Peroxisome proliferator-activated receptor-γ activation enhances insulin-stimulated glucose disposal by reducing ped/pea-15 gene expression in skeletal muscle cells: evidence for involvement of activator protein-1

Activation of GFRAL+ neurons induces hypothermia and glucoregulatory responses associated with nausea and torpor

GFRAL-expressing neurons actuate aversion and nausea, are targets for obesity treatment, and may mediate metformin effects by long-term GDF15-GFRAL agonism. Whether GFRAL+ neurons acutely regulate glucose and energy homeostasis is, however, underexplored. Here, we report that cell-specific activation of GFRAL+ neurons using a variety of techniques causes a torpor-like state, including hypothermia, the release of stress hormones, a shift from glucose to lipid oxidation, and impaired insulin sensitivity, glucose tolerance, and skeletal muscle glucose uptake but augmented glucose uptake in visceral fat. Metabolomic analysis of blood and transcriptomics of muscle and fat indicate alterations in ketogenesis, insulin signaling, adipose tissue differentiation and mitogenesis, and energy fluxes. Our findings indicate that acute GFRAL+ neuron activation induces endocrine and gluco- and thermoregulatory responses associated with nausea and torpor. While chronic activation of GFRAL signaling promotes weight loss in obesity, these results show that acute activation of GFRAL+ neurons causes hypothermia and hyperglycemia.

ZMAT3 hypomethylation contributes to early senescence of preadipocytes from healthy first-degree relatives of type 2 diabetics

Senescence of adipose precursor cells (APC) impairs adipogenesis, contributes to the age-related subcutaneous adipose tissue (SAT) dysfunction, and increases risk of type 2 diabetes (T2D). First-degree relatives of T2D individuals (FDR) feature restricted adipogenesis, reflecting the detrimental effects of APC senescence earlier in life and rendering FDR more vulnerable to T2D. Epigenetics may contribute to these abnormalities but the underlying mechanisms remain unclear. In previous methylome comparison in APC from FDR and individuals with no diabetes familiarity (CTRL), ZMAT3 emerged as one of the top-ranked senescence-related genes featuring hypomethylation in FDR and associated with T2D risk. Here, we investigated whether and how DNA methylation changes at ZMAT3 promote early APC senescence. APC from FDR individuals revealed increases in multiple senescence markers compared to CTRL. Senescence in these cells was accompanied by ZMAT3 hypomethylation, which caused ZMAT3 upregulation. Demethylation at this gene in CTRL APC led to increased ZMAT3 expression and premature senescence, which were reverted by ZMAT3 siRNA. Furthermore, ZMAT3 overexpression in APC determined senescence and activation of the p53/p21 pathway, as observed in FDR APC. Adipogenesis was also inhibited in ZMAT3-overexpressing APC. In FDR APC, rescue of ZMAT3 methylation through senolytic exposure simultaneously downregulated ZMAT3 expression and improved adipogenesis. Interestingly, in human SAT, aging and T2D were associated with significantly increased expression of both ZMAT3 and the P53 senescence marker. Thus, DNA hypomethylation causes ZMAT3 upregulation in FDR APC accompanied by acquisition of the senescence phenotype and impaired adipogenesis, which may contribute to FDR predisposition for T2D.

Screening a Molecular Fragment Library to Modulate the PED/PEA15-Phospholipase D1 Interaction in Cellular Lysate Environments

The overexpression of PED/PEA15, the phosphoprotein enriched in diabetes/phosphoprotein enriched in the astrocytes 15 protein (here referred simply to as PED), observed in some forms of type II diabetes, reduces the transport of insulin-stimulated glucose by binding to the phospholipase D1 (PLD1). The inhibition of the PED/PLD1 interaction was shown to restore basal glucose transport, indicating PED as a pharmacological target for the development of drugs capable of improving insulin sensitivity and glucose tolerance. We here report the identification and selection of PED ligands by means of NMR screening of a library of small organic molecules, NMR characterization of the PED/PLD1 interaction in lysates of cells expressing PLD1, and modulation of such interactions using BPH03, the best selected ligand. Overall, we complement the available literature data by providing detailed information on the structural determinants of the PED/PLD1 interaction in a cellular lysate environment and indicate BPH03 as a precious scaffold for the development of novel compounds that are able to modulate such interactions with possible therapeutic applications in type II diabetes.

