A Free Fatty Acid Synthetic Agonist Accelerates Wound Healing and Improves Scar Quality in Mice

BACKGROUND

Impaired wound healing is a health problem around the world, and the search for a novel product to repair wounded skin is a major topic in the field. GW9508 is a synthetic molecule described as a selective agonist of free fatty acid receptors (FFARs) 1 and 4, and there is evidence of its anti-inflammatory effects on several organs of the body.

PURPOSE

Here, we aimed to evaluate the effects of topical GW9508 on wound healing in mice.

RESEARCH DESIGN

First, we used bioinformatic methods to determine the expression of FFAR1 and FFAR4 mRNA in the skin from a human cell atlas assembled with single-cell transcriptomes. Next, we employed 6-week-old C57BL6J mice with 2 wounds inflicted in the back. The mice were randomly divided into 2 groups, a control group, which received topical vehicle, and a treatment group, which received GW9508, for 12 days. The wound was monitored by photographic documentation every 2 days, and samples were collected at day 6 and 12 post injury for RT-PCR, western blot and histology analyses.

RESULTS

FFAR1 and FFAR4 mRNA are expressed in skin cells in similar amounts to those in other tissues. Topical GW9508 accelerated wound healing and decreased gene expression of IL-10 and metalloproteinase 9 on days 6 and 12 post injury. It increased the quantity of Collagen I and improved the organization of collagen fibres. Conclusions: Our results show that GW9508 could be an attractive drug treatment for wounded skin. Future studies need to be performed to assess the impact of GW9508 in chronic wound models.

Downregulation of the Protein C Signaling System Is Associated with COVID-19 Hypercoagulability-A Single-Cell Transcriptomics Analysis

Because of the interface between coagulation and the immune response, it is expected that COVID-19-associated coagulopathy occurs via activated protein C signaling. The objective was to explore putative changes in the expression of the protein C signaling network in the liver, peripheral blood mononuclear cells, and nasal epithelium of patients with COVID-19. Single-cell RNA-sequencing data from patients with COVID-19 and healthy subjects were obtained from the COVID-19 Cell Atlas database. A functional protein-protein interaction network was constructed for the protein C gene. Patients with COVID-19 showed downregulation of protein C and components of the downstream protein C signaling cascade. The percentage of hepatocytes expressing protein C was lower. Part of the liver cell clusters expressing protein C presented increased expression of ACE2. In PBMC, there was increased ACE2, inflammatory, and pro-coagulation transcripts. In the nasal epithelium, PROC, ACE2, and PROS1 were expressed by the ciliated cell cluster, revealing co-expression of ACE-2 with transcripts encoding proteins belonging to the coagulation and immune system interface. Finally, there was upregulation of coagulation factor 3 transcript in the liver and PBMC. Protein C could play a mechanistic role in the hypercoagulability syndrome affecting patients with severe COVID-19.

Isolating and cryopreserving pig skin cells for single-cell RNA sequencing study

The pig skin architecture and physiology are similar to those of humans. Thus, the pig model is very valuable for studying skin biology and testing therapeutics. The single-cell RNA sequencing (scRNA-seq) technology allows quantitatively analyzing cell types, compositions, states, signaling, and receptor-ligand interactome at single-cell resolution and at high throughput. scRNA-seq has been used to study mouse and human skins. However, studying pig skin with scRNA-seq is still rare. A critical step for successful scRNA-seq is to obtain high-quality single cells from the pig skin tissue. Here we report a robust method for isolating and cryopreserving pig skin single cells for scRNA-seq. We showed that pig skin could be efficiently dissociated into single cells with high cell viability using the Miltenyi Human Whole Skin Dissociation kit and the Miltenyi gentleMACS Dissociator. Furthermore, the obtained single cells could be cryopreserved using 90% FBS + 10% DMSO without causing additional cell death, cell aggregation, or changes in gene expression profiles. Using the developed protocol, we were able to identify all the major skin cell types. The protocol and results from this study are valuable for the skin research scientific community.

A Smartphone App for Individual Xylazine/Ketamine Calculation Decreased Anesthesia-Related Mortality in Mice

Currently, experimental animals are widely used in biological and medical research. However, the scientific community has raised several bioethical concerns, such as the number of animals required to achieve reproducible and statistically relevant results. These concerns involve aspects related to pain, discomfort, and unwanted animal loss. Retrospectively, we compare two different approaches for anesthesia dosage: a mobile app for dose calculation and a standard dose calculation. A total of 939 C57BL/6J and Swiss mice were analyzed. We collected data on intraoperative and anesthesia-related mortality as described in electronic or physical handwritten records. Our results showed that the mobile app approach significantly reduces anesthetic-related deaths upon using doses of ketamine and xylazine. The results suggest that anesthesia-related mortality can be minimized even more using information technology approaches, helping to solve an old but transversal challenge for researchers working with experimental mice. The mobile app is a free and open code which could be implemented worldwide as an essential requirement for all anesthetic procedures in mice using xylazine and ketamine combination. As an open code app, the Labinsane initiative could also represent the starting point to unify and validate other anesthetic procedures in different species and strains.

Asthma and COVID-19: a systematic review

Background

Severe coronavirus disease-19 (COVID-19) presents with progressive dyspnea, which results from acute lung inflammatory edema leading to hypoxia. As with other infectious diseases that affect the respiratory tract, asthma has been cited as a potential risk factor for severe COVID-19. However, conflicting results have been published over the last few months and the putative association between these two diseases is still unproven.

Methods

Here, we systematically reviewed all reports on COVID-19 published since its emergence in December 2019 to June 30, 2020, looking into the description of asthma as a premorbid condition, which could indicate its potential involvement in disease progression.

Results

We found 372 articles describing the underlying diseases of 161,271 patients diagnosed with COVID-19. Asthma was reported as a premorbid condition in only 2623 patients accounting for 1.6% of all patients.

Conclusions

As the global prevalence of asthma is 4.4%, we conclude that either asthma is not a premorbid condition that contributes to the development of COVID-19 or clinicians and researchers are not accurately describing the premorbidities in COVID-19 patients.

