Resveratrol Improves Endothelial Function by A PREP1-Mediated Pathway in Mouse Aortic Endothelial Cells

PREP1 is a homeodomain transcription factor that impairs metabolism and is involved in age-related aortic thickening. In this study, we evaluated the role of PREP1 on endothelial function. Mouse Aortic Endothelial Cells (MAECs) transiently transfected with a Prep1 cDNA showed a 1.5- and 1.6-fold increase in eNOSThr495 and PKCα phosphorylation, respectively. Proinflammatory cytokines Tnf-α and Il-6 increased by 3.5 and 2.3-fold, respectively, in the presence of Prep1, while the antioxidant genes Sod2 and Atf4 were significantly reduced. Bisindolylmaleimide reverted the effects induced by PREP1, suggesting PKCα to be a mediator of PREP1 action. Interestingly, resveratrol, a phenolic micronutrient compound, reduced the PREP1 levels, eNOSThr495, PKCα phosphorylation, and proinflammatory cytokines and increased Sod2 and Atf4 mRNA levels. The experiments performed on the aorta of 18-month-old Prep1 hypomorphic heterozygous mice (Prep1i/+) expressing low levels of this protein showed a 54 and 60% decrease in PKCα and eNOSThr495 phosphorylation and a 45% reduction in Tnf-α levels, with no change in Il-6, compared to same-age WT mice. However, a significant decrease in Sod2 and Atf4 was observed in Prep1i/+ old mice, indicating the lack of age-induced antioxidant response. These results suggest that Prep1 deficiency partially improved the endothelial function in aged mice and suggested PREP1 as a novel target of resveratrol.

EVOO Polyphenols Exert Anti-Inflammatory Effects on the Microglia Cell through TREM2 Signaling Pathway

In Alzheimer's disease (AD), microglia, brain resident immune cells, become chronically inflammatory and neurotoxic. In recent years, neuroinflammation has attracted particular interest in the scientific community. The genetic variants of molecules associated with ''microgliopathies'', including the triggering receptor expressed in myeloid cells-2 (TREM2), result in increased risk of developing AD and cognitive decline. We performed a set of in vitro assays using human neuronal (SH-SY5Y) and microglial (BV2 and C13NJ) cell models. Cells were differentially treated with extra virgin olive oil (EVOO) polyphenols, oleuropein aglycone (OleA) and hydroxytyrosol (HT) before adding LPS. We evaluated the protective effects of these EVOO products by a set of biochemical and cell biology assays, including ELISA, MTT, ROS detection, Western blotting and immunofluorescence. Our results provide an integrated understanding of the neuroprotection exerted by polyphenols in terms of: (i) reduction of pro-inflammatory cytokines release (IL-6, IL-8, IP-10 and RANTES); (ii) activation of the TREM2-dependent anti-inflammatory pathway; (iii) enhancement of protective microglial activity favoring the M2 polarization phenotype. Such findings provide new and important insights into the mechanisms by which the dietary olive polyphenols exert beneficial properties against neuroinflammation and neuronal impairment.

SARS-CoV-2 Affects Both Humans and Animals: What Is the Potential Transmission Risk? A Literature Review

In March 2020, the World Health Organization Department declared the coronavirus (COVID-19) outbreak a global pandemic, as a consequence of its rapid spread on all continents. The COVID-19 pandemic has been not only a health emergency but also a serious general problem as fear of contagion and severe restrictions put economic and social activity on hold in many countries. Considering the close link between human and animal health, COVID-19 might infect wild and companion animals, and spawn dangerous viral mutants that could jump back and pose an ulterior threat to us. The purpose of this review is to provide an overview of the pandemic, with a particular focus on the clinical manifestations in humans and animals, the different diagnosis methods, the potential transmission risks, and their potential direct impact on the human-animal relationship.

Interleukin 6 reduces vascular smooth muscle cell apoptosis via Prep1 and is associated with aging

Aging exacerbates neointimal formation by reducing apoptosis of vascular smooth muscle cells (VSMCs) and induces inflammation within vascular wall. Prep1 is a homeodomain transcription factor which stimulates the expression of proinflammatory cytokines in aortic endothelial cell models and plays a primary role in the regulation of apoptosis. In this study, we have investigated the role of Prep1 in aorta of Prep1 hypomorphic heterozygous mice (Prep1^i/+ ) and in VSMCs, and its correlation with aging. Histological analysis from Prep1^i/+ aortas revealed a 25% reduction in medial smooth muscle cell density compared to WT animals. This result paralleled higher apoptosis, caspase 3, caspase 9 and p53 levels in Prep1^i/+ mice and lower Bcl-xL. Prep1 overexpression in VSMCs decreased apoptosis by 25% and caspase 3 and caspase 9 expression by 40% and 37%. In parallel, Bcl-xL inhibition by BH3I-1 and p53 induction by etoposide reverted the antiapoptotic effect of Prep1. Experiments performed in aorta from 18 months old WT mice showed a significant increase in Prep1, p16^INK4 , p21^Waf1 and interleukin 6 (IL-6) compared to youngest animals. Similar results have been observed in H₂ O₂ -induced senescent VSMCs. Interestingly, the synthetic Prep1 inhibitory peptide Prep1 (54-72) reduced the antiapoptotic effects mediated by IL-6, particularly in senescent VSMCs. These results indicate that IL-6-Prep1 signaling reduces apoptosis, by modulating Bcl-xL and p53 both in murine aorta and in VSMCs. In addition, age-dependent increase in IL-6 and Prep1 in senescent VSMCs and in old mice may be involved in the aging-related vascular dysfunction.

Zoonotic Risk of Encephalitozoon cuniculi in Animal-Assisted Interventions: Laboratory Strategies for the Diagnosis of Infections in Humans and Animals

The involvement of animals for therapeutic purposes has very ancient roots. To date, it is clear that animal-assisted interventions (AAIs), in addition to ensuring the replacement of missing or deficient affects, improves psychophysiological parameters connected to human health. However, AAI could potentially present risks related to the transmission of infectious agents from animals to humans. Among these microorganisms, E. cuniculi is a microspore which induces pathological effects (fever, headache, nausea, vomiting, diarrhea, breathlessness, respiratory symptoms, and weakness) in both humans and animals. Consequently, an accurate and fast diagnosis of E. cuniculi infection, as well as the identification of new diagnostic approaches, is of fundamental importance. This literature review was carried out to provide an extensive and comprehensive analysis of the most recent diagnostic techniques to prevent and care for E. cuniculi-associated risks in the AAI field.

Leishmania spp.-Infected Dogs Have Circulating Anti-Skeletal Muscle Autoantibodies Recognizing SERCA1

Leishmania spp. infection is associated with an inflammatory myopathy (IM) in dogs. The pathomechanism underlying this disorder is still elusive, however, the pattern of cellular infiltration and MHC I and II upregulation indicate an immune-mediated myositis. This study aimed to investigate the presence of autoantibodies targeting the skeletal muscle in sera of leishmania-infected dogs and individuate the major autoantigen. We tested sera from 35 leishmania-infected dogs and sera from 10 negative controls for the presence of circulating autoantibodies with indirect immunofluorescence. Immunoblot and mass spectrometry were used to identify the main target autoantigen. Immunocolocalization and immunoblot on immunoprecipitated muscle proteins were performed to confirm the individuated major autoantigen. We identified circulating autoantibodies that recognize skeletal muscle antigen(s) in sera of leishmania-infected dogs. The major antigen was identified as the sarcoplasmic/endoplasmic reticulum Ca2+-ATPase 1 (SERCA1). We also found that canine SERCA1 presents several identical traits to the calcium-translocating P-type ATPase of Leishmania infantum. In the present study, we defined circulating anti-SERCA1 autoantibodies as part of the pathogenesis of the leishmania-associated IM in dogs. Based on our data, we hypothesize that antigen mimicry is the mechanism underlying the production of these autoantibodies in leishmania-infected dogs.

