Overcoming insulin resistance with CNTF

IL-6 family cytokines as potential therapeutic strategies to treat metabolic diseases

Metabolic disease is highly prevalent. Here we discuss the therapeutic utility of using gp130 receptor ligands as a therapeutic strategy to treat metabolic disease.

Changes in Visceral and Subcutaneous Fat in Youth With Type 2 Diabetes in the TODAY Study

OBJECTIVE

In the Treatment Options for Type 2 Diabetes in Adolescents and Youth (TODAY) study, metformin plus rosiglitazone (M + R) maintained glycemic control better than metformin alone (M) or metformin plus lifestyle (M + L) in youth with type 2 diabetes (T2D). We hypothesized that changes in visceral adipose tissue (VAT) and subcutaneous adipose tissue (SAT) would explain the differential treatment effects on glycemia.

RESEARCH DESIGN AND METHODS

In 626 youth ages 11-17 years with T2D duration <2 years, VAT and SAT were estimated by DXA at baseline and at 6 and 24 months. Changes from baseline were analyzed in linear mixed models.

RESULTS

Baseline mean age was 13.9 years, 66.4% were female, 72.2% were Hispanic/non-Hispanic black, and 20.3% were non-Hispanic white (NHW). Mean BMI was 33.7 kg/m². VAT increased more in M + R (13.1%) than M + L (3.9%, P = 0.0006) or M (6.5%, P = 0.0146). SAT also increased more in M + R (13.3%) than in M + L (5.4%, P < 0.0001) or M (6.4%, P = 0.0005), indicating no significant fat redistribution in M + R. In NHWs, VAT increased more in M + R than M (P = 0.0192) and M + L (P = 0.0482) but did not explain the race-ethnicity differences in treatment effects on glycemic control among treatment groups. VAT and SAT increases correlated with higher HbA_1c, lower insulin sensitivity, and lower oral disposition index (all P < 0.05), but associations did not differ by treatment group.

CONCLUSIONS

In contrast to the existing reports in adults with T2D, in TODAY, M + R resulted in the most VAT accumulation compared with M + L or M. Differential effects on depot-specific indirect measures of adiposity are unrelated to treatment effects in sustaining glycemic control. Additional studies are needed to understand the clinical markers of metabolic risk profile in youth with T2D on rosiglitazone.

Does Visceral or Subcutaneous Fat Influence Peripheral Cortical Bone Strength During Adolescence? A Longitudinal Study

This study evaluated the longitudinal relationships among visceral adipose tissue (VAT), subcutaneous adipose tissue (SAT), and peripheral bone strength during adolescence. Fat and lean mass, VAT and SAT area, and android/gynoid (A/G) ratio were estimated with DXA. Our main outcome was strength-strain index (SSI), an indicator of peripheral bone strength estimated by pQCT at the radius and tibia. Sex-specific analyses evaluated the longitudinal bone-fat relationship from ages 11 to 19 years with linear mixed models using biological age as the time variable and adjusted for limb length and lean mass in 182 girls and 167 boys. Variables were standardized (mean = 0, SD = 1) prior to model fitting and results shown are parameter estimates ± SE. Fat mass and SAT were positively associated with SSI (radius: 0.07 ± 0.02, p = 0.003 and 0.05 ± 0.02, 0.041, respectively; tibia: 0.09 ± 0.02, p < 0.001 and 0.08 ± 0.02, p < 0.001, respectively) prior to, but not following adjustment for lean mass in girls. In contrast, fat mass and SAT were negatively associated with radial SSI, both before and after adjustment for lean mass in boys (fat mass: -0.05 ± 0.01, p = 0.001; SAT: -0.04 ± 0.01, p = 0.004). In full models, negative associations were limited to VAT in girls and included radial (-0.06 ± 0.02, p = 0.001) and tibial SSI (-0.04 ± 0.02, p = 0.033). For boys, there were no significant associations present between VAT and SSI at the radius or tibia. In analyses limited to obese participants, an A/G ratio was not significantly associated with SSI in girls, but was negatively associated with radial SSI regardless of adjustment for lean mass in boys (-0.06 ± 0.02, p = 0.018). These results that show a negative relationship between peripheral bone strength and VAT in girls, but greater total and central adiposity in boys, suggest these factors play a role in adequate acquisition of bone strength during adolescence. © 2017 American Society for Bone and Mineral Research.

Endurance training inhibits insulin clearance and IDE expression in Swiss mice

INTRODUCTION

Endurance training improves peripheral insulin sensitivity in the liver and the skeletal muscle, but the mechanism for this effect is poorly understood. Recently, it was proposed that insulin clearance plays a major role in both glucose homeostasis and insulin sensitivity. Therefore, our goal was to determine the mechanism by which endurance training improves insulin sensitivity and how it regulates insulin clearance in mice.

METHODS

Mice were treadmill-trained for 4 weeks at 70-80% of maximal oxygen consumption (VO2 max) for 60 min, 5 days a week. The glucose tolerance and the insulin resistance were determined using an IPGTT and an IPITT, respectively, and the insulin decay rate was calculated from the insulin clearance. Protein expression and phosphorylation in the liver and the skeletal muscle were ascertained by Western blot.

