Mechanisms of circadian clock interactions with aryl hydrocarbon receptor signalling

Transcriptomic analysis of AHR wildtype and Knock-out rat livers supports TCDD's role in AHR/ARNT-mediated circadian disruption and hepatotoxicity

Single, high doses of TCDD in rats are known to cause wasting, a progressive loss of 30 to 50% body weight and death within several weeks. To identify pathway perturbations at or near doses causing wasting, we examined differentially gene expression (DGE) and pathway enrichment in centrilobular (CL) and periportal (PP) regions of female rat livers following 6 dose levels of TCDD - 0, 3, 22, 100, 300, and 1000 ng/kg/day, 5 days/week for 4 weeks. At the higher doses, rats lost weight, had increased liver/body weight ratios and nearly complete cessation of liver cell proliferation, signs consistent with wasting. DGE curves were left shifted for the CL versus the PP regions. Canonical Phase I and Phase II genes were maximally increased at lower doses and remained elevated at all doses. At lower doses, ≤ 22 ng/kg/day in the CL and ≤ 100 ng/kg/day, upregulated genes showed transcription factor (TF) enrichment for AHR and ARNT. At the mid- and high-dose doses, there was a large number of downregulated genes and pathway enrichment for DEGs which showed downregulation of many cellular metabolism processes including those for steroids, fatty acid metabolism, pyruvate metabolism and citric acid cycle. There was significant TF enrichment of the hi-dose downregulated genes for RXR, ESR1, LXR, PPARalpha. At the highest dose, there was also pathway enrichment with upregulated genes for extracellular matrix organization, collagen formation, hemostasis and innate immune system. TCDD demonstrates most of its effects through binding the aryl hydrocarbon receptor (AHR) while the downregulation of metabolism genes at higher TCDD doses is known to be independent of AHR binding to DREs. Based on our results with DEG, we provide a hypothesis for wasting in which high doses of TCDD shift circadian processes away from the resting state, leading to greatly reduced synthesis of steroids and complex lipids needed for cell growth, and producing gene expression signals consistent with an epithelial-to-mesenchymal transition in hepatocytes.

Bipolar disorder and the gut microbiota: a bibliometric analysis

Background

Previous studies have explored the relationship between bipolar disorder and gut microbiota. However, there has been no bibliometric analysis to summarize and analyze these publications. Our objective was to perform a bibliometric analysis to investigate the current status and frontiers of the publications in the field of the association between bipolar disorder and the gut microbiota.

Methods

We retrieved publications concerning the interplay between the gut microbiota and bipolar disorder from the Web of Science Core Collection (WoSCC). The analysis was executed using WoSCC's literature analysis tool and VOSviewer 1.6.16.

Results

In total, we identified 177 publications originating from 362 institutions across 39 countries/regions, and these articles were disseminated in 104 different journals. The most productive institutions, authors, countries/regions, and journals were Zhejiang University contributing 18 publications, Shaohua Hu authoring 12 publications, China with 53 publications, and Frontiers in Psychiatry with 11 publications. The first high-cited document was published in the Journal of Psychiatric Research in 2017, and authored by Evans. In this article, they found gut microbiome composition was associated with BD and its illness severity, and they concluded that targeting the gut microbiota may be helpful to develop the effective treatment for bipolar disorder. The top 5 keywords with the highest frequency except for bipolar disorder and gut microbiota were as follows: depression, inflammation, probiotic, gut-brain axis, and anxiety.

Conclusion

In conclusion, this is the first bibliometric analysis to explore the publications in the field of the association between bipolar disorder and the gut microbiota. The main research hotspots regarding this field were the characteristics, abundance, and diversity of gut microbiome in bipolar disorder, the role of treatment and gut microbiome in bipolar disorder, microbiome-brain connections in bipolar disorder, and interventions for bipolar disorder based on microbiota composition modification. The number of studies about the association between gut microbiota and bipolar disorder is relatively small, and more studies are needed to expand our understanding the association between gut microbiota and bipolar disorder.

The role of circadian clock in regulating cell functions: implications for diseases

The circadian clock system orchestrates daily behavioral and physiological rhythms, facilitating adaptation to environmental and internal oscillations. Disruptions in circadian rhythms have been linked to increased susceptibility to various diseases and can exacerbate existing conditions. This review delves into the intricate regulation of diurnal gene expression and cell function by circadian clocks across diverse tissues. . Specifically, we explore the rhythmicity of gene expressions, behaviors, and functions in both immune and non-immune cells, elucidating the regulatory effects and mechanisms imposed by circadian clocks. A detailed discussion is centered on elucidating the complex functions of circadian clocks in regulating key cellular signaling pathways. We further review the circadian regulation in diverse diseases, with a focus on inflammatory diseases, cancers, and systemic diseases. By highlighting the intimate interplay between circadian clocks and diseases, especially through clock-controlled cell function, this review contributes to the development of novel disease intervention strategies. This enhanced understanding holds significant promise for the design of targeted therapies that can exploit the circadian regulation mechanisms for improved treatment efficacy.

