Expression of α2- and β-adrenoceptor subtypes in human islets of Langerhans

Abstract

Sequences from cDNA molecules encoding alpha 2-adrenoceptor subtype genes were subcloned into prokaryotic vectors and riboprobes generated to hybridise selectively with each of the human alpha 2C2-, alpha 2C4- and alpha 2C10-adrenoceptor subtype mRNA species. The riboprobes were labelled with either 32P or digoxigenin and used to study the expression of alpha 2-adrenoceptor subtypes in sections of human pancreas, in isolated human islets of Langerhans and in clonal HIT-T15 pancreatic beta-cells. Using a ribonuclease protection assay protocol, expression of mRNA species encoding both alpha 2 C2 and alpha 2 C10 was demonstrated in preparations of isolated human islets of Langerhans. mRNA encoding alpha 2C4 was also detected in human islet RNA, using reverse transcription coupled with the polymerase chain reaction. In situ hybridisation was then employed to examine the distribution of each alpha 2-adrenoceptor subtype in sections of human pancreas. All three subtypes of alpha 2-adrenoceptor mRNA were identified in sections of formalin-fixed, paraffin-embedded human pancreas using riboprobes labelled with digoxigenin. Although some labelling of the three alpha 2-adrenoceptor mRNA subtypes was seen in the islets, the labelling was most intense in the exocrine tissue of the pancreas for each receptor subtype. The specificity of the digoxigenin-labelled RNA probes was confirmed in several control tissues and by in situ hybridisation studies using sense probes in the pancreas. The integrity of the pancreas sections was confirmed by in situ hybridisation with an antisense riboprobe derived from human insulin cDNA. The results demonstrate that multiple alpha 2-adrenoceptor subtypes are expressed in human pancreas. Both the exocrine and endocrine cells express more than one receptor subtype, although the islets stain less intensely than the bulk of the tissue suggesting that the islet cells may have lower levels of expression than the acinar tissue. The presence of alpha 2-adrenoceptor subtype mRNA species in pancreatic beta-cells was confirmed by Northern blotting of RNA extracted from the clonal beta-cell line, HIT-T15. Transcripts encoding each of the three cloned alpha 2-adrenoceptor subtypes were detected in HIT-T15 cells. Hybridisation of sections of human pancreas with oligodeoxynucleotide probes designed to hybridise with beta 2-adrenoceptor mRNA revealed expression of this species in islet beta-cells but not in the exocrine tissue of the pancreas.

Probing cell type–specific functions of Gi in vivo identifies GPCR regulators of insulin secretion

“…39 and our unpublished observations), but whether local synthesis, storage, and release can indeed increase local T1AM concentration remains to be determined. TAAR1 and ADRA2A are expressed in human islets (Supplemental Figure 6) (40), and regardless of whether T1AM is a physiological stimulator of insulin release via Taar1 or an inhibitor of insulin release via Adra2a, our results support the notion that pharmacological agonism of Taar1 and/or antagonism of Adra2a might be explored to augment insulin secretion for therapeutic purposes.…”

Possible modulatory effect of endogenous islet catecholamines on insulin secretion

“…Conversely, P and T diminished insulin secretion by 40-49% and 51-45%, respectively, with the doses currently employed. As shown by other authors, the uneven effect of adrenergic antagonists could be ascribed to the relative abundance or activity of α 2 -adrenoceptors in B-cells, as compared with α 1 -and β 2 -adrenoceptors [5][6][7][8]. On the other hand, Schuit et al showed that P was ineffective in both a and B-cells [31]; such discrepancy with our results can be attributed to the method used in each case.…”

“…Catecholamines (CAs) contribute to this mechanism by exerting a direct and dual effect on the B-cell to induce either inhibition or stimulation of insulin secretion through their interaction with α 2 or α 1 and β 2 adrenergic receptors, respectively [3,4]. Since islet B-cells have more α 2 than α 1 and β 2 adrenergic receptors, physiological concentrations of CAs will bind mainly to the α 2 population receptors and thus inhibit insulin secretion [5][6][7][8].…”

Peroxisome proliferator-activated receptor γ coactivator-1-dependent uncoupling protein-2 expression in pancreatic islets of rats: a novel pathway for neural control of insulin secretion

“…In contrast, norepinephrine (NE) released by sympathetic terminals stimulates beta-cell α2 adrenergic receptors that acting through G i or G 0 proThe role played by neural inputs on beta-cell function has been a matter of intense investigation over the latest forty years [1]. The highest effect is believed to be exerted by parasympathetic fibres originated at the teins negatively modulate adenyl cyclase activity, reducing cAMP production and, ultimately, insulin secretion [7,8,9].…”