Microfluidic device integrating a network of hyper-elastic valves for automated glucose stimulation and insulin secretion collection from a single pancreatic islet

Advances in microphysiological systems have prompted the need for robust and reliable cell culture devices. While microfluidic technology has made significant progress, devices often lack user-friendliness and are not designed to be industrialized on a large scale. Pancreatic islets are often being studied using microfluidic platforms in which the monitoring of fluxes is generally very limited, especially because the integration of valves to direct the flow is difficult to achieve. Considering these constraints, we present a thermoplastic manufactured microfluidic chip with an automated control of fluxes for the stimulation and secretion collection of pancreatic islet. The islet was directed toward precise locations through passive hydrodynamic trapping and both dynamic glucose stimulation and insulin harvesting were done automatically via a network of large deformation valves, directing the reagents and the pancreatic islet toward different pathways. This device we developed enables monitoring of insulin secretion from a single islet and can be adapted for the study of a wide variety of biological tissues and secretomes.

The Nutrient Sensor mTORC1 Regulates Insulin Secretion by Modulating ß-cell Autophagy

The dynamic regulation of autophagy in b-cells by cycles of fasting-feeding and its effects on insulin secretion are unknown. In b-cells mTORC1 is inhibited while fasting, and is rapidly stimulated during refeeding by a single amino acid, leucine, and glucose. Stimulation of mTORC1 by nutrients inhibited the autophagy initiator ULK1 and the transcription factor TFEB, thereby preventing autophagy when b-cells are continuously exposed to nutrients. Inhibition of mTORC1 by <i>Raptor</i> knockout mimicked the effects of fasting and stimulated autophagy while inhibiting insulin secretion, whereas moderate inhibition of autophagy under these conditions rescued insulin secretion. These results show that mTORC1 regulates insulin secretion through modulation of autophagy under different nutritional situations. In the fasting state, autophagy is regulated in an mTORC1-dependent manner and its stimulation is required to keep insulin levels low, thereby preventing hypoglycemia. Reciprocally, stimulation of mTORC1 by elevated leucine and glucose, which is common in obesity, may promote hyperinsulinemia by inhibiting autophagy.

The Nutrient Sensor mTORC1 Regulates Insulin Secretion by Modulating ß-cell Autophagy

The dynamic regulation of autophagy in b-cells by cycles of fasting-feeding and its effects on insulin secretion are unknown. In b-cells mTORC1 is inhibited while fasting, and is rapidly stimulated during refeeding by a single amino acid, leucine, and glucose. Stimulation of mTORC1 by nutrients inhibited the autophagy initiator ULK1 and the transcription factor TFEB, thereby preventing autophagy when b-cells are continuously exposed to nutrients. Inhibition of mTORC1 by <i>Raptor</i> knockout mimicked the effects of fasting and stimulated autophagy while inhibiting insulin secretion, whereas moderate inhibition of autophagy under these conditions rescued insulin secretion. These results show that mTORC1 regulates insulin secretion through modulation of autophagy under different nutritional situations. In the fasting state, autophagy is regulated in an mTORC1-dependent manner and its stimulation is required to keep insulin levels low, thereby preventing hypoglycemia. Reciprocally, stimulation of mTORC1 by elevated leucine and glucose, which is common in obesity, may promote hyperinsulinemia by inhibiting autophagy.

Pancreatic α and β cells are globally phase-locked

The Ca2+ modulated pulsatile secretion of glucagon and insulin by pancreatic α and β cells plays a key role in glucose homeostasis. However, how α and β cells coordinate via paracrine interaction to produce various Ca2+ oscillation patterns is still elusive. Using a microfluidic device and transgenic mice in which α and β cells were labeled with different colors, we were able to record islet Ca2+ signals at single cell level for long times. Upon glucose stimulation, we observed heterogeneous Ca2+ oscillation patterns intrinsic to each islet. After a transient period, the oscillations of α and β cells were globally phase-locked, i.e., the two types of cells in an islet each oscillate synchronously but with a phase shift between the two. While the activation of α cells displayed a fixed time delay of ~20 s to that of β cells, β cells activated with a tunable delay after the α cells. As a result, the tunable phase shift between α and β cells set the islet oscillation period and pattern. Furthermore, we demonstrated that the phase shift can be modulated by glucagon. A mathematical model of islet Ca2+ oscillation taking into consideration of the paracrine interaction was constructed, which quantitatively agreed with the experimental data. Our study highlights the importance of cell-cell interaction to generate stable but tunable islet oscillation patterns.