Aryl hydrocarbon receptor activation alters immune cell populations in the lung and bone marrow during coronavirus infection

Respiratory viral infections are one of the major causes of illness and death worldwide. Symptoms associated with respiratory infections can range from mild to severe, and there is limited understanding of why there is large variation in severity. Environmental exposures are a potential causative factor. The aryl hydrocarbon receptor (AHR) is an environment-sensing molecule expressed in all immune cells. Although there is considerable evidence that AHR signaling influences immune responses to other immune challenges, including respiratory pathogens, less is known about the impact of AHR signaling on immune responses during coronavirus (CoV) infection. In this study, we report that AHR activation significantly altered immune cells in the lungs and bone marrow of mice infected with a mouse CoV. AHR activation transiently reduced the frequency of multiple cells in the mononuclear phagocyte system, including monocytes, interstitial macrophages, and dendritic cells in the lung. In the bone marrow, AHR activation altered myelopoiesis, as evidenced by a reduction in granulocyte-monocyte progenitor cells and an increased frequency of myeloid-biased progenitor cells. Moreover, AHR activation significantly affected multiple stages of the megakaryocyte lineage. Overall, these findings indicate that AHR activation modulates multiple aspects of the immune response to a CoV infection. Given the significant burden of respiratory viruses on human health, understanding how environmental exposures shape immune responses to infection advances our knowledge of factors that contribute to variability in disease severity and provides insight into novel approaches to prevent or treat disease.NEW & NOTEWORTHY Our study reveals a multifaceted role for aryl hydrocarbon receptor (AHR) signaling in the immune response to coronavirus (CoV) infection. Sustained AHR activation during in vivo mouse CoV infection altered the frequency of mature immune cells in the lung and modulated emergency hematopoiesis, specifically myelopoiesis and megakaryopoiesis, in bone marrow. This provides new insight into immunoregulation by the AHR and extends our understanding of how environmental exposures can impact host responses to respiratory viral infections.

Circadian rhythm regulation in the sea cucumber Apostichopus japonicus: Insights into clock gene expression, photoperiod susceptibility, and neurohormone signaling

Sea cucumber Apostichopus japonicus displays the typical circadian rhythms. This present study investigated the molecular regulation of clock genes, as well as monoamines and melatonin, in multiple tissues of A. japonicus, responding to the photoperiod. In order to determine their pivotal role in circadian rhythms, the crucial clock genes, namely AjClock, AjArnt1, AjCry1, and AjTimeless, were identified and a comprehensive analysis of their expressions across various tissues in adult A. japonicus was conducted, revealing the potential existence of central and peripheral oscillators. Results demonstrated that the tissues of polian vesicle and nerve ring exhibited significant clock gene expression associated with the orchestration of circadian regulation, and that environmental light fluctuations exerted influence on the expression of these clock genes. However, a number of genes, such as AjArnt1 and AjCry1, maintained their circadian rhythmicity even under continuous light conditions. Moreover, we further investigated the circadian patterns of melatonin (MT), serotonin (5-HT), and dopamine (DA) secretion in A. japonicus, data that underscored the tissue-specific regulatory differences and the inherent adaptability to dynamic light environments. Collectively, these findings will provide the molecular mechanisms controlling the circadian rhythm in echinoderms and the candidate tissues playing the role of central oscillators in sea cucumbers.

The Role of the Gut Microbiome in Bipolar Disorder and its Common Comorbidities

Bipolar disorder is a decidedly heterogeneous and multifactorial disease, with significant psychosocial and medical disease burden. Much difficulty has been encountered in developing novel therapeutics and objective biomarkers for clinical use in this population. In that regard, gut-microbial homeostasis appears to modulate several key pathways relevant to a variety of psychiatric, metabolic, and inflammatory disorders. Microbial impact on immune, endocrine, endocannabinoid, kynurenine, and other pathways are discussed throughout this review. Emphasis is placed on this system's relevance to current pharmacology, diet, and comorbid illness in bipolar disorder. Despite the high level of optimism promoted in many reviews on this topic, substantial obstacles exist before any microbiome-related findings can provide meaningful clinical utility. Beyond a comprehensive overview of pathophysiology, this review hopes to highlight several key areas where progress is needed. As well, novel microbiome-associated suggestions are presented for future research.

Aryl hydrocarbon receptor (AhR) impairs circadian regulation: impact on the aging process

Circadian clocks control the internal sleep-wake rhythmicity of 24hours which is synchronized by the solar cycle. Circadian regulation of metabolism evolved about 2.5 billion years ago, i.e., the rhythmicity has been conserved from cyanobacteria and Archaea through to mammals although the mechanisms utilized have developed with evolution. While the aryl hydrocarbon receptor (AhR) is an evolutionarily conserved defence mechanism against environmental threats, it has gained many novel functions during evolution, such as the regulation of cell cycle, proteostasis, and many immune functions. There is robust evidence that AhR signaling impairs circadian rhythmicity, e.g., by interacting with the core BMAL1/CLOCK complex and disturbing the epigenetic regulation of clock genes. The maintenance of circadian rhythms is impaired with aging, disturbing metabolism and many important functions in aged organisms. Interestingly, it is known that AhR signaling promotes an age-related tissue degeneration, e.g., it is able to inhibit autophagy, enhance cellular senescence, and disrupt extracellular matrix. These alterations are rather similar to those induced by a long-term impairment of circadian rhythms. However, it is not known whether AhR signaling enhances the aging process by impairing circadian homeostasis. I will examine the experimental evidence indicating that AhR signaling is able to promote the age-related degeneration via a disruption of circadian rhythmicity.

