Endocrine Abstracts

Pluripotent mesenchymal stem cells (MSCs) have the capacity to differentiate into osteoblasts, adipocytes and chondrocytes and are characterised by expression of CD105, CD90 and CD73. CD73 is the enzyme that dephosphorylates AMP to adenosine. The role of adenosine in MSCs is unknown and we have thus investigated whether it plays a role in the differentiation process to osteoblasts.

MSCs, obtained from the bone marrow of 10 week old male rats, were expanded in tissue culture and used at passages 1–2. Cultures, induced to differentiate (into osteoblasts) and to mineralize were treated with adenosine receptor (AR) agonists. A2a, A2b and A3 but not A1 receptors were detectable by RT-PCR. AR agonists stimulated cAMP accumulation (radioimmunoassay) and the rank order of potency was NECA (universal AR agonist)>adenosine>CGS21680 (A2aR agonist); at 100 μM agonist, the respective increases were 100, 20 and 3.5-fold (P<0.001). Similarly, AR agonists also increased alkaline phosphatase (ALP) by up to 70% (P<0.001) after 2, 5 and 7 days of inducing osteoblast differentiation.

The A2b AR antagonist, MRS1706 reversed the stimulatory effects of NECA on ALP activity (P<0.001) whereas the A1 AR antagonist PSB36 was ineffective (P<0.385). Adenosine (100 μM) and NECA (10 μM) also increased (by up to 300%, P<0.003) mineralization (alizarin red staining of calcium deposits) of MSCs after 10 days of incubation. These findings thus indicate a functional predominance of the A2b receptor.

In summary, our data demonstrate the presence of functional adenosine receptors on rat MSCs; the absence of the A1 receptor (by RT-PCR) needs to be confirmed. Our findings suggest that adenosine may be a significant signalling molecule in regulating differentiation and mineralization of osteoblast precursors via possibly the A2b receptor. Targeting adenosine signal pathways may therefore benefit the treatment of osteoporosis and osteoarthritis, diseases that are associated with alterations in osteoblast function.