High-content screening identifies a role for Na+ channels in insulin production

• Published in: Royal Society open science Vol. 2; no. 12; p. 150306
• Main Authors: Szabat, Marta, Modi, Honey, Ramracheya, Reshma, Girbinger, Vroni, Chan, Forson, Lee, Jason T. C., Piske, Micah, Kamal, Sepehr, Carol Yang, Yu Hsuan, Welling, Andrea, Rorsman, Patrik, Johnson, James D.
• Format: Journal Article
• Language: English
• Published: England The Royal Society Publishing 01.12.2015; The Royal Society
• Subjects: Cellular And Molecular Biology; High-Content Screening; Insulin Synthesis; Islet Beta-Cells; Live-Cell Imaging; Sodium Channels; islet beta-cells; sodium channels; insulin synthesis; live-cell imaging; high-content screening
• ISSN: 2054-5703; 2054-5703
• DOI: 10.1098/rsos.150306

Insulin production is the central feature of functionally mature and differentiated pancreatic β-cells. Reduced insulin transcription and dedifferentiation have been implicated in type 2 diabetes, making drugs that could reverse these processes potentially useful. We have previously established ratiometric live-cell imaging tools to identify factors that increase insulin promoter activity and promote β-cell differentiation. Here, we present a single vector imaging tool with eGFP and mRFP, driven by the Pdx1 and Ins1 promoters, respectively, targeted to the nucleus to enhance identification of individual cells in a high-throughput manner. Using this new approach, we screened 1120 off-patent drugs for factors that regulate Ins1 and Pdx1 promoter activity in MIN6 β-cells. We identified a number of compounds that positively modulate Ins1 promoter activity, including several drugs known to modulate ion channels. Carbamazepine was selected for extended follow-up, as our previous screen also identified this use-dependent sodium channel inhibitor as a positive modulator of β-cell survival. Indeed, carbamazepine increased Ins1 and Ins2 mRNA in primary mouse islets at lower doses than were required to protect β-cells. We validated the role of sodium channels in insulin production by examining Nav1.7 (Scn9a) knockout mice and remarkably islets from these animals had dramatically elevated insulin content relative to wild-type controls. Collectively, our experiments provide a starting point for additional studies aimed to identify drugs and molecular pathways that control insulin production and β-cell differentiation status. In particular, our unbiased screen identified a novel role for a β-cell sodium channel gene in insulin production.