Hypoxia-reperfusion affects osteogenic lineage and promotes sickle cell bone disease

Abstract

Key Points• In SCD, recurrent vasoocclusive crisis suppresses osteogenic lineage and activates osteoclasts.• Zoledronic acid acting on both osteoclast and osteoblast compartments is a multimodal therapy to prevent SBD.Sickle cell disease (SCD) is a worldwide distributed hereditary red cell disorder, characterized by severe organ complication. Sickle bone disease (SBD) affects a large part of the SCD patient population, and its pathogenesis has been only partially investigated. Here, we studied bone homeostasis in a humanized mouse model for SCD. Under normoxia, SCD mice display bone loss and bone impairment, with increased osteoclast and reduced osteoblast activity. Hypoxia/reperfusion (H/R) stress, mimicking acute vaso-occlusive crises (VOCs), increased bone turnover, osteoclast activity (RankL), and osteoclast recruitment (Rank) with upregulation of IL-6 as proresorptive cytokine. This was associated with further suppression of osteogenic lineage (Runx2, Sparc). To interfere with the development of SBD, zoledronic acid (Zol), a potent inhibitor of osteoclast activity/ osteoclastogenesis and promoter of osteogenic lineage, was used in H/R-exposed mice. Zol markedly inhibited osteoclast activity and recruitment, promoting osteogenic lineage. The recurrent H/R stress further worsened bone structure, increased bone turnover, depressed osteoblastogenesis (Runx2, Sparc), and increased both osteoclast activity (RankL, Cathepsin k) and osteoclast recruitment (Rank) in SCD mice compared with either normoxic or single-H/R-episode SCD mice. Zol used before recurrent VOCs prevented bone impairment and promoted osteogenic lineage. Our findings support the view that SBD is related to osteoblast impairment, and increased osteoclast activity resulted from local hypoxia, oxidative stress, and the release of proresorptive cytokine such as IL-6. Zol might act on both the osteoclast and osteoblast compartments as multimodal therapy to prevent SBD. (Blood. 2015;126(20):2320-2328 IntroductionSickle cell disease (SCD) is a worldwide distributed hereditary red cell disorder, which affects approximately 75 000 individuals in the United States and almost 20 000 to 25 000 individuals in Europe, this latter mainly related to the immigration fluxes from endemic areas such as Sub-Saharan Africa to European countries.1-3 Studies of the global burden of disease have pointed out the invalidating impact of SCD on patient quality of life.2 This requires the development of new therapeutic options to treat sickle cell-related acute and chronic complications.SCD is caused by a point mutation in the b-globin gene resulting in the synthesis of pathologic hemoglobin S (HbS). HbS displays peculiar biochemical characteristics, polymerizing when deoxygenated with associated reduction in cell ion and water content (cell dehydration), increased red cell density, and further acceleration of HbS polymerization. [4][5][6] Pathophysiologic studies have shown that dense, dehydrated red cells play a central role in acute and chronic clinical manifestations of ...

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