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

Development of a liver-specific Tet-off AAV8 vector for improved safety of insulin gene therapy for diabetes

Background

Diabetes mellitus is caused by a partial or complete lack of insulin production in the body. We have previously shown that a single injection of an adeno‐associated virus serotype 8 (AAV8) vector carrying a modified and codon optimized human insulin gene induced hepatic production of insulin and corrected streptozotocin (STZ)‐induced diabetes in mice for more than 1 year. Insulin production was constitutive, analogous to long‐acting insulin therapy.

Methods

We have developed a single AAV8 vector with a Tet‐Off regulatable system as a safety mechanism to turn off insulin secretion should hypoglycaemia develop in vector‐treated diabetic mice. We first transfected HepG2 cells or freshly isolated rat hepatocytes in vitro with the Tet‐Off system (pAAV‐Tetoff_bidir‐Alb‐luc) regulating a luciferase reporter gene. We subsequently incorporated a furin‐cleavable codon‐optimised human proinsulin cDNA into pAAV‐Tetoff_bidir backbone to form the doxycycline inducible pAAV‐Tetoff_bidir‐Alb‐hINSco.

Results

Using STZ‐induced diabetic mice, we were able to switch off insulin secretion repeatedly with doxycycline administration, and showed full restoration of insulin secretion on withdrawing doxycycline.

Conclusions

The present study provides proof of concept that, under circumstances when inappropriate basal insulin secretion is a safety concern, insulin secretion from AAV8 gene therapy can be turned off reversibly with doxycycline.

Long-Term Efficacy and Safety of Insulin and Glucokinase Gene Therapy for Diabetes: 8-Year Follow-Up in Dogs

Diabetes is a complex metabolic disease that exposes patients to the deleterious effects of hyperglycemia on various organs. Achievement of normoglycemia with exogenous insulin treatment requires the use of high doses of hormone, which increases the risk of life-threatening hypoglycemic episodes. We developed a gene therapy approach to control diabetic hyperglycemia based on co-expression of the insulin and glucokinase genes in skeletal muscle. Previous studies proved the feasibility of gene delivery to large diabetic animals with adeno-associated viral (AAV) vectors. Here, we report the long-term (∼8 years) follow-up after a single administration of therapeutic vectors to diabetic dogs. Successful, multi-year control of glycemia was achieved without the need of supplementation with exogenous insulin. Metabolic correction was demonstrated through normalization of serum levels of fructosamine, triglycerides, and cholesterol and remarkable improvement in the response to an oral glucose challenge. The persistence of vector genomes and therapeutic transgene expression years after vector delivery was documented in multiple samples from treated muscles, which showed normal morphology. Thus, this study demonstrates the long-term efficacy and safety of insulin and glucokinase gene transfer in large animals and especially the ability of the system to respond to the changes in metabolic needs as animals grow older.

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.

Long-term glycemic control with hepatic insulin gene therapy in streptozotocin-diabetic mice

BACKGROUND

Insulin self-administration is burdensome and can produce dangerous hypoglycemia. Insulin gene therapy may improve and simplify the treatment of diabetes mellitus. In rats, metabolically responsive hepatic insulin gene therapy (HIGT) delivered by adenovirus normalizes random blood sugars but with a limited duration. To prolong glycemic control, we delivered a metabolically regulated insulin transgene by adeno-associated virus (AAV).

METHODS

We administered increasing doses of self-complementary (SC), pseudotyped AAV8 expressing the (GlRE)3 BP1-2xfur insulin transgene to streptozotocin-diabetic CD-1 mice, and monitored blood sugar and body weight. We also compared responses to intraperitoneal glucose and chow withdrawal, assessed for viral genomes in liver by Southern blotting, and measured hepatic glycogen.

RESULTS

Glucose lowering required the combination of SC genomes and AAV capsid pseudotyping. HIGT controlled glycemia in diabetic mice (DM) for > 1 year. However, glycemic responses were variable. Approximately 30% of mice succumbed to hypoglycemia, and approximately 30% of mice again became hyperglycemic. During an intraperitoneal glucose tolerance test, blood sugars declined to normal within 180 min in HIGT-treated DM compared to 90 min in control mice. Hypoglycemia was common among HIGT-treated mice during a 24-h fast. However, HIGT mice lost less weight than either diabetic or nondiabetic controls as a result of increased water intake. HIGT treatment reduced the hepatic glycogen content of fed mice.

CONCLUSIONS

Our studies demonstrate the possibility for long-term glycemic correction following AAV-mediated HIGT in mice. However, the dose-response relationship is irregular, and metabolic responsiveness may be less than that observed in rats.

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.

Glucose-responsive artificial promoter-mediated insulin gene transfer improves glucose control in diabetic mice

AIM: To investigate the effect of insulin gene therapy using a glucose-responsive synthetic promoter in type 2 diabetic obese mice.

METHODS: We employed a recently developed novel insulin gene therapy strategy using a synthetic promoter that regulates insulin gene expression in the liver in response to blood glucose level changes. We intravenously administered a recombinant adenovirus expressing furin-cleavable rat insulin under the control of the synthetic promoter (rAd-SP-rINSfur) into diabetic Lepr^db/db mice. A recombinant adenovirus expressing β-galactosidase under the cytomegalovirus promoter was used as a control (rAd-CMV-βgal). Blood glucose levels and body weights were monitored for 50 d. Glucose and insulin tolerance tests were performed. Immunohistochemical staining was performed to investigate islet morphology and insulin content.

