Na AR et al. (2008) Biochem Biophys Res Commun "A critical role for Romo1-derived ROS in cell proliferation."

Na AR, Lee SB, Lee MS, Yoo YD, Park SH, Chung YM

[Biochem Biophys Res Commun, 2008]

Low levels of endogenous reactive oxygen species (ROS) originating from NADPH oxidase have been implicated in various signaling pathways induced by growth factors and mediated by cytokines. However, the main source of ROS is known to be the mitochondria, and increased levels of ROS from the mitochondria have been observed in many cancer cells. Thus far, the mechanism of ROS production in cancer cell proliferation in the mitochondria is not well-understood. We recently identified a novel protein, ROS modulator 1 (Romo1), and reported that increased expression of Romo1-triggered ROS production in the mitochondria. The experiments conducted in the present study showed that Romo1-derived ROS were indispensable for the proliferation of both normal and cancer cells. Furthermore, whilst cell growth was inhibited by blocking the ERK pathway in cells transfected with siRNA directed against Romo1, the cell growth was recovered by addition of exogenous hydrogen peroxide. The results of this study suggest that Romo1-induced ROS may play an important role in redox signaling in cancer cells.

Zou J et al. (2023) Nat Biotechnol "A DNA nanodevice for mapping sodium at single-organelle resolution."

Gupta PD, Mitra K, Smith JJ, Rao R, Ramirez JR, Zou J, Anees P, Krishnan Y, Oettinger D, Veetil AT, Kratsios P

[Nat Biotechnol, 2023]

Cellular sodium ion (Na⁺) homeostasis is integral to organism physiology. Our current understanding of Na⁺ homeostasis is largely limited to Na⁺ transport at the plasma membrane. Organelles may also contribute to Na⁺ homeostasis; however, the direction of Na⁺ flow across organelle membranes is unknown because organellar Na⁺ cannot be imaged. Here we report a pH-independent, organelle-targetable, ratiometric probe that reports lumenal Na⁺. It is a DNA nanodevice containing a Na⁺-sensitive fluorophore, a reference dye and an organelle-targeting domain. By measuring Na⁺ at single endosome resolution in mammalian cells and Caenorhabditis elegans, we discovered that lumenal Na⁺ levels in each stage of the endolysosomal pathway exceed cytosolic levels and decrease as endosomes mature. Further, we find that lysosomal Na⁺ levels in nematodes are modulated by the Na⁺/H⁺ exchanger NHX-5 in response to salt stress. The ability to image subcellular Na⁺ will unveil mechanisms of Na⁺ homeostasis at an increased level of cellular detail.

Furuhashi T et al. (2016) Biochem Biophys Res Commun "L-arginine, an active component of salmon milt nucleoprotein, promotes thermotolerance via Sirtuin in Caenorhabditis elegans."

Furuhashi T, Matsunaga M, Sakamoto K, Asahara Y

[Biochem Biophys Res Commun, 2016]

We previously showed that salmon milt nucleoprotein (NP) promotes thermotolerance in Caenorhabditis elegans; however, the active component and physiological mechanism of this effect has remained unclear. l-arginine (AR) is a major component of protamine and thus it has been proposed as the possible active component of NP. In this study, the viability of C. elegans treated with AR under heat stress was assessed and AR was shown to extend the survival term of the heat-stressed organisms. Additionally, AR was shown to restore the thrashing movement of the worms that is suppressed by heat stress. Treatment with AR was furthermore shown to promote thermotolerance in a DAF-16- and SIR-2.1-dependent manner, where DAF-16 and SIR-2.1 are homologs of FoxO and SirT1, respectively. Taken together, these data suggest that AR is one of the active components of NP and promotes thermotolerance via the activation of DAF-16 and SIR-2.1.

Yuan A et al. (2003) Neuron "The sodium-activated potassium channel is encoded by a member of the Slo gene family."