Potential Mechanisms of Bisphenol A (BPA) Contributing to Human Disease

Bisphenol A (BPA) is an organic synthetic compound serving as a monomer to produce polycarbonate plastic, widely used in the packaging for food and drinks, medical devices, thermal paper, and dental materials. BPA can contaminate food, beverage, air, and soil. It accumulates in several human tissues and organs and is potentially harmful to human health through different molecular mechanisms. Due to its hormone-like properties, BPA may bind to estrogen receptors, thereby affecting both body weight and tumorigenesis. BPA may also affect metabolism and cancer progression, by interacting with GPR30, and may impair male reproductive function, by binding to androgen receptors. Several transcription factors, including PPARγ, C/EBP, Nrf2, HOX, and HAND2, are involved in BPA action on fat and liver homeostasis, the cardiovascular system, and cancer. Finally, epigenetic changes, such as DNA methylation, histones modification, and changes in microRNAs expression contribute to BPA pathological effects. This review aims to provide an extensive and comprehensive analysis of the most recent evidence about the potential mechanisms by which BPA affects human health.

Diagnosis of Flier's syndrome in a patient with nondiabetic hypoglycemia: a case report and critical appraisal of the literature

PURPOSE

Autoimmune hypoglycemia includes rare syndromes characterized by the presence of either anti-insulin antibodies (IAA) (Hirata's disease) or anti-insulin receptor (anti-ISR) antibodies (Flier's syndrome). Diagnosis is usually based on identification of the specific antibodies, in presence of the Whipple triad. However, most of these cases are classified as idiopathic diseases due to the difficulty to define the pathogenic culprit.

METHODS

Basic research methodologies, including Western Blot and ELISA tests, have been used in this study.

RESULTS

We describe a 21-year-old young woman (PT), non-obese and non-diabetic, with a positive history of autoimmune diseases, admitted to the hospital for recurrent episodes of severe symptomatic hypoglycemia. Counterregulatory response to hypoglycemia was normal as well as the fasting test, so excluding both hormone deficiencies and insulinoma. Since an autoimmune hypoglycemic syndrome was suspected, the hyperactivation of the insulin pathway was experimentally evaluated. At this purpose, human hepatocarcinoma (HepG2) cells were incubated with serum obtained from the patient (PT) and from control individuals. Interestingly, a significant increase of phosphorylation of insulin receptor, Akt, and ERK1/2 was observed in the HepG2 cells incubated with PT serum compared with the controls. ELISA tests revealed significantly increased levels of anti-ISR antibodies in PT serum, while IAA were similar both in PT and in control sera, supporting diagnosis of Flier's syndrome.

CONCLUSIONS

This study emphasizes the importance to identify new strategies for the differential diagnosis of hypoglycemia, not always possible with the routinely used diagnostic tests.

Platelet-rich plasma counteracts detrimental effect of high-glucose concentrations on mesenchymal stem cells from Bichat fat pad

Diabetic patients display increased risk of periodontitis and failure in bone augmentation procedures. Mesenchymal stem cells (MSCs) and platelet-rich plasma (PRP) represent a relevant advantage in tissue repair process and regenerative medicine. We isolated MSCs from Bichat's buccal fat pad (BFP) and measured the effects of glucose and PRP on cell number and osteogenic differentiation potential. Cells were cultured in the presence of 5.5-mM glucose (low glucose [LG]) or 25-mM glucose (high glucose [HG]). BFP-MSC number was significantly lower when cells were cultured in HG compared with those in LG. Following osteogenic differentiation procedures, calcium accumulation, alkaline phosphatase activity, and expression of osteogenic markers were significantly lower in HG compared with LG. Exposure of BFP-MSC to PRP significantly increased cell number and osteogenic differentiation potential, reaching comparable levels in LG and in HG. Thus, high-glucose concentrations impair BFP-MSC growth and osteogenic differentiation. However, these detrimental effects are largely counteracted by PRP.

Autophagy and NLRP3 inflammasome crosstalk in neuroinflammation in aged bovine brains

NLRP3 inflammasome is a multiprotein complex that can sense several stimuli such as autophagy dysregulation and increased reactive oxygen species production stimulating inflammation by priming the maturation of proinflammatory cytokines interleukin-1β and interleukin-18 in their active form. In the aging brain, these cytokines can mediate the innate immunity response priming microglial activation. Here, we describe the results of immunohistochemical and molecular analysis carried out on bovine brains. Our results support the hypothesis that the age-related impairment in cellular housekeeping mechanisms and the increased oxidative stress can trigger the inflammatory danger sensor NLRP3. Moreover, according to the recent scientific literature, we demonstrate the presence of an age-related proinflammatory environment in aged brains consisting in an upregulation of interleukin-1β, an increased microglial activation and increased NLRP3 expression. Finally, we suggest that bovine may potentially be a pivotal animal model for brain aging studies.

Low-dose Bisphenol-A regulates inflammatory cytokines through GPR30 in mammary adipose cells

The dramatic rise in obesity and metabolic syndrome can be related, at least in part, to environmental chemical factors such as Bisphenol-A (BPA). In this study, we aimed to understand the effects of low-dose Bisphenol-A on the human mature adipocytes and stromal vascular fraction (SVF) cells, obtained from subcutaneous mammary adipose tissue of overweight female patients, undergoing surgical mammary reduction. 24 and/or 48-h exposure to BPA 0.1 nM elicited significant increase of the inflammatory molecules interleukin-6 (IL-6), interleukin-8 (IL-8), monocyte chemo-attractant protein 1α (MCP1α) and induced G protein-coupled estrogen receptor 30 (GPR30) levels more than two-fold both in mature adipocytes and SVF cells. These effects were similar to that obtained in the presence of GPR30-specific agonist G1 (100 nM) and were reverted by G15 (1 µM), a GPR30-selective antagonist. As a result of BPA-GPR30 signaling activation, fatty acid synthase (FAS) and leptin mRNA levels were significantly higher upon BPA exposure (P < 0.05) in mature adipocytes, with an opposite effect on adiponectin (ADIPOQ). In addition, an increase in SVF cell proliferation and ERK1/2 phosphorylation, was observed, compared to untreated cells. G15 reverted all of these effects. Interestingly, the action of BPA on SVF cell growth was mimicked by IL-8 treatment and was reverted by incubation with anti-IL8 antibodies. All these data suggest that BPA at 0.1 nM, a ten times lower concentration than environmental exposure, increases the expression of pro-inflammatory cytokines via GPR30 both in mature mammary adipocytes and in SVF cells with a possible involvement of IL-8.

Prep1 regulates angiogenesis through a PGC-1α-mediated mechanism

Angiogenesis depends on a delicate balance between the different transcription factors, and their control should be considered necessary for preventing or treating diseases. Pre-B-cell leukemia transcription factor regulating protein 1 (Prep1) is a homeodomain transcription factor that plays a primary role in organogenesis and metabolism. Observations performed in a Prep1 hypomorphic mouse model, expressing 3-5% of the protein, show an increase of embryonic lethality due, in part, to defects in angiogenesis. In this study, we provide evidence that overexpression of Prep1 in mouse aortic endothelial cells (MAECs) stimulates migration, proliferation, and tube formation. These effects are paralleled by an increase of several proangiogenic factors and by a decrease of the antiangiogenic gene neurogenic locus notch homolog protein 1 (Notch1). Prep1-mediated angiogenesis involves the activation of the p160 Myb-binding protein (p160)/peroxisome proliferator-activated receptor γ coactivator 1α (PGC-1α) pathway. Indeed, Prep1 overexpression increases its binding with p160 and induces a 4-fold increase of p160 and 70% reduction of PGC-1α compared with control cells. Incubation of MAECs with a synthetic Prep1(54-72) peptide, mimicking the Prep1 region involved in the interaction with p160, reverts the proangiogenic effects mediated by Prep1. In addition, Prep1 levels increase by 3.2-fold during the fibroblast growth factor β (bFGF)-mediated endothelial colony-forming cells' activation, whereas Prep1(54-72) peptide reduces the capability of these cells to generate tubular-like structures in response to bFGF, suggesting a possible role of Prep1 both in angiogenesis from preexisting vessels and in postnatal vasculogenesis. Finally, Prep1 hypomorphic heterozygous mice, expressing low levels of Prep1, show attenuated placental angiogenesis and vessel formation within Matrigel plugs. All of these observations indicate that Prep1, complexing with p160, decreases PGC-1α and stimulates angiogenesis.-Cimmino, I., Margheri, F., Prisco, F., Perruolo, G., D'Esposito, V., Laurenzana, A., Fibbi, G., Paciello, O., Doti, N., Ruvo, M., Miele, C., Beguinot, F., Formisano, P., Oriente, F. Prep1 regulates angiogenesis through a PGC-1α-mediated mechanism.

