Human adenovirus Ad-36 induces adipogenesis via its E4 orf-1 gene

Dogs are a susceptible species to human adenovirus 36 infection: New insights into the host range of the virus causing infectious obesity

The prevalence of obesity within the human population is escalating globally yearly. Obesity constitutes a complex ailment with diverse etiological factors. Recently, the infectious side of obesity aetiology, implicating pathogens such as human adenovirus 36 (HAdV-D36), has gained attention. Research indicates that HAdV-D36 can infect humans and various animal species, including mice, monkeys, and chickens, inducing obesity in the animals. The present study aimed to confirm whether companion animals, like dogs, can also host HAdV-D36 and which biochemical markers can be helpful to indicate its presence. The blood of 118 canine subjects was analysed using serological techniques for determining the presence of antibodies and screened for biochemical parameters like leptin, cholesterol, and triglycerides. The presence of anti-HAdV-D36 antibodies was confirmed in 80 of the 118 tested individuals. The investigation of the relationship between antibody levels and the concentrations of cholesterol, triglycerides, and leptin in blood serum revealed a positive correlation between antibody titers and triglyceride levels in the tested samples. Furthermore, utilizing cell cultures facilitated successful isolation of HAdV-D36 from the adipose tissue of 14 dogs under investigation. Our study adds to general knowledge of the range of hosts susceptible to the pathogen in question and highlights the discrepancies in the virus mechanisms found in the existing literature. Given the diverse host range of the virus, which extends to companion animals, a zoonotic potential cannot be ruled out, which, however, requires further extensive research.

Adenovirus 36 seropositivity is related to the expression of anti-adipogenic lncRNAs GAS5 and MEG3 in adipose tissue obtained from subjects with obesity

BACKGROUND

Human Adenovirus D-36 (HAdV-D36) promotes adipogenesis in cellular and animal models and may contribute to the development of human obesity. Induction of PPARγ by HAdV-D36 seems to have a central role in the maintenance of adipogenic status. There is limited information about epigenetic mechanisms contributing to this process in human adipose tissue. This study evaluated the expression of lncRNAs (ADINR, GAS5 and MEG3) and miRNAs (miR-18a and miR-140) involved in the adipogenic process in visceral adipose tissue (VAT) of subjects with obesity with previous HAdV-D36 infection (seropositive) and unexposed (seronegative) subjects with obesity.

METHODS

Individuals with obesity were grouped according to the presence of antibodies against HAdV-D36 (Seropositive: HAdV-D36[+], n = 29; and Seronegative: HAdV-D36[-], n = 28). Additionally, a group of individuals without obesity (n = 17) was selected as a control group. The HAdV-D36 serology was carried out by ELISA. Biopsies of VAT were obtained during an elective and clinically indicated surgery (bariatric or cholecystectomy). RNA extraction from VAT was performed and the expression of PPARG and non-coding RNAs was evaluated by qPCR.

RESULTS

HAdV-D36[+] individuals had lower expression of anti-adipogenic lncRNAs GAS5 (p = 0.016) and MEG3 (p = 0.035) compared with HAdV-D36[-] subjects with obesity. HAdV-D36[+] subjects also presented increased expression of the adipogenic miRNA miR-18a (p = 0.042), which has been reported to be modulated by GAS5 through a RNA sponging mechanism during adipogenic differentiation. Additionally, an inverse correlation of GAS5 with PPARG expression was observed (r = -0.917, p = 0.01).

CONCLUSION

Our results suggest that HAdV-D36 is related to non-coding RNAs implicated in adipogenesis, representing a potential mechanism by which previous HAdV-D36 infection could be associated with the long-term maintenance of adipogenic status, probably through the GAS5/miR-18a axis.

An Observational Study Suggests That Natural HAdV-36 Infection Decreases Blood Glucose Levels without Affecting Insulin Levels in Obese Young Subjects

Human adenovirus-36 (HAdV-36) infection has been linked to obesity, low lipid levels, and improvements in blood glucose levels and insulin sensitivity in animal models and humans, although epidemiological studies remain controversial. Therefore, this study investigated the relationship between HAdV-36 seropositivity and glycemic control in youths. This observational study examined 460 youths (246 with normal weight and 214 obese subjects). All participants underwent assessments for anthropometry, blood pressure, circulating fasting levels of glucose, lipids, insulin, and anti-HAdV-36 antibodies; additionally, the homeostatic model assessment of insulin resistance (HOMA-IR) was calculated. In all, 57.17% of the subjects were HAdV-36 seropositive. Moreover, HAdV-36 seroprevalence was higher in obese subjects compared to their normal weight counterparts (59% vs. 55%). BMI (33.1 vs. 32.3 kg/m2, p = 0.03), and waist circumference (107 vs. 104 cm, p = 0.02), insulin levels (21 vs. 16.3 µU/mL, p = 0.003), and HOMA-IR (4.6 vs. 3.9, p = 0.02) were higher in HAdV-36-positive subjects with obesity compared to seronegative subjects. In the obese group, HAdV-36 seropositivity was associated with a reducing effect in blood glucose levels in a model adjusted for total cholesterol, triglyceride levels, age and sex (β = -10.44, p = 0.014). Furthermore, a statistically significant positive relationship was observed between HAdV-36 seropositivity and insulin levels in the obesity group. These findings suggest that natural HAdV-36 infection improves glycemic control but does not ameliorate hyperinsulinemia in obese subjects.

E4orf1: The triple agent of adenovirus - Unraveling its roles in oncogenesis, infectious obesity and immune responses in virus replication and vector therapy

Human Adenoviruses (HAdV) are nearly ubiquitous pathogens comprising numerous sub-types that infect various tissues and organs. Among many encoded proteins that facilitate viral replication and subversion of host cellular processes, the viral E4orf1 protein has emerged as an intriguing yet under-investigated player in the complex interplay between the virus and its host. E4orf1 has gained attention as a metabolism activator and oncogenic agent, while recent research is showing that E4orf1 may play a more important role in modulating cellular pathways such as PI3K-Akt-mTOR, Ras, the immune response and further HAdV replication stages than previously anticipated. In this review, we aim to explore the structure, molecular mechanisms, and biological functions of E4orf1, shedding light on its potentially multifaceted roles during HAdV infection, including metabolic diseases and oncogenesis. Furthermore, we discuss the role of functional E4orf1 in biotechnological applications such as Adenovirus (AdV) vaccine vectors and oncolytic AdV. By dissecting the intricate relationships between HAdV types and E4orf1 proteins, this review provides valuable insights into viral pathogenesis and points to promising areas of future research.

The human adenovirus PI3K-Akt activator E4orf1 is targeted by the tumor suppressor p53

Human adenoviruses (HAdV) are classified as DNA tumor viruses due to their potential to mediate oncogenic transformation in non-permissive mammalian cells and certain human stem cells. To achieve transformation, the viral early proteins of the E1 and E4 regions must block apoptosis and activate proliferation: the former predominantly through modulating the cellular tumor suppressor p53 and the latter by activating cellular pro-survival and pro-metabolism protein cascades, such as the phosphoinositide 3-kinase (PI3K-Akt) pathway, which is activated by HAdV E4orf1. Focusing on HAdV-C5, we show that E4orf1 is necessary and sufficient to stimulate Akt activation through phosphorylation in H1299 cells, which is not only hindered but repressed during HAdV-C5 infection with a loss of E4orf1 function in p53-positive A549 cells. Contrary to other research, E4orf1 localized not only in the common, cytoplasmic PI3K-Akt-containing compartment, but also in distinct nuclear aggregates. We identified a novel inhibitory mechanism, where p53 selectively targeted E4orf1 to destabilize it, also stalling E4orf1-dependent Akt phosphorylation. Co-IP and immunofluorescence studies showed that p53 and E4orf1 interact, and since p53 is bound by the HAdV-C5 E3 ubiquitin ligase complex, we also identified E4orf1 as a novel factor interacting with E1B-55K and E4orf6 during infection; overexpression of E4orf1 led to less-efficient E3 ubiquitin ligase-mediated proteasomal degradation of p53. We hypothesize that p53 specifically subverts the pro-survival function of E4orf1-mediated PI3K-Akt activation to protect the cell from metabolic hyper-activation or even transformation.IMPORTANCEHuman adenoviruses (HAdV) are nearly ubiquitous pathogens comprising numerous subtypes that infect various tissues and organs. Among many encoded proteins that facilitate viral replication and subversion of host cellular processes, the viral E4orf1 protein has emerged as an intriguing yet under-investigated player in the complex interplay between the virus and its host. Nonetheless, E4orf1 has gained attention as a metabolism activator and oncogenic agent, while recent research is showing that E4orf1 may play a more important role in modulating the cellular pathways such as phosphoinositide 3-kinase-Akt-mTOR. Our study reveals a novel and general impact of E4orf1 on host mechanisms, providing a novel basis for innovative antiviral strategies in future therapeutic settings. Ongoing investigations of the cellular pathways modulated by HAdV are of great interest, particularly since adenovirus-based vectors actually serve as vaccine or gene vectors. HAdV constitute an ideal model system to analyze the underlying molecular principles of virus-induced tumorigenesis.

