Nuclear hormone receptors: Roles of xenobiotic detoxification and sterol homeostasis in healthy aging

Activation of Nuclear Receptor CAR: A Pathway to Delay Aging through Enhanced Capacity for Xenobiotic Resistance

Environmental factors are linked to aging and age-related diseases. Emerging evidence suggests that enhancing body's resistance to xenobiotics might be an anti-aging strategy. The constitutive androstane receptor (CAR) regulates drug-metabolizing enzymes and transporters, coordinating metabolism and immune responses to adapt to stress triggered by exogenous exposure. However, the impact of activating CAR on aging remains unknown. In this study, Caenorhabditis elegans (C. elegans), drug-induced premature aging mice, and senescence accelerated P8 (SAMP8) mice are used as models to explore the effects of CAR activation on lifespan and healthspan, along with the underlying mechanisms. The results showed that hCAR agonist CITCO and mCAR agonist TCPOBOP prolonged the lifespan and healthspan in model organism. The longevity effects of CITCO and TCPOBOP were attenuated in CAR homozygous nhr-8/daf-12 mutant C. elegans as well as CAR-/- mice. In C. elegans, CITCO activated both anti-stress and detoxification genes, and increased the resistance to environmental adversities. Additionally, the lifespan-extending and xenobiotic resistant effects of CITCO might be related to the regulation of age-related pathways. Furthermore, CITCO improved age-related neurodegeneration in C. elegans models. Taken together, the results suggest that the longevity effects of CAR agonists may be related to the enhancement of xenobiotic resistance of animals.

27-Hydroxymangiferolic Acid Extends Lifespan and Improves Neurodegeneration in Caenorhabditis elegans by Activating Nuclear Receptors

27-Hydroxymangiferolic acid (27-HMA) is a naturally occurring compound in mango fruits that exhibits diverse biological functions. Here, we show that 27-HMA activates the transcriptional activity of farnesoid X receptor (FXR), a nuclear receptor transcription factor, extending the lifespan and healthspan in Caenorhabditis elegans (C. elegans). Meanwhile, the longevity-promoting effect of 27-HMA was attenuated in the mutants of nhr-8 and daf-12, the FXR homologs, indicating that the longevity effects of 27-HMA in C. elegans may depend on nuclear hormone receptors (NHRs). Further analysis revealed potential associations between the longevity effects of 27-HMA and the insulin/insulin-like growth factor-1 signaling (IIS)/TORC1 pathway. Moreover, 27-HMA increased the toxin resistance of nematodes and activated the expression of detoxification genes, which rely on NHRs. Finally, 27-HMA improved the age-related neurodegeneration in Alzheimer's disease (AD) and Parkinson's disease (PD) C. elegans models. Taken together, our findings suggest that 27-HMA is a novel FXR agonist and may prolong lifespan and healthspan via activating NHRs.

Isotschimgine promotes lifespan, healthspan and neuroprotection of Caenorhabditis elegans via the activation of nuclear hormone receptors

Isotschimgine (ITG) is a bornane-type monoterpenoid derivative naturally occurring in genus Ferula plants and propolis. Its effects on aging and the underlying mechanisms are not yet well understood. This study employed Caenorhabditis elegans (C. elegans) as a model organism to evaluate the potential of ITG in extending lifespan, enhancing healthspan, and promoting neuroprotection, while exploring the underlying mechanisms involved. The results showed that ITG extended the lifespan and healthspan of C. elegans, significantly enhanced stress resistance and detoxification functions. Studies on mutants and qPCR data indicated that ITG-mediated lifespan extension was modulated by the insulin/IGF-1 signaling pathway and nuclear hormone receptors. Furthermore, ITG markedly increased stress-responsive genes, including daf-16 and its downstream genes sod-3 and hsp-16.2, as well as NHR downstream detoxification-related genes cyp35a1, cyp35b3, cyp35c1, gst-4, pgp-3 and pgp-13. Additionally, ITG alleviated β-amyloid-induced paralysis and behavioral dysfunction in transgenic C. elegans strains. The neuroprotective efficacy of ITG was weakened by RNAi knockdown of nuclear hormone receptors daf-12 and nhr-8. Overall, our study identifies ITG as a potential compound for promoting longevity and neuroprotection, mediated through nuclear hormone receptors.

P-glycoproteins in anthelmintic safety, efficacy, and resistance

P-glycoprotein (PGP) is a pivotal transmembrane transporter governing the cellular flux of diverse substances shielding mammals from toxics. It can thwart the effectiveness of medicines such as ivermectin (IVM) and other macrocyclic lactone (ML) anthelmintics, undermining therapeutic efforts. We analyze the role of PGPs in limiting the toxicity of these drugs in hosts, and their potential contribution to anthelmintic resistance in nematodes. Targeting nematode PGPs to increase drug sensitivity to MLs seems interesting, but is hampered by the lack of selective inhibitors. The nuclear hormone receptor (NHR)-8 should be seriously considered as a target because it upregulates multiple PGPs involved in anthelmintic resistance and it is specific to nematodes. This would advance our understanding of host-pathogen dynamics and foster innovative therapeutic strategies.

TNF compromises intestinal bile-acid tolerance dictating colitis progression and limited infliximab response

The intestine constantly encounters and adapts to the external environment shaped by diverse dietary nutrients. However, whether and how gut adaptability to dietary challenges is compromised in ulcerative colitis is incompletely understood. Here, we show that a transient high-fat diet exacerbates colitis owing to inflammation-compromised bile acid tolerance. Mechanistically, excessive tumor necrosis factor (TNF) produced at the onset of colitis interferes with bile-acid detoxification through the receptor-interacting serine/threonine-protein kinase 1/extracellular signal-regulated kinase pathway in intestinal epithelial cells, leading to bile acid overload in the endoplasmic reticulum and consequent apoptosis. In line with the synergy of bile acids and TNF in promoting gut epithelial damage, high intestinal bile acids correlate with poor infliximab response, and bile acid clearance improves infliximab efficacy in experimental colitis. This study identifies bile acids as an "opportunistic pathogenic factor" in the gut that would represent a promising target and stratification criterion for ulcerative colitis prevention/therapy.

