High neural activity accelerates the decline of cognitive plasticity with age in Caenorhabditis elegans

Neurogenesis in Caenorhabditis elegans

Animals rely on their nervous systems to process sensory inputs, integrate these with internal signals, and produce behavioral outputs. This is enabled by the highly specialized morphologies and functions of neurons. Neuronal cells share multiple structural and physiological features, but they also come in a large diversity of types or classes that give the nervous system its broad range of functions and plasticity. This diversity, first recognized over a century ago, spurred classification efforts based on morphology, function, and molecular criteria. Caenorhabditis elegans, with its precisely mapped nervous system at the anatomical level, an extensive molecular description of most of its neurons, and its genetic amenability, has been a prime model for understanding how neurons develop and diversify at a mechanistic level. Here, we review the gene regulatory mechanisms driving neurogenesis and the diversification of neuron classes and subclasses in C. elegans. We discuss our current understanding of the specification of neuronal progenitors and their differentiation in terms of the transcription factors involved and ensuing changes in gene expression and chromatin landscape. The central theme that has emerged is that the identity of a neuron is defined by modules of gene batteries that are under control of parallel yet interconnected regulatory mechanisms. We focus on how, to achieve these terminal identities, cells integrate information along their developmental lineages. Moreover, we discuss how neurons are diversified postembryonically in a time-, genetic sex-, and activity-dependent manner. Finally, we discuss how the understanding of neuronal development can provide insights into the evolution of neuronal diversity.

Understanding exogenous factors and biological mechanisms for cognitive frailty: A multidisciplinary scoping review

Cognitive frailty (CF) is the conjunction of cognitive impairment without dementia and physical frailty. While predictors of each element are well-researched, mechanisms of their co-occurrence have not been integrated, particularly in terms of relationships between social, psychological, and biological factors. This interdisciplinary scoping review set out to categorise a heterogenous multidisciplinary literature to identify potential pathways and mechanisms of CF, and research gaps. Studies were included if they used the definition of CF OR focused on conjunction of cognitive impairment and frailty (by any measure), AND excluded studies on specific disease populations, interventions, epidemiology or prediction of mortality. Searches used Web of Science, PubMed and Science Direct. Search terms included "cognitive frailty" OR (("cognitive decline" OR "cognitive impairment") AND (frail*)), with terms to elicit mechanisms, predictors, causes, pathways and risk factors. To ensure inclusion of animal and cell models, keywords such as "behavioural" or "cognitive decline" or "senescence", were added. 206 papers were included. Descriptive analysis provided high-level categorisation of determinants from social and environmental through psychological to biological. Patterns distinguishing CF from Alzheimer's disease were identified and social and psychological moderators and mediators of underlying biological and physiological changes and of trajectories of CF development were suggested as foci for further research.

The angiotensin II receptors type 1 and 2 modulate astrocytes and their crosstalk with microglia and neurons in an in vitro model of ischemic stroke

BACKGROUND

Astrocytes are the most abundant cell type of the central nervous system and are fundamentally involved in homeostasis, neuroprotection, and synaptic plasticity. This regulatory function of astrocytes on their neighboring cells in the healthy brain is subject of current research. In the ischemic brain we assume disease specific differences in astrocytic acting. The renin-angiotensin-aldosterone system regulates arterial blood pressure through endothelial cells and perivascular musculature. Moreover, astrocytes express angiotensin II type 1 and 2 receptors. However, their role in astrocytic function has not yet been fully elucidated. We hypothesized that the angiotensin II receptors impact astrocyte function as revealed in an in vitro system mimicking cerebral ischemia. Astrocytes derived from neonatal wistar rats were exposed to telmisartan (angiotensin II type 1 receptor-blocker) or PD123319 (angiotensin II type 2 receptor-blocker) under normal conditions (control) or deprivation from oxygen and glucose. Conditioned medium (CM) of astrocytes was harvested to elucidate astrocyte-mediated indirect effects on microglia and cortical neurons.

