Diabetes is a disease characterized by uncontrolled elevated blood glucose levels which affects close to 400 million people worldwide and leads to numerous diabetic complications. The inability of β-cells within the islets of Langerhans in the pancreas to secrete sufficient insulin for regulating blood glucose homeostasis is the common cause of most forms of diabetes. Clinical interventions to treat and cure diabetes broadly aim to restore or replace the dysfunctional pancreatic islets to provide a well regulated source of insulin secretion. However, it is important to note that current treatments are not cures and patients are still at increased risk from chronic diabetic complications, including kidney failure, cardiovascular diseases, blindness and limb amputations, as well as hypoglycemia that can cause coma and death. Many areas of research are trying to develop improved therapies or potential cures for diabetes, which include pharmacological treatments for elevating insulin secretion; artificial pancreas (closed loop glucose monitoring and insulin pump); and β-cell replacement strategies including islet transplantation or β-cell regeneration. Our lab's primary research goals involve understanding how the pancreatic islet functions and how the islet becomes disrupted during the development of diabetes. Our goal is to improve both clinical diagnostics and therapeutic treatments for patients with type 1 and type 2 diabetes, as well as rarer monogenic forms of diabetes.
We have several projects underway that move us towards achieving our research goals. A brief description of each is listed, but for more information, please contact Dr. Benninger.
Emergent multi-cellular properties regulating the islets of Langerans
Most tissues/organs exist as multicellular structures where physiological function is regulated through cellular interactions. We have a good understanding of the signaling processes within individual β-cells. However, β-cells do not act autonomously, but rather complex cellular interactions are necessary for the regulation of insulin secretion and its underlying signaling. Within the islet β-cells secrete insulin many-times more effectively than equivalent isolated β-cells, with characteristic pulsatile dynamics. One of our main areas of research is to understand how interactions between cells within the islet control the dynamics and regulation of insulin secretion.
Imaging multicellular dynamics. In studying how different cellular populations within the islet interact, we follow an approach whereby precise perturbations in signaling activity are introduced into a well-defined population of cells in the islet, utilizing transgenic mouse models, biomaterials, microfluidics and optogenetics. Quantitative confocal and two-photon microscopy, together with biochemical approaches, are applied to measure the effect of these perturbations across the islet and how they manifest in the overall islet response. These results can then be compared with predictions form quantitative models of islet function. We have shown how gap junction channel mediated electrical communciaiton is critical for the formation of coordinated electrical and insulin secretory dynamics.
Optogenetic control of islet function. Optogenetics is a powerful experimental technique that uses light to control the excitability of cells, via light activated ion channels. We can express light-activated ion channels in the islet to allow precise spatiotemporal control of electrical activity, as well as other cell-signaling processes. We use confocal microscopy, fluorescent indicators and biochemical assays in our pursuit of characterizing how different spatial subpopulations of beta cells regulate global islet function. We hope to discover and characterize how sub-populations of cells can act as a defacto pacemaker to disproportionately control the regulation and dynamics of islet electrical activity and insulin secretion. Localization of synchronized [Ca2+] oscillations to discrete regions in 2D. (A) False-color map indicating regions of high cross-correlation coefficient in a 2D aggregate, with respect to reference cells. Areas with no color (gray) have cells with no synchronization compared to the other regions. (B) Fluo4 time-courses of corresponding colored areas of synchronization depicted in A.
Left: Normal calcium oscillations in pancreatic islet at 11mM glucose (above) and corresponding heatmap (below) which shows synchronized oscillations throughout the islet.
Right: Channel rhodopsin 2 (ChR2) is expressed in pancreatic beta cells and light pulses are used to drive calcium oscillations (above) and entrain a new oscillatory frequency (below).
Computational models of islet function. Computational modeling of islet dynamics provides theoretical quantitative predictions that can then be tested in experimental applications. We use computational models to understand how the islet of Langerhans functions under different stimulatory conditions. Importantly we can also test how mutations linked to diabetes can impact islet dynamics and function.
Computational modeling of an overactive K-ATP channel mutation shows disruption of coordinated intracellular calcium oscillations. A comprehensive computational model of islet function shows well-coordinated intracellular calcium oscillations in control islets (left) and disrupted calcium signaling in islets in which 35% of the cells express an overactive K-ATP mutation (right). Adapted from Hraha et al., 2014, PLoS Computational Biology.