Epigenetic Mechanisms of Endocrine-Disrupting Chemicals in Obesity

The incidence of obesity has dramatically increased over the last decades. Recently, there has been a growing interest in the possible association between the pandemics of obesity and some endocrine-disrupting chemicals (EDCs), termed “obesogens”. These are a heterogeneous group of exogenous compounds that can interfere in the endocrine regulation of energy metabolism and adipose tissue structure. Oral intake, inhalation, and dermal absorption represent the major sources of human exposure to these EDCs. Recently, epigenetic changes such as the methylation of cytosine residues on DNA, post-translational modification of histones, and microRNA expression have been considered to act as an intermediary between deleterious effects of EDCs and obesity development in susceptible individuals. Specifically, EDCs exposure during early-life development can detrimentally affect individuals via inducing epigenetic modifications that can permanently change the epigenome in the germline, enabling changes to be transmitted to the next generations and predisposing them to a multitude of diseases. The purpose of this review is to analyze the epigenetic alterations putatively induced by chemical exposures and their ability to interfere with the control of energy metabolism and adipose tissue regulation, resulting in imbalances in the control of body weight, which can lead to obesity.

Role of Epigenetics in Type 2 Diabetes and Obesity

Epigenetic marks the genome by DNA methylation, histone modification or non-coding RNAs. Epigenetic marks instruct cells to respond reversibly to environmental cues and keep the specific gene expression stable throughout life. In this review, we concentrate on DNA methylation, the mechanism often associated with transgenerational persistence and for this reason frequently used in the clinic. A large study that included data from 10,000 blood samples detected 187 methylated sites associated with body mass index (BMI). The same study demonstrates that altered methylation results from obesity (OB). In another study the combined genetic and epigenetic analysis allowed us to understand the mechanism associating hepatic insulin resistance and non-alcoholic disease in Type 2 Diabetes (T2D) patients. The study underlines the therapeutic potential of epigenetic studies. We also account for seemingly contradictory results associated with epigenetics.

Molecular basis of ageing in chronic metabolic diseases

AIM

Over the last decades, the shift in age distribution towards older ages and the progressive ageing which has occurred in most populations have been paralleled by a global epidemic of obesity and its related metabolic disorders, primarily, type 2 diabetes (T2D). Dysfunction of the adipose tissue (AT) is widely recognized as a significant hallmark of the ageing process that, in turn, results in systemic metabolic alterations. These include insulin resistance, accumulation of ectopic lipids and chronic inflammation, which are responsible for an elevated risk of obesity and T2D onset associated to ageing. On the other hand, obesity and T2D, the paradigms of AT dysfunction, share many physiological characteristics with the ageing process, such as an increased burden of senescent cells and epigenetic alterations. Thus, these chronic metabolic disorders may represent a state of accelerated ageing.

MATERIALS AND METHODS

A more precise explanation of the fundamental ageing mechanisms that occur in AT and a deeper understanding of their role in the interplay between accelerated ageing and AT dysfunction can be a fundamental leap towards novel therapies that address the causes, not just the symptoms, of obesity and T2D, utilizing strategies that target either senescent cells or DNA methylation.

RESULTS

In this review, we summarize the current knowledge of the pathways that lead to AT dysfunction in the chronological ageing process as well as the pathophysiology of obesity and T2D, emphasizing the critical role of cellular senescence and DNA methylation.

CONCLUSION

Finally, we highlight the need for further research focused on targeting these mechanisms.