RESULT

The blockade of angiotensin II type 1 receptor by telmisartan increased the survival of astrocytes during ischemic conditions in vitro without affecting their proliferation rate or disturbing their expression of S100A10, a marker of activation. The inhibition of the angiotensin II type 2 receptor pathway by PD123319 resulted in both increased expression of S100A10 and proliferation rate. The CM of telmisartan-treated astrocytes reduced the expression of pro-inflammatory mediators with simultaneous increase of anti-inflammatory markers in microglia. Increased neuronal activity was observed after treatment of neurons with CM of telmisartan- as well as PD123319-stimulated astrocytes.

CONCLUSION

Data show that angiotensin II receptors have functional relevance for astrocytes that differs in healthy and ischemic conditions and effects surrounding microglia and neuronal activity via secretory signals. Above that, this work emphasizes the strong interference of the different cells in the CNS and that targeting astrocytes might serve as a therapeutic strategy to influence the acting of glia-neuronal network in de- and regenerative context.

Zebrafish and nematodes as whole organism models to measure developmental neurotoxicity

Despite the growing epidemiological evidence of an association between toxin exposure and developmental neurotoxicity (DNT), systematic testing of DNT is not mandatory in international regulations for admission of pharmaceuticals or industrial chemicals. However, to date around 200 compounds, ranging from pesticides, pharmaceuticals and industrial chemicals, have been tested for DNT in the current OECD test guidelines (TG-443 or TG-426). There are calls for the development of new approach methodologies (NAMs) for DNT, which has resulted in a DNT testing battery using in vitro human cell-based assays. These assays provide a means to elucidate the molecular mechanisms of toxicity in humans which is lacking in animal-based toxicity tests. However, cell-based assays do not represent all steps of the complex process leading to DNT. Validated models with a multi-organ network of pathways that interact at the molecular, cellular and tissue level at very specific timepoints in a life cycle are currently missing. Consequently, whole model organisms are being developed to screen for, and causally link, new molecular targets of DNT compounds and how they affect whole brain development and neurobehavioral endpoints. Given the practical and ethical restraints associated with vertebrate testing, lower animal models that qualify as 3 R (reduce, refine and replace) models, including the nematode (Caenorhabditis elegans) and the zebrafish (Danio rerio) will prove particularly valuable for unravelling toxicity pathways leading to DNT. Although not as complex as the human brain, these 3 R-models develop a complete functioning brain with numerous neurodevelopmental processes overlapping with human brain development. Importantly, the main signalling pathways relating to (neuro)development, metabolism and growth are highly conserved in these models. We propose the use of whole model organisms specifically zebrafish and C. elegans for DNT relevant endpoints.

Adult Single-nucleus Neuronal Transcriptomes of Insulin Signaling Mutants Reveal Regulators of Behavior and Learning

The insulin/insulin-like signaling (IIS) pathway regulates many of C. elegans' adult functions, including learning and memory 1 . While whole-worm and tissue-specific transcriptomic analyses have identified IIS targets 2,3 , a higher-resolution single-cell approach is required to identify changes that confer neuron-specific improvements in the long-lived insulin receptor mutant, daf-2 . To understand how behaviors that are controlled by a small number of neurons change in daf-2 mutants, we used the deep resolution of single-nucleus RNA sequencing to define each neuron type's transcriptome in adult wild-type and daf-2 mutants. First, we found surprising differences between wild-type L4 larval neurons and young adult neurons in chemoreceptor expression, synaptic genes, and learning and memory genes. These Day 1 adult neuron transcriptomes allowed us to identify adult AWC-specific regulators of chemosensory function and to predict neuron-to-neuron peptide/receptor pairs. We then identified gene expression changes that correlate with daf-2's improved cognitive functions, particularly in the AWC sensory neuron that controls learning and associative memory 4 , and used behavioral assays to test their roles in cognitive function. Combining deep single-neuron transcriptomics, genetic manipulation, and behavioral analyses enabled us to identify genes that may function in a single adult neuron to control behavior, including conserved genes that function in learning and memory.

One-Sentence Summary

Single-nucleus sequencing of adult wild-type and daf-2 C. elegans neurons reveals functionally relevant transcriptional changes, including regulators of chemosensation, learning, and memory.

