Dynamic changes in β-cell electrical activity and [Ca²⁺] regulates NFATc3 activation and downstream gene transcription

Abstract

Diabetes results from insufficient insulin secretion as a result of dysfunction to β-cells within the islet of Langerhans. Elevated glucose causes β-cell membrane depolarization and action potential generation, voltage gated Ca²⁺ channel activation and oscillations in free-Ca²⁺ activity ([Ca²⁺]), triggering insulin release. Nuclear Factor of Activated T-cell (NFAT) is a transcription factor that is regulated by increases in [Ca²⁺] and calceineurin (CaN) activation. NFAT regulation links cell activity with gene transcription in many systems, and within the β-cell regulates proliferation and insulin granule biogenesis. However the link between the regulation of β-cell electrical activity and oscillatory [Ca²⁺], with NFAT activation and downstream transcription is poorly understood. In this study we tested whether dynamic changes to β-cell electrical activity and [Ca²⁺] regulates NFAT activation and downstream transcription. In cell lines, mouse islets and human islets, including those from donors with type2 diabetes, we applied both agonists/antagonists of ion channels together with optogenetics to modulate β-cell electrical activity. Both glucose-induced membrane depolarization and optogenetic-stimulation triggered NFAT activation, and increased transcription of NFAT targets and intermediate early genes (IEGs). Importantly only conditions in which slow sustained [Ca²⁺] oscillations were generated led to NFAT activation and downstream transcription. In contrast in human islets from donors with type2 diabetes NFAT activation by glucose was diminished, but rescued upon pharmacological stimulation of electrical activity. Thus, we gain insight into the specific patterns of electrical activity that regulate NFAT activation and gene transcription and how this is disrupted in diabetes.