In Vivo Imaging of Liver Spheroids Engrafted in the Anterior Chamber of the Mouse Eye.

Biomedical studies of the liver in mammals are hindered by the lack of methods for in vivo noninvasive longitudinal imaging at cellular resolution. Until now, optical imaging of the liver in situ is possible by intravital imaging, which offers high-resolution imaging at the cellular level but cannot be performed multiple times and, therefore, longitudinally in the same animal. Noninvasive imaging methods, such as bioluminescence, allow repeated imaging sessions on the same animal but do not achieve cell resolution.

Transplantation and Noninvasive Longitudinal Imaging of Parathyroid Cells: A Proof-of-Concept Study.

The parathyroid cell is a vital regulator of extracellular calcium levels, operating through the secretion of parathyroid hormone (PTH). Despite its importance, the regulation of PTH secretion remains complex and not fully understood, representing a unique interplay between extracellular and intracellular calcium, and hormone secretion. One significant challenge in parathyroid research has been the difficulty in maintaining cells for in-depth cellular investigations.

Intraocular liver spheroids for non-invasive high-resolution in vivo monitoring of liver cell function.

Longitudinal monitoring of liver function in vivo is hindered by the lack of high-resolution non-invasive imaging techniques. Using the anterior chamber of the mouse eye as a transplantation site, we have established a platform for longitudinal in vivo imaging of liver spheroids at cellular resolution. Transplanted liver spheroids engraft on the iris, become vascularized and innervated, retain hepatocyte-specific and liver-like features and can be studied by in vivo confocal microscopy.

Multiple Inositol Polyphosphate Phosphatase Compartmentalization Separates Inositol Phosphate Metabolism from Inositol Lipid Signaling.

Multiple inositol polyphosphate phosphatase (MINPP1) is an enigmatic enzyme that is responsible for the metabolism of inositol hexakisphosphate (Ins) and inositol 1,3,4,5,6 pentakisphosphate (Ins(1,3,4,5,6) in mammalian cells, despite being restricted to the confines of the ER. The reason for this compartmentalization is unclear. In our previous studies in the insulin-secreting HIT cell line, we expressed MINPP1 in the cytosol to artificially reduce the concentration of these higher inositol phosphates.

Uncommon Transplantation Sites: Transplantation of Islets and Islet Organoids in the Anterior Chamber of the Eye of Rodents and Monkeys.

The anterior chamber of the eye is a highly vascularized and innervated location that is also particularly rich in oxygen and immune privileged. This uncommon transplantation site offers unique possibilities for the observation of the transplanted material as well as for local pharmacological intervention. Transplantation of islets and islet organoids to the anterior chamber of the eye of mice and monkeys facilitates a multitude of new approaches for research into islet physiology and pathophysiology and for the treatment of diabetes.

Novel aspects of intra-islet communication: Primary cilia and filopodia.

Pancreatic islets are micro-organs composed of a mixture of endocrine and non-endocrine cells, where the former secrete hormones and peptides necessary for metabolic homeostasis. Through vasculature and innervation the cells within the islets are in communication with the rest of the body, while they interact with each other through juxtacrine, paracrine and autocrine signals, resulting in fine-tuned sensing and response to stimuli. In this context, cellular protrusion in islet cells, such as primary cilia and filopodia, have gained attention as potential signaling hubs.

Mitochondrial impairment and intracellular reactive oxygen species alter primary cilia morphology.

Primary cilia have recently emerged as cellular signaling organelles. Their homeostasis and function require a high amount of energy. However, how energy depletion and mitochondria impairment affect cilia have barely been addressed.

Local Dexamethasone Administration Delays Allogeneic Islet Graft Rejection in the Anterior Chamber of the Eye of Non-Human Primates.

Pancreatic islet transplantation into the anterior chamber of the eye (ACE) has been shown to improve glycemic control and metabolic parameters of diabetes in both murine and primate models. This novel transplantation site also allows the delivery of therapeutic agents, such as immunosuppressive drugs, locally to prevent islet graft rejection and circumvent unwanted systemic side effects. Local intravitreal administration of micronized dexamethasone implant was performed prior to allogeneic islet transplantation into the ACEs of non-human primates.