The Relevance of Insulin Action in the Dopaminergic System

The advances in medicine, together with lifestyle modifications, led to a rising life expectancy. Unfortunately, however, aging is accompanied by an alarming boost of age-associated chronic pathologies, including neurodegenerative and metabolic diseases. Interestingly, a non-negligible interplay between alterations of glucose homeostasis and brain dysfunction has clearly emerged. In particular, epidemiological studies have pointed out a possible association between Type 2 Diabetes (T2D) and Parkinson’s Disease (PD). Insulin resistance, one of the major hallmark for etiology of T2D, has a detrimental influence on PD, negatively affecting PD phenotype, accelerating its progression and worsening cognitive impairment. This review aims to provide an exhaustive analysis of the most recent evidences supporting the key role of insulin resistance in PD pathogenesis. It will focus on the relevance of insulin in the brain, working as pro-survival neurotrophic factor and as a master regulator of neuronal mitochondrial function and oxidative stress. Insulin action as a modulator of dopamine signaling and of alpha-synuclein degradation will be described in details, too. The intriguing idea that shared deregulated pathogenic pathways represent a link between PD and insulin resistance has clinical and therapeutic implications. Thus, ongoing studies about the promising healing potential of common antidiabetic drugs such as metformin, exenatide, DPP IV inhibitors, thiazolidinediones and bromocriptine, will be summarized and the rationale for their use to decelerate neurodegeneration will be critically assessed.

Prep1 deficiency improves metabolic response in white adipose tissue

Prep1 is a gene encoding for a homeodomain transcription factor which induces hepatic and muscular insulin resistance. In this study, we show that Prep1 hypomorphic heterozygous (Prep1^i/+) mice, expressing low levels of protein, featured a 23% and a 25% reduction of total body lipid content and epididymal fat, respectively. The percentage of the small adipocytes (25-75 μm) was 30% higher in Prep1^i/+ animals than in the WT, with a reciprocal difference in the large adipose cells (100-150 and >150 μm). Insulin-stimulated insulin receptor tyrosine and Akt serine phosphorylation markedly increased in Prep1^i/+ mice, paralleled by 3-fold higher glucose uptake and a significant increase of proadipogenic genes such as C/EBPα, GLUT4, and FABP4. Moreover, T cells infiltration and TNF-α, IFNγ and leptin expression were reduced in adipose tissue from Prep1^i/+ mice, while adiponectin levels were 2-fold higher. Furthermore, Prep1^i/+ mature adipocytes released lower amounts of pro-inflammatory cytokines and higher amount of adiponectin compared to WT cells. Incubation of murine liver cell line (NMuLi) with conditioned media (CM) from mature adipocytes of Prep1^i/+ mice improved glucose metabolism, while those from WT mice had no effect. Consistent with these data, Prep1 overexpression in 3T3-L1 adipocytes impaired adipogenesis and insulin signaling, and increased proinflammatory cytokine secretion. All these findings suggest that Prep1 silencing reduces inflammatory response and increases insulin sensitivity in adipose tissue. In addition, CM from mature adipocytes of Prep1^i/+ mice improve metabolism in hepatic cells.

Prep1, A Homeodomain Transcription Factor Involved in Glucose and Lipid Metabolism

The three-amino acid loop extension (TALE) homeodomain proteins are a family of transcription factor including the mammalian Pbx, MEIS and Prep proteins. TALE proteins can bind other transcription factors such as Pdx-1 and play an important role in the regulation of glucose metabolism. Experiments performed in mutant mice have shown that while the single Pbx1 or Pdx-1 knockout mice feature pancreatic islet malformations, impaired glucose tolerance and hypoinsulinemia, the trans-heterozygous Pbx1^+/-Pdx1^+/- mice develop age-dependent overt diabetes mellitus. In contrast, Prep1 plays a different role with respect to these proteins. Indeed, Prep1 hypomorphic mice, expressing low levels of protein, feature pancreatic islet hypoplasia accompanied by hypoinsulinemia similar to Pbx1 or Pdx1. Nevertheless, these animals show increased insulin sensitivity in skeletal muscle, liver and adipose tissue accompanied by protection from streptozotocin-induced diabetes. In addition, Prep1 hypomorphic mice feature reduced triglyceride synthesis and do not develop steatohepatitis after a methionine and coline deficient diet. In this review we have underlined how important metabolic functions are controlled by TALE proteins, in particular by Prep1, leading to hypothesis that its suppression might represent beneficial effect in the care of metabolic diseases.

A peptide antagonist of Prep1-p160 interaction improves ceramide-induced insulin resistance in skeletal muscle cells

Prep1 is a homeodomain transcription factor belonging to the TALE protein family. Its overexpression affects glucose metabolism in several tissues. In particular, in skeletal muscle tissue the interaction of Prep1 with its cofactor p160 impairs GLUT4 expression and glucose uptake. In this study, we show that ceramides (C2cer), a class of lipids antagonizing insulin signalling, increase the levels of Prep1 and p160 in a dose and time-dependent fashion in L6 cells and induce their association by 80%. We find that C2cer exposure inhibits insulin receptor, IRS1 and Akt phosphorylation and reduces insulin-stimulated glycogen content and glucose uptake by 1.3- and 2.1-fold, respectively. The synthetic Prep1(54-72) peptide, mimicking the Prep1 region involved in the interaction with p160, reduces in vitro Prep1-p160 binding in a dose-dependent way (IC₅₀ = 0.20μM). In C2cer-treated L6 cells, 10μM Prep1(54-72) restores insulin signalling impaired by ceramide treatment. Prep1 overexpressing L6 cells display similar metabolic alterations observed in ceramide-treated L6 cells and the presence of Prep1(54-72) mitigates these events. All these findings suggest that disruption of the Prep1/p160 molecular interaction enhances insulin sensitivity impaired by ceramides in skeletal muscle cells and indicate this complex as an important target for type 2 diabetes.

Substrate-zymography: a still worthwhile method for gelatinases analysis in biological samples

Matrix metallo-proteinases (MMPs) are a family of zinc-dependent endopeptidases, capable of degrading all the molecular components of extracellular matrix. A class of MMPs is gelatinases which includes gelatinase A or MMP-2 (72 kDa) and gelatinase B or MMP-9 (92 kDa), which have been shown to play critical roles in pathophysiology of many human disease and, in particular, cancer progression. For these reasons they obtained a great interest as potential non-invasive biomarker in providing useful clinical information in cancer diagnosis and therapy. A sensitive and unexpensive method for analysis of gelatinases is the gelatine zymography, which allows to measure the relative amounts of active and inactive enzymes in body fluids and tissue extracts. The procedure involves the electrophoretic separation of proteins under denaturing but non reducing conditions through a polyacrylamide gel containing a synthetic substrate (gelatin). The aim of this mini-review has been to describe the general principles of gelatine zymography technique, underling the main advantages and disadvantages. Even though an improvement of this method is necessary for a better applicability in laboratory medicine, gelatine zymography represents the most convenient method to detect the activity of the different gelatinases from a wide range of biological samples.

Platelet-Rich Plasma Increases Growth and Motility of Adipose Tissue-Derived Mesenchymal Stem Cells and Controls Adipocyte Secretory Function

Adipose tissue‐derived mesenchymal stem cells (Ad‐MSC) and platelet derivatives have been used alone or in combination to achieve regeneration of injured tissues. We have tested the effect of platelet‐rich plasma (PRP) on Ad‐MSC and adipocyte function. PRP increased Ad‐MSC viability, proliferation rate and G1‐S cell cycle progression, by at least 7‐, 2‐, and 2.2‐fold, respectively, and reduced caspase 3 cleavage. Higher PRP concentrations or PRPs derived from individuals with higher platelet counts were more effective in increasing Ad‐MSC growth. PRP also accelerated cell migration by at least 1.5‐fold. However, PRP did not significantly affect mature adipocyte viability, differentiation and expression levels of PPAR‐γ and AP‐2 mRNAs, while it increased leptin production by 3.5‐fold. Interestingly, PRP treatment of mature adipocytes also enhanced the release of Interleukin (IL)‐6, IL‐8, IL‐10, Interferon‐γ, and Vascular Endothelial Growth Factor. Thus, data are consistent with a stimulatory effect of platelet derivatives on Ad‐MSC growth and motility. Moreover, PRP did not reduce mature adipocyte survival and increased the release of pro‐angiogenic factors, which may facilitate tissue regeneration processes. © 2015 The Authors. Journal of Cellular Biochemistry Published by Wiley Periodicals, Inc. J. Cell. Biochem. 116: 2408–2418, 2015. © 2015 The Authors. Journal of Cellular Biochemistry Published by Wiley Periodicals, Inc.