Inflammatory cytokines and chemokines in obese adolescents with antibody against to adenovirus 36

Obesity in adolescents has reached epidemic proportions and is associated with the inflammatory response and viral infections. The aim of this study was to understand the profile of inflammatory cytokines and chemokines associated with the inflammatory response and metabolic syndrome (MetS) in obese adolescents with positive serology for adenovirus 36 (ADV36). Thirty-six overweight, 36 obese, and 25 severe obesity adolescents aged 10 to 16 years were included in the study. The following variables were analyzed: sex, age, body mass index (BMI), blood pressure, total cholesterol and fractions, triglycerides, glucose, serum cytokine concentrations, and ADV36 antibodies. Cytokines and chemokines were quantified by cytometry and ADV36 serology was determined by enzyme-linked immunosorbent assay (ELISA). The results showed higher levels of the cytokines interleukin-1beta (IL-1β), IL-6, IL-10 and of the chemokine interferon-gamma-inducible protein 10 (IP-10) in severe obesity adolescents compared to the obese and overweight groups, as well as in the group with MetS compared to the group without this syndrome. The frequency of ADV36-positive individuals did not differ between groups. The findings revealed differences in BMI between the obese and severe obesity groups versus the overweight group in the presence of positivity for ADV36, suggesting an association with weight gain and possibly MetS installation.

Adipocyte commitment of 3T3-L1 cells is required to support human adenovirus 36 productive replication concurrent with altered lipid and glucose metabolism

Human adenovirus 36 (HAdV-D36) can cause obesity in animal models, induces an adipogenic effect and increased adipocyte differentiation in cell culture. HAdV-D36 infection alters gene expression and the metabolism of the infected cells resulting in increased glucose internalization and triglyceride accumulation. Although HAdV-D36 prevalence correlates with obesity in humans, whether human preadipocytes may be targeted in vivo has not been determined and metabolic reprogramming of preadipocytes has not been explored in the context of the viral replication cycle. HAdV-D36 infection of the mouse fibroblasts, 3T3-L1 cells, which can differentiate into adipocytes, promotes proliferation and differentiation, but replication of the virus in these cells is abortive as indicated by short-lived transient expression of viral mRNA and a progressive loss of viral DNA. Therefore, we have evaluated whether a productive viral replication cycle can be established in the 3T3-L1 preadipocyte model under conditions that drive the cell differentiation process. For this purpose, viral mRNA levels and viral DNA replication were measured by RT-qPCR and qPCR, respectively, and viral progeny production was determined by plaque assay. The lipogenic effect of infection was evaluated with Oil Red O (ORO) staining, and expression of genes that control lipid and glucose metabolism was measured by RT-qPCR. In the context of a viral productive cycle, HAdV-D36 modulated the expression of the adipogenic genes, C/EBPα, C/EBPβ and PPARγ, as well as intracellular lipid accumulation, and the infection was accompanied by altered expression of glucolytic genes. The results show that only adipocyte-committed 3T3-L1 cells are permissive for the expression of early and late viral mRNAs, as well as viral DNA replication and progeny production, supporting productive HAdV-D36 viral replication, indicating that a greater effect on adipogenesis occurs in adipocytes that support productive viral replication.

The Immune Response in Adipocytes and Their Susceptibility to Infection: A Possible Relationship with Infectobesity

The current obesity pandemic has been expanding in both developing and developed countries. This suggests that the factors contributing to this condition need to be reconsidered since some new factors are arising as etiological causes of this disease. Moreover, recent clinical and experimental findings have shown an association between the progress of obesity and some infections, and the functions of adipose tissues, which involve cell metabolism and adipokine release, among others. Furthermore, it has recently been reported that adipocytes could either be reservoirs for these pathogens or play an active role in this process. In addition, there is abundant evidence indicating that during obesity, the immune system is exacerbated, suggesting an increased susceptibility of the patient to the development of several forms of illness or death. Thus, there could be a relationship between infection as a trigger for an increase in adipose cells and the impact on the metabolism that contributes to the development of obesity. In this review, we describe the findings concerning the role of adipose tissue as a mediator in the immune response as well as the possible role of adipocytes as infection targets, with both roles constituting a possible cause of obesity.

Adenovirus 36 infection and obesity risk: current understanding and future therapeutic strategies

INTRODUCTION

Obesity, a multifactorial disease caused by the interaction between genetic characteristics, metabolism, lifestyle, and environmental factors, is a major global health problem and is currently defined as a pandemic phenomenon. This disease is determined by an interaction of several factors, but the imbalance between energy consumption and expenditure seems to be the crucial point. In some cases, there is no linearity between exposure to those factors that cause the onset of obesity. A striking example of the occurrence of obesity despite no obvious risk factors is that of obesity induced by viral infections. The most important of such viruses appears to be human adenovirus 36 (Adv36).

AREAS COVERED

This review covers the relation between obesity and infection by Adv36 in humans. Also, discussed are the opportunities of prevention or treatment for the effects of Adv36 in human body.

EXPERT OPINION

The role of Ad36 in the development of obesity has already been established. Future research should focus on the development of vaccines against this agent, drug discovery for infected individuals, and effective therapeutic uses of E4orf1 gene protein for diabetes and other diseases in clinical practice.

Viral dUTPases: Modulators of Innate Immunity

Most free-living organisms encode for a deoxyuridine triphosphate nucleotidohydrolase (dUTPase; EC 3.6.1.23). dUTPases represent a family of metalloenzymes that catalyze the hydrolysis of dUTP to dUMP and pyrophosphate, preventing dUTP from being incorporated into DNA by DNA polymerases, maintaining a low dUTP/dTTP pool ratio and providing a necessary precursor for dTTP biosynthesis. Thus, dUTPases are involved in maintaining genomic integrity by preventing the uracilation of DNA. Many DNA-containing viruses, which infect mammals also encode for a dUTPase. This review will summarize studies demonstrating that, in addition to their classical enzymatic activity, some dUTPases possess novel functions that modulate the host innate immune response.

Findings from Studies Are Congruent with Obesity Having a Viral Origin, but What about Obesity-Related NAFLD?

Infection has recently started receiving greater attention as an unusual causative/inducing factor of obesity. Indeed, the biological plausibility of infectobesity includes direct roles of some viruses to reprogram host metabolism toward a more lipogenic and adipogenic status. Furthermore, the probability that humans may exchange microbiota components (virome/virobiota) points out that the altered response of IFN and other cytokines, which surfaces as a central mechanism for adipogenesis and obesity-associated immune suppression, is due to the fact that gut microbiota uphold intrinsic IFN signaling. Last but not least, the adaptation of both host immune and metabolic system under persistent viral infections play a central role in these phenomena. We hereby discuss the possible link between adenovirus and obesity-related nonalcoholic fatty liver disease (NAFLD). The mechanisms of adenovirus-36 (Ad-36) involvement in hepatic steatosis/NAFLD consist in reducing leptin gene expression and insulin sensitivity, augmenting glucose uptake, activating the lipogenic and pro-inflammatory pathways in adipose tissue, and increasing the level of macrophage chemoattractant protein-1, all of these ultimately leading to chronic inflammation and altered lipid metabolism. Moreover, by reducing leptin expression and secretion Ad-36 may have in turn an obesogenic effect through increased food intake or decreased energy expenditure via altered fat metabolism. Finally, Ad-36 is involved in upregulation of cAMP, phosphatidylinositol 3-kinase, and p38 signaling pathways, downregulation of Wnt10b expression, increased expression of CCAAT/enhancer binding protein-beta, and peroxisome proliferator-activated receptor gamma 2 with consequential lipid accumulation.

Adenovirus-36 infection and obesity: A case control study of Turkish women with polycystic ovary syndrome

BACKGROUND AND AIMS

Adenovirus-36 (Ad-36) seropositivity has been shown to be involved in the aetiology of obesity. The aim of this study was to examine Ad-36 positivity in obese and normal-weight patients with polycystic ovary syndrome (PCOS).

METHODS

There were two groups including 92 and 110 subjects. This study was a prospective case-control study. The enzyme-immunoassay method was used to quantitatively determine antibodies (Abs) specific to human Ad-36 in the serum samples. Age, body mass index (BMI), fasting glucose levels and insulin levels of the participants were recorded. The PCOS and control group patients were divided into two groups: the overweight group with BMI ≥25 kg/m² and non-obese group with BMI <25 kg/m².

