Binding of the fibronectin-mimetic peptide, PR-b, to α ₅β1 on pig islet cells increases fibronectin production and facilitates internalization of PR-b functionalized liposomes

Islet transplantation is a promising treatment for type 1 diabetes. Recent studies have demonstrated that human islet allografts can restore insulin independence to patients with this disease. As islet isolation and immunotherapeutic techniques improve, the demand for this cell-based therapy will dictate the need for other sources of islets. Pig islets could provide an unlimited supply for xenotransplantation and have shown promise as an alternative to human islet allografts. However, stresses imposed during islet isolation and transplantation decrease islet viability, leading to loss of graft function. In this study, we investigated the ability of a fibronectin-mimetic peptide, PR-b, which specifically binds to the R5β1 integrin, to re-establish lost extracellular matrix (ECM) around isolated pig islets and increase internalization of liposomes. Confocal microscopy and Western blotting were used to show the presence of the integrin α₅β1 on the pig islets on day 0 (day of isolation) as well as on different days of islet culture. Islets cultured in medium supplemented with free PR-b for 48 h were found to have increased levels ofECMfibronectin secretion compared to islets in normal culture conditions. Using confocal microscopy and flow cytometry, we found that PR-b peptide-amphiphile functionalized liposomes delivered to the pig islets internalized into the cells in a PR-b concentration dependent manner and nonfunctionalized liposomes showed minimal internalization. These studies proved that the fibronectin-mimetic peptide, PR-b, is an appropriate peptide bullet for applications involving α₅β1 expressing pig islet cells. Fibronectin production stimulated through α5β1 PR-b binding may decrease apoptosis and therefore increase islet viability in culture. In addition, PR-b peptide-amphiphile functionalized liposomes may be used for targeted delivery of different agents to pig islet cells.