Low-Dose Bisphenol-A Impairs Adipogenesis and Generates Dysfunctional 3T3-L1 Adipocytes

Environmental endocrine disruptors (EDCs), including bisphenol-A (BPA), have been recently involved in obesity and diabetes by dysregulating adipose tissue function. Our aim was to examine whether prolonged exposure to low doses of BPA could affect adipogenesis and adipocyte metabolic functions. Therefore, 3T3-L1 pre-adipocytes were cultured for three weeks with BPA 1 nM to mimic human environmental exposure. We evaluated BPA effect on cell proliferation, differentiation, gene expression and adipocyte metabolic function. BPA significantly increased pre-adipocyte proliferation (p<0.01). In 3T3-L1 adipocytes differentiated in the presence of BPA, the expression of Peroxisome proliferator-activated receptor gamma (PPARγ), Fatty Acid Binding Protein 4/Adipocyte Protein 2 (FABP4/AP2) and CCAAT/enhancer binding protein (C/EBPα) was increased by 3.5, 1.5 and 3 folds, respectively. Mature adipocytes also showed a significant increase in lipid accumulation (p<0.05) and alterations of insulin action, with significant reduction in insulin-stimulated glucose utilization (p<0.001). Moreover, in mature adipocytes, mRNA levels of Leptin, interleukin-6 (IL6) and interferon-γ (IFNγ) were significantly increased (p<0.05). In conclusion, BPA prolonged exposure at low doses, consistent with those found in the environment, may affect adipocyte differentiation program, enhancing pre-adipocyte proliferation and anticipating the expression of the master genes involved in lipid/glucose metabolism. The resulting adipocytes are hypertrophic, with impaired insulin signaling, reduced glucose utilization and increased pro-inflammatory cytokine expression. Thus, these data supported the hypothesis that BPA exposure, during critical stages of adipose tissue development, may cause adipocyte metabolic dysfunction and inflammation, thereby increasing the risk of developing obesity-related diseases.

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.

Bisphenol-A impairs insulin action and up-regulates inflammatory pathways in human subcutaneous adipocytes and 3T3-L1 cells

Current evidence indicates that chemical pollutants may interfere with the homeostatic control of nutrient metabolism, thereby contributing to the increased prevalence of metabolic disorders. Bisphenol-A (BPA) is a lipophilic compound contained in plastic which is considered a candidate for impairing energy and glucose metabolism. We have investigated the impact of low doses of BPA on adipocyte metabolic functions. Human adipocytes derived from subcutaneous adipose tissue and differentiated 3T3-L1 cells were incubated with BPA, in order to evaluate the effect on glucose utilization, insulin sensitivity and cytokine secretion. Treatment with 1nM BPA significantly inhibited insulin-stimulated glucose utilization, without grossly interfering with adipocyte differentiation. Accordingly, mRNA levels of the adipogenic markers PPARγ and GLUT4 were unchanged upon BPA exposure. BPA treatment also impaired insulin-activated receptor phosphorylation and signaling. Moreover, adipocyte incubation with BPA was accompanied by increased release of IL-6 and IFN-γ, as assessed by multiplex ELISA assays, and by activation of JNK, STAT3 and NFkB pathways. Treatment of the cells with the JNK inhibitor SP600125 almost fully reverted BPA effect on insulin signaling and glucose utilization. In conclusion, low doses of BPA interfere with inflammatory/insulin signaling pathways, leading to impairment of adipose cell function.

PREP1 deficiency downregulates hepatic lipogenesis and attenuates steatohepatitis in mice

AIMS/HYPOTHESIS

The aim of this study was to investigate the function of Prep1 (also known as Pknox1) in hepatic lipogenesis.

METHODS

The hepatic lipogenesis pathway was evaluated by real-time RT-PCR and Western blot. Biochemical variables were assessed using a clinical chemistry analyser.

RESULTS

Serum triacylglycerols and liver expression of fatty acid synthase (FAS) were significantly decreased in Prep1 hypomorphic heterozygous (Prep1 (i/+) ) mice compared with their non-hypomorphic littermates. Upstream FAS expression, phosphorylation of protein kinase C (PKC)ζ, liver kinase B1 (LKB1), AMP-activated protein kinase (AMPK) and acetyl-CoA carboxylase (ACC) increased in Prep1 (i/+) mice, while protein and mRNA levels of the lipid phosphatase inhibitor of PKCζ, SH2-containing inositol 5'-phosphatase 2 (SHIP2), was more than 60% reduced. Consistent with these findings, HepG2 cells transfected with Prep1 cDNA exhibited increased triacylglycerol accumulation and FAS expression, with strongly reduced PKCζ, LKB1, AMPK and ACC phosphorylation. Further experiments revealed the presence of both Prep1 and its major partner Pbx1 at the Ship2 (also known as Inppl1) promoter. PBX-regulating protein 1 (PREP1) and pre-B cell leukaemia transcription factor 1 (PBX1) enhanced Ship2 transcription. The PREP1HR mutant, which is unable to bind PBX1, exhibited no effect on Ship2 function, indicating transcriptional activation of Ship2 by the PREP1/PBX1 complex. Treatment with a methionine- and choline-deficient diet (MCDD) induced steatosis in both Prep1 (i/+) and non-hypomorphic control mice. However, alanine aminotransferase increase, intracellular triacylglycerol content and histological evidence of liver steatosis, inflammation and necrosis were significantly less evident in Prep1 (i/+) mice, indicating that Prep1 silencing protects mice from MCDD-induced steatohepatitis.

CONCLUSIONS/INTERPRETATION

Our results indicate that Prep1 silencing reduces lipotoxicity by increasing PKCζ/LKB1/AMPK/ACC signalling, while levels of PREP1 expression may determine the risk of steatohepatitis and its progression.

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

The gene network responsible for inflammation-induced insulin resistance remains enigmatic. In this study, we show that, in L6 cells, rosiglitazone- as well as pioglitazone-dependent activation of peroxisome proliferator-activated receptor-γ (PPARγ) represses transcription of the ped/pea-15 gene, whose increased activity impairs glucose tolerance in mice and humans. Rosiglitazone enhanced insulin-induced glucose uptake in L6 cells expressing the endogenous ped/pea-15 gene but not in cells expressing ped/pea-15 under the control of an exogenous promoter. The ability of PPARγ to affect ped/pea-15 expression was also lost in cells and in C57BL/6J transgenic mice expressing ped/pea-15 under the control of an exogenous promoter, suggesting that ped/pea-15 repression may contribute to rosiglitazone action on glucose disposal. Indeed, high fat diet mice showed insulin resistance and increased ped/pea-15 levels, although these effects were reduced by rosiglitazone treatment. Both supershift and ChIP assays revealed the presence of the AP-1 component c-JUN at the PED/PEA-15 promoter upon 12-O-tetradecanoylphorbol-13-acetate stimulation of the cells. In these experiments, rosiglitazone treatment reduced c-JUN presence at the PED/PEA-15 promoter. This effect was not associated with a decrease in c-JUN expression. In addition, c-jun silencing in L6 cells lowered ped/pea-15 expression and caused nonresponsiveness to rosiglitazone, although c-jun overexpression enhanced the binding to the ped/pea-15 promoter and blocked the rosiglitazone effect. These results indicate that PPARγ regulates ped/pea-15 transcription by inhibiting c-JUN binding at the ped/pea-15 promoter. Thus, ped/pea-15 is downstream of a major PPARγ-regulated inflammatory network. Repression of ped/pea-15 transcription might contribute to the PPARγ regulation of muscle sensitivity to insulin.

