Cadherin Engagement Protects Human β-Cells from Apoptosis

Abstract

The aim of this study was to assess the expression of different types of cadherins in human islets and their role in human β-cell apoptosis. Expression of E-, N-, and P-cadherins was studied by immunofluorescence on pancreas sections and islet cells, and by Western blotting on protein extracts of isolated islets and islet cells. The effects of specific cadherins on cell adhesion and apoptosis were studied using chimeric proteins containing functional E-, N-, or P-cadherin ectodomains fused to Fc fragment of Ig (E-cad/Fc, N-cad/Fc, and P-cad/Fc) and immobilized on glass substrate. β-Cells were identified by immunofluorescence for insulin and apoptotic cells by terminal deoxynucleotide transferase-mediated 2'-deoxyuridine, 5'-triphosphate nick-end labeling. By immunofluorescence, we showed that E- and N-, and not P-, cadherins were expressed at the surface of islet cells. By triple staining, we showed that E-cadherin was expressed at similar extent in β- and α-cells, whereas N-cadherin was preferentially expressed in β-cells. These results were confirmed by Western blot analysis using protein extracts from fluorescence-activated cell sorting-sorted β- and non-β-cells. Adhesion tests showed that the affinity of islet cells for E-cad/Fc and N-cad/Fc and not for P-cad/Fc was increased compared with control. By terminal deoxynucleotide transferase-mediated 2'-deoxyuridine, 5'-triphosphate nick-end labeling, we showed that the percentage of apoptotic cells was lower in aggregated β-cells compared with single β-cells and that attachment to E-cad/Fc and N-cad/Fc and not to P-cad/Fc decreased apoptosis of single β-cells compared with control. Our results show that at least E- and N-cadherins are expressed at the surface of human β-cells and that these adhesion molecules are involved in the maintenance of β-cell viability.

Cadherin Engagement Improves Insulin Secretion of Single Human β-Cells

“…As expected from our previous study (21), Western blotting showed that expressions of N-and E-cadherins were low immediately after Accutase treatment and time-dependently increased after incubation ( Fig. 1).…”

“…Under the studied conditions, E-cad/Fc had more effect that N-cad/Fc in increasing glucoseinduced insulin secretion. The same difference was previously observed when similar experiments were conducted to assess the effect of cadherin engagement on apoptosis of b-cells (21). The reason for the differential effects of N-and E-cadherins is not yet understood.…”

“…Using this strategy, we have previously shown that E-cadherin and N-cadherin engagements were able to reduce apoptosis in isolated b-cells (21). These two cadherin types were shown to be expressed at the surface of human b-cells (21). In this study, we used a similar strategy aimed to show that stimulation of insulin secretion was able to promote adhesion of b-cells to cadherins and that cadherin engagement was able to affect insulin secretion.…”

“…To overcome this difficulty, we worked with isolated b-cells obliged to engage one type of adhesion molecule, immobilized on an inert substrate. Using this strategy, we have previously shown that E-cadherin and N-cadherin engagements were able to reduce apoptosis in isolated b-cells (21). These two cadherin types were shown to be expressed at the surface of human b-cells (21).…”

Vascular instruction of pancreas development

“…Secondary wave endocrine cells primarily differentiate into -cells, along with other endocrine lineages, delaminate from the epithelium and coalesce into small islet-like clusters that progressively form larger islet aggregates during postnatal development. Cell-cell interactions both between -cells, and between -cells and ECs are important for islet development and insulin secretion (Nikolova et al, 2006;Parnaud et al, 2011). Interactions between -cells within islets, occurring via EphA-ephrin A signaling, were shown to reduce insulin secretion under conditions of low glucose and to enhance secretion when blood glucose levels increased (Konstantinova et al, 2007).…”