Activation of aryl hydrocarbon receptor (AhR) in Alzheimer's disease: role of tryptophan metabolites generated by gut host-microbiota

Gut microbiota in interaction with intestinal host tissues influences many brain functions and microbial dysbiosis has been linked with brain disorders, such as neuropsychiatric conditions and Alzheimer's disease (AD). L-tryptophan metabolites and short-chained fatty acids (SCFA) are major messengers in the microbiota-brain axis. Aryl hydrocarbon receptors (AhR) are main targets of tryptophan metabolites in brain microvessels which possess an enriched expression of AhR protein. The Ah receptor is an evolutionarily conserved, ligand-activated transcription factor which is not only a sensor of xenobiotic toxins but also a pleiotropic regulator of both developmental processes and age-related tissue degeneration. Major microbiota-produced tryptophan metabolites involve indole derivatives, e.g., indole 3-pyruvic acid, indole 3-acetaldehyde, and indoxyl sulfate, whereas indoleamine and tryptophan 2,3-dioxygenases (IDO/TDO) of intestine host cells activate the kynurenine (KYN) pathway generating KYN metabolites, many of which are activators of AhR signaling. Chronic kidney disease (CKD) increases the serum level of indoxyl sulfate which promotes AD pathogenesis, e.g., it disrupts integrity of blood-brain barrier (BBB) and impairs cognitive functions. Activation of AhR signaling disturbs vascular homeostasis in brain; (i) it controls blood flow via the renin-angiotensin system, (ii) it inactivates endothelial nitric oxide synthase (eNOS), thus impairing NO production and vasodilatation, and (iii) it induces oxidative stress, stimulates inflammation, promotes cellular senescence, and enhances calcification of vascular walls. All these alterations are evident in cerebral amyloid angiopathy (CAA) in AD pathology. Moreover, AhR signaling can disturb circadian regulation and probably affect glymphatic flow. It seems plausible that dysbiosis of gut microbiota impairs the integrity of BBB via the activation of AhR signaling and thus aggravates AD pathology. KEY MESSAGES: Dysbiosis of gut microbiota is associated with dementia and Alzheimer's disease. Tryptophan metabolites are major messengers from the gut host-microbiota to brain. Tryptophan metabolites activate aryl hydrocarbon receptor (AhR) signaling in brain. The expression of AhR protein is enriched in brain microvessels and blood-brain barrier. Tryptophan metabolites disturb brain vascular integrity via AhR signaling. Dysbiosis of gut microbiota promotes inflammation and AD pathology via AhR signaling.

Evolutive emergence and divergence of an Ig regulatory node: An environmental sensor getting cues from the aryl hydrocarbon receptor?

One gene, the immunoglobulin heavy chain (IgH) gene, is responsible for the expression of all the different antibody isotypes. Transcriptional regulation of the IgH gene is complex and involves several regulatory elements including a large element at the 3' end of the IgH gene locus (3'RR). Animal models have demonstrated an essential role of the 3'RR in the ability of B cells to express high affinity antibodies and to express different antibody classes. Additionally, environmental chemicals such as aryl hydrocarbon receptor (AhR) ligands modulate mouse 3'RR activity that mirrors the effects of these chemicals on antibody production and immunocompetence in mouse models. Although first discovered as a mediator of the toxicity induced by the high affinity ligand 2,3,7,8-tetracholordibenzo-p-dioxin (dioxin), understanding of the AhR has expanded to a physiological role in preserving homeostasis and maintaining immunocompetence. We posit that the AhR also plays a role in human antibody production and that the 3'RR is not only an IgH regulatory node but also an environmental sensor receiving signals through intrinsic and extrinsic pathways, including the AhR. This review will 1) highlight the emerging role of the AhR as a key transducer between environmental signals and altered immune function; 2) examine the current state of knowledge regarding IgH gene regulation and the role of the AhR in modulation of Ig production; 3) describe the evolution of the IgH gene that resulted in species and population differences; and 4) explore the evidence supporting the environmental sensing capacity of the 3'RR and the AhR as a transducer of these cues. This review will also underscore the need for studies focused on human models due to the premise that understanding genetic differences in the human population and the signaling pathways that converge at the 3'RR will provide valuable insight into individual sensitivities to environmental factors and antibody-mediated disease conditions, including emerging infections such as SARS-CoV-2.

