Chalasani S H et al. (2010) Neuronal Development, Synaptic Function and Behavior, Madison, WI "Neuropeptide feedback modifies odor induced responses in Caenorhabditis elegans olfactory neurons"

Bargmann C I, Kato S, Chalasani S H, Albrecht D R

[Neuronal Development, Synaptic Function and Behavior, Madison, WI, 2010]

Neural circuits transform sensory signals to generate behaviors on timescales from seconds to hours. In some C.elegans behaviors, sensory inputs lead to long lasting and complex behavioral outputs. Animals that have been removed from food spend about 15 minutes exploring a local area by interrupting long forward movements with reversals and turns (Wakabayashi et al., 2004, Gray et al 2005). AWC sensory neurons regulate this behavior by releasing two neurotransmitters, glutamate (promoting turns) and NLP-1 (inhibiting turns). AWC sensory neuron released glutamate activates AIB and inhibits AIY and AIA interneurons (Chalasani et al 2007). In contrast to glutamate, AWC neuron released NLP-1 acts on AIA interneurons to suppress reversals, indicating that turn frequencies are regulated by at least two opposing systems. AWC calcium responses are modulated in these neurotransmitter mutants suggesting that multiple pathways can influence AWC dependent behavior and neuronal activity. ReferencesChalasani, S. H., et. al. Dissecting a neural circuit for olfactory behaviour in Caenorhabditis elegans. Nature 450, 63-70 (2007).Gray, J.M., et. al. A circuit for navigation in Caenorhabditis elegans. Proc. Natl. Acad. Sci. 102, 3184-3191 (2005).Wakabayashi, T., et. al. Neurons regulating the duration of forward locomotion in Caenorhabditis elegans. Neurosci. Res. 50, 103-111 (2004).

Chalasani, Sreekanth H. et al. (2009) International Worm Meeting "AWC sensory neurons release two neurotransmitters to regulate exploratory behavior upon removal from food."

Albrecht, Dirk, Bargmann, Cornelia I., Chalasani, Sreekanth H., Kato, Saul

[International Worm Meeting, 2009]

Animals increase their pirouette frequency in response to removal from food stimulus for a period of 15 min. The AWC and ASK sensory neurons and the AIB interneurons stimulate pirouettes immediately after removal from food, while the AIY and AIA interneurons inhibit pirouettes (Wakabayashi et al 2004, Gray et al 2005). We have found that AWC sensory neurons become active in response to removal of stimulus, releasing two neurotransmitters (glutamate and a neuropeptide NLP-1). The released glutamate acts to activate AIB and inhibit AIY interneurons, promoting reversals (Chalasani et al 2007). In contrast to glutamate, AWC-released NLP-1 acts on AIA interneurons to suppress reversals, suggesting that reversal frequencies are regulated by at least two opposing signaling systems. AWC calcium responses are modulated in these neurotransmitter mutants, suggesting that feedback pathways affect AWC neuronal activity. References: Chalasani, S. H., Chronis, N., Tsunozaki, M., Gray, J. M., Ramot, D., Goodman, M. B., and Bargmann, C. I. (2007). Dissecting a circuit for olfactory behaviour in Caenorhabditis elegans. Nature 450, 63-70. Gray, J.M., Hill, J.J., and Bargmann, C.I. (2005). A circuit for navigation in Caenorhabditis elegans. Proc. Natl. Acad. Sci. 102, 3184-3191. Wakabayashi, T., Kitagawa, I., and Shingai, R. (2004). Neurons regulating the duration of forward locomotion in Caenorhabditis elegans. Neurosci. Res. 50, 103-111.

Singh, A. et al. (2019) International Worm Meeting "Role of neuronal-peptides in intestinal and organismal aging."

Singh, A., Hansen , M., Chalasani , S.

