Sellegounder D et al. (2018) MBio "Octopaminergic Signaling Mediates Neural Regulation of Innate Immunity in Caenorhabditis elegans."

Wibisono P, Liu Y, Yuan CH, Sellegounder D, Sun J

[MBio, 2018]

Upon pathogen infection, the nervous system regulates innate immunity to confer coordinated protection to the host. However, the precise mechanisms of such regulation remain unclear. Previous studies have demonstrated that OCTR-1, a putative G protein-coupled receptor for catecholamine, functions in the sensory neurons designated &quot;ASH&quot; to suppress innate immune responses in <i>Caenorhabditis elegans</i> It is unknown what molecules act as OCTR-1 ligands in the neural immune regulatory circuit. Here we identify neurotransmitter octopamine (OA) as an endogenous ligand for OCTR-1 in immune regulation and show that the OA-producing RIC neurons function in the OCTR-1 neural circuit to suppress innate immunity. RIC neurons are deactivated in the presence of pathogens but transiently activated by nonpathogenic bacteria. Our data support a model whereby an octopaminergic immunoinhibitory pathway is tonically active under normal conditions to maintain immunological homeostasis or suppress unwanted innate immune responses but downregulated upon pathogen infection to allow enhanced innate immunity. As excessive innate immune responses have been linked to a myriad of human health concerns, our study could potentially benefit the development of more-effective treatments for innate immune disorders.<b>IMPORTANCE</b> Insufficient or excessive immune responses to pathogen infection are major causes of disease. Increasing evidence indicates that the nervous system regulates the immune system to help maintain immunological homeostasis. However, the precise mechanisms of this regulation are largely unknown. Here we show the existence of an octopaminergic immunoinhibitory pathway in <i>Caenorhabditis elegans</i> Our study results indicate that this pathway is tonically active under normal conditions to maintain immunological homeostasis or suppress unwanted innate immune responses but downregulated upon pathogen infection to allow enhanced innate immunity. As excessive innate immune responses have been linked to human health conditions such as Crohn's disease, rheumatoid arthritis, atherosclerosis, diabetes, and Alzheimer's disease, elucidating octopaminergic neural regulation of innate immunity could be helpful in the development of new treatments for innate immune diseases.

Sellegounder, D. et al. (2019) International Worm Meeting "Neuronal GPCR NPR-8 regulates C. elegans defense against pathogen infection."

Sun, J., Sellegounder, D., Liu, Y.

[International Worm Meeting, 2019]

Increasing evidence indicates that the nervous system regulates infection-triggered host defenses, including behavioral and immune responses. However, the precise mechanisms of such regulation are not well understood. Using the survival and behavioral assays, we demonstrate that NPR-8, a G protein-coupled receptor related to mammalian neuropeptide Y receptors, negatively regulates Caenorhabditis elegans defense against pathogen infection by suppressing the expression of cuticular collagen genes. The nematode cuticle is an exoskeleton composed predominantly of cross-linked collagens that form the barrier between the animal and its environment. We further show that the defense activity of NPR-8 is confined to amphid sensory neurons AWB, ASJ, and AWC. This suggests that the nervous system regulates the dynamics of cuticle structure in response to pathogen infection. It is generally believed that physical barrier defenses are not a response to infections, but are part of the body's basic innate defense against pathogens. Our results challenge this view by indicating not only that C. elegans cuticle structure dynamically changes in response to pathogen infection, but also that the nervous system regulates the cuticle barrier defense. Because collagen production is important for lifespan assurance, neural regulation of collagens required for host defense against pathogen attack could also be essential for resisting other environmental assaults and might play a role in general longevity control.

Sellegounder, D. et al. (2017) International Worm Meeting "Characterization of neuronal receptor NPR-8 for its role in regulating C. elegans immunity."

Sellegounder, D., Liu, Y., Yuan , C-H., Sun, J.

[International Worm Meeting, 2017]

