Glucose regulated production of human insulin in rat hepatocytes

Applications of Genome-Editing Technologies for Type 1 Diabetes

Type 1 diabetes (T1D) is a chronic autoimmune disease characterized by the destruction of insulin-producing pancreatic β-cells by the immune system. Although conventional therapeutic modalities, such as insulin injection, remain a mainstay, recent years have witnessed the emergence of novel treatment approaches encompassing immunomodulatory therapies, such as stem cell and β-cell transplantation, along with revolutionary gene-editing techniques. Notably, recent research endeavors have enabled the reshaping of the T-cell repertoire, leading to the prevention of T1D development. Furthermore, CRISPR-Cas9 technology has demonstrated remarkable potential in targeting endogenous gene activation, ushering in a promising avenue for the precise guidance of mesenchymal stem cells (MSCs) toward differentiation into insulin-producing cells. This innovative approach holds substantial promise for the treatment of T1D. In this review, we focus on studies that have developed T1D models and treatments using gene-editing systems.

Modification of a Constitutive to Glucose-Responsive Liver-Specific Promoter Resulted in Increased Efficacy of Adeno-Associated Virus Serotype 8-Insulin Gene Therapy of Diabetic Mice

We have previously used a hepatotropic adeno-associated viral (AAV) vector with a modified human insulin gene to treat diabetic mice. The HLP (hybrid liver-specific promoter) used was constitutively active and non-responsive to glucose. In this study, we examined the effects of addition of glucose responsive elements (R3G) and incorporation of a 3' albumin enhancer (3'iALB) on insulin expression. In comparison with the original promoter, glucose responsiveness was only observed in the modified promoters in vitro with a 36 h lag time before the peak expression. A 50% decrease in the number of viral particles at 5 × 10⁹ vector genome (vg)/mouse was required by AAV8-R3GHLP-hINSco to reduce the blood sugar level to near normoglycemia when compared to the original AAV8-HLP-hINSco that needed 1 × 10¹⁰ vg/mouse. The further inclusion of an 860 base-pairs 3'iALB enhancer component in the 3' untranslated region increased the in vitro gene expression significantly but this increase was not observed when the packaged virus was systemically injected in vivo. The addition of R3G to the HLP promoter in the AAV8-human insulin vector increased the insulin expression and secretion, thereby lowering the required dosage for basal insulin treatment. This in turn reduces the risk of liver toxicity and cost of vector production.

Partial pancreatic transdifferentiation of primary human hepatocytes in the livers of a humanised mouse model

BACKGROUND

Gene therapy is one treatment that may ultimately cure type 1 diabetes. We have previously shown that the introduction of furin-cleavable human insulin (INS-FUR) to the livers in several animal models of diabetes resulted in the reversal of diabetes and partial pancreatic transdifferentiation of liver cells. The present study investigated whether streptozotocin-diabetes could be reversed in FRG mice in which chimeric mouse-human livers can readily be established and, in addition, whether pancreatic transdifferentiation occurred in the engrafted human hepatocytes.

METHODS

Engraftment of human hepatocytes was confirmed by measuring human albumin levels. Following delivery of the empty vector or the INS-FUR vector to diabetic FRG mice, mice were monitored for weight and blood glucose levels. Intraperitoneal glucose tolerance tests (IPGTTs) were performed. Expression levels of pancreatic hormones and transcription factors were determined by a reverse transcriptase-polymerase chain reaction (RT-PCR) and immunohistochemistry.

RESULTS

Diabetes was reversed for a period of 60 days (experimental endpoint) after transduction with INS-FUR. IPGTTs of the insulin-transduced animals were not significantly different from nondiabetic animals. Immunofluorescence microscopy revealed the expression of human albumin and insulin in transduced liver samples. Quantitative RT-PCR showed expression of human and mouse endocrine hormones and β-cell transcription factors, indicating partial pancreatic transdifferentiation of mouse and human hepatocytes. Nonfasting human C-peptide levels were significantly higher than mouse levels, suggesting that transdifferentiated human hepatocytes made a significant contribution to the reversal of diabetes.

CONCLUSIONS

These data show that human hepatocytes can be induced to undergo partial pancreatic transdifferentiation in vivo, indicating that the technology holds promise for the treatment of type 1 diabetes.

Harnessing endogenous signals from hepatocytes using a low volume multi-well plate

Hepatocytes are highly differentiated epithelial cells that lose their phenotype and function when removed from the in vivo environment. Given the importance of hepatic cultures for drug toxicity, bioartificial liver assist devices and basic biology studies, considerable efforts have been focused on the maintenance of hepatic function in vitro. The methods used to date include co-cultivation of hepatocytes with stromal cells, organizing these cells into spheroids and imbedding them into bioactive gels. Our team has recently demonstrated that primary rat hepatocytes confined to microfluidic channels in the absence of convection maintained the epithelial phenotype through upregulation of endogenous signals including hepatocyte growth factor (HGF). The objective of the present study was to transition from microfluidic devices, which are somewhat specialized and challenging to use, towards low volume multiwell plates ubiquitous in biology laboratories. Using a combination of 3D printing and micromolding we have constructed inserts that can be placed into standard 12-well plates and can be used to create low volume culture conditions under which primary hepatocytes maintained a differentiated phenotype. This phenotype enhancement was confirmed by hepatic function assays including albumin synthesis and expression. Importantly we confirmed upregulation of HGF inside the low volume culture plates and demonstrated that inhibition of HGF signaling degraded the hepatic phenotype in our cell culture platform. Overall, this study outlines a new cell culture system that leverages the low volume effects of microfluidic channels in a multiwell plate format. Beyond hepatocytes, such a system may be of use in the maintenance of other difficult-to-culture cells including stem cells and primary cancer cells.

The Morphology of Islets within the Porcine Donor Pancreas Determines the Isolation Result: Successful Isolation of Pancreatic Islets can Now be Achieved from Young Market Pigs

Clinical islet allotransplantation has become an increasingly efficient “routine ” therapy in recent years. Shortage of human donor organs leads to porcine pancreatic islets as a potential source for islet xenotransplantation. Yet it is still very difficult to isolate sufficient numbers of intact porcine islets, particularly from young market pigs. In the following study islets were successfully isolated from retired breeders [4806 ± 720 islet equivalents per gram organ (IEQ/g); n = 25; 2–3 years old; RB] and also from young hybrid pigs [2868 ± 260 IEQ/g; n = 65; 4–6 months old; HY] using LiberasePI and a modified version of Ricordi's digestion-filtration technique. As expected, isolations from RB showed significantly better results (p < 0.002). A retrospective histological analysis of almost all donor pancreases showed that the majority of organs from RB (80%) contained mainly large islets (diameter >200 μm), in contrast to only 35% of all pancreases from HY. Remarkably, the islet size in situ, regardless whether detected in RB or HY, strongly determined the isolation result. A donor organ with predominantly large islets resulted in significantly higher numbers of IEQs compared with a donor organ with predominantly small islets [RBLarge Islets: 5680 ± 3,318 IEQ/g n = 20); RBSmall Islets: 1353 ± 427 IEQ/g (n = 5); p < 0.02]. In addition, isolation results were strongly influenced by the quality of the LiberasePI batch, and therefore single batch testing is invariably required. Purification was performed using Ficoll or OptiPrep™ density gradient centrifugation manually or in the COBE cell processor. Although islet purity was highest when OptiPrep™ was used, final islet yields did not differ between the different purification methods. Our study demonstrates that islet size in situ is an extremely critical parameter for highly successful islet isolation; consequently, we are now performing a morphological screening of each donor organ prior to the isolation process. Under these conditions highly successful isolations can reliably be performed even from young market pigs.

mRNA destabilization improves glycemic responsiveness of transcriptionally regulated hepatic insulin gene therapy in vitro and in vivo

BACKGROUND

Hepatic insulin gene therapy (HIGT) employing a glucose and insulin sensitive promoter to direct insulin transcription can lower blood sugars within 2 h of an intraperitoneal glucose challenge. However, post-challenge blood sugars frequently decline to below baseline. We hypothesize that this 'over-shoot' hypoglycemia results from sustained translation of long-lived transgene message, and that reducing pro-insulin message half-life will ameliorate post-challenge hypoglycemia.

