Chemical methods to induce Beta-cell proliferation

From islet transplantation to beta-cell regeneration: an update on beta-cell-based therapeutic approaches in type 1 diabetes

INTRODUCTION

Type 1 diabetes (T1D) mellitus is an autoimmune disease in which immune cells, predominantly effector T cells, destroy insulin-secreting beta-cells. Beta-cell destruction led to various consequences ranging from retinopathy and nephropathy to neuropathy. Different strategies have been developed to achieve normoglycemia, including exogenous glucose compensation, whole pancreas transplantation, islet transplantation, and beta-cell replacement.

AREAS COVERED

The last two decades of experience have shown that indigenous glucose compensation through beta-cell regeneration and protection is a peerless method for T1D therapy. Tremendous studies have tried to find an unlimited source for beta-cell regeneration, on the one hand, and beta-cell protection against immune attack, on the other hand. Recent advances in stem cell technology, gene editing methods, and immune modulation approaches provide a unique opportunity for both beta-cell regeneration and protection.

EXPERT OPINION

Pluripotent stem cell differentiation into the beta-cell is considered an unlimited source for beta-cell regeneration. Devising engineered pancreas-specific regulatory T cells using Chimeric Antigen Receptor (CAR) technology potentiates an effective immune tolerance induction for beta-cell protection. Beta-cell regeneration using pluripotent stem cells and beta-cell protection using pancreas-specific engineered regulatory T cells promises to develop a curative protocol in T1D.

BefA, a microbiota-secreted membrane disrupter, disseminates to the pancreas and increases β cell mass

Microbiome dysbiosis is a feature of diabetes, but how microbial products influence insulin production is poorly understood. We report the mechanism of BefA, a microbiome-derived protein that increases proliferation of insulin-producing β cells during development in gnotobiotic zebrafish and mice. BefA disseminates systemically by multiple anatomic routes to act directly on pancreatic islets. We detail BefA's atomic structure, containing a lipid-binding SYLF domain, and demonstrate that it permeabilizes synthetic liposomes and bacterial membranes. A BefA mutant impaired in membrane disruption fails to expand β cells, whereas the pore-forming host defense protein, Reg3, stimulates β cell proliferation. Our work demonstrates that membrane permeabilization by microbiome-derived and host defense proteins is necessary and sufficient for β cell expansion during pancreas development, potentially connecting microbiome composition with diabetes risk.

Emerging diabetes therapies: Bringing back the β-cells

BACKGROUND

Stem cell therapies are finally coming of age as a viable alternative to pancreatic islet transplantation for the treatment of insulin-dependent diabetes. Several clinical trials using human embryonic stem cell (hESC)-derived β-like cells are currently underway, with encouraging preliminary results. Remaining challenges notwithstanding, these strategies are widely expected to reduce our reliance on human isolated islets for transplantation procedures, making cell therapies available to millions of diabetic patients. At the same time, advances in our understanding of pancreatic cell plasticity and the molecular mechanisms behind β-cell replication and regeneration have spawned a multitude of translational efforts aimed at inducing β-cell replenishment in situ through pharmacological means, thus circumventing the need for transplantation.

SCOPE OF REVIEW

We discuss here the current state of the art in hESC transplantation, as well as the parallel quest to discover agents capable of either preserving the residual mass of β-cells or inducing their proliferation, transdifferentiation or differentiation from progenitor cells.

MAJOR CONCLUSIONS

Stem cell-based replacement therapies in the mold of islet transplantation are already around the corner, but a permanent cure for type 1 diabetes will likely require the endogenous regeneration of β-cells aided by interventions to restore the immune balance. The promise of current research avenues and a strong pipeline of clinical trials designed to tackle these challenges bode well for the realization of this goal.

Synthetic Small Molecules to Induce Insulin Secretion and Pancreatic Beta Cell Specific Gene Expression