RESULTS: Administration of rAd-SP-rINSfur lowered blood glucose levels and normoglycemia was maintained for 50 d, whereas the rAd-CMV-βgal control virus-injected mice remained hyperglycemic. Glucose tolerance tests showed that rAd-SP-rINSfur-treated mice cleared exogenous glucose from the blood more efficiently than control virus-injected mice at 4 wk [area under the curve (AUC): 21  508.80 ± 2248.18 vs 62  640.00 ± 5014.28, P < 0.01] and at 6 wk (AUC: 29  956.60 ± 1757.33 vs 60  016.60 ± 3794.47, P < 0.01). In addition, insulin sensitivity was also significantly improved in mice treated with rAd-SP-rINSfur compared with rAd-CMV-βgal-treated mice (AUC: 9150.17 ± 1007.78 vs 11  994.20 ± 474.40, P < 0.05). The islets from rAd-SP-rINSfur-injected mice appeared to be smaller and to contain a higher concentration of insulin than those from rAd-CMV-βgal-injected mice.

CONCLUSION: Based on these results, we suggest that insulin gene therapy might be one therapeutic option for remission of type 2 diabetes.

Remission of diabetes by insulin gene therapy using a hepatocyte-specific and glucose-responsive synthetic promoter

Efficient production of insulin in response to changes in glucose levels has been a major issue for insulin gene therapy to treat diabetes. To express target genes in response to glucose specifically in hepatocytes, we generated a synthetic promoter library containing hepatocyte nuclear factor-1, CAAT/enhancer-binding protein (C/EBP) response element, and glucose-response element. Combinations of these three cis-elements in 3-, 6-, or 9-element configurations were screened for transcriptional activity and then glucose responsiveness in vitro. The most effective promoter (SP23137) was selected for further study. Intravenous administration of a recombinant adenovirus expressing furin-cleavable rat insulin under control of the SP23137 promoter into streptozotocin (STZ)-induced diabetic mice resulted in normoglycemia, which was maintained for >30 days. Glucose tolerance tests showed that treated mice produced insulin in response to glucose and cleared exogenous glucose from the blood in a manner similar to nondiabetic control mice, although the clearance was somewhat delayed. Insulin expression was seen specifically in the liver and not in other organs. These observations indicate the potential of this synthetic, artificial promoter to regulate glucose-responsive insulin production and remit hyperglycemia, thus providing a new method of liver-directed insulin gene therapy for type 1 diabetes.

Minireview: beta-cell replacement therapy for diabetes in the 21st century: manipulation of cell fate by directed differentiation

Pancreatic beta-cell failure underlies type 1 diabetes; it also contributes in an essential way to type 2 diabetes. beta-Cell replacement is an important component of any cure for diabetes. The current options of islet and pancreas transplantation are not satisfactory as definitive forms of therapy. Here, we review strategies for induced de novo pancreatic beta-cell formation, which depend on the targeted differentiation of cells into pancreatic beta-cells. With this objective in mind, one can manipulate the fate of three different types of cells: 1) from terminally differentiated cells, e.g. exocrine pancreatic cells, into beta-cells; 2) from multipotent adult stem cells, e.g. hepatic oval cells, into pancreatic islets; and 3) from pluripotent stem cells, e.g. embryonic stem cells and induced pluripotent stem cells, into beta-cells. We will examine the pros and cons of each strategy as well as the hurdles that must be overcome before these approaches to generate new beta-cells will be ready for clinical application.

Gene therapy with neurogenin 3 and betacellulin reverses major metabolic problems in insulin-deficient diabetic mice

Insulin deficiency in type 1 diabetes leads to disruptions in glucose, lipid, and ketone metabolism with resultant hyperglycemia, hyperlipidemia, and ketonemia. Exogenous insulin and hepatic insulin gene therapy cannot mimic the robust glucose-stimulated insulin secretion (GSIS) from native pancreatic islets. Gene therapy of streptozotocin-diabetic mice with neurogenin 3 (Ngn3) and betacellulin (Btc) leads to the induction of periportal oval cell-derived neo-islets that exhibit GSIS. We hence hypothesized that this gene therapy regimen may lead to a complete correction of the glucose and lipid metabolic abnormalities associated with insulin deficiency; we further hypothesized that the neo-islets formed in response to Ngn3-Btc gene delivery may display an ultrastructure and transcription profile similar to that of pancreatic islets. We injected streptozotocin-diabetic mice with helper-dependent adenoviral vectors carrying Ngn3 and Btc, which restored GSIS and reversed hyperglycemia in these animals. The treatment also normalized hepatic glucose secretion and reversed ketonemia. Furthermore, it restored hepatic glycogen content and reinstated hepatic lipogenesis-related gene transcripts back to nondiabetic levels. By transmission electron microscopy, the neo-islets displayed electron-dense granules that were similar in appearance to those in pancreatic islets. Finally, using RNA obtained by laser capture microdissection of the periportal neo-islets and normal pancreatic islets, we found that the neo-islets and pancreatic islets exhibited a very similar transcription profile on microarray-based transcriptome analysis. Taken together, this indicates that Ngn3-Btc gene therapy corrects the underlying dysregulated glucose and lipid metabolism in insulin-deficient diabetic mice by inducing neo-islets in the liver that are similar to pancreatic islets in structure and gene expression profile.