C. elegans DAF-12, Nuclear Hormone Receptors and human longevity and disease at old age

A mechanistic analysis of metformin's biphasic effects on lifespan and healthspan in C. elegans: Elixir in youth, poison in elder

Aging, a complex biological process influenced by genetic, environmental, and pharmacological factors, presents a significant challenge in understanding its underlying mechanisms. In this study, we explored the divergent impacts of metformin treatment on the lifespan and healthspan of young and old C. elegans, demonstrating a intriguing "elixir in youth, poison in elder" phenomenon. By scrutinizing the gene expression changes in response to metformin in young (day 1 of adulthood) and old (days 8) groups, we identified nhr-57 and C46G7.1 as potential modulators of age-specific responses. Notably, nhr-57 and C46G7.1 exhibit contrasting regulation patterns, being up-regulated in young worms but down-regulated in old counterparts following metformin treatment. Functional studies employing knockdown approaches targeting nhr-57, a gene under the control of hif-1 with a documented protective function against pore-forming toxins in C. elegans, and C46G7.1, unveiled their critical roles in modulating lifespan and healthspan, as well as in mediating the biphasic effects of metformin. Furthermore, deletion of hif-1 retarded the influence of metformin, implicating the involvement of hif-1/nhr-57 in age-specific drug responses. These findings underscored the necessity of deciphering the mechanisms governing age-related susceptibility to pharmacological agents to tailor interventions for promoting successful aging.

Oxysterols are potential physiological regulators of ageing

Delaying and even reversing ageing is a major public health challenge with a tremendous potential to postpone a plethora of diseases including cancer, metabolic syndromes and neurodegenerative disorders. A better understanding of ageing as well as the development of innovative anti-ageing strategies are therefore an increasingly important field of research. Several biological processes including inflammation, proteostasis, epigenetic, oxidative stress, stem cell exhaustion, senescence and stress adaptive response have been reported for their key role in ageing. In this review, we describe the relationships that have been established between cholesterol homeostasis, in particular at the level of oxysterols, and ageing. Initially considered as harmful pro-inflammatory and cytotoxic metabolites, oxysterols are currently emerging as an expanding family of fine regulators of various biological processes involved in ageing. Indeed, depending of their chemical structure and their concentration, oxysterols exhibit deleterious or beneficial effects on inflammation, oxidative stress and cell survival. In addition, stem cell differentiation, epigenetics, cellular senescence and proteostasis are also modulated by oxysterols. Altogether, these data support the fact that ageing is influenced by an oxysterol profile. Further studies are thus required to explore more deeply the impact of the "oxysterome" on ageing and therefore this cholesterol metabolic pathway constitutes a promising target for future anti-ageing interventions.

Biotechnological Applications of Probiotics: A Multifarious Weapon to Disease and Metabolic Abnormality

Consumption of live microorganisms "Probiotics" for health benefits and well-being is increasing worldwide. Their use as a therapeutic approach to confer health benefits has fascinated humans for centuries; however, its conceptuality gradually evolved with methodological advancement, thereby improving our understanding of probiotics-host interaction. However, the emerging concern regarding safety aspects of live microbial is enhancing the interest in non-viable or microbial cell extracts, as they could reduce the risks of microbial translocation and infection. Due to technical limitations in the production and formulation of traditionally used probiotics, the scientific community has been focusing on discovering new microbes to be used as probiotics. In many scientific studies, probiotics have been shown as potential tools to treat metabolic disorders such as obesity, type-2 diabetes, non-alcoholic fatty liver disease, digestive disorders (e.g., acute and antibiotic-associated diarrhea), and allergic disorders (e.g., eczema) in infants. However, the mechanistic insight of strain-specific probiotic action is still unknown. In the present review, we analyzed the scientific state-of-the-art regarding the mechanisms of probiotic action, its physiological and immuno-modulation on the host, and new direction regarding the development of next-generation probiotics. We discuss the use of recently discovered genetic tools and their applications for engineering the probiotic bacteria for various applications including food, biomedical applications, and other health benefits. Finally, the review addresses the future development of biological techniques in combination with clinical and preclinical studies to explain the molecular mechanism of action, and discover an ideal multifunctional probiotic bacterium.

let-7 microRNAs: Their Role in Cerebral and Cardiovascular Diseases, Inflammation, Cancer, and Their Regulation

