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iPSCs derived from insulin resistant offspring of type 2 diabetic patients show increased oxidative stress and lactate secretion

Background

The genetic factors associated with insulin resistance (IR) are not well understood. Clinical studies on first-degree relatives of type 2 diabetic (T2D) patients, which have the highest genetic predisposition to T2D, have given insights into the role of IR in T2D pathogenesis. Induced pluripotent stem cells (iPSCs) are excellent tools for disease modeling as they can retain the genetic imprint of the disease. Therefore, in this study, we aimed to investigate the genetic perturbations associated with insulin resistance (IR) in the offspring of T2D parents using patient-specific iPSCs.

Methods

We generated iPSCs from IR individuals (IR-iPSCs) that were offspring of T2D parents as well as from insulin-sensitive (IS-iPSCs) individuals. We then performed transcriptomics to identify key dysregulated gene networks in the IR-iPSCs in comparison to IS-iPSCs and functionally validated them.

Results

Transcriptomics on IR-iPSCs revealed dysregulated gene networks and biological processes indicating that they carry the genetic defects associated with IR that may lead to T2D. The IR-iPSCs had increased lactate secretion and a higher phosphorylation of AKT upon stimulation with insulin. IR-iPSCs have increased cellular oxidative stress indicated by a high production of reactive oxygen species and higher susceptibility to H2O2 -induced apoptosis.

Conclusions

IR-iPSCs generated from offspring of diabetic patients confirm that oxidative stress and increased lactate secretion, associated with IR, are inherited in this population, and may place them at a high risk of T2D. Overall, our IR-iPSC model can be employed for T2D modeling and drug screening studies that target genetic perturbations associated with IR in individuals with a high risk for T2D.

Insulin resistance in diabetes: The promise of using induced pluripotent stem cell technology

Insulin resistance (IR) is associated with several metabolic disorders, including type 2 diabetes (T2D). The development of IR in insulin target tissues involves genetic and acquired factors. Persons at genetic risk for T2D tend to develop IR several years before glucose intolerance. Several rodent models for both IR and T2D are being used to study the disease pathogenesis; however, these models cannot recapitulate all the aspects of this complex disorder as seen in each individual. Human pluripotent stem cells (hPSCs) can overcome the hurdles faced with the classical mouse models for studying IR. Human induced pluripotent stem cells (hiPSCs) can be generated from the somatic cells of the patients without the need to destroy a human embryo. Therefore, patient-specific hiPSCs can generate cells genetically identical to IR individuals, which can help in distinguishing between genetic and acquired defects in insulin sensitivity. Combining the technologies of genome editing and hiPSCs may provide important information about the genetic factors underlying the development of different forms of IR. Further studies are required to fill the gaps in understanding the pathogenesis of IR and diabetes. In this review, we summarize the factors involved in the development of IR in the insulin-target tissues leading to diabetes. Also, we highlight the use of hPSCs to understand the mechanisms underlying the development of IR.

Insulin/Glucose-Responsive Cells Derived from Induced Pluripotent Stem Cells: Disease Modeling and Treatment of Diabetes

Type 2 diabetes, characterized by dysfunction of pancreatic β-cells and insulin resistance in peripheral organs, accounts for more than 90% of all diabetes. Despite current developments of new drugs and strategies to prevent/treat diabetes, there is no ideal therapy targeting all aspects of the disease. Restoration, however, of insulin-producing β-cells, as well as insulin-responsive cells, would be a logical strategy for the treatment of diabetes. In recent years, generation of transplantable cells derived from stem cells in vitro has emerged as an important research area. Pluripotent stem cells, either embryonic or induced, are alternative and feasible sources of insulin-secreting and glucose-responsive cells. This notwithstanding, consistent generation of robust glucose/insulin-responsive cells remains challenging. In this review, we describe basic concepts of the generation of induced pluripotent stem cells and subsequent differentiation of these into pancreatic β-like cells, myotubes, as well as adipocyte- and hepatocyte-like cells. Use of these for modeling of human disease is now feasible, while development of replacement therapies requires continued efforts.

Genetic insulin resistance is a potent regulator of gene expression and proliferation in human iPS cells

Insulin resistance is central to diabetes and metabolic syndrome. To define the consequences of genetic insulin resistance distinct from those secondary to cellular differentiation or in vivo regulation, we generated induced pluripotent stem cells (iPSCs) from individuals with insulin receptor mutations and age-appropriate control subjects and studied insulin signaling and gene expression compared with the fibroblasts from which they were derived. iPSCs from patients with genetic insulin resistance exhibited altered insulin signaling, paralleling that seen in the original fibroblasts. Insulin-stimulated expression of immediate early genes and proliferation were also potently reduced in insulin resistant iPSCs. Global gene expression analysis revealed marked differences in both insulin-resistant iPSCs and corresponding fibroblasts compared with control iPSCs and fibroblasts. Patterns of gene expression in patients with genetic insulin resistance were particularly distinct in the two cell types, indicating dependence on not only receptor activity but also the cellular context of the mutant insulin receptor. Thus, iPSCs provide a novel approach to define effects of genetically determined insulin resistance. This study demonstrates that effects of insulin resistance on gene expression are modified by cellular context and differentiation state. Moreover, altered insulin receptor signaling and insulin resistance can modify proliferation and function of pluripotent stem cell populations.

The role of glycogen synthase in the development of hyperglycemia in type 2 diabetes: 'To store or not to store glucose, that's the question'

This review deals with the role of glycogen storage in skeletal muscle for the development of insulin resistance and type 2 diabetes. Specifically, the role of the enzyme glycogen synthase, which seems to be locked in its hyperphosphorylated and inactivated state, is discussed. This defect seems to be secondary to ectopic lipid disposition in the muscle cells. These molecular defects are discussed in the context of the overall pathophysiology of hyperglycemia in type 2 diabetic subjects.