Functions of the aryl hydrocarbon receptor (AHR) beyond the canonical AHR/ARNT signaling pathway

The aryl hydrocarbon receptor (AHR) is a ligand-dependent transcription factor regulating adaptive and maladaptive responses toward exogenous and endogenous signals. Research from various biomedical disciplines has provided compelling evidence that the AHR is critically involved in the pathogenesis of a variety of diseases and disorders, including autoimmunity, inflammatory diseases, endocrine disruption, premature aging and cancer. Accordingly, AHR is considered an attractive target for the development of novel preventive and therapeutic measures. However, the ligand-based targeting of AHR is considerably complicated by the fact that the receptor does not always follow the beaten track, i.e. the canonical AHR/ARNT signaling pathway. Instead, AHR might team up with other transcription factors and signaling molecules to shape gene expression patterns and associated physiological or pathophysiological functions in a ligand-, cell- and micromilieu-dependent manner. Herein, we provide an overview about some of the most important non-canonical functions of AHR, including crosstalk with major signaling pathways involved in controlling cell fate and function, immune responses, adaptation to low oxygen levels and oxidative stress, ubiquitination and proteasomal degradation. Further research on these diverse and exciting yet often ambivalent facets of AHR biology is urgently needed in order to exploit the full potential of AHR modulation for disease prevention and treatment.

Aryl hydrocarbon receptor affects circadian-regulated lipolysis through an E-Box-dependent mechanism

An internal circadian clock regulates timing of systemic energy homeostasis. The central clock in the hypothalamic suprachiasmatic nucleus (SCN) directs local clocks in peripheral tissues such as liver, muscle, and adipose tissue to synchronize metabolism with food intake and rest/activity cycles. Aryl hydrocarbon receptor (AhR) interacts with the molecular circadian clockworks. Activation of AhR dampens rhythmic expression of core clock genes, which may lead to metabolic dysfunction. Given the importance of appropriately-timed adipose tissue function to regulation of energy homeostasis, this study focused on mechanisms by which AhR may influence clock-controlled adipose tissue activity. We hypothesized that AhR activation in adipose tissue would impair lipolysis by dampening adipose rhythms, leading to a decreased lipolysis rate during fasting, and subsequently, altered serum glucose concentrations. Levels of clock gene and lipolysis gene transcripts in mouse mesenchymal stem cells (BMSCs) differentiated into mature adipocytes were suppressed by the AhR agonist β-napthoflavone (BNF), in an AhR dependent manner. BNF altered rhythms of core clock gene and lipolysis gene transcripts in C57bl6/J mice. BNF reduced serum free fatty acids, glycerol and liver glycogen. Chromatin immunoprecipitation indicated that BNF increased binding of AhR to E-Box elements in clock gene and lipolysis gene promoters. These data establish a link between AhR activation and impaired lipolysis, specifically by altering adipose tissue rhythmicity. In response to the decreased available energy from impaired lipolysis, the body increases glycogenolysis, thereby degrading more glycogen to provide necessary energy.

Gene fusions, micro-exons and splice variants define stress signaling by AP2/ERF and WRKY transcription factors in the sesame pan-genome

Evolutionary dynamics of AP2/ERF and WRKY genes, the major components of defense response were studied extensively in the sesame pan-genome. Massive variation was observed for gene copy numbers, genome location, domain structure, exon-intron structure and protein parameters. In the pan-genome, 63% of AP2/ERF members were devoid of introns whereas >99% of WRKY genes contained multiple introns. AP2 subfamily was found to be micro-exon rich with the adjoining intronic sequences sharing sequence similarity to many stress-responsive and fatty acid metabolism genes. WRKY family included extensive multi-domain gene fusions where the additional domains significantly enhanced gene and exonic sizes as well as gene copy numbers. The fusion genes were found to have roles in acquired immunity, stress response, cell and membrane integrity as well as ROS signaling. The individual genomes shared extensive synteny and collinearity although ecological adaptation was evident among the Chinese and Indian accessions. Significant positive selection effects were noticed for both micro-exon and multi-domain genes. Splice variants with changes in acceptor, donor and branch sites were common and 6-7 splice variants were detected per gene. The study ascertained vital roles of lipid metabolism and chlorophyll biosynthesis in the defense response and stress signaling pathways. 60% of the studied genes localized in the nucleus while 20% preferred chloroplast. Unique cis-element distribution was noticed in the upstream promoter region with MYB and STRE in WRKY genes while MYC was present in the AP2/ERF genes. Intron-less genes exhibited great diversity in the promoter sequences wherein the predominance of dosage effect indicated variable gene expression levels. Mimicking the NBS-LRR genes, a chloroplast localized WRKY gene, Swetha_24868, with additional domains of chorismate mutase, cAMP and voltage-dependent potassium channel was found to act as a master regulator of defense signaling, triggering immunity and reducing ROS levels.

Tryptophan metabolism is a physiological integrator regulating circadian rhythms

OBJECTIVE

The circadian clock aligns physiology with the 24-hour rotation of Earth. Light and food are the main environmental cues (zeitgebers) regulating circadian rhythms in mammals. Yet, little is known about the interaction between specific dietary components and light in coordinating circadian homeostasis. Herein, we focused on the role of essential amino acids.

METHODS

Mice were fed diets depleted of specific essential amino acids and their behavioral rhythms were monitored and tryptophan was selected for downstream analyses. The role of tryptophan metabolism in modulating circadian homeostasis was studied using isotope tracing as well as transcriptomic- and metabolomic- analyses.