The let-7 family is among the first microRNAs found. Recent investigations have indicated that it is highly expressed in many systems, including cerebral and cardiovascular systems. Numerous studies have implicated the aberrant expression of let-7 members in cardiovascular diseases, such as stroke, myocardial infarction (MI), cardiac fibrosis, and atherosclerosis as well as in the inflammation related to these diseases. Furthermore, the let-7 microRNAs are involved in development and differentiation of embryonic stem cells in the cardiovascular system. Numerous genes have been identified as target genes of let-7, as well as a number of the let-7’ regulators. Further studies are necessary to identify the gene targets and signaling pathways of let-7 in cardiovascular diseases and inflammatory processes. The bulk of the let-7’ regulatory proteins are well studied in development, proliferation, differentiation, and cancer, but their roles in inflammation, cardiovascular diseases, and/or stroke are not well understood. Further knowledge on the regulation of let-7 is crucial for therapeutic advances. This review focuses on research progress regarding the roles of let-7 and their regulation in cerebral and cardiovascular diseases and associated inflammation.

Caenorhabditis elegans, a Host to Investigate the Probiotic Properties of Beneficial Microorganisms

Caenorhabditis elegans, a non-parasitic nematode emerges as a relevant and powerful candidate as an in vivo model for microorganisms-microorganisms and microorganisms-host interactions studies. Experiments have demonstrated the probiotic potential of bacteria since they can provide to the worm a longer lifespan, an increased resistance to pathogens and to oxidative or heat stresses. Probiotics are used to prevent or treat microbiota dysbiosis and associated pathologies but the molecular mechanisms underlying their capacities are still unknown. Beyond safety and healthy aspects of probiotics, C. elegans represents a powerful way to design large-scale studies to explore transkingdom interactions and to solve questioning about the molecular aspect of these interactions. Future challenges and opportunities would be to validate C. elegans as an in vivo tool for high-throughput screening of microorganisms for their potential probiotic use on human health and to enlarge the panels of microorganisms studied as well as the human diseases investigated.

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.

Probiotic Lactobacillus fermentum strain JDFM216 stimulates the longevity and immune response of Caenorhabditis elegans through a nuclear hormone receptor

Here, we examined the functionality of Lactobacillus fermentum strain JDFM216, a newly isolated probiotic bacterium, using a Caenorhabditis elegans model. We determined bacterial colonization in the intestinal tract of C. elegans by plate counting and transmission electron microscopy and examined the survival of C. elegans using a solid killing assay. In addition, we employed DNA microarray analysis, quantitative real time-polymerase chain reaction, and immunoblotting assays to explore health-promoting pathways induced by probiotic bacteria in C. elegans. Initially, we found that the probiotic bacterium L. fermentum strain JDFM216 was not harmful to the C. elegans host. Conditioning with JDFM216 led to its colonization in the nematode intestine and enhanced resistance in nematodes exposed to food-borne pathogens, including Staphylococcus aureus and Escherichia coli O157:H7. Interestingly, this probiotic strain significantly prolonged the life span of C. elegans. Whole-transcriptome analysis and transgenic worm assays revealed that the health-promoting effects of JDFM216 were mediated by a nuclear hormone receptor (NHR) family and PMK-1 signaling. Taken together, we described a new C. elegans-based system to screen novel probiotic activity and demonstrated that preconditioning with the probiotic L. fermentum strain JDFM216 may positively stimulate the longevity of the C. elegans host via specific pathway.

Lifespan Extension of Caenorhabditis elegans by Butyricicoccus pullicaecorum and Megasphaera elsdenii with Probiotic Potential

Butyricicoccus pullicaecorum and Megasphaera elsdenii inhabit the human intestine and have probiotic potential. The aim of this study was to evaluate the effects of B. pullicaecorum and M. elsdenii on the lifespan of Caenorhabditis elegans. They significantly (P < 0.05) extended the lifespan of C. elegans compared with Escherichia coli OP50, a standard food for the worm. Analysis of age-related biomarkers such as lipofuscin, body size, and locomotory activity showed that they retarded aging. They all failed to extend the lifespan of daf-12 or dbl-1 loss-of-function C. elegans mutants compared with E. coli OP50-fed worms. However, the increase in lifespan was observed in daf-16, jnk-1, pmk-1, and skn-1 mutants. Moreover, they increased the resistance of C. elegans to a human pathogen, Salmonella typhimurium. In conclusion, B. pullicaecorum and M. elsdenii extend the lifespan of C. elegans via the transforming growth factor-beta (TGF-β) pathway associated with anti-inflammatory processes in the innate immune system.

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.