CHES1 modulated tumorigenesis and senescence of pancreas cancer cells through repressing AKR1B10

Pancreatic ductal adenocarcinoma (PDAC), is characteristic by a heterogeneous tumor microenvironment and gene mutations, conveys a dismal prognosis and low response to chemotherapy and immunotherapy. Here, we found that checkpoint suppressor 1 (CHES1) served as a tumor repressor in PDAC and was associated with patient prognosis. Functional experiments indicated that CHES1 suppressed the proliferation and invasion of PDAC by modulating cellular senescence. To further identify the downstream factor of CHES1 in PDAC, label-free quantitative proteomics analysis was conducted, which showed that the oncogenic Aldo-keto reductase 1B10 (AKR1B10) was transcriptionally repressed by CHES1 in PDAC. And AKR1B10 facilitated the malignant activity and repressed senescent phenotype of PDAC cells. Moreover, pharmaceutical inhibition of AKR1B10 with Oleanolic acid (OA) significantly induced tumor regression and sensitized PDAC cells to gemcitabine, and this combined therapy did not cause obvious side effects. Rescued experiments revealed that CHES1 regulated the tumorigenesis and gemcitabine sensitivity through AKR1B10-mediated senescence in PDAC. In summary, this study revealed that the CHES1/AKR1B10 axis modulated the progression and cellular senescence in PDAC, which might provide revenues for drug-targeting and senescence-inducing therapies for PDAC.

Mulberrin extends lifespan in Caenorhabditis elegans through detoxification function

Mulberrin, a naturally occurring flavone found in mulberry and Romulus Mori, exhibits diverse biological functions. Here, we showed that mulberrin extended both the lifespan and healthspan in C. elegans. Moreover, mulberrin increased the worms' resistance to toxicants and activated the expression of detoxification genes. The longevity-promoting effect of mulberrin was attenuated in nuclear hormone receptor (NHR) homologous nhr-8 and daf-12 mutants, indicating that the lifespan extending effects of mulberrin in C. elegans may depend on nuclear hormone receptors NHR-8/DAF-12. Further analyses revealed the potential associations between the longevity effects of mulberrin and the insulin/insulin-like growth factor signaling (IIS) and adenosine 5'-monophosphate-activated protein kinase (AMPK) pathways. Together, our findings suggest that mulberrin may prolong lifespan and healthspan by activating detoxification functions mediated by nuclear receptors.

Characterization and transcriptomic analyses of the toxicity induced by toosendanin in Spodoptera frugipreda

The fall armyworm, Spodoptera frugiperda, is a destructive agricultural pest that seriously threatens global food security. Insecticide resistance of this pest has gradually formed in recent years due to improper usage, and alternative methods are badly needed. Toosendanin (TSN) is a botanical compound with broad-spectrum insecticidal activities against many pests. However, the effects of TSN on S. frugiperda are still unclear. In this study, the growth inhibition phenomenon, including weight loss and prolonged developmental duration, in the larvae with TSN exposure was clearly observed. Compared to the control group, a total of 450 and 3314 differentially expressed genes (DEGs) were identified by RNA-Seq in the larvae groups treated with 10 and 20 mg/kg TSN, respectively. Furthermore, the DEGs involved in the juvenile hormone and ecdysone signal pathways and downstream processes, including detoxifying enzyme genes, chitin synthesis and metabolism genes, and cuticular protein genes, were found. Our findings suggest that TSN regulates the expression of key genes in juvenile hormone and ecdysone signal pathways and a series of downstream processes to alter the hormone balance and cuticle formation and eventually inhibit larval growth, which laid the foundation for the molecular toxicological mechanism research of TSN on S. frugiperda larvae.

A preliminary study on the pathology and molecular mechanism of fumonisin B1 nephrotoxicity in young quails

Fumonisin B1 (FB1) is a widely present mycotoxin that accumulates in biological systems and poses a health risk to animals. However, few studies have reported the molecular mechanism by which FB1 induces nephrotoxicity. The aim of this study was to assess the extent of nephrotoxicity during FB1 exposure and the possible molecular mechanisms behind it. Therefore, 180 young quails were equally divided into two groups. The control group was fed typical quail food, while the experimental group was fed quail food containing 30 mg·kg-1 FB1. Various parameters were assessed, which included histopathological, ultrastructural changes, levels of biochemical parameters, oxidative indicators, inflammatory factors, possible target organelles mitochondrial and endoplasmic reticulum (ER)-related factors, nuclear xenobiotic receptors (NXR) response, and cytochrome P450 system (CYP450s)-related factors in the kidneys on days 14, 28, and 42. The results showed that FB1 can induce oxidative stress through NXR response and disorder of the CYP450s system, leading to mitochondrial dysfunction and ER stress, promoting the expression of inflammatory factors (including IL-1β, IL-6, and IL-8) and causing kidney damage. This study elucidated the possible molecular mechanism by which FB1 induces nephrotoxicity in young quails.

Nuclear hormone receptor NHR-49 is an essential regulator of stress resilience and healthy aging in Caenorhabditis elegans

The genome of Caenorhabditis elegans encodes 284 nuclear hormone receptor, which perform diverse functions in development and physiology. One of the best characterized of these is NHR-49, related in sequence and function to mammalian hepatocyte nuclear factor 4α and peroxisome proliferator-activated receptor α. Initially identified as regulator of lipid metabolism, including fatty acid catabolism and desaturation, additional important roles for NHR-49 have since emerged. It is an essential contributor to longevity in several genetic and environmental contexts, and also plays vital roles in the resistance to several stresses and innate immune response to infection with various bacterial pathogens. Here, we review how NHR-49 is integrated into pertinent signaling circuits and how it achieves its diverse functions. We also highlight areas for future investigation including identification of regulatory inputs that drive NHR-49 activity and identification of tissue-specific gene regulatory outputs. We anticipate that future work on this protein will provide information that could be useful for developing strategies to age-associated declines in health and age-related human diseases.

Pregnane X receptor agonist nomilin extends lifespan and healthspan in preclinical models through detoxification functions

Citrus fruit has long been considered a healthy food, but its role and detailed mechanism in lifespan extension are not clear. Here, by using the nematode C. elegans, we identified that nomilin, a bitter-taste limoloid that is enriched in citrus, significantly extended the animals' lifespan, healthspan, and toxin resistance. Further analyses indicate that this ageing inhibiting activity depended on the insulin-like pathway DAF-2/DAF-16 and nuclear hormone receptors NHR-8/DAF-12. Moreover, the human pregnane X receptor (hPXR) was identified as the mammalian counterpart of NHR-8/DAF-12 and X-ray crystallography showed that nomilin directly binds with hPXR. The hPXR mutations that prevented nomilin binding blocked the activity of nomilin both in mammalian cells and in C. elegans. Finally, dietary nomilin supplementation improved healthspan and lifespan in D-galactose- and doxorubicin-induced senescent mice as well as in male senescence accelerated mice prone 8 (SAMP8) mice, and induced a longevity gene signature similar to that of most longevity interventions in the liver of bile-duct-ligation male mice. Taken together, we identified that nomilin may extend lifespan and healthspan in animals via the activation of PXR mediated detoxification functions.