RESULTS

Dietary tryptophan depletion alters behavioral rhythms in mice. Furthermore, tryptophan metabolism was shown to be regulated in a time- and light- dependent manner. A multi-omics approach and combinatory diet/light interventions demonstrated that tryptophan metabolism modulates temporal regulation of metabolism and transcription programs by buffering photic cues. Specifically, tryptophan metabolites regulate central circadian functions of the suprachiasmatic nucleus and the core clock machinery in the liver.

CONCLUSIONS

Tryptophan metabolism is a modulator of circadian homeostasis by integrating environmental cues. Our findings propose tryptophan metabolism as a potential point for pharmacologic intervention to modulate phenotypes associated with disrupted circadian rhythms.

[Recent research on gene polymorphisms related to caffeine therapy in preterm infants with apnea of prematurity]

Apnea of prematurity (AOP) is one of the common diseases in preterm infants. The main cause of AOP is immature development of the respiratory control center. If AOP is not treated timely and effectively, it will lead to respiratory failure, hypoxic brain injury, and even death in severe cases. Caffeine is the first choice for the treatment of AOP, but its effectiveness varies in preterm infants. With the deepening of AOP research, more and more genetic factors have been confirmed to play important roles in the pathogenesis and treatment of AOP; in particular, the influence of single nucleotide polymorphism on the efficacy of caffeine has become a research hotspot in recent years. This article reviews the gene polymorphisms that affect the efficacy of caffeine, in order to provide a reference for individualized caffeine therapy. Citation.

The 4th dimension of in vitro systems - Time to level up

Various in vitro model systems have been established over the last decades to understand physiological processes, the causalities of diseases and the response of humans to environmental and industrial chemicals or therapeutic drugs. Common to all is a limited biological significance due to the impairment of functionality, for instance by the lack of physiological 3D tissue architecture or the loss of fundamental regulatory mechanisms including the circadian rhythm. The circadian rhythm is an adaption of living organisms to rhythmic environmental changes of the day-night cycle and coordinates behavior as well as various crucial physiological processes in a 24-hour pattern. Here, we discuss the impact of integrating circadian regulation in experimental approaches and toxicological assessments to improve the biological relevance of the obtained results. In particular, it is known for some time that an ongoing disruption of the circadian rhythmicity is associated with an increased risk for cardiovascular disease, metabolic dysfunction or cancer. In the context of health recovery, the importance of circadian control mechanism is recognized by chronopharmacological concepts to increase the efficiency of pharmacological treatment strategies. Despite the undeniable circadian dependency and the biological relevance of manifold cellular and molecular processes, the impact of circadian regulation is hardly considered in a wide range of biomedical and toxicological research areas. Reactivating the circadian regulation holds the promise to enhance the biological relevance and reliability of in vitro approaches. In the context of human health protection the implementation of a circadian regulation will subsequently generate advanced physiologically relevant in vitro approaches and allows an improved toxicological assessment of health risks. In addition, the establishment of circadian disruption as a novel toxicological endpoint will provide a better understanding of toxicological mode of actions of environmental and industrial chemicals or drugs and enlarge the knowledge of disease development.

TCDD exposure alters fecal IgA concentrations in male and female mice

Background

Activation of the aryl hydrocarbon receptor (AhR) can alter diurnal rhythms including those for innate lymphoid cell numbers, cytokine and hormone levels, and feeding behaviors. Because immune responses and antibody levels are modulated by exposure to AhR agonists, we hypothesized that some of the variation previously reported for the effects of AhR activation on fecal secretory immunoglobulin A (sIgA) levels could be explained by dysregulation of the diurnal sIgA rhythm.

Methods

C57Bl/6 J mice were exposed to peanut oil or 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD, 10 or 40 μg/Kg) and fecal sIgA levels were determined in samples collected every 4 h over 4 days.

Results

Fecal sIgA concentrations were not significantly different between light and dark phases of the photoperiod in either male or female mice, and there were no significant circadian rhythms observed, but TCDD exposure significantly altered both fecal mesor sIgA and serum IgA concentrations, in parallel, in male (increased) and female (biphasic) mice.

Conclusions

AhR activation can contribute to the regulation of steady state IgA/sIgA concentrations.

Supplementary Information

The online version contains supplementary material available at 10.1186/s40360-022-00563-9.

Role of the Synergistic Interactions of Environmental Pollutants in the Development of Cancer

There is a growing awareness that the large number of environmental pollutants we are exposed to on a daily basis are causing major health problems. Compared to traditional studies that focus on individual pollutants, there are relatively few studies on how pollutants mixtures interact. Several studies have reported a relationship between environmental pollutants and the development of cancer, even when pollutant levels are below toxicity reference values. The possibility of synergistic interactions between different pollutants could explain how even low concentrations can cause major health problems. These intricate that molecular interactions can occur through a wide variety of mechanisms, and our understanding of the physiological effects of mixtures is still limited. The purpose of this paper is to discuss recent reports that address possible synergistic interactions between different types of environmental pollutants that could promote cancer development. Our literature studies suggest that key biological pathways are frequently implicated in such processes. These include increased production of reactive oxygen species, activation by cytochrome P450, and aryl hydrocarbon receptor signaling, among others. We discuss the need to understand individual pathological vulnerability not only in relation to basic genetics and gene expression, but also in terms of measurable exposure to contaminants. We also mention the need for significant improvements in future studies using a multitude of disciplines, such as the development of high-throughput study models, better tools for quantifying pollutants in cancer patients, innovative pharmacological and toxicological studies, and high-efficiency computer analysis, which allow us to analyze the molecular mechanisms of mixtures.