Dairy Propionibacterium extends the mean lifespan of Caenorhabditis elegans via activation of the innate immune system

Dairy Propionibacterium freudenreichii is a candidate non-lactic acid probiotic. However, little information is available on the effect of P. freudenreichii on lifespan extension in humans. The aim of this study was to evaluate the effects of P. freudenreichii on lifespan extension and to elucidate the mechanism of P. freudenreichii-dependent lifespan extension in Caenorhabditis elegans. The results showed that P. freudenreichii significantly (p < 0.05) extended the lifespan of C. elegans compared with Escherichia coli OP50, a standard food for the worm. Analysis of age-related biomarkers showed that P. freudenreichii retards ageing. Moreover, P. freudenreichii increased resistance against a human pathogen, Salmonella typhimurium, through the activation of skn-1, which is involved in pathogen resistance in C. elegans. Furthermore, P. freudenreichii-fed daf-16, jnk-1, skn-1 or daf-7 loss-of-function mutants showed an extended mean lifespan compared with E. coli OP50-fed worms. However, the increase in lifespan was not observed in pmk-1, sek-1, mek-1, dbl-1, daf-12 or daf-2 mutants, which suggests potential roles for these genes in P. freudenreichii-induced longevity in C. elegans. In conclusion, P. freudenreichii extends the lifespan of C. elegans via the p38 MAPK pathway involved in stress response and the TGF-β pathways associated with anti-inflammation processes in the immune system.

Polychlorinated Biphenyl-Xenobiotic Nuclear Receptor Interactions Regulate Energy Metabolism, Behavior, and Inflammation in Non-alcoholic-Steatohepatitis

Polychlorinated biphenyls (PCBs) are environmental pollutants associated with non-alcoholic-steatohepatitis (NASH), diabetes, and obesity. We previously demonstrated that the PCB mixture, Aroclor 1260, induced steatohepatitis and activated nuclear receptors in a diet-induced obesity mouse model. This study aims to evaluate PCB interactions with the pregnane-xenobiotic receptor (Pxr: Nr1i2) and constitutive androstane receptor (Car: Nr1i3) in NASH. Wild type C57Bl/6 (WT), Pxr(-/-) and Car(-/-) mice were fed the high fat diet (42% milk fat) and exposed to a single dose of Aroclor 1260 (20 mg/kg) in this 12-week study. Metabolic phenotyping and analysis of serum, liver, and adipose was performed. Steatohepatitis was pathologically similar in all Aroclor-exposed groups, while Pxr(-/-) mice displayed higher basal pro-inflammatory cytokine levels. Pxr repressed Car expression as evident by increased basal Car/Cyp2b10 expression in Pxr(-/-) mice. Both Pxr(-/-) and Car(-/-) mice showed decreased basal respiratory exchange rate (RER) consistent with preferential lipid metabolism. Aroclor increased RER and carbohydrate metabolism, associated with increased light cycle activity in both knockouts, and decreased food consumption in the Car(-/-) mice. Aroclor exposure improved insulin sensitivity in WT mice but not glucose tolerance. The Aroclor-exposed, Pxr(-/-) mice displayed increased gluconeogenic gene expression. Lipid-oxidative gene expression was higher in WT and Pxr(-/-) mice although RER was not changed, suggesting PCB-mediated mitochondrial dysfunction. Therefore, Pxr and Car regulated inflammation, behavior, and energy metabolism in PCB-mediated NASH. Future studies should address the 'off-target' effects of PCBs in steatohepatitis.

Let-7 microRNAs target the lineage-specific transcription factor PLZF to regulate terminal NKT cell differentiation and effector function

Lethal-7 (let-7) microRNAs are the most abundant in the genome but their role in developing thymocytes is unclear. We now report that let-7 miRNAs target Zbtb16 mRNA, which encodes the lineage-specific transcription factor PLZF, to post-transcriptionally regulate PLZF expression and NKT cell effector function. Dynamic up-regulation of let-7 miRNAs during NKT thymocyte development down-regulates PLZF expression and directs terminal differentiation into interferon-γ-producing NKT1 cells. Without let-7 up-regulation, NKT thymocytes maintain high PLZF expression and terminally differentiate into IL-4-producing NKT2 and IL-17-producing NKT17 cells. Let-7 up-regulation in developing NKT thymocytes can be signaled by IL-15, vitamin D and retinoic acid. Such miRNA targeting of a lineage-specific transcription factor constitutes a new level of developmental regulation in the thymus.

