Differential function of the alpha2A-adrenoceptor and Phosphodiesterase-3B in human adipocytes of different origin.
OBJECTIVE: Human adipocytes can be obtained in vitro by differentiation of human preadipocytes or mesenchymal stem cells ( hMSC). Although functionally similar to freshly isolated cells, no detailed comparison of the different cell types has been performed. The antilipolytic alpha2A-adrenoceptor (AR) and the cAMP-degrading enzyme Phosphodiesterase-3B (PDE3B) have been implicated in the fine-tuning of lipolysis but little is known regarding their role in human adipocytes nor whether their expression and/or function differs in fat cells from different precursors. METHODS: The effects of alpha2A-AR and PDE3B inhibition in mature adipocytes was determined and compared to that in differentiated preadipocytes and hMSC-derived fat cells. Gene expression was determined by real-time PCR and protein expression by Western blot. RESULTS: Noradrenaline (NA) stimulated lipolysis in preadipocytes and mature adipocytes but markedly reduced lipolysis in differentiated hMSC derived-adipocytes. This was due to a potent stimulation of alpha2A-AR since co-incubation with NA and the alpha2-AR-inhibitor yohimbine restored NA-induced lipolysis. The order of Yohimbine response was hMSC>preadipocytes>mature adipocytes. Although alpha2-AR mRNA expression was highest in mature adipocytes there was no difference in alpha2A-AR protein levels between the cell types. In contrast, Galphai2 mRNA and protein expression was significantly higher in MSC-derived adipocytes, suggesting that differences in the response to alpha2A-AR inhibition reside at the postreceptor level. Incubation with the cAMP-analog 8-bromo(8b) cAMP increased lipolysis in hMSC-derived fat cells while co-incubation with the PDE3-specific inhibitor OPC3911 did not alter the lipolytic effect. In contrast, OPC3911 increased 8bcAMP-induced lipolysis significantly in preadipocytes and mature adipocytes. The response to PDE3B inhibition was; mature adipocytes>preadipocytes>hMSC a finding that correlated significantly with both PDE3B mRNA expression and enzymatic activity. CONCLUSION: Although differentiated adipocytes of different origins display similar functional characteristics there are important differences in the regulation of lipolysis with a marked alpha2A-AR and less pronounced PDE3B effect in fat cells from MSCs.[1]References
- Differential function of the alpha2A-adrenoceptor and Phosphodiesterase-3B in human adipocytes of different origin. Dicker, A., Kaaman, M., van Harmelen, V., Aström, G., Blanc, K.L., Rydén, M. International journal of obesity (2005) (2005) [Pubmed]
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