The role of the P2X7 receptor on bone loss in a mouse model of inflammation-mediated osteoporosis

In inflammatory autoimmune diseases, bone loss is frequent. In most cases, secondary osteoporosis is caused by treatment with systemic glucocorticoid. However, the pathogenesis behind the bone loss is presumed multifactorial. We aimed to elucidate the role of the P2X7 receptor on bone mineral density (BMD), microarchitecture, and bone strength in a standardized mouse model of inflammation-mediated osteoporosis (IMO). In total 146 mice completed our protocol, 70 wild type (WT) mice and 76 P2X7 -/- (knockout, KO). BMD at the femur and spine decreased significantly from baseline to day 20 in the WT IMO mice (p < 0.01). In the WT vehicle, KO vehicle and KO IMO, no significant BMD changes were found. Bone strength showed a lower mid-shaft max strength (p = 0.038) and also a non-significant trend towards lower strength at the femoral neck of the WT IMO group. Trabecular bone volume fraction (BV/TV) and connectivity density (CD) after 20 days were significantly decreased in the WT IMO group (p = 0.001). In contrast, the WT vehicle and KO vehicle, BV/TV and CD did no change at 20 days. Cortical bone revealed no significant microarchitectural changes after 20 days in the WT IMO group, whereas the total cortical area increased significantly in WT vehicle and KO IMO after 20 days (5.2% and 8.8%, respectively). In conclusion, the P2X7 receptor KO mice did not respond to inflammation with loss of BMD whereas the WT mice had a significant loss of BMD, bone strength and trabecular microarchitecture, demonstrating a role for the P2X7 receptor in inflammatory bone loss.