Structural conservation of ligand binding reveals a bile acid-like signaling pathway in nematodes

Bile acid-like molecules named dafachronic acids (DAs) control the dauer formation program in Caenorhabditis elegans through the nuclear receptor DAF-12. This mechanism is conserved in parasitic nematodes to regulate their dauer-like infective larval stage, and as such, the DAF-12 ligand binding domain has been identified as an important therapeutic target in human parasitic hookworm species that infect more than 600 million people worldwide. Here, we report two x-ray crystal structures of the hookworm Ancylostoma ceylanicum DAF-12 ligand binding domain in complex with DA and cholestenoic acid (a bile acid-like metabolite), respectively. Structure analysis and functional studies reveal key residues responsible for species-specific ligand responses of DAF-12. Furthermore, DA binds to DAF-12 mechanistically and is structurally similar to bile acids binding to the mammalian bile acid receptor farnesoid X receptor. Activation of DAF-12 by cholestenoic acid and the cholestenoic acid complex structure suggest that bile acid-like signaling pathways have been conserved in nematodes and mammals. Together, these results reveal the molecular mechanism for the interplay between parasite and host, provide a structural framework for DAF-12 as a promising target in treating nematode parasitism, and provide insight into the evolution of gut parasite hormone-signaling pathways.

The new biology of ageing

Human life expectancy in developed countries has increased steadily for over 150 years, through improvements in public health and lifestyle. More people are hence living long enough to suffer age-related loss of function and disease, and there is a need to improve the health of older people. Ageing is a complex process of damage accumulation, and has been viewed as experimentally and medically intractable. This view has been reinforced by the realization that ageing is a disadvantageous trait that evolves as a side effect of mutation accumulation or a benefit to the young, because of the decline in the force of natural selection at later ages. However, important recent discoveries are that mutations in single genes can extend lifespan of laboratory model organisms and that the mechanisms involved are conserved across large evolutionary distances, including to mammals. These mutations keep the animals functional and pathology-free to later ages, and they can protect against specific ageing-related diseases, including neurodegenerative disease and cancer. Preliminary indications suggest that these new findings from the laboratory may well also apply to humans. Translating these discoveries into medical treatments poses new challenges, including changing clinical thinking towards broad-spectrum, preventative medicine and finding novel routes to drug development.

Liver X receptor β: maintenance of epidermal expression in intrinsic and extrinsic skin aging

Aging in human skin is the composite of time-dependent intrinsic aging plus photoaging induced by chronic exposure to ultraviolet radiation. Nuclear hormone receptors coordinate diverse processes including metabolic homeostasis. Liver X receptor β (LXRβ) is a close human homologue of daf-12, a regulator of nematode longevity. LXRβ is positively regulated by sirtuin-1 and resveratrol, while LXRβ-null mice show transcriptional profiles similar to those seen in aged human skin. In these studies, we examined LXRβ expression in aged and photoaged human skin. Volunteers were recruited to assess intrinsic aging and photoaging. Epidermal LXRβ mRNA was examined by in situ hybridization while protein was identified by immunofluorescence. No significant changes were observed in either LXRβ mRNA or protein expression between young and aged volunteers (mRNA p = 0.90; protein p = 0.26). Similarly, LXRβ protein expression was unaltered in photoaged skin (p = 0.75). Our data therefore suggest that, while not playing a major role in skin aging, robust cutaneous expression implies a fundamental role for LXRβ in epidermal biology.

Vitamin D, nervous system and aging

This is a mini-review of vitamin D(3), its active metabolites and their functioning in the central nervous system (CNS), especially in relation to nervous system pathologies and aging. The vitamin D(3) endocrine system consists of 3 active calcipherol hormones: calcidiol (25OHD(3)), 1alpha-calcitriol (1alpha,25(OH)2D(3)) and 24-calcitriol (24,25(OH)2D(3)). The impact of the calcipherol hormone system on aging, health and disease is discussed. Low serum calcidiol concentrations are associated with an increased risk of several chronic diseases including osteoporosis, cancer, diabetes, autoimmune disorders, hypertension, atherosclerosis and muscle weakness all of which can be considered aging-related diseases. The relationship of many of these diseases and aging-related changes in physiology show a U-shaped response curve to serum calcidiol concentrations. Clinical data suggest that vitamin D(3) insufficiency is associated with an increased risk of several CNS diseases, including multiple sclerosis, Alzheimer's and Parkinson's disease, seasonal affective disorder and schizophrenia. In line with this, recent animal and human studies suggest that vitamin D insufficiency is associated with abnormal development and functioning of the CNS. Overall, imbalances in the calcipherol system appear to cause abnormal function, including premature aging, of the CNS.