Nuclear receptors potentially regulate phytochemical detoxification in Spodoptera litura

Phytochemicals are a class of potential pesticides for pest control. Our previous studies have demonstrated that the development of Spodoptera litura is suppressed by two phytochemicals, flavone and xanthotoxin. Generally, phytochemical is metabolized by insect detoxification enzyme systems. Nuclear receptor (NR) is the ligand-activated transcription factor that involved in the regulation of detoxification gene expressions. To explore how NR responds to phytochemical to mediate detoxification gene expression, in the present study, 19 NRs were firstly identified in S. litura genome. The transcriptional levels of most NRs were significantly induced in the midgut of S. litura larvae after exposure to flavone and xanthotoxin. RNAi-mediated knockdown of FTZF1, EcR, Dsf, and HR3 remarkably reduced the larval tolerance to flavone or xanthotoxin. In addition, many crucial detoxification genes were downregulated by dsNR administrations, which might be responsible for the high sensitivity of S. litura to phytochemicals. Molecular docking indicated that phytochemicals as the potential ligands had high affinity to bind to NRs. This study suggested that NR potentially regulated the transcriptional expression of detoxification genes in response to phytochemical stresses, which partially elucidated the mechanism of extensive host adaptation in S. litura and provided the theoretical evidences for the development of NR-targeted insecticides.

Potential therapeutic targets for age-related macular degeneration: The nuclear option

The functions and activities of nuclear receptors, the largest family of transcription factors in the human genome, have classically focused on their ability to act as steroid and hormone sensors in endocrine organs. However, they are responsible for a diverse array of physiological functions, including cellular homeostasis and metabolism, during development and aging. Though the eye is not a traditional endocrine organ, recent studies have revealed high expression levels of nuclear receptors in cells throughout the posterior pole. These findings have precipitated an interest in investigating the role of these transcription factors in the eye as a function of age and ocular disease, in particular age-related macular degeneration (AMD). As the leading cause of vision impairment in the elderly, identifying signaling pathways that may be targeted for AMD therapy is of great importance, given the lack of therapeutic options for over 85% of patients with this disease. Herein we review this relatively new field and recent findings supporting the hypothesis that the eye is a secondary endocrine organ, in which nuclear receptors serve as the bedrock for biological processes in cells vulnerable in AMD, including retinal pigment epithelial and choroidal endothelial cells, and discuss the therapeutic potential of targeting these receptors for AMD.

C. elegans orphan nuclear receptor NHR-42 represses innate immunity and promotes lipid loss downstream of HLH-30/TFEB

In recent years, transcription factors of the Microphthalmia-TFE (MiT) family, including TFEB and TFE3 in mammals and HLH-30 in Caenorhabditis elegans, have emerged as important regulators of innate immunity and inflammation in invertebrates and vertebrates. Despite great strides in knowledge, the mechanisms that mediate downstream actions of MiT transcription factors in the context of innate host defense remain poorly understood. Here, we report that HLH-30, which promotes lipid droplet mobilization and host defense, induces the expression of orphan nuclear receptor NHR-42 during infection with Staphylococcus aureus. Remarkably, NHR-42 loss of function promoted host infection resistance, genetically defining NHR-42 as an HLH-30-controlled negative regulator of innate immunity. During infection, NHR-42 was required for lipid droplet loss, suggesting that it is an important effector of HLH-30 in lipid immunometabolism. Moreover, transcriptional profiling of nhr-42 mutants revealed wholesale activation of an antimicrobial signature, of which abf-2, cnc-2, and lec-11 were important for the enhanced survival of infection of nhr-42 mutants. These results advance our knowledge of the mechanisms by which MiT transcription factors promote host defense, and by analogy suggest that TFEB and TFE3 may similarly promote host defense via NHR-42-homologous nuclear receptors in mammals.

A Single Nucleotide Variant in the PPARγ-homolog Eip75B Affects Fecundity in Drosophila

Single nucleotide polymorphisms are the most common type of genetic variation, but how these variants contribute to the adaptation of complex phenotypes is largely unknown. Experimental evolution and genome-wide association studies have demonstrated that variation in the PPARγ-homolog Eip75B has associated with longevity and life-history differences in the fruit fly Drosophila melanogaster. Using RNAi knockdown, we first demonstrate that reduced expression of Eip75B in adult flies affects lifespan, egg-laying rate, and egg volume. We then tested the effects of a naturally occurring SNP within a cis-regulatory domain of Eip75B by applying two complementary approaches: a Mendelian randomization approach using lines of the Drosophila Genetic Reference Panel, and allelic replacement using precise CRISPR/Cas9-induced genome editing. Our experiments reveal that this natural polymorphism has a significant pleiotropic effect on fecundity and egg-to-adult viability, but not on longevity or other life-history traits. Our results provide a rare functional validation at the nucleotide level and identify a natural allelic variant affecting fitness and life-history adaptation.

In silico identification of the potential molecular mechanisms involved in protective effects of prolactin on motor and memory deficits induced by 1,2-Diacetylbenzene in young and old rats

We aimed to identify the molecular mechanisms through which prolactin protects against 1,2-Diacetylbenzene (DAB)-induced memory and motor impairments. The gene expression omnibus database (no. GSE119435), transcriptomic data, GeneMANIA, ToppGeneSuite, Metascape, STRING database, Cytoscape, and Autodock were used as the core tools in in-silico analyses. We observed that prolactin may improve memory and motor deficits caused by DAB via 13 genes (Scn5a, Lmntd1, LOC100360619, Rgs9, Srpk3, Syndig1l, Gpr88, Egr2, Ctxn3, Drd2, Ttr, Gpr6, and Ecel1) in young rats and 9 genes (Scn5a, Chat, RGD1560608, Ucma, Lrrc31, Gpr88, Col1a2, Cnbd1, and Ttr) in old rats. Almost all of these genes were downregulated in both young and old rats given DAB, but they were increased in both young and old rats given prolactin. Co-expression interactions were identified as the most important interactions (83.2 % for young rats and 100 % for old rats). The most important mechanisms associated with prolactin's ability to counteract DAB were identified, including "learning and memory," and "positive regulation of ion transport" in young rats, as well as "acetylcholine related pathways," "inflammatory response pathway," and "neurotransmitter release cycle" in old rats. We also identified several key miRNAs associated with memory and motor deficits, as well as prolactin and DAB exposure (rno-miR-141-3p, rno-miR-200a-3p, rno-miR-124-3p, rno-miR-26, and rno-let-7 families). The most significant transcription factors associated with differentially expressed gene regulation were Six3, Rxrg, Nkx26, and Tbx20. These findings will contribute to our understanding of the processes through which prolactin's beneficial effects counteract DAB-induced memory and motor deficits.