METHODS

We compared pro-insulin message content and insulin secretion from primary rat hepatocytes expressing insulin from either a standard construct (2xfur), or a construct producing a destabilized pro-insulin message (InsTail), following exposure to stimulating or inhibitory conditions.

RESULTS

Hepatocytes transduced with a 2xfur construct accumulated pro-insulin message, and exhibited increased insulin secretion, under conditions that both inhibit or stimulate transcription. By contrast, pro-insulin message content remained stable in InsTail expressing cells, and insulin secretion increased less than 2xfur during prolonged stimulation. During transitions from stimulatory to inhibitory conditions, or vice versa, amounts of pro-insulin message changed more rapidly in InsTail expressing cells than 2xfur expressing cells. Importantly, insulin secretion increased during the transition from stimulation to inhibition in 2xfur expressing cells, although it remained unchanged in InsTail expressing cells. Use of the InsTail destabilized insulin message tended to more rapidly reduce glucose induced glycemic excursions, and limit post-load hypoglycemia in STZ-diabetic mice in vivo.

CONCLUSIONS

The data obtained in the present study suggest that combining transcriptional and post-transcriptional regulatory strategies may reduce undesirable glycemic excursion in models of HIGT.

Cell biology is different in small volumes: endogenous signals shape phenotype of primary hepatocytes cultured in microfluidic channels

The approaches for maintaining hepatocytes in vitro are aimed at recapitulating aspects of the native liver microenvironment through the use of co-cultures, surface coatings and 3D spheroids. This study highlights the effects of spatial confinement-a less studied component of the in vivo microenvironment. We demonstrate that hepatocytes cultured in low-volume microfluidic channels (microchambers) retain differentiated hepatic phenotype for 21 days whereas cells cultured in regular culture plates under identical conditions de-differentiate after 7 days. Careful consideration of nutrient delivery and oxygen tension suggested that these factors could not solely account for enhanced cell function in microchambers. Through a series of experiments involving microfluidic chambers of various heights and inhibition of key molecular pathways, we confirmed that phenotype of hepatocytes in small volumes was shaped by endogenous signals, both hepato-inductive growth factors (GFs) such as hepatocyte growth factor (HGF) and hepato-disruptive GFs such as transforming growth factor (TGF)-β1. Hepatocytes are not generally thought of as significant producers of GFs–this role is typically assigned to nonparenchymal cells of the liver. Our study demonstrates that, in an appropriate microenvironment, hepatocytes produce hepato-inductive and pro-fibrogenic signals at the levels sufficient to shape their phenotype and function.

Hepatic insulin gene therapy prevents diabetic enteropathy in STZ-treated CD-1 mice

Depending on the population examined, from 6 to 83% of people with diabetes mellitus exhibit symptoms of altered gut motility, manifesting as dysphagia, reflux, early satiety, nausea, abdominal pain, diarrhea, or constipation. Hyperglycemia-induced cell loss within the enteric nervous system has been demonstrated in both diabetic rodents and patients with diabetes. Glycemic control is recommended to prevent diabetic gastroenteropathy but is often difficult to achieve with current treatment modalities. We asked if hepatic insulin gene therapy (HIGT) could inhibit the development of diabetic gastroenteropathy in mice. Bowel length, bowel transit, colonic muscle relaxation, and the numbers of both stimulatory and inhibitory neurons in the colonic myenteric plexus were compared in groups of diabetic mice (DM), control nondiabetic mice (Con), and diabetic mice treated with HIGT (HIGT). Delivery of a metabolically responsive insulin transgene to the liver of STZ-diabetic mice with an adeno-associated virus, sero-type 8 (AAV8) produced near-normal blood sugars for over 1 month and prevented anatomic, functional, and neurohistologic changes observed in diabetic mice. We conclude that in addition to normalizing oxidative metabolism in diabetic rodents, HIGT is sufficient to prevent the development of diabetic gastroenteropathy.

Engineered insulin secretion from neuroendocrine cells isolated from human thyroid

BACKGROUND

Insulin-secreting beta-like cells are vulnerable to diabetic autoimmunity. We hypothesized that human thyroid neuroendocrine (NE) cells could be engineered to secrete human insulin, be glucose-responsive, and avoid autoimmunity.

METHODS

Collagenase-digested thyroid tissue was cultured and subjected to size-based fluorescence-activated cell sorting. Insulin secretion and storage in NE cells transduced with viral vectors carrying an insulin sequence was assessed by enzyme-linked immunosorbent assay (ELISA) and immunogold transmission electron microscopy (TEM). Baseline mRNA expression was assessed by Illumina expression array analysis. Transduction with retrovirus expressing transcription factors PDX1, NGN3, MAFA, or HNF6 altered mRNA expression in a custom polymerase chain reaction (PCR) array. Gastrin-releasing peptide (GRP) in conditioned medium and cell lysates was determined by reverse transcription (RT)-PCR, ELISA, and immunohistochemistry.

RESULTS

Isolation yielded an average of 2.2 × 10(6) cells/g thyroid tissue, which stained for calcitonin/calcitonin gene-related protein, expressed genes consistent with NE origins, and secreted GRP. Transduced cells secreted 56 % and retained 48 % of total insulin produced. Immunogold TEM revealed insulin in secretory vesicles. PDX1, NGN3, and MAFA overexpression increased expression of genes typical for hepatocytes and beta cells. Overexpression of HNF6 also increased the message of genes critical for glucose sensing.

CONCLUSIONS

Human thyroid NE cells can produce human insulin, fractions of which are both secreted and retained in secretory granules. Overexpression of HNF6, PDX1, or NGN3 enhances expression of both hepatocyte and beta cell typical mRNAs, including the message of proteins critical for glucose sensing. These data suggest that reimplantation of engineered autologous NE cells may develop as a viable treatment for diabetes mellitus type 1.

Therapeutic effects of a non-β cell bioartificial pancreas in diabetic mice

BACKGROUND

Cell-based insulin therapies can potentially improve glycemic regulation in insulin-dependent diabetic patients. Enteroendocrine cells engineered to secrete recombinant insulin have exhibited glycemic efficacy, but have been primarily studied as uncontrollable growth systems in immune incompetent mice. Furthermore, reports suggest that suboptimal insulin secretion remains a barrier to expanded application.