Assessment of liver fibrosis progression and regression by a serological collagen turnover profile

There is a need for noninvasive biomarkers that can identify patients with progressive liver fibrosis and monitor response to antifibrotic therapy. An equally important need is identification of patients with spontaneous fibrosis regression, since they may not need treatment nor be included in clinical studies with fibrosis as end point. Circulating biomarkers, originating from defined fragments of the scar tissue itself, may serve as valuable tools for this aspect of precision medicine. We investigated a panel of serological collagen formation and degradation markers to identify patients likely to regress or progress in absence of a therapeutic intervention. Plasma samples from patients with moderate-stage hepatitis C receiving placebo treatment in a phase II trial of the peroxisome proliferator-activated receptor agonist farglitazar were included. The patients had matched liver biopsies at baseline and 52 wk of follow-up. Serological biomarkers of collagen formation (PRO-C3, PRO-C4, PRO-C5) and collagen degradation (C3M, C4M, and C6M) were analyzed. Logistic regression analysis including PRO-C3 and C6M identified subjects with progressive liver fibrosis with an AUROC of 0.91 ( P < 0.0001) and positive and negative predictive values (PPV/NPV) of 75.0%/88.6%. Low levels of PRO-C5 predicted a spontaneous regression phenotype, with an odds ratio of 33.8 times higher compared with patients with high levels ( P < 0.0025) with an AUROC of 0.78 ( P < 0.0001) and PPV/NPV of 60.0%/95.7%. Two collagen fragments (PRO-C3 and C6M) identified liver fibrosis progressors, and one collagen fragment (PRO-C5) identified liver fibrosis regressors. These biomarkers may improve patient stratification and monitor treatment efficacy in studies with fibrosis as clinical end point. NEW & NOTEWORTHY In this study we report two biomarkers of collagen fragments (PRO-C3 and C6M) that are able to identify liver fibrosis progressors while one biomarker (PRO-C5) identified liver fibrosis regressors. In particular, we present three noninvasive biomarkers that can be used to identify patients with progressive liver fibrosis, monitor response to antifibrotic therapy, and also identify the spontaneous liver fibrosis regression phenotype.

Circadian expression and functional characterization of PEA-15 within the mouse suprachiasmatic nucleus

The circadian timing system influences the functional properties of most, if not all, physiological processes. Central to the mammalian timing system is the suprachiasmatic nucleus (SCN) of the hypothalamus. The SCN functions as a 'master clock' that sets the phasing of ancillary circadian oscillator populations found throughout the body. Further, via an entraining input from the retina, the SCN ensures that the clock oscillators are synchronized to the daily light/dark cycle. A critical component of the SCN timing and entrainment systems is the p44/42 mitogen-activated protein kinase (ERK/MAPK) pathway. Here, we examined the expression and function of phosphoprotein-enriched in astrocytes (PEA-15), an ERK scaffold protein that serves as a key regulator of MAPK signaling. A combination of immunolabeling and Western blotting approaches revealed high levels of PEA-15 within the SCN. PEA-15 expression was enriched in distinct subpopulations of SCN neurons, including arginine vasopressin (AVP)-positive neurons of the SCN shell region. Further, expression profiling detected a significant circadian oscillation in PEA-15 expression within the SCN. Brief photic stimulation during the early subjective night led to a significant increase in PEA-15 phosphorylation, an event that can trigger ERK/PEA-15 dissociation. Consistent with this, co-immunoprecipitation assays revealed that PEA-15 is directly bound to ERK in the SCN and that photic stimulation leads to their dissociation. Finally, we show that PEA-15 regulates ERK/MAPK-dependent activation of the core clock gene period1. Together, these data raise the prospect that PEA-15 functions as a key regulator of the SCN timing system.

Eicosapentaenoic acid abolishes inhibition of insulin-induced mTOR phosphorylation by LPS via PTP1B downregulation in skeletal muscle