PED/PEA-15 controls fibroblast motility and wound closure by ERK1/2-dependent mechanisms

Cell migration is dependent on the control of signaling events that play significant roles in creating contractile force and in contributing to wound closure. We evaluated wound closure in fibroblasts from mice overexpressing (TgPED) or lacking ped/pea-15 (KO), a gene overexpressed in patients with type 2 diabetes. Cultured skin fibroblasts isolated from TgPED mice showed a significant reduction in the ability to recolonize wounded area during scratch assay, compared to control fibroblasts. This difference was observed both in the absence and in the presence of mytomicin C, an inhibitor of mitosis. In time-lapse experiments, TgPED fibroblasts displayed about twofold lower velocity and diffusion coefficient, as compared to controls. These changes were accompanied by reduced spreading and decreased formation of stress fibers and focal adhesion plaques. At the molecular level, TgPED fibroblasts displayed decreased RhoA activation and increased abundance of phosphorylated extracellular signal-regulated kinase 1/2 (ERK1/2). Inhibition of ERK1/2 activity by PD98059 restored RhoA activation, cytoskeleton organization and cell motility, and almost completely rescued wound closure of TgPED fibroblasts. Interestingly, skin fibroblasts isolated from KO mice displayed an increased wound closure ability. In vivo, healing of dorsal wounds was delayed in TgPED and accelerated in KO mice. Thus, PED/PEA-15 may affect fibroblast motility by a mechanism, at least in part, mediated by ERK1/2. J. Cell. Physiol. 227: 2106–2116, 2012. © 2011 Wiley Periodicals, Inc.

PED/PEA-15 induces autophagy and mediates TGF-beta1 effect on muscle cell differentiation

TGF-beta1 has been shown to induce autophagy in certain cells but whether and how this action is exerted in muscle and whether this activity relates to TGF-beta1 control of muscle cell differentiation remains unknown. Here, we show that expression of the autophagy-promoting protein phosphoprotein enriched in diabetes/phosphoprotein enriched in astrocytes (PED/PEA-15) progressively declines during L6 and C2C12 skeletal muscle cell differentiation. PED/PEA-15 underwent rapid induction upon TGF-beta1 exposure of L6 and C2C12 myoblasts, accompanied by impaired differentiation into mature myotubes. TGF-beta1 also induced autophagy in the L6 and C2C12 cells through a PP2A/FoxO1-mediated mechanism. Both the TGF-beta1 effect on differentiation and that on autophagy were blocked by specific PED/PEA-15 ShRNAs. Myoblasts stably overexpressing PED/PEA-15 did not differentiate and showed markedly enhanced autophagy. In these same cells, the autophagy inhibitor 3-methyladenine rescued TGF-beta1 effect on both autophagy and myogenesis, indicating that PED/PEA-15 mediates TGF-beta1 effects in muscle. Muscles from transgenic mice overexpressing PED/PEA-15 featured a significant number of atrophic fibers, accompanied by increased light chain 3 (LC3)II to LC3I ratio and reduced PP2A/FoxO1 phosphorylation. Interestingly, these mice showed significantly impaired locomotor activity compared with their non-transgenic littermates. TGF-beta1 causes transcriptional upregulation of the autophagy-promoting gene PED/PEA-15, which in turn is capable to induce atrophic responses in skeletal muscle in vivo.

Prep1 controls insulin glucoregulatory function in liver by transcriptional targeting of SHP1 tyrosine phosphatase

OBJECTIVE

We investigated the function of the Prep1 gene in insulin-dependent glucose homeostasis in liver.

RESEARCH DESIGN AND METHODS

Prep1 action on insulin glucoregulatory function has been analyzed in liver of Prep1-hypomorphic mice (Prep1(i/i)), which express 2-3% of Prep1 mRNA.

RESULTS

Based on euglycemic hyperinsulinemic clamp studies and measurement of glycogen content, livers from Prep1(i/i) mice feature increased sensitivity to insulin. Tyrosine phosphorylation of both insulin receptor (IR) and insulin receptor substrate (IRS)1/2 was significantly enhanced in Prep1(i/i) livers accompanied by a specific downregulation of the SYP and SHP1 tyrosine phosphatases. Prep1 overexpression in HepG2 liver cells upregulated SYP and SHP1 and inhibited insulin-induced IR and IRS1/2 phosphorylation and was accompanied by reduced glycogen content. Consistently, overexpression of the Prep1 partner Pbx1, but not of p160MBP, mimicked Prep1 effects on tyrosine phosphorylations, glycogen content, and on SYP and SHP1 expression. In Prep1 overexpressing cells, antisense silencing of SHP1, but not that of SYP, rescued insulin-dependent IR phosphorylation and glycogen accumulation. Both Prep1 and Pbx1 bind SHP1 promoter at a site located between nucleotides -2,113 and -1,778. This fragment features enhancer activity and induces luciferase function by 7-, 6-, and 30-fold, respectively, in response to Prep1, Pbx1, or both.

CONCLUSIONS

SHP1, a known silencer of insulin signal, is a transcriptional target of Prep1. In liver, transcriptional activation of SHP1 gene by Prep1 attenuates insulin signal transduction and reduces glucose storage.

Overproduction of phosphoprotein enriched in diabetes (PED) induces mesangial expansion and upregulates protein kinase C-beta activity and TGF-beta1 expression

AIMS/HYPOTHESIS

Overproduction of phosphoprotein enriched in diabetes (PED, also known as phosphoprotein enriched in astrocytes-15 [PEA-15]) is a common feature of type 2 diabetes and impairs insulin action in cultured cells and in mice. Nevertheless, the potential role of PED in diabetic complications is still unknown.

METHODS

We studied the effect of PED overproduction and depletion on kidney function in animal and cellular models.

RESULTS

Transgenic mice overexpressing PED (PEDTg) featured age-dependent increases of plasma creatinine levels and urinary volume, accompanied by expansion of the mesangial area, compared with wild-type littermates. Serum and kidney levels of TGF-beta1 were also higher in 6- and 9-month-old PEDTg. Overexpression of PED in human kidney 2 cells significantly increased TGF-beta1 levels, SMAD family members (SMAD)2/3 phosphorylation and fibronectin production. Opposite results were obtained following genetic silencing of PED in human kidney 2 cells by antisense oligonucleotides. Inhibition of phospholipase D and protein kinase C-beta by 2-butanol and LY373196 respectively reduced TGF-beta1, SMAD2/3 phosphorylation and fibronectin production. Moreover, inhibition of TGF-beta1 receptor activity and SMAD2/3 production by SB431542 and antisense oligonucleotides respectively reduced fibronectin secretion by about 50%. TGF-beta1 circulating levels were significantly reduced in Ped knockout mice and positively correlated with PED content in peripheral blood leucocytes of type 2 diabetic patients.

CONCLUSIONS/INTERPRETATION

These data indicate that PED regulates fibronectin production via phospholipase D/protein kinase C-beta and TGF-beta1/SMAD pathways in kidney cells. Raised PED levels may therefore contribute to the abnormal accumulation of extracellular matrix and renal dysfunction in diabetes.

In skeletal muscle advanced glycation end products (AGEs) inhibit insulin action and induce the formation of multimolecular complexes including the receptor for AGEs

Chronic hyperglycemia promotes insulin resistance at least in part by increasing the formation of advanced glycation end products (AGEs). We have previously shown that in L6 myotubes human glycated albumin (HGA) induces insulin resistance by activating protein kinase Calpha (PKCalpha). Here we show that HGA-induced PKCalpha activation is mediated by Src. Coprecipitation experiments showed that Src interacts with both the receptor for AGE (RAGE) and PKCalpha in HGA-treated L6 cells. A direct interaction of PKCalpha with Src and insulin receptor substrate-1 (IRS-1) has also been detected. In addition, silencing of IRS-1 expression abolished HGA-induced RAGE-PKCalpha co-precipitation. AGEs were able to induce insulin resistance also in vivo, as insulin tolerance tests revealed a significant impairment of insulin sensitivity in C57/BL6 mice fed a high AGEs diet (HAD). In tibialis muscle of HAD-fed mice, insulin-induced glucose uptake and protein kinase B phosphorylation were reduced. This was paralleled by a 2.5-fold increase in PKCalpha activity. Similarly to in vitro observations, Src phosphorylation was increased in tibialis muscle of HAD-fed mice, and co-precipitation experiments showed that Src interacts with both RAGE and PKCalpha. These results indicate that AGEs impairment of insulin action in the muscle might be mediated by the formation of a multimolecular complex including RAGE/IRS-1/Src and PKCalpha.