Enhancement of cellular activity in hyperglycemic mice dermal wounds dressed with chitosan-alginate membranes

The use of specially designed wound dressings could be an important alternative to facilitate the healing process of wounds in the hyperglycemic state. Biocompatible dressings combining chitosan and alginate can speed up wound healing by modulating the inflammatory phase, stimulating fibroblast proliferation, and aiding in remodeling phases. However, this biomaterial has not yet been explored in chronic and acute lesions of diabetic patients. The aim of this study was to evaluate the effect of topical treatment with a chitosan-alginate membrane on acute skin wounds of hyperglycemic mice. Diabetes mellitus was induced by streptozotocin (60 mg · kg^-1 · day^-1 for 5 days, intraperitoneally) and the cutaneous wound was performed by removing the epidermis using a surgical punch. The results showed that after 10 days of treatment the chitosan and alginate membrane (CAM) group exhibited better organization of collagen fibers. High concentrations of interleukin (IL)-1α, IL-1β, granulocyte colony-stimulating factor (G-CSF), and tumor necrosis factor-alpha (TNF-α) were detected in the first and second days of treatment. G-CSF and TNF-α level decreased after 5 days, as well as the concentrations of TNF-α and IL-10 compared with the control group (CG). In this study, the inflammatory phase of cutaneous lesions of hyperglycemic mice was modulated by the use of CAM, mostly regarding the cytokines IL-1α, IL-1β, TNF-α, G-CSF, and IL-10, resulting in better collagen III deposition. However, further studies are needed to better understand the healing stages associated with CAM use.

Interleukin-6 Expression by Hypothalamic Microglia in Multiple Inflammatory Contexts: A Systematic Review

Interleukin-6 (IL-6) is a unique cytokine that can play both pro- and anti-inflammatory roles depending on the anatomical site and conditions under which it has been induced. Specific neurons of the hypothalamus provide important signals to control food intake and energy expenditure. In individuals with obesity, a microglia-dependent inflammatory response damages the neural circuits responsible for maintaining whole-body energy homeostasis, resulting in a positive energy balance. However, little is known about the role of IL-6 in the regulation of hypothalamic microglia. In this systematic review, we asked what types of conditions and stimuli could modulate microglial IL-6 expression in murine model. We searched the PubMed and Web of Science databases and analyzed 13 articles that evaluated diverse contexts and study models focused on IL-6 expression and microglia activation, including the effects of stress, hypoxia, infection, neonatal overfeeding and nicotine exposure, lipopolysaccharide stimulus, hormones, exercise protocols, and aging. The results presented in this review emphasized the role of "injury-like" stimuli, under which IL-6 acts as a proinflammatory cytokine, concomitant with marked microglial activation, which drive hypothalamic neuroinflammation. Emerging evidence indicates an important correlation of basal IL-6 levels and microglial function with the maintenance of hypothalamic homeostasis. Advances in our understanding of these different contexts will lead to the development of more specific pharmacological approaches for the management of acute and chronic conditions, like obesity and metabolic diseases, without disturbing the homeostatic functions of IL-6 and microglia in the hypothalamus.

Hypothalamic Microglial Activation in Obesity: A Mini-Review

Emerging data demonstrate that microglia activation plays a pivotal role in the development of hypothalamic inflammation in obesity. Early after the introduction of a high-fat diet, hypothalamic microglia undergo morphological, and functional changes in response to excessive dietary saturated fats. Initially the resident microglia are affected; however, as diet-induced obesity persists, bone marrow-derived myeloid cells gradually replace resident microglia. Genetic and pharmacological approaches aimed at dampening the inflammatory activity in the hypothalamus of experimental models of obesity have proven beneficial to correct the obese phenotype and improve metabolic abnormalities commonly associated with obesity. These approaches provide an experimental proof-of-concept that hypothalamic inflammation is central to the pathophysiology of obesity; understanding the details of the roles played by microglia in this process may help the development of preventive and therapeutic advances in the field. In this review, we discuss the potential mechanisms underlying hypothalamic microglial activation in high-fat induced obesity.

TGF-β1 down-regulation in the mediobasal hypothalamus attenuates hypothalamic inflammation and protects against diet-induced obesity

BACKGROUND

The consumption of large amounts of dietary fats induces hypothalamic inflammation and impairs the function of the melanocortin system, leading to a defective regulation of caloric intake and whole-body energy expenditure. In mice fed a high-fat diet (HFD), TGF-β1 expression was increased and NF-κB signaling was activated in proopiomelanocortin neurons, which plays an important role in the obesity-associated hypothalamic inflammation scenario. However, whether excessive hypothalamic TGF-β1 impairs energy homeostasis remains unclear.

OBJECTIVES

We aimed to investigate the role of diet-induced hypothalamic TGF-β1 on inflammation and whole-body energy homeostasis.

METHODS

A TGF-β1 inhibitory lentiviral shRNA particle was stereotaxically injected bilaterally in the arcuate nucleus (ARC) of C57BL/6 mice fed a HFD. We assessed changes in body mass and adiposity, food intake, inflammatory markers, and the function of energy and glucose metabolism.

RESULTS

TGF-β1 down-regulation in the ARC-attenuated body-mass gain, reduced fat-mass accumulation, decreased hypothalamic inflammatory markers, and protected against HFD-induced lipohypertrophy of brown adipose tissue. In addition, the inhibition of hypothalamic TGF-β1 increased the locomotor activity and improved whole-body lipid metabolism, which attenuated hepatic fat accumulation and serum triglyceride levels. No changes were observed in food intake and glucose homeostasis.

CONCLUSION

Hypothalamic TGF-β1 down-regulation attenuates hypothalamic inflammation and improves energy metabolism, resulting in lower body-mass gain and lower fat-mass accumulation, which protects mice from the development of obesity. Our data suggest that modulation of hypothalamic TGF-β1 expression might be an effective strategy to treat obesity.