METHODS

Genetic and tissue engineering strategies were applied to improve recombinant insulin secretion from intestinal L-cells on both a per-cell and per-graft basis. Transduction of insulin-expressing GLUTag L-cells with lentivirus carrying an additional human insulin gene-enhanced secretion twofold. We infected cells with lentivirus expressing a luciferase reporter gene to track cell survival in vivo. To provide a growth-controlled and immune protective environment without affecting secretory capacity, cells were microencapsulated in barium alginate. Approximately 9×10(7) microencapsulated cells were injected intraperitoneally in immune competent streptozotocin-induced diabetic mice for therapeutic efficacy evaluation.

RESULTS

Graft insulin secretion was increased to 16 to 24 mU insulin per day. Transient normoglycemia was achieved in treated mice two days after transplantation, and endogenous insulin was sufficient to sustain body weights of treated mice receiving minimal supplementation.

CONCLUSION

Glycemic efficacy of a bioartificial pancreas based on insulin-secreting enteroendocrine cells is insufficient as a standalone therapy, despite enhancement of graft insulin secretion capacity. Supplemental strategies to alleviate secretion limitations should be pursued.

Engineered hair follicle mesenchymal stem cells overexpressing controlled-release insulin reverse hyperglycemia in mice with type L diabetes

Genetically engineered stem cells that overexpress genes encoding therapeutic products can be exploited to correct metabolic disorders by repairing and regenerating diseased organs or restoring their function. Hair follicles are readily accessible and serve as a rich source of autologous stem cells for cell-based gene therapy. Here we isolated mesenchymal stem cells from human hair follicles (HF-MSCs) and engineered them to overexpress the human insulin gene and release human insulin in a time- and dose-dependent manner in response to rapamycin. The engineered HF-MSCs retained their characteristic cell surface markers and retained their potential to differentiate into adipocytes and osteoblasts. When mice with streptozotocin-induced type 1 diabetes were engrafted with these engineered HF-MSCs, these cells expressed and released a dose of human insulin, dramatically reversed hyperglycemia, and significantly reduced death rate. Moreover, the engineered HF-MSCs did not form detectable tumors throughout the 120-day animal tests in our experiment. Our results show that HF-MSCs can be used to safely and efficiently express therapeutic transgenes and therefore show promise for cell-based gene therapy of human disease.

Pancreatic transdifferentiation in porcine liver following lentiviral delivery of human furin-cleavable insulin

Type I diabetes mellitus (TID) results from the autoimmune destruction of the insulin-producing pancreatic β-cells. Gene therapy is one strategy being actively explored to cure TID by affording non-β-cells the ability to secrete insulin in response to physiologic stimuli. In previous studies, we used a novel surgical technique to express furin-cleavable human insulin (INS-FUR) in the livers of streptozotocin (STZ)-diabetic Wistar rats and nonobese diabetic (NOD) mice with the use of the HMD lentiviral vector. Normoglycemia was observed for 500 and 150 days, respectively (experimental end points). Additionally, some endocrine transdifferentiation of the liver, with storage of insulin in granules, and expression of some β-cell transcription factors (eg, Pdx1, Neurod1, Neurog3, Nkx2-2, Pax4) and pancreatic hormones in both studies. The aim of this study was to determine if this novel approach could induce liver to pancreatic transdifferentiation to reverse diabetes in pancreatectomized Westran pigs. Nine pigs were used in the study, however only one pig maintained normal fasting blood glucose levels for the period from 10 to 44 days (experimental end point). This animal was given 2.8 × 10(9) transducing units/kg of the lentiviral vector expressing INS-FUR. A normal intravenous glucose tolerance test was achieved at 30 days. Reverse-transcription polymerase chain reaction analysis of the liver tissue revealed expression of several β-cell transcription factors, including the key factors, Pdx-1 and Neurod1, pancreatic hormones, glucagon, and somatostatin; however, endogenous pig insulin was not expressed. Triple immunofluorescence showed extensive insulin expression, as was previously observed in our studies with rodents. Additionally, a small amount of glucagon and somatostatin protein expression was seen. Collectively, these data indicate that pancreatic transdifferentiation of the liver tissue had occurred. Our data suggest that this regimen may ultimately be used clinically to cure TID, however more work is required to replicate the successful reversal of diabetes in increased numbers of pigs.

Long-term reversal of diabetes in non-obese diabetic mice by liver-directed gene therapy

BACKGROUND

Type 1 diabetes (T1D) results from an autoimmune attack against the insulin-producing β-cells of the pancreas. The present study aimed to reverse T1D by gene therapy.

METHODS

We used a novel surgical technique, which involves isolating the liver from the circulation before the delivery of a lentiviral vector carrying furin-cleavable human insulin (INS-FUR) or empty vector to the livers of diabetic non-obese diabetic mice (NOD). This was compared with the direct injection of the vector into the portal circulation. Mice were monitored for body weight and blood glucose. Intravenous glucose tolerance tests were performed. Expression of insulin and pancreatic transcription factors was determined by the reverse transcriptase-polymerase chain reaction and immunohistochemistry and immunoelectron microscopy was used to localise insulin.

RESULTS

Using the novel surgical technique, we achieved long-term transduction (42% efficiency) of hepatocytes, restored normoglycaemia for 150 days (experimental endpoint) and re-established normal glucose tolerance. We showed the expression of β-cell transcription factors, murine insulin, glucagon and somatostatin, and hepatic storage of insulin in granules. The expression of hepatic markers, C/EBP-β, G6PC, AAT and GLUI was down-regulated in INS-FUR-treated livers. Liver function tests remained normal, with no evidence of intrahepatic inflammation or autoimmune destruction of the insulin-secreting liver tissue. By comparison, direct injection of INS-FUR reduced blood glucose levels, and no pancreatic transdifferentiation or normal glucose tolerance was observed.

CONCLUSIONS

This gene therapy protocol has, for the first time, permanently reversed T1D with normal glucose tolerance in NOD mice and, as such, represents a novel therapeutic strategy for the treatment of T1D.

Correction of Diabetic Hyperglycemia and Amelioration of Metabolic Anomalies by Minicircle DNA Mediated Glucose-Dependent Hepatic Insulin Production

Type 1 diabetes mellitus (T1DM) is caused by immune destruction of insulin-producing pancreatic β-cells. Commonly used insulin injection therapy does not provide a dynamic blood glucose control to prevent long-term systemic T1DM-associated damages. Donor shortage and the limited long-term success of islet transplants have stimulated the development of novel therapies for T1DM. Gene therapy-based glucose-regulated hepatic insulin production is a promising strategy to treat T1DM. We have developed gene constructs which cause glucose-concentration-dependent human insulin production in liver cells. A novel set of human insulin expression constructs containing a combination of elements to improve gene transcription, mRNA processing, and translation efficiency were generated as minicircle DNA preparations that lack bacterial and viral DNA. Hepatocytes transduced with the new constructs, ex vivo, produced large amounts of glucose-inducible human insulin. In vivo, insulin minicircle DNA (TA1m) treated streptozotocin (STZ)-diabetic rats demonstrated euglycemia when fasted or fed, ad libitum. Weight loss due to uncontrolled hyperglycemia was reversed in insulin gene treated diabetic rats to normal rate of weight gain, lasting ∼1 month. Intraperitoneal glucose tolerance test (IPGT) demonstrated in vivo glucose-responsive changes in insulin levels to correct hyperglycemia within 45 minutes. A single TA1m treatment raised serum albumin levels in diabetic rats to normal and significantly reduced hypertriglyceridemia and hypercholesterolemia. Elevated serum levels of aspartate transaminase, alanine aminotransferase, and alkaline phosphatase were restored to normal or greatly reduced in treated rats, indicating normalization of liver function. Non-viral insulin minicircle DNA-based TA1m mediated glucose-dependent insulin production in liver may represent a safe and promising approach to treat T1DM.

