New Regulatory Mechanisms of Bone Marrow Mesenchymal Stem Cell Differentiation Involving An Adenosine Receptor.

Abstract 2584

The bone marrow cellular environment, including existing and newly formed bone cells, are important for the process of hematopoiesis at baseline and under stress, such as bone fracture. The A2b adenosine receptor (A2bAR) has a protective role in various models of chronic injury and in inflammation, particularly through its expression in macrophages. Bone fracture healing is a complex process composed of an initial inflammatory response, followed by differentiation of mesenchymal stem cells (MSC) into chondrocytes and osteoblasts to form bone, and finally resorption by osteoclasts to remodel the structure. Here we find A2bAR expression in bone marrow MSC cultures, and A2bAR knockout (KO) mice have lower bone density than wildtype counterparts. In vitro, induced differentiation of bone marrow derived MSCs from A2bAR KO mice resulted in lower expression of osteoblast differentiation genes and formed fewer mineralized nodules, as compared to wildtype mice. Furthermore, concurrent treatment of bone marrow derived MSCs with A2bAR agonists, and consequently an increase in cAMP levels, during differentiation resulted in elevated expression of the osteoblast differentiation gene Osterix. Examination of an in vivo model of bone fracture and showed a significant decrease in bone formation in the A2bAR KO mice, compensated for by upregulation of chondrocyte differentiation markers and cartilage formation. Delayed fracture healing in the A2bAR KO mice was associated with lower expression of genes involved in osteoblast differentiation. These results demonstrate a new role for the A2bAR and its ligand in promoting differentiation of MSCs into osteoblasts, which would affect the integrity of the bone marrow niche under stress.