RESULTS

Ad-36 Ab positivity in the PCOS group was found to be significantly higher than that in the control group (p < 0.001). Ad-36 Ab positivity was significantly higher in the PCOS obese group than in the control obese group (p < 0.001). Ad-36 Ab positivity and BMI ≥25 kg/m² were identified as independent predictors of PCOS in logistic regression analysis.

CONCLUSION

Ad-36 Ab positivity was significantly higher in the obese/overweight PCOS patients. Obesity can be prevented in patients with PCOS by treating Ad-36.

Presence of Adenovirus-36 DNA in Adipose Tissue of Women: Relationship with Adipocyte Morphology and the Expression of C/EBPβ and HIF-1α

BACKGROUND

Human adenovirus 36 (HAd36) infection has been associated with obesity. Experiments using 3T3-L1 adipocyte cultured cells and human adipose stem cells (hASCc) have shown that HAd36 stimulates the expression of genes implicated in cell differentiation and increased lipid accumulation. The presence of HAd36 in adipose tissue of overweight and obese women has also been confirmed. This study aims to analyze the presence of HAd36 DNA in the adipose tissue of women undergoing surgery for weight reduction and its relationship with obesity through changes in adipocyte morphology as well as the expression of C/EBPβ and HIF-1α.

METHODS

Fifty-two subcutaneous adipose tissue biopsies were collected. The anthropometric parameters measured were weight, height, skin folds, body circumferences, and body fat percentage. Biochemical measures were performed for glucose, cholesterol, triglycerides, cholesterol HDL-c, and LDL-c. The presence of HAd36 DNA was performed by conventional PCR. Adipocyte morphology was analyzed in H&E-stained sections using ImageJ/Fiji software. The expression of genes C/EBPβ, HIF-1α and β-actin was determined using TaqMan probes.

RESULTS

HAd36 DNA was detected in 31% of adipose tissue samples. The presence of viral DNA was not significantly associated with anthropometric, clinical, or metabolic measurements, or with changes in adipose tissue morphology. The levels of mRNA expression for C/EBPβ and HIF-1α did not show significant differences between positive and negative samples for HAd36 (p>0.05).

CONCLUSION

The presence of HAd36 DNA in adipose tissue was identified, but it was not related to morphological changes of adipocytes, or the expression of C/EBPβ and HIF-1α. Further studies are needed to confirm these findings.

Adenovirus 36 prevalence and association with human obesity: a systematic review

INTRODUCTION

Obesity has numerous etiologies and includes biological factors. Studies have demonstrated that the human adenovirus subtype 36 (Adv36) is an adipogenic agent and causes metabolic alterations. Study results on the prevalence of Adv36 and clinical effects in humans vary substantially. This was a systematic review to summarize the studies on the prevalence of Adv36 infection and its association with human obesity.

METHODS

A systematic literature review was conducted using the preferred reporting items for systematic reviews and meta-analysis (PRISMA). Observational or experimental studies found in the Medline, Embase, LILACS, Science Direct and SciELO databases that presented results on the prevalence of Adv36 in humans were included.

RESULTS

Thirty-seven studies were screened. A total of 10,300 adults aged 18-70 years and 4585 children and adolescents aged 3-18 years were assessed. The average prevalence of Adv36 among adults was 22.9%, ranging from 5.5% to 49.8%. Among children and adolescents, the average prevalence of Adv36 was 28.9%, ranging from 7.5% to 73.9%. There was a positive statistical relationship between Adv36 and weight gain, obesity, or metabolic changes in 31 studies. However, in four studies there was no association with obesity, and in one, no association was described. One of the studies showed an inverse correlation, i.e., Adv36 was a protective factor against obesity.

CONCLUSION

Strong evidence suggested a positive association between viral infection and obesity. However, due to the multi-causality of obesity and heterogeneity of studies, diagnostic tests should be standardized and easily accessible by the population to estimate the overall prevalence of Adv36 infection and its association with obesity.

Characterization of the adipogenic protein E4orf1 from adenovirus 36 through an in silico approach

Adenovirus 36 (Ad-36) is related to human obesity due to its adipogenic activity mediated by the early 4 open reading frame 1 (E4orf1) protein. Mechanisms underlying the adipogenic effect of E4orf1 are not completely understood; however, the proliferation and differentiation of fat cells are increased through the activation of the phosphatidyl inositol 3 kinase pathway by binding proteins containing PDZ domain. This study characterized E4orf1 tridimensional structure and analyzed its interactions with PDZ domain-containing proteins in order to provide new information about the behavior of this viral protein and its targets, which could provide an interesting druggable target for obesity-related cardiometabolic alterations. In silico strategies such as homology modeling, docking, and molecular dynamics (MD) were used to study the interaction of E4orf1 with five PDZ domains of disk large homolog 1 (PDZ-1 and PDZ-2), membrane-associated guanylate kinase 1 (PDZ-3), and multi-PDZ domain protein 1 (PDZ-7 and PDZ-10). Mutagenesis analysis of selected residues was performed to evaluate their effects on the stabilization of E4orf1:PDZ complexes. MD simulations showed that the E4orf1:PDZ10 complex was more stable than the others ones. The highly hydrophobic residues at the C-terminal region (114-125) of the E4orf1 are essential in the initial phase stabilization of the complexes. Moreover, the residues 80-85 in the core region contribute to longer stabilization of the E4orf1:PDZ10 complex, a result that was confirmed by in silico mutagenesis. In conclusion, E4orf1 forms a stable complex with PDZ10 domain, and the residues 80-85 are of particular importance. The characterization of E4orf1 interactions with PDZ domains provides an initial approach to discover druggable targets for Ad-36-induced obesity.

E4orf1 protein reduces the need for endogenous insulin

Background

E4orf1 protein derived from adenovirus-36 reduces glucose excursion in mice, and lowers endogenous insulin response, suggesting a reduced need for insulin. We tested if the E4orf1-mediated lowering of insulin response is due to increased tissue sensitivity to insulin, reduced ability to produce or release insulin, or a reduced need for insulin release.

Methods

Experiment 1: hyperinsulinemic–euglycemic clamps (HEC) and glucose tolerance test (GTT) were performed in high fat fed transgenic mice expressing E4orf1 or non-transgenic littermates (n = 12 each), for 4 weeks. Experiments 2, 3, and 4: E4orf1 or null vectors were expressed in rat-pancreatic β-cell line (INS-1) for 72 h, and cells were exposed to varying levels of glucose. Cell lysates and media were collected. Experiment 5: 3T3L1-preadipocytes that express E4orf1 upon doxycycline induction, or null vector were induced with doxycycline and then exposed to protein transport inhibitor. Supernatant and cell lysate were collected. Experiment 6: 3T3L1-preadipocytes that express E4orf1 upon doxycycline induction, or null vector were co-cultured with INS-1 cells for 24 h. Media was collected.

Results

Experiment 1: E4orf1 transgenic mice cleared glucose faster compared to non-transgenic mice during GTT. HEC showed that E4orf1 did not alter tissue sensitivity to exogenous insulin in mice. Experiments 2, 3, and 4: in INS1 cells, E4orf1 did not alter Glut2 abundance or Akt activation, suggesting no reduction in glucose sensing or insulin synthesis, respectively. E4orf1 did not influence glucose-stimulated insulin secretion in media by INS1 cells. Experiment 5: E4orf1 was present in cell lysate, but not in media, indicating it is not a secretory protein. Experiment 6: INS1 cells released less insulin in media when co-cultured in the presence of E4orf1-expressing 3T3-L1 cells.

Conclusions

Our studies support the working hypothesis that the E4orf1-mediated lowering of insulin response is not due to increased tissue sensitivity to insulin, or reduced ability to produce or release insulin, but likely to be due to a reduced need for insulin release.

Twenty-five years of research about adipogenic adenoviruses: A systematic review

Infectious etiology is implicated in chronic diseases such as gastric ulcer or atherosclerosis. However, "infection" is a recent term in the field of obesity. Since the first report in 1982 of obesity due to infection, several microbes have been linked to obesity. Among the adipogenic microbes, avian adenovirus SMAM-1 and human adenovirus Ad36 have been studied most extensively for the past 25 years. Here, we present a systematic review of literature about SMAM-1 and Ad36. Reports from North America, Europe, and Asia reveal strong evidence that Ad36 causes obesity in animals and paradoxically improves glycemic control, and in vitro data provides mechanistic explanation. Considering that experimental Ad36 infection of humans is unlikely, its causative role in human obesity or glycemic control has not been demonstrated unequivocally. Nonetheless, most, but not all, observational studies in children and adults link Ad36 infection to obesity and improvement in glycemic control. The E4orf1 gene of Ad36 was identified as responsible for better glycemic control. Overall, 25 years have considerably advanced knowledge about the role of infection in obesity. Potential translational benefits include the development of vaccines to prevent Ad36-induced obesity and drug development based on the E4orf1 protein to improve glycemic control.