Evolutionarily conserved transcription factors as regulators of longevity and targets for geroprotection

Aging is the single largest risk factor for many debilitating conditions, including heart diseases, stroke, cancer, diabetes, and neurodegenerative disorders. While far from understood in its full complexity, it is scientifically well-established that aging is influenced by genetic and environmental factors, and can be modulated by various interventions. One of aging's early hallmarks are aberrations in transcriptional networks, controlling for example metabolic homeostasis or the response to stress. Evidence in different model organisms abounds that a number of evolutionarily conserved transcription factors, which control such networks, can affect lifespan and healthspan across species. These transcription factors thus potentially represent conserved regulators of longevity and are emerging as important targets in the challenging quest to develop treatments to mitigate age-related diseases, and possibly even to slow aging itself. This review provides an overview of evolutionarily conserved transcription factors that impact longevity or age-related diseases in at least one multicellular model organism (nematodes, flies, or mice), and/or are tentatively linked to human aging. Discussed is the general evidence for transcriptional regulation of aging and disease, followed by a more detailed look at selected transcription factor families, the common metabolic pathways involved, and the targeting of transcription factors as a strategy for geroprotective interventions.

6-Formylindolo[3,2-b]carbazole, a Potent Ligand for the Aryl Hydrocarbon Receptor Produced Both Endogenously and by Microorganisms, can Either Promote or Restrain Inflammatory Responses

The aryl hydrocarbon receptor (AHR) binds major physiological modifiers of the immune system. The endogenous 6-formylindolo[3,2-b]carbazole (FICZ), which binds with higher affinity than any other compound yet tested, including TCDD, plays a well-documented role in maintaining the homeostasis of the intestines and skin. The effects of transient activation of AHR by FICZ differ from those associated with continuous stimulation and, depending on the dose, include either differentiation into T helper 17 cells that express proinflammatory cytokines or into regulatory T cells or macrophages with anti-inflammatory properties. Moreover, in experimental models of human diseases high doses stimulate the production of immunosuppressive cytokines and suppress pathogenic autoimmunity. In our earlier studies we characterized the formation of FICZ from tryptophan via the precursor molecules indole-3-pyruvate and indole-3-acetaldehyde. In the gut formation of these precursor molecules is catalyzed by microbial aromatic-amino-acid transaminase ArAT. Interestingly, tryptophan can also be converted into indole-3-pyruvate by the amino-acid catabolizing enzyme interleukin-4 induced gene 1 (IL4I1), which is secreted by host immune cells. By thus generating derivatives of tryptophan that activate AHR, IL4I1 may have a role to play in anti-inflammatory responses, as well as in a tumor escape mechanism that reduces survival in cancer patients. The realization that FICZ can be produced from tryptophan by sunlight, by enzymes expressed in our cells (IL4I1), and by microorganisms as well makes it highly likely that this compound is ubiquitous in humans. A diurnal oscillation in the level of FICZ that depends on the production by the fluctuating number of microbes might influence not only intestinal and dermal immunity locally, but also systemic immunity.

Caffeine Therapy for Apnea of Prematurity: Role of the Circadian CLOCK Gene Polymorphism

Standard-dose caffeine citrate has been routinely prescribed for apnea of prematurity (AOP) management; however, some preterm infants respond well to the therapy while others do not. The AOP phenotype has been attributed solely to the immature control of the respiratory system consequent to preterm birth, but there are also important genetic influences. Based on our previous report, we tested the hypothesis that the human circadian locomotor output cycles kaput (CLOCK) gene polymorphisms play a role in the response to caffeine citrate therapy in preterm infants. We also studied the interactions of the circadian clock with aryl hydrocarbon receptor (AHR) signaling pathways in preterm babies who received caffeine citrate. This single-center study collected data from 112 preterm infants (<35 weeks gestational age) between July 2017 and July 2018, including apnea-free (n = 48) and apneic (n = 64) groups. Eighty-eight candidate single nucleotide polymorphisms (SNPs) were tested using the MassARRAY system. Association analysis was performed using the PLINK Whole Genome Data Analysis Toolset and SNPStats software. Linkage disequilibrium (LD) and haplotype analyses were performed using Hapview software. No significant intergroup differences in allele distributions or genotype frequencies of CYP1A2, CYP3A4, CYP3A5, and CYP3A7 were detected in our study on preterm babies. Two more SNPs in AHR were found to be associated with determining the response to caffeine citrate therapy in our pediatric patients. Of the 46 candidate SNPs in the CLOCK gene, 26 were found to be associated with determining the response to caffeine treatment in these babies. Interestingly, a significant association was retained for 18 SNPs in the CLOCK gene after false discovery rate correction. Moreover, strong LD formed in those variants in AHR, ADORA2A, and CLOCK genes was confirmed to be significantly associated with a better response to standard-dose caffeine therapy. In summary, CLOCK gene polymorphisms play a role in determining the response to caffeine therapy in premature neonates with AOP. However, whether the AHR and CLOCK signaling pathways crosstalk with each other during caffeine treatment remains largely unclear. Future clinical studies including more immature babies and basic research are needed to explore the mechanism by which circadian rhythms affect the response to caffeine therapy.

