Fig. 5: Neuregulin1 promotes β cell proliferation in an ERBB2/3-ERK dependent manner.

a, b Immunoblots (a) and corresponding quantification (b) of total and phosphorylated forms of ERBBs, AKT, and ERK in MIN6 cells treated with either PBS or indicated concentrations of recombinant protein encompassing the Neuregulin1 α type EGF-like domain (rNRG1α) for 30 min. Tubulin served as a loading control. The average value of the ratio of phosphorylated to non-phosphorylated protein in samples from the group treated without rNRG1, normalized by the expression level of TUBULIN, was set to 1. Data represent mean ± SEM; n = 5 (pERBB1/ERBB1, pERBB4/ERBB4, pAKT/AKT, and pERK/ERK) and 6 (pERBB2/ERBB2 and pERBB3/ERBB3) per group. The samples derive from the same experiment, and blots were processed in parallel. This experiment was repeated at least five times independently. c Percentage of Ki-67-positive cells in isolated mouse islets treated with control PBS or rNRG1α in the absence or presence of indicated inhibitors. Inhibitors were added to the medium 30 min before rNRG1α stimulation (10 nM, 24 h). LPT; lapatinib, TX1; TX1-85-1, GEFI; gefitinib, LY; LY294002, SCH; SCH772984. Data represent mean ± SEM; n = 18 (PBS), 19 (rNRG1α), and 5 (rNRG1α plus each inhibitor) islets per group. d Glucose-stimulated insulin secretion. Islets were stimulated for 1 h with either low (2.5 mM) or high (25 mM) glucose in the absence or presence of rNRG1α (10 nM). Data represent mean ± SEM; n = 4 islets per group. No statistically significant differences were found between the two groups. An unpaired Student’s t test (b, d) and a one-way ANOVA (c) and were performed.