Inward and outward currents of native and cloned K(ATP) channels (Kir6.2/SUR1) share single-channel kinetic properties.

Background: The ATP-sensitive K (K(ATP)) channel is found in a variety of tissues extending from the heart and vascular smooth muscles to the endocrine pancreas and brain. Common to all K(ATP) channels is the pore-forming subunit Kir6.x, a member of the family of small inwardly rectifying K channels, and the regulatory subunit sulfonylurea receptor (SURx).

Expression of truncated Kir6.2 promotes insertion of functionally inverted ATP-sensitive K channels.

ATP-sensitive K (K) channels couple cellular metabolism to electrical activity in many cell types. Wild-type K channels are comprised of four pore forming (Kir6.x) and four regulatory (sulfonylurea receptor, SURx) subunits that each contain RKR endoplasmic reticulum retention sequences that serve to properly translocate the channel to the plasma membrane.

Ectopic Leptin Production by Intraocular Pancreatic Islet Organoids Ameliorates the Metabolic Phenotype of Mice.

The pancreatic islets of Langerhans consist of endocrine cells that secrete peptide hormones into the blood circulation in response to metabolic stimuli. When transplanted into the anterior chamber of the eye (ACE), pancreatic islets engraft and maintain morphological features of native islets as well as islet-specific vascularization and innervation patterns. In sufficient amounts, intraocular islets are able to maintain glucose homeostasis in diabetic mice.

Tissue-specific expression of insulin receptor isoforms in obesity/type 2 diabetes mouse models.

The two insulin receptor (IR) isoforms IR-A and IR-B are responsible for the pleiotropic actions of insulin and insulin-like growth factors. Consequently, changes in IR isoform expression and in the bioavailability of their ligands will impact on IR-mediated functions. Although alteration of IR isoform expression has been linked to insulin resistance, knowledge of IR isoform expression and mechanisms underlying tissue/cell-type-specific changes in metabolic disease are lacking.

Human Islet Microtissues as an In Vitro and an In Vivo Model System for Diabetes.

Loss of pancreatic β-cell function is a critical event in the pathophysiology of type 2 diabetes. However, studies of its underlying mechanisms as well as the discovery of novel targets and therapies have been hindered due to limitations in available experimental models. In this study we exploited the stable viability and function of standardized human islet microtissues to develop a disease-relevant, scalable, and reproducible model of β-cell dysfunction by exposing them to long-term glucotoxicity and glucolipotoxicity.

Glucokinase intrinsically regulates glucose sensing and glucagon secretion in pancreatic alpha cells.

The secretion of glucagon by pancreatic alpha cells is regulated by a number of external and intrinsic factors. While the electrophysiological processes linking a lowering of glucose concentrations to an increased glucagon release are well characterized, the evidence for the identity and function of the glucose sensor is still incomplete. In the present study we aimed to address two unsolved problems: (1) do individual alpha cells have the intrinsic capability to regulate glucagon secretion by glucose, and (2) is glucokinase the alpha cell glucose sensor in this scenario.

Alpha cell regulation of beta cell function.

The islet of Langerhans is a complex endocrine micro-organ consisting of a multitude of endocrine and non-endocrine cell types. The two most abundant and prominent endocrine cell types, the beta and the alpha cells, are essential for the maintenance of blood glucose homeostasis. While the beta cell produces insulin, the only blood glucose-lowering hormone of the body, the alpha cell releases glucagon, which elevates blood glucose.

In vivo Ca dynamics in single pancreatic β cells.

The dynamics of cytoplasmic free Ca concentration ([Ca]) in pancreatic β cells is central to our understanding of β-cell physiology and pathology. In this context, there are numerous in vitro studies available but existing in vivo data are scarce. We now critically evaluate the anterior chamber of the eye as an in vivo, non-invasive, imaging site for measuring [Ca] dynamics longitudinally in three dimensions and at single-cell resolution.