Glucose regulates secretion of exogenously expressed insulin from HepG2 cells in vitro and in a mouse model of diabetes mellitus in vivo

Glucose-controlled insulin secretion is a key component of its regulation. Here, we examined whether liver cell secretion of insulin derived from an engineered construct can be regulated by glucose. Adenovirus constructs were designed to express proinsulin or mature insulin containing the conditional binding domain (CBD). This motif binds GRP78 (HSPA5), an endoplasmic reticulum (ER) protein that enables the chimeric hormone to enter into and stay within the ER until glucose regulates its release from the organelle. Infected HepG2 cells expressed proinsulin mRNA and the protein containing the CBD. Immunocytochemistry studies suggested that GRP78 and proinsulin appeared together in the ER of the cell. The amount of hormone released from infected cells varied directly with the ambient concentration of glucose in the media. Glucose-regulated release of the hormone from infected cells was rapid and sustained. Removal of glucose from the cells decreased release of the hormone. In streptozotocin-induced diabetic mice, when infected with adenovirus expressing mature insulin, glucose levels declined. Our data show that glucose regulates release of exogenously expressed insulin from the ER of liver cells. This approach may be useful in devising new ways to treat diabetes mellitus.

Regulation of insulin biosynthesis in non-beta cells by a heat shock promoter

Insulin production under the stringent control is the main issue in gene-based therapeutic strategies directed to type 1 diabetes. As a novel approach, inducible promoters may provide a promising tool for this purpose. In this study, we hypothesize that this control may be achieved via a promoter derived from the heat shock multigene family, Hsp70 A1A, which is inducible at 42°C. To yield mature insulin in transfected fibroblasts (3T3/NIH), a recombinant human insulin gene consisting of sequences corresponding to furin cleavable sites was fused to the promoter. Heat-stimulated cells initiated to release biologically active insulin within 30 min with a ten-fold increase after 24 h. The role of upstream regulatory elements of the promoter on its activity in heat stress conditions was examined. No significant difference between the activity of the minimal and full-length promoters was observed. This promoter exhibited low basal expression in non-inducing conditions. Results indicate that this promoter is responsive to a heat induction after approximately 30 min which causes an efficient insulin production over a relatively short period of time. These potential features of this promoter may provide an insight to control the insulin production in vivo upon an external and physical stimulation.

Insulin gene therapy from design to beta cell generation

Despite the fact that insulin injection can protect diabetic patients from developing diabetes-related complications, recent meta-analyses indicate that rapid and long-acting insulin analogues only provide a limited benefit compared with conventional insulin regarding glycemic control. As insulin deficiency is the main sequel of type-1 diabetes (T1D), transfer of the insulin gene-by-gene therapy is becoming an attractive treatment modality even though T1D is not caused by a single genetic defect. In contrast to human insulin and insulin analogues, insulin gene therapy targets to supplement patients not only with insulin but also with C-peptide. So far, insulin gene therapy has had limited success because of delayed and/or transient gene expression. Sustained insulin gene expression is now feasible using current gene-therapy vectors providing patients with basal insulin coverage, but management of postprandial hyperglycaemia is still difficult to accomplish because of the inability to properly control insulin secretion. Enteroendocrine cells of the gastrointestinal track (K cells and L cells) may be ideal targets for insulin gene therapy, but cell-targeting difficulties have limited practical implementation of insulin gene therapy for diabetes treatment. Therefore, recent gene transfer technologies developed to generate authentic beta cells through transdifferentiation are also highlighted in this review.

Novel diabetes mellitus treatment: mature canine insulin production by canine striated muscle through gene therapy

Muscle-targeted gene therapy using insulin genes has the potential to provide an inexpensive, low maintenance alternative or adjunctive treatment method for canine diabetes mellitus. A canine skeletal muscle cell line was established through primary culture, as well as through transdifferentiation of canine fibroblasts after infection with a myo-differentiation gene containing adenovirus vector. A novel mutant furin-cleavable canine preproinsulin gene insert (cppI4) was designed and created through de novo gene synthesis. Various cell lines, including the generated canine muscle cell line, were transfected with nonviral plasmids containing cppI4. Insulin and desmin immunostaining were used to prove insulin production by muscle cells and specific canine insulin ELISA to prove mature insulin secretion into the medium. The canine myoblast cultures proved positive on desmin immunostaining. All cells tolerated transfection with cppI4-containing plasmid, and double immunostaining for insulin and desmin proved present in the canine cells. Canine insulin ELISA assessment of medium of cppI4-transfected murine myoblasts and canine myoblast and fibroblast mixture proved presence of mature fully processed canine insulin, 24 and 48 h after transfection. The present study provides proof of principle that canine muscle cells can be induced to produce and secrete canine insulin on transfection with nonviral plasmid DNA containing a novel mutant canine preproinsulin gene that produces furin-cleavable canine preproinsulin. This technology could be developed to provide an alternative canine diabetes mellitus treatment option or to provide a constant source for background insulin, as well as C-peptide, alongside current treatment options.

Gene regulation systems for gene therapy applications in the central nervous system

Substantial progress has been made in the development of novel gene therapy strategies for central nervous system (CNS) disorders in recent years. However, unregulated transgene expression is a significant issue limiting human applications due to the potential side effects from excessive levels of transgenic protein that indiscriminately affect both diseased and nondiseased cells. Gene regulation systems are a tool by which tight tissue-specific and temporal regulation of transgene expression may be achieved. This review covers the features of ideal regulatory systems and summarises the mechanics of current exogenous and endogenous gene regulation systems and their utility in the CNS.

Construction of Plasmid Insulin Gene Vector Containing Metallothionein IIA (pcDNAMTChIns) and Carbohydrate Response Element (ChoRE), and Its Expression in NIH3T3 Cell Line

BACKGROUND

Type 1 diabetes mellitus is one of the metabolic diseases that cause insulin-producing pancreatic ß cells be destroyed by immune system self-reactive T cells. Recent-ly, new treatment methods have been developed including use of the stem cells, ß islet cells transplantation and gene therapy by viral and non-viral gene constructs.

OBJECTIVES

The aim of this project was preparing the non-viral vector containing the glucose inducible insulin gene and using it in the NIH3T3 cell line.

MATERIALS AND METHODS

Cloning was carried out by standard methods. Total RNA was extracted from pancreatic tissue, RNA was converted to cDNA using RT-PCR reaction and preproinsulin gene was amplified using specific primers. PNMTCH plasmid was extract-ed and digested by NotI, HindIII, and MTIIA and ChoRE genes were purified and cloned into pcDNA3.1 (-) plasmid and named pcDNAMTCh. Finally, the preproinsulin genes were cloned into pcDNA3.1 (-) plasmid and pcDNAMTChIns was built.

RESULTS

The cloned gene constructs were evaluated by restriction enzyme digestion and RT-PCR. The NIH3T3 cells were transfected by plasmid naked DNA containing preproinsu-lin gene and expression was confirmed by Reverse Transcriptase PCR and Western Blot-ting Techniques.