[International Worm Meeting, 2019]

Inter-tissue communications are vital for organism development and survival. This becomes particularly relevant in the context of aging, as various tissues have been shown to age at different rates. One particular challenge is to identify age-altered, cross-tissue signals that can modulate organ health and organismal survival. To identify such signals, we engineered C. elegans for tissue-specific RNAi to probe neuron-to-intestine peptide signals in modulating intestinal health. We focused on the readily quantifiable age-associated increase in intestinal leakiness, which is conserved from worms to mammals. Interestingly, we found that abrogating the secretion of neuronal peptides delayed age-related intestinal leakiness, and extended survival. These findings imply that neuronal peptides might play a role in timing intestinal aging. Next, we posited that neuronal peptides likely exert their effect on intestinal health by signaling through, either G-coupled protein receptor- (GPCR-) or non-GPCR class of peptide-receptors. Interestingly, the intestine-specific knockdown of both G-protein gamma subunit encoding genes, as well as the insulin/IGF-1-like receptor daf-2,cell-autonomously delayed age-associated intestinal leakiness. These results indicate that aged neurons may release peptide signals that are sensed by DAF-2/InR and/or possibly GPCR-like receptors on the intestine, modifying the integrity of intestinal cells in aged animals. To identify the specific neuronal peptide(s) that exert a pro-aging effect on intestine, we knocked-down individual insulin-like peptides specifically in the neurons. Our preliminary data indicate that knockdown of at least one insulin gene delayed the age-related intestinal leakiness, similar to the effect of blocking peptide secretion in neurons. These studies implicate a novel role for neuronal peptides in modifying intestinal health. In future experiments, we aim to establish the precise neuronal circuitry of intestine-modifying peptide signals, and the key intestine-specific genes and pathways that modulate intestinal aging downstream of neuronal peptides. As a long-term goal, this study seeks to establish the functional conservation of neuronal peptides in the etiology of intestinal and organismal aging.

Vinci CR et al. (2007) J Biol Chem "Recognition of age-damaged (R,S)-adenosyl-L-methionine by two methyltransferases in the yeast Saccharomyces cerevisiae."

Vinci CR, Clarke SG

[J Biol Chem, 2007]

The biological methyl donor, S adenosylmethionine (AdoMet), can exist in two diastereoisomeric states with respect to its sulfonium ion. The "S" configuration, (S,S)AdoMet, is the only form that is produced enzymatically as well as the only form used in almost all biological methylation reactions. Under physiological conditions, however, the sulfonium ion can spontaneously racemize to the "R" form, producing (R,S)AdoMet. As of yet, (R,S)AdoMet has no known physiological function and may inhibit cellular reactions. In this study, two enzymes have been found in Saccharomyces cerevisiae that are capable of recognizing (R,S)AdoMet and using it to methylate homocysteine to form methionine. These enzymes are the products of the SAM4 and MHT1 genes, previously identified as homocysteine methyltransferases dependent upon AdoMet and S-methylmethionine respectively. We find here that Sam4 recognizes both (S,S) and (R,S)AdoMet, but its activity is much higher with the R,S form. Mht1 reacts with only the R,S form of AdoMet while no activity is seen with the S,S form. R,S-specific homocysteine methyltransferase activity is also shown here to occur in extracts of Arabidopsis thaliana, Drosophila melanogaster, and Caenorhabditis elegans, but has not been detected in several tissue extracts of Mus musculus. Such activity may function to prevent the accumulation of (R,S)AdoMet in these organisms.

Cecere, Z. et al. (2017) International Worm Meeting "Probing receptive fields in c. elegans."

Cecere, Z., Sharpee, T., Chalasani, S.

[International Worm Meeting, 2017]

The best way to probe receptive fields in a neural circuit is to inject uncorrelated stimulation into the circuit. We have built an optogenetics-based system to do just this. We use a custom Arduino control system to integrate a selective plane illumination microscope with an LED light engine. This system is capable of simultaneously performing full brain calcium imaging at 5 volumes per second and injecting uncorrelated activity into the C. elegans nervous system on the timescale of milliseconds. Here, we show preliminary results on the complexity of C. elegans receptive fields: how they are affected by the level of correlation and the predictability of their inputs.

Fanning S et al. (2018) Mol Cell "Lipidomic Analysis of -Synuclein Neurotoxicity Identifies Stearoyl CoA Desaturase as a Target for Parkinson Treatment."