The Role of AhR in the Hallmarks of Brain Aging: Friend and Foe

In recent years, aryl hydrocarbon receptor (AhR), a ligand-activated transcription factor, has been considered to be involved in aging phenotypes across several species. This receptor is a highly conserved biosensor that is activated by numerous exogenous and endogenous molecules, including microbiota metabolites, to mediate several physiological and toxicological functions. Brain aging hallmarks, which include glial cell activation and inflammation, increased oxidative stress, mitochondrial dysfunction, and cellular senescence, increase the vulnerability of humans to various neurodegenerative diseases. Interestingly, many studies have implicated AhR signaling pathways in the aging process and longevity across several species. This review provides an overview of the impact of AhR pathways on various aging hallmarks in the brain and the implications for AhR signaling as a mechanism in regulating aging-related diseases of the brain. We also explore how the nature of AhR ligands determines the outcomes of several signaling pathways in brain aging processes.

DNA methylome perturbations: an epigenetic basis for the emergingly heritable neurodevelopmental abnormalities associated with maternal smoking and maternal nicotine exposure†

Maternal smoking during pregnancy is associated with an ensemble of neurodevelopmental consequences in children and therefore constitutes a pressing public health concern. Adding to this burden, contemporary epidemiological and especially animal model research suggests that grandmaternal smoking is similarly associated with neurodevelopmental abnormalities in grandchildren, indicative of intergenerational transmission of the neurodevelopmental impacts of maternal smoking. Probing the mechanistic bases of neurodevelopmental anomalies in the children of maternal smokers and the intergenerational transmission thereof, emerging research intimates that epigenetic changes, namely DNA methylome perturbations, are key factors. Altogether, these findings warrant future research to fully elucidate the etiology of neurodevelopmental impairments in the children and grandchildren of maternal smokers and underscore the clear potential thereof to benefit public health by informing the development and implementation of preventative measures, prophylactics, and treatments. To this end, the present review aims to encapsulate the burgeoning evidence linking maternal smoking to intergenerational epigenetic inheritance of neurodevelopmental abnormalities, to identify the strengths and weaknesses thereof, and to highlight areas of emphasis for future human and animal model research therein.

Aryl Hydrocarbon Receptors in Indole Derivative Treated Mice: Neuropharmacological Perspectives

Aim/objective. When applied in pharmacological doses, the indole derivative melatonin exhibits neuroactive and neuroprotective effects. Indoles and their metabolites, such as kynurenine, are ligands of aryl hydrocarbon receptors (AhR). This study aimed to evaluate the antiepileptic and analgesic activity of melatonin and two synthetic melatonin derivatives. The possible involvement of AhR and kynurenine in their neuropharmacological effects were also tested.

Methods. The tested substances were: melatonin, two melatonin derivatives bearing aryl hydrocarbon moiety with either furyl or thienyl substitute (3e and 3f), and alpha naphthoflavone (ANF), an antagonist of AhR. After intraperitoneal injection of 30, 100, or 300 mg/kg of the tested agents for seven days, male mice ICR (25-30 g) were subjected to a corneal kindling seizure model. Two tests for analgesia, i.e., the hot plate test and the formalin test, were also applied. AhR and kynurenine concentrations were evaluated in brain homogenates.

Results. Substances 3e and 3f demonstrated an antiepileptic activity comparable to that of melatonin. Some analgesic activity was also shown, albeit lower than that of melatonin in equivalent doses. For melatonin and 3f treated mice, dose-dependent increases in AhR and kynurenine levels in brain homogenates were recorded. The antagonist ANF neither blocks the antiseizure activity of the tested indoles, nor demonstrated analgesic activity.

Conclusion. Melatonin and the two tested melatonin-aroylhydrazone derivatives bearing either furyl or thienyl substitute exhibit antiepileptic and analgesic activity. Our results did not support the involvement of AhR in the demonstrated neurobiological activity. Further studies are needed to elucidate their exact molecular mechanisms.

The melatonergic pathway and its interactions in modulating respiratory system disorders

Melatonin is a key intracellular neuroimmune-endocrine regulator and coordinator of multiple complex and interrelated biological processes. The main functions of melatonin include the regulation of neuroendocrine and antioxidant system activity, blood pressure, rhythms of the sleep-wake cycle, the retardation of ageing processes, as well as reseting and optimizing mitochondria and thereby the cells of the immune system. Melatonin and its agonists have therefore been mooted as a treatment option across a wide array of medical disorders. This article reviews the role of melatonin in the regulation of respiratory system functions under normal and pathological conditions. Melatonin can normalize the structural and functional organization of damaged lung tissues, by a number of mechanisms, including the regulation of signaling molecules, oxidant status, lipid raft function, optimized mitochondrial function and reseting of the immune response over the circadian rhythm. Consequently, melatonin has potential clinical utility for bronchial asthma, chronic obstructive pulmonary disease, lung cancer, lung vascular diseases, as well as pulmonary and viral infections. The integration of melatonin's effects with the alpha 7 nicotinic receptor and the aryl hydrocarbon receptor in the regulation of mitochondrial function are proposed as a wider framework for understanding the role of melatonin across a wide array of diverse pulmonary disorders.

