Insulin, CCAAT/enhancer-binding proteins and lactate regulate the human 11β-hydroxysteroid dehydrogenase type 2 gene expression in colon cancer cell lines.

11β-Hydroxysteroid dehydrogenases (11beta-HSD) modulate mineralocorticoid receptor transactivation by glucocorticoids and regulate access to the glucocorticoid receptor. The isozyme 11beta-HSD2 is selectively expressed in mineralocorticoid target tissues and its activity is reduced in various disease states with abnormal sodium retention and hypertension, including the apparent mineralocorticoid excess. As 50% of patients with essential hypertension are insulin resistant and hyperinsulinemic, we hypothesized that insulin downregulates the 11beta-HSD2 activity. In the present study we show that insulin reduced the 11beta-HSD2 activity in cancer colon cell lines (HCT116, SW620 and HT-29) at the transcriptional level, in a time and dose dependent manner. The downregulation was reversible and required new protein synthesis. Pathway analysis using mRNA profiling revealed that insulin treatment modified the expression of the transcription factor family C/EBPs (CCAAT/enhancer-binding proteins) but also of glycolysis related enzymes. Western blot and real time PCR confirmed an upregulation of C/EBP beta isoforms (LAP and LIP) with a more pronounced increase in the inhibitory isoform LIP. EMSA and reporter gene assays demonstrated the role of C/EBP beta isoforms in HSD11B2 gene expression regulation. In addition, secretion of lactate, a byproduct of glycolysis, was shown to mediate insulin-dependent HSD11B2 downregulation. In summary, we demonstrate that insulin downregulates HSD11B2 through increased LIP expression and augmented lactate secretion. Such mechanisms are of interest and potential significance for sodium reabsorption in the colon.

Regulation of human trophoblast GLUT1 glucose transporter by insulin-like growth factor I (IGF-I)

Glucose transport to the fetus across the placenta takes place via glucose transporters in the opposing faces of the barrier layer, the microvillous and basal membranes of the syncytiotrophoblast. While basal membrane content of the GLUT1 glucose transporter appears to be the rate-limiting step in transplacental transport, the factors regulating transporter expression and activity are largely unknown. In view of the many studies showing an association between IGF-I and fetal growth, we investigated the effects of IGF-I on placental glucose transport and GLUT1 transporter expression. Treatment of BeWo choriocarcinoma cells with IGF-I increased cellular GLUT1 protein. There was increased basolateral (but not microvillous) uptake of glucose and increased transepithelial transport of glucose across the BeWo monolayer. Primary syncytial cells treated with IGF-I also demonstrated an increase in GLUT1 protein. Term placental explants treated with IGF-I showed an increase in syncytial basal membrane GLUT1 but microvillous membrane GLUT1 was not affected. The placental dual perfusion model was used to assess the effects of fetally perfused IGF-I on transplacental glucose transport and syncytial GLUT1 content. In control perfusions there was a decrease in transplacental glucose transport over the course of the perfusion, whereas in tissues perfused with IGF-I through the fetal circulation there was no change. Syncytial basal membranes from IGF-I perfused tissues showed an increase in GLUT1 content. These results demonstrate that IGF-I, whether acting via microvillous or basal membrane receptors, increases the basal membrane content of GLUT1 and up-regulates basal membrane transport of glucose, leading to increased transepithelial glucose transport. These observations provide a partial explanation for the mechanism by which IGF-I controls nutrient supply in the regulation of fetal growth.

The Effect of Parathyroid Hormone on Osseointegration in Insulin-Treated Diabetic Rats.

OBJECTIVES Uncontrolled diabetes mellitus is associated with impaired osseointegration. Diabetic individuals might benefit from bone anabolic therapies. Intermittent administration of 1-34 parathyroid hormone (PTH) stimulates bone formation in rodent models. However, this anabolic effect fails in diabetic rats. Whether the anabolic effect of PTH can be achieved in insulin-controlled diabetic rats has not been investigated yet. MATERIALS AND METHODS After diabetes induction with streptozotocin in 40 female Wistar rats, the animals were randomly divided into 4 groups: diabetes, diabetes plus PTH, insulin-treated diabetes, and insulin-treated diabetes plus PTH. After 1 week, miniscrews were inserted in the tibiae. Osmotic pumps with insulin or saline solution were implanted. Animals received 60 mg/kg PTH or saline solution. Histomorphometric analysis was performed. RESULTS In diabetic rats, no changes of medullary periimplant bone area or bone-to-implant contacts (BICs) were achieved with or without treatment with PTH. However, also animals treated with insulin failed to response significantly to PTH regarding bone area (7.4 ± 4.1% and 8.1 ± 4.1%) and BICs (33.7 ± 16.9% and 49.9 ± 11.9%). CONCLUSION These results demonstrate that the metabolic characteristics of the diabetic rats produced a condition unable to respond to PTH treatment, even when hyperglycemia was controlled with insulin.

Insulin activates Na(+)/H(+) exchanger 3: biphasic response and glucocorticoid dependence.