Development of islet organoids from human induced pluripotent stem cells in a cross-linked collagen scaffold

Islets organoids would have value in the cell replacement therapy for diabetes apart from usual personalized drug screening routes. Generation of a large number of Islets like clusters, with ability to respond to glucose stimulation appears to be an ideal choice. In this study we have generated islet organoids with the ability to respond to glucose stimulation by insulin release. The source of the cells was an iPSC cell line differentiated into the pancreatic progenitors. These cells were assembled in matrigel or cross-linked collagen scaffold and compared for their efficacy to release insulin upon stimulation with glucose. The assembled organoids were examined by immunohistochemistry and expression of the relevant marker genes. The organoids showed expression of islet like markers in both - matrigel and crosslinked collagen scaffold. The islet organoids in both the cases showed release of insulin upon stimulation with glucose. The crosslinked collagen scaffold is quite stable and supports islet cells growth and function.

iDEP-assisted isolation of insulin secretory vesicles

ABSTRACTOrganelle heterogeneity and inter-organelle associations within a single cell contribute to the limited sensitivity of current organelle separation techniques, thus hindering organelle subpopulation characterization. Here we use direct current insulator-based dielectrophoresis (DC-iDEP) as an unbiased separation method and demonstrate its capability by identifying distinct distribution patterns of insulin vesicles from pancreatic β-cells. A multiple voltage DC-iDEP strategy with increased range and sensitivity has been applied, and a differentiation factor (ratio of electrokinetic to dielectrophoretic mobility) has been used to characterize features of insulin vesicle distribution patterns. We observed a significant difference in the distribution pattern of insulin vesicles isolated from glucose-stimulated cells relative to unstimulated cells, in accordance with functional maturation of vesicles upon glucose stimulation, and interpret this to be indicative of high-resolution separation of vesicle subpopulation. DC-iDEP provides a path for future characterization of subtle biochemical differences of organelle subpopulations within any biological system.

The Role of MicroRNA-155 in Glomerular Endothelial Cell Injury of Diabetic Nephropathy

Objective: To investigate the role of microRNA-155-5p (miR-155-5p) on apoptosis and inflammatory response in human glomerular endothelial cells (HRGEC) cultured with high glucose.Methods: The primary human glomerular endothelial cells (HRGEC) were studied, QPCR, WB , IF were used to detect cell morphology, target gene ETS-1 (ETS-1), downstream factors VCAM-1 and MCP-1, and apoptosis of cells in each group after high glucose stimulation and transfection with miR-155 overexpression or inhibitor.Results:1.The expression of inflammatory factors and apoptosis of HRGEC cells increased under high glucose stimulation.2.The overexpression of miR-155 in HRGEC cells under high glucose stimulation decreased the expression of ETS-1, while the expression of ETS-1 increased when miR-155 was inhibited. These results suggest that miR-155 may be involved in endothelial cell injury by negatively regulating the expression of ETS-1.3.HRGEC cells were transfected with miR-155 mimic and ETS-1 siRNA with high glucose stimulation. The expression of ETS-1 was positively correlated with the expression of downstream factors VCAM-1 and MCP-1. These results suggest that ETS-1 can mediate endothelial cell inflammation by regulating VCAM-1 and MCP-1.

Up-regulating Lipin1 Attenuates High Glucose-Induced Apoptosis in RSC96 cells Through Regulating Mitochondrial Dynamics

Diabetic peripheral neuropathy, one of the major complications resulting from diabetes, affects diabetic patients with high morbidity and mortality. It has emerged as a severe public health problem. However, its underlying pathogenesis and effective treatment strategies have not been fully studied. In the present study, we explored the role of lipin1 on mitochondrial function of Schwann cells under diabetic conditions. With high glucose stimulation or lipin1 down-regulation, the cell viability of Schwann cells was inhibited,accompanied with mitochondrial dysfunction and morphological abnormality. Besides, we found that high glucose stimulation or lipin1 silencing also disturbed the balance of mitochondrial dynamics, presented as increased levels of mitochondrial fission-related proteins (including DRP1 and FIS1) and decreased levels of mitochondrial fusion-related proteins (including MFN1 and OPA1). Furthermore, we demonstrated that up-regulating lipin1 ameliorated high glucose-induced disorder of mitochondrial dynamics and functions, and ultimately improved cell viability. Our results suggest that lipin1 may play a protective role on high glucose-stimulated Schwann cells through regulating the balance of mitochondrial dynamics.

Exploring Insulin Production Following Alveolar Islet Transplantation (AIT)

Recent studies have demonstrated the feasibility of islet implantation into the alveoli. However, until today, there are no data on islet behavior and morphology at their transplant site. This study is the first to investigate islet distribution as well insulin production at the implant site. Using an ex vivo postmortem swine model, porcine pancreatic islets were isolated and aerosolized into the lung using an endoscopic spray-catheter. Lung tissue was explanted and bronchial airways were surgically isolated and connected to a perfusor. Correct implantation was confirmed via histology. The purpose of using this new lung perfusion model was to measure static as well as dynamic insulin excretions following glucose stimulation. Alveolar islet implantation was confirmed after aerosolization. Over 82% of islets were correctly implanted into the intra-alveolar space. The medium contact area to the alveolar surface was estimated at 60 +/− 3% of the total islet surface. The new constructed lung perfusion model was technically feasible. Following static glucose stimulation, insulin secretion was detected, and dynamic glucose stimulation revealed a biphasic insulin secretion capacity during perfusion. Our data indicate that islets secrete insulin following implantation into the alveoli and display an adapted response to dynamic changes in glucose. These preliminary results are encouraging and mark a first step toward endoscopically assisted islet implantation in the lung.