Glucose regulates diacylglycerol intracellular levels and protein kinase C activity by modulating diacylglycerol kinase subcellular localization

Although chronic hyperglycemia reduces insulin sensitivity and leads to impaired glucose utilization, short term exposure to high glucose causes cellular responses positively regulating its own metabolism. We show that exposure of L6 myotubes overexpressing human insulin receptors to 25 mm glucose for 5 min decreased the intracellular levels of diacylglycerol (DAG). This was paralleled by transient activation of diacylglycerol kinase (DGK) and of insulin receptor signaling. Following 30-min exposure, however, both DAG levels and DGK activity returned close to basal levels. Moreover, the acute effect of glucose on DAG removal was inhibited by >85% by the DGK inhibitor R59949. DGK inhibition was also accompanied by increased protein kinase C-alpha (PKCalpha) activity, reduced glucose-induced insulin receptor activation, and GLUT4 translocation. Glucose exposure transiently redistributed DGK isoforms alpha and delta, from the prevalent cytosolic localization to the plasma membrane fraction. However, antisense silencing of DGKdelta, but not of DGKalpha expression, was sufficient to prevent the effect of high glucose on PKCalpha activity, insulin receptor signaling, and glucose uptake. Thus, the short term exposure of skeletal muscle cells to glucose causes a rapid induction of DGK, followed by a reduction of PKCalpha activity and transactivation of the insulin receptor signaling. The latter may mediate, at least in part, glucose induction of its own metabolism.

PED/PEA-15 regulates glucose-induced insulin secretion by restraining potassium channel expression in pancreatic beta-cells

The phosphoprotein enriched in diabetes/phosphoprotein enriched in astrocytes (ped/pea-15) gene is overexpressed in human diabetes and causes this abnormality in mice. Transgenic mice with beta-cell-specific overexpression of ped/pea-15 (beta-tg) exhibited decreased glucose tolerance but were not insulin resistant. However, they showed impaired insulin response to hyperglycemia. Islets from the beta-tg also exhibited little response to glucose. mRNAs encoding the Sur1 and Kir6.2 potassium channel subunits and their upstream regulator Foxa2 were specifically reduced in these islets. Overexpression of PED/PEA-15 inhibited the induction of the atypical protein kinase C (PKC)-zeta by glucose in mouse islets and in beta-cells of the MIN-6 and INS-1 lines. Rescue of PKC-zeta activity elicited recovery of the expression of the Sur1, Kir6.2, and Foxa2 genes and of glucose-induced insulin secretion in PED/PEA-15-overexpressing beta-cells. Islets from ped/pea-15-null mice exhibited a twofold increased activation of PKC-zeta by glucose; increased abundance of the Sur1, Kir6.2, and Foxa2 mRNAs; and enhanced glucose effect on insulin secretion. In conclusion, PED/PEA-15 is an endogenous regulator of glucose-induced insulin secretion, which restrains potassium channel expression in pancreatic beta-cells. Overexpression of PED/PEA-15 dysregulates beta-cell function and is sufficient to impair glucose tolerance in mice.

Phorbol esters induce intracellular accumulation of the anti-apoptotic protein PED/PEA-15 by preventing ubiquitinylation and proteasomal degradation

Phosphoprotein enriched in diabetes/phosphoprotein enriched in astrocytes (PED/PEA)-15 is an anti-apoptotic protein whose expression is increased in several cancer cells and following experimental skin carcinogenesis. Exposure of untransfected C5N keratinocytes and transfected HEK293 cells to phorbol esters (12-O-tetradecanoylphorbol-13-acetate (TPA)) increased PED/PEA-15 cellular content and enhanced its phosphorylation at serine 116 in a time-dependent fashion. Ser-116 --> Gly (PED(S116G)) but not Ser-104 --> Gly (PED(S104G)) substitution almost completely abolished TPA regulation of PED/PEA-15 expression. TPA effect was also prevented by antisense inhibition of protein kinase C (PKC)-zeta and by the expression of a dominant-negative PKC-zeta mutant cDNA in HEK293 cells. Similar to long term TPA treatment, overexpression of wild-type PKC-zeta increased cellular content and phosphorylation of WT-PED/PEA-15 and PED(S104G) but not of PED(S116G). These events were accompanied by the activation of Ca2+-calmodulin kinase (CaMK) II and prevented by the CaMK blocker, KN-93. At variance, the proteasome inhibitor lactacystin mimicked TPA action on PED/PEA-15 intracellular accumulation and reverted the effects of PKC-zeta and CaMK inhibition. Moreover, we show that PED/PEA-15 bound ubiquitin in intact cells. PED/PEA-15 ubiquitinylation was reduced by TPA and PKC-zeta overexpression and increased by KN-93 and PKC-zeta block. Furthermore, in HEK293 cells expressing PED(S116G), TPA failed to prevent ubiquitin-dependent degradation of the protein. Accordingly, in the same cells, TPA-mediated protection from apoptosis was blunted. Taken together, our results indicate that TPA increases PED/PEA-15 expression at the post-translational level by inducing phosphorylation at serine 116 and preventing ubiquitinylation and proteosomal degradation.

The PEA15 gene is overexpressed and related to insulin resistance in healthy first-degree relatives of patients with type 2 diabetes

AIMS/HYPOTHESIS

Overexpression of the gene encoding phosphoprotein enriched in astrocytes 15 (PEA15), also known as phosphoprotein enriched in diabetes (PED), causes insulin resistance and diabetes in transgenic mice and has been observed in type 2 diabetic individuals. The aim of this study was to investigate whether PEA15 overexpression occurs in individuals at high risk of diabetes and whether it is associated with specific type 2 diabetes subphenotypes.

SUBJECTS AND METHODS

We analysed PEA15 expression in euglycaemic first-degree relatives (FDR) of type 2 diabetic subjects.

RESULTS

The expression of PEA15 in peripheral blood leucocytes (PBLs) paralleled that in fat and skeletal muscle tissues. In PBLs from the FDR, PEA15 expression was two-fold higher than in euglycaemic individuals with no family history of diabetes (control subjects), both at the protein and the mRNA level (p < 0.001). The expression of PEA15 was comparable in FDR and type 2 diabetic subjects and in each group close to one-third of the subjects expressed PEA15 levels more than 2 SD higher than the mean of control subjects. Subjects with IFG with at least one type 2 diabetes-affected FDR also overexpressed PEA15 (p < 0.05). In all the groups analysed, PEA15 expression was independent of sex and unrelated to age, BMI, waist circumference, systolic and diastolic BP, and fasting cholesterol, triacylglycerol and glucose levels. However, in euglycaemic FDR of type 2 diabetic subjects, PEA15 expression was inversely correlated with insulin sensitivity (r = -557, p = 0.01).

CONCLUSIONS/INTERPRETATION

We conclude that PEA15 overexpression represents a common defect in FDR of patients with type 2 diabetes and is correlated with reduced insulin sensitivity in these individuals.

Thrombin‐activated platelets induce proliferation of human skin fibroblasts by stimulating autocrine production of insulin‐like growth factor‐1

Platelet components have found successful clinical utilization to initiate or to accelerate tissue-repair mechanisms. However, the molecular pathways by which platelet factors contribute to tissue regeneration have not been fully elucidated. We have studied the effect of thrombin-activated platelets (TAPs) on cell growth in vivo and in cultured cell systems. Application of TAPs to ulcerative skin lesions of diabetic patients induced local activation of ERK1/2 and Akt/PKB. Moreover, when applied to cultured human skin fibroblasts, TAPs promoted cell growth and DNA synthesis and activated platelet-derived growth factor (PDGF) and insulin-like growth factor (IGF)-1 receptor tyrosine kinases. PDGF was released by TAPs and rapidly achieved a plateau. At variance, the release of IGF-1 was mainly provided by the TAPs-stimulated fibroblasts and progressively increased up to 48 h. The PDGF-R blocker Ag1296 reduced the activation of Akt/PKB and, at a lesser extent, of ERK1/2. Conversely, inhibition of IGF-1 signaling by Ag1024 and expression of a dominant-negative IGF-1R mutant selectively reduced the stimulation of ERK1/2 by TAPs and fibroblast-released factors, with minor changes of Akt/PKB activity. Thus, platelet factors promote fibroblast growth by acutely activating Akt/PKB and ERK1/2. Sustained activation of ERK1/2, however, requires autocrine production of IGF-1 by TAPs-stimulated fibroblasts.