CONCLUSIONS

Gel electrophoresis of PCR products confirmed that cloning was per-formed correctly. The expression of preproinsulin gene in recombinant plasmid in NI-H3T3 cell line was observed for the first time. The findings in this study can be the basis of further research on diabetes mellitus type 1 gene therapy on animals.

Combinatorial insulin secretion dynamics of recombinant hepatic and enteroendocrine cells

One of the most promising cell-based therapies for combating insulin-dependent diabetes entails the use of genetically engineered non-β cells that secrete insulin in response to physiologic stimuli. A normal pancreatic β cell secretes insulin in a biphasic manner in response to glucose. The first phase is characterized by a transient stimulation of insulin to rapidly lower the blood glucose levels, which is followed by a second phase of insulin secretion to sustain the lowered blood glucose levels over a longer period of time. Previous studies have demonstrated hepatic and enteroendocrine cells to be appropriate hosts for recombinant insulin expression. Due to different insulin secretion kinetics from these cells, we hypothesized that a combination of the two cell types would mimic the biphasic insulin secretion of normal β cells with higher fidelity than either cell type alone. In this study, insulin secretion experiments were conducted with two hepatic cell lines (HepG2 and H4IIE) transduced with 1 of 3 adenoviruses expressing the insulin transgene and with a stably transfected recombinant intestinal cell line (GLUTag-INS). Insulin secretion was stimulated by exposing the cells to glucose only (hepatic cells), meat hydrolysate only (GLUTag-INS), or to a cocktail of the two secretagogues. It was found experimentally that the recombinant hepatic cells secreted insulin in a more sustained manner, whereas the recombinant intestinal cell line exhibited rapid insulin secretion kinetics upon stimulation. The insulin secretion profiles were computationally combined at different cell ratios to arrive at the combinatorial kinetics. Results indicate that combinations of these two cell types allow for tuning the first and second phase of insulin secretion better than either cell type alone. This work provides the basic framework in understanding the secretion kinetics of the combined system and advances it towards preclinical studies.

Delivery of a therapeutic protein by immune-privileged Sertoli cells

Immune-privileged Sertoli cells survive long term after allogeneic or xenogeneic transplantation without the use of immunosuppressive drugs, suggesting they could be used as a vehicle to deliver therapeutic proteins. As a model to test this, we engineered Sertoli cells to transiently produce basal levels of insulin and then examined their ability to lower blood glucose levels after transplantation into diabetic SCID mice. Mouse and porcine Sertoli cells transduced with a recombinant adenoviral vector containing furin-modified human proinsulin cDNA expressed insulin mRNA and secreted insulin protein. Transplantation of 5-20 million insulin-expressing porcine Sertoli cells into diabetic SCID mice significantly decreased blood glucose levels in a dose-dependent manner, with 20 million Sertoli cells decreasing blood glucose levels to 9.8 ± 2.7 mM. Similar results were obtained when 20 million insulin-positive, BALB/c mouse Sertoli cells were transplanted; blood glucose levels dropped to 6.3 ± 2.4 mM and remained significantly lower for 5 days. To our knowledge, this is the first study to demonstrate Sertoli cells can be engineered to produce and secrete a clinically relevant factor that has a therapeutic effect, thus supporting the concept of using immune-privileged Sertoli cells as a potential vehicle for gene therapy.

Glucose-responsive gene expression system for gene therapy

Regulation of gene expression by glucose is an important mechanism for mammals in adapting to their nutritional environment. Glucose, the primary fuel for most cells, modulates gene expression that is crucial in the cellular adaptation to glycemic variation. Transcription of the genes for insulin and glycolytic and lipogenic enzymes is stimulated by glucose in pancreatic beta-cells and liver. Recent findings further support the key role of the carbohydrate-responsive element binding protein in the regulation of glycolytic and lipogenic genes by glucose and dietary carbohydrates. Herein, we review the transcriptional regulation of glucose-responsive genes, and recent advances in the gene therapy using glucose-responsive gene expression for diabetes.

A cell-based approach for diabetes treatment using engineered non-beta cells

BACKGROUND

Implantation of insulin-secreting cells has the potential to provide tight glycemic regulation in diabetic subjects. Implantation of cadaveric human islets in immunosuppressed human patients is currently applied at a very small scale. To overcome the limitations of tissue availability and recipient immunosuppression, encapsulation of nonautologous cells and use of potentially autologous nonislet cells, the latter engineered for insulin secretion, are being pursued. This article reports on recent findings with the implantation of tissue constructs containing enteroendocrine cells stably expressing recombinant insulin in diabetic mice. The concept of a dual recombinant hepatic and enteroendocrine cell system, which may better approximate the secretory response of islets, is discussed.

METHODS

Mouse GLUTag-INS cells engineered to secrete human insulin were developed and incorporated in tissue constructs as reported previously. Constructs were implanted intraperitoneally in diabetic mice, and blood glucose levels, animal weights, and plasma insulin levels were measured at various time points.

RESULTS

GLUTag-INS-containing tissue constructs secreted insulin preimplantation and postexplantation, and human insulin was detected in the plasma of diabetic mice. However, normoglycemia was not restored.

CONCLUSIONS

A variety of cell types and of encapsulation methods to enhance immune acceptance of insulin-secreting grafts are being pursued. Recombinant enteroendocrine cells show promise, but it is likely that they need to be combined with recombinant hepatic cells to achieve glycemic normalization.

Hepatic insulin gene therapy normalizes diurnal fluctuation of oxidative metabolism in diabetic BB/Wor rats

Previous studies of hepatic insulin gene therapy (HIGT) focused on glycemic effects of insulin produced from hepatocytes. In this study, we extend the observations of glycemic control with metabolically regulated HIGT to include systemic responses and whole-body metabolism. An insulin transgene was administered with an adenoviral vector [Ad/(GlRE)(3)BP1-2xfur] to livers of BB/Wor rats made diabetic with polyinosinic polycytidilic acid (poly-I:C) (HIGT group), and results compared with nondiabetic controls (non-DM), and diabetic rats receiving different doses of continuous-release insulin implants (DM-low BG and DM-high BG). Blood glucose and growth normalized in HIGT, with lower systemic insulin levels, elevated glucagon, and increased heat production compared with non-DM. Minimal regulation of systemic insulin levels were observed with HIGT, yet the animals maintained normal switching from carbohydrate to lipid metabolism determined by respiratory quotients (RQs), and tolerated 24-hour fasts without severe hypoglycemia. HIGT did not restore serum lipids as we observed increased triglycerides (TGs) and increased free fatty acids, but reduced weight of visceral fat pads despite normal total body fat content and retroperitoneal fat depots. HIGT favorably affects blood glucose, normalizes metabolic switching in diabetic rats, and reduces intra-abdominal fat deposition.

Co-transfection of GK and mhPINS genes into HepG2 cells confers glucose-stimulated insulin secretion

BACKGROUND

The purpose of this study was to construct an 'artificial beta cell' that can exhibit physiologic glucose-stimulated insulin secretion for the treatment of type 1 diabetes.

METHODS

Retroviral vector containing the glucokinase (GK) gene and mutated human proinsulin (mhPINS) gene was constructed. HepG2 cells were first infected with recombinant retrovirus carrying the GK and mhPINS genes, then selectively cultured with G418 to obtain the positive clones. GK and mhPINS gene transcription and expression were identified by radioimmunity, Western blot and RT-PCR techniques. Finally, the dose-response effect of glucose on insulin secretion from those HepG2 cells that expressed both GK and mhPINS genes was tested with HepG2 cells that only expressed the mhPINS gene as a control.