Adenovirus type 36 regulates adipose stem cell differentiation and glucolipid metabolism through the PI3K/Akt/FoxO1/PPARγ signaling pathway

Background

This study aims to investigate the molecular mechanism of Adenovirus type 36 (Ad36) in adipocyte differentiation and glucolipid metabolism.

Methods

Rat obesity model was established by Ad36 infection and high-fat diet, respectively. Comparison of the body weight, clinical biochemical indicators, insulin sensitivity and lipid heterotopic deposition between these two models was performed. Ad36-induced adipocyte in vitro model was also established. The binding rate of FoxO1, PPARγ and its target gene promoter was detected using ChIP. The mRNA and protein expression levels of PPARγ and downstream target genes were detected by RT-PCR and Western blot, respectively. Oil red O staining was used to measure differentiation into adipocyte. Wortmannin (WM), inhibitor of PI3K, was used to act on Ad36-induced hADSCs.

Results

Ad36-induced obese rats did not exhibit disorders in blood glucose and blood TG, insulin resistance and lipid ectopic deposition. The expression of Adipoq, Lpin1 and Glut4 in the adipose tissue increased. Oil red O staining showed that Ad36 induced the differentiation of hAMSCs into human adipocytes in vitro. During this process, the binding rate of FoxO1 and PPARγ promoter regions was weakened. However, the binding rate of the transcription factor PPARγ to its target genes Acc, Adipoq, Lpin1 and Glut4 was enhanced, and thus increased the protein expression of P-FoxO1, PPARγ2, ACC, LPIN1, GLUT4 and ADIPOQ. The PI3K inhibitor Wortmannin reduced the expression of P-Akt, P-FoxO1 and PPARγ2, thereby inhibiting adipogenesis of hADSC.

Conclusion

Ad36 may promote fatty acid and triglyceride synthesis, and improve insulin sensitivity by affecting the PI3K/Akt/FoxO1/PPARγ signaling pathway.

Adenovirus 5 produces obesity and adverse metabolic, morphological, and functional changes in the long term in animals fed a balanced diet or a high-fat diet: a study on hamsters

Adenovirus 5 (Ad-5) infection is a common cause of acute respiratory infections and the main vector used in gene therapy. There are few studies on the relationship of Ad-5 to obesity. In the present study, we evaluated the chronic effects of Ad-5 infection on golden (Syrian) hamsters fed either a balanced diet (BD) or a high-fat diet (HFD). After a single inoculation with Ad-5 (1 × 10⁷ pfu), the body weight of the animals was measured weekly. Medium-term (22 weeks) serum biochemical analyses and long-term (44 weeks) liver morphology, adiposity, and locomotive functionality (movement velocity) assessments were carried out. In the animals fed the BD, adenovirus infection produced hyperglycemia and hyperlipidemia. In the long term, it produced a 57% increase in epididymal pad fat and a 30% body weight gain compared with uninoculated animals. In addition, morphological changes related to non-alcoholic fatty liver disease (NAFLD) were observed. The animals fed the HFD had similar but more severe changes. In addition, the hamsters presented an obesity paradox: at the end of the study, the animals that had the most morphological and functional changes (significantly reduced movement velocity) had the lowest body weight. Despite the fact that an HFD appears to be a more harmful factor in the long term than adenovirus infection alone, infection could increase the severity of harmful effects in individuals with an HFD. Epidemiological studies are needed to evaluate the effect of adenovirus as a precursor of chronic liver and cardiovascular diseases, including the chronic effects of gene therapy.

Adenovirus 36 seropositivity is related to obesity risk, glycemic control, and leptin levels in Chilean subjects

BACKGROUND

Adenovirus 36 (Ad-36) has been associated to adiposity in animal and in vitro studies. Ad-36 seropositivity has also been reported to contribute to obesity risk in children and adult populations. We investigated the relationship of Ad-36 serology with obesity and metabolic parameters in a Chilean population.

SUBJECTS AND METHODS

Clinical and anthropometric data were obtained and blood samples were drawn from 99 lean (BMI: 18.5-24.9 kg/m²) and 151 obese (BMI > 30 kg/m²) subjects. Laboratory tests included lipid profile as well as glucose, insulin, leptin, and adiponectin levels. Ad-36 seropositivity was evaluated in serum samples by enzyme-linked immunosorbent assay.

RESULTS

Seroprevalence of Ad-36 was higher in the obese group (58%) than in lean controls (34%) demonstrating that individuals previously infected with Ad-36 have higher risk of obesity in the study population (OR: 2.67, 95%CI: 1.58-4.51, p < 0.001). Interestingly, Ad-36 was related to lower concentrations of triglycerides and VLDL cholesterol in lean subjects (p = 0.049) and lower leptin in obese individuals (p = 0.014). Previous Ad-36 infection was also related to lower glycemia, insulinemia, and HOMA-IR (p < 0.05) in obese subjects who were not under antidiabetic drugs.

CONCLUSIONS

Our results provide evidence of the contribution of previous Ad-36 infection to an increased risk of obesity in adult Chilean population. Ad-36 seropositivity was also associated to lipid profile, glycemic control, and leptin levels in adult Chilean population.

Bone Marrow Adipocyte Developmental Origin and Biology

PURPOSE OF REVIEW

This review explores how the relationships between bone marrow adipose tissue (BMAT) adipogenesis with advancing age, obesity, and/or bone diseases (osteopenia or osteoporosis) contribute to mechanisms underlying musculoskeletal pathophysiology.

RECENT FINDINGS

Recent studies have re-defined adipose tissue as a dynamic, vital organ with functions extending beyond its historic identity restricted solely to that of an energy reservoir or sink. "State of the art" methodologies provide novel insights into the developmental origin, physiology, and function of different adipose tissue depots. These include genetic tracking of adipose progenitors, viral vectors application, and sophisticated non-invasive imaging modalities. While constricted within the rigid bone cavity, BMAT vigorously contributes to local and systemic metabolic processes including hematopoiesis, osteogenesis, and energy metabolism and undergoes dynamic changes as a function of age, diet, bone topography, or sex. These insights will impact future research and therapies relating to osteoporosis.

Phenotype diffusion and one health: A proposed framework for investigating the plurality of obesity epidemics across many species

We propose the idea of "phenotype diffusion," which is a rapid convergence of an observed trait in some human and animal populations. The words phenotype and diffusion both imply observations independent of mechanism as phenotypes are observed traits with multiple possible genetic mechanisms and diffusion is an observed state of being widely distributed. Recognizing shared changes in phenotype in multiple species does not by itself reveal a particular mechanism such as a shared exposure, shared adaptive need, particular stochastic process or a transmission pathway. Instead, identifying phenotype diffusion suggests the mechanism should be explored to help illuminate the ways human and animal health are connected and new opportunities for optimizing these links. Using the plurality of obesity epidemics across multiple species as a prototype for shared changes in phenotype, the goal of this review was to explore eco-evolutionary theories that could inform further investigation. First, evolutionary changes described by hologenome evolution, pawnobe evolution, transposable element (TE) thrust and the drifty gene hypothesis will be discussed within the context of the selection asymmetries among human and animal populations. Secondly, the ecology of common source exposures (bovine milk, xenohormesis and "obesogens"), niche evolution and the hygiene hypothesis will be summarized. Finally, we synthesize these considerations. For example, many agricultural breeds have been aggressively selected for weight gain, microbiota (e.g., adenovirus 36, toxoplasmosis) associated with (or infecting) these breeds cause experimental weight gain in other animals, and these same microbes are associated with human obesity. We propose applications of phenotype diffusion could include zoonotic biosurveillance, biocontainment, antibiotic stewardship and environmental priorities. The One Health field is focused on the connections between the health of humans, animals and the environment, and so identification of phenotype diffusion is highly relevant for practitioners (public health officials, physicians and veterinarians) in this field.

