Our Research Areas
Diabetes is characterized by uncontrolled elevated blood glucose levels and affects close to 400 million people worldwide. Dysfunction to insulin-secreting β-cells within the islets of Langerhans in the pancreas is the common cause of most forms of diabetes. To treat and cure diabetes strategies broadly aim to restore or replace the dysfunctional pancreatic islets to provide a well-regulated source of insulin secretion. However, 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. Our lab's research involves understanding how the pancreatic islet functions, how the islet becomes disrupted during the development of diabetes. and how we can monitor this function and dysfunction using imaging approaches. With this, we hope to improve both clinical diagnosis and therapeutic treatments for patients with type 1 and type 2 diabetes, as well as rarer monogenic diabetes.
Cellular networks and emergent multi-cellular properties regulating the islets of Langerhans
The islet is not simply a collection of cells acting autonomously. Rather, complex cellular interactions are necessary for the regulation of insulin secretion. 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 beta cell electrical networks. Beta cells are coupled by electrical synapses (gap junction channels) which coordinates electrical activity and insulin secretion dynamics. We employ high speed Ca2+ imaging and signal processing to examine the organization of electrical communication in the islet and how it changes in conditions such as aging.
Fig. 1. Human islets show a wide range of [Ca2+] activity and coordination:
A: Representative false color map of [Ca2+] activity and coordination in C57/B6 WT and Cx362/2 islets (left) with time courses from four individual cells (i–iv) indicated in these islets (right). [Ca2+] activity is represented by presence of false color, with each color representing a separate region of [Ca2+] coordination, as indicated in legend above.
B: Representative [Ca2+] activity and coordination maps in human islets from donors where high coordination similar to mouse islets is observed (left), as in A, with time courses from four individual cells indicated in these islets (right).
A: Representative false color map of [Ca2+] activity and coordination in C57/B6 WT and Cx362/2 islets (left) with time courses from four individual cells (i–iv) indicated in these islets (right). [Ca2+] activity is represented by presence of false color, with each color representing a separate region of [Ca2+] coordination, as indicated in legend above.
B: Representative [Ca2+] activity and coordination maps in human islets from donors where high coordination similar to mouse islets is observed (left), as in A, with time courses from four individual cells indicated in these islets (right).
Sub-populations of beta cells and pacemakers. Optogenetics uses light to control the excitability of cells via light-activated ion channels such as channelrhodopsin. We express optogenetic constructs in the islet to allow precise spatiotemporal control of electrical activity, as well as other cell-signaling processes. Combined with confocal microscopy and fluorescent indicators, this has allowed us to identify different subpopulations of beta cells and characterize how they regulate islet function. This includes a sub-population that disproportionately controls islet activation, and separate 'pacemaker' like sub-populations that entrains oscillatory dynamics.
Fig. 2. Discovering novel populations of beta cells using optogenetics
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. We use computational models to understand how the structure of the islet impacts function under different stimulatory conditions. We also test how mutations linked to diabetes can impact islet dynamics and function.
|
|
Fig. 3. Computational modeling of a wave dynamics. Glucose is stepped up between 5 and 11 mM including initial [Ca2+] influx before settling into persistent [Ca2+] oscillations. Adapted from Westacott et al. "Spatially organized beta-cell subpopulations control electrical dynamics across islets of Langerhans", 2017, Biophysical Journal. |
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, such as obesity. However, not all individuals who are obese develop T2D, and 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. We are examining aspects of islet function that are disrupted early in diabetes progression to discover new and novel ways of preserving β-cell function and islet mass.
Altered electrical coupling and gap junction formation in diabetes. We have found that ability of β-cells to interact and promote the regulation and dynamics of insulin secretion is disrupted in the early stages of Type2 diabetes and in aging. We are investigating mechanisms that mediate the disruption of gap junction formation that prevent β-cell communication, including identifying post-translational modifications and measuring trafficking and membrane organization with super-resolution imaging (STED).