Despite various efficient pharmaceuticals which are already used to manage diabetes, new drugs are needed to preserve and restore the function of pancreatic β-cells (pβCs) including cell specific gene expression and insulin production and secretion. Newly developed small molecules (SMs) with potential anti-diabetic activity need to be preliminary tested. Mice insulinoma MIN6 cells (MIN6) can be utilized as an in vitro screening model. These cells have pancreatic β-cells characteristics and can secrete insulin in response to glucose level changes. As well, β-cell-specific gene expression pattern of these cells is similar to that of mouse pancreatic islet cells. It is possible to use this cell line as a research tool to study the function of the pancreatic β-cells. To date, approximately 60 genes have been identified which, are effective in the pβCs embryonic development and insulin production and secretion during puberty, including pancreas/duodenum homeobox protein 1 (Pdx1), neuronal differentiation 1 (Neurod1), neurogenin3 (Ngn3), and insulin-1 precursor (Ins1). In this study, a family of new SMs that are structurally similar to glinides was synthesized through three different synthetic methods and categorized into three categories (C1-C3). Then, these novel SMs were characterized by testing their effects on cell viability, pβCs-specific gene expression, and insulin secretion of MIN6 in four different concentrations and three time points. According to our results, SMs of C1 (1j, 1k, and 1l) and two SMs of C3 (1f, 1I), at 200 μM concentration, were able to increase the expression levels of Pdx1, Neurod1, Ngn3, and Ins1 as well as the insulin secretion after 24 hours. However, C2 (1a, 1b, 1c and 1d) did not show significant bio-activity of MIN6 cells. These investigated molecules can provide a tool for exploring pseudo-islet functionality in MIN6 cells or provide a possible basis for future therapeutic interventions for diabetes.

The Effects of Major Mushroom Bioactive Compounds on Mechanisms That Control Blood Glucose Level

Diabetes mellitus is a life-threatening multifactorial metabolic disorder characterized by high level of glucose in the blood. Diabetes and its chronic complications have a significant impact on human life, health systems, and countries' economies. Currently, there are many commercial hypoglycemic drugs that are effective in controlling hyperglycemia but with several serious side-effects and without a sufficient capacity to significantly alter the course of diabetic complications. Over many centuries mushrooms and their bioactive compounds have been used in the treatment of diabetes mellitus, especially polysaccharides and terpenoids derived from various mushroom species. This review summarizes the effects of these main mushroom secondary metabolites on diabetes and underlying molecular mechanisms responsible for lowering blood glucose. In vivo and in vitro data revealed that treatment with mushroom polysaccharides displayed an anti-hyperglycemic effect by inhibiting glucose absorption efficacy, enhancing pancreatic β-cell mass, and increasing insulin-signaling pathways. Mushroom terpenoids act as inhibitors of α-glucosidase and as insulin sensitizers through activation of PPARγ in order to reduce hyperglycemia in animal models of diabetes. In conclusion, mushroom polysaccharides and terpenoids can effectively ameliorate hyperglycemia by various mechanisms and can be used as supportive candidates for prevention and control of diabetes in the future.

Native Zinc Catalyzes Selective and Traceless Release of Small Molecules in β-Cells

The loss of insulin-producing β-cells is the central pathological event in type 1 and 2 diabetes, which has led to efforts to identify molecules to promote β-cell proliferation, protection, and imaging. However, the lack of β-cell specificity of these molecules jeopardizes their therapeutic potential. A general platform for selective release of small-molecule cargoes in β-cells over other islet cells ex vivo or other cell-types in an organismal context will be immensely valuable in advancing diabetes research and therapeutic development. Here, we leverage the unusually high Zn(II) concentration in β-cells to develop a Zn(II)-based prodrug system to selectively and tracelessly deliver bioactive small molecules and fluorophores to β-cells. The Zn(II)-targeting mechanism enriches the inactive cargo in β-cells as compared to other pancreatic cells; importantly, Zn(II)-mediated hydrolysis triggers cargo activation. This prodrug system, with modular components that allow for fine-tuning selectivity, should enable the safer and more effective targeting of β-cells.

Fluorescence-Based Nano-Oxygen Particles for Spatiometric Monitoring of Cell Physiological Conditions

Closed-loop artificial pancreas systems have recently been proposed as a solution for treating stage I diabetes by reproducing the function of the pancreas. However, there are many unresolved issues associated with their development, including monitoring and controlling oxygen, immune responses, and the optimization of glucose, all of which need to be monitored and controlled to produce an efficient and viable artificial organ that can become integrated in the patient and maintain homeostasis. This research focused on monitoring the oxygen concentration, specifically achieving this kinetically as the oxygen gradient in an artificial pancreas made of alginate spheres containing islet cells. Functional nanoparticles (NPs) for measuring the oxygen gradient in different hydrogel cellular environments using fluorescence-based (F) microscopy were developed and tested. By the ester bond, a linker Pluronic F127 was conjugated with a carboxylic acid-modified polystyrene NP (510 nm). A hydrophilic/hydrophobic interaction between the commercially available oxygen-sensitive fluorophore and F127 results in fluorescence-based nano-oxygen particles (FNOPs). The in-house synthesized FNOP was calibrated inside electrosprayed alginate-filled hydrogels and demonstrated a good broad dynamic range (2.73-22.23) mg/L as well as a resolution of -0.01 mg/L with an accuracy of ±4%. The calibrated FNOP was utilized for continuous measuring of the oxygen concentration gradient for cell lines RIN-m5F/HeLa for more than 5 days in alginate hydrogel spheres in vitro.