Liver X Receptor Alpha Associates With Human Life Span

In the nematode Caenorhabditis elegans, nuclear hormone receptor DAF-12 regulates the decision to go into a resistant dauer diapause, in which the worm exhibits a decreased rate of aging. Using sequence similarity searches, we previously identified the liver X receptor alpha (LXRalpha) as one of the human nuclear hormone receptors the protein sequence of which is most similar to C. elegans DAF-12. Here, we studied whether variation in the gene encoding LXRalpha associates with human life span. In the Leiden 85-Plus Study, a population-based prospective follow-up study, we genotyped four polymorphisms spanning the gene coding for LXRalpha (NR1H3) and tagged four common haplotypes. Among 563 participants, haplotype 2 associated with reduced mortality during the 7-year follow-up (hazard ratio 0.78; p =.015), predominantly caused by reduced mortality from infectious disease (hazard ratio 0.31; p =.023). Haplotype 2 also associated with higher levels of plasma apolipoprotein E, a target gene of the LXRalpha (p =.018), and higher levels of triglycerides (p =.041). Genetic variation in the gene coding for the LXRalpha (NR1H3) associates with human life span.

A steroid hormone that extends the lifespan of Caenorhabditis elegans

Removing the germline of Caenorhabditis elegans extends lifespan. This lifespan extension requires the nuclear receptor DAF-12 and the cytochrome P450 DAF-9, suggesting that a lipophilic hormone is involved. Here we show that C. elegans contains several hormonal steroids that are also present in humans, including pregnenolone (3beta-hydroxy-pregn-5-en-20-one; PREG) and other pregnane and androstane derivatives. We find that PREG can extend the lifespan of C. elegans. Moreover, PREG levels rise when the germline is removed in a daf-9-dependent fashion. PREG extends the lifespan of germline-defective daf-9 mutants dramatically, but has no effect on daf-12 mutants. Thus, germline removal may extend lifespan, at least in part, by stimulating the synthesis of PREG.

DAF-12-dependent rescue of dauer formation in Caenorhabditis elegans by (25S)-cholestenoic acid

Population density, temperature and food availability all regulate the formation of the Caenorhabditis elegans dauer larva by modulating endocrine signaling pathways. The orphan nuclear receptor DAF-12 is pivotal for the decision to form a dauer or to undergo normal reproductive development. The DAF-12 ligand has been predicted to be a sterol that is metabolized by DAF-9, a cytochrome P450. Here we chemically characterize purified lipophilic nematode extracts and show that the ligand for DAF-12 contains a carboxyl moiety and is likely to be derived from a sterol. Using a candidate ligand approach we find that the C27 bile acid cholestenoic acid (5-cholesten-3beta-ol-(25S)-carboxylic acid) promotes reproductive growth in dauer-constitutive mutants in a daf-9- and daf-12-dependent manner. Furthermore, we find that cholestenoic acid can act as a DAF-12 ligand by activating DAF-12 in a cell-based transcription assay. Analysis of dauer-rescuing lipophilic extracts from nematodes by gas chromatography-mass spectrometry indicates the presence of several regioisomers of cholestenoic acid that are distinct from Delta(5)-cholestenoic acid and are not present in extracts from daf-9 mutants. These data suggest that carboxylated sterols may be key determinants of life history.

Identification of ligands for DAF-12 that govern dauer formation and reproduction in C. elegans

In response to environmental and dietary cues, the C. elegans orphan nuclear receptor, DAF-12, regulates dauer diapause, reproductive development, fat metabolism, and life span. Despite strong evidence for hormonal control, the identification of the DAF-12 ligand has remained elusive. In this work, we identified two distinct 3-keto-cholestenoic acid metabolites of DAF-9, a cytochrome P450 involved in hormone production, that function as ligands for DAF-12. At nanomolar concentrations, these steroidal ligands (called dafachronic acids) bind and transactivate DAF-12 and rescue the hormone deficiency of daf-9 mutants. Interestingly, DAF-9 has a biochemical activity similar to mammalian CYP27A1 catalyzing addition of a terminal acid to the side chain of sterol metabolites. Together, these results define the first steroid hormones in nematodes as ligands for an invertebrate orphan nuclear receptor and demonstrate that steroidal regulation of reproduction, from biology to molecular mechanism, is conserved from worms to humans.