Differential expression of E-cadherin at the surface of rat β-cells as a marker of functional heterogeneity

Abstract

The aim of this study was to assess whether the expression of E-cadherin at the surface of rat b-cells is regulated by insulin secretagogues and correlates with insulin secretion. When cultured under standard conditions, virtually all b-cells expressed E-cadherin observed by immunofluorescence, but heterogeneous staining was observed. Using fluorescence-activated cell sorting (FACS), two b-cell sub-populations were sorted: one that was poorly labeled ('ECad-low') and another that was highly labeled ('ECad-high'). After 1-h stimulation with 16 . 7 mM glucose, insulin secretion (reverse hemolytic plaque assay) from individual ECad-high b-cells was higher than that from ECad-low b-cells. Ca 2C-dependent b-cell aggregation was increased at 16 . 7 mM glucose when compared with 2 . 8 mM glucose. E-cadherin at the surface of b-cells was increased after 18 h at 11 . 1 and 22 . 2 mM glucose when compared with 2 . 8 mM glucose, with the greatest increase at 22 . 2 mM glucoseC0 . 5 mM isobutylmethylxanthine (IBMX).While no labeling was detected on freshly trypsinized cells, the proportion of stained cells increased in a time-dependent manner during culture for 1, 3, and 24 h. This recovery was faster when cells were incubated at 16 . 7 vs 2 . 8 mM glucose. Cycloheximide inhibited expression of E-cadherin at 2 . 8 mM glucose, but not at 16 . 7 mM, while depolymerization of actin by either cytochasin B or latrunculin B increased surface Ecadherin at low glucose. In conclusion, these results show that expression of E-cadherin at the surface of islet b-cells is controlled by secretagogues including glucose, correlates with insulin secretion, and can serve as a surface marker of b-cell function.

Cadherin Engagement Improves Insulin Secretion of Single Human β-Cells

“…First, we showed that cadherin expression in human islet cells was not affected by insulin secretagogues, including glucose, in contrast to what is seen in rat islet cells (6). This discrepancy is not understood, but is not surprising given the increasing published evidence of structural differences between rodent and human islet cells (24).…”

“…In this regard, it has been known that insulin release from intact islets or aggregated islet cells is increased compared with that of isolated islet cells (3)(4)(5). Using a reverse hemolytic plaque assay (RHPA) to analyze insulin secretion at the single-cell level, it has been shown that only one contact between homologous rat b-cells was sufficient to markedly increase glucoseinduced insulin secretion (6). More recently, similar results were obtained with isolated human b-cells (7).…”

“…Particular attention should be paid to the members of the cadherin family and especially to E-cadherin. This molecule was found to be downregulated in secretory defective b-cells (2,12,13) and the intensity of expression at the surface of isolated b-cells correlated with their secretory ability (6). Furthermore, treatment of b-cells with an anti-E-cadherin blocking antibody affected intracellular Ca 2+ levels and insulin secretion (14).…”

Insulin secretion from human beta cells is heterogeneous and dependent on cell-to-cell contacts

“…Specifically, beta cells are interconnected by gap junctions, which form channels across the extracellular space and allow direct exchanges of small cytoplasmic molecules, ensuring electrical coupling and promoting insulin secretion [16]. Adhesion molecules such as integrins, cadherins and neural cell adhesion molecule have been described in islets and they somehow influence insulin secretion and are also involved in maintaining correct islet architecture [17][18][19].…”

In vivo functional heterogeneity among β-cells

“…[1][2][3] Based on surface expression for the polysialylated form of the Neural Cell Adhesion Molecule (PSA-NCAM), we have characterized two groups of β-cells: β high -cells expressing high levels of surface PSA-NCAM and β low -cells expressing low levels of surface PSA-NCAM and investigated their physiological relevance in animal models of increased insulin demand. We showed that β high -cells were highly responsive to glucose and to other secretagogues like leucine and GLP-1 contrary to β low -cells which were poorly responsive.…”