Yuan A, Santi CM, Pollak K, Kaczmarek L, Crowder CM, Wang ZW, Wei A, Nonet M, Salkoff L

[Neuron, 2003]

Na+-activated potassium channels (K-Na) have been identified in cardiomyocytes and neurons where they may provide protection against ischemia. We now report that K-Na is encoded by the rSlo2 gene (also called Slack), the mammalian ortholog of slo-2 in C. elegans. rSlo2, heterologously expressed, shares many properties of native K-Na including activation by intracellular Na+, high conductance, and prominent subconductance states. In addition to activation by Na+, we report that rSLO-2 channels are cooperatively activated by intracellular Cl-, similar to C. elegans SLO-2 channels. Since intracellular Na+ and Cl- both rise in oxygen-deprived cells, coactivation may more effectively trigger the activity of rSLO-2 channels in ischemia. In C. elegans, mutational and physiological analysis revealed that the SLO-2 current is a major component of the delayed rectifier. We demonstrate in C. elegans that slo-2 mutants are hypersensitive to hypoxia, suggesting a conserved role for the slo-2 gene

Wang L et al. (2017) J Neurosci "A Gustatory Neural Circuit of Caenorhabditis elegans Generates Memory-Dependent Behaviors in Na+ Chemotaxis."

Wang L, Sato H, Kunitomo H, Tomioka M, Satoh Y, Iino Y

[J Neurosci, 2017]

Animals show various behaviors in response to environmental chemicals. These behaviors are often plastic depending on previous experiences. Caenorhabditis elegans, which has highly developed chemosensory system with a limited number of sensory neurons, is an ideal model for analyzing the role of each neuron in innate and learned behaviors. Here we report a new type of memory-dependent behavioral plasticity in Na(+) chemotaxis generated by the left member of bilateral gustatory neuron pair ASE (ASEL neuron). When worms were cultivated in the presence of Na(+), they showed positive chemotaxis towards Na(+); but when worms were cultivated under Na(+)-free conditions, they showed no preference in Na(+) concentration. Both channelrhodopsin-2 (ChR2) activation with blue light and upsteps of Na(+) concentration activated ASEL only after cultivation with Na(+), as judged by increase in intracellular Ca(2+) Under cultivation conditions with Na(+), photoactivation of ASEL caused activation of its downstream interneurons AIY and AIA, which stimulate forward locomotion, and inhibition of its downstream interneuron AIB, which inhibits the turning/reversal behavior, and overall drove worms towards higher Na(+) concentrations. We also found that the Gq signaling pathway and the neurotransmitter glutamate are both involved in the behavioral response generated by ASEL. SIGNIFICANCE STATEMENT: Animals have acquired various types of behavioral plasticity during their long evolutionary history. C. elegans prefers odors associated with food, but plastically changes its behavioral response according to previous experience. Here we report a new type of behavioral response generated by a single gustatory sensory neuron, the ASE-left neuron (ASEL). ASEL did not respond to photostimulation or upsteps of Na(+) concentration when worms were cultivated in Na(+)-free conditions; however, when worms were cultivated with Na(+), ASEL responded and inhibited AIB to avoid turning, and stimulated AIY and AIA to promote forward locomotion, which collectively drove worms towards higher Na(+) concentrations. Glutamate and the Gq signaling pathway are essential for driving worms towards higher Na(+) concentrations.

Toshiaki Suzuki et al. (2003) International Worm Meeting "Analysis of Ce-PARKIN in C. elegans"

Nobutaka Hattori, Toshiaki Suzuki, Keiji Tanaka, Yoshikuni Mizuno, Shohei MItani, Noriyuki Matsuda, Hideki Yashiroda, Toshiaki Kitami, Keiko Gengyo-Ando

[International Worm Meeting, 2003]

