Impact of integrin-matrix interaction and signaling on insulin gene expression and the mesenchymal transition of human beta-cells.

A critical shortage of donor pancreata currently prevents the development of a universal cell-based therapy for type I diabetes. The ex vivo expansion of insulin-producing beta-cells offers a potential solution but is problematic due to the inherent tendency of these cells to transition into mesenchymal-like cells that are devoid of function. Here, we demonstrate for the first time that exposure to elements of the extracellular matrix (ECM) directly potentiates the mesenchymal transition of cultured fetal beta-cells and causes associated declines in insulin gene expression. Individual ECM constituents varied in their ability to induce such responses, with collagen-IV (C-IV) and fibronectin inducing strong responses, whereas laminin-1 had no significant effect. Mesenchymal transition and concomitant losses in insulin gene expression observed on C-IV were found to be dependent on beta(1)-integrin ligation and were augmented in the presence of hepatocyte growth factor. Importantly, selective inhibition of c-Src, c-Jun N-terminal kinase (JNK), and extracellular signal-regulated kinase (ERK) prior to exposure to C-IV prevented mesenchymal transition and effectively preserved insulin expression. Fetal beta-cells undergoing mesenchymal transition were found to acquire alpha(1)beta(1) expression, and ligation of this integrin then promotes declines in insulin gene expression and a marked increase in beta-cell motility. Inhibition of Src-, ERK-, or JNK-dependent signaling combined with the selective regulation of matrix exposure may ultimately facilitate the development of more effective beta-cell expansion protocols.

Cytotoxic and mutagenic action of 193-nm and 213-nm laser radiation.

PURPOSE: To compare the cytotoxic and mutagenic effect of 213-nm and 193-nm laser radiation on cultured mammalian cells. METHODS: Chinese hamster lung (V79) cells were exposed to 193-nm radiation from an argon fluorine excimer laser or 213-nm radiation from a 5th harmonic Nd:YAG laser. The cytotoxic action of the lasers was compared by determining the number of V79 cell colonies that formed 1 week after irradiating cells with different doses of 193-nm or 213-nm laser radiation or with continuous wave 254-nm radiation. The cytotoxic action of the lasers on primary cultures of human corneal fibroblasts was also compared. The mutagenic potential of the lasers was compared by measuring the number of ouabain or 6-Thioguanine(6TG)-resistant V79 mutants that formed after exposing V79 cells to 193-nm or 213-nm radiation. RESULTS: The dose of 193-nm laser radiation that resulted in 37% survival (D37) of V79 cells was estimated to be 11.3 mJ/cm2 compared to 3.2 mJ/cm2 for 213-nm laser radiation and 1.2 mJ/cm2 for 254-nm UV radiation. The mean number of ouabain-induced mutants induced at the D37 for 193-nm, 213-nm, and 254-nm laser radiation were 28, 166, and 279 mutants/10(7) cells, respectively. Continuous wave 254-nm radiation induced 6TG-resistant colonies, but there was no significant induction of 6TG-resistant mutants by either laser. CONCLUSIONS: Although the in vitro data presented herein may or may not be meaningful to humans, the 213-nm Nd:YAG laser was more cytotoxic and mutagenic than the 193-nm excimer laser on cultured mammalian cells but was less cytotoxic and mutagenic than 254-nm radiation.