Evaluating the Effect of 3% Papain Gel Application in Cutaneous Wound Healing in Mice

While the US Food and Drug Administration has not approved the use of 3% papain gel in the United States, the authors feel this study adds to the literature regarding its use.

INTRODUCTION

The aim of this study was to evaluate the effect of 3% papain gel on wounds in mice.

MATERIALS AND METHODS

Thirty healthy C57BL mice (25-30 g) aged 10 weeks were randomly divided into 2 groups: mice treated with 3% papain gel and mice treated with placebo gel. Skin incisions were performed with a 6-mm metallic punch with a cutting blade edge. On days 3 and 7 after creating the lesion, the mice were euthanized and lesion samples were collected. The lesion samples were processed and sectioned into 3 fragments of skin to be stained with 3 types of dye: hematoxylin and eosin, Picrosirius red, and Weigert. In addition, immunohistochemical analysis (α-SM actin and Ki67) followed by real-time polymerase chain reaction (PCR) protocol was performed on the samples.

RESULTS

On gross examination, the 3% papain-treated group took less time to heal the wounds compared with the control. On day 7, microscopic examination showed the 3% papain-treated group had lower numbers of inflammatory cells, increased neovascularization, and improved organization of collagen and elastic fibers. Using PCR analysis, the 3% papain-treated group showed a significant increase in transforming growth factor beta and interleukin-6 expression compared with the control (P < .05).

CONCLUSION

Due to a reduced local inflammatory response, increased angiogenesis, and improved organization of collagen deposition, these findings demonstrate 3% papain gel can improve cutaneous wound healing in mice.

Topical Docosahexaenoic Acid (DHA) Accelerates Skin Wound Healing in Rats and Activates GPR120

Background:

The development of methods for improving skin wound healing may have an impact on the outcomes of a number of medical conditions. The topical use of polyunsaturated fatty acids (PUFAs) can accelerate skin wound healing through mechanisms that involve, at least in part, the modulation of inflammatory activity.

Purpose:

We evaluated whether G-protein-coupled receptor 120 (GPR120), a recently identified receptor for docosahexaenoic acid (DHA) with anti-inflammatory activity, is expressed in the skin and responds to topical DHA.

Method:

Male Wistar rats were submitted to an 8.0-mm wound on the back and were immediately administered a topical treatment of a solution containing 30 μM of DHA once a day. The healing process was photodocumented, and tissues were collected on Days 5, 9, and 15 for protein and RNA analyses and histological evaluation.

Results:

GPR120 was expressed in the intact skin and in the wound. Keratinocytes expressed the most skin GPR120, while virtually no expression was detected in fibroblasts. Upon DHA topical treatment, wound healing was significantly accelerated and was accompanied by the molecular activation of GPR120, as determined by its association with β-arrestin-2. In addition, DHA promoted a reduction in the expression of interleukin (IL) 1β and an increase in the expression of IL-6. Furthermore, there was a significant increase in expression of transforming growth factor β (TGF-β) and the keratinocyte marker involucrin.

Discussion:

Topical DHA improved skin wound healing. The activation of GPR120 is potentially involved in this process.

Topical 5-azacytidine accelerates skin wound healing in rats

The development of new methods to improve skin wound healing may affect the outcomes of a number of medical conditions. Here, we evaluate the molecular and clinical effects of topical 5-azacytidine on wound healing in rats. 5-Azacytidine decreases the expression of follistatin-1, which negatively regulates activins. Activins, in turn, promote cell growth in different tissues, including the skin. Eight-week-old male Wistar rats were submitted to 8.0-mm punch-wounding in the dorsal region. After 3 days, rats were randomly assigned to receive either a control treatment or the topical application of a solution containing 5-azacytidine (10 mM) once per day. Photo documentation and sample collection were performed on days 5, 9, and 15. Overall, 5-azacytidine promoted a significant acceleration of complete wound healing (99.7% ± 0.7.0 vs. 71.2% ± 2.8 on day 15; n = 10; p < 0.01), accompanied by up to threefold reduction in follistatin expression. Histological examination of the skin revealed efficient reepithelization and cell proliferation, as evaluated by the BrdU incorporation method. 5-Azacytidine treatment also resulted in increased gene expression of transforming growth factor-beta and the keratinocyte markers involucrin and cytokeratin, as well as decreased expression of cytokines such as tumor necrosis factor-alpha and interleukin-10. Lastly, when recombinant follistatin was applied to the skin in parallel with topical 5-azacytidine, most of the beneficial effects of the drug were lost. Thus, 5-azacytidine acts, at least in part through the follistatin/activin pathway, to improve skin wound healing in rodents.

Topical insulin accelerates wound healing in diabetes by enhancing the AKT and ERK pathways: a double-blind placebo-controlled clinical trial

BACKGROUND

Wound healing is impaired in diabetes mellitus, but the mechanisms involved in this process are virtually unknown. Proteins belonging to the insulin signaling pathway respond to insulin in the skin of rats.

OBJECTIVE

The purpose of this study was to investigate the regulation of the insulin signaling pathway in wound healing and skin repair of normal and diabetic rats, and, in parallel, the effect of a topical insulin cream on wound healing and on the activation of this pathway.

RESEARCH DESIGN AND METHODS

We investigated insulin signaling by immunoblotting during wound healing of control and diabetic animals with or without topical insulin. Diabetic patients with ulcers were randomized to receive topical insulin or placebo in a prospective, double-blind and placebo-controlled, randomized clinical trial (NCT 01295177) of wound healing.

RESULTS AND CONCLUSIONS

Expression of IR, IRS-1, IRS-2, SHC, ERK, and AKT are increased in the tissue of healing wounds compared to intact skin, suggesting that the insulin signaling pathway may have an important role in this process. These pathways were attenuated in the wounded skin of diabetic rats, in parallel with an increase in the time of complete wound healing. Upon topical application of insulin cream, the wound healing time of diabetic animals was normalized, followed by a reversal of defective insulin signal transduction. In addition, the treatment also increased expression of other proteins, such as eNOS (also in bone marrow), VEGF, and SDF-1α in wounded skin. In diabetic patients, topical insulin cream markedly improved wound healing, representing an attractive and cost-free method for treating this devastating complication of diabetes.

