Translation-dependent and -independent mRNA decay occur through mutually exclusive pathways defined by ribosome density during T cell activation.

mRNA translation and decay are tightly interconnected processes both in the context of mRNA quality-control pathways and for the degradation of functional mRNAs. Cotranslational mRNA degradation through codon usage, ribosome collisions, and the recruitment of specific proteins to ribosomes is an important determinant of mRNA turnover. However, the extent to which translation-dependent mRNA decay (TDD) and translation-independent mRNA decay (TID) pathways participate in the degradation of mRNAs has not been studied yet. Here we describe a comprehensive analysis of basal and signal-induced TDD and TID in mouse primary CD4+ T cells. Our results indicate that most cellular transcripts are decayed to some extent in a translation-dependent manner. Our analysis further identifies the length of untranslated regions, the density of ribosomes, and GC3 content as important determinants of TDD magnitude. Consistently, all transcripts that undergo changes in ribosome density within their coding sequence upon T cell activation display a corresponding change in their TDD level. Moreover, we reveal a dynamic modulation in the relationship between GC3 content and TDD upon T cell activation, with a reversal in the impact of GC3- and AU3-rich codons. Altogether, our data show a strong and dynamic interconnection between mRNA translation and decay in mammalian primary cells.

The DEAD box RNA helicase DDX42 is an intrinsic inhibitor of positive-strand RNA viruses.

Genome-wide screens are powerful approaches to unravel regulators of viral infections. Here, a CRISPR screen identifies the RNA helicase DDX42 as an intrinsic antiviral inhibitor of HIV-1. Depletion of endogenous DDX42 increases HIV-1 DNA accumulation and infection in cell lines and primary cells. DDX42 overexpression inhibits HIV-1 infection, whereas expression of a dominant-negative mutant increases infection. Importantly, DDX42 also restricts LINE-1 retrotransposition and infection with other retroviruses and positive-strand RNA viruses, including CHIKV and SARS-CoV-2. However, DDX42 does not impact the replication of several negative-strand RNA viruses, arguing against an unspecific effect on target cells, which is confirmed by RNA-seq analysis. Proximity ligation assays show DDX42 in the vicinity of viral elements, and cross-linking RNA immunoprecipitation confirms a specific interaction of DDX42 with RNAs from sensitive viruses. Moreover, recombinant DDX42 inhibits HIV-1 reverse transcription in vitro. Together, our data strongly suggest a direct mode of action of DDX42 on viral ribonucleoprotein complexes. Our results identify DDX42 as an intrinsic viral inhibitor, opening new perspectives to target the life cycle of numerous RNA viruses.

Low-dose food contaminants trigger sex-specific, hepatic metabolic changes in the progeny of obese mice.

Environmental contaminants are suspected to be involved in the epidemic incidence of metabolic disorders, food ingestion being a primarily route of exposure. We hypothesized that life-long consumption of a high-fat diet that contains low doses of pollutants will aggravate metabolic disorders induced by obesity itself. Mice were challenged from preconception throughout life with a high-fat diet containing pollutants commonly present in food (2,3,7,8-tetrachlorodibenzo-p-dioxin, polychlorinated biphenyl 153, diethylhexyl phthalate, and bisphenol A), added at low doses in the tolerable daily intake range. We measured several blood parameters, glucose and insulin tolerance, hepatic lipid accumulation, and gene expression in adult mice. Pollutant-exposed mice exhibited significant sex-dependent metabolic disorders in the absence of toxicity and weight gain. In males, pollutants increased the expression of hepatic genes (from 36 to 88%) encoding proteins related to cholesterol biosynthesis and decreased (40%) hepatic total cholesterol levels. In females, there was a marked deterioration of glucose tolerance, which may be related to the 2-fold induction of estrogen sulfotransferase and reduced expression of estrogen receptor α (25%) and estrogen target genes (>34%). Because of the very low doses of pollutants used in the mixture, these findings may have strong implications in terms of understanding the potential role of environmental contaminants in food in the development of metabolic diseases.

Stable structures or PABP1 loading protects cellular and viral RNAs against ISG20-mediated decay.