RESULTS

Trained mice exhibited an increased VO2 max, time to exhaustion, glucose tolerance and insulin sensitivity. They had smaller fat pads and lower plasma concentrations of insulin and glucose. Endurance training inhibited insulin clearance and reduced expression of IDE in the liver, while also inhibiting insulin secretion by pancreatic islets. There was increased phosphorylation of both the canonical (IR-AKT) and the non-canonical (CaMKII-AMPK-ACC) insulin pathways in the liver of trained mice, whereas only the CaMKII-AMPK pathway was increased in the skeletal muscle.

CONCLUSION

Endurance training improved glucose homeostasis not only by increasing peripheral insulin sensitivity but also by decreasing insulin clearance and reducing IDE expression in the liver.

Ciliary neurotrophic factor protects mice against streptozotocin-induced type 1 diabetes through SOCS3: the role of STAT1/STAT3 ratio in β-cell death

Type 1 diabetes is characterized by a loss of islet β-cells. Ciliary neurotrophic factor (CNTF) protects pancreatic islets against cytokine-induced apoptosis. For this reason, we assessed whether CNTF protects mice against streptozotocin-induced diabetes (a model of type 1 diabetes) and the mechanism for this protection. WT and SOCS3 knockdown C57BL6 mice were treated for 5 days with citrate buffer or 0.1 mg/kg CNTF before receiving 80 mg/kg streptozotocin. Glycemia in non-fasted mice was measured weekly from days 0-28 after streptozotocin administration. Diabetes was defined as a blood glucose > 11.2 mmol/liter. Wild-type (WT) and SOCS3 knockdown MIN6 cells were cultured with CNTF, IL1β, or both. CNTF reduced diabetes incidence and islet apoptosis in WT but not in SOCS3kd mice. Likewise, CNTF inhibited apoptosis in WT but not in SOCS3kd MIN6 cells. CNTF increased STAT3 phosphorylation in WT and SOCS3kd mice and MIN6 cells but reduced STAT1 phosphorylation only in WT mice, in contrast to streptozotocin and IL1β. Moreover, CNTF reduced NFκB activation and required down-regulation of inducible NO synthase expression to exert its protective effects. In conclusion, CNTF protects mice against streptozotocin-induced diabetes by increasing pancreatic islet survival, and this protection depends on SOCS3. In addition, SOCS3 expression and β-cell fate are dependent on STAT1/STAT3 ratio.

Plasticity and cross-talk of interleukin 6-type cytokines

Interleukin (IL)-6-type cytokines are critically involved in health and disease. The duration and strength of IL-6-type cytokine-mediated signaling is tightly regulated to avoid overshooting activities. Here, molecular mechanisms of inter-familiar cytokine cross-talk are reviewed which regulate dynamics and strength of IL-6 signal transduction. Both plasticity and cytokine cross-talk are significantly involved in pro- and anti-inflammatory/regenerative properties of IL-6-type cytokines. Furthermore, we focus on IL-6-type cytokine/cytokine receptor plasticity and cross-talk exemplified by the recently identified composite cytokines IL-30/IL-6R and IL-35, the first inter-familiar IL-6/IL-12 family member. The complete understanding of the intra- and extracellular cytokine networks will aid to develop novel tailor-made therapeutic strategies with reduced side effects.

Ciliary neurotrophic factor (CNTF) protects non-obese Swiss mice against type 2 diabetes by increasing beta cell mass and reducing insulin clearance

AIMS/HYPOTHESIS

Ciliary neurotrophic factor (CNTF) improves metabolic variables of obese animals with characteristics of type 2 diabetes, mainly by reducing insulin resistance. We evaluated whether CNTF was able to improve other metabolic variables in mouse models of type 2 diabetes, such as beta cell mass and insulin clearance, and whether CNTF has any effect on non-obese mice with characteristics of type 2 diabetes.

METHODS

Neonatal mice were treated with 0.1 mg/kg CNTF or citrate buffer via intraperitoneal injections, before injection of 250 mg/kg alloxan. HEPG2 cells were cultured for 3 days in the presence of citrate buffer, 1 nmol/l CNTF or 50 mmol/l alloxan or a combination of CNTF and alloxan. Twenty-one days after treatment, we determined body weight, epididymal fat weight, blood glucose, plasma insulin, NEFA, glucose tolerance, insulin resistance, insulin clearance and beta cell mass. Finally, we assessed insulin receptor and protein kinase B phosphorylation in peripheral organs, as well as insulin-degrading enzyme (IDE) protein production and alternative splicing in the liver and HEPG2 cells.

RESULTS

CNTF improved insulin sensitivity and beta cell mass, while reducing glucose-stimulated insulin secretion and insulin clearance in Swiss mice, improving glucose handling in a non-obese type 2 diabetes model. This effect was associated with lower IDE production and activity in liver cells. All these effects were observed even at 21 days after CNTF treatment.