Nuclear receptor Nr1d1 alleviates asthma by abating GATA3 gene expression and Th2 cell differentiation

Nuclear receptors are a unique family of transcription factors that play cardinal roles in physiology and plethora of human diseases. The adopted orphan nuclear receptor Nr1d1 is a constitutive transcriptional repressor known to modulate several biological processes. In this study, we found that Nr1d1 plays a decisive role in T helper (Th)-cell polarization and transcriptionally impedes the formation of Th2 cells by directly binding to the promoter region of GATA binding protein 3 (GATA3) gene. Nr1d1 interacts with its cellular companion, the nuclear receptor corepressor and histone deacetylase 3 to form a stable repression complex on the GATA3 promoter. The presence of Nr1d1 also imparts protection against associated inflammatory responses in murine model of asthma and its ligand SR9011 eased disease severity by suppressing Th2 responses. Moreover, Chip-seq profiling uncovered Nr1d1 interactions with other gene subsets that impedes Th2-linked pathways and regulates metabolism, immunity and brain functions, therefore, providing empirical evidence regarding the genetic link between asthma and other comorbid conditions. Thus, Nr1d1 emerges as a molecular switch that could be targeted to subdue asthma.

Nematodes as Ghosts of Land Use Past: Elucidating the Roles of Soil Nematode Community Studies as Indicators of Soil Health and Land Management Practices

Soil health is a matter of growing concern because of its degradation due to unsustainable anthropogenic activities over the last few decades. It is maintained by interactions among the components of the soil food web commonly concentrated in the vicinity of the plant roots, called the rhizosphere. The soil food web is dominated by nematodes. They occupy various trophic positions because of their diverse feeding habits. The free-living forms are mainly dependent on soil bacteria and fungi for their nutrition, while the parasitic forms feed on plant roots. The population of these two groups is regulated by the activities of predatory nematodes which can be carnivorous or omnivorous. The soil nematodes thereby partake responsibilities in nutrient cycling, mineralization and decomposition pathways which, in turn, affects the aboveground productivity. This intricately connected food web structure is vulnerable to disturbances like increased soil salinity, acidity, nitrogen enrichment, tillage, crop rotations, fertilizers, pesticides, soil amendment techniques and heavy metal pollution. The effects are reflected by alterations in the abundance and diversity of soil nematodes belonging to various trophic groups. These alterations have been formulated into measurable indices like maturity index (MI), structure index (SI), enrichment index (EI) and channel index (CI). The faunal profile and metabolic footprints of soil nematodes are latest developments in the field of nematode community analyses. Though these indices cannot replace the conventional soil ecotoxicological assays, they can give added information about soil biology which can be utilized to design sustainable land use practices.

Immunomodulatory drug discovery from herbal medicines: Insights from organ-specific activity and xenobiotic defenses

Traditional herbal medicines, which emphasize a holistic, patient-centric view of disease treatment, provide an exciting starting point for discovery of new immunomodulatory drugs. Progress on identification of herbal molecules with proven single agent activity has been slow, in part because of insufficient consideration of pharmacology fundamentals. Many molecules derived from medicinal plants exhibit low oral bioavailability and rapid clearance, leading to low systemic exposure. Recent research suggests that such molecules can act locally in the gut or liver to activate xenobiotic defense pathways that trigger beneficial systemic effects on the immune system. We discuss this hypothesis in the context of four plant-derived molecules with immunomodulatory activity: indigo, polysaccharides, colchicine, and ginsenosides. We end by proposing research strategies for identification of novel immunomodulatory drugs from herbal medicine sources that are informed by the possibility of local action in the gut or liver, leading to generation of systemic immune mediators.

Filtering of Data-Driven Gene Regulatory Networks Using Drosophila melanogaster as a Case Study

Gene Regulatory Networks (GRNs) allow the study of regulation of gene expression of whole genomes. Among the most relevant advantages of using networks to depict this key process, there is the visual representation of large amounts of information and the application of graph theory to generate new knowledge. Nonetheless, despite the many uses of GRNs, it is still difficult and expensive to assign Transcription Factors (TFs) to the regulation of specific genes. ChIP-Seq allows the determination of TF Binding Sites (TFBSs) over whole genomes, but it is still an expensive technique that can only be applied one TF at a time and requires replicates to reduce its noise. Once TFBSs are determined, the assignment of each TF and its binding sites to the regulation of specific genes is not trivial, and it is often performed by carrying out site-specific experiments that are unfeasible to perform in all possible binding sites. Here, we addressed these relevant issues with a two-step methodology using Drosophila melanogaster as a case study. First, our protocol starts by gathering all transcription factor binding sites (TFBSs) determined with ChIP-Seq experiments available at ENCODE and FlyBase. Then each TFBS is used to assign TFs to the regulation of likely target genes based on the TFBS proximity to the transcription start site of all genes. In the final step, to try to select the most likely regulatory TF from those previously assigned to each gene, we employ GENIE3, a random forest-based method, and more than 9,000 RNA-seq experiments from D. melanogaster. Following, we employed known TF protein-protein interactions to estimate the feasibility of regulatory events in our filtered networks. Finally, we show how known interactions between co-regulatory TFs of each gene increase after the second step of our approach, and thus, the consistency of the TF-gene assignment. Also, we employed our methodology to create a network centered on the Drosophila melanogaster gene Hr96 to demonstrate the role of this transcription factor on mitochondrial gene regulation.

Xenobiotic metabolism and transport in Caenorhabditis elegans

Caenorhabditis elegans has emerged as a major model in biomedical and environmental toxicology. Numerous papers on toxicology and pharmacology in C. elegans have been published, and this species has now been adopted by investigators in academic toxicology, pharmacology, and drug discovery labs. C. elegans has also attracted the interest of governmental regulatory agencies charged with evaluating the safety of chemicals. However, a major, fundamental aspect of toxicological science remains underdeveloped in C. elegans: xenobiotic metabolism and transport processes that are critical to understanding toxicokinetics and toxicodynamics, and extrapolation to other species. The aim of this review was to initially briefly describe the history and trajectory of the use of C. elegans in toxicological and pharmacological studies. Subsequently, physical barriers to chemical uptake and the role of the worm microbiome in xenobiotic transformation were described. Then a review of what is and is not known regarding the classic Phase I, Phase II, and Phase III processes was performed. In addition, the following were discussed (1) regulation of xenobiotic metabolism; (2) review of published toxicokinetics for specific chemicals; and (3) genetic diversity of these processes in C. elegans. Finally, worm xenobiotic transport and metabolism was placed in an evolutionary context; key areas for future research highlighted; and implications for extrapolating C. elegans toxicity results to other species discussed.

The nuclear receptor 4A family members: mediators in human disease and autophagy

The Nuclear receptor 4A (NR4A) subfamily, which belongs to the nuclear receptor (NR) superfamily, has three members: NR4A1 (Nur77), NR4A2 (Nurr1) and NR4A3 (Nor1). They are gene regulators with broad involvement in various signaling pathways and human disease responses, including autophagy. Here, we provide a concise overview of the current understanding of the role of the NR4A subfamily members in human diseases and review the research into their regulation of cell autophagy. A deeper understanding of these mechanisms has potential to improve drug development processes and disease therapy.