Autosomal recessive juvenile parkinsonism (AR-JP) is one of the most common forms of familial parkinsons disease characterized by selective loss of dopaminergic neurons in substantia nigra and the locus coeruleus. parkin is the causative gene of AR-JP. The human parkin gene encodes 465 amino acids with a ubiquitin-like domain in the amino-terminus and two RING finger motifs in the carboxy terminus. So far, various deletion mutations and point mutations have been discovered in patients of AR-JP, suggesting that the loss of function of Parkin is the cause of AR-JP. Recently we and others showed that Parkin has a ubiquitin-protein ligase activity and therefore suggested that the defect of protein degradation in the neurons of AR-JP patients (Shimura H. et al. Nat. Genet. 25, 302-5, 2000). To investigate the function of Parkin in vivo, we began to analyze the Ce-PARKIN of C. elegans. Two deletion mutations in parkin genes show no defect in their viabilities. The expression of Ce-PARKIN seems to be specific to subset of neurons. Therefore, we focused on the function of Ce-PARKIN in the neurons and the analysis is underway.

Johnson CK et al. (2020) J Neurophysiol "The Na+/K+-ATPase is needed in glia of touch receptors for responses to touch in C. elegans."

Wang Y, Bianchi L, Fernandez-Abascal J, Johnson CK, Wang L

[J Neurophysiol, 2020]

Four of the five types of mammalian mechanosensors are composed of nerve endings and accessory cells. In C. elegans we showed that glia supports the function of nose touch neurons via the activity of glial Na⁺ and K⁺channels. We show here that a third regulator of Na⁺ and K⁺, the Na⁺/K⁺-ATPase, is needed in glia of nose touch neurons for touch. Importantly, we show that the two Na⁺/K⁺-ATPase genes are needed for the function rather than structural integrity and that their ion transport activity is crucial for touch. Finally, when glial Na⁺/K⁺-ATPase genes are knocked-out, touch can be restored by activation of a third Na⁺/K⁺-ATPase. Taken together, these data show the requirement in glia of touch neurons of the function of the Na⁺/K⁺-ATPase. These data underscore the importance of the homeostasis of Na⁺ and K⁺, most likely in the space surrounding touch neurons, in touch sensation, a function that might be conserved across species.

Bruckbauer A et al. (2017) Am J Cardiovasc Dis "Leucine-nicotinic acid synergy stimulates AMPK/Sirt1 signaling and regulates lipid metabolism and lifespan in Caenorhabditis elegans, and hyperlipidemia and atherosclerosis in mice."

Zemel MB, Li F, Cao Q, Cui X, Bruckbauer A, Zha L, Jing J, Xue B, Banerjee J, Shi H

[Am J Cardiovasc Dis, 2017]

BACKGROUND/AIMS: Nicotinic acid (NA), a lipid-lowering drug, serves as a source of NAD(+), the cofactor for Sirt1. Leucine (Leu) stimulates the AMPK/Sirt1 axis and amplifies the effects of other AMPK/Sirt1 activating compounds. Therefore, we tested the interactive effects of leucine and low dose NA on AMPK/Sirt1 signaling and downstream effects of lipid metabolism in cell culture, C. elegans and mice. METHODS: LDL-receptor knockout mice were fed an atherogenic Western diet supplemented with leucine (24 g/kg diet) and sub-therapeutic NA combinations (50 mg/kg diet and 250 mg/kg diet) or low therapeutic NA (1000 mg/kg diet) for 8 weeks to evaluate markers of hyperlipidemia and atherosclerosis. RESULTS: NA-Leu increased P-AMPK and Sirt1 in adipocytes and myotubes. In C. elegans, NA-Leu increased P-AMPK and DAF-16 (FOXO), reduced lipid accumulation and increased median survival under mild oxidative stress conditions. In the mice, NA-Leu reduced total cholesterol, cholesterol esters, plasma triglycerides, atherosclerotic lesion size, lipid area, and aortic macrophage infiltration, similar to the therapeutic NA dose. CONCLUSION: Leu amplifies the effects of NA on lipid metabolism, hyperlipidemia and atherosclerosis in mice, at least in part by activation of the AMPK/Sirt1 axis. This combination may be a potential therapeutic alternative for hyperlipidemia and atherosclerosis.

