Biology subjects

Dwulet, J. M.

Publications and source records attributed to Dwulet, J. M..

3 recordsLinked to original sources

bioRxiv2020

Caloric Restriction recovers impaired β-cell-β-cell coupling, calcium oscillation coordination and insulin secretion in prediabetic mice

Caloric restriction has been shown to decrease the incidence of metabolic diseases such as obesity and type 2 diabetes mellitus (T2DM). The mechanisms underlying the benefits of caloric restriction involved in insulin secretion and glucose homeostasis and are not fully understood. Intercellular communication within the islets of Langerhans, mediated by Connexin36 (Cx36) gap junctions, regulates insulin secretion dynamics and glucose homeostasis. The goal of this study was to determine if caloric restriction can protect against decreases in Cx36 gap junction coupling and altered islet function induced in models of obesity and prediabetes. C57BL6 mice were fed with a high fat diet (HFD), showing indications of prediabetes after 2 months, including weight gain, insulin resistance, and elevated fasting glucose and insulin levels. Subsequently, mice were submitted to one month of 40% caloric restriction (2g/day of HFD). Mice under 40% caloric restriction showed reversal in weight gain and recovered insulin sensitivity, fasting glucose and insulin levels. In islets of mice fed the HFD, caloric restriction protected against obesity-induced decreases in gap junction coupling and preserved glucose-stimulated calcium signaling, including Ca2+ oscillation coordination and oscillation amplitude. Caloric restriction also promoted a slight increase in glucose metabolism, as measured by increased NAD(P)H autofluorescence, as well as recovering glucose-stimulated insulin secretion. We conclude that declines in Cx36 gap junction coupling that occur in obesity can be completely recovered by caloric restriction and obesity reversal, improving Ca2+ dynamics and insulin secretion regulation. This suggests a critical role for caloric restriction in the context of obesity to prevent islet dysfunction.

physiology↗

bioRxiv2019

Islet architecture controls synchronous β cell response to glucose in the intact mouse pancreas in vivo

The spatial architecture of the islets of Langerhans is hypothesized to facilitate synchronized insulin secretion between {beta} cells, yet testing this in vivo in the intact pancreas is challenging. Robo {beta}KO mice, in which the genes Robo1 and Robo2 are deleted selectively in {beta} cells, provide a unique model of altered islet spatial architecture without loss of {beta} cell differentiation or islet damage from diabetes. Combining Robo {beta}KO mice with intravital microscopy, we show here that Robo {beta}KO islets lose synchronized intra-islet Ca2+ oscillations between {beta} cells in vivo. We provide evidence that this loss is not due to a {beta} cell-intrinsic function of Robo, loss of Connexin36 gap junctions, or changes in islet vascularization, 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.

developmental biology↗

bioRxiv2019

How heterogeneity in glucokinase and gap junction coupling determines the islet electrical response

Understanding how cell sub-populations in a tissue impact the function of the overall system is often challenging. There is extensive heterogeneity among insulin-secreting {beta}-cells within islets of Langerhans, including their insulin secretory response and gene expression profile; and this heterogeneity can be altered in diabetes. Several studies have identified variations in nutrient sensing between {beta}-cells, including glucokinase (GK) levels, mitochondrial function or expression of genes important for glucose metabolism. Sub-populations of {beta}-cells with defined electrical properties can disproportionately influence islet-wide free-calcium activity ([Ca2+]) and insulin secretion, via gap junction electrical coupling. However, it is poorly understood how sub-populations of {beta}-cells with altered glucose metabolism may impact islet function. To address this, we utilized a multicellular computational model of the islet in which a population of cells deficient in GK activity and glucose metabolism was imposed on the islet, or where {beta}-cells were heterogeneous in glucose metabolism and GK kinetics were altered. This included simulating Glucokinase gene (GCK) mutations that cause monogenic diabetes. We combined these approaches with experimental models in which gck was genetically deleted in a population of cells or GK was pharmacologically inhibited. In each case we modulated gap junction electrical coupling. Both the simulated islet and the experimental system required 30-50% of the cells to have near-normal glucose metabolism. Below this number, the islet lacked any glucose-stimulated [Ca2+] elevations. In the absence of electrical coupling the change in [Ca2+] was more gradual. As such, given heterogeneity in glucose metabolism, electrical coupling allows a large minority of cells with normal glucose metabolism to promote glucose-stimulated [Ca2+]. If insufficient numbers of cells are present, which we predict can be caused by a subset of GCK mutations that cause monogenic diabetes, electrical coupling exacerbates [Ca2+] suppression. This demonstrates precisely how heterogeneous {beta}-cell populations interact to impact islet function.\n\nSIGNIFICANCEBiological tissues contain heterogeneous populations of cells. Insulin-secreting {beta}-cells within the islets of Langerhans are critical for regulating blood glucose homeostasis. {beta}-cells are heterogeneous but it is unclear how the islet response is impacted by different cell populations and their interactions. We use a multicellular computational model and experimental systems to predict and quantify how cellular populations defined by varied glucose metabolism interact via electrical communication to impact islet function. When glucose metabolism is heterogeneous, electrical coupling is critical to promote electrical activity. However, when cells deficient in glucose metabolism are in the majority, electrical activity is completely suppressed. Thus modulating electrical communication can promotes islet electrical activity, following dysfunction caused by gene mutations that impact glucose metabolism.

biophysics↗