Glial regulators of ions and solutes required for specific chemosensory functions in Caenorhabditis elegans

KCN Channels "Cue" Up GABA Release from Astrocytes

Glial KCNQ K+ Channels Control Neuronal Output by Regulating GABA Release From Glia in C. elegans Graziano B, Wang L, White OR, Kaplan DH, Fernandez-Abascal J, Bianchi L. Neuron . 2024;112(11):1832–1847.e7. doi: 10.1016/j.neuron.2024.02.013. Epub 2024 Mar 8. PMID: 38460523; PMCID: PMC11156561. KCNQs are voltage-gated K+ channels that control neuronal excitability and are mutated in epilepsy and autism spectrum disorder. KCNQs have been extensively studied in neurons, but their function in glia is unknown. Using voltage, calcium, and GABA imaging, optogenetics, and behavioral assays, we show here for the first time in Caenorhabditis elegans (C. elegans ) that glial KCNQ channels control neuronal excitability by mediating GABA release from glia via regulation of the function of L-type voltage-gated Ca2+ channels. Further, we show that human KCNQ channels have the same role when expressed in nematode glia, underscoring conservation of function across species. Finally, we show that pathogenic loss-of-function and gain-of-function human KCNQ2 mutations alter glia-to-neuron GABA signaling in distinct ways and that the KCNQ channel opener retigabine exerts rescuing effects. This work identifies glial KCNQ channels as key regulators of neuronal excitability via control of GABA release from glia.

Glial KCNQ K+ channels control neuronal output by regulating GABA release from glia in C. elegans

KCNQs are voltage-gated K+ channels that control neuronal excitability and are mutated in epilepsy and autism spectrum disorder (ASD). KCNQs have been extensively studied in neurons, but their function in glia is unknown. Using voltage, calcium, and GABA imaging, optogenetics, and behavioral assays, we show here for the first time in Caenorhabditis elegans (C. elegans) that glial KCNQ channels control neuronal excitability by mediating GABA release from glia via regulation of the function of L-type voltage-gated Ca2+ channels. Further, we show that human KCNQ channels have the same role when expressed in nematode glia, underscoring conservation of function across species. Finally, we show that pathogenic loss-of-function and gain-of-function human KCNQ2 mutations alter glia-to-neuron GABA signaling in distinct ways and that the KCNQ channel opener retigabine exerts rescuing effects. This work identifies glial KCNQ channels as key regulators of neuronal excitability via control of GABA release from glia.

Comparison of avoidance assay techniques to determine the response to 1-octanol in C. elegans

In C. elegans , avoidance behaviors are vital for the nematode's ability to respond to noxious environmental stimuli, including the odorant 1-octanol. To test avoidance to 1-octanol, researchers expose C. elegans to this odorant and determine the time taken to initiate backward locomotion. However, the 1-octanol avoidance assay is sensitive to sensory adaptation, where the avoidance response is reduced due to overexposure to the odorant. Here, we examined two methods to expose nematodes to 1-octanol, using an eyelash hair or a p10 pipette tip, to compare their susceptibility to cause sensory adaptation.

A helping hand: roles for accessory cells in the sense of touch across species

During touch, mechanical forces are converted into electrochemical signals by tactile organs made of neurons, accessory cells, and their shared extracellular spaces. Accessory cells, including Merkel cells, keratinocytes, lamellar cells, and glia, play an important role in the sensation of touch. In some cases, these cells are intrinsically mechanosensitive; however, other roles include the release of chemical messengers, the chemical modification of spaces that are shared with neurons, and the tuning of neural sensitivity by direct physical contact. Despite great progress in the last decade, the precise roles of these cells in the sense of touch remains unclear. Here we review the known and hypothesized contributions of several accessory cells to touch by incorporating research from multiple organisms including C. elegans, D. melanogaster, mammals, avian models, and plants. Several broad parallels are identified including the regulation of extracellular ions and the release of neuromodulators by accessory cells, as well as the emerging potential physical contact between accessory cells and sensory neurons via tethers. Our broader perspective incorporates the importance of accessory cells to the understanding of human touch and pain, as well as to animal touch and its molecular underpinnings, which are underrepresented among the animal welfare literature. A greater understanding of touch, which must include a role for accessory cells, is also relevant to emergent technical applications including prosthetics, virtual reality, and robotics.

