(DCP086) MECHANISMS OF CONTROL OF PANCREATIC β-CELL PROLIFERATION BY NUTRIENTS

Background: Both forms of diabetes are characterized by a loss of pancreatic β cells. Hence, increasing β-cell mass is considered a promising therapeutic approach. Under nutrient excess, β-cell mass expands to maintain normoglycemia, partly via replication of existing β cells. In the presence of high glucose, we showed that the mono-unsaturated fatty acid oleate increases β-cell proliferation. Single-cell RNA sequencing analyses of oleate-cultured islets suggested a role of reactive oxygen species (ROS), the antioxidant enzymes peroxiredoxins, and the transcription factor MYC in oleate-induced β-cell proliferation, which was confirmed in functional studies.
This project aims to test the hypothesis that ROS/peroxiredoxin signaling via MAPK/MYC promotes oleate-induced β-cell proliferation.

METHODS AND RESULTS: Isolated human or adult male rat islets were exposed to glucose (2.8 - 16.7mM) with or without oleate (0.25 - 0.5mM) for 48 hours. Proliferative β cells were detected by staining for c-peptide and the proliferative marker MKi67 and quantified by flow cytometry. To block the MAPK pathway, islets were treated with the MEK1/2 inhibitor, U0126 (10uM).

In human islets, oleate (OL) increased β-cell proliferation compared to glucose (GLU) alone (11.1mM GLU= 0.99+/-0.36%, 11.1mM GLU+0.5mM OL= 3.32+/-1.35%, n=5). To assess the effect of glucose concentration on oleate-induced β-cell proliferation in rat islets, a glucose-dose response with or without 0.25 or 0.5mM oleate was performed. Oleate dose-dependently potentiated β-cell proliferation at all glucose concentrations tested (2.8mM GLU= 0.55+/-0.15%, +0.25mM OL= 1.52+/-0.33%, +0.5mM OL= 3.95+/-0.57%; 11.1mM GLU= 0.55+/-0.11%, +0.25mM OL= 1.2+/-0.10%, +0.5mM OL= 2.72+/-0.47%; 16.7mM GLU= 0.65+/-0.21%, +0.25mM OL= 1.62+/-0.46%, +0.5mM OL= 2.7+/-0.35%, n=4). Inhibition of the MAPK pathway decreased oleate-induced β-cell proliferation (16.7mM GLU= 3.56+/-0.84%, +0.5mM OL= 8.25+/-1.81%, +0.5mM OL+U0126= 2.08+/-0.59%, n=6).

Conclusion: We conclude that the mitogenic effect of oleate is conserved in humans and that oleate increases β-cell proliferation independently of glucose concentration. We provide evidence that the MAPK signaling pathway is likely to be involved as a downstream effector of ROS/peroxiredoxin signaling in oleate-induced β-cell proliferation.