Tyrosine phosphorylation of phosphoinositide-dependent kinase 1 by the insulin receptor is necessary for insulin metabolic signaling

In L6 myoblasts, insulin receptors with deletion of the C-terminal 43 amino acids (IR(Delta43)) exhibited normal autophosphorylation and IRS-1/2 tyrosine phosphorylation. The L6 cells expressing IR(Delta43) (L6(IRDelta43)) also showed no insulin effect on glucose uptake and glycogen synthase, accompanied by a >80% decrease in insulin induction of 3-phosphoinositide-dependent protein kinase 1 (PDK-1) activity and tyrosine phosphorylation and of protein kinase B (PKB) phosphorylation at Thr(308). Insulin induced the phosphatidylinositol 3 kinase-dependent coprecipitation of PDK-1 with wild-type IR (IR(WT)), but not IR(Delta43). Based on overlay blotting, PDK-1 directly bound IR(WT), but not IR(Delta43). Insulin-activated IR(WT), and not IR(Delta43), phosphorylated PDK-1 at tyrosines 9, 373, and 376. The IR C-terminal 43-amino-acid peptide (C-terminal peptide) inhibited in vitro PDK-1 tyrosine phosphorylation by the IR. Tyr-->Phe substitution prevented this inhibitory action. In the L6(hIR) cells, the C-terminal peptide coprecipitated with PDK-1 in an insulin-stimulated fashion. This peptide simultaneously impaired the insulin effect on PDK-1 coprecipitation with IR(WT), on PDK-1 tyrosine phosphorylation, on PKB phosphorylation at Thr(308), and on glucose uptake. Upon insulin exposure, PDK-1 membrane persistence was significantly reduced in L6(IRDelta43) compared to control cells. In L6 cells expressing IR(WT), the C-terminal peptide also impaired insulin-dependent PDK-1 membrane persistence. Thus, PDK-1 directly binds to the insulin receptor, followed by PDK-1 activation and insulin metabolic effects.

Protein kinase C-alpha regulates insulin action and degradation by interacting with insulin receptor substrate-1 and 14-3-3 epsilon

Protein kinase C (PKC)-alpha exerts a regulatory function on insulin action. We showed by overlay blot that PKCalpha directly binds a 180-kDa protein, corresponding to IRS-1, and a 30-kDa molecular species, identified as 14-3-3epsilon. In intact NIH-3T3 cells overexpressing insulin receptors (3T3-hIR), insulin selectively increased PKCalpha co-precipitation with IRS-1, but not with IRS-2, and with 14-3-3epsilon, but not with other 14-3-3 isoforms. Overexpression of 14-3-3epsilon in 3T3-hIR cells significantly reduced IRS-1-bound PKCalpha activity, without altering IRS-1/PKCalpha co-precipitation. 14-3-3epsilon overexpression also increased insulin-stimulated insulin receptor and IRS-1 tyrosine phosphorylation, followed by increased activation of Raf1, ERK1/2, and Akt/protein kinase B. Insulin-induced glycogen synthase activity and thymidine incorporation were also augmented. Consistently, selective depletion of 14-3-3epsilon by antisense oligonucleotides caused a 3-fold increase of IRS-1-bound PKCalpha activity and a similarly sized reduction of insulin receptor and IRS-1 tyrosine phosphorylation and signaling. In turn, selective inhibition of PKCalpha expression by antisense oligonucleotides reverted the negative effect of 14-3-3epsilon depletion on insulin signaling. Moreover, PKCalpha inhibition was accompanied by a >2-fold decrease of insulin degradation. Similar results were also obtained by overexpressing 14-3-3epsilon. Thus, in NIH-3T3 cells, insulin induces the formation of multimolecular complexes, including IRS-1, PKCalpha, and 14-3-3epsilon. The presence of 14-3-3epsilon in the complex is not necessary for IRS-1/PKCalpha interaction but modulates PKCalpha activity, thereby regulating insulin signaling and degradation.

Raised expression of the antiapoptotic protein ped/pea-15 increases susceptibility to chemically induced skin tumor development

ped/pea-15 is a cytosolic protein performing a broad antiapoptotic function. We show that, upon DMBA/TPA-induced skin carcinogenesis, transgenic mice overexpressing ped/pea-15 (Tg(ped/pea-15)) display early development of papillomas and a four-fold increase in papilloma number compared to the nontransgenic littermates (P<0.001). The malignant conversion frequency was 24% for the Tg(ped/pea-15) mice and only 5% in controls (P<0.01). The isolated application of TPA, but not that of DMBA, was sufficient to reversibly upregulate ped/pea-15 in both untransformed skin and cultured keratinocytes. ped/pea-15 protein levels were also increased in DMBA/TPA-induced papillomas of both Tg(ped/pea-15) and control mice. Isolated TPA applications induced Caspase-3 activation and apoptosis in nontransformed mouse epidermal tissues. The induction of both Caspase-3 and apoptosis by TPA were four-fold inhibited in the skin of the Tg(ped/pea-15) compared to the nontransgenic mice, accompanied by a similarly sized reduction in TPA-induced JNK and p38 stimulation and by constitutive induction of cytoplasmic ERK activity in the transgenics. ped/pea-15 expression was stably increased in cell lines from DMBA/TPA-induced skin papillomas and carcinomas, paralleled by protection from TPA apoptosis. In the A5 spindle carcinoma cell line, antisense inhibition of ped/pea-15 expression simultaneously rescued sensitivity to TPA-induced Caspase-3 function and apoptosis. The antisense also reduced A5 cell ability to grow in semisolid media by 65% (P<0.001) and increased by three-fold tumor latency time (P<0.01). Thus, the expression levels of ped/pea-15 control Caspase-3 function and epidermal cell apoptosis in vivo and determine susceptibility to skin tumor development.

Omi/HtrA2 Promotes Cell Death by Binding and Degrading the Anti-apoptotic Protein ped/pea-15

ped/pea-15 is a ubiquitously expressed 15-kDa protein featuring a broad anti-apoptotic function. In a yeast two-hybrid screen, the pro-apoptotic Omi/HtrA2 mitochondrial serine protease was identified as a specific interactor of the ped/pea-15 death effector domain. Omi/HtrA2 also bound recombinant ped/pea-15 in vitro and co-precipitated with ped/pea-15 in 293 and HeLa cell extracts. In these cells, the binding of Omi/HtrA2 to ped/pea-15 was induced by UVC exposure and followed the mitochondrial release of Omi/HtrA2 into the cytoplasm. Upon UVC exposure, cellular ped/pea-15 protein expression levels decreased. This effect was prevented by the ucf-101 specific inhibitor of the Omi/HtrA2 proteolytic activity, in a dose-dependent fashion. In vitro incubation of ped/pea-15 with Omi/HtrA2 resulted in ped/pea-15 degradation. In intact cells, the inhibitory action of ped/pea-15 on UVC-induced apoptosis progressively declined at increasing Omi/HtrA2 expression. This further effect of Omi/HtrA2 was also inhibited by ucf-101. In addition, ped/pea-15 expression blocked Omi/HtrA2 co-precipitation with the caspase inhibitor protein XIAP and caspase 3 activation. Thus, in part, apoptosis following Omi/HtrA2 mitochondrial release is mediated by reduction in ped/pea-15 cellular levels. The ability of Omi/HtrA2 to relieve XIAP inhibition on caspases is modulated by the relative levels of Omi/HtrA2 and ped/pea-15.

Overexpression of the ped/pea-15 gene causes diabetes by impairing glucose-stimulated insulin secretion in addition to insulin action

Overexpression of the ped/pea-15 gene is a common feature of type 2 diabetes. In the present work, we show that transgenic mice ubiquitously overexpressing ped/pea-15 exhibited mildly elevated random-fed blood glucose levels and decreased glucose tolerance. Treatment with a 60% fat diet led ped/pea-15 transgenic mice to develop diabetes. Consistent with insulin resistance in these mice, insulin administration reduced glucose levels by only 35% after 45 min, compared to 70% in control mice. In vivo, insulin-stimulated glucose uptake was decreased by almost 50% in fat and muscle tissues of the ped/pea-15 transgenic mice, accompanied by protein kinase Calpha activation and block of insulin induction of protein kinase Czeta. These changes persisted in isolated adipocytes from the transgenic mice and were rescued by the protein kinase C inhibitor bisindolylmaleimide. In addition to insulin resistance, ped/pea-15 transgenic mice showed a 70% reduction in insulin response to glucose loading. Stable overexpression of ped/pea-15 in the glucose-responsive MIN6 beta-cell line also caused protein kinase Calpha activation and a marked decline in glucose-stimulated insulin secretion. Antisense block of endogenous ped/pea-15 increased glucose sensitivity by 2.5-fold in these cells. Thus, in vivo, overexpression of ped/pea-15 may lead to diabetes by impairing insulin secretion in addition to insulin action.