Aryl hydrocarbon receptor: Its roles in physiology

Aryl hydrocarbon receptor (AHR) was initially discovered as a cellular protein involved in mediating the detoxification of xenobiotic compounds. Extensive research in the past two decades has identified several families of physiological ligands and uncovered important functions of AHR in normal development and homeostasis. Deficiency in AHR expression disrupts major signaling systems and transcriptional programs, which appear to be responsible for the development of numerous developmental abnormalities including cardiac hypertrophy and epidermal hyperplasia. This mini review primarily summarizes recent advances in our understanding of AHR functions in normal physiology with an emphasis on the cardiovascular, gastrointestinal, integumentary, nervous, and immunomodulatory systems.

The Aryl Hydrocarbon Receptor in Energy Balance: The Road from Dioxin-Induced Wasting Syndrome to Combating Obesity with Ahr Ligands

The aryl hydrocarbon receptor (AHR) has been studied for over 40 years, yet our understanding of this ligand-activated transcription factor remains incomplete. Each year, novel findings continually force us to rethink the role of the AHR in mammalian biology. The AHR has historically been studied within the context of potent activation via AHR agonist 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD), with a focus on how the AHR mediates TCDD toxicity. Research has subsequently revealed that the AHR is actively involved in distinct physiological processes ranging from the development of the liver and reproductive organs, to immune system function and wound healing. More recently, the AHR was implicated in the regulation of energy metabolism and is currently being investigated as a potential therapeutic target for obesity. In this review, we re-trace the steps through which the early toxicological studies of TCDD led to the conceptual framework for the AHR as a potential therapeutic target in metabolic disease. We additionally discuss the key discoveries that have been made concerning the role of the AHR in energy metabolism, as well as the current and future directions of the field.

Ecological adaptation in Atlantic herring is associated with large shifts in allele frequencies at hundreds of loci

Atlantic herring is widespread in North Atlantic and adjacent waters and is one of the most abundant vertebrates on earth. This species is well suited to explore genetic adaptation due to minute genetic differentiation at selectively neutral loci. Here, we report hundreds of loci underlying ecological adaptation to different geographic areas and spawning conditions. Four of these represent megabase inversions confirmed by long read sequencing. The genetic architecture underlying ecological adaptation in herring deviates from expectation under a classical infinitesimal model for complex traits because of large shifts in allele frequencies at hundreds of loci under selection.

Chronodisruption: A Poorly Recognized Feature of CKD

Multiple physiological variables change over time in a predictable and repetitive manner, guided by molecular clocks that respond to external and internal clues and are coordinated by a central clock. The kidney is the site of one of the most active peripheral clocks. Biological rhythms, of which the best known are circadian rhythms, are required for normal physiology of the kidneys and other organs. Chronodisruption refers to the chronic disruption of circadian rhythms leading to disease. While there is evidence that circadian rhythms may be altered in kidney disease and that altered circadian rhythms may accelerate chronic kidney disease (CKD) progression, there is no comprehensive review on chronodisruption and chronodisruptors in CKD and its manifestations. Indeed, the term chronodisruption has been rarely applied to CKD despite chronodisruptors being potential therapeutic targets in CKD patients. We now discuss evidence for chronodisruption in CKD and the impact of chronodisruption on CKD manifestations, identify potential chronodisruptors, some of them uremic toxins, and their therapeutic implications, and discuss current unanswered questions on this topic.

Accumulation of kynurenine elevates oxidative stress and alters microRNA profile in human bone marrow stromal cells

Kynurenine, a metabolite of tryptophan breakdown, has been shown to increase with age, and plays a vital role in a number of age-related pathophysiological changes, including bone loss. Accumulation of kynurenine in bone marrow stromal cells (BMSCs) has been associated with a decrease in cell proliferation and differentiation, though the exact mechanism by which kynurenine mediates these changes is poorly understood. MiRNAs have been shown to regulate BMSC function, and accumulation of kynurenine may alter the miRNA expression profile of BMSCs. The aim of this study was to identify differentially expressed miRNAs in human BMSCs in response to treatment with kynurenine, and correlate miRNAs function in BMSCs biology through bioinformatics analysis. Human BMSCs were cultured and treated with and without kynurenine, and subsequent miRNA isolation was performed. MiRNA array was performed to identify differentially expressed miRNA. Microarray analysis identified 50 up-regulated, and 36 down-regulated miRNAs in kynurenine-treated BMSC cultures. Differentially expressed miRNA included miR-1281, miR-330-3p, let-7f-5p, and miR-493-5p, which are important for BMSC proliferation and differentiation. KEGG analysis found up-regulated miRNA targeting glutathione metabolism, a pathway critical for removing oxidative species. Our data support that the kynurenine dependent degenerative effect is partially due to changes in the miRNA profile of BMSCs.