Insulin is an important regulator of renal salt and water excretion, and hyperinsulinemia has been implicated to play a role in hypertension. One of the target proteins of insulin action in the kidney is Na(+)/H(+) exchanger 3 (NHE3), a principal Na(+) transporter responsible for salt absorption in the mammalian proximal tubule. The molecular mechanisms involved in activation of NHE3 by insulin have not been studied so far. In opossum kidney (OK) cells, insulin increased Na(+)/H(+) exchange activity in a time- and concentration-dependent manner. This effect is due to activation of NHE3 as it persisted after pharmacological inhibition of NHE1 and NHE2. In the early phase of stimulation (2-12 h), NHE3 activity was increased without changes in NHE3 protein and mRNA. At 24 h, enhanced NHE3 activity was accompanied by an increase in total and cell surface NHE3 protein and NHE3 mRNA abundance. All the effects of insulin on NHE3 activity, protein, and mRNA were amplified in the presence of hydrocortisone. These results suggest that insulin stimulates renal tubular NHE3 activity via a biphasic mechanism involving posttranslational factors and an increase in NHE3 gene expression and the effects are dependent on the permissive action of hydrocortisone.

Growth hormone replacement therapy regulates microRNA-29a and targets involved in insulin resistance

Replacement of growth hormone (GH) in patients suffering from GH deficiency (GHD) offers clinical benefits on body composition, exercise capacity, and skeletal integrity. However, GH replacement therapy (GHRT) is also associated with insulin resistance, but the mechanisms are incompletely understood. We demonstrate that in GH-deficient mice (growth hormone-releasing hormone receptor (Ghrhr)(lit/lit)), insulin resistance after GHRT involves the upregulation of the extracellular matrix (ECM) and the downregulation of microRNA miR-29a in skeletal muscle. Based on RNA deep sequencing of skeletal muscle from GH-treated Ghrhr(lit/lit) mice, we identified several upregulated genes as predicted miR-29a targets that are negative regulators of insulin signaling or profibrotic/proinflammatory components of the ECM. Using gain- and loss-of-function studies, five of these genes were confirmed as endogenous targets of miR-29a in human myotubes (PTEN, COL3A1, FSTL1, SERPINH1, SPARC). In addition, in human myotubes, IGF1, but not GH, downregulated miR-29a expression and upregulated COL3A1. These results were confirmed in a group of GH-deficient patients after 4 months of GHRT. Serum IGF1 increased, skeletal muscle miR-29a decreased, and miR-29a targets were upregulated in patients with a reduced insulin response (homeostatic model assessment of insulin resistance (HOMA-IR)) after GHRT. We conclude that miR-29a could contribute to the metabolic response of muscle tissue to GHRT by regulating ECM components and PTEN. miR-29a and its targets might be valuable biomarkers for muscle metabolism following GH replacement. KEY MESSAGES GHRT most significantly affects the ECM cluster in skeletal muscle from mice. GHRT downregulates miR-29a and upregulates miR-29a targets in skeletal muscle from mice. PTEN, COL3A1, FSTL1, SERPINH1, and SPARC are endogenous miR-29a targets in human myotubes. IGF1 decreases miR-29a levels in human myotubes. miR-29a and its targets are regulated during GHRT in skeletal muscle from humans.

Treatment intensification with insulin glargine in patients with inadequately controlled type 2 diabetes improves glycaemic control with a high treatment satisfaction and no weight gain

PRINCIPLES We aimed to evaluate the efficacy of, and treatment satisfaction with, insulin glargine administered with SoloSTAR® or ClikSTAR® pens in patients with type 2 diabetes mellitus managed by primary care physicians in Switzerland. METHODS A total of 327 patients with inadequately controlled type 2 diabetes were enrolled by 72 physicians in this prospective observational study, which aimed to evaluate the efficacy of a 6-month course of insulin glargine therapy measured as development of glycaemic control (glycosylated haemoglobin [HbA1c] and fasting plasma glucose [FPG]) and weight change. We also assessed preference for reusable or disposable pens, and treatment satisfaction. RESULTS After 6 months, the mean daily dose of insulin glargine was 27.7±14.3 U, and dose titration was completed in 228 (72.4%) patients. Mean HbA1c decreased from 8.9%±1.6% (n=327) to 7.3%±1.0% (n=315) (p<0.0001), and 138 (43.8%) patients achieved an HbA1c≤7.0%. Mean FPG decreased from 10.9±4.5 to 7.3±1.8 mmol/l (p<0.0001). Mean body weight did not change (85.4±17.2 kg vs 85.0±16.5 kg; p=0.11). Patients' preference was in favour of the disposable SoloStar® pen (80%), as compared with the reusable ClickStar® pen (20%). Overall, 92.6% of physicians and 96.3% of patients were satisfied or very satisfied with the insulin glargine therapy. CONCLUSIONS In patients with type 2 diabetes insulin glargine administered by SoloSTAR® or ClikSTAR® pens, education on insulin injection and on self-management of diabetes was associated with clinically meaningful improvements in HbA1c and FPG without a mean collective weight gain. The vast majority of both patients and primary care physicians were satisfied with the treatment intensification.