Dietary n-3 polyunsaturated fatty acids (n-3 PUFAs) increase insulin signaling in skeletal muscle. In the current study, we investigated the effect of eicosapentaenoic acid (EPA) on insulin-induced mammalian target of rapamycin (mTOR) phosphorylation in myotubes. We showed that EPA did not affect basal and insulin-induced mTOR phosphorylation in myotubes. However, EPA abolished lipopolysaccharide (LPS) -induced deficiency in insulin signaling (P < 0.05). Pre-incubation of nuclear factor κB (NF-κΒ) and c-Jun N-terminal kinases (JNK) inhibitors prevented the decreased insulin-induced mTOR phosphorylation elicited by LPS (P < 0.05). In addition, in protein tyrosine phosphatase-1B (PTP1B) knockdown myotubes, LPS failed to decrease insulin-induced mammalian target of rapamycin (mTOR) phosphorylation in myotubes (P > 0.05). In myotubes, LPS stimulated PTP1B expression via NF-κB and activation protein-1 (AP1). Pre-incubation of 50 μM EPA prevented the LPS-induced activation of AP1 and NF-κΒ as well as PTP1B expression (P < 0.05). Interestingly, incubation of peroxisome proliferator-activated receptor γ (PPARγ) antagonist (GW9662) prior to EPA treatment, the effect of EPA on insulin-induced mTOR phosphorylation was blocked. Accordingly, EPA did not inhibit the LPS-induced activation of AP1 or NF-κΒ as well as PTP1B expression when incubation of GW9662 prior to EPA treatment. The in vivo study showed that EPA prevented LPS-induced PTPT1B expression and a decrease in insulin-induced mTOR phosphorylation in muscle of mice. In summary, EPA abolished LPS inhibition of insulin-induced mTOR phosphorylation in myotubes, and one of the key mechanisms was to inhibit AP1 and NF-κB activation and PTP1B transcription.

Fibrogenesis assessed by serological type III collagen formation identifies patients with progressive liver fibrosis and responders to a potential antifibrotic therapy

There are no approved treatments for liver fibrosis. To aid development of antifibrotic therapies, noninvasive biomarkers that can identify patients with progressive fibrosis and that permit monitoring of the response to antifibrotic therapy are much needed. Samples from a phase II antifibrotic trial of the glitazone farglitazar in patients with advanced hepatitis C, with matched follow-up liver biopsies, and from a phase III study of balaglitazone in patients with late-stage Type 2 diabetes (BALLET study) were analyzed for serological Pro-C3 levels in conjunction with other disease parameters. In the farglitazar study, a predefined cutoff value for Pro-C3 as a selection criterion led to the identification of subjects who 1) progressed by histological scores and 2) responded to therapy, as documented by attenuated fibrosis in liver biopsies. In the BALLET trial, subjects with the highest tertile of Pro-C3 levels responded to balaglitazone with reductions in levels of alanine aminotransferase and Pro-C3, as well as improved insulin sensitivity and lipid profile. Elevated Pro-C3 levels are indicative of active fibrogenesis and structural progression of fibrosis, and it can potentially identify patients most likely to benefit from antimetabolic and antifibrotic treatments. Serum Pro-C3 may facilitate patient selection and could help to speed up antifibrotic drug development and validation.

Glucose-induced expression of the homeotic transcription factor Prep1 is associated with histone post-translational modifications in skeletal muscle

AIMS/HYPOTHESIS

Chronic hyperglycaemia worsens insulin resistance in individuals with type 2 diabetes. Whether this effect is contributed by epigenetic dysregulation and which genes are involved remain unclear. Prep1 (also known as Pknox1) is a gene exerting major effects on the sensitivity of the glucose transport machinery to insulin. Here, we show that dysregulation of Prep1 expression by high glucose levels is associated with histone modifications at its 5' regulatory region.

METHODS

We used mouse and cell models to investigate Prep1 transcriptional regulation by glucose.

RESULTS

Differentiated L6 skeletal muscle cells were grown in the presence of either 5.5 or 25 mmol/l glucose (normal [NG] and high glucose [HG], respectively). The HG exposure increased nuclear factor κ light chain enhancer of activated B cells (NF-κB) p65 binding and recruitment of the su(var)3-9, enhancer-of-zeste, trithorax domain-containing lysine methyltransferase 7 (SET7) histone methyltransferase and p300 acetyltransferase to the 5' region of Prep1, leading to enhanced transcription. In addition, chromatin immunoprecipitation assays revealed concomitantly increased histone H3 mono- and dimethylation and acetylation at Lys4 and Lys9/14, respectively. Skeletal muscle tissue from streptozotocin-treated diabetic mice also showed Prep1 overexpression accompanied by similarly increased recruitment of NF-κB p65 and histone modifications at the 5' region of Prep1. In these same mice, as well as in Prep1-overexpressing L6 cells, Prep1-induced recruitment of the repressor complex myocyte enhancer factor 2 (MEF2)/histone deacetylase 5 (HDAC5) at the Glut4 promoter was also increased, leading to reduced Glut4 expression.