TRIAL REGISTRATION

ClinicalTrials.gov NCT01295177.

Inflammation of the hypothalamus leads to defective pancreatic islet function

Type 2 diabetes mellitus results from the complex association of insulin resistance and pancreatic β-cell failure. Obesity is the main risk factor for type 2 diabetes mellitus, and recent studies have shown that, in diet-induced obesity, the hypothalamus becomes inflamed and dysfunctional, resulting in the loss of the perfect coupling between caloric intake and energy expenditure. Because pancreatic β-cell function is, in part, under the control of the autonomic nervous system, we evaluated the role of hypothalamic inflammation in pancreatic islet function. In diet-induced obesity, the earliest markers of hypothalamic inflammation are present at 8 weeks after the beginning of the high fat diet; similarly, the loss of the first phase of insulin secretion is detected at the same time point and is restored following sympathectomy. Intracerebroventricular injection of a low dose of tumor necrosis factor α leads to a dysfunctional increase in insulin secretion and activates the expression of a number of markers of apoptosis in pancreatic islets. In addition, the injection of stearic acid intracerebroventricularly, which leads to hypothalamic inflammation through the activation of tau-like receptor-4 and endoplasmic reticulum stress, produces an impairment of insulin secretion, accompanied by increased expression of markers of apoptosis. The defective insulin secretion, in this case, is partially dependent on sympathetic signal-induced peroxisome proliferator receptor-γ coactivator Δα and uncoupling protein-2 expression and is restored after sympathectomy or following PGC1α expression inhibition by an antisense oligonucleotide. Thus, the autonomic signals generated in concert with hypothalamic inflammation can impair pancreatic islet function, a phenomenon that may explain the early link between obesity and defective insulin secretion.

Hypothalamic inflammation and obesity

Obesity is one of the most prevalent diseases in the modern world. It results from the progressive loss of balance between food intake and whole body energy expenditure. Recent studies have shown that consumption of fat-rich diets induces hypothalamic inflammation and dysfunction which is characterized by defective response to anorexygenic and thermogenic hormones, such as leptin and insulin, leading to anomalous neurotransmitter production and favoring body mass gain. In this chapter, we present the main recent advances in this rapidly evolving field, focusing on the role of hypothalamic inflammation on the genesis of obesity.

Augmentation of insulin secretion by leucine supplementation in malnourished rats: possible involvement of the phosphatidylinositol 3-phosphate kinase/mammalian target protein of rapamycin pathway

A regimen of low-protein diet induces a reduction of pancreatic islet function that is associated with development of metabolic disorders including diabetes and obesity afterward. In the present study, the influence of leucine supplementation on metabolic parameters, insulin secretion to glucose and to amino acids, as well as the levels of proteins that participate in the phosphatidylinositol 3-phosphate kinase (PI3K) pathway was investigated in malnourished rats. Four groups were fed with different diets for 12 weeks: a normal protein diet (17%) without (NP) or with leucine supplementation (NPL) or a low (6%)-protein diet without (LP) or with leucine supplementation (LPL). Leucine was given in the drinking water during the last 4 weeks. As indicated by the intraperitoneal glucose tolerance test, LPL rats exhibited increased glucose tolerance as compared with NPL group. Both NPL and LPL rats had higher circulating insulin levels than controls. The LPL rats also showed increased insulin secretion by pancreatic islets in response to glucose or arginine compared with those observed in islets from LP animals. Glucose oxidation was significantly reduced in NPL, LP, and LPL isolated islets as compared with NP; but no alteration was observed for leucine and glutamate oxidation among the 4 groups. Western blotting analysis demonstrated increased PI3K and mammalian target protein of rapamycin protein contents in LPL compared with LP islets. A significant increase in insulin-induced insulin receptor substrate 1-associated PI3K activation was also observed in LPL compared with LP islets. These findings indicate that leucine supplementation can augment islet function in malnourished rats and that activation of the PI3K/mammalian target protein of rapamycin pathway may play a role in this process.

Fyn mediates leptin actions in the thymus of rodents

BACKGROUND

Several effects of leptin in the immune system rely on its capacity to modulate cytokine expression and apoptosis in the thymus. Surprisingly, some of these effects are dependent on signal transduction through the IRS1/PI3-kinase, but not on the activation of JAK2. Since all the well known effects of leptin in different cell types and tissues seem to be dependent on JAK2 activation, we hypothesized that, at least for the control of thymic function, another, unknown kinase could mediate the transduction of the leptin signal from the ObR towards the IRS1/PI3-kinase signaling cascade.

METHODOLOGY/PRINCIPAL FINDINGS

Here, by employing immunoblot, real-time PCR and flow citometry we show that the tyrosine kinase, Fyn, is constitutively associated with the ObR in thymic cells. Following a leptin stimulus, Fyn undergoes an activating tyrosine phosphorylation and a transient association with IRS1. All these effects are independent of JAK2 activation and, upon Fyn inhibition, the signal transduction towards IRS1/PI3-kinase is abolished. In addition, the inhibition of Fyn significantly modifies the effects of leptin on thymic cytokine expression.

CONCLUSION/SIGNIFICANCE

Therefore, in the thymus, Fyn acts as a tyrosine kinase that transduces the leptin signal independently of JAK2 activation, and mediates some of the immunomodulatory effects of leptin in this tissue.

UCP2 protects hypothalamic cells from TNF-alpha-induced damage

Uncoupling protein 2 (UCP2) is highly expressed in the hypothalamus; however, little is known about the functions it exerts in this part of the brain. Here, we hypothesized that UCP2 protects hypothalamic cells from oxidative and pro-apoptotic damage generated by inflammatory stimuli. Intracerebroventricular injection of tumor necrosis factor alpha (TNF-alpha)-induced an increase of UCP2 expression in the hypothalamus, which was accompanied by increased expression of markers of oxidative stress and pro-apoptotic proteins. The inhibition of UCP2 expression by an antisense oligonucleotide enhanced the damaging effects of TNF-alpha. Conversely, increasing the hypothalamic expression of UCP2 by cold exposure reversed most of the effects of the cytokine. Thus, UCP2 acts as a protective factor against cellular damage induced by an inflammatory stimulus in the hypothalamus.