Lou Y, Haque A, Freyzon Y, Farese RV, Terry-Kantor E, Hofbauer HF, Termine D, Welte MA, Barrasa MI, Imberdis T, Noble T, Lindquist S, Clish CB, Jaenisch R, Pincus D, Nuber S, Sandoe J, Kohlwein SD, Kim TE, Ho GPH, Ramalingam N, Walther TC, Baru V, Selkoe D, Srinivasan S, Landgraf D, Soldner F, Dettmer U, Fanning S, Becuwe M, Newby G

[Mol Cell, 2018]

In Parkinson's disease (PD), -synuclein (S) pathologically impacts the brain, a highly lipid-rich organ. We investigated how alterations in S or lipid/fattyacid homeostasis affect each other. Lipidomic profiling of human S-expressing yeast revealed increases in oleic acid (OA, 18:1), diglycerides, and triglycerides. These findings were recapitulated in rodent and human neuronal models of S dyshomeostasis (overexpression; patient-derived triplication or E46K mutation; E46K mice). Preventing lipid droplet formation or augmenting OA increased S yeast toxicity; suppressing the OA-generating enzyme stearoyl-CoA-desaturase (SCD) was protective. Genetic or pharmacological SCD inhibition ameliorated toxicity in S-overexpressing rat neurons. In a C.elegans model, SCD knockout prevented S-induced dopaminergic degeneration. Conversely, we observed detrimental effects of OA on S homeostasis: in human neural cells, excess OA caused S inclusion formation, which was reversed by SCD inhibition. Thus, monounsaturated fatty acid metabolism is pivotal for S-induced neurotoxicity, and inhibiting SCD represents a novel PD therapeutic approach.

Vandecandelaere I et al. (2017) PLoS One "Metabolic activity, urease production, antibiotic resistance and virulence in dual species biofilms of Staphylococcus epidermidis and Staphylococcus aureus."

Deforce D, Coenye T, Van Nieuwerburgh F, Vandecandelaere I

[PLoS One, 2017]

In this paper, the metabolic activity in single and dual species biofilms of Staphylococcus epidermidis and Staphylococcus aureus isolates was investigated. Our results demonstrated that there was less metabolic activity in dual species biofilms compared to S. aureus biofilms. However, this was not observed if S. aureus and S. epidermidis were obtained from the same sample. The largest effect on metabolic activity was observed in biofilms of S. aureus Mu50 and S. epidermidis ET-024. A transcriptomic analysis of these dual species biofilms showed that urease genes and genes encoding proteins involved in metabolism were downregulated in comparison to monospecies biofilms. These results were subsequently confirmed by phenotypic assays. As metabolic activity is related to acid production, the pH in dual species biofilms was slightly higher compared to S. aureus Mu50 biofilms. Our results showed that S. epidermidis ET-024 in dual species biofilms inhibits metabolic activity of S. aureus Mu50, leading to less acid production. As a consequence, less urease activity is required to compensate for low pH. Importantly, this effect was biofilm-specific. Also S. aureus Mu50 genes encoding virulence-associated proteins (Spa, SplF and Dps) were upregulated in dual species biofilms compared to monospecies biofilms and using Caenorhabditis elegans infection assays, we demonstrated that more nematodes survived when co-infected with S. epidermidis ET-024 and S. aureus mutants lacking functional spa, splF or dps genes, compared to nematodes infected with S. epidermidis ET-024 and wild- type S. aureus. Finally, S. epidermidis ET-024 genes encoding resistance to oxacillin, erythromycin and tobramycin were upregulated in dual species biofilms and increased resistance was subsequently confirmed. Our data indicate that both species in dual species biofilms of S. epidermidis and S. aureus influence each other's behavior, but additional studies are required necessary to elucidate the exact mechanism(s) involved.

Vandecandelaere I et al. (2014) Pathog Dis "Protease production by Staphylococcus epidermidis and its effect on Staphylococcus aureus biofilms."

