Glucose-regulated insulin production in the liver improves glycemic control in type 1 diabetic mice

Ectopic expression of insulin in a type 1 diabetic rat model by injection of manipulated mesenchymal stem cells with an insulin construct driven by a glucose-sensitive promoter in the port vein

The treatment of type 1 diabetes through islet cell transplantation is a complex process, facing challenges such as allograft rejections and a limited supply of donors. One potential solution is to utilize the liver as an alternative for natural insulin production, as hepatocytes can secrete proteins and respond to glucose levels. Recent research has shown promising results in using mesenchymal stem cells as a potential cure for diabetes. The study utilized a diabetic rat model, confirmed through blood sugar measurement. A plasmid vector was designed with specific genetic components, synthesized by biotech company, and then Inserted vector into a plasmid with resistance genes and bacterial origin. Bone marrow-derived mesenchymal stem cells (BM-MSCs) were cultured and transfected with the plasmid using Lipofectamine 3000. Polymerase chain reaction was employed to confirm successful transfection using specific primers. For the animal study, 30 male Wistar rats were divided into six groups, each comprising five rats. The control group did not receive any treatment, while the second group received MSCs via Portal Vein Injection. The third group received MSCs transfected with a specific construct via Portal Vein Injection. The fourth group was induced to develop diabetes through streptozotocin (STZ) injection, the fifth group developed diabetes and received untransfected MSCs via Portal Vein Injection, and the sixth group received MSCs transfected with the specific construct via Portal Vein Injection. To manage Pain, appropriate pain control was administered to the rats for 3 days after the surgery. Fixed liver tissues obtained from the euthanized rats were utilized for immunohistochemistry. In this study, immunohistochemical techniques were used to examine insulin expression in different groups of rats. The control groups showed high levels of insulin expression, while the diabetic groups exhibited lower expression. However, there was a significant difference between the diabetic groups treated with MSC and transgenic MSC cells. All groups had similar baseline glucose levels, but the diabetic groups showed a significant increase after STZ injection, whereas the control and MSC groups did not. Postintervention, both the control and MSC groups had similar glucose levels to the post-STZ levels. However, diabetes-induced groups experienced a significant decrease in glucose levels, with the transfected MSCs showing a greater decrease than the untransfected MSCs. The study suggested that treatment with MSCs, especially transfected ones, can effectively reduce glucose levels in rats with diabetes. In this research, rat BM-MSCs were utilized to create insulin-producing mesenchymal cells with glucose-sensitive insulin expression. The cells were transferred to the liver of diabetic rats via portal vein injection, leading to an increase in insulin expression. This study proposes a novel approach for cell therapy and delivery in the treatment of type 1 diabetes.

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.

Generation of insulin-producing hepatocyte-like cells from human Wharton's jelly mesenchymal stem cells as an alternative source of islet cells

Islet cell transplantation, as a treatment of type 1 diabetes, has a lot of complexity such as allograft rejections and an insufficient number of donors. The liver can be used as a replacement for endogenous insulin production. Hepatocytes can inherently respond to glucose levels and secrete proteins. Utilization of mesenchymal stem cells for curing diabetes represents a major focus of recent investigations. As a new choice for transplantation, we have proposed glucose-regulated insulin-producing hepatocyte-like cells, which produce insulin dependent on glucose levels. We have transfected human Wharton's jelly mesenchymal stem cells with the special construct, which included homology arms and glucose-responsive elements upstream of the minimum liver-type pyruvate kinase promoter-directed insulin gene. Then, we have differentiated these transfected cells to hepatocyte-like cells by using serial exposure of different inducing material and exogenous growth factors. Immunofluorescence analyses have demonstrated the expression of albumin, cytokeratin-18, Hep-Par1, α-fetoprotein, and insulin. The expression of hepatocyte marker genes in the differentiated cells was confirmed by reverse-transcription polymerase chain reaction. Interestingly, flow cytometry results showed that approximately 60% of the insulin-producing hepatocyte-like cells were simultaneously cytochrome P450 3A4 (CYP3A4) and insulin positive. CYP3A4 is a significant enzyme found in mature liver tissue. This confirmed that the differentiation and the transfection procedures were done correctly. They were functionally active by releasing insulin in response to elevated glucose concentrations in vitro. These applicable cells could be used in the liver for cell therapy of diabetes.

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.