AdipoR1 mediates the anorexigenic and insulin/leptin-like actions of adiponectin in the hypothalamus

Adiponectin exerts an insulin-sensitizing effect, improving insulin action in peripheral tissues and restraining insulin resistance. Here, we explore the hypothesis that adiponectin can reproduce some of the actions of insulin/leptin in the hypothalamus. The presence of AdipoR1 and AdipoR2 was mapped to the arcuate and lateral hypothalamic nuclei. Icv adiponectin reduced food intake, which was accompanied by activation/engagement of IRS1/2, ERK, Akt, FOXO1, JAK2 and STAT3. All these actions were dependent on AdipoR1, since inhibition of this receptor, and not of AdipoR2, completely reversed the effects described above. Thus, adiponectin acts in the hypothalamus, activating elements of the canonical insulin and leptin signaling pathways and promoting reduction of food intake.

Interleukin-10 is a protective factor against diet-induced insulin resistance in liver

BACKGROUND/AIMS

The anti-inflammatory cytokine, interleukin-10 (IL-10), is known to exert a protective role in hepatic damage caused by viruses, alcohol, autoimmunity and a number of experimental aggressors. Recently, a protective role for IL-10 has also been proposed in diet-induced hepatic dysfunction. However, studies about the mechanisms involved in this process are controversial. The objective of this study was to evaluate the role of endogenous IL-10 in the development of hepatic insulin resistance, associated with diet-induced fatty liver disease.

METHODS

Male Swiss mice treated for eight weeks with a high-fat diet became diabetic and developed non-alcoholic fatty liver disease, which is characterized by increased hepatic fat deposition and liver infiltration by F4/80 positive cells. This was accompanied by an increased hepatic expression of TNF-alpha, IL-6, IL-1beta and IL-10, and by an impaired insulin signal transduction through the insulin receptor/IRS1-IRS2/PI3-kinase/Akt/FOXO1 signaling pathway.

RESULTS

Upon endogenous IL-10 inhibition for 5 days, using two distinct methods, a neutralizing anti-IL-10 antibody and an antisense oligonucleotide against IL-10, increased hepatic expression of the inflammatory markers TNF-alpha, IL-6, IL-1beta and F4/80 was observed. This was accompanied by a significant negative modulation of insulin signal transduction through insulin receptor/IRS1-IRS2/PI3-kinase/Akt/FOXO1, and by the stimulation of hepatic signaling proteins involved in gluconeogenesis and lipid synthesis.

CONCLUSIONS

Thus, in an animal model of diet-induced fatty liver disease, the inhibition of IL-10 promotes the increased expression of inflammatory cytokines, the worsening of insulin signaling and the activation of gluconeogenic and lipidogenic pathways.

Diet-induced inflammation of the hypothalamus in obesity

Dysfunction of specific hypothalamic neurons is regarded as an important mechanism predisposing to the development of obesity. Recent studies have revealed that the consumption of fat-rich foods can activate an inflammatory response in the hypothalamus, which disturbs the anorexigenic and thermogenic signals generated by the hormones leptin and insulin, leading in turn to anomalous body mass control. Depending on diet composition, cytokines are expressed in the hypothalamus, contributing to the activation of intracellular inflammatory signal transduction. At least 4 distinct signaling pathways have been identified and the molecular mechanisms leading to the impairment of the leptin and insulin actions have been determined. Here, we present the mechanisms involved in diet-induced resistance to leptin and insulin action in the hypothalamus and discuss some of the potential applications of this knowledge in the therapeutics of obesity.

Infliximab restores glucose homeostasis in an animal model of diet-induced obesity and diabetes

TNF-alpha plays an important role in obesity-linked insulin resistance and diabetes mellitus by activating at least two serine kinases capable of promoting negative regulation of key elements of the insulin signaling pathway. Pharmacological inhibition of TNF-alpha is currently in use for the treatment of rheumatoid and psoriatic arthritis, and some case reports have shown clinical improvement of diabetes in patients treated with the TNF-alpha blocking monoclonal antibody infliximab. The objective of this study was to evaluate the effect of infliximab on glucose homeostasis and insulin signal transduction in an animal model of diabetes. Diabetes was induced in Swiss mice by a fat-rich diet. Glucose and insulin homeostasis were evaluated by glucose and insulin tolerance tests and by the hyperinsulinemic-euglycemic clamp. Signal transduction was evaluated by immunoprecipitation and immunoblotting assays. Short-term treatment with infliximab rapidly reduced blood glucose and insulin levels and glucose and insulin areas under the curve during a glucose tolerance test. Furthermore, infliximab increased the glucose decay constant during an insulin tolerance test and promoted a significant increase in glucose infusion rate during a hyperinsulinemic-euglycemic clamp. In addition, the clinical outcomes were accompanied by improved insulin signal transduction in muscle, liver, and hypothalamus, as determined by the evaluation of insulin-induced insulin receptor, insulin receptor substrate-1, and receptor substrate-2 tyrosine phosphorylation and Akt and forkhead box protein O1 serine phosphorylation. Thus, pharmacological inhibition of TNF-alpha may be an attractive approach to treat severely insulin-resistant patients with type 2 diabetes mellitus.

