An elastin-based vasculogenic scaffold promotes marginal islet mass engraftment and function at an extrahepatic site

Abstract

In islet transplantation, one of the major obstacles to optimal engraftment is the loss of islet natural vascularization and islet-specific extracellular matrix (ECM) during the islet isolation process. Thus, transplanted islets must re-establish nutritional and physical support through formation of new blood vessels and new ECM. To promote this critical process, we developed an elastin-based vasculogenic and ECM-promoting scaffold engineered for extrahepatic islet transplantation. The scaffold by design consisted of type I collagen (Coll) blended with 20wt% of elastin (E) shown to promote angiogenesis as well as de novo ECM deposition. The resulting “CollE” scaffolds had interconnected pores with a size distribution tailored to accommodate seeding of islets as well as growth of new blood vessels. In vitro, CollE scaffolds enabled prolonged culture of murine islets for up to one week while preserving their integrity, viability and function. In vivo, after only four weeks post-transplant of a marginal islet mass, CollE scaffolds demonstrated enhanced vascularization of the transplanted islets in the epididymal fat pad and promoted a prompt reversal of hyperglycemia in previously diabetic recipients. This outcome was comparable to that of kidney capsular (KC) islet transplantation, and superior to that of islets transplanted on the control collagen-only scaffolds (Coll). Crucial genes associated with angiogenesis (VEGFA, PDGFB, FGF1, and COL3A1) as well as de novo islet-specific matrix deposition (COL6A1, COL4A1, LAMA2 and FN1) were all significantly upregulated in islets on CollE scaffolds in comparison to those on Coll scaffolds. Finally, CollE scaffolds were also able to support human islet culture in vitro. In conclusion, CollE scaffolds have the potential to improve the clinical outcome of marginal islet transplantation at extrahepatic sites by promoting angiogenesis and islet-specific ECM deposition.