Adenovirus Protein E4-ORF1 Activation of PI3 Kinase Reveals Differential Regulation of Downstream Effector Pathways in Adipocytes

Insulin activation of phosphatidylinositol 3-kinase (PI3K) regulates metabolism, including the translocation of the Glut4 glucose transporter to the plasma membrane and inactivation of the FoxO1 transcription factor. Adenoviral protein E4-ORF1 stimulates cellular glucose metabolism by mimicking growth-factor activation of PI3K. We have used E4-ORF1 as a tool to dissect PI3K-mediated signaling in adipocytes. E4-ORF1 activation of PI3K in adipocytes recapitulates insulin regulation of FoxO1 but not regulation of Glut4. This uncoupling of PI3K effects occurs despite E4-ORF1 activating PI3K and downstream signaling to levels achieved by insulin. Although E4-ORF1 does not fully recapitulate insulin's effects on Glut4, it enhances insulin-stimulated insertion of Glut4-containing vesicles to the plasma membrane independent of Rab10, a key regulator of Glut4 trafficking. E4-ORF1 also stimulates plasma membrane translocation of ubiquitously expressed Glut1 glucose transporter, an effect that is likely essential for E4-ORF1 to promote an anabolic metabolism in a broad range of cell types.

Mouse adenovirus type 1 infection of adipose tissue

Human adenovirus (HAdV) type 36 seropositivity has been linked to obesity in humans. That link is supported by a small number of studies using HAdV-36 infection of animals that are not natural hosts for HAdVs. In this study, we infected mice with mouse adenovirus type 1 (MAV-1), a mouse pathogen, to determine whether MAV-1 infected adipose tissue and was associated with adipose tissue inflammation and obesity. We detected MAV-1 in adipose tissue during acute MAV-1 infection, but we did not detect virus-induced increases in adipose tissue cytokine expression or histological evidence of adipose tissue inflammation during acute infection. MAV-1 did not persist in adipose tissue at later times, and we did not detect long-term adipose inflammation, increased adipose tissue mass, or body weight in infected mice. Our data indicate that MAV-1 is not associated with obesity in infected mice.

Blaming the Brain for Obesity: Integration of Hedonic and Homeostatic Mechanisms

The brain plays a key role in the controls of energy intake and expenditure, and many genes associated with obesity are expressed in the central nervous system. Technological and conceptual advances in both basic and clinical neurosciences have expanded the traditional view of homeostatic regulation of body weight by mainly the hypothalamus to include hedonic controls of appetite by cortical and subcortical brain areas processing external sensory information, reward, cognition, and executive functions. Hedonic controls interact with homeostatic controls to regulate body weight in a flexible and adaptive manner that takes environmental conditions into account. This new conceptual framework has several important implications for the treatment of obesity. Because much of this interactive neural processing is outside awareness, cognitive restraint in a world of plenty is made difficult and prevention and treatment of obesity should be more rationally directed to the complex and often redundant mechanisms underlying this interaction.

Metformin Is Associated With Higher Relative Abundance of Mucin-Degrading Akkermansia muciniphila and Several Short-Chain Fatty Acid-Producing Microbiota in the Gut

The global obesity epidemic, dubbed “globesity” by the World Health Organisation, is a pressing public health issue. The aetiology of obesity is multifactorial incorporating both genetic and environmental factors. Recently, epidemiological studies have observed an association between microbes and obesity. Obesity-promoting microbiome and resultant gut barrier disintegration have been implicated as key factors facilitating metabolic endotoxaemia. This is an influx of bacterial endotoxins into the systemic circulation, believed to underpin obesity pathogenesis. Adipocyte dysfunction and subsequent adipokine secretion characterised by low grade inflammation, were conventionally attributed to persistent hyperlipidaemia. They were thought of as pivotal in perpetuating obesity. It is now debated whether infection and endotoxaemia are also implicated in initiating and perpetuating low grade inflammation. The fact that obesity has a prevalence of over 600 million and serves as a risk factor for chronic diseases including cardiovascular disease and type 2 diabetes mellitus is testament to the importance of exploring the role of microbes in obesity pathobiology. It is on this basis that Massachusetts General Hospital is sponsoring the Faecal Microbiota Transplant for Obesity and Metabolism clinical trial, to study the impact of microbiome composition on weight. The association of microbes with obesity, namely, adenovirus infection and metabolic endotoxaemia, is reviewed.

E4orf1 Enhances Glucose Uptake Independent of Proximal Insulin Signaling

Impaired proximal insulin signaling is often present in diabetes. Hence, approaches to enhance glucose disposal independent of proximal insulin signaling are desirable. Evidence indicates that Adenovirus-derived E4orf1 protein may offer such an approach. This study determined if E4orf1 improves insulin sensitivity and downregulates proximal insulin signaling in vivo and enhances cellular glucose uptake independent of proximal insulin signaling in vitro. High fat fed mice were injected with a retrovirus plasmid expressing E4orf1, or a null vector. E4orf1 significantly improved insulin sensitivity in response to a glucose load. Yet, their proximal insulin signaling in fat depots was impaired, as indicated by reduced tyrosine phosphorylation of insulin receptor (IR), and significantly increased abundance of ectonucleotide pyrophosphatase/phosphodiesterase-1 (ENPP1). In 3T3-L1 pre-adipocytes E4orf1 expression impaired proximal insulin signaling. Whereas, treatment with rosiglitazone reduced ENPP1 abundance. Unaffected by IR-KD (insulin receptor knockdown) with siRNA, E4orf1 significantly up-regulated distal insulin signaling pathway and enhanced cellular glucose uptake. In vivo, E4orf1 impairs proximal insulin signaling in fat depots yet improves glycemic control. This is probably explained by the ability of E4orf1 to promote cellular glucose uptake independent of proximal insulin signaling. E4orf1 may provide a therapeutic template to enhance glucose disposal in the presence of impaired proximal insulin signaling.

Infectobesity: the evaluation of adenovirus-36 infection and obesity

Obesity, which causes some cancer types and other diseases, is not only a global public health problem, but also a factor that affects country's economy. Endocrinal, environmental, neuronal and genetic factors have important roles on the etiology of obesity. When the possibility that SMAM‐1 animal virus could have a relationship with obesity was observed, obesity studies focused on human adenoviruses. Adenovirus‐36 was first isolated in 1978 and was the first human adenovirus to be tested in terms of infectobesity. Both in vivo and in vitro studies proved the strong relationship between adenovirus‐36 presence and obesity. Therefore, a large-scale study incorporating various ethnicities and age groups is required to investigate the worldwide epidemic of obesity and its links with viruses.

An adenovirus-derived protein: A novel candidate for anti-diabetic drug development

AIMS

Exposure to human adenovirus Ad36 is causatively and correlatively linked with better glycemic control in animals and humans, respectively. Although the anti-hyperglycemic property of Ad36 may offer some therapeutic potential, it is impractical to use an infectious agent for therapeutic benefit. Cell-based studies identified that Ad36 enhances cellular glucose disposal via its E4orf1 protein. Ability to improve glycemic control in vivo is a critical prerequisite for further investigating the therapeutic potential of E4orf1. Therefore, the aim of this study was to determine the ability of E4orf1 to improve glycemic control independent of insulin despite high fat diet.

MATERIALS & METHODS

8-9wk old male C57BL/6J mice fed a high-fat diet (60% kcal) were injected with a retrovirus plasmid expressing E4orf1, or a null vector (Control). Glycemic control was determined by glucose and insulin tolerance test. Islet cell size, amount of insulin and glucagon were determined in formalin-fixed pancreas. Rat insulinoma cell line (832/13) was infected with E4orf1 or control to determine changes in glucose stimulated insulin secretion. Protein from flash frozen adipose tissue depots, liver and muscle was used to determine molecular signaling by western blotting.

RESULTS

In multiple experiments, retrovirus-mediated E4orf1 expression in C57BL/6J mice significantly and reproducibly improved glucose excursion following a glucose load despite a high fat diet (60% energy). Importantly, E4orf1 improved glucose clearance without increasing insulin sensitivity, production or secretion, underscoring its insulin-independent effect. E4orf1 modulated molecular signaling in mice tissue, which included greater protein abundance of adiponectin, p-AKT and Glucose transporter Glu4.

CONCLUSIONS

This study provides the proof of concept for translational development of E4orf1 as a potential anti-diabetic agent. High fat intake and impaired insulin signaling are often associated with obesity, diabetes and insulin resistance. Hence, the ability of E4orf1 to improve glycemic control despite high fat diet and independent of insulin, is particularly attractive.