Loss-of-function mutation in Toll-like receptor 4 prevents diet-induced obesity and insulin resistance

Obesity is associated with insulin resistance and a state of abnormal inflammatory response. The Toll-like receptor (TLR)4 has an important role in inflammation and immunity, and its expression has been reported in most tissues of the body, including the insulin-sensitive ones. Because it is activated by lipopolysaccharide and saturated fatty acids, which are inducers of insulin resistance, TLR4 may be a candidate for participation in the cross-talk between inflammatory and metabolic signals. Here, we show that C3H/HeJ mice, which have a loss-of-function mutation in TLR4, are protected against the development of diet-induced obesity. In addition, these mice demonstrate decreased adiposity, increased oxygen consumption, a decreased respiratory exchange ratio, improved insulin sensitivity, and enhanced insulin-signaling capacity in adipose tissue, muscle, and liver compared with control mice during high-fat feeding. Moreover, in these tissues, control mice fed a high-fat diet show an increase in IkappaB kinase complex and c-Jun NH(2)-terminal kinase activity, which is prevented in C3H/HeJ mice. In isolated muscles from C3H/HeJ mice, protection from saturated fatty acid-induced insulin resistance is observed. Thus, TLR4 appears to be an important mediator of obesity and insulin resistance and a potential target for the therapy of these highly prevalent medical conditions.

Inhibition of UCP2 expression reverses diet-induced diabetes mellitus by effects on both insulin secretion and action

Recent characterization of the ability of uncoupling protein 2 (UCP2) to reduce ATP production and inhibit insulin secretion by pancreatic beta-cells has placed this mitochondrial protein as a candidate target for therapeutics in diabetes mellitus. In the present study we evaluate the effects of short-term treatment of two animal models of type 2 diabetes mellitus with an antisense oligonucleotide to UCP2. In both models, Swiss mice (made obese and diabetic by a hyperlipidic diet) and ob/ob mice, the treatment resulted in a significant improvement in the hyperglycemic syndrome. This effect was due not only to an improvement of insulin secretion, but also to improved peripheral insulin action. In isolated pancreatic islets, the partial inhibition of UCP2 increased ATP content, followed by increased glucose-stimulated insulin secretion. This was not accompanied by increased expression of enzymes involved in protection against oxidative stress. The evaluation of insulin action in peripheral tissues revealed that the inhibition of UCP2 expression significantly improved insulin signal transduction in adipose tissue. In conclusion, short-term inhibition of UCP2 expression ameliorates the hyperglycemic syndrome in two distinct animal models of obesity and diabetes. Metabolic improvement is due to a combined effect on insulin-producing pancreatic islets and in at least one peripheral tissue that acts as a target for insulin.

Amelioration of diet-induced diabetes mellitus by removal of visceral fat

The effect of visceral fat removal upon glucose homeostasis, insulin signal transduction, and serum adipokine levels in an animal model of diet-induced obesity and diabetes mellitus (DIO) was evaluated. Swiss mice were initially divided into two groups fed with regular rodent chow or with chow containing 24 g% saturated fat (DIO). DIO mice became obese and overtly diabetic after 8 weeks. DIO mice were then divided into three groups: control, sham, and visceral (epididymal and perinephric) fat removal. All groups were submitted to evaluation of basal glucose and insulin levels and i.p. insulin tolerance test. Insulin signal transduction in muscle was evaluated by immunoprecipitation and immunoblot, and serum adipokine levels were determined by ELISA. DIO mice became diabetic (228 versus 115 mg/dl), hyperinsulinemic (7.59 versus 3.15 ng/ml) and insulin resistant (K(itt) 2.88 versus 4.97%/min) as compared with control. Visceral fat removal partially reverted all parameters (147 mg/dl glucose; 3.82 ng/ml insulin; and 4.20%/min K(itt)). In addition, visceral fat removal completely reversed the impairment of insulin signal transduction through insulin receptor, insulin receptor substrate (IRS)-1, IRS-2 and Akt in muscle. Finally, serum levels of the pro-inflammatory cytokines tumour necrosis factor-alpha, interleukin (IL)-1beta and IL-6 were significantly increased, while adiponectin levels were significantly reduced in DIO mice. After visceral fat removal the levels of adipokines returned to near control levels. The present study shows that removal of visceral fat improves insulin signal transduction and glucose homeostasis in an animal model of diet-induced obesity and diabetes mellitus and these metabolic and molecular outcomes are accompanied by the restoration of adipokine levels.

Phosphoinositide-specific inositol polyphosphate 5-phosphatase IV inhibits inositide trisphosphate accumulation in hypothalamus and regulates food intake and body weight

The enzyme phosphatidylinositol 3-kinase (PI3-kinase) exerts an important role in the transduction of the anorexigenic and thermogenic signals delivered by insulin and leptin to first-order neurons of the arcuate nucleus in the hypothalamus. The termination of the intracellular signals generated by the activation of PI3-kinase depends on the coordinated activity of specific inositol phosphatases. Here we show that phosphoinositide-specific inositol polyphosphate 5-phosphatase IV (5ptase IV) is highly expressed in neurons of the arcuate and lateral nuclei of the hypothalamus. Upon intracerebroventricular (ICV) treatment with insulin, 5ptase IV undergoes a time-dependent tyrosine phosphorylation, which follows the same patterns of canonical insulin signaling through the insulin receptor, insulin receptor substrate-2, and PI3-kinase. To evaluate the participation of 5ptase IV in insulin action in hypothalamus, we used a phosphorthioate-modified antisense oligonucleotide specific for this enzyme. The treatment of rats with this oligonucleotide for 4 d reduced the hypothalamic expression of 5ptase IV by approximately 80%. This was accompanied by an approximately 70% reduction of insulin-induced tyrosine phosphorylation of 5ptase IV and an increase in basal accumulation of phosphorylated inositols in the hypothalamus. Finally, inhibition of hypothalamic 5ptase IV expression by the antisense approach resulted in reduced daily food intake and body weight loss. Thus, 5ptase IV is a powerful regulator of signaling through PI3-kinase in hypothalamus and may become an interesting target for therapeutics of obesity and related disorders.