Transcriptome Analysis of the Nematode Caenorhabditis elegans in Acidic Stress Environments

Ocean acidification and acid rain, caused by modern industries' fossil fuel burning, lead to a decrease in the living environmental pH, which results in a series of negative effects on many organisms. However, the underlying mechanisms of animals' response to acidic pH stress are largely unknown. In this study, we used the nematode Caenorhabditis elegans as an animal model to explore the regulatory mechanisms of organisms' response to pH decline. Two major stress-responsive pathways were found through transcriptome analysis in acidic stress environments. First, when the pH dropped from 6.33 to 4.33, the worms responded to the pH stress by upregulation of the col, nas, and dpy genes, which are required for cuticle synthesis and structure integrity. Second, when the pH continued to decrease from 4.33, the metabolism of xenobiotics by cytochrome P450 pathway genes (cyp, gst, ugt, and ABC transporters) played a major role in protecting the nematodes from the toxic substances probably produced by the more acidic environment. At the same time, the slowing down of cuticle synthesis might be due to its insufficient protective ability. Moreover, the systematic regulation pattern we found in nematodes might also be applied to other invertebrate and vertebrate animals to survive in the changing pH environments. Thus, our data might lay the foundation to identify the master gene(s) responding and adapting to acidic pH stress in further studies, and might also provide new solutions to improve assessment and monitoring of ecological restoration outcomes, or generate novel genotypes via genome editing for restoring in challenging environments especially in the context of acidic stress through global climate change.

The development of the dog heartworm is highly sensitive to sterols which activate the orthologue of the nuclear receptor DAF-12

Prevention therapy against Dirofilaria immitis in companion animals is currently threatened by the emergence of isolates resistant to macrocyclic lactone anthelmintics. Understanding the control over developmental processes in D. immitis is important for elucidating new approaches to heartworm control. The nuclear receptor DAF-12 plays a role in the entry and exit of dauer stage in Caenorhabditis elegans and in the development of free-living infective third-stage larvae (iL3) of some Clade IV and V parasitic nematodes. We identified a DAF-12 ortholog in the clade III nematode D. immitis and found that it exhibited a much higher affinity for dafachronic acids than described with other nematode DAF-12 investigated so far. We also modelled the DimDAF-12 structure and characterized the residues involved with DA binding. Moreover, we showed that cholesterol derivatives impacted the molting process from the iL3 to the fourth-stage larvae. Since D. immitis is unable to synthesize cholesterol and only completes its development upon host infection, we hypothesize that host environment contributes to its further molting inside the host vertebrate. Our discovery contributes to a better understanding of the developmental checkpoints of D. immitis and offers new perspectives for the development of novel therapies against filarial infections.

Cholesterol Regulates Innate Immunity via Nuclear Hormone Receptor NHR-8

Cholesterol is an essential nutrient for the function of diverse biological processes and for steroid biosynthesis across metazoans. However, the role of cholesterol in immune function remains understudied. Using the nematode Caenorhabditis elegans, which depends on the external environment for cholesterol, we studied the relationship between cholesterol and innate immunity. We found that the transporter CHUP-1 is required for the effect of cholesterol in the development of innate immunity and that the cholesterol-mediated immune response requires the nuclear hormone receptor NHR-8. Cholesterol acts through NHR-8 to transcriptionally regulate immune genes that are controlled by conserved immune pathways, including a p38/PMK-1 MAPK pathway, a DAF-2/DAF-16 insulin pathway, and an Nrf/SKN-1 pathway. Our results indicate that cholesterol plays a key role in the activation of conserved microbicidal pathways that are essential for survival against bacterial infections.

Detoxification-related gene expression accompanies anhydrobiosis in the foliar nematode (Aphelenchoides fragariae)

The foliar nematode (Aphelenchoides fragariae) is a quarantined pest that infects a broad range of herbaceous and woody plants. Previous work has demonstrated its remarkable ability to survive rapid and extreme desiccation, although the specific molecular mechanisms underlying its anhydrobiotic response have not been characterized. The authors used RNA sequencing and de novo transcriptome assembly to compare patterns of gene expression between hydrated and 24-hr desiccated nematodes. In total, 2,083 and 953 genes were significantly up- and downregulated, respectively, in desiccated nematodes. Of the 100 annotated genes with the largest positive fold-changes, more than one third encoded putative detoxification-related proteins. Genes encoding enzymes of Phase I and Phase II detoxification systems were among the most strongly upregulated in the transcriptome, including 35 cytochrome p450s, 23 short chain dehydrogenase/reductases, 5 glutathione-S-transferases, and 22 UDP-glucuronosyltransferases. Genes encoding heat shock proteins, unfolded protein response enzymes, and intrinsically disordered proteins were also upregulated. Anhydrobiosis in A. fragariae appears to involve both strategies to minimize protein misfolding and aggregation, and wholesale induction of the cellular detoxification machinery. These processes may be controlled in part through the activity of forkhead transcription factors similar to Caenorhabditis elegans’ daf-16, a number of which were differentially expressed under desiccation.

The etiological effect of a new low-frequency ESR1 variant on Mild Cognitive Impairment and Alzheimer's Disease: a population-based study

Latent genetic variations of cholesterol metabolism-related genes in late-onset Alzheimer’s disease, especially, as well as in mild cognitive impairment pathogenesis are still to be studied extensively. Thus, we performed the targeted-sequencing of 12 nuclear receptor genes plus APOE which were involved in cholesterol content modulation to screen susceptible genetic variants and focused on a new risk variant ESR1 rs9340803 at 6q25.1 for both late-onset Alzheimer’s disease (OR=3.30[1.84~4.22], p<0.001) and mild cognitive impairment (OR=3.08[1.75~3.89], p<0.001). This low-frequency variant was validated in three independent cohorts totaling 854 late-onset Alzheimer’s disease cases, 1059 mild cognitive impairment cases and 1254 controls from nine provinces of China mainland. Preliminary functional study on it revealed decreased ESR1 expression in vitro. Besides, we detected higher serum Aβ1-40 concentration in participants carrying this variant (p=0.038) and lower plasma total cholesterol level in this variant carriers with late-onset Alzheimer’s disease (p=0.009). In summary, we identified a susceptible variant which might contribute to developing mild cognitive impairment at earlier stage and Alzheimer’s Disease later. Our study would provide new insight into the disease causation of late-onset Alzheimer’s disease and could be exploited therapeutically.