Protein Kinase C-ζ and Protein Kinase B Regulate Distinct Steps of Insulin Endocytosis and Intracellular Sorting

We have investigated the molecular mechanisms regulating insulin internalization and intracellular sorting. Insulin internalization was decreased by 50% upon incubation of the cells with the phosphatidylinositol 3-kinase (PI3K) inhibitors wortmannin and LY294002. PI3K inhibition also reduced insulin degradation and intact insulin release by 50 and 75%, respectively. Insulin internalization was reduced by antisense inhibition of protein kinase C-zeta (PKCzeta) expression and by overexpression of a dominant negative PKCzeta mutant (DN-PKCzeta). Conversely, overexpression of PKCzeta increased insulin internalization as a function of the PKCzeta levels achieved in the cells. Expression of wild-type protein kinase B (PKB)-alpha or of a constitutively active form (myr-PKB) did not significantly alter insulin internalization and degradation but produced a 100% increase of intact insulin release. Inhibition of PKB by a dominant negative mutant (DN-PKB) or by the pharmacological inhibitor ML-9 reduced intact insulin release by 75% with no effect on internalization and degradation. In addition, overexpression of Rab5 completely rescued the effect of PKCzeta inhibition on insulin internalization but not that of PKB inhibition on intact insulin recycling. Indeed, PKCzeta bound to and activated Rab5. Thus, PI3K controls different steps within the insulin endocytic itinerary. PKCzeta appears to mediate the PI3K effect on insulin internalization in a Rab5-dependent manner, whereas PKB directs intracellular sorting toward intact insulin release.

Human glycated albumin affects glucose metabolism in L6 skeletal muscle cells by impairing insulin-induced insulin receptor substrate (IRS) signaling through a protein kinase C alpha-mediated mechanism

Nonenzymatic glycation is increased in diabetes and leads to increased levels of glycated proteins. Most studies have focused on the role of glycation products in vascular complications. Here, we have investigated the action of human glycated albumin (HGA) on insulin signaling in L6 skeletal muscle cells. Exposure of these cells to HGA inhibited insulin-stimulated glucose uptake and glycogen synthase activity by 95 and 80%, respectively. These effects were time- and dose-dependent, reaching a maximum after 12 h incubation with 0.1 mg/ml HGA. In contrast, exposure of the cells to HGA had no effect on thymidine incorporation. Further, HGA reduced insulin-stimulated serine phosphorylation of PKB and GSK3, but did not alter ERK1/2 activation. HGA did not affect either insulin receptor kinase activity or insulin-induced Shc phosphorylation on tyrosine. In contrast, insulin-dependent IRS-1 and IRS-2 tyrosine phosphorylation was severely reduced in cells preincubated with HGA for 24 h. Insulin-stimulated association of PI3K with IRS-1 and IRS-2, and PI3K activity were reduced by HGA in parallel with the changes in IRS tyrosine phosphorylation, while Grb2-IRS association was unchanged. In L6 myotubes, exposure to HGA increased PKC activity by 2-fold resulting in a similar increase in Ser/Thr phosphorylation of IRS-1 and IRS-2. These phosphorylations were blocked by the PKC inhibitor bisindolylmaleimide (BDM). BDM also blocked the action of HGA on insulin-stimulated PKB and GSK3 alpha. Simultaneously, BDM rescued insulin-stimulation of glucose uptake and glycogen synthase activity in cells exposed to HGA. The use of antibodies specific to PKC isoforms shows that this effect appears to be mediated by activated PKC alpha, independent of reactive oxygen species production. In summary, in L6 skeletal muscle cells, exposure to HGA leads to insulin resistance selectively in glucose metabolism with no effect on growth-related pathways regulated by the hormone.

Protein kinase B/Akt binds and phosphorylates PED/PEA-15, stabilizing its antiapoptotic action

The antiapoptotic protein PED/PEA-15 features an Akt phosphorylation motif upstream from Ser(116). In vitro, recombinant PED/PEA-15 was phosphorylated by Akt with a stoichiometry close to 1. Based on Western blotting with specific phospho-Ser(116) PED/PEA-15 antibodies, Akt phosphorylation of PED/PEA-15 occurred mainly at Ser(116). In addition, a mutant of PED/PEA-15 featuring the substitution of Ser(116)-->Gly (PED(S116-->G)) showed 10-fold-decreased phosphorylation by Akt. In intact 293 cells, Akt also induced phosphorylation of PED/PEA-15 at Ser(116). Based on pull-down and coprecipitation assays, PED/PEA-15 specifically bound Akt, independently of Akt activity. Serum activation of Akt as well as BAD phosphorylation by Akt showed no difference in 293 cells transfected with PED/PEA-15 and in untransfected cells (which express no endogenous PED/PEA-15). However, the antiapoptotic action of PED/PEA-15 was almost twofold reduced in PED(S116-->G) compared to that in PED/PEA-15(WT) cells. PED/PEA-15 stability closely paralleled Akt activation by serum in 293 cells. In these cells, the nonphosphorylatable PED(S116-->G) mutant exhibited a degradation rate threefold greater than that observed with wild-type PED/PEA-15. In the U373MG glioma cells, blocking Akt also reduced PED/PEA-15 levels and induced sensitivity to tumor necrosis factor-related apoptosis-inducing ligand apoptosis. Thus, phosphorylation by Akt regulates the antiapoptotic function of PED/PEA-15 at least in part by controlling the stability of PED/PEA-15. In part, Akt survival signaling may be mediated by PED/PEA-15.

Insulin-regulated hepatic gluconeogenesis through FOXO1-PGC-1alpha interaction

Hepatic gluconeogenesis is absolutely required for survival during prolonged fasting or starvation, but is inappropriately activated in diabetes mellitus. Glucocorticoids and glucagon have strong gluconeogenic actions on the liver. In contrast, insulin suppresses hepatic gluconeogenesis. Two components known to have important physiological roles in this process are the forkhead transcription factor FOXO1 (also known as FKHR) and peroxisome proliferative activated receptor-gamma co-activator 1 (PGC-1alpha; also known as PPARGC1), a transcriptional co-activator; whether and how these factors collaborate has not been clear. Using wild-type and mutant alleles of FOXO1, here we show that PGC-1alpha binds and co-activates FOXO1 in a manner inhibited by Akt-mediated phosphorylation. Furthermore, FOXO1 function is required for the robust activation of gluconeogenic gene expression in hepatic cells and in mouse liver by PGC-1alpha. Insulin suppresses gluconeogenesis stimulated by PGC-1alpha but co-expression of a mutant allele of FOXO1 insensitive to insulin completely reverses this suppression in hepatocytes or transgenic mice. We conclude that FOXO1 and PGC-1alpha interact in the execution of a programme of powerful, insulin-regulated gluconeogenesis.

Protein kinase Calpha activation by RET: evidence for a negative feedback mechanism controlling RET tyrosine kinase

We have studied the role of protein kinase C (PKC) in signaling of the RET tyrosine kinase receptor. By using a chimeric receptor (E/R) in which RET kinase can be tightly controlled by the addition of epidermal growth factor (EGF), we have found that RET triggering induces a strong increase of PKCalpha, PKCdelta and PKCzeta activity and that PKCalpha, not PKCdelta and PKCzeta, forms a ligand-dependent protein complex with E/R. We have identified tyrosine 1062 in the RET carboxyl-terminal tail as the docking site for PKCalpha. Block of PKC activity by bisindolylmaleimide or chronic phorbol esters treatment decreased EGF-induced serine/threonine phosphorylation of E/R, while it caused a similarly sized increase of EGF-induced E/R tyrosine kinase activity and mitogenic signaling. Conversely, acute phorbol esters treatment, which promotes PKC activity, increased the levels of E/R serine/threonine phosphorylation and significantly decreased its phosphotyrosine content. A threefold reduction of tyrosine phosphorylation levels of the constitutively active RET/MEN2A oncoprotein was observed upon coexpression with PKCalpha. We conclude that RET binds to and activates PKCalpha. PKCalpha, in turn, causes RET phosphorylation and downregulates RET tyrosine kinase and downstream signaling, thus functioning as a negative feedback loop to modulate RET activity.