CONCLUSIONS/INTERPRETATION

CNTF protection against type 2 diabetes is partially independent of the anti-obesity actions of CNTF, requiring a reduction in insulin clearance and increased beta cell mass, besides increased insulin sensitivity. Furthermore, knowledge of the long-term effects of CNTF expands its pharmacological relevance.

Ciliary neurotrophic factor (CNTF) signals through STAT3-SOCS3 pathway and protects rat pancreatic islets from cytokine-induced apoptosis

CNTF is a cytokine that promotes survival and/or differentiation in many cell types, including rat pancreatic islets. In this work, we studied the mechanism of CNTF signal in neonatal rats pancreatic islets isolated by the collagenase method and cultured for 3 days in RPMI medium without (CTL) or with 1 nM of CNTF. The medium contained, when necessary, specific inhibitors of the PI3K, MAPK and JAK/STAT3 pathways. mRNA expression (RT-PCR) and protein phosphorylation (Western blot) of Akt, ERK1/2 and STAT3, and SOCS-3 (RT-PCR and Western blot), as well as glucose-stimulated insulin secretion (GSIS) (Radioimmunoassay), were analyzed. Our results showed that Akt, ERK1 and STAT3 mRNA expression, as well as phosphorylated Akt and ERK1/2, was not affected by CNTF treatment. CNTF increased cytoplasmatic and nuclear phosphorylated STAT3, and the SOCS3 mRNA and protein expression. In addition, CNTF lowered apoptosis and impaired GSIS. These effects were blocked by the JAK inhibitor, AG490 and by the STAT3 inhibitor Curcumin, but not by the MAPK inhibitor, PD98059, nor by the PI3K inhibitor, Wortmannin. In conclusion, CNTF signals through the JAK2/STAT3 cascade, increases SOCS3 expression, impairs GSIS and protects neonatal pancreatic rat islets from cytokine-induced apoptosis. These findings indicate that CNTF may be a potential therapeutic tool against Type 1 and/or Type 2 diabetes.

The cytokine basis of cachexia and its treatment: are they ready for prime time?

Cachexia is a hypercatabolic condition that is often associated with the terminal stages of many diseases, in which the patient's resting metabolic rate is high and loss of muscle and fat tissue mass occur at an alarming rate. The patient also usually has concurrent anorexia, amplifying the wasting syndrome that is cachexia. The greater the extent of cachexia (regardless of underlying disease), the worse the prognosis. Efforts to treat cachexia over the years have fallen short of satisfactorily reversing the wasting syndrome. This article reviews the pathophysiology of cachexia, enumerating the different pro-inflammatory cytokines that contribute to the syndrome and attempting to illustrate their interwoven pathways. We also review the different treatments that have been explored, as well as the recent literature addressing the use of anti-cytokine therapy to treat cachexia.

gp130 receptor ligands as potential therapeutic targets for obesity

Obesity and its related cluster of pathophysiologic conditions including insulin resistance, glucose intolerance, dyslipidemia, and hypertension are recognized as growing threats to world health. It is now estimated that 10% of the world's population is overweight or obese. As a result, new therapeutic options for the treatment of obesity are clearly warranted. Recent research has focused on the role that gp130 receptor ligands may play as potential therapeutic targets in obesity. One cytokine in particular, ciliary neurotrophic factor (CNTF), acts both centrally and peripherally and mimics the biologic actions of the appetite control hormone leptin, but unlike leptin, CNTF appears to be effective in obesity and as such may have therapeutic potential. In addition, CNTF suppresses inflammatory signaling cascades associated with lipid accumulation in liver and skeletal muscle. This review examines the potential role of gp130 receptor ligands as part of a therapeutic strategy to treat obesity.

AMP-activated protein kinase impairs endothelial actin cytoskeleton assembly by phosphorylating vasodilator-stimulated phosphoprotein

Vasodilator-stimulated phosphoprotein (VASP) is an actin regulatory protein that links signaling pathways to remodeling of the cytoskeleton. VASP functions are modulated by protein kinases, which phosphorylate the sites Ser-157, Ser-239, and Thr-278. The kinase responsible for Thr-278 phosphorylation, biological functions of the phosphorylation, and association with disease states have remained enigmatic. Using VASP phosphorylation status-specific antibodies, we identified AMP-activated protein kinase (AMPK), a serine-threonine kinase and fundamental sensor of energy homeostasis, in a screen for kinases that phosphorylate the Thr-278 site of VASP in endothelial cells. Pharmacological AMPK inhibitors and activators and AMPK mutants revealed that the kinase specifically targets residue Thr-278 but not Ser-157 or Ser-239. Quantitative fluorescence-activated cell sorter analysis and serum response factor transcriptional reporter assays, which quantify the cellular F-/G-actin equilibrium, indicated that AMPK-mediated VASP phosphorylation impaired actin stress fiber formation and altered cell morphology. In the Zucker Diabetic Fatty (ZDF) rat model for type II diabetes, AMPK activity and Thr-278 phosphorylation were substantially reduced in arterial vessel walls. These findings suggest that VASP is a new AMPK substrate, that VASP Thr-278 phosphorylation translates metabolic signals into actin cytoskeleton rearrangements, and that this signaling system becomes down-regulated in diabetic vessels.