We have developed a panel of rabbit polyclonal antipeptide antibodies against the five human somatostatin receptor subtypes (hSSTR1-5) and used them to analyze the pattern of expression of hSSTR1-5 in normal human islet cells by quantitative double-label confocal fluorescence immunocytochemistry. All five hSSTR subtypes were variably expressed in islets. The number of SSTR immunopositive cells showed a rank order of SSTR1 > SSTR5 > SSTR2 > SSTR3 > SSTR4. SSTR1 was strongly colocalized with insulin in all β-cells. SSTR5 was also an abundant isotype, being colocalized in 87% of β-cells. SSTR2 was found in 46% of β-cells, whereas SSTR3 and SSTR4 were relatively poorly expressed. SSTR2 was strongly colocalized with glucagon in 89% of α-cells, whereas SSTR5 and SSTR1 colocalized with glucagon in 35 and 26% of α-cells, respectively. SSTR3 was detected in occasional α-cells, and SSTR4 was absent. SSTR5 was preferentially expressed in 75% of SST-positive cells and was the principal δ-cell SSTR subtype, whereas SSTR1-3 were colocalized in only a few δ-cells, and SSTR4 was absent. These studies reveal predominant expression of SSTR1, SSTR2, and SSTR5 in human islets. β-Cells, α-cells, and δ-cells each express multiple SSTR isoforms, β-cells being rich in SSTR1 and SSTR5, α-cells in SSTR2, and δ-cells in SSTR5. Although there is no absolute specificity of any SSTR for an islet cell type, SSTR1 is β-cell selective, and SSTR2 is α-cell selective. SSTR5 is well expressed in β- cells and δ-cells and moderately well expressed in α-cells, and thereby it lacks the islet cell selectivity displayed by SSTR1 and SSTR2. Subtype- selective SSTR expression in islet cells could be the basis for preferential insulin suppression by SSTR1-specific ligands and of glucagon inhibition by SSTR2-selective compounds.
ASJC Scopus subject areas
- Internal Medicine
- Endocrinology, Diabetes and Metabolism