ISG20 is an IFN-induced 3'-5' RNA exonuclease that acts as a broad antiviral factor. At present, the features that expose RNA to ISG20 remain unclear, although recent studies have pointed to the modulatory role of epitranscriptomic modifications in the susceptibility of target RNAs to ISG20. These findings raise the question as to how cellular RNAs, on which these modifications are abundant, cope with ISG20. To obtain an unbiased perspective on this topic, we used RNA-seq and biochemical assays to identify elements that regulate the behavior of RNAs against ISG20. RNA-seq analyses not only indicate a general preservation of the cell transcriptome, but they also highlight a small, but detectable, decrease in the levels of histone mRNAs. Contrarily to all other cellular ones, histone mRNAs are non-polyadenylated and possess a short stem-loop at their 3' end, prompting us to examine the relationship between these features and ISG20 degradation. The results we have obtained indicate that poly(A)-binding protein loading on the RNA 3' tail provides a primal protection against ISG20, easily explaining the overall protection of cellular mRNAs observed by RNA-seq. Terminal stem-loop RNA structures have been associated with ISG20 protection before. Here, we re-examined this question and found that the balance between resistance and susceptibility to ISG20 depends on their thermodynamic stability. These results shed new light on the complex interplay that regulates the susceptibility of different classes of viruses against ISG20.

Cortical inflammation and brain signs of high-risk atherosclerosis in a non-human primate model.

Atherosclerosis is a chronic systemic inflammatory disease, inducing cardiovascular and cerebrovascular acute events. A role of neuroinflammation is suspected, but not yet investigated in the gyrencephalic brain and the related activity at blood-brain interfaces is unknown. A non-human primate model of advanced atherosclerosis was first established using longitudinal blood samples, multimodal imaging and gene analysis in aged animals. Non-human primate carotid lesions were compared with human carotid endarterectomy samples. During the whole-body imaging session, imaging of neuroinflammation and choroid plexus function was performed. Advanced plaques were present in multiple sites, premature deaths occurred and downstream lesions (myocardial fibrosis, lacunar stroke) were present in this model. Vascular lesions were similar to in humans: high plaque activity on PET and MRI imaging and systemic inflammation (high plasma C-reactive protein levels: 42 ± 14 µg/ml). We also found the same gene association (metabolic, inflammatory and anti-inflammatory markers) as in patients with similar histological features. Metabolic imaging localized abnormal brain glucose metabolism in the frontal cortex. It corresponded to cortical neuro-inflammation (PET imaging) that correlated with C-reactive protein level. Multimodal imaging also revealed pronounced choroid plexus function impairment in aging atherosclerotic non-human primates. In conclusion, multimodal whole-body inflammation exploration at the vascular level and blood-brain interfaces identified high-risk aging atherosclerosis. These results open the way for systemic and central inflammation targeting in atherosclerosis in the new era of immunotherapy.

Evidence for estrogeno-mimetic effects of a mixture of low-dose pollutants in a model of ovariectomized mice.

We recently hypothesized that a mixture of low-dosed dioxin, polychlorobiphenyl, phthalate and bisphenol may induce estrogeno-mimetic activities in a model of lifelong-exposed female mice. Herein, we evaluated the impact of this mixture in estrogen deficiency conditions. Based on the protective effects of estrogens against metabolic disorders, we reasoned that exposure to pollutants should attenuate the deleterious metabolic effects induced by ovariectomy. In line with the hypothesis, exposure to pollutants was found to reduce the impact of ovariectomy on glucose intolerance and insulin resistance, to enhance the expression levels of the hepatic estrogen receptor α and to attenuate the ovariectomy-induced enhancement of the chemokine MCP-1/CCL2 considered as an indicator of estrogen signalling. Because of the very low doses of pollutants used in mixture, these findings may have strong implications in terms of understanding the potential role of environmental contaminants in the development of metabolic diseases, specifically in females during menopausal transition.

Endocrine disrupting chemicals in mixture and obesity, diabetes and related metabolic disorders.