Coenye T, Vandecandelaere I, Depuydt P, Nelis HJ

[Pathog Dis, 2014]

Due to the resistance of Staphylococcus aureus to several antibiotics, treatment of S. aureus infections is often difficult. As an alternative to conventional antibiotics, the field of bacterial interference is investigated. Staphylococcus epidermidis produces a serine protease (Esp) which inhibits S. aureus biofilm formation and which degrades S. aureus biofilms. In this study, we investigated the protease production of 114 S. epidermidis isolates, obtained from biofilms on endotracheal tubes (ET). Most of the S. epidermidis isolates secreted a mixture of serine, cysteine and metalloproteases. We found a link between high protease production by S. epidermidis and the absence of S. aureus in ET biofilms obtained from the same patient. Treating S. aureus biofilms with the supernatant (SN) of the most active protease producing S. epidermidis isolates resulted in a significant biomass decrease compared to untreated controls, while the number of metabolically active cells was not affected. The effect on the biofilm biomass was mainly due to serine proteases. Staphylococcus aureus biofilms treated with the SN of protease producing S. epidermidis were thinner with almost no extracellular matrix. An increased survival of Caenorhabditis elegans, infected with S. aureus Mu50, was observed when the SN of protease positive S. epidermidis was added.

Kamp F et al. (2010) EMBO J "Inhibition of mitochondrial fusion by -synuclein is rescued by PINK1, Parkin and DJ-1."

Haass C, Hegermann J, Giese A, Eimer S, Kamp F, Lutz AK, Nuscher B, Wender N, Brunner B, Winklhofer KF, Exner N, Beyer K, Bartels T

[EMBO J, 2010]

Aggregation of -synuclein (S) is involved in the pathogenesis of Parkinson's disease (PD) and a variety of related neurodegenerative disorders. The physiological function of S is largely unknown. We demonstrate with in vitro vesicle fusion experiments that S has an inhibitory function on membrane fusion. Upon increased expression in cultured cells and in Caenorhabditis elegans, S binds to mitochondria and leads to mitochondrial fragmentation. In C. elegans age-dependent fragmentation of mitochondria is enhanced and shifted to an earlier time point upon expression of exogenous S. In contrast, siRNA-mediated downregulation of S results in elongated mitochondria in cell culture. S can act independently of mitochondrial fusion and fission proteins in shifting the dynamic morphologic equilibrium of mitochondria towards reduced fusion. Upon cellular fusion, S prevents fusion of differently labelled mitochondrial populations. Thus, S inhibits fusion due to its unique membrane interaction. Finally, mitochondrial fragmentation induced by expression of S is rescued by coexpression of PINK1, parkin or DJ-1 but not the PD-associated mutations PINK1 G309D and parkin 1-79 or by DJ-1 C106A.

Tames, M. L. et al. (2017) International Worm Meeting "Dissecting the role of neurexin and neuroligin in C. elegans chemosensory behaviors."

Chalasani, S., Liu, Z., Tames, M. L.

[International Worm Meeting, 2017]

Neuroligins are evolutionarily conserved post-synaptic cell adhesion molecules that form trans-synaptic complexes with presynaptic neurexins. Importantly, mutations in these proteins are associated with devastating human conditions including autism, schizophrenia and others. Mammals have four Neuroligins (NL1-NL4) and three Neurexins (NRXN1-3). Both are type I membrane proteins found at most excitatory and inhibitory synapses. Although it is clear that this is an important pair of signaling molecules, less is known about the mechanisms that contribute to human brain disorders. The C. elegans genome includes two genes, nrx-1 and nlg-1, that encode single-pass transmembrane proteins that are structurally like vertebrate Neurexins and Neuroligins, respectively. While these proteins localize to most C. elegans synapses, animals with deletion mutations in nrx-1 or nlg-1 are viable and show normal locomotion, suggesting that these genes are not required for general synaptic function. However, others and we have identified specific and robust chemosensory behavioral defects in these mutants. We are using genetic and pharmacological methods to probe the role of nrx-1 and nlg-1 in modifying behavior.