Integrin Signaling via RGD Peptides and Anti-β1 Antibodies Confers Resistance to Apoptosis in Islets of Langerhans

Abstract

Islet transplantation is associated with a high rate of early graft failure caused by early immune attack and poor functionality of islets. Apoptosis of islet cells appears soon after islet isolation and primarily involves the ␤-cell. The purpose of this study was to determine the effect of ligation to extracellular matrix (ECM) proteins on survival of the islets of Langerhans following islet isolation. Islets that had been cultured for 24 h on collagen type I showed an islet survival of 59.7 ؎ 8.7%, while islets that had been cultured on collagen type IV and laminin showed an islet survival of 88.6 ؎ 10.3 and 94.3 ؎ 5.6%, respectively. Islets that had been pretreated with anti-␤1 antibodies and argenin-glycin-aspartic acid (RGD) peptides showed a decrease in the level of apoptosis by a factor of 2.5 and 3.1, respectively, and an increase of phospho-Akt Ser 473 activity by a factor of 3.1 and 2.9, respectively, compared with untreated islets. When detached from their natural ECM surrounding in the pancreas, islet cells undergo apoptosis, unless islets are cultured on collagen IV or laminin or treated with anti-␤1 integrin antibodies or RGD peptides to mimic ECM ligation. These results indicate that inhibition of anoikis may offer opportunities to improve function and viability of islet cells. Diabetes 55:312-317, 2006 T ransplantation of islets of Langerhans has the potential to become a widely applicable treatment for type 1 diabetes. Unfortunately, islet transplantation is associated with a high rate of early graft failure (1-4), which is caused by early immune attack, poorly functioning islets that were presumably damaged during isolation, or both. Apoptosis of islet cells appears soon after islet isolation and primarily involves the ␤-cell (5).During islet isolation by collagenase treatment, during purification, and during pretransplanting culture, the microenvironment of the islet is destroyed. Extracellular matrix (ECM) is an important component of the islet microenvironment that prevents cellular stress, which could impair ␤-cell function and survival (6,7). The islet basement membrane is composed of the ECM proteins laminin, fibronectin, and collagen types I, III, IV, and V (8,9). Cell-matrix interactions are necessary because they provide signals for proliferation, differentation, and migration (10). These interactions are mediated by integrins, which are a diverse class of ␣␤ heterodimeric transmembrane receptors that form ligands for the ECM (10 -12).Cells disconnected from their ECM can undergo apoptosis by an integrin-mediated death signal called anoikis (6,13,14). The pancreatic cells express the integrins ␣3␤1, ␣5␤1, and ␣v␤3 (7,15), which are also known to bind argenin-glycin-aspartic acid (RGD) sequences on ECM molecules. Cell attachment mediated by the ␣5␤1 and the ␣v␤3 integrin promotes cell survival by upregulation of Bcl-2 (16,17). Integrins are believed to mediate survival by activating a specific signaling pathway. One of its ligands is integrin-linked kinase (ILK), which can phosphorylate...

Postnatal Pancreas of Mice Contains Tripotent Progenitors Capable of Giving Rise to Duct, Acinar, and Endocrine Cells In Vitro

“…Among these, laminins were found to induce Insulin gene expression and increase b-cell proliferation in islets from VEGF-A tissue-specific knockout mice that do not have normal amounts of laminin surrounding the b-cells [26]. Laminins also enhance survival and function (glucosestimulated insulin secretion) of isolated islets [28][29][30]. Laminins are complex proteins composed of three subunits (a, b and g) with sizes ranging from 400 to 800 kDa (depending on subunit composition) [31,32].…”

Islet Encapsulation: Strategies to Enhance Islet Cell Functions

“…For instance, glucose-stimulated insulin secretion is greater when islets are cultured on surfaces treated with ECM molecules such as collagen type I or IV, laminin, fibronectin, or arginineglycine-aspartate (RGD) peptides. 53,[114][115][116] These findings indicate that incorporation of these ECM factors on the surface of the encapsulation material may improve islet survival and function. The exploitation of integrin/ECM interactions may also prove to be a vital element in creating a viable bioartificial pancreas.…”

“…86,112,113 Additionally, islets cultured on surfaces treated with anti-b 1 or anti-a 1 antibodies show an increase in cell survival and glucose-stimulated insulin secretion. 53,[114][115][116] In addition to the use of integrin antibodies, ECM mimicry can be accomplished through incorporation of other ECM proteins and peptides.…”

THERAPY OF ENDOCRINE DISEASE: Islet transplantation for type 1 diabetes: so close and yet so far away

“…Some synthetic peptide epitopes have been identified that mimic the effect of ECM proteins by binding to the integrins. Arginine-glycine-aspartic acid is the most extensively studied epitope which reduces the apoptosis rate of islets (101). Transplantation of islets in a fibroblast populated collagen matrix is also used to prevent anoikis in which fibroblasts produce fibronectin and growth factors to enhance viability and functionality of the islets (102).…”