Obesity and associated metabolic disorders represent a major societal challenge in health and quality of life with large psychological consequences in addition to physical disabilities. They are also one of the leading causes of morbidity and mortality. Although, different etiologic factors including excessive food intake and reduced physical activity have been well identified, they cannot explain the kinetics of epidemic evolution of obesity and diabetes with prevalence rates reaching pandemic proportions. Interestingly, convincing data have shown that environmental pollutants, specifically those endowed with endocrine disrupting activities, could contribute to the etiology of these multifactorial metabolic disorders. Within this review, we will recapitulate characteristics of endocrine disruption. We will demonstrate that metabolic disorders could originate from endocrine disruption with a particular focus on convincing data from the literature. Eventually, we will present how handling an original mouse model of chronic exposition to a mixture of pollutants allowed demonstrating that a mixture of pollutants each at doses beyond their active dose could induce substantial deleterious effects on several metabolic end-points. This proof-of-concept study, as well as other studies on mixtures of pollutants, stresses the needs for revisiting the current threshold model used in risk assessment which does not take into account potential effects of mixtures containing pollutants at environmental doses, e.g., the real life exposure. Certainly, more studies are necessary to better determine the nature of the chemicals to which humans are exposed and at which level, and their health impact. As well, research studies on substitute products are essential to identify harmless molecules.

Low-dose pollutant mixture triggers metabolic disturbances in female mice leading to common and specific features as compared to a high-fat diet.

Environmental pollutants are potential etiologic factors of obesity and diabetes that reach epidemic proportions worldwide. However, it is important to determine if pollutants could exert metabolic defects without directly inducing obesity. The metabolic disturbances triggered in nonobese mice lifelong exposed to a mixture of low-dose pollutants (2,3,7,8-tetrachlorodibenzo-p-dioxine, polychlorinated biphenyl 153, diethylhexyl-phthalate, and bisphenol A) were compared with changes provoked by a high-fat high-sucrose (HFHS) diet not containing the pollutant mixture. Interestingly, females exposed to pollutants exhibited modifications in lipid homeostasis including a significant increase of hepatic triglycerides but also distinct features from those observed in diet-induced obese mice. For example, they did not gain weight nor was glucose tolerance impacted. To get more insight, a transcriptomic analysis was performed in liver for comparison. We observed that in addition to the xenobiotic/drug metabolism pathway, analysis of the hepatic signature illustrated that the steroid/cholesterol, fatty acid/lipid and circadian clock metabolic pathways were targeted in response to pollutants as observed in the diet-induced obese mice. However, the specific sets of dysregulated annotated genes (>1300) did not overlap more than 40% between both challenges with some genes specifically altered only in response to pollutant exposure. Collectively, results show that pollutants and HFHS affect common metabolic pathways, but by different, albeit overlapping, mechanisms. This is highly relevant for understanding the synergistic effects between pollutants and the obesogenic diet reported in the literature.

Metabolic outcome of female mice exposed to a mixture of low-dose pollutants in a diet-induced obesity model.

Pollutants are suspected to contribute to the etiology of obesity and related metabolic disorders. Apart from occupational exposure which concerns a subset of chemicals, humans are mostly exposed to a large variety of chemicals, all life-long and at low doses. Food ingestion is a major route of exposure and it is suggested that pollutants have a worsened impact when combined with a high-fat diet. In the experimental studies described herein, we aimed to add further evidence on the metabolic impact of food pollutants using a recently set up model in which mice are life-long fed a high-fat/high-sucrose diet (HFSD) with/without common food pollutants shown to exhibit metabolic disrupting activities. Specifically, this mixture comprised bisphenol A, dioxin, polychlorobiphenyl PCB153, and phthalate and was added in HFSD at doses resulting in mice exposure at the Tolerable Daily Intake dose range for each pollutant. We herein focused on the 7-week-old females which exhibited early signs of obesity upon HFSD feeding. We observed no signs of toxicity and no additional weight gain following exposure to the mixture but alleviated HFSD-induced glucose intolerance in the absence of alteration of gluconeogenesis and steatosis. It suggested that the observed metabolic improvement was more likely due to effects on muscle and/or adipose tissues rather than on the liver. Consistently, female mice exhibited enhanced lean/fat mass ratio and skeletal muscle insulin sensitivity. Moreover, expression levels of inflammatory markers were reduced in adipose tissue at 7 but enhanced at 12 weeks of age in agreement with the inverse alterations of glucose tolerance observed at these ages upon pollutant exposure in the HFSD-fed females. Collectively, these data suggest apparent biphasic effects of pollutants upon HFSD feeding along with obesity development. These effects were not observed in males and may depend on interactions between diet and pollutants.