G protein-coupled receptors (GPCRs) are membrane-bound signaling proteins with diverse functions regulating important pathways from development to immunity. Caenorhabditis elegans has evolved as a powerful model for studying G-protein signaling in tissues as well as in the entire organism. In C. elegans, a single neuron expresses numerous GPCRs that responds to diverse stimuli, including damage signals from non-neuronal cells. With advancement in genetic tools and imaging techniques, the function of several GPCRs has been deciphered recently. However, the mechanisms by which distant non-neuronal cells communicate with the nervous system remain unclear. In the current study, we characterized the role of NPR-8, a neuronal GPCR related to the mammalian neuropeptide Y-like receptor, in immune regulation. Survival assays against bacterial pathogens revealed that functional loss of NPR-8 in C. elegans enhances the nematode resistance to the pathogen and increases survival. The observed extension in life span was not due to enhanced pathogen avoidance but facilitated through pathogen clearance. Expression of npr-8 was localized to AWB, AWC, and ASJ sensory neurons. Through forward and reverse genetic approaches, we identified that NPR-8 functions to 1) suppress abu genes involved in maintaining proteostasis through unfolded protein response pathway at an early stage of infection, and 2) regulate structural integrity in non-neuronal tissues by controlling the expression of collagen genes during late phase against bacterial infection. Blocking or silencing individual neurons expressing npr-8 did not enhance the nematode survival. Expressing NPR-8 in AWB, AWC, or ASJ neurons in npr-8 mutant animals partially rescued their mutant phenotype of enhanced survival. This study reveals that alongside the immune activation the structural components play a crucial role in enhancing resistance and longevity against pathogenic insults. Our findings suggest that NPR-8 may regulate C. elegans immunity by maintaining the organismal proteostasis and structural integrity.

Sellegounder D et al. (2019) Sci Adv "Neuronal GPCR NPR-8 regulates C. elegans defense against pathogen infection."

Wibisono P, Leap D, Chen CH, Sellegounder D, Liu Y, Sun J

[Sci Adv, 2019]

Increasing evidence indicates that infection-triggered host defenses are regulated by the nervous system. However, the precise mechanisms of this regulation are not well understood. Here, we demonstrate that neuronal G protein-coupled receptor NPR-8 negatively regulates <i>Caenorhabditis elegans</i> defense against pathogen infection by suppressing cuticular collagen expression. NPR-8 controls the dynamics of cuticle structure in response to infection, likely through its regulation of cuticular collagen genes which, in turn, affects the nematode's defense. We further show that the defense activity of NPR-8 is confined to amphid sensory neurons AWB, ASJ, and AWC. It is generally believed that physical barrier defenses are not a response to infections but are part of the body's basic innate defense against pathogens. Our results challenge this view by showing not only that <i>C. elegans</i> cuticle structure dynamically changes in response to infection but also that the cuticle barrier defense is regulated by the nervous system.

Sakoguchi H et al. (2016) Biosci Biotechnol Biochem "Screening of biologically active monosaccharides: growth inhibitory effects of d-allose, d-talose, and l-idose against the nematode Caenorhabditis elegans."

Izumori K, Yoshihara A, Sakoguchi H, Sato M

[Biosci Biotechnol Biochem, 2016]

We compared the growth inhibitory effects of all aldohexose stereoisomers against the model animal Caenorhabditis elegans. Among the tested compounds, the rare sugars d-allose (d-All), d-talose (d-Tal), and l-idose (l-Ido) showed considerable growth inhibition under both monoxenic and axenic culture conditions. 6-Deoxy-d-All had no effect on growth, which suggests that C6-phosphorylation by hexokinase is essential for inhibition by d-All.

Sakoguchi H et al. (2016) Bioorg Med Chem Lett "Growth inhibitory effect of d-arabinose against the nematode Caenorhabditis elegans: Discovery of a novel bioactive monosaccharide."

Shintani T, Izumori K, Sato M, Sakoguchi H, Okuma K, Yoshihara A

[Bioorg Med Chem Lett, 2016]

Biological activities of unusual monosaccharides (rare sugars) have largely remained unstudied until recently. We compared the growth inhibitory effects of aldohexose stereoisomers against the animal model Caenorhabditis elegans cultured in monoxenic conditions with Escherichia coli as food. Among these stereoisomers, the rare sugar d-arabinose (d-Ara) showed particularly strong growth inhibition. The IC50 value for d-Ara was estimated to be 7.5mM, which surpassed that of the potent glycolytic inhibitor 2-deoxy-d-glucose (19.5mM) used as a positive control. The inhibitory effect of d-Ara was also observed in animals cultured in axenic conditions using a chemically defined medium; this excluded the possible influence of E. coli. To our knowledge, this is the first report of biological activity of d-Ara. The d-Ara-induced inhibition was recovered by adding either d-ribose or d-fructose, but not d-glucose. These findings suggest that the inhibition could be induced by multiple mechanisms, for example, disturbance of d-ribose and d-fructose metabolism.

Yoshihara A et al. (2019) Bioorg Med Chem Lett "Growth inhibition by 1-deoxy-d-allulose, a novel bioactive deoxy sugar, screened using Caenorhabditis elegans assay."