Sharma V et al. (2016) Bioinform Biol Insights "Nematode Sodium Calcium Exchangers: A Surprising Lack of Transport."

O'Halloran DM, Sharma V

[Bioinform Biol Insights, 2016]

Na(+)/Ca(2+) exchangers are low-affinity, high-capacity transporters that rapidly transport calcium against a gradient of Na(+) ions. Na(+)/Ca(2+) exchangers are divided into three groups based upon substrate specificity: Na(+)/Ca(2+) exchangers (NCX), Na(+)/Ca(2+)/K(+) exchangers (NCKX), and Ca(2+)/cation exchangers (NCLX). In mammals, there are three NCX genes, five NCKX genes, and a single NCLX gene. The genome of the nematode Caenorhabditis elegans contains 10 Na(+)/Ca(2+) exchanger genes: three NCX, five NCLX, and two NCKX genes. In a previous study, we characterized the structural and taxonomic specializations within the family of Na(+)/Ca(2+) exchangers across the phylum Nematoda and observed a complex picture of Na(+)/Ca(2+) exchanger evolution across diverse nematode species. We noted multiple cases of putative gene gain and loss and, most surprisingly, did not detect members of the NCLX type of exchangers within subsets of nematode species. In this commentary, we discuss these findings and speculate on the functional outcomes and physiology of these observations. Our data highlight the importance of studying diverse systems in order to get a deeper understanding of the evolution and regulation of Ca(2+) signaling critical for animal function.

Blaustein MP et al. (1999) Physiol Rev "Sodium/calcium exchange: its physiological implications."

Blaustein MP, Lederer WJ

[Physiol Rev, 1999]

The Na+/Ca2+ exchanger, an ion transport protein, is expressed in the plasma membrane (PM) of virtually all animal cells. It extrudes Ca2+ in parallel with the PM ATP-driven Ca2+ pump. As a reversible transporter, it also mediates Ca2+ entry in parallel with various ion channels. The energy for net Ca2+ transport by the Na+/Ca2+ exchanger and its direction depend on the Na+, Ca2+, and K+ gradients across the PM, the membrane potential, and the transport stoichiometry. In most cells, three Na+ are exchanged for one Ca2+. In vertebrate photoreceptors, some neurons, and certain other cells, K+ is transported in the same direction as Ca2+, with a coupling ratio of four Na+ to one Ca2+ plus one K+. The exchanger kinetics are affected by nontransported Ca2+, Na+, protons, ATP, and diverse other modulators. Five genes that code for the exchangers have been identified in mammals: three in the Na+/Ca2+ exchanger family (NCX1, NCX2, and NCX3) and two in the Na+/Ca2+ plus K+ family (NCKX1 and NCKX2). Genes homologous to NCX1 have been identified in frog, squid, lobster, and Drosophila. In mammals, alternatively spliced variants of NCX1 have been identified; dominant expression of these variants is cell type specific, which suggests that the variations are involved in targeting and/or functional differences. In cardiac myocytes, and probably other cell types, the exchanger serves a housekeeping role by maintaining a low intracellular Ca2+ concentration; its possible role in cardiac excitation-contraction coupling is controversial. Cellular increases in Na+ concentration lead to increases in Ca2+ concentration mediated by the Na+/Ca2+ exchanger; this is important in the therapeutic action of cardiotonic steroids like digitalis. Similarly, alterations of Na+ and Ca2+ apparently modulate basolateral K+ conductance in some epithelia, signaling in some special sense organs (e.g., photoreceptors and olfactory receptors) and Ca2+-dependent secretion in neurons and in many secretory cells. The juxtaposition of PM and sarco(endo)plasmic reticulum membranes may permit the PM Na+/Ca2+ exchanger to regulate sarco(endo)plasmic reticulum Ca2+ stores and influence cellular Ca2+ signaling.