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

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.

Designing an Engineered Construct Gene Sensitive to Carbohydrate In-vitro and Candidate for Human Insulin Gene Therapy In-vivo

Diabetes is a common disorder worldwide, and exhaustive efforts have been made to cure this disease. Gene therapy has been considered as a potential curative method that has had more stability in comparison with other pharmaceutical methods. However, the application of gene therapy as a definitive treatment demands further investigation. This study is aimed to prepare a suitable high- performance vector for gene therapy in diabetes mellitus. The designed vector has had prominent characteristics, such as directed replacement, which makes it a suitable method for treating or preventing other genetic disorders. The whole rDNA sequence of the human genome was scanned. The 800 bp two homology arms were digested by EcoRI, synthesized and cloned into the pGEM-B1 plasmid (prokaryotic moiety). The carbohydrate sensitive promoter, L-pyruvate kinase, and insulin gene were sub-cloned between homologous arms (eukaryotic moiety). The PGEM-B1 plasmid was digested by EcoRI, and the eukaryotic fragments were purified and transfected into Hela cell and then cultured. Afterward, the 300 µg/mL of glucose were added to the culture medium. Insulin expression in the transfected cells with 200 and 400 ng of the construct in comparison with negative control was detected using western blot and ELISA methods. Results have shown insulin expression in different glucose concentrates.

Generation of an efficient artificial promoter of bovine skeletal muscle α-actin gene (ACTA1) through addition of cis-acting element

The promoter of skeletal muscle α-actin gene (ACTA1) is highly muscle specific. The core of the bovine ACTA1 promoter extends from +29 to -233, about 262 base pairs (bp), which is sufficient to activate transcription in bovine muscle satellite cells. In this study, analysis by PCR site-specific mutagenesis showed that the cis-acting element SRE (serum response element binding factor) was processed as a transcriptional activator. In order to enhance the bovine ACTA1 promoter's activity, we used a strategy to modify it. We cloned a fragment containing three SREs from the promoter of ACTA1, and then one or two clones were linked upstream of the core promoter (262 bp) of ACTA1. One and two clones increased the activity of the ACTA1 promoter 3-fold and 10-fold, respectively, and maintained muscle tissue specificity. The modified promoter with two clones could increase the level of ACTA1 mRNA and protein 4-fold and 1.1-fold, respectively. Immunofluorescence results showed that green fluorescence of ACTA1 increased. Additionally, the number of total muscle microfilaments increased. These genetically engineered promoters might be useful for regulating gene expression in muscle cells and improving muscle mass in livestock.

Glucose-6-phosphatase (G6PC1) promoter polymorphism associated with glycogen storage disease type 1a among the Indian population

Promoter polymorphism rs559748047 inG6PC1from GSD-1a among Indian population.

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.

Restoring insulin production for type 1 diabetes

Current therapies for the treatment of type 1 diabetes include daily administration of exogenous insulin and, less frequently, whole-pancreas or islet transplantation. Insulin injections often result in inaccurate insulin doses, exposing the patient to hypo- and/or hyperglycemic episodes that lead to long-term complications. Islet transplantation is also limited by lack of high-quality islet donors, early graft failure, and chronic post-transplant immunosuppressive treatment. These barriers could be circumvented by designing a safe and efficient strategy to restore insulin production within the patient's body. Porcine islets have been considered as a possible alternative source of transplantable insulin-producing cells to replace human cadaveric islets. More recently, embryonic or induced pluripotent stem cells have also been examined for their ability to differentiate in vitro into pancreatic endocrine cells. Alternatively, it may be feasible to generate new β-cells by ectopic expression of key transcription factors in endogenous non-β-cells. Finally, engineering surrogate β-cells by in vivo delivery of the insulin gene to specific tissues is also being studied as a possible therapy for type 1 diabetes. In the present review, we discuss these different approaches to restore insulin production.

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.

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.