Predict novel ways to control islet function in diabetes. Glucose-stimulated insulin secretion from β-cells in the islet is regulated via a series of metabolic and electrical events. In diabetes, these mechanisms are disrupted. We utilize genetic, pharmacological and biophysical techniques to manipulate insulin secretion from β-cells in several models of diabetes. Specifically we have shown that modulating gap junction channel function can prevent the emergence of diabetes resulting from over-active KATP channels that cause neonatal diabetes (Kir6.2[ΔN30,K185Q]; see below). These findings were predicted through computational models of the islet incorporating changes in KATP channel function and gap junction channel activity.
Reducing gap junction coupling prevents hyperglycemia in an animal model of neonatal diabetes. Left: Mean time course of blood glucose levels in mice expressing an inducible neonatal diabetic mutation (Kir6.2[ΔN30,K185Q]; black open diamonds) compared to control littermates (Cx36+/+; black solid squares). Right: Functional knockout of Connexin36 in the neonatal diabetic mutation (Cx36−/−;Kir6.2[ΔN30,K185Q]; red open diamonds) prevents uncontrolled blood glucose compared to control mice (Cx36−/−; red solid squares). Adapted from Nguyen et al., 2014, Diabetes.
Islet dysfunction in Type2 diabetes and Type1 diabetes
Type2 Diabetes. Type2 diabetes (T2D) is a complex multi-factorial disease, where β-cells in the islets of Langerhans fail to secrete sufficient insulin to control blood glucose following metabolic stress. Importantly, while obesity and associated insulin resistance is a major risk factor for the development of T2D, not all individuals who are obese develop T2D. The mechanisms of islet dysfunction that lead to some individuals developing T2D in the face of insulin resistance, while others are able to compensate for insulin resistance, are poorly understood. Understanding the mechanisms of islet dysfunction underlying this lack of compensation and cause of diabetes is central to developing effective treatments. An area of research in the lab examines biophysical and physiological factors underlying islet function that are disrupted early in T2D progression or are present in pre-diabetes. These studies include the application of a number of state-of-the-art quantitative fluorescence microscopy approaches, and transgenic mouse models and human islets from healthy organ donors and those with T2D. Our aim is to discover new and novel ways of preserving β-cell function and islet mass; to identifying potential new therapeutic targets for preventative treatments for type2 diabetes.
Type1 Diabetes. Type1 diabetes (T1D, childhood diabetes) results from the autoimmune destruction of insulin secreting β-cells in the islets of Langerhans. While much research is investigating ways to blunt β-cell autoimmunity to prevent the destruction of insulin producing β-cells, recent research is discovering that an altered function of β-cells themselves during the disease progression may be an important factor. We are examining factors associated with islet function that are disrupted early in the progression of T1D, prior to the clinical onset of disease, as a result of β-cell autoimmunity. We are further testing whether correcting for disruption to these factors can protect against β-cell death and blunt the onset of diabetes. Towards this we use both animal models of T1D, together with human tissue from healthy organ donors and those with T1D. Our aim is to discover a therapy that can normalize islet function, which in combination with an immune-targeting therapy, could significantly delay or halt the emergence of type1 diabetes in at-risk populations.
Developing new imaging diagnostics for diabetes
Non-invasive imaging of islet dysfunction associated with the development of type1 diabetes. Currently, diagnosis of diabetes is based upon the measurement of elevated blood glucose (hyperglycemia), which unfortunately represents a time point in disease progression at which extensive dysfunction within the islets of Langerhans or β-cell death already exists. It is therefore important to develop methods that can predict or diagnose islet dysfunction and β-cell death prior to the development of hyperglycemia. Furthermore, in the context of type1 diabetes, early diagnosis of islet dysfunction would allow the use of preventative immune-modulatory interventions and would provide an opportunity to monitor their effectiveness. Currently, there exists no reliable method to non-invasively quantify the progression of islet dysfunction and β-cell death. We are working to develop in vivo imaging techniques that will allow us to identify and monitor islet dysfunction in early-stages of diabetes progression. Ultimately, we hope to develop a non-invasive method for both identifying pre-clinical signs of diabetes in humans prior to overt diabetes onset and for following the efficacy of diabetic treatment interventions over time.