Characterization of the Cytochrome P450 Gene CYP305A1 of the Cotton Aphid (Hemiptera: Aphididae) and Its Responsive Cis-Elements to Plant Allelochemicals

Insect cytochrome P450 monooxygenases play an important role in plant allelochemical detoxification. In this study, a full-length gene CYP305A1 of the P450 Clan 2 family was cloned from Aphis gossypii Glover, and its promoter was identified and characterized. The transcript level of CYP305A1 and its promoter activity were significantly induced by two plant allelochemicals, gossypol and 2-tridecanone. Furthermore, the 5'-end promoter region from -810 to +62 bp was demonstrated to be essential for basal transcriptional activity of CYP305A1, and the promoter region from -810 to -581 bp was shown as an essential plant allelochemical responsive element and had a cis-element 5'-CACACTA-3' as the binding site of aryl hydrocarbon receptor. Interestingly, there was an identical overlapping region of 1,094 bp between CYP305A1 promoter and the venom protease gene. When the expression of CYP305A1 gene was knocked down by RNA interference with CYP305A1 dsRNA, the expression of the venom protease gene was decreased. However, the knockdown of the expression of the venom protease gene did not affect the CYP305A1 expression. These results provide important insights for understanding the functions of P450 genes and the regulatory mechanism of P450 gene expressions in the resistance of Aphis gossypii Glover to plant allelochemicals.

Nuclear Receptors: A Historical Perspective

In this chapter, we summarize the birth of the field of nuclear receptors. These receptors exhibit a multitude of roles in cell biology and hence have attracted a great deal of interest in the drug discovery field. It is not certain whether these receptors evolved independently or an ancestral protein acquired various functions upon binding to preexisting small molecules, ligands. Currently, members of this receptor superfamily are categorized in six groups, including "orphan receptors." Research in the area has resulted in several clinically used drugs and continues to reveal further previously unknown roles for these receptors paving the road toward more valuable discoveries in the future.

Amyloid-beta induced paralysis is reduced by cholecalciferol through inhibition of the steroid-signaling pathway in an Alzheimer model of Caenorhabditis elegans

Objectives: Alzheimer's disease (AD) is a neurodegenerative disorder resulting from the accumulation of toxic β-amyloid (Aβ) aggregates in the human brain. Epidemiological studies have shown that elevated cholesterol plasma levels are associated with the development of AD and we have previously shown that cholesterol restriction reduces the Aβ-induced paralysis in an Alzheimer model of the nematode Caenorhabditis elegans. In the present study we investigated the effects of the cholesterol homolog cholecalciferol, i.e. vitamin D, on Aβ-induced paralysis in C. elegans and its interference with the steroid-signaling pathway. Methods: Aβ-induced paralysis was assessed in the C. elegans strain CL2006, expressing human Aβ_1-42 under control of a muscle-specific promoter. Knockdown of members of the steroid-signaling pathway was achieved by RNA interference (RNAi). Nuclear translocation of foxo transcription factor DAF-16 was visualized using the strain TJ356, carrying a daf-16::gfp transgene. Results: Cholecalciferol at a concentration of 1 µM reduced the Aβ-induced paralysis in CL2006 significantly, which was reverted by increasing the cholesterol concentration in the medium. Knockdown of nhr-8, daf-36, daf-9 or daf-12, all reduced Aβ-induced paralysis to the same extent as cholecalciferol with no additional or synergistic effects under co-application. Functional DAF-16 proved to be crucial for the effects of cholecalciferol and DAF-16 nuclear translocation was increased by cholecalciferol and also RNAi versus nhr-8, daf-36, daf-9 or daf-12 with no additive or synergistic effects. Conclusions: Our results suggest, that cholecalciferol inhibits Aβ-induced paralysis in C. elegans through inhibition of steroid-signaling and the concomitant nuclear translocation of DAF-16.

CYP4CJ1-mediated gossypol and tannic acid tolerance in Aphis gossypii Glover

Cytochrome P450 monooxygenases play a key role in herbivorous pest adaptation to host plants by the detoxification against plant allelochemicals. A new P450 gene (CYP4CJ1) was identified from Aphis gossypii, which displayed a positive response to plant allelochemicals. The transcript levels of CYP4CJ1 could be significantly induced by both gossypol and tannic acid. Knockdown of CYP4CJ1 increased the sensitivity of A. gossypii to these two plant allelochemicals. These results suggest that CYP4CJ1 could be involved in the tolerance of A. gossypii to some plant allelochemicals. Subsequently, we examined the regulatory mechanism of CYP4CJ1 based on the transcriptional and post-transcriptional level. A promoter region from -1422 to -1166 of CYP4CJ1 was identified, which was an essential plant allelochemical responsive region. In addition, miR-4133-3p was found to participate in the regulation of CYP4CJ1 post-transcriptionally. Our results suggest that the transcript abundance of CYP4CJ1, following the exposure of A. gossypii to gossypol and tannic acid can be attributed to both the transcriptional and post-transcriptional regulation mechanisms. These results are important for understanding the roles of P450s in the plant allelochemical tolerance of A. gossypii.

The transcription factor NHR-8: A new target to increase ivermectin efficacy in nematodes

Resistance to the anthelmintic macrocyclic lactone ivermectin (IVM) has a great impact on the control of parasitic nematodes. The mechanisms by which nematodes adapt to IVM remain to be deciphered. We have identified NHR-8, a nuclear hormone receptor involved in the xenobiotic response in Caenorhabditis elegans, as a new regulator of tolerance to IVM. Loss-of-function nhr-8(ok186) C. elegans mutants subjected to larval development assays and electropharyngeogram measurements, displayed hypersensitivity to IVM, and silencing of nhr-8 in IVM-resistant worms increased IVM efficacy. In addition, compared to wild-type worms, nhr-8 mutants under IVM selection pressure failed to acquire tolerance to the drug. In addition, IVM-hypersensitive nhr-8(ok186) worms displayed low transcript levels of several genes from the xenobiotic detoxification network and a concomitant low Pgp-mediated drug efflux activity. Interestingly, some pgp and cyp genes known to impact IVM tolerance in many nematode species, were down regulated in nhr-8 mutants and inversely upregulated in IVM-resistant worms. Moreover, pgp-6 overexpression in nhr-8(ok186) C. elegans increased tolerance to IVM. Importantly, NHR-8 function was rescued in nhr-8(ok186) C. elegans with the homolog of the parasitic nematode Haemonchus contortus, and silencing of Hco-nhr-8 by RNAi on L2 H. contortus larvae increased IVM susceptibility in both susceptible and resistant H. contortus isolates. Thus, our data show that NHR-8 controls the tolerance and development of resistance to IVM in C. elegans and the molecular basis for this relates to the NHR-8-mediated upregulation of IVM detoxification genes. Since our results show that Hco-nhr-8 functions similarly to Cel-nhr-8, this study helps to better understand mechanisms underlying failure in drug efficacy and open perspectives in finding new compounds with NHR-8 antagonist activity to potentiate IVM efficacy.