Engineered glucagon-like peptide-1-producing hepatocytes lower plasma glucose levels in mice

Glucagon-like peptide (GLP)-1 is an incretin hormone with well-characterized antidiabetic properties, including glucose-dependent stimulation of insulin secretion and enhancement of beta-cell mass. GLP-1 agonists have recently been developed and are now in clinical use for the treatment of type 2 diabetes. Rapid degradation of GLP-1 by enzymes including dipeptidyl-peptidase (DPP)-IV and neutral endopeptidase (NEP) 24.11, along with renal clearance, contribute to a short biological half-life, necessitating frequent injections to maintain therapeutic efficacy. Gene therapy may represent a promising alternative approach for achieving long-term increases in endogenous release of GLP-1. We have developed a novel strategy for glucose-regulated production of GLP-1 in hepatocytes by expressing a DPP-IV-resistant GLP-1 peptide in hepatocytes under control of the liver-type pyruvate kinase promoter. Adenoviral delivery of this construct to hepatocytes in vitro resulted in production and secretion of bioactive GLP-1 as measured by a luciferase-based bioassay developed to detect the NH2-terminally modified GLP-1 peptide engineered for this study. Transplantation of encapsulated hepatocytes into CD-1 mice resulted in an increase in plasma GLP-1 levels that was accompanied by a significant reduction in fasting plasma glucose levels. The results from this study demonstrate that a gene therapy approach designed to induce GLP-1 production in hepatocytes may represent a novel strategy for long-term secretion of bioactive GLP-1 for the treatment of type 2 diabetes.

Genetic networks of liver metabolism revealed by integration of metabolic and transcriptional profiling

Although numerous quantitative trait loci (QTL) influencing disease-related phenotypes have been detected through gene mapping and positional cloning, identification of the individual gene(s) and molecular pathways leading to those phenotypes is often elusive. One way to improve understanding of genetic architecture is to classify phenotypes in greater depth by including transcriptional and metabolic profiling. In the current study, we have generated and analyzed mRNA expression and metabolic profiles in liver samples obtained in an F2 intercross between the diabetes-resistant C57BL/6 leptin^ob/ob and the diabetes-susceptible BTBR leptin^ob/ob mouse strains. This cross, which segregates for genotype and physiological traits, was previously used to identify several diabetes-related QTL. Our current investigation includes microarray analysis of over 40,000 probe sets, plus quantitative mass spectrometry-based measurements of sixty-seven intermediary metabolites in three different classes (amino acids, organic acids, and acyl-carnitines). We show that liver metabolites map to distinct genetic regions, thereby indicating that tissue metabolites are heritable. We also demonstrate that genomic analysis can be integrated with liver mRNA expression and metabolite profiling data to construct causal networks for control of specific metabolic processes in liver. As a proof of principle of the practical significance of this integrative approach, we illustrate the construction of a specific causal network that links gene expression and metabolic changes in the context of glutamate metabolism, and demonstrate its validity by showing that genes in the network respond to changes in glutamine and glutamate availability. Thus, the methods described here have the potential to reveal regulatory networks that contribute to chronic, complex, and highly prevalent diseases and conditions such as obesity and diabetes.

Although numerous quantitative trait loci (QTL) influencing disease-related phenotypes have been detected through gene mapping and positional cloning, identifying individual genes and their potential roles in molecular pathways leading to disease remains a challenge. In this study, we include transcriptional and metabolic profiling in genomic analyses to address this limitation. We investigated an F2 intercross between the diabetes-resistant C57BL/6 leptin^ob/ob and the diabetes-susceptible BTBR leptin^ob/ob mouse strains that segregates for genotype and diabetes-related physiological traits; blood glucose, plasma insulin and body weight. Our study shows that liver metabolites (comprised of amino acids, organic acids, and acyl-carnitines) map to distinct genetic regions, thereby indicating that tissue metabolites are heritable. We also demonstrate that genomic analysis can be integrated with liver mRNA expression and metabolite profiling data to construct causal, testable networks for control of specific metabolic processes in liver. We apply an in vitro study to confirm the validity of this integrative method, and thus provide a novel approach to reveal regulatory networks that contribute to chronic, complex, and highly prevalent diseases and conditions such as obesity and diabetes.