Signal transduction pathways controllingIns2gene activity and β cell state transitions

Abstract

Pancreatic β cells exist in low and high insulin gene activity states that are dynamic on a scale of hours to days. Cells with higherIns2gene activity have a ‘mature’ β cell transcriptomic profile but are more fragile. Information remains unknown on the spatial relationship between these β cell states, their proteomic signatures, and the signaling mechanisms underlying state transitions. Here, we used live 3D imaging, mass spectrometry proteomics, and 48 targeted perturbations of β cell signaling pathways to comprehensively investigateIns2(GFP)HIGHandIns2(GFP)LOWβ cell states. We found that the twoIns2gene activity states exist in intact isolated islets, and cells in the same state were more likely to be nearer to each other. We report the proteomes of pure β cells to a depth of 5555 proteins and show that β cells with highIns2gene activity had increased transcriptional and mRNA processing factors, as well as increased translation rate. We identified activators of cAMP signaling (GLP1, IBMX) as powerful drivers of both GFP expression and transitions fromIns2(GFP)LOWto theIns2(GFP)HIGHstates. Okadaic acid and cyclosporine A had the opposite effects. This study provides new insight into the proteomic profiles and regulation of β cell states.Article highlightsWhy did we undertake this study?We sought to define the proteomic signatures of β cell maturity states and understand the mechanisms regulatingIns2gene activity and state transitions.What are the specific questions we wanted to answer?What are the islet spatial distribution and proteomic profiles of β cell maturity states?What are the molecular mechanisms controllingIns2gene activity and state transitions?What did we find?In intact islets, β cells in the highIns2state are more likely to be close to each other.IRF3, CLIP1, PAPSS2, YWHAZ, and AIFM1 are the most β cell-specific proteins in mouse islets.HighIns2activity coincides with upregulation of proteins involved in transcriptional regulation and processing.Agonists and drugs that augment cAMP signaling increaseIns2gene activity while calcineurin inhibitors cyclosporine A and okadaic acid reducedIns2gene activity.What are the implications of our findings?Cells with highIns2gene activity have evidence of increased transcriptional capacity. cAMP and calcineurin signaling regulateIns2gene activity and cell state transitions.