Direct effect of glucocorticoids on glucose-activated adult rat β-cells increases their cell number and their functional mass for transplantation

Compounds that increase β-cell number can serve as β-cell replacement therapies in diabetes. In vitro studies have identified several agents that can activate DNA synthesis in primary β-cells but only in small percentages of cells and without demonstration of increases in cell number. We used whole well multiparameter imaging to first screen a library of 1,280 compounds for their ability to recruit adult rat β-cells into DNA synthesis and then assessed influences of stimulatory agents on the number of living cells. The four compounds with highest β-cell recruitment were glucocorticoid (GC) receptor ligands. The GC effect occurred in glucose-activated β-cells and was associated with increased glucose utilization and oxidation. Hydrocortisone and methylprednisolone almost doubled the number of β-cells in 2 wk. The expanded cell population provided an increased functional β-cell mass for transplantation in diabetic animals. These effects are age dependent; they did not occur in neonatal rat β-cells, where GC exposure suppressed basal replication and was cytotoxic. We concluded that GCs can induce the replication of adult rat β-cells through a direct action, with intercellular differences in responsiveness that have been related to differences in glucose activation and in age. These influences can explain variability in GC-induced activation of DNA synthesis in rat and human β-cells. Our study also demonstrated that β-cells can be expanded in vitro to increase the size of metabolically adequate grafts.

Inhibition of DYRK1A Stimulates Human β-Cell Proliferation

Restoring functional β-cell mass is an important therapeutic goal for both type 1 and type 2 diabetes (1). While proliferation of existing β-cells is the primary means of β-cell replacement in rodents (2), it is unclear whether a similar principle applies to humans, as human β-cells are remarkably resistant to stimulation of division (3,4). Here, we show that 5-iodotubercidin (5-IT), an annotated adenosine kinase inhibitor previously reported to increase proliferation in rodent and porcine islets (5), strongly and selectively increases human β-cell proliferation in vitro and in vivo. Remarkably, 5-IT also increased glucose-dependent insulin secretion after prolonged treatment. Kinome profiling revealed 5-IT to be a potent and selective inhibitor of the dual-specificity tyrosine phosphorylation-regulated kinase (DYRK) and cell division cycle-like kinase families. Induction of β-cell proliferation by either 5-IT or harmine, another natural product DYRK1A inhibitor, was suppressed by coincubation with the calcineurin inhibitor FK506, suggesting involvement of DYRK1A and nuclear factor of activated T cells signaling. Gene expression profiling in whole islets treated with 5-IT revealed induction of proliferation- and cell cycle-related genes, suggesting that true proliferation is induced by 5-IT. Furthermore, 5-IT promotes β-cell proliferation in human islets grafted under the kidney capsule of NOD-scid IL2Rg(null) mice. These results point to inhibition of DYRK1A as a therapeutic strategy to increase human β-cell proliferation.

TRPV6 channel modulates proliferation of insulin secreting INS-1E beta cell line

Transient receptor potential channel vanilloid type 6 (TRPV6) is a non-selective cation channel with high permeability for Ca²⁺ ions. So far, the role of TRPV6 in pancreatic beta cells is unknown. In the present study, we characterized the role of TRPV6 in controlling calcium signaling, cell proliferation as well as insulin expression, and secretion in experimental INS-1E beta cell model. TRPV6 protein production was downregulated using siRNA by approx. 70%, as detected by Western blot. Intracellular free Ca²⁺ ([Ca²⁺]i) was measured by fluorescence Ca²⁺ imaging using fura-2. Calcineurin/NFAT signaling was analyzed using a NFAT reporter assay as well as a calcineurin activity assay. TRPV6 downregulation resulted in impaired cellular calcium influx. Its downregulation also reduced cell proliferation and decreased insulin mRNA expression. These changes were companied by the inhibition of the calcineurin/NFAT signaling. In contrast, insulin exocytosis was not affected by TRPV6 downregulation. In conclusion, this study demonstrates for the first time the expression of TRPV6 in INS-1E cells and rat pancreatic beta cells and describes its role in modulating calcium signaling, beta cell proliferation and insulin mRNA expression. In contrast, TRPV6 fails to influence insulin secretion.