Obesity and Infection: Reciprocal Causality

Associations between different infectious agents and obesity have been reported in humans for over thirty years. In many cases, as in nosocomial infections, this relationship reflects the greater susceptibility of obese individuals to infection due to impaired immunity. In such cases, the infection is not related to obesity as a causal factor but represents a complication of obesity. In contrast, several infections have been suggested as potential causal factors in human obesity. However, evidence of a causal linkage to human obesity has only been provided for adenovirus 36 (Adv36). This virus activates lipogenic and proinflammatory pathways in adipose tissue, improves insulin sensitivity, lipid profile and hepatic steatosis. The E4orf1 gene of Adv36 exerts insulin senzitizing effects, but is devoid of its pro-inflammatory modalities. The development of a vaccine to prevent Adv36-induced obesity or the use of E4orf1 as a ligand for novel antidiabetic drugs could open new horizons in the prophylaxis and treatment of obesity and diabetes. More experimental and clinical studies are needed to elucidate the mutual relations between infection and obesity, identify additional infectious agents causing human obesity, as well as define the conditions that predispose obese individuals to specific infections.

The role of Ad-36 as a risk factor in males with gynecomastia

Gynecomastia is highly prevalent worldwide and Adenovirus-36 (Ad-36), recently implicated in increased adipose tissue deposition due to its affinity for adipose tissue, is a potential etiological agent in the development of obesity and therefore we hypothesized that Ad-36 may also play a role in the development of gynecomastia by possibly accompanying increased regional adiposity. To support our hypothesis, we conducted a study that included 33 adult males with gynecomastia (PG) and 15 adult males as the patient control group (HCG). Leptin and adiponectin levels were monitored using ELISA. A significant difference in Ad-36 antibody positivity was found between the groups (p<0.05). Average leptin levels were found to be higher, but average adiponectin levels were found to be lower in Ad-36 Ab(+) patient group. No Ad-36 DNA was detected in any tissue samples. In conclusion, we hypothesize that low-grade chronic inflammation, which was caused by Ad-36 infection, possibly caused an increase in circulating leptin. This in turn may have caused an increase in local or circulating estrogens and/or the estrogen/androgen ratio by stimulating the aromatase enzyme activity in adipose stromal cells and breast tissues. We suggest that gynecomastia may develop following an increase in aromatase enzyme activity, by which more oestrogen is produced and the estrogen-androgen balance disrupted. Also, regional adipose tissue enlargements may cause the excessive production of estrogens leading to gynecomastia. Adipose tissue has been recognized as a major endocrine organ in recent years. Another plausible explanation is excessive aromatization of androgens to estrogens by peripheral adipose tissue may promote gynecomastia in males. Moreover, our results suggest that there might be a relationship between Ad-36 and gynecomastia.

Characteristics of adipose tissue macrophages and macrophage-derived insulin-like growth factor-1 in virus-induced obesity

BACKGROUND

Various pathogens are implicated in the induction of obesity. Previous studies have confirmed that human adenovirus 36 (Ad36) is associated with increased adiposity, improved glycemic control and induction of inflammation. The Ad36-induced inflammation is reflected in the infiltration of macrophages into adipose tissue. However, the characteristics and role of adipose tissue macrophages (ATMs) and macrophage-secreted factors in virus-induced obesity (VIO) are unclear. Although insulin-like growth factor-1 (IGF-1) is involved in obesity metabolism, the contribution of IGF secreted by macrophages in VIO has not been studied.

METHODS

Four-week-old male mice were studied 1 week and 12 weeks after Ad36 infection for determining the characteristics of ATMs in VIO and diet-induced obesity (DIO). In addition, macrophage-specific IGF-1-deficient (MIKO) mice were used to study the involvement of IGF-1 in VIO.

RESULTS

In the early stage of VIO (1 week after Ad36 infection), the M1 ATM sub-population increased, which increased the M1/M2 ratio, whereas DIO did not cause this change. In the late stage of VIO (12 weeks after Ad36 infection), the M1/M2 ratio did not change because the M1 and M2 ATM sub-populations increased to a similar extent, despite an increase in adiposity. By contrast, DIO increased the M1/M2 ratio. In addition, VIO in wild-type mice upregulated angiogenesis in adipose tissue and improved glycemic control. However, MIKO mice showed no increase in adiposity, angiogenesis, infiltration of macrophages into adipose tissue, or improvement in glycemic control after Ad36 infection.

CONCLUSIONS

These data suggest that IGF-1 secreted by macrophages may contribute to hyperplasia and hypertrophy in adipose tissue by increasing angiogenesis, which helps to maintain the 'adipose tissue robustness'.

Role of adenoviruses in obesity

Five human adenovirus subtypes, Ad5, Ad9, Ad31, Ad36, and Ad37, and a non-human adenovirus, SMAM1, are linked to increased adiposity in vitro or in vivo. Experimental infection with Ad5, Ad36, and Ad37 produced excess adiposity or weight gain in animals. Ad9 and Ad31 increase fat storage in tissue culture but are not associated with animal or human obesity. Ad36 is the most extensively studied adipogenic adenovirus and is correlated with some measure of overweight/obesity in humans from multiple countries. The correlation is strongest and most consistent in children, but some studies have been negative in both children and adults. About 30% of overweight/obese children and adults and about 15-20% of lean individuals have Ad36 antibodies in epidemiologic studies. The mechanisms of action of Ad36 are due to the early gene 4, open reading frame 1 (E4-ORF1). Blocking E4-ORF1 with siRNA prevents the effects of Ad36, and transfection of lentivirus with E4-ORF1 reproduces the Ad36 effects. Increased adiposity is caused by stimulation of at least three pathways by Ad36. Cell membrane glucose receptors are increased via the Ras pathway, leading to increased intracellular glucose. Fatty acid synthase is increased, which converts the glucose to fatty acids. Finally, peroxisome proliferator-activated receptor-γ is increased, resulting in differentiation of adult stem cells into adipocytes.

CONCLUSIONS

several adenoviruses increase adiposity in animals and are associated with obesity in humans. There are critical gaps in the literature needing further investigation including evaluation of other adenovirus subtypes and better research designs to improve the strength of causal inferences.

Adenovirus E4-ORF1 Dysregulates Epidermal Growth Factor and Insulin/Insulin-Like Growth Factor Receptors To Mediate Constitutive Myc Expression

The E4-ORF1 protein encoded by human adenovirus stimulates viral replication in human epithelial cells by binding and activating cellular phosphatidylinositol 3-kinase (PI3K) at the plasma membrane and cellular Myc in the nucleus. In this study, we showed that E4-ORF1 hijacks the tyrosine kinase activities of cellular epidermal growth factor receptor (EGFR) and insulin receptor (InsR)/insulin-like growth factor receptor 1 (IGF1R), as well as the lipid kinase activity of PI3K, to mediate constitutive Myc protein expression. We additionally demonstrated that EGFR contributes to constitutive Myc expression through the capacity of E4-ORF1 to induce ligand-independent EGFR activation and stimulation of the Ras/Mek/Erk pathway, the latter activity of which was conserved by human adenoviruses. Results further suggested that EGFR normally forms a complex with the cellular PDZ protein Discs Large 1 (Dlg1), a component of the Dlg1:E4-ORF1:PI3K ternary complex that mediates E4-ORF1-induced PI3K activation, and that E4-ORF1 binds the Dlg1:EGFR complex and promotes the association of EGFR with InsR and IGF1R. In addition to its role in constitutive Myc expression, InsR/IGF1R also negatively regulates EGFR autophosphorylation and EGFR-mediated Ras/Mek/Erk signaling, and data suggested that E4-ORF1 binding to Dlg1 antagonizes these activities. Collectively, our findings suggest that in human epithelial cells, E4-ORF1 targets EGFR, InsR/IGF1R, and PI3K at the plasma membrane to activate cytosolic signaling pathways that sustain Myc protein levels in the nucleus. We postulate that E4-ORF1-induced constitutive Myc expression functions to ensure the formation of nuclear E4-ORF1:Myc complexes, which have been shown to activate Myc and to enhance adenovirus replication.

IMPORTANCE

While human adenoviruses primarily produce self-limited acute infections in humans, these agents are associated with life-threatening diseases in immunocompromised patients and in otherwise healthy individuals infected with certain virulent serotypes. The adenovirus E4-ORF1 protein enhances viral replication by activating the cellular lipid kinase PI3K and the cellular transcription factor Myc. Here we report that E4-ORF1 usurps the functions of the cellular tyrosine kinase receptors EGFR and InsR /: IGF1R, as well as PI3K, to sustain Myc protein expression in cells. Furthermore, sustained Myc expression depended on E4-ORF1-induced ligand-independent EGFR activation that stimulated Ras/Mek/Erk signaling, a function found to be conserved by human adenoviruses. Given the established roles of PI3K, the Ras/Mek/Erk pathway, and Myc in the adenovirus life cycle, our findings may aid in the development of safer, more effective therapeutic strategies to treat severe adenovirus infections as well as improved adenovirus vectors for use in vaccination and gene and cancer therapy.