Sakoguchi H, Fleet GWJ, Izumori K, Shintani T, Sato M, Yoshihara A

[Bioorg Med Chem Lett, 2019]

The biological activities of deoxy sugars (deoxy monosaccharides) have remained largely unstudied until recently. We compared the growth inhibition by all 1-deoxyketohexoses using the animal model Caenorhabditis elegans. Among the eight stereoisomers, 1-deoxy-d-allulose (1d-d-Alu) showed particularly strong growth inhibition. The 50% inhibition of growth (GI₅₀) concentration by 1d-d-Alu was estimated to be 5.4mM, which is approximately 10 times lower than that of d-allulose (52.7mM), and even lower than that of the potent glycolytic inhibitor, 2-deoxy-d-glucose (19.5mM), implying that 1d-d-Alu has a strong growth inhibition. In contrast, 5-deoxy- and 6-deoxy-d-allulose showed no growth inhibition of C. elegans. The inhibition by 1d-d-Alu was alleviated by the addition of d-ribose or d-fructose. Our findings suggest that 1d-d-Alu-mediated growth inhibition could be induced by the imbalance in d-ribose metabolism. To our knowledge, this is the first report of biological activity of 1d-d-Alu which may be considered as an antimetabolite drug candidate.

Katane M et al. (2020) Biochim Biophys Acta Proteins Proteom "Biochemical characterization of d-aspartate oxidase from Caenorhabditis elegans: Its potential use in the determination of free D-glutamate in biological samples."

Katane M, Sekine M, Nakayama K, Homma H, Kuwabara H, Saitoh Y, Miyamoto T

[Biochim Biophys Acta Proteins Proteom, 2020]

d-Aspartate oxidase (DDO) is a flavin adenine dinucleotide (FAD)-containing flavoprotein that stereospecifically acts on acidic D-amino acids (i.e., free d-aspartate and D-glutamate). Mammalian DDO, which exhibits higher activity toward d-aspartate than D-glutamate, is presumed to regulate levels of d-aspartate in the body and is not thought to degrade D-glutamate in vivo. By contrast, three DDO isoforms are present in the nematode Caenorhabditis elegans, DDO-1, DDO-2, and DDO-3, all of which exhibit substantial activity toward D-glutamate as well as d-aspartate. In this study, we optimized the Escherichia coli culture conditions for production of recombinant C. elegans DDO-1, purified the protein, and showed that it is a flavoprotein with a noncovalently but tightly attached FAD. Furthermore, C. elegans DDO-1, but not mammalian (rat) DDO, efficiently and selectively degraded D-glutamate in addition to d-aspartate, even in the presence of various other amino acids. Thus, C. elegans DDO-1 might be a useful tool for determining these acidic D-amino acids in biological samples.

Shintani T et al. (2019) J Appl Glycosci (1999) "D-Allose, a Stereoisomer of D-Glucose, Extends the Lifespan of Caenorhabditis elegans via Sirtuin and Insulin Signaling."

Izumori K, Sakoguchi H, Yoshihara A, Shintani T, Sato M

[J Appl Glycosci (1999), 2019]

D-Allose (D-All), C-3 epimer of D-glucose, is a rare sugar known to suppress reactive oxygen species generation and prevent hypertension. We previously reported that D-allulose, a structural isomer of D-All, prolongs the lifespan of the nematode Caenorhabditis elegans. Thus, D-All was predicted to affect longevity. In this study, we provide the first empirical evidence that D-All extends the lifespan of C. elegans. Lifespan assays revealed that a lifespan extension was induced by 28 mM D-All. In particular, a lifespan extension of 23.8 % was achieved (p< 0.0001). We further revealed that the effects of D-All on lifespan were dependent on the insulin gene daf-16 and the longevity gene sir-2.1, indicating a distinct mechanism from those of other hexoses, such as D-allulose, with previously reported antiaging effects.

Sato M et al. (2008) J Nat Med "Potential anthelmintic: D-psicose inhibits motility, growth and reproductive maturity of L1 larvae of Caenorhabditis elegans."

Izumori K, Yamasaki T, Kurose H, Sato M

[J Nat Med, 2008]

No anthelmintic sugars have yet been identified. Eight ketohexose stereoisomers (D- and L-forms of psicose, fructose, tagatose and sorbose), along with D-galactose and D-glucose, were examined for potency against L1 stage Caenorhabditis elegans fed Escherichia coli. Of the sugars, D-psicose specifically inhibited the motility, growth and reproductive maturity of the L1 stage. D-Psicose probably interferes with the nematode nutrition. The present results suggest that D-psicose, one of the rare sugars, is a potential anthelmintic.