Glia in Invertebrate Models: Insights from Caenorhabditis elegans

Glial cells modulate brain development, function, and health across all bilaterian animals, and studies in the past two decades have made rapid strides to uncover the underlying molecular mechanisms of glial functions. The nervous system of the invertebrate genetic model Caenorhabditis elegans (C. elegans) has small cell numbers with invariant lineages, mapped connectome, easy genetic manipulation, and a short lifespan, and the animal is also optically transparent. These characteristics are revealing C. elegans to be a powerful experimental platform for studying glial biology. This chapter discusses studies in C. elegans that add to our understanding of how glia modulate adult neural functions, and thereby animal behaviors, as well as emerging evidence of their roles as autonomous sensory cells. The rapid molecular and cellular advancements in understanding C. elegans glia in recent years underscore the utility of this model in studies of glial biology. We conclude with a perspective on future research avenues for C. elegans glia that may readily contribute molecular mechanistic insights into glial functions in the nervous system.

Protocols for treating C. elegans with pharmacological agents, osmoles, and salts for imaging and behavioral assays

Research rigor can be enhanced by pairing genetic tools with pharmacology and manipulations of solutes or ions. Here, we present a protocol for treating C. elegans with pharmacological agents, osmoles, and salts. We describe steps for agar plate supplementation, addition of the compound to the polymerized plates, and using liquid culture for exposure to the chemical. Treatment type depends on the stability and solubility of each compound. This protocol is applicable to both behavioral and in vivo imaging experiments. For complete details on the use and execution of this protocol, please refer to Wang et al. (2022),1 Fernandez-Abascal et al. (2022),2 and Johnson et al. (2020).3.

Gold Nanoparticles Reduce Food Sensation in Caenorhabditis elegans via the Voltage-Gated Channel EGL-19

Introduction

The increasing use of gold nanoparticles (Au NPs) in the medical field has raised concerns about the potential adverse effect of Au NPs exposure. However, it is difficult to assess the health risks of Au NPs exposure at the individual organ level using current measurement techniques.

Methods

The physical and chemical properties of Au NPs were characterized by transmission electron microscope (TEM), Fourier transform infrared (FTIR), and zeta sizer. The RNA-seq data of Au NPs-exposed worms were analyzed. The food intake was measured by liquid culture and Pharyngeal pumping rate. The function of the smell and taste neurons was evaluated by the chemotaxis and avoidance assay. The activation of ASE neurons was analyzed by calcium imaging. The gene expression of ins-22 and egl-19 was obtained from the C. elegans single cell RNA-seq databases.

Results

Our data analysis indicated that 62.8% of the significantly altered genes were functional in the nervous system. Notably, developmental stage analysis demonstrated that exposure to Au NPs interfered with animal development by regulating foraging behavior. Also, our chemotaxis results showed that exposure to Au NPs reduced the sensation of C. elegans to NaCl, which was consistent with the decrease in calcium transit of ASEL. Further studies confirmed that the reduced calcium transit was dependent on voltage-gated calcium channel EGL-19. The neuropeptide INS-22 was partially involved in Au NPs-induced NaCl sensation defect. Therefore, we proposed that Au NPs reduced the calcium transit in the ASEL neuron through egl-19-dependent calcium channels. It was partially regulated by the DAF-16 targeting neuropeptide INS-22.

Discussion

Our results demonstrate that Au NPs affect food sensation by reducing the calcium transit in ASEL neurons, which further leads to reduced pharynx pumping and feeding defects. The toxicology studies of Au NPs from worms have great potential to guide the usage of Au NPs in the medical field such as targeted drug delivery.