Leptin inhibits apoptosis in thymus through a janus kinase-2-independent, insulin receptor substrate-1/phosphatidylinositol-3 kinase-dependent pathway

The cytokine-like hormone leptin is known to exert important functions on the modulation of immune responses. Some of these effects are dependent on the property of leptin to modulate the apoptosis of thymic cells. In the present study, we used Wistar rats to investigate the molecular mechanisms involved in leptin-dependent control of apoptosis in thymus. Apoptosis was evaluated by flow cytometry and ELISA for nucleosome determination, whereas signal transduction was evaluated by immunoprecipitation, immunoblot, and confocal microscopy. The Ob receptor (ObR) was expressed in most thymic cells and its relative amount reduced progressively during thymocyte maturation. ObR expression was colocalized with Janus kinase (JAK)-2 and signal transducer and activator of transcription-3, and an acute, in vivo, injection of leptin promoted the tyrosine phosphorylation of JAK-2 and the engagement of signal transducer and activator of transcription-3. The treatment with leptin also led to the tyrosine phosphorylation of insulin receptor substrate (IRS)-1 and serine phosphorylation of Akt. Chronic treatment with leptin reduced thymic apoptosis, an effect that was not inhibited by the JAK inhibitor AG(490) but was significantly inhibited by the phosphatidylinositol 3-kinase inhibitor LY(294002) and an antisense oligonucleotide to IRS-1. Thus, leptin inhibits the apoptosis of thymic cells through a mechanism that is independent of the activation of JAK-2 but depends on the engagement of the IRS-1/phosphatidylinositol 3-kinase pathway.

Short-term inhibition of peroxisome proliferator-activated receptor-gamma coactivator-1alpha expression reverses diet-induced diabetes mellitus and hepatic steatosis in mice

AIMS/HYPOTHESIS

The coactivator of nuclear receptors, peroxisome proliferator-activated receptor-gamma coactivator-1alpha (PGC-1alpha) has been implicated in a series of events that contribute to the control of glucose metabolism. We have recently reported the use of a PGC-1alpha antisense oligonucleotide (PGC-1alphaAS) that inhibits up to 60% of PGC-1alpha expression in pancreatic islets, leading to increased insulin secretion. This oligonucleotide was used in this study to try to ameliorate diet-induced type 2 diabetes in a genetically predisposed mouse strain (Swiss mice).

MATERIALS AND METHODS

Glucose and insulin tolerance tests, euglycaemic-hyperinsulinaemic clamp, immunoprecipitation assays, immunoblotting assays and immunohistochemistry were used in this investigation.

RESULTS

Swiss mice became obese and overtly diabetic after 8 weeks of feeding with chow containing 24% saturated fat. One daily dose (1.0 nmol) of PGC-1alphaAS significantly reduced glucose and increased insulin blood levels without affecting food intake and body weight. These effects were accompanied by a reduced area under the glucose curve during an intraperitoneal glucose tolerance test, an increased constant of glucose decay (K(itt)) during an insulin tolerance test, and an increased glucose consumption rate during a euglycaemic-hyperinsulinaemic clamp. Moreover, mice treated with PGC-1alphaAS presented an outstanding reduction of macroscopic and microscopic features of hepatic steatosis. These effects were accompanied by reduced expression or function of a series of proteins involved in lipogenesis.

CONCLUSIONS/INTERPRETATION

PGC-1alpha is an attractive target for pharmacological therapeutics in type 2 diabetes mellitus and diet-induced hepatic steatosis.

Short-term in vivo inhibition of insulin receptor substrate-1 expression leads to insulin resistance, hyperinsulinemia, and increased adiposity

Insulin receptor substrate-1 (IRS-1) has an important role as an early intermediary between the insulin and IGF receptors and downstream molecules that participate in insulin and IGF-I signal transduction. Here we employed an antisense oligonucleotide (IRS-1AS) to inhibit whole-body expression of IRS-1 in vivo and evaluate the consequences of short-term inhibition of IRS-1 in Wistar rats. Four days of treatment with IRS-1AS reduced the expression of IRS-1 by 80, 75, and 65% (P < 0.05) in liver, skeletal muscle, and adipose tissue, respectively. This was accompanied by a 40% (P < 0.05) reduction in the constant of glucose decay during an insulin tolerance test, a 78% (P < 0.05) reduction in glucose consumption during a hyperinsulinemic-euglycemic clamp, and a 90% (P < 0.05) increase in basal plasma insulin level. The metabolic effects produced by IRS-1AS were accompanied by a significant reduction in insulin-induced [Ser (473)] Akt phosphorylation in liver (85%, P < 0.05), skeletal muscle (40%, P < 0.05), and adipose tissue (85%, P < 0.05) and a significant reduction in insulin-induced tyrosine phosphorylation of ERK in liver (20%, P < 0.05) and skeletal muscle (30%, P < 0.05). However, insulin-induced tyrosine phosphorylation of ERK was significantly increased (60%, P < 0.05) in adipose tissue of IRS-1AS-treated rats. In rats treated with IRS-1AS for 8 d, a 100% increase (P < 0.05) in relative epididymal fat weight and a 120% (P < 0.05) increase in nuclear expression of peroxisome proliferator-activated receptor-gamma were observed. Thus, acute inhibition of IRS-1 expression in rats leads to insulin resistance accompanied by activation of a growth-related pathway exclusively in white adipose tissue.

Cross-talk between the insulin and leptin signaling systems in rat hypothalamus

OBJECTIVE

To investigate whether insulin and leptin share common intracellular signal transduction pathways and to determine whether these hormonal signaling systems modulate each other's action in rat hypothalamus.

RESEARCH METHODS AND PROCEDURES

Male Wistar rats were studied after chronic implantation of an intracerebroventricular catheter into the third ventricle. Immunoprecipitation and immunoblotting were used to examine the activation of insulin and leptin signaling molecules in the rat hypothalamus.

RESULTS

Insulin alone is able to produce molecular activation of insulin receptor substrates (IRSs)/phosphatidylinositol 3-kinase (PI 3-kinase)/Akt and mitogen-activated protein (MAP) kinase signaling pathways in hypothalamus, whereas leptin alone activates MAP kinase and IRSs/PI 3-kinase signaling with no effect on Akt. Combined infusion of leptin and insulin provokes a dual action. There was no quantitative potentialization of any single hormone's action on the elements of the insulin signaling pathway, IRSs/PI 3-kinase/Akt, and MAP kinase. Conversely, leptin plus insulin leads to quantitative potentialization of molecular signaling through the Janus kinase/signal transducer and activator of transcription pathway.