Adenovirus 36 and Obesity: An Overview

There is an epidemic of obesity starting about 1980 in both developed and undeveloped countries definitely associated with multiple etiologies. About 670 million people worldwide are obese. The incidence of obesity has increased in all age groups, including children. Obesity causes numerous diseases and the interaction between genetic, metabolic, social, cultural and environmental factors are possible cofactors for the development of obesity. Evidence emerging over the last 20 years supports the hypothesis that viral infections may be associated with obesity in animals and humans. The most widely studied infectious agent possibly linked to obesity is adenovirus 36 (Adv36). Adv36 causes obesity in animals. In humans, Adv36 associates with obesity both in adults and children and the prevalence of Adv36 increases in relation to the body mass index. In vivo and in vitro studies have shown that the viral E4orf1 protein (early region 4 open reading frame 1, Adv) mediates the Adv36 effect including its adipogenic potential. The Adv36 infection should therefore be considered as a possible risk factor for obesity and could be a potential new therapeutic target in addition to an original way to understand the worldwide rise of the epidemic of obesity. Here, the data indicating a possible link between viral infection and obesity with a particular emphasis to the Adv36 will be reviewed.

The relationship between adenovirus-36 seropositivity, obesity and metabolic profile in Turkish children and adults

Obesity potentially arising from viral infection is known as 'infectobesity'. The latest reports suggest that adenovirus-36 (Adv36) is related to obesity in adults and children. Our aim was not only to determine the Adv36 seropositivity in both obese and non-obese children and adults, but also to investigate correlations between antibody positivity and serum lipid profiles. Both Adv36 positivity and tumour-necrosis-factor-alpha, leptin and interleukin-6 levels were detected in blood samples collected from 146 children and 130 adults by ELISA. Fasting plasma triglycerides, total cholesterol and low-density lipoprotein levels were also measured. Adv36 positivity was determined to be 27·1% and 6% in obese and non-obese children and 17·5% and 4% in obese and non-obese adults, respectively. There was no difference with regard to total cholesterol, low-density lipoprotein, triglyceride, tumour-necrosis-factor-alpha and interleukin-6 levels (P > 0·05). However, there was a significant difference between groups in terms of leptin levels (P < 0·05). We determined the prevalence of Adv36 positivity in obese children and adults. Our results showed that Adv36 may be an obesity agent for both adults and children, parallel with current literature data. However, the available data on a possible relationship between Adv36 infection and obesity both in children and adults do not completely solve the problem.

The role of adenovirus 36 as a risk factor in obesity: the first clinical study made in the fatty tissues of adults in Turkey

Obesity which developes due to multifactorial reasons, was associated recently with human Adenovirus-36 (Ad-36). The aim of this study was to investigate the prevalence of Ad-36 antibodies in obese adults and also to investigate the DNA of Ad-36 in their adipose tissue. In this cross-sectional and case-control based study, 49 obese adults, with BMI ≥ 30 kg/m(2), and 49 non-obese adults, with BMI ≤ 25 kg/m(2), applied for esthetic purposes and were included in this study as patient and control groups, respectively. Adipose tissue samples, obtained by the lipoaspiration method, were studied by single-step PCR and nested-PCR methods. Simultaneously, the presence of Ad-36 antibodies and serum leptin and adiponectin levels were assessed by serum neutralization assay (SNA) and ELISA, respectively. Serum samples which didn't cause a cytopathic effect at ≥ 1:8 were accepted as positive. Ad-36 antibody was detected in 6 (12.2%) of 49 patients by SNA and was statistically significant (p < 0.05). Ad-36 DNA was not detected in any of the adipose tissue samples of the patient or control groups. Mean BMI and leptin levels were higher in the Ad-36-positive group, while adiponectin levels were found to be lower in the Ad-36-positive group. Although no statistically significant difference was found in cholesterol and triglyceride levels between the two groups (p > 0.05), lower mean serum cholesterol and triglyceride levels were found in the Ad-36-positive patients. In conclusion, we couldn't detect Ad-36 DNA in adipose tissue; however, we detected significantly higher Ad-36 antibody levels in the obese group compared to the non-obese group, according to the both univariant and multivariant analyses, suggesting that Ad-36 may play a role in obesity. There is a need for new and extended serial, particularly cohort and human-based, studies in order to have a clear understanding of the Ad-36-obesity relationship.

Human adenovirus-36 is uncommon in type 2 diabetes and is associated with increased insulin sensitivity in adults in Sweden

BACKGROUND

Human adenovirus-36 (Adv36) increases adiposity, but also upregulates distal insulin signaling in vitro in human adipose and muscle tissue and in vivo in the rodent independently of adiposity. Accordingly, healthy adults and children with antibodies against Adv36 had increased insulin sensitivity and reduced hepatic lipid accumulation. We hypothesized that Adv36 infection would be less frequent in individuals with type 2 diabetes or impaired glycemic control.

METHODS

Presence of antibodies against Adv36 was analyzed for association to type 2 diabetes or impaired glycemic control in a two-wave population-based sample of well-characterized adults (n = 1734). Indices of impaired glycemic control included oral glucose tolerance, and circulating fasting levels of glucose, insulin, and insulin-like growth factor binding protein-1 (IGFBP-1).

RESULTS

Adv36 seropositivity was more common in those with normal glucose tolerance (NGT) than in those with diabetes (females: OR 17.2, 95% CI 4.0-74.3; males: OR 3.5, 95% CI 1.8-6.7). Also, females with NGT had higher frequency of Adv36 seropositivity than females with prediabetes (impaired glucose tolerance and/or impaired fasting glucose; OR 1.8, 95% CI 1.1-3.1). Within the female prediabetes group Adv36 seropositivity was associated with higher insulin sensitivity reflected by reduced HOMA-IR and increased IGFBP-1.

CONCLUSION

Adv36 infection is associated with lower occurrence of type 2 diabetes and better insulin sensitivity in adults, particularly among females.

Human herpesviruses-encoded dUTPases: a family of proteins that modulate dendritic cell function and innate immunity

We have previously shown that Epstein-Barr virus (EBV)-encoded dUTPase can modulate innate immune responses through the activation of TLR2 and NF-κB signaling. However, whether this novel immune function of the dUTPase is specific for EBV or a common property of the Herpesviridae family is not known. In this study, we demonstrate that the purified viral dUTPases encoded by herpes simplex virus type 2 (HSV-2), human herpesvirus-6A (HHV-6A), human herpesvirus-8 (HHV-8) and varicella-zoster virus (VZV) differentially activate NF-κB through ligation of TLR2/TLR1 heterodimers. Furthermore, activation of NF-κB by the viral dUTPases was inhibited by anti-TLR2 blocking antibodies (Abs) and the over-expression of dominant-negative constructs of TLR2, lacking the TIR domain, and MyD88 in human embryonic kidney 293 cells expressing TLR2/TLR1. In addition, treatment of human dendritic cells and PBMCs with the herpesviruses-encoded dUTPases from HSV-2, HHV-6A, HHV-8, and VZV resulted in the secretion of the inflammatory cytokines IL-1β, IL-6, IL-8, IL-12, TNF-α, IL-10, and IFN-γ. Interestingly, blocking experiments revealed that the anti-TLR2 Ab significantly reduced the secretion of cytokines by the various herpesviruses-encoded dUTPases (p < 0.05). To our knowledge, this is the first report demonstrating that a non-structural protein encoded by herpesviruses HHV-6A, HHV-8, VZV and to a lesser extent HSV-2 is a pathogen-associated molecular pattern. Our results reveal a novel function of the virus-encoded dUTPases, which may be important to the pathophysiology of diseases caused by these viruses. More importantly, this study demonstrates that the immunomodulatory functions of dUTPases are a common property of the Herpesviridae family and thus, the dUTPase could be a potential target for the development of novel therapeutic agents against infections caused by these herpesviruses.

Adenovirus36 infection expresses cellular APMI and Visfatin genes in overweight Uygur individuals

Objective

This study is to determine if Adenovirus type 36 (Ad36) infection is related to macrophage infiltration in the obese group and non-obese group and the related molecular mechanisms.

Methods

Ninety obesity patients and 95 non-obesity Uygur individuals were enrolled in this study. CD68 levels in abdominal subcutaneous and omental adipose tissues were detected by immunohistochemistry. The cytokine expression levels of adiponectin (APMI) and visfatin in serum were measured by enzyme-linked immunosorbent assay. Infection of 3T3-L1 cells with Ad36 was performed. Real-time PCR was performed to determine expression levels of APMI and Visfatin genes in the 3T3-L1 preadipocytes infected with Ad36.

