Endocrine Abstracts

Osteoblasts and adipocytes are derived from mesenchymal stem cells (MSC), although the mechanisms involved are not fully understood. Our previous findings showed that MSCs express functional adenosine receptors (ARs) and that adenosine stimulates osteoblastogenesis. Here we describe changes in AR expression as MSCs differentiate into osteoblasts and adipocytes, and provide evidence that ARs are involved in these differentiation pathways.

Rat MSCs were differentiated into osteoblasts using dexamethasone and ascorbate-2-phosphate, whilst adipogenesis was induced by indomethacin, dexamethasone and insulin. AR expression was assessed by QRT-PCR and western blotting, and cAMP concentrations determined by radioimmunoassay.

NECA (universal AR agonist) stimulated osteoblastogenesis and adipogenesis as determined by increased mineralization (Alizarin Red) and fat deposition (Oil Red O; Nile Red FACS analysis). When compared to undifferentiated MSCs, alkaline phosphatase mRNA was increased during osteoblastogenesis (day 7) by 12- and 27-fold (P<0.05) in the absence or presence of NECA respectively. Similarly, NECA significantly (P<0.0001) increased (day 12) C/EBPα, PPARγ and LPL expression from 11-, 8- and 25-fold to 65-, 30- and 150-fold respectively during adipogenesis. Compared to undifferentiated cells, NECA stimulated cAMP production increased 10-fold (P<0.05) in osteoblasts and 2-fold (P<0.05) in adipocytes. Osteoblasts also showed increased A2aR (8-fold; P<0.0001) and A2bR (2-fold; P<0.001) mRNA and protein (7- and 2-fold; P<0.05) expression, and an 8-fold change in A1R mRNA. Adipocytes, on the other hand showed increased A1R (>750-fold; P<0.001) and A2aR (25-fold; P<0.0001) mRNA and increased A1R (3-fold; P<0.05) protein expression.

This work suggests that osteoblast differentiation from MSCs is associated with increased A2aR and A2bR expression, whilst adipocyte differentiation is associated with A1R and possibly A2aR expression. These results show that ARs are differentially expressed as MSCs undergo specific lineage differentiation and targeting AR signal pathways may be useful in preventing or treating conditions in which there is insufficient bone or excessive adipocyte formation.