IVM is the most important broad-spectrum deworming drug used today but resistance to this drug has appeared in parasites of both animals and humans. This seriously jeopardizes the success of current parasite control. Preserving IVM efficacy is a public health issue, whose outcome depends on the understanding of the molecular basis of selection for resistance to these drugs. We unambiguously show that the nuclear hormone receptor NHR-8, is crucial for protection of the nematode model Caenorhabditis elegans against IVM toxicity. Worms deficient in NHR-8 are hypersensitive to IVM and fail to become resistant to IVM under drug pressure. NHR-8 functions in the parasitic nematode of ruminants Haemonchus contortus and similar mechanisms could occur in other target pathogens. By controlling the xenobiotic detoxification network, NHR-8 may contribute to the biotransformation and elimination of IVM and help to desensitize the worm to the drug. This provides novel molecular targets involved in IVM drug tolerance in parasitic nematodes. Such findings could be exploited for targeted therapeutic intervention to treat parasitic nematode infections and delay the process of resistance development to anthelmintic drugs.

Chlorpyrifos stimulates expression of vitamin D3 receptor in skin cells irradiated with UVB

Skin, the organ responsible for vitamin D synthesis, is fully exposed to many xenobiotics, e.g. polycyclic aromatic hydrocarbons and pesticides. A broad spectrum organophosphorus insecticides (OP's), such as chlorpyrifos (CPS), are commonly used in agriculture and to control domestic insects. Thus, the aim of this study was to investigate the effect of chlorpyrifos, on the expression of vitamin D₃ receptor (VDR) in human keratinocytes cell line HaCaT and fibroblasts cell line BJ. The impact of CPS and UVB radiation on cell viability were examined by Neutral Red assay. The effect of CPS on VDR expression was evaluated by RT-qPCR and flow cytometry (FC). The presented study demonstrated that exposure to CPS and UVB significantly affects the viability of HaCaT and BJ cells lines. Results also revealed that exposure to CPS induced the expression at mRNA and protein level of VDR nuclear receptor in both cell lines exposed to UVB. In HaCaT incubated with 250 μM CPS and 15 mJ/cm² UVB, the relative VDR expression was ∼2-fold higher; whereas in BJ incubated with 250 μM CPS and 20 mJ/cm², UVB was∼3-fold higher. Results from FC confirmed this result, as VDR expression increased by ~250% in HaCaT incubated with 250 μM CPS and 20 mJ/cm² UVB, and in BJ incubated with 250 μM CPS, and 20 mJ/cm² UVB cells VDR expression increased by ~190%, compared with control. It can therefore be concluded that OPs pesticide might interfere with vitamin D₃ metabolism in skin cells.

Emerging topics in C. elegans aging research: Transcriptional regulation, stress response and epigenetics

Key discoveries in aging research have been made possible with the use of model organisms. Caenorhabditis elegans is a short-lived nematode that has become a well-established system to study aging. The practicality and powerful genetic manipulations associated with this metazoan have revolutionized our ability to understand how organisms age. 25 years after the publication of the discovery of the daf-2 gene as a genetic modifier of lifespan, C. elegans remains as relevant as ever in the quest to understand the process of aging. Nematode aging research has proven useful in identifying transcriptional regulators, small molecule signals, cellular mechanisms, epigenetic modifications associated with stress resistance and longevity, and lifespan-extending compounds. Here, we review recent discoveries and selected topics that have emerged in aging research using this incredible little worm.

The Nuclear Receptor Field: A Historical Overview and Future Challenges

In this article we summarize the birth of the field of nuclear receptors, the discovery of untransformed and transformed isoforms of ligand-binding macromolecules, the discovery of the three-domain structure of the receptors, and the properties of the Hsp90-based heterocomplex responsible for the overall structure of the oligomeric receptor and many aspects of the biological effects. The discovery and properties of the subfamily of receptors called orphan receptors is also outlined. Novel molecular aspects of the mechanism of action of nuclear receptors and challenges to resolve in the near future are discussed.

Opposing roles of microRNA Argonautes during Caenorhabditis elegans aging

Argonaute (AGO) proteins partner with microRNAs (miRNAs) to target specific genes for post-transcriptional regulation. During larval development in Caenorhabditis elegans, Argonaute-Like Gene 1 (ALG-1) is the primary mediator of the miRNA pathway, while the related ALG-2 protein is largely dispensable. Here we show that in adult C. elegans these AGOs are differentially expressed and, surprisingly, work in opposition to each other; alg-1 promotes longevity, whereas alg-2 restricts lifespan. Transcriptional profiling of adult animals revealed that distinct miRNAs and largely non-overlapping sets of protein-coding genes are misregulated in alg-1 and alg-2 mutants. Interestingly, many of the differentially expressed genes are downstream targets of the Insulin/ IGF-1 Signaling (IIS) pathway, which controls lifespan by regulating the activity of the DAF-16/ FOXO transcription factor. Consistent with this observation, we show that daf-16 is required for the extended lifespan of alg-2 mutants. Furthermore, the long lifespan of daf-2 insulin receptor mutants, which depends on daf-16, is strongly reduced in animals lacking alg-1 activity. This work establishes an important role for AGO-mediated gene regulation in aging C. elegans and illustrates that the activity of homologous genes can switch from complementary to antagonistic, depending on the life stage.

Ageing sensitized by iPLA2β deficiency induces liver fibrosis and intestinal atrophy involving suppression of homeostatic genes and alteration of intestinal lipids and bile acids

Ageing is a major risk factor for various forms of liver and gastrointestinal (GI) disease and genetic background may contribute to the pathogenesis of these diseases. Group VIA phospholipase A2 or iPLA₂β is a homeostatic PLA₂ by playing a role in phospholipid metabolism and remodeling. Global iPLA₂β^-/- mice exhibit aged-dependent phenotypes with body weight loss and abnormalities in the bone and brain. We have previously reported the abnormalities in these mutant mice showing susceptibility for chemical-induced liver injury and colitis. We hypothesize that iPLA₂β deficiency may sensitize with ageing for an induction of GI injury. Male wild-type and iPLA₂β^-/- mice at 4 and 20-22months of age were studied. Aged, but not young, iPLA₂β^-/-mice showed increased hepatic fibrosis and biliary ductular expansion as well as severe intestinal atrophy associated with increased apoptosis, pro-inflammation, disrupted tight junction, and reduced number of mucin-containing globlet cells. This damage was associated with decreased expression of intestinal endoplasmic stress XBP1 and its regulator HNF1α, FATP4, ACSL5, bile-acid transport genes as well as nuclear receptors LXRα and FXR. By LC/MS-MS profiling, iPLA₂β deficiency in aged mice caused an increase of intestinal arachidonate-containing phospholipids concomitant with a decrease in ceramides. By the suppression of intestinal FXR/FGF-15 signaling, hepatic bile-acid synthesis gene expression was increased leading to an elevation of secondary and hydrophobic bile acids in liver, bile, and intestine. In conclusions, ageing sensitized by iPLA₂β deficiency caused a decline of key intestinal homeostatic genes resulting in the development of GI disease in a gut-to-liver manner.