CONCLUSIONS/INTERPRETATION

These studies indicate that HG exposure induces NF-κB recruitment and histone modification at the Prep1 5' region, thereby enhancing the transcription of Prep1 and repressing that of Glut4. Histone changes at the Prep1 gene may contribute to insulin resistance in individuals with type 2 diabetes.

Understanding type 2 diabetes: from genetics to epigenetics

The known genetic variability (common DNA polymorphisms) does not account either for the current epidemics of type 2 diabetes or for the family transmission of this disorder. However, clinical, epidemiological and, more recently, experimental evidence indicates that environmental factors have an extraordinary impact on the natural history of type 2 diabetes. Some of these environmental hits are often shared in family groups and proved to be capable to induce epigenetic changes which alter the function of genes affecting major diabetes traits. Thus, epigenetic mechanisms may explain the environmental origin as well as the familial aggregation of type 2 diabetes much easier than common polymorphisms. In the murine model, exposure of parents to environmental hits known to cause epigenetic changes reprograms insulin sensitivity as well as beta-cell function in the progeny, indicating that certain epigenetic changes can be transgenerationally transmitted. Studies from different laboratories revealed that, in humans, lifestyle intervention modulates the epigenome and reverts environmentally induced epigenetic modifications at specific target genes. Finally, specific human epigenotypes have been identified which predict adiposity and type 2 diabetes with much greater power than any polymorphism so far identified. These epigenotypes can be recognized in easily accessible white cells from peripheral blood, indicating that, in the future, epigenetic profiling may enable effective type 2 diabetes prediction. This review discusses recent evidence from the literature supporting the immediate need for further investigation to uncover the power of epigenetics in the prediction, prevention and treatment of type 2 diabetes.

Personalized medicine and type 2 diabetes: lesson from epigenetics

Similarly to genetic polymorphisms, epigenetic modifications may alter transcriptional activity and contribute to different traits of the Type 2 diabetes phenotype. The establishment of these epigenetic marks may precede diabetes onset and predict the disease. Current evidence now indicates that epigenetic differences represent markers of diabetes risk. Studies on epigenome plasticity revealed that cytokines and other metabolites, by affecting DNA methylation, may acutely reprogram gene expression and contribute to the Type 2 diabetes phenotype even in the adult life. The available evidence further indicates that epigenetic marks across the genome are subject to dynamic variations in response to environmental cues. Finally, different genes responsible for the interindividual variability in antidiabetic drug response are subjected to epigenetic regulation. Determining how specific epigenetic profiles determine diabetes is a challenging task. In the near future, the identification of epigenetic marks predictive of diabetes risk or response to treatment may offer unanticipated opportunities to personalize Type 2 diabetes management.

Phosphoprotein enriched in astrocytes (PEA)-15: a potential therapeutic target in multiple disease states

Phosphoprotein enriched in astrocytes-15 (PEA-15) is a cytoplasmic protein that sits at an important junction in intracellular signalling and can regulate diverse cellular processes, such as proliferation and apoptosis, dependent upon stimulation. Regulation of these processes occurs by virtue of the unique interaction of PEA-15 with other signalling proteins. PEA-15 acts as a cytoplasmic tether for the mitogen-activated protein kinases, extracellular signal-regulated kinase 1/2 (ERK1/2) preventing nuclear localisation. In order to release ERK1/2, PEA-15 requires to be phosphorylated via several potential pathways. PEA-15 (and its phosphorylation state) therefore regulates many ERK1/2-dependent processes, including proliferation, via regulating ERK1/2 nuclear translocation. In addition, PEA-15 contains a death effector domain (DED) which allows interaction with other DED-containing proteins. PEA-15 can bind the DED-containing apoptotic adaptor molecule, Fas-associated death domain protein (FADD) which is also dependent on the phosphorylation status of PEA-15. PEA-15 binding of FADD can inhibit apoptosis as bound FADD cannot participate in the assembly of apoptotic signalling complexes. Through these protein–protein interactions, PEA-15-regulated cellular effects have now been investigated in a number of disease-related studies. Changes in PEA-15 expression and regulation have been observed in diabetes mellitus, cancer, neurological disorders and the cardiovascular system. These changes have been suggested to contribute to the pathology related to each of these disease states. As such, new therapeutic targets based around PEA-15 and its associated interactions are now being uncovered and could provide novel avenues for treatment strategies in multiple diseases.

