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

Abstract

Insulin production is the central feature of functionally mature and differentiated pancreaticβ-cells. Reduced insulin transcription and dedifferentiation have been implicated in type2 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 promoteβ-cell differentiation. Here, we present a single vector imaging tool with eGFP and mRFP, driven by thePdx1andIns1promoters, 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 regulateIns1andPdx1promoter activity in MIN6β-cells. We identified a number of compounds that positively modulateIns1promoter 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 ofβ-cell survival. Indeed, carbamazepine increasedIns1andIns2mRNA in primary mouse islets at lower doses than were required to protectβ-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 andβ-cell differentiation status. In particular, our unbiased screen identified a novel role for aβ-cell sodium channel gene in insulin production.