Author Correction: Structural basis for delta cell paracrine regulation in pancreatic islets.

An amendment to this paper has been published and can be accessed via a link at the top of the paper.

Structural basis for delta cell paracrine regulation in pancreatic islets.

Little is known about the role of islet delta cells in regulating blood glucose homeostasis in vivo. Delta cells are important paracrine regulators of beta cell and alpha cell secretory activity, however the structural basis underlying this regulation has yet to be determined. Most delta cells are elongated and have a well-defined cell soma and a filopodia-like structure.

SMPDL3b modulates insulin receptor signaling in diabetic kidney disease.

Sphingomyelin phosphodiesterase acid-like 3b (SMPDL3b) is a lipid raft enzyme that regulates plasma membrane (PM) fluidity. Here we report that SMPDL3b excess, as observed in podocytes in diabetic kidney disease (DKD), impairs insulin receptor isoform B-dependent pro-survival insulin signaling by interfering with insulin receptor isoforms binding to caveolin-1 in the PM. SMPDL3b excess affects the production of active sphingolipids resulting in decreased ceramide-1-phosphate (C1P) content as observed in human podocytes in vitro and in kidney cortexes of diabetic db/db mice in vivo.

Diet-induced β-cell insulin resistance results in reversible loss of functional β-cell mass.

Although convincing in genetic models, the relevance of β-cell insulin resistance in diet-induced type 2 diabetes (T2DM) remains unclear. Exemplified by diabetes-prone, male, C57B1/6J mice being fed different combinations of Western-style diet, we show that β-cell insulin resistance occurs early during T2DM progression and is due to a combination of lipotoxicity and increased β-cell workload. Within 8 wk of being fed a high-fat, high-sucrose diet, mice became obese, developed impaired insulin and glucose tolerances, and displayed noncompensatory insulin release, due, at least in part, to reduced expression of syntaxin-1A.

Paracrine Interactions within the Pancreatic Islet Determine the Glycemic Set Point.

Every animal species has a signature blood glucose level or glycemic set point. These set points are different, and the normal glycemic levels (normoglycemia) of one species would be life threatening for other species. Mouse normoglycemia can be considered diabetic for humans.

Mechanistic understanding of insulin receptor modulation: Implications for the development of anti-diabetic drugs.

The insulin receptor is an important regulator of metabolic processes in the body, and in particular of glucose homeostasis, including glucose uptake into peripheral tissues. Thus, insulin administration is an effective treatment for diabetes, which is characterized by chronic elevation of blood glucose. However, insulin is not only a metabolic regulator, but also functions as a growth hormone.

Intraocular imaging of pancreatic islet cell physiology/pathology.

Background: Diabetes mellitus has reached epidemic proportions and requires new strategies for treatment. Unfortunately, the efficacy of treatment regimens on maintaining/re-gaining functional beta cell mass can, at the present, only be determined indirectly. Direct monitoring of beta cell mass is complicated by the anatomy of the endocrine pancreas, which consists of thousands to a million of discrete micro-organs, i.

Pancreatic Islet Blood Flow Dynamics in Primates.

Blood flow regulation in pancreatic islets is critical for function but poorly understood. Here, we establish an in vivo imaging platform in a non-human primate where islets transplanted autologously into the anterior chamber of the eye are monitored non-invasively and longitudinally at single-cell resolution. Engrafted islets were vascularized and innervated and maintained the cytoarchitecture of in situ islets in the pancreas.

Non-invasive cell type selective in vivo monitoring of insulin resistance dynamics.

Insulin resistance contributes to the development of cardio-vascular disease and diabetes. An important but unresolved task is to study the dynamics of insulin resistance in selective cell types of insulin target tissues in vivo. Here we present a novel technique to monitor insulin resistance dynamics non-invasively and longitudinally in vivo in a cell type-specific manner, exemplified by the pancreatic β-cell situated within the micro-organ the islet of Langerhans.