Fat feeding impairs glycogen synthase activity in mice without effects on its gene expression

To examine whether the effects of high-fat feeding on glycogen synthase (GS) activity and mRNA levels differ between diabetes-prone (C57BL/6J) and diabetes-resistant mice (NMRI), we measured GS activity and mRNA levels in muscle from C57BL/6J and NMRI mice fed a high-fat or normal chow diet for 3, 6, and 15 months. As compared with chow feeding, fat feeding increased plasma insulin levels in C57BL/6J mice at 15 months (464 +/- 29 v 267 +/- 47 pmol/L, P =.005), which was associated with elevated plasma glucose levels at 15 months (5.3 +/- 0.3 v 3.8 +/- 0.2 mmol/L, P =.001). Fat feeding increased plasma insulin levels also in NMRI mice at 15 months (705 +/- 145 v 275 +/- 64 pmol/L, P =.01) without, however, a rise of plasma glucose levels. In parallel with increased insulin levels, decreased muscle GS fractional velocity (FV) was observed at 6 (49.0% +/- 2.6% v 69.1% +/- 7.3%, P =.04) and 15 (45.8% +/- 1.8% v 53.4% +/- 1.6 %, P <.01) months but not at 3 months in the fat-fed C57BL/6J mice. Similarly, there was a significant decrease in GS fractional activity at 3 (57.9% +/- 4.3% v 70.4% +/- 2.6 %, P <.03) and 15 (47.3% +/- 2.4% v 56.4% +/- 2.1%, P =.02) but not at 6 months in the fat-fed NMRI mice. The decrease in GS activity was not associated with changes in mRNA levels at any time points. We conclude that (1) fat feeding results in similar elevation of plasma insulin levels and impairs GS activity in C57BL/6J and NMRI mice, and (2) the changes in GS activity do not involve effects on gene expression.

Impaired insulin-stimulated expression of the glycogen synthase gene in skeletal muscle of type 2 diabetic patients is acquired rather than inherited

To examine whether defective muscle glycogen synthase (GYS1) expression is associated with impaired glycogen synthesis in type 2 diabetes and whether the defect is inherited or acquired, we measured GYS1 gene expression and enzyme activity in muscle biopsies taken before and after an insulin clamp in 12 monozygotic twin pairs discordant for type 2 diabetes and in 12 matched control subjects. The effect of insulin on GYS1 fractional activity, when expressed as the increment over the basal values, was significantly impaired in diabetic (15.7 +/- 3.3%; P < 0.01), but not in nondiabetic (23.7 +/- 1.8%; P = NS) twins compared with that in control subjects (28.1 +/- 2.3%). Insulin increased GYS1 messenger ribonucleic acid (mRNA) expression in control subjects (from 0.14 +/- 0.02 to 1.74 +/- 0.10 relative units; P < 0.01) and in nondiabetic (from 0.24 +/- 0.05 to 1.81 +/- 0.16 relative units; P < 0.01) and diabetic (from 0.20 +/- 0.07 to 1.08 + 0.14 relative units; P < 0.01) twins. The effect of insulin on GYS1 expression was, however, significantly reduced in the diabetic (P < 0.003), but not in the nondiabetic, twins compared with that in control subjects. The postclamp GYS1 mRNA levels correlated strongly with the hemoglobin A1c levels (r = -0.61; P < 0.001). Despite the decrease in postclamp GYS1 mRNA levels, the GYS1 protein levels were not decreased in the diabetic twins compared with those in the control subjects (2.10 +/- 0.46 vs. 2.10 +/- 0.34 relative units; P = NS). We conclude that 1) insulin stimulates GYS1 mRNA expression; and 2) impaired stimulation of GYS1 gene expression by insulin in patients with type 2 diabetes is acquired and most likely is secondary to chronic hyperglycemia.

Reconstitution of insulin-sensitive glucose transport in fibroblasts requires expression of both PPARgamma and C/EBPalpha

Adipocyte differentiation is regulated by at least two major transcription factors, CCAAT/enhancer-binding protein alpha (C/EBPalpha) and peroxisome proliferator-activated receptor gamma (PPARgamma). Expression of PPARgamma in fibroblasts converts them to fat-laden cells with an adipocyte-like morphology. Here, we investigate the ability of PPARgamma to confer insulin-sensitive glucose transport to a variety of murine fibroblast cell lines. When cultured in the presence of a PPARgamma ligand, Swiss-3T3 and BALB/c-3T3 cells ectopically expressing PPARgamma accumulate lipid droplets, express C/EBPalpha, aP2, insulin-responsive aminopeptidase, and glucose transporter isoform 4 (GLUT4), and exhibit highly insulin-responsive 2-deoxyglucose uptake. In contrast, PPARgamma-expressing NIH-3T3 cells, despite similar lipid accumulation, adipocyte morphology, and aP2 expression, do not express C/EBPalpha or GLUT4 and fail to acquire insulin sensitivity. In cells ectopically expressing PPARgamma, the development of insulin-responsive glucose uptake correlates with C/EBPalpha expression. Furthermore, ectopic expression of C/EBPalpha in NIH-3T3 cells converts them to the adipocyte phenotype and restores insulin-sensitive glucose uptake. We propose that the pathway(s) leading to fat accumulation and morphological changes are distinct from that leading to insulin-dependent glucose transport. Our results suggest that although PPARgamma is sufficient to trigger the adipogenic program, C/EBPalpha is required for establishment of insulin-sensitive glucose transport.