RESULTS

HepG2 cells with transferred GK and mhPINS genes were selectively cultured with G418 and the positive clones were obtained in 3 weeks. Four clones with GK and mhPINS gene expression were selected from 20 positive clones by radioimmunity and Western blot. We picked up one clone with a strong GK and mhPINS gene expression and named it clone Beta. In clone Beta, differences in insulin secretion at 0.5 and 0.75 mmol/L glucose concentrations were not significant (P>0.05) and differences in insulin secretion at 2.0, 3.0, 4.0, 5.0 and 6.0 mmol/L glucose concentrations were not significant (P>0.05), while there were significant differences in insulin secretion at other glucose concentrations(P<0.05). The artificial beta cell, clone Beta, obtained a glucose-stimulated insulin secretion with maximal insulin secretion at 1.75-2.00 mmol/L glucose concentrations.

DISCUSSION

An artificial beta cell that exhibits glucose-stimulated insulin secretion can be constructed successfully.

Long-term correction of diabetes in rats after lentiviral hepatic insulin gene therapy

AIMS/HYPOTHESIS

Type 1 diabetes results from the autoimmune destruction of pancreatic beta cells. Exogenous insulin therapy cannot achieve precise physiological control of blood glucose concentrations, and debilitating complications develop. Lentiviral vectors are promising tools for liver-directed gene therapy. However, to date, transduction rates in vivo remain low in hepatocytes, without the induction of cell cycling. We investigated long-term transgene expression in quiescent hepatocytes in vitro and determined whether the lentiviral delivery of furin-cleavable insulin to the liver could reverse diabetes in rats.

MATERIALS AND METHODS

To improve transduction efficiency in vitro, we optimised hepatocyte isolation and maintenance protocols and, using an improved surgical delivery method, delivered furin-cleavable insulin alone or empty vector to the livers of streptozotocin-induced diabetic rats by means of a lentiviral vector. Rats were monitored for changes in body weight and blood glucose, and intravenous glucose tolerance tests were performed. Expression of insulin was determined by RT-PCR, immunohistochemistry and electron microscopy.

RESULTS

We achieved long-term transgene expression in quiescent hepatocytes in vitro (87 +/- 1.2% transduction efficiency), with up to 60 +/- 3.2% transduction in vivo. We normalised blood glucose for 500 days-a significantly longer period than previously reported-making this the first successful study using a lentiviral vector. This procedure resulted in the expression of genes encoding several beta cell transcription factors, some pancreatic endocrine transdifferentiation, hepatic insulin storage in granules, and restoration of glucose tolerance. Liver function tests remained normal. Importantly, pancreatic exocrine transdifferentiation did not occur.

CONCLUSIONS/INTERPRETATION

Our data suggest that this regimen may ultimately be employed for the treatment of type 1 diabetes.

Efficient Production of Bioactive Insulin from Human Epidermal Keratinocytes and Tissue-Engineered Skin Substitutes: Implications for Treatment of Diabetes

Despite many years of research, daily insulin injections remain the gold standard for diabetes treatment. Gene therapy may provide an alternative strategy by imparting the ability to secrete insulin from an ectopic site. The epidermis is a self-renewing tissue that is easily accessible and can provide large numbers of autologous cells to generate insulin-secreting skin substitutes. Here we used a recombinant retrovirus to modify human epidermal keratinocytes with a gene encoding for human proinsulin containing the furin recognition sequences at the A-C and B-C junctions. Keratinocytes were able to process proinsulin and secrete active insulin that promoted glucose uptake. Primary epidermal cells produced higher amounts of insulin than cell lines, suggesting that insulin secretion may depend on the physiological state of the producer cells. Modified cells maintained the ability to stratify into 3-dimensional skin equivalents that expressed insulin at the basal and suprabasal layers. Modifications at the furin recognition sites did not improve proinsulin processing, but a single amino acid substitution in the proinsulin B chain enhanced C-peptide secretion from cultured cells and bioengineered skin substitutes 10- and 28-fold, respectively. These results suggest that gene-modified bioengineered skin may provide an alternative means of insulin delivery for treatment of diabetes.

Adeno-associated viral delivery of a metabolically regulated insulin transgene to hepatocytes

Transduction with a liver specific, metabolically responsive insulin transgene produces near-normal blood sugars in STZ-diabetic rats. To overcome the limited duration of hepatic transgene expression induced by E1A-deleted adenoviral vectors, we evaluated recombinant adeno-associated virus (rAAV2) for cell type specificity and glucose responsiveness in vitro. Co-infection of AAV2 containing the glucose responsive, liver-specific (GlRE)(3)BP-1 promoter with an empty adenovirus enhanced transduction efficiency, and shortened the duration of transgene expression in HepG2 hepatoma cells, but not primary hepatocytes. However, in the context of rAAV2, (GlRE)(3)BP-1 promoter activity remained confined to cells of hepatocyte lineage, and retained glucose responsiveness. While isolated infection with an insulin expressing rAAV2 failed to attenuate blood sugars in diabetic mice, adenoviral co-administration with the same rAAV2 induced transient, near-normal random blood sugars in a diabetic animal. We conclude that rAAV2 can induce metabolically responsive insulin secretion from hepatocytes in vitro and in vivo. However, alternative AAV serotypes will likely be required to efficiently deliver therapeutic genes to the liver for the treatment of diabetes mellitus.

Insulin-expressing engineered cell lines and primary cells: surrogate β cells from liver, gut, and other sources

PURPOSE OF REVIEW

Islet transplantation is being used to treat type 1 diabetes but is currently limited by the shortage of tissue available and by insufficient long-term function of transplanted islets. Thus, there remains significant interest in developing substitute sources of insulin-producing cells. Here we review progress in this area, focusing on insulin gene therapy and generation of new insulin-producing cells by redirecting hepatic and intestinal tissues towards a β-cell phenotype.

RECENT FINDINGS

Insulin gene therapy using non-β cells has been improved by utilizing modified insulin constructs controlled by regulatory elements to confer nutrient responsiveness, and by inducing insulin production in endocrine cells that are equipped for rapid and in some cases glucose-responsive secretion. Significant advances have also been made towards generation of insulin-producing cells via transcriptional manipulation of hepatic and intestinal cells. These approaches offer the potential of generating a virtually limitless supply of insulin-producing cells.

SUMMARY

The major challenge associated with insulin gene therapy in non-β cells is to achieve rapid, glucose-responsive secretion, while transdifferentiation approaches require additional characterization of the function and stability of insulin-producing cells. Continued efforts in these areas are warranted, as re-establishment of endogenous insulin production would be a welcome replacement to insulin injections for diabetes treatment.

Coupling of glucose response element from L-type pyruvate kinase and G6Pase promoter enhances glucose responsive activity in hepatoma cells

Type 1 diabetes results from the autoimmune destruction of pancreatic beta-cells, which leads to severe insulin deficiency. Insulin gene therapy provides an attractive approach to cure diabetes. The critical factor for insulin gene therapy in surrogate cells is to select an appropriate site for insulin expression and a tissue-specific promoter that is responsive to both physiological glucose and insulin concentrations. A novel chimeric promoter, (GIRE)n-G6Pase, consisting of a 1.6 kb glucose 6-phosphatase (G6Pase) promoter and a segment of the regulatory element derived from the L-type pyruvate kinase (L-PK) promoter, was designed to provide strong and tight control of insulin expression in liver. One or three copies of GIRE were linked to the G6Pase promoter, which showed a stronger promoter activity than the G6Pase promoter alone. The chimeric promoter was inhibited by insulin in a dosage-dependent manner and activated by glucose, two features essential for glucose metabolism. The promoter activity is conserved between species and highly specific for liver cells. The construction of a chimeric promoter with stronger and more sensitive responsive activity to glucose and insulin in liver cells could further advance studies in insulin gene therapy.

