Reduced synchroneity of intra-islet Ca2+ oscillations in vivo in Robo-deficient β cells.

Melissa T Adams,Sutichot D Nimkulrat,Jennifer K Briggs,Joseph M Szulczewski,Jaeann M Dwulet,Matthew J Merrins,Melissa R Lyman,Raghavendra G Mirmira,Christopher A Reissaus,Erli Jin,Amelia K Linnemann,Richard Kp Benninger,Suzanne M Ponik,Sophia M Sdao,Barak Blum,Vira Kravets

doi:10.7554/elife.61308

Abstract

The spatial architecture of the islets of Langerhans is hypothesized to facilitate synchronized insulin secretion among β cells, yet testing this in vivo in the intact pancreas is challenging. Robo βKO mice, in which the genes Robo1 and Robo2 are deleted selectively in β cells, provide a unique model of altered islet spatial architecture without loss of β cell differentiation or islet damage from diabetes. Combining Robo βKO mice with intravital microscopy, we show here that Robo βKO islets have reduced synchronized intra-islet Ca2+ oscillations among β cells in vivo. We provide evidence that this loss is not due to a β cell-intrinsic function of Robo, mis-expression or mis-localization of Cx36 gap junctions, or changes in islet vascularization or innervation, suggesting that the islet architecture itself is required for synchronized Ca2+ oscillations. These results have implications for understanding structure-function relationships in the islets during progression to diabetes as well as engineering islets from stem cells.

Highlights

The islets of Langerhans, which comprise the endocrine pancreas, are highly organized micro-organs responsible for maintaining blood glucose homeostasis
We have previously shown that genetic deletion of Robo[1] and Robo[2] selectively in β cells using either Ins1Cre;Robo1Δ/ΔRobo2flx/flx or Tg(Ucn3-Cre);Robo1Δ/ΔRobo2flx/flx mice (Robo βKO) results in disrupted islet architecture and endocrine cell type sorting without affecting β 126 cell death or the expression of the β cell maturation markers MafA and Ucn[365]
We provide evidence for the importance of islet architecture for proper islet function in vivo

Summary

Introduction

The islets of Langerhans, which comprise the endocrine pancreas, are highly organized micro-organs responsible for maintaining blood glucose homeostasis. Direct empirical evidence supporting this hypothesis is lacking This is because of the fact that while most genetic mouse models that show abnormally disorganized islet architecture display defects in glucose homeostasis[19], the disrupted islet architecture is usually linked to either developmental defects in β cell differentiation or maturation[49,50,51,52,53,54,55,56,57,58,59,60] or to pathologies related to β cell damage in diabetes[20,21,61,62,63,64]. Unlike other models of disrupted islet architecture and endocrine cell type sorting in the islet, the β cells in the islets of Robo βKO express normal levels of markers for β cell differentiation, functional maturity, and regulation of glucose stimulated insulin secretion, and show normal β cell-intrinsic response to glucose. We reasoned that this model would allow us to test the role of islet architecture and endocrine cell type sorting in regulating synchronous [Ca2+]i oscillations in response to glucose among β cells in a fully differentiated, non-diabetic islet setting

Results

Discussion

Materials and Methods