PEP-1-PEA-15 protects against toxin-induced neuronal damage in a mouse model of Parkinson's disease

BACKGROUND

PEA-15 is abundantly expressed in both neurons and astrocytes throughout the brain. It is a multifunctional protein with the ability to increase cell survival via anti-apoptotic and anti-proliferative properties. However, the function of PEA-15 in neuronal diseases such as Parkinson's disease (PD) remains unclear. In this study, we investigated the protective effects of PEA-15 on neuronal damage induced by MPP(+) in neuroblastoma SH-SY5Y and BV2 microglia cells and in a MPTP-induced PD mouse model using cell-permeable PEP-1-PEA-15.

METHODS

PEP-1-PEA-15 was purified using affinity chromatography. Cell viability and DNA fragmentation were examined by MTT assay and TUNEL staining. Dopaminergic neuronal cell death in the animal model was examined by immunohistochemistry.

RESULTS

PEP-1-PEA-15 transduced into the SH-SY5Y and BV2 cells in a time- and dose-dependent manner. Transduced PEP-1-PEA-15 protected against MPP(+)-induced toxicity by inhibiting intracellular ROS levels and DNA fragmentation. Further, it enhanced the expression levels of Bcl-2 and caspase-3 while reducing the expression levels of Bax and cleaved caspase-3. We found that PEP-1-PEA-15 transduced into the substantia nigra and prevented dopaminergic neuronal cell death in a MPTP-induced PD mouse. Also, we showed the neuroprotective effects in the model by demonstrating that treatment with PEP-1-PEA-15 ameliorated MPTP-induced behavioral dysfunctions and increased dopamine levels in the striatum.

CONCLUSIONS

PEP-1-PEA-15 can efficiently transduce into cells and protects against neurotoxin-induced neuronal cell death in vitro and in vivo.

GENERAL SIGNIFICANCE

These results demonstrate the potential for PEP-1-PEA-15 to provide a new strategy for protein therapy treatment of a variety of neurodegenerative diseases including PD.

Adenoviral gene transfer of PLD1-D4 enhances insulin sensitivity in mice by disrupting phospholipase D1 interaction with PED/PEA-15

Over-expression of phosphoprotein enriched in diabetes/phosphoprotein enriched in astrocytes (PED/PEA-15) causes insulin resistance by interacting with the D4 domain of phospholipase D1 (PLD1). Indeed, the disruption of this association restores insulin sensitivity in cultured cells over-expressing PED/PEA-15. Whether the displacement of PLD1 from PED/PEA-15 improves insulin sensitivity in vivo has not been explored yet. In this work we show that treatment with a recombinant adenoviral vector containing the human D4 cDNA (Ad-D4) restores normal glucose homeostasis in transgenic mice overexpressing PED/PEA-15 (Tg _ped/pea-15) by improving both insulin sensitivity and secretion. In skeletal muscle of these mice, D4 over-expression inhibited PED/PEA-15-PLD1 interaction, decreased Protein Kinase C alpha activation and restored insulin induced Protein Kinase C zeta activation, leading to amelioration of insulin-dependent glucose uptake. Interestingly, Ad-D4 administration improved insulin sensitivity also in high-fat diet treated obese C57Bl/6 mice. We conclude that PED/PEA-15-PLD1 interaction may represent a novel target for interventions aiming at improving glucose tolerance.