Regulation of islet electrical synapse (gap junction channel) plasticity. Phosphorylation of connexins is major regulatory mechanism of gating and trafficking. We have found that connexin36 is phosphorylated under conditions associated with diabetes. We have developed c-terminal mimetic peptides that can block this phosphorylation and that can rescue coordination of electrical activity and regulation of insulin secretion.
Islet dysfunction in Type1 Diabetes. Type1 diabetes (T1D, childhood diabetes) results from the autoimmune destruction of insulin secreting β-cells in the islets of Langerhans. While clinical onset occurs upon most (but not all) β-cell mass being destroyed, prior to onset there is a marked dysfunction to the islet. We have found this to include altered Ca2+ regulation. We hypothesize that this altered regulation will predispose β-cells to increased apoptosis, and are exploring the mechanism underlying this and ways to restore Ca2+ regulation and potentially blunt β-cell decline.
Altered electrical coupling and gap junction formation in diabetes. We have found that ability of β-cells to interact and promote the regulation and dynamics of insulin secretion is disrupted in the early stages of Type2 diabetes and in aging. We are investigating mechanisms that mediate the disruption of gap junction formation that prevent β-cell communication, including identifying post-translational modifications and measuring trafficking and membrane organization with super-resolution imaging (STED).
Regulation of islet electrical synapse (gap junction channel) plasticity. Phosphorylation of connexins is major regulatory mechanism of gating and trafficking. We have found that connexin36 is phosphorylated under conditions associated with diabetes. We have developed c-terminal mimetic peptides that can block this phosphorylation and that can rescue coordination of electrical activity and regulation of insulin secretion.
Islet dysfunction in Type1 Diabetes. Type1 diabetes (T1D, childhood diabetes) results from the autoimmune destruction of insulin secreting β-cells in the islets of Langerhans. While clinical onset occurs upon most (but not all) β-cell mass being destroyed, prior to onset there is a marked dysfunction to the islet. We have found this to include altered Ca2+ regulation. We hypothesize that this altered regulation will predispose β-cells to increased apoptosis, and are exploring the mechanism underlying this and ways to restore Ca2+ regulation and potentially blunt β-cell decline.
Ultrasound-based imaging diagnostics for diabetes
For most patients with Type1 diabetes, there is an asymptomatic phase of several years prior to clinical presentation of diabetes, where insulin secreiton and glucose homeostasis are normal but immunological abnormalities are present . This asymptomatic phase of type1 diabetes presents an opportunity for early therapeutic intervention to preserve β-cell mass and prevent type1 diabetes. However there are limited approaches for reliable diagnosis and tracking of disease progression during this asymptomatic phase, as well as for monitoring disease reversal following preventative treatments. We are developing approaches involving microbubble ultrasound contrast agents for tracking type1 diabetes progression and reversal. This includes developing and applying utilizing novel ultrasound contrast agents and ultrasound imaging approaches, and translating approaches to clinical application.
|
|
Fig. 4. Blood flow kinetics in the pancreas obtained using contrast-enhanced ultrasound.
Gas-filled lipid micro-bubbles were introduced into the venous circulation to visualize the blood flow. On the right represented nonlinear mode of the pancreas in a pre-clinical model. On the left: B-mode image used to locate the pancreas. The time-course presented for ~20 s. Green bar (flash) represents high mechanical index bursting of the gas bubbles (contrast agent). |
|
|
Fig. 5. Parameters underlying blood flow kinetics (indicating inflammation) increase substantially during the progression of type1 diabetes, prior to disease onset. These parameters can be used to identify a population of subjects that progress more slowly to diabetes and more rapidly to diabetes, thereby predicting rapid diabetes onset. Adapted from St Clair, Ramirez et al. "Contrast-enhanced ultrasound measurements of pancreatic blood flow dynamics predicts type 1 diabetes progression in preclinical models", 2018, Nature Communications.
|