Use of glucose-responsive material to regulate insulin release from constitutively secreting cells

Genetically-engineered cells offer a solution to the cell availability problem in tissue engineering a pancreatic substitute for the treatment of insulin-dependent diabetes. These cells can be non-beta cells, such as hepatocytes or myoblasts, retrieved as a biopsy from the same patient and genetically engineered to secrete recombinant insulin constitutively or under transcriptional regulation. However, the continuous or slowly responsive insulin secretion dynamics from these cells cannot provide physiologic glucose regulation in patients. Our objective consists of using such cells as an insulin source and of regulating insulin release by incorporating a glucose-responsive material, which acts as a control barrier for insulin in a cell-material hybrid device. Experiments were performed with insulinoma betaTC3 cells, HepG2 hepatomas, and C2C12 myoblasts, the latter two genetically-modified to constitutively secrete insulin. The control barrier consisted of concanavalin A (con A)-based glucose-responsive material, which forms a gel at low and a sol at high glucose concentrations. Results demonstrated that the device released insulin at a higher rate in response to glucose challenges. In contrast, a device containing an inert hydrogel instead of glucose-responsive material released insulin at an essentially constant rate, irrespective of the surrounding glucose concentration. Necessary material improvements include increased sensitivity to glucose, so that the material responds to physiologically relevant glucose concentrations, and increased stability. The prospects of developing a properly functional, implantable substitute based on engineered non-beta cells and glucose-responsive material, and the material and device improvements that need to be made prior to in vivo experiments, are discussed.

Hepatic insulin gene therapy prevents deterioration of vascular function and improves adipocytokine profile in STZ-diabetic rats

Hepatic insulin gene therapy (HIGT) ameliorates hyperglycemia in diabetic rodents, suggesting that similar approaches may eventually provide a means to improve treatment of diabetes mellitus. However, whether the metabolic and hormonal changes produced by HIGT benefit vascular function remains unclear. The impact of HIGT on endothelium-dependent vasodilation, nitrosyl-hemoglobin content (NO-Hb), and insulin sensitivity were studied using aortic ring preparations, electron spin resonance spectroscopy (ESR), homeostasis assessment of insulin resistance (HOMA-IR) calculations, and insulin tolerance testing (ITT). Data were correlated with selected hormone and adipocytokine concentrations. Rats made diabetic with streptozotocin were treated with subcutaneous insulin pellets dosed to sustain body weights and hyperglycemia or with HIGT; nondiabetic rats served as controls. Hyperglycemic rats demonstrated impaired endothelium-dependent vasodilation, reduced levels of NO-Hb, and diminished insulin, leptin, and adiponectin concentrations compared with controls. In contrast, HIGT treatment significantly reduced blood sugars and sustained both endothelium-mediated vasodilation and NO-Hb at control levels. HOMA-IR calculations and ITT indicated enhanced insulin sensitivity among HIGT-treated rats. HIGT partially restored suppressed leptin levels in hyperglycemic rats and increased adiponectin concentrations to supranormal levels, consistent with indicators of insulin sensitivity. Our findings indicate that the metabolic milieu produced by HIGT is sufficient to preserve vascular function in diabetic rodents. These data suggest that improved glycemia, induction of a beneficial adipocytokine profile, and enhanced insulin sensitivity combine to preserve endothelium-dependent vascular function in HIGT-treated diabetic rats. Consequently, HIGT may represent a novel and efficacious approach to reduce diabetes-associated vascular dysfunction.

The bioartificial pancreas: progress and challenges

Diabetes remains a devastating disease, with tremendous cost in terms of human suffering and healthcare expenditures. A bioartificial pancreas has the potential as a promising approach to preventing or reversing complications associated with this disease. Bioartificial pancreatic constructs are based on encapsulation of islet cells with a semipermeable membrane so that cells can be protected from the host's immune system. Encapsulation of islet cells eliminates the requirement of immunosuppressive drugs, and offers a possible solution to the shortage of donors as it may allow the use of animal islets or insulin-producing cells engineered from stem cells. During the past 2 decades, several major approaches for immunoprotection of islets have been studied. The microencapsulation approach is quite promising because of its improved diffusion capacity, and technical ease of transplantation. It has the potential for providing an effective long-term treatment or cure of Type 1 diabetes.

Release of transgenic human insulin from gastric g cells: a novel approach for the amelioration of diabetes

We explored the hypothesis that meal-regulated release of insulin from gastric G cells can be used for gene therapy for diabetes. We generated transgenic mice in which the coding sequence of human insulin has been knocked into the mouse gastrin gene. Insulin was localized specifically to antral G cells of G-InsKi mice by double immunofluorescence staining using antibodies against insulin and gastrin. Insulin extracted from antral stomach of G-InsKi mice decreased blood glucose upon injection into streptozotocin-diabetic mice. Intragastric administration of peptone, a known potent luminal stimulant of gastrin secretion, induced an increase in circulating levels of transgenic human insulin from 10.7 +/- 2 to 23.3 +/- 4 pm in G-InsKi mice. Although G cell-produced insulin decreased blood glucose in G-InsKi mice, it did not cause toxic hypoglycemia. Proton pump inhibitors, pharmacological agents that increase gastrin output, caused a further increase in the circulating levels of gastric insulin (41.5 +/- 2 pm). G cell-produced insulin was released into circulation in response to the same meal-associated stimuli that control release of gastrin. The most striking aspect of the results presented here is that in the presence of the G-InsKi allele, Ins2(Akita/+) mice exhibited a marked prolongation of life span. These results imply that G cell-derived transgenic insulin is beneficial in the amelioration of diabetes. We suggest that an efficient G cells-based insulin gene therapy can relieve diabetic patients from daily insulin injections and protect them from complications of insulin insufficiency while avoiding episodes of toxic hypoglycemia.

Pharmacological regulation of the insulin receptor signaling pathway mimics insulin action in cells transduced with viral vectors

Diabetes mellitus derives from either insulin deficiency (type I) or resistance (type II). Homozygous mutations in the insulin receptor (IR) gene cause the rare leprechaunism and Rabson-Mendenhall syndromes, severe forms of hyperinsulinemic insulin resistance for which no therapy is currently available. Systems have been developed that allow protein-protein interactions to be brought under the control of small-molecule dimerizer drugs. As a potential tool to rescue glucose homeostasis at will in both insulin and insulin receptor deficiencies, we developed a recombinant chimeric insulin receptor (LFv2IRE) that can be homodimerized and activated by the small-molecule dimerizer AP20187. In HepG2 cells transduced with adeno-associated viral (AAV) vectors encoding LFv2IRE, AP20187 induces LFv2IRE homodimerization and transphosphorylation minutes after drug administration, resulting in the phosphorylation of a canonical substrate of the insulin receptor tyrosine kinase, IRS-1. AP20187 activation of LFv2IRE is dependent on the dose of drug and the amount of chimeric receptor expressed in AAV-transduced cells. Finally, AP20187-dependent activation of LFv2IRE results in insulin-like effects, such as induction of glycogen synthase activity and cellular proliferation. In vivo LFv2IRE transduction of insulin target tissues followed by AP20187 dosing may represent a therapeutic strategy to be tested in animal models of insulin resistance due to insulin receptor deficiency or of type I diabetes. This system may also represent a useful tool to dissect in vivo the independent contribution of insulin target tissues to hormone action.

