Adenovirus 36 attenuates weight loss from exercise but improves glycemic control by increasing mitochondrial activity in the liver

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.

Modulating effect of vitamin D status on serum anti-adenovirus 36 antibody amount in children with obesity: National Food and Nutrition Surveillance

Background

The association of ADV-36 infection and obesity has been reported in children.

The objective of this study was to examine the hypothesis that the association between ADV-36 infection and adiposity may be mediated by sub-optimal vitamin D status of the host.

Methods

Ninety one apparently healthy children in different weight categories (normal weight: 33, overweight: 33, obesity: 25) aged 5–18 years were randomly selected from the registered population at National Food and Nutrition Surveillance Program (NFNS). The groups were matched based on age and sex. Anthropometric, biochemical and serological assessments were performed.

Results

The amount of anti-ADV36-Ab increased whereas circulating concentrations of 25(OH) D decreased across BMI categories with higher amounts in children with normal weight than in children with overweight and obesity (31.0 ± 16.4, 22.5 ± 10.5 and 21.9 ± 9.8 nmol/L, respectively, p = 0.004). Logistic regression analysis revealed that for each unit increment of anti-ADV36-Ab, the chance of increase in weight was 8.5 times (OR: 8.5, p = 0.029). Interestingly, when 25(OH) D was introduced into the model, anti-ADV36-Ab was no longer the predictor of weight increment and the chance of increase in weight reduced 5% for each unit increase in 25(OH) D concentration (OR: 0.95, p = 0.012).

Conclusion

It is suggested that ADV36-induced lipogenesis may be mediated by vitamin D deficiency in children with obesity.

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.

High adenovirus 36 seroprevalence among a population of Hispanic American youth

Infection with adenovirus 36 (Ad36) has been associated with risk of obesity in youth in some studies, but the seroprevalence of this virus has not been examined among all populations. As Hispanic-American youth are of greater risk for obesity than other American youth, we sought to determine the proportion of Ad36 seropositive (Ad36+) students in an urban middle school serving a Hispanic population. We further examined if Ad36+ students were more likely to have obesity, and if Ad36 serostatus impacted changes in weight status following a health intervention. We determined body mass index (BMI) at the beginning and end of a 16-week health intervention among 40 Hispanic-American middle-school students. Ad36 serostatus was determined by enzyme-linked immunsorbent assay (ELISA). Seventy percent of the students were Ad36+. Ad36+ and Ad36 seronegative (Ad36-) did not differ before or after the intervention in body weight measures. The odds of being classified as obese was 1.4 times greater among Ad36+ than Ad36- at baseline, and 2.4 times greater post-intervention, but these were not statistically significant. We report a high seroprevalence of Ad36 among a population of Hispanic-American students. Ad36 seropositivity was associated with a trend for a greater likelihood of having obesity, but did not impact response to a health intervention.

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.

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.

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.

E4orf1 induction in adipose tissue promotes insulin-independent signaling in the adipocyte

Background/Purpose

Type 2 diabetes remains a worldwide epidemic with major pathophysiological changes as a result of chronic insulin resistance. Insulin regulates numerous biochemical pathways related to carbohydrate and lipid metabolism.

Methods

We have generated a novel mouse model that allows us to constitutively activate, in an inducible fashion, the distal branch of the insulin signaling transduction pathway specifically in adipocytes.

Results

Using the adenoviral 36 E4orf1 protein, we chronically stimulate locally the Ras-ERK-MAPK signaling pathway. At the whole body level, this leads to reduced body-weight gain under a high fat diet challenge. Despite overlapping glucose tolerance curves, there is a reduced requirement for insulin action under these conditions. The mice further exhibit reduced circulating adiponectin levels that ultimately lead to impaired lipid clearance, and inflamed and fibrotic white adipose tissues. Nevertheless, they are protected from diet-induced hepatic steatosis. As we observe constitutively elevated p-Akt levels in the adipocytes, even under conditions of low insulin levels, this pinpoints enhanced Ras-ERK-MAPK signaling in transgenic adipocytes as a potential alternative route to bypass proximal insulin signaling events.

Conclusion

We conclude that E4orf1 expression in the adipocyte leads to enhanced baseline activation of the distal insulin signaling node, yet impaired insulin receptor stimulation in the presence of insulin, with important implications for the regulation of adiponectin secretion. The resulting systemic phenotype is complex, yet highlights the powerful nature of manipulating selective branches of the insulin signaling network within the adipocyte.

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Inducible activation of the distal branch of the insulin pathway in adipocytes.

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Insulin-sparing characteristics during glucose tolerance testing.

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Chronic activation of the distal Ras-ERK-MAPK signaling pathway.

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Reduced body-weight during metabolic challenge.

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Preserved carbohydrate metabolism at the expense of lipid metabolism.

Targeting species D adenoviruses replication to counteract the epidemic keratoconjunctivitis

Human adenoviruses are non-enveloped DNA viruses causing various infections; their pathogenicity varies dependent on virus species and type. Although acute infections can sometimes take severe courses, they are rarely fatal in immune-competent individuals. Adenoviral conjunctivitis and epidemic keratoconjunctivitis are hyperacute and highly contagious infections of the eye caused by human adenovirus types within species D. Currently there is no causal treatment available to counteract these diseases effectively. The E2B region of the adenovirus genome encodes for the viral DNA polymerase, which is required for adenoviral DNA replication. Here we propose novel model systems to test this viral key factor, DNA polymerase, as a putative target for the development of efficient antiviral therapy based on RNA interference. Using our model cell lines we found that different small interfering RNAs mediate significant suppression (up to 90%) of expression levels of viral DNA polymerase upon transfection. Moreover, permanent expression of short hairpin RNA based on the most effective small interfering RNA led to a highly significant, more than tenfold reduction in replication for different human group D adenoviruses involved in ocular infections.