Emergent Multi-Cellular Properties Regulating Pancreatic Islet Function

About This Grant

PROJECT SUMMARY Type2 diabetes mellitus (T2DM) is caused by a failure of insulin-secreting 13-cells to secrete sufficient insulin following increased insulin resistance under metabolic stress. During increased insulin demand under metabolic stress 13-cells show adaptation to increase insulin release, which includes increasing the insulin release by each 13-cell. However, the mechanisms underlying this 13-cell adaptation and its failure in T2DM are poorly understood. It has long been known that 13-cells are heterogenous in their capacity to secrete insulin. We previously demonstrated mechanistically how distinct sub-populations of 13-cells with differing patterns of electrical activity can influence the dynamics and glucose-regulation of islet electrical activity and insulin secretion. However, it is unclear how sub-populations of 13-cells influence islet adaptation under metabolic stress, and whether these subpopulations are more susceptible to dysfunction during T2DM development In part this has been due to a lack of tools to genetically mark and track these sub-populations of 13-cells. We have developed an overall hypothesis: that 'functionally adapted' B-cells exist in small numbers within the healthy islet that influence islet function, where this subset is increased in number under metabolic stress but is susceptible to progressing to a dysfunctional state and thus contributing to islet dysfunction during T2DM. To test this overall hypothesis, we will conduct the following specific aims: 1 ): Characterize the molecular properties underlying heterogeneous 13-cell glucose responses within the islet, by using a novel CAMPARI activity reporter to mark active cells and perform detailed functional and molecular analysis. 2): Determine the fate of 13-cells with heterogeneous glucose responses under metabolic stress, by using a novel genetic reporter for basal-active cells together with intravital imaging and longitudinal Ca2' imaging. 3): Determine the role of activity-responsive genes in maintaining 13-cell heterogeneity, by tracking active cells in the presence and absence of cFos activity and characterizing their response to metabolic stress. By understanding the characteristics of heterogenous 13-cell populations within the islet, we will gain fundamental understanding how islet function is regulated in both healthy conditions and under metabolic stress. Thus, therapeutic agents that can target a specific population of 'functionally adapted' 13-cells, including targets we will identify in this project, may provide new ways to control the islet under pathogenic conditions.