The role of transforming growth factor-beta (TGF-) in the transdifferentiation of islets of Langerhans to duct-like epithelial structures /

Abstract

The process of islet isolation destroys extracellular matrix and eliminates potentially important inter-cellular relationships. We have previously shown that isolated islets embedded in a type I collagen gel, in the presence of a defined medium, undergo a phenotypic switch to duct-like epithelial structures through a process known as transdifferentiation. The aim of this study was to characterize the specific effectors implicated in islet cell transdifferentiation in order to better understand the factors that confer morphogenetic stability on cells in the isolated islets.We demonstrated cytoplasmic immunoreactivity for TGF-beta isoforms over 8 days post isolation using canine islets. Islet-to-duct epithelial transdifferentiation was correlated with the total amount of TGF-beta and was maximal at 48 h of culture. Up regulation of TGF-betaRI and TGF-betaRII expression on day 2 post-isolation was demonstrated by immunohistochemistry and Western blot analysis, and correlated temporally with the induction of cell proliferation. The presence of TGF-beta1 in culture supernatants was detected using the PAI/L assay. The peak TGF-beta1 level was 10.94 +/- 2.27 pM (active form) and 52.23 +/- 1.57 pM (total TGF-beta) at 48h. Addition of exogenous TGF-beta1 at different concentrations caused an accelerated and more pronounced epithelial transformation at 5--10 ng/mL compared to lower concentrations (0.5--1 ng/mL).These studies confirm the biological potential of islets of Langerhans to transdifferentiate to duct epithelial structures. TGF-beta signal transduction appears to play an important role in this process