WS6 induces both alpha and beta cell proliferation without affecting differentiation or viability

Agents that stimulate human pancreatic beta cell proliferation are needed to improve diabetes mellitus treatment. Recently, a small molecule, WS6, was observed to stimulate human beta cell proliferation. However, little is known about its other effects on human islets. To better understand the role of WS6 as a possible beta cell regenerative therapy, we carried out in-depth phenotypic analysis of WS6-treated human islets, exploring its effects on non-beta cell proliferation, beta cell differentiation, and islet cell viability. WS6 not only stimulated beta cell proliferation in cultured human islets (in agreement with previous reports), but also human alpha cell proliferation, indicating that WS6 is not a beta cell-specific mitogen. WS6 did not change the proportion of insulin-positive beta cells or the expression of beta cell-specific transcription factors, suggesting that WS6 does not alter beta cell differentiation, and WS6 had no effect on human islet cell apoptosis or viability. In conclusion, WS6 stimulates proliferation of both human beta and alpha cells while maintaining cellular viability and the beta cell differentiated phenotype. These findings expand the literature on WS6 and support the suggestion that WS6 may help increase human islet mass needed for successful treatment of diabetes.

Protective Effects of the Mushroom Lactarius deterrimus Extract on Systemic Oxidative Stress and Pancreatic Islets in Streptozotocin-Induced Diabetic Rats

The aim of this study was to assess the in vivo effects of the extract of the medicinal mushroom, Lactarius deterrimus, when administered (60 mg/kg, i.p.) daily for four weeks to streptozotocin- (STZ-) induced diabetic rats. Diabetic rats treated with the L. deterrimus extract displayed several improved biochemical parameters in the circulation: reduced hyperglycemia, lower triglyceride concentration and reduced glycated hemoglobin, glycated serum protein, and advanced glycation end product (AGE) levels. This treatment also adjusted the diabetes-induced redox imbalance. Thus, higher activities of the antioxidative enzymes, superoxide dismutase, and catalase in the circulation were accompanied by increased levels of free intracellular thiols and glutathionylated proteins after treatment with the L. deterrimus extract. In addition to a systemic antioxidant effect, the administration of the extract to diabetic rats also had a positive localized effect on pancreatic islets where it decreased AGE formation, and increased the expression of chemokine CXCL12 protein that mediates the restoration of β-cell population through the activation of the serine/threonine-specific Akt protein kinase prosurvival pathway. As a result, the numbers of proliferating cell nuclear antigen- (PCNA-) and insulin-positive β-cells were increased. These results show that the ability of the L. deterrimus extract to alleviate oxidative stress and increase β-cell mass represents a therapeutic potential for diabetes management.

Targeting the pancreatic β-cell to treat diabetes

Diabetes is a leading cause of morbidity and mortality worldwide, and predicted to affect over 500 million people by 2030. However, this growing burden of disease has not been met with a comparable expansion in therapeutic options. The appreciation of the pancreatic β-cell as a central player in the pathogenesis of both type 1 and type 2 diabetes has renewed focus on ways to improve glucose homeostasis by preserving, expanding and improving the function of this key cell type. Here, we provide an overview of the latest developments in this field, with an emphasis on the most promising strategies identified to date for treating diabetes by targeting the β-cell.

Making β cells from adult cells within the pancreas

Cell therapy is currently considered as a potential therapeutic alternative to traditional treatments of diabetes. Islet and whole pancreas transplantations provided the proof-of-concept of glucose homeostasis restoration after replenishment of the deficiency of β cells responsible for the disease. Current limitations of these procedures have led to the search for strategies targeting replication of pre-existing β cells or transdifferentiation of progenitors and adult cells. These investigations revealed an unexpected plasticity towards β cells of adult cells residing in pancreatic epithelium (eg, acinar, duct, and α cells). Here we discuss recent developments in β-cell replication and β-cell transdifferentiation of adult epithelial pancreatic cells, with an emphasis on techniques with a potential for clinical translation.

Small-molecule inducer of β cell proliferation identified by high-throughput screening

The identification of factors that promote β cell proliferation could ultimately move type 1 diabetes treatment away from insulin injection therapy and toward a cure. We have performed high-throughput, cell-based screens using rodent β cell lines to identify molecules that induce proliferation of β cells. Herein we report the discovery and characterization of WS6, a novel small molecule that promotes β cell proliferation in rodent and human primary islets. In the RIP-DTA mouse model of β cell ablation, WS6 normalized blood glucose and induced concomitant increases in β cell proliferation and β cell number. Affinity pulldown and kinase profiling studies implicate Erb3 binding protein-1 and the IκB kinase pathway in the mechanism of action of WS6.