Host Cells Reduce Glucose Uptake and Glycogen Deposition in Response to Hepatic Insulin Gene Therapy

BACKGROUND

Hepatic insulin gene therapy (HIGT) restores weight gain and near-normal glycemia in rodent models of insulin-deficient diabetes mellitus. However, the effect of transgenic insulin on endogenous genes and recipient cell function is relatively unexplored. To investigate hepatocellular effects of transgenic insulin expression, we evaluated intermediary glucose metabolism in primary cultured hepatocytes treated with HIGT.

METHODS

Rat hepatocytes were transduced with adenovirus expressing a glucose-responsive human insulin transgene and cultured in high-glucose and high-insulin conditions. We determined glycogen content in cell cultures and intact liver directly. Glycogenolysis was compared using glucose production of cultured cells. Glucose uptake, oxidative, and glycolytic processing were determined by radiotracer analysis or direct end-product assessment. Quantitative real-time reverse transcriptase polymerase chain reaction was used to determine expression of glucose transporter 2 (GLUT2) and glucokinase genes. GLUT2 protein abundance was determined by Western blot analysis.

RESULTS

HIGT-treated hepatocytes contained significantly less glycogen than either untreated hepatocytes or those treated with an empty virus. Glucose release owing to glycogenolysis remained normal. However, HIGT treatment significantly impaired glucose uptake and processing. Metabolic synthetic processes were not generally inhibited, as indicated by enhanced beta-hydroxybutyrate secretion. While preserving cell viability, HIGT treatment diminished expression of both glucokinase and GLUT2. In HIGT-treated streptozocin-treated diabetic rats, total liver glycogen was intermediate between diabetic animals and normal controls.

CONCLUSIONS

These results suggest gene-specific effects in recipient hepatocytes following HIGT treatment and underscore the need for expanded studies examining host cell responses to the transfer of metabolically active transgenes.

Hybrid pancreatic tissue substitute consisting of recombinant insulin-secreting cells and glucose-responsive material

Insulin-dependent diabetes is a serious pathological condition, currently treated by blood glucose monitoring and daily insulin injections, which, however, do not prevent long-term complications. A tissue-engineered pancreatic substitute has the potential to provide a more physiologic, less invasive, and potentially less costly treatment of the disease. A major issue in developing such a substitute is the cells being used. Nonpancreatic cells, retrieved from the same patient and genetically engineered to secrete insulin constitutively or with some glucose responsiveness, offer the significant advantages of being immune-acceptable and relaxing the tissue availability limitations, which exist with islets from cadaveric donors. These cells, however, do not have insulin secretion dynamics appropriate for restoration of euglycemia in higher animals and, eventually, humans. In this study, we present the concept of a hybrid pancreatic substitute consisting of such cells sequestered in a material exhibiting glucose-dependent changes of its permeability to insulin. A Concanavalin A-glycogen material sandwiched between two polycarbonate membranes and exhibiting glucose-dependent sol-gel transformations was used. Rates of insulin transport through this material in gel and sol forms were characterized for both FITC-labeled insulin in solution and insulin secreted by betaTC3 mouse insulinoma cells. Effective diffusivities through sol were found to be up to 3.5-fold higher than through the gel state of the material. A mathematical model of a hybrid construct was formulated and analyzed to simulate the secretory behavior in response to step ups and downs in the surrounding glucose concentration. The experimental and modeling studies indicate that a hybrid pancreatic substitute consisting of constitutively secreting cells and glucose-responsive material has the potential to provide a more physiologic regulation of insulin release than the cells by themselves or in an inert material.

In vivo gene therapy for diabetes mellitus

Gene therapy has been hyped as a possible 'cure' for diabetes mellitus in the near future ever since insulin was first cloned and expressed in cultured cells in the late 1970s. In the past decade, however, the bar for gene therapy for diabetes has been raised because of recent advances in the clinical management of diabetes. Although current treatment modalities fall far short of a cure, they produce greatly improved, if imperfect, glycemic control. In this context, we review the latest advances in in vivo gene therapy and conclude that the most widely applied strategy of insulin gene transfer does not measure up to the existing treatment options, whereas the recently proved concept of induced islet neogenesis has the potential of bettering the currently available therapy. Much work remains to be done, however, before this regimen can be taken from the bench to the bedside.

Glucose-responsive hepatic insulin gene therapy of spontaneously diabetic BB/Wor rats

Hepatic insulin gene therapy (HIGT) ameliorates hyperglycemia in multiple rodent models of diabetes mellitus, with variable degrees of glucose control. We demonstrate here that adenoviral delivery of a glucose-regulated transgene into rat hepatocytes produces near-normal glycemia in spontaneously diabetic BB/Wor rats without administration of exogenous insulin. We compared growth, glycemia, counterregulatory hormones, and lipids in HIGT-treated diabetic rats to nondiabetic rats and diabetic rats treated with either insulin injections or sustained-release insulin pellets. HIGT-treated rats achieved near-normal blood glucose levels within 1 week and maintained glycemic control for up to 3 months. Rats treated with sustained release insulin implants had similar blood sugars, but more hypoglycemia and gained more weight than HIGT-treated rats. HIGT-treated rats normalized blood glucose within 2 hr after a glucose load, and tolerated a 24-hr fast without hypoglycemia. HIGT treatment suppressed ketogenesis similarly to peripheral insulin. However, glucagon levels and free fatty acids were increased in HIGT-treated rats compared to either nondiabetic controls or rats treated with exogenous insulin. In addition to extending successful application of HIGT to a rat model of autoimmune diabetes, these findings emphasize the relative contribution of hepatic insulin effect in the metabolic stabilization of diabetes mellitus.

Transient alteration of cell fate using a nuclear and cytoplasmic extract of an insulinoma cell line

We report a transient modulation of cell fate in fibroblasts briefly exposed to an extract derived from the rat insulin-producing beta cell line, INS-1E. Primary fetal rat fibroblasts were reversibly permeabilized with Streptolysin O, incubated for 1h in a 15,000g INS-1E nuclear and cytoplasmic extract, resealed, and cultured. A first marker of change in cell fate was a reduction of cell and nuclear size within days of exposure to extract such that in some instances the fibroblasts resembled INS-1E cells. Second, two beta cell transcripts, Pdx-1 and insulin, were detected in the fibroblasts for up to 4 weeks. Third, (pro)insulin labeling was detected in 5-30% of the cells for a period of 8-14 days after incubation in extract. These phenotypes were absent from fibroblasts exposed to heat-treated INS-1E extracts, a human fibroblast cell line-derived extract or buffer. The results indicate that the extract of an insulinoma-derived cell line can promote at least a transient modification of cell fate towards a beta cell phenotype in non-beta cells. Because they are easily accessible, cell extracts may represent a practical source of material for investigating the mechanisms of alteration of a nuclear and cellular program.