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Changes in adenosine A1- and A2-receptor expression during adipose cell differentiation
J D Børglum1, G Vassaux, B Richelsen
1Department of Endocrinology and Metabolism, Aarhus Amtssygehus, Aarhus University Hospital, Denmark.
Abstract:
Two adenosine receptors A1 and A2 are associated with either stimulation (A2) or inhibition (A1) of adenylate cyclase. Using the clonal cell line Ob1771, we have studied the expression of the two receptors during the process of adipose conversion accelerated by exposure to dexamethasone and 3-isobutyl-l-methylxanthine (IBMX) during the first 3 days post-confluence. The effects mediated by the two receptors on preadipocyte differentiation and adipocyte metabolism were also investigated. The two adenosine agonists NECA and PIA were used as preferential agonists of the A2- and A1-receptor, respectively. In preadipose cells (just confluent), both of the mouse clonal line and human primary culture, NECA dose-dependently stimulated cAMP production with a significant higher potency (P < 0.01) than did PIA. In adipose cells (16-day post-confluent) NECA was found to exert a biphasic effect on forskolin-stimulated cAMP production: i.e., NECA was clearly inhibitory in the femto- to picomolar concentration range whereas this effect gradually diminished at higher concentrations. The effect of PIA in 16-day post-confluent adipose cells however, was purely inhibitory on both cAMP production (IC50: 33.52 +/- 0.44 fM) and lipolysis (64% +/- 7%; P < 0.01). These findings were corroborated by Northern blot analysis which revealed A1-receptor mRNA to be exclusively expressed in the mature adipocytes, whereas A2-receptor mRNA gradually declined during the differentiation process except in 16-day post-confluent cells. In addition, NECA significantly enhanced the effect of corticosterone-induced differentiation by 46.8% (P < 0.05) but failed to have any adipogenic potency acting either alone or in concert with carbaprostacyclin (cPGI2). Thus, endogenous adenosine may have a bimodal action on adipose tissue metabolism mediated through stimulatory A2- and inhibitory A1-receptors, respectively, as a function of adipose conversion.
Insights
Adenosine receptors A1 and A2 play dual roles in fat cell development. A2 receptors stimulate, while A1 receptors inhibit processes like cAMP production and lipolysis during adipose conversion.
Area of Science:
- Biochemistry
- Cell Biology
- Endocrinology
Background:
- Adenosine receptors, specifically A1 and A2, modulate adenylate cyclase activity, influencing cellular signaling pathways.
- Understanding adenosine receptor roles is crucial for deciphering adipocyte differentiation and metabolism regulation.
Purpose of the Study:
- To investigate the expression and function of adenosine A1 and A2 receptors during adipocyte differentiation.
- To elucidate the impact of these receptors on preadipocyte differentiation and mature adipocyte metabolism.
Main Methods:
- Utilized the Ob1771 clonal cell line and human primary cultures for studying adipose conversion.
- Employed adenosine agonists (NECA and PIA) to selectively stimulate A2 and A1 receptors, respectively.
- Measured cAMP production and lipolysis; performed Northern blot analysis for receptor mRNA expression.
Main Results:
- In preadipocytes, NECA (A2 agonist) stimulated cAMP production more potently than PIA (A1 agonist).
- In mature adipocytes, NECA showed biphasic effects on cAMP, while PIA strongly inhibited cAMP production and lipolysis.
- A1 receptor mRNA was found in mature adipocytes, whereas A2 receptor mRNA declined during differentiation, with an exception in 16-day post-confluent cells.
Conclusions:
- Adenosine receptors exhibit distinct expression patterns and functional roles during adipose conversion.
- Endogenous adenosine likely exerts a bimodal influence on adipose tissue metabolism via A1 and A2 receptors, dependent on the stage of differentiation.