DISCUSSION

We provide evidence for a convergence of leptin and insulin signaling at the level of IRSs-PI 3-kinase and a divergence at the level of Akt. Moreover, our results indicate a direct and positive cross-talk between insulin and leptin at the level of Janus kinase 2 and signal transducer and activator of transcription 3 tyrosine phosphorylation. This mechanism may serve to potentiate the activity of both insulin and leptin pathways and to increase stimulation in physiological processes such as the control of food intake and body weight, which are under the combined control of insulin and leptin.

Selective impairment of insulin signalling in the hypothalamus of obese Zucker rats

AIM/HYPOTHESIS

By acting in the brain, insulin suppresses food intake. However, little is known with regard to insulin signalling in the hypothalamus in insulin-resistant states.

METHODS

Western blotting, immunohistochemistry and polymerase chain reaction assays were combined to compare in vivo hypothalamic insulin signalling through the PI3-kinase and MAP kinase pathways between lean and obese Zucker rats.

RESULTS

Intracerebroventricular insulin infusion reduced food intake in lean rats to a greater extent than that observed in obese rats, and pre-treatment with PI3-kinase inhibitors prevented insulin-induced anorexia. The relative abundance of IRS-2 was considerably higher than that of IRS-1 in hypothalamus of both lean and obese rats. Insulin-stimulated phosphorylation of IR, IRS-1/2, the associations of PI 3-kinase to IRS-1/2 and phosphorylation of Akt in hypothalamus were decreased in obese rats compared to lean rats. These effects seem to be mediated by increased phosphoserine content of IR, IRS-1/2 and decreased protein levels of IRS-1/2 in obese rats. In contrast, insulin stimulated the phosphorylation of MAP kinase equally in lean and obese rats.

CONCLUSION/INTERPRETATION

This study provides direct measurements of insulin signalling in hypothalamus, and documents selective resistance to insulin signalling in hypothalamus of Zucker rats. These findings provide support for the hypothesis that insulin could have anti-obesity actions mediated by the PI3-kinase pathway, and that impaired insulin signalling in hypothalamus could play a role in the development of obesity in this animal model of insulin-resistance.

Peroxisome proliferator-activated receptor gamma coactivator-1-dependent uncoupling protein-2 expression in pancreatic islets of rats: a novel pathway for neural control of insulin secretion

AIMS/HYPOTHESIS

Sympathetic inputs inhibit insulin secretion through alpha2-adrenergic receptors coupled with Gi protein. High adrenergic tonus generated by exposure of homeothermic animals to cold reduces insulin secretion. In this study we evaluate the participation of UCP-2 in cold-induced regulation of insulin secretion.

METHODS

Static insulin secretion studies, western blotting and immunohistochemistry were used in this investigation.

RESULTS

Exposure of rats to cold during 8 days promoted 60% ( n=15, p<0.05) reduction of basal serum insulin levels concentration accompanied by reduction of the area under insulin curve during i.p. GTT (50%, n=15, p<0.05). Isolated islets from cold-exposed rats secreted 57% ( n=6, p<0.05) less insulin following a glucose challenge. Previous sympathectomy, partially prevented the effect of cold exposure upon insulin secretion. Islets isolated from cold-exposed rats expressed 51% ( n=6, p<0.5) more UCP-2 than islets from control rats, while the inhibition of UCP-2 expression by antisense oligonucleotide treatment partially restored insulin secretion of islets obtained from cold-exposed rats. Cold exposure also induced an increase of 69% ( n=6, p<0.05) in PGC-1 protein content in pancreatic islets. Inhibition of islet PGC-1 expression by antisense oligonucleotide abrogated cold-induced UCP-2 expression and partially restored insulin secretion in islets exposed to cold.

CONCLUSION/INTERPRETATION

Our data indicate that sympathetic tonus generated by exposure of rats to cold induces the expression of PGC-1, which participates in the control of UCP-2 expression in pancreatic islets. Increased UCP-2 expression under these conditions could reduce the beta-cell ATP/ADP ratio and negatively regulate insulin secretion.

Decreased cholinergic stimulation of insulin secretion by islets from rats fed a low protein diet is associated with reduced protein kinase calpha expression

Undernutrition has been shown to affect the autonomic nervous system, leading to permanent alterations in insulin secretion. To understand these interactions better, we investigated the effects of carbamylcholine (CCh) and phorbol 12-myristate 13-acetate (PMA) on insulin secretion in pancreatic islets from rats fed a normal (17%; NP) or low (6%; LP) protein diet for 8 wk. Isolated islets were incubated for 1 h in Krebs-bicarbonate solution containing 8.3 mmol glucose/L, with or without PMA (400 nmol/L) and CCh. Increasing concentrations of CCh (0.1-1000 micro mol/L) dose dependently increased insulin secretion by islets from both groups of rats. However, insulin secretion by islets from rats fed the NP diet was significantly higher than that of rats fed the LP diet, and the dose-response curve to CCh was shifted to the right in islets from rats fed LP with a 50% effective concentration (EC(50)) of 2.15 +/- 0.7 and 4.64 +/- 0.1 micro mol CCh/L in islets of rats fed NP and LP diets, respectively (P < 0.05). PMA-induced insulin secretion was higher in islets of rats fed NP compared with those fed LP. Western blotting revealed that the protein kinase (PK)Calpha and phospholipase (PL)Cbeta(1) contents of islets of rats fed LP were 30% lower than those of islets of rats fed NP (P < 0.05). In addition, PKCalpha mRNA expression was reduced by 50% in islets from rats fed LP. In conclusion, a reduced expression of PKCalpha and PLCbeta(1) may be involved in the decreased insulin secretion by islets from LP rats after stimulation with CCh and PMA.