods: Bone marrow macrophage (BMM)-mediated efferocytosis of apoptotic cells from MFG-E8 mutant (KO) and wildtype (WT) C57BL/6 mice was assessed via flow cytometry and live-cell imaging. Primary osteoblast and osteoclast cultures were used to assess mineralization and resorption. Skeletal phenotypes were analyzed at 6 and 22wks. KO and WT mice were administered anabolic PTH (iPTH) (50µg/kg/d) or vehicle to assess therapeutic potential. Mice were assessed for skeletal phenotypes, including micro-CT, serum biomarkers, static, and dynamic histomorphometry.
Results: MFG-E8KO BMMs displayed significantly decreased efferocytosis vs WT. KO and WT osteoblasts and osteoclasts displayed similar differentiation, mineralization and resorption. Although similar parameters of trabecular and cortical bone were found in MFG-E8KO and WT mice at 6 wks, 22wk old KO mice displayed significantly reduced trabecular and cortical bone and reduced serum TRAcP5b compared to WT. Interestingly, KO mice treated with iPTH showed a robust anabolic response in trabecular bone volume (+122%), exceeding the anabolic response in iPTH-treated WT mice (+48%).
Conclusions: These data suggest that MFG-E8-mediated apoptotic cell clearance plays an important role in age-related bone loss. The strong anabolic response in KO vs. WT demonstrates that iPTH therapy may be more effective in models of age-related bone loss and/or inflammatory states. These data give us insight into the role of MFG-E8-mediated efferocytosis in aging, provide a new model of age-associated bone loss, and suggest anabolic PTH may be a valuable therapeutic approach for autoimmune associated skeletal disease.