Crypt Organoid Culture as an in Vitro Model in Drug Metabolism and Cytotoxicity Studies

The gastrointestinal tract is enriched with xenobiotic processing proteins that play important roles in xenobiotic bioactivation, metabolism, and detoxification. The application of genetically modified mouse models has been instrumental in characterizing the function of xenobiotic processing genes (XPG) and their proteins in drug metabolism. Here, we report the utilization of three-dimensional crypt organoid cultures from these animal models to study intestinal drug metabolism and toxicity. With the successful culturing of crypt organoids, we profiled the abundance of Phase I and Phase II XPG expression, drug transporter gene expression, and xenobiotic nuclear receptor (XNR) gene expression. Functions of XNRs were examined by treating crypt cells with XNR prototypical agonists. Real-time quantitative polymerase chain reaction demonstrated that the representative downstream target genes were induced. These findings were validated from cultures developed from XNR-null mice. In crypt cultures isolated from Pxr-/- mice, pregnenolone 16α-carbonitrile failed to induce Cyp3a11 gene expression; similarly, WY14643 failed to induce Cyp4a10 in the Pparα-/- crypts. Crypt cultures from control (Ugt1F/F ) and intestinal epithelial cell (IEC) specific Ugt1 null mice (Ugt1ΔIEC ) were treated with camptothecin-11, an anticancer prodrug with severe intestinal toxicity that originates from insufficient UGT1A1-dependent glucuronidation of its active metabolite SN-38. In the absence of Ugt1 gene expression, Ugt1ΔIEC crypt cultures exhibit very limited production of SN-38 glucuronide, concordant with increased apoptosis in comparison with Ugt1F/F crypt cultures. This study suggests crypt organoid cultures as an effective in vitro model for studying intestinal drug metabolism and toxicity.

A CK2-RNF4 interplay coordinates non-canonical SUMOylation and degradation of nuclear receptor FXR

Farnesoid X receptor (FXR) is a ligand-activated nuclear receptor that plays a central role in regulating genes involved in bile acid homeostasis, and fat and glucose metabolism. Here, we demonstrate a post-translational interplay between FXR phosphorylation, SUMOylation, and ubiquitination that directs the receptor into an activation-degradation pathway in hepatocytes. We identify a non-canonical SUMOylation motif termed pSuM that conjugates SUMO2 at Lys-325 of FXR under the direct control of casein kinase 2 (CK2), which provides the required negative charge for Ubc9 and PIAS1 to perform SUMOylation, by phosphorylating Ser-327. Lys-325 SUMOylation is indispensable to the promotion of efficient ligand activation and transcriptional coactivation of FXR. Constitutive pSuM activation using a phospho-mimic Ser-327 mutant or catalytic CK2 expression strongly induces SUMO2 conjugation, which directs FXR ubiquitination and proteasome-dependent degradation. We also determine that such SUMOylation-dependent ubiquitination of FXR is mediated by the E3 ubiquitin ligase RNF4, which is required to achieve maximal induction of FXR and optimal up- or downregulation of responsive genes involved in bile acid homeostasis and liver regeneration. Our findings identify a highly regulated atypical SUMO conjugation motif that serves to coordinate FXR transcriptional competence, thereby expanding the intricate dynamics of the SUMOylation process used by incoming signals to govern metabolic gene regulation.

Evolutionary Origin of the Interferon-Immune Metabolic Axis: The Sterol-Vitamin D Link

In vertebrate animals, the sterol metabolic network is emerging as a central player in immunity and inflammation. Upon infection, flux in the network is acutely moderated by the interferon (IFN) response through direct molecular and bi-directional communications. How sterol metabolism became linked to IFN control and for what purpose is not obvious. Here, we deliberate on the origins of these connections based on a systematic review of the literature. A narrative synthesis of publications that met eligibility criteria allowed us to trace an evolutionary path and functional connections between cholesterol metabolism and immunity. The synthesis supports an ancestral link between toxic levels of cholesterol-like products and the vitamin D receptor (VDR). VDR is an ancient nuclear hormone receptor that was originally involved in the recognition and detoxification of xenobiotic marine biotoxins exhibiting planar sterol ring scaffolds present in aquatic environments. Coadaptation of this receptor with the acquisition of sterol biosynthesis and IFNs in vertebrate animals set a stage for repurposing and linking a preexisting host-protection mechanism of harmful xenobiotics to become an important regulator in three key interlinked biological processes: bone development, immunity, and calcium homeostasis. We put forward the hypothesis that sterol metabolites, especially oxysterols, have acted as evolutionary drivers in immunity and may represent the first example of small-molecule metabolites linked to the adaptive coevolution and diversification of host metabolic and immune regulatory pathways.

CONSERVED AND EXAPTED FUNCTIONS OF NUCLEAR RECEPTORS IN ANIMAL DEVELOPMENT

The nuclear receptor gene family includes 18 members that are broadly conserved among multiple disparate animal phyla, indicating that they trace their evolutionary origins to the time at which animal life arose. Typical nuclear receptors contain two major domains: a DNA-binding domain and a C-terminal domain that may bind a lipophilic hormone. Many of these nuclear receptors play varied roles in animal development, including coordination of life cycle events and cellular differentiation. The well-studied genetic model systems of Drosophila, C. elegans, and mouse permit an evaluation of the extent to which nuclear receptor function in development is conserved or exapted (repurposed) over animal evolution. While there are some specific examples of conserved functions and pathways, there are many clear examples of exaptation. Overall, the evolutionary theme of exaptation appears to be favored over strict functional conservation. Despite strong conservation of DNA-binding domain sequences and activity, the nuclear receptors prove to be highly-flexible regulators of animal development.

Lithium Promotes Longevity through GSK3/NRF2-Dependent Hormesis

The quest to extend healthspan via pharmacological means is becoming increasingly urgent, both from a health and economic perspective. Here we show that lithium, a drug approved for human use, promotes longevity and healthspan. We demonstrate that lithium extends lifespan in female and male Drosophila, when administered throughout adulthood or only later in life. The life-extending mechanism involves the inhibition of glycogen synthase kinase-3 (GSK-3) and activation of the transcription factor nuclear factor erythroid 2-related factor (NRF-2). Combining genetic loss of the NRF-2 repressor Kelch-like ECH-associated protein 1 (Keap1) with lithium treatment revealed that high levels of NRF-2 activation conferred stress resistance, while low levels additionally promoted longevity. The discovery of GSK-3 as a therapeutic target for aging will likely lead to more effective treatments that can modulate mammalian aging and further improve health in later life.