Results

In the obese individuals infected with Ad36, the expression levels of adiponectin and visfatin in serum was elevated. For the individuals infected with Ad36, the macrophage infiltration (as indicated by CD68 level) in the obese group was also significantly higher than that in the non-obese group (P < 0.05) in both abdominal subcutaneous and omental adipose tissues. The real-time PCR results indicated that APMI mRNA levels and Visfatin mRNA levels in Ad36 infected cells were significantly increased.

Conclusions

Ad36 infection may be a factor related with macrophage infiltration in adipose tissues of the obese patients. The APMI and Visfatin genes may be involved in the mechanism underlying the effect of Ad36 infection on the obese patients.

Virtual Slides

The virtual slide(s) for this article can be found here: http://www.diagnosticpathology.diagnomx.eu/vs/1849614638119816

Serological data analyses show that adenovirus 36 infection is associated with obesity: a meta-analysis involving 5739 subjects

OBJECTIVE

Serological studies on the relationship between adenovirus 36 (Ad36) and an increased risk of obesity development have shown conflicting results. We reviewed the published studies and carried out a meta-analysis to explore this relationship.

METHODS

PubMed was searched until December 2012 for the relative references with sufficient information to estimate odds ratios (ORs) and 95% confidence intervals (CIs). A total of 11 case-control studies, including 2508 obese subjects and 3005 controls, were selected.

RESULTS

Compared with nonobese controls, Ad36 infection significantly increased the obesity risk by a pooled OR of 1.60 (95% CI = 1.14-2.25; P < 0.01). Meta-regression showed that the types of subject and obesity assessments were potential risk factors. In the subgroup analysis, a significantly increased risk was found in children (OR = 1.95; 95% CI = 1.34-2.85; z = 3.45; P < 0.01) and those with an obesity assessment of BMI ≥ 30 kg/cm2 (OR = 1.89; 95% CI = 1.15-3.10; P < 0.05).

CONCLUSIONS

Ad36 infection is associated with an increased risk of obesity development. To our knowledge, this is the first report to reveal the significant relationship in children with a serological data analysis.

Harnessing the beneficial properties of adipogenic microbes for improving human health

Obesity is associated with numerous metabolic comorbidities. Weight loss is an effective measure for alleviating many of these metabolic abnormalities. However, considering the limited success of most medical weight-management approaches in producing a sustained weight loss, approaches that improve obesity-related metabolic abnormalities independent of weight loss would be extremely attractive and of practical benefit. Metabolically healthy obesity supports the notion that a better metabolic profile is possible despite obesity. Moreover, adequate expansion of adipose tissue appears to confer protection from obesity-induced metabolic comorbidities. To this end, the 10th Stock conference examined new approaches to improve metabolic comorbidities independent of weight loss. In particular, human adenovirus 36 (Ad36) and specific gut microbes were examined for their potential to influence lipid and glucose homeostasis in animals and humans. While these microbes possess some undesirable properties, research has identified attributes of adenovirus Ad36 and gut microbes that may be selectively harnessed to improve metabolic profile without the obligatory weight loss. Furthermore, identifying the host signalling pathways that these microbes recruit to improve the metabolic profile may offer new templates and targets, which may facilitate the development of novel treatment strategies for obesity-related metabolic conditions.

Doxycycline-regulated 3T3-L1 preadipocyte cell line with inducible, stable expression of adenoviral E4orf1 gene: a cell model to study insulin-independent glucose disposal

Impaired glycemic control and excessive adiposity are major risk factors for Type 2 Diabetes mellitus. In rodent models, Ad36, a human adenovirus, improves glycemic control, independent of dietary fat intake or adiposity. It is impractical to use Ad36 for therapeutic action. Instead, we identified that E4orf1 protein of Ad36, mediates its anti-hyperglycemic action independent of insulin signaling. To further evaluate the therapeutic potential of E4orf1 to improve glycemic control, we established a stable 3T3-L1 cell system in which E4orf1 expression can be regulated. The development and characterization of this cell line is described here. Full-length adenoviral-36 E4orf1 cDNA obtained by PCR was cloned into a tetracycline responsive element containing vector (pTRE-Tight-E4orf1). Upon screening dozens of pTRE-Tight-E4orf1 clones, we identified the one with the highest expression of E4orf1 in response to doxycycline treatment. Furthermore, using this inducible system we characterized the ability of E4orf1 to improve glucose disposal in a time dependent manner. This stable cell line offers a valuable resource to carefully study the novel signaling pathways E4orf1 uses to enhance cellular glucose disposal independent of insulin.

Insulin sparing action of adenovirus 36 and its E4orf1 protein

Additional drugs are required to effectively manage diabetes and its complications. Recent studies have revealed protective effects of Ad36, a human adenovirus, and its E4orf1 protein on glucose disposal, which may be creatively harnessed to develop novel anti-diabetic agents. Experimental Ad36 infection improves hyperglycemia in animal models and natural Ad36 infection in humans is associated with better glycemic control. Available data indicate distinctive advantages for a drug that may mimic the action of Ad36/E4orf1. The key features of such a potential drug include the ability to increase glucose uptake by adipose tissue and skeletal muscle, to reduce hepatic glucose output independent of proximal insulin signaling, and to up-regulate adiponectin and its hepatic action. The effect of Ad36/E4orf1 on hepatocyte metabolism suggests a role for treating hepatic steatosis. Despite these potential advantages, considerable research is required before such a drug is developed. The in vivo efficacy and safety of E4orf1 in improving hyperglycemia remain unknown, and an appropriate drug delivery system is required. Nonetheless, Ad36 E4orf1 offers a research opportunity to develop a new anti-diabetic agent with multiple potential advantages and conceptually advances the use of a rather unconventional source, microbial proteins, for anti-diabetic drug development.

Adenovirus-36 is associated with obesity in children and adults in Sweden as determined by rapid ELISA

BACKGROUND

Experimental and natural human adenovirus-36 (Adv36) infection of multiple animal species results in obesity through increasing adipogenesis and lipid accumulation in adipocytes. Presence of Adv36 antibodies detected by serum neutralization assay has previously been associated with obesity in children and adults living in the USA, South Korea and Italy, whereas no association with adult obesity was detected in Belgium/The Netherlands nor among USA military personnel. Adv36 infection has also been shown to reduce blood lipid levels, increase glucose uptake by adipose tissue and skeletal muscle biopsies, and to associate with improved glycemic control in non-diabetic individuals.

PRINCIPAL FINDINGS

Using a novel ELISA, 1946 clinically well-characterized individuals including 424 children and 1522 non-diabetic adults, and 89 anonymous blood donors, residing in central Sweden representing the population in Stockholm area, were studied for the presence of antibodies against Adv36 in serum. The prevalence of Adv36 positivity in lean individuals increased from ∼7% in 1992-1998 to 15-20% in 2002-2009, which paralleled the increase in obesity prevalence. We found that Adv36-positive serology was associated with pediatric obesity and with severe obesity in females compared to lean and overweight/mildly obese individuals, with a 1.5 to 2-fold Adv36 positivity increase in cases. Moreover, Adv36 positivity was less common among females and males on antilipid pharmacological treatment or with high blood triglyceride level. Insulin sensitivity, measured as lower HOMA-IR, showed a higher point estimate in Adv36-positive obese females and males, although it was not statistically significant (p = 0.08).

CONCLUSION

Using a novel ELISA we show that Adv36 infection is associated with pediatric obesity, severe obesity in adult females and lower risk of high blood lipid levels in non-diabetic Swedish individuals.

Adenovirus 36 as an obesity agent maintains the obesity state by increasing MCP-1 and inducing inflammation

BACKGROUND

Although it is well known that adenovirus 36 (Ad36) is associated with obesity in humans as well as in animals, the detailed cellular mechanism is unclear.

METHODS

Wild-type (WT) mice and monocyte chemoattractant protein-1 knockout (MCP-1(-/-)) mice were infected with Ad36, and their weights and inflammatory status were measured. Macrophage infiltration was examined in their reproductive fat pads and in a coculture system. The correlation between Ad36 antibody presence and MCP-1 levels was tested in human samples.

RESULTS

We have shown that Ad36 infection stimulated an inflammatory state by increasing the level of MCP-1 through the activation of nuclear factor κB, which in turn induced the infiltration of macrophages into adipocytes. This induced inflammation resulted in viral obesity, which caused chronic inflammation and affected lipid metabolism. In contrast to WT mice, MCP-1(-/-) mice were protected from Ad36-induced inflammation and obesity. The MCP-1 levels in Ad36-antibody-positive human group were higher than those in the antibody-negative group.

CONCLUSIONS

These findings support the proposition that virus-induced inflammation is the cellular mechanism underlying Ad36-induced obesity. These results also suggest that MCP-1 plays a critical role in Ad36-induced obesity and that MCP-1 may be a therapeutic target in preventing virus-induced obesity.