Enhancing axonal myelination in seniors: A review exploring the potential impact cannabis has on myelination in the aged brain

Consumption of cannabis is on the rise as public opinion trends toward acceptance and its consequent legalization. Specifically, the senior population is one of the demographics increasing their use of cannabis the fastest, but research aimed at understanding cannabis' impact on the aged brain is still scarce. Aging is characterized by many brain changes that slowly alter cognitive ability. One process that is greatly impacted during aging is axonal myelination. The slow degradation and loss of myelin (i.e., demyelination) in the brain with age has been shown to associate with cognitive decline and, furthermore, is a common characteristic of numerous neurological diseases experienced in aging. It is currently not known what causes this age-dependent degradation, but it is likely due to numerous confounding factors (i.e., heightened inflammation, reduced blood flow, cellular senescence) that impact the many cells responsible for maintaining overall homeostasis and myelin integrity. Importantly, animal studies using non-human primates and rodents have also revealed demyelination with age, providing a reliable model for researchers to try and understand the cellular mechanisms at play. In rodents, cannabis was recently shown to modulate the myelination process. Furthermore, studies looking at the direct modulatory impact cannabis has on microglia, astrocytes and oligodendrocyte lineage cells hint at potential mechanisms to prevent some of the more damaging activities performed by these cells that contribute to demyelination in aging. However, research focusing on how cannabis impacts myelination in the aged brain is lacking. Therefore, this review will explore the evidence thus far accumulated to show how cannabis impacts myelination and will extrapolate what this knowledge may mean for the aged brain.

Unconventional Myosins from Caenorhabditis elegans as a Probe to Study Human Orthologues

Unconventional myosins are a superfamily of actin-based motor proteins that perform a number of roles in fundamental cellular processes, including (but not limited to) intracellular trafficking, cell motility, endocytosis, exocytosis and cytokinesis. 40 myosins genes have been identified in humans, which belong to different 12 classes based on their domain structure and organisation. These genes are widely expressed in different tissues, and mutations leading to loss of function are associated with a wide variety of pathologies while over-expression often results in cancer. Caenorhabditis elegans (C. elegans) is a small, free-living, non-parasitic nematode. ~38% of the genome of C. elegans has predicted orthologues in the human genome, making it a valuable tool to study the function of human counterparts and human diseases. To date, 8 unconventional myosin genes have been identified in the nematode, from 6 different classes with high homology to human paralogues. The hum-1 and hum-5 (heavy chain of an unconventional myosin) genes encode myosin of class I, hum-2 of class V, hum-3 and hum-8 of class VI, hum-6 of class VII and hum-7 of class IX. The hum-4 gene encodes a high molecular mass myosin (307 kDa) that is one of the most highly divergent myosins and is a member of class XII. Mutations in many of the human orthologues are lethal, indicating their essential properties. However, a functional characterisation for many of these genes in C. elegans has not yet been performed. This article reviews the current knowledge of unconventional myosin genes in C. elegans and explores the potential use of the nematode to study the function and regulation of myosin motors to provide valuable insights into their role in diseases.

Aerotaxis Assay in Caenorhabditis elegans to Study Behavioral Plasticity

C. elegans shows robust and reproducible behavioral responses to oxygen. Specifically, worms prefer O 2 levels of 5-10% and avoid too high or too low O 2 . Their O 2 preference is not fixed but shows plasticity depending on experience, context, or genetic background. We recently showed that this experience-dependent plasticity declines with age, providing a useful behavioral readout for studying the mechanisms of age-related decline of neural plasticity. Here, we describe a technique to visualize behavioral O 2 preference and its plasticity in C. elegans , by creating spatial gradients of [O 2 ] in a microfluidic polydimethylsiloxane (PDMS) chamber and recording the resulting spatial distribution of the animals.

Molecular lesions in alleles of the Caenorhabditis elegans lin-11 gene

The LIM homeodomain transcription factor LIN-11 is a key regulator of vulva, uterine, and neuron development in C. elegans. Multiple alleles of lin-11 are available, but none had been sequenced. We found that the reference allele, n389, is a 15900 bp deletion that also affects two other protein-coding genes, ZC247.1 and ZC247.2. The frequently used n566 allele is a 288bp deletion located in an intron and affecting the splice acceptor site.

Tyraminergic corollary discharge filters reafferent perception in a chemosensory neuron

Interpreting sensory information requires its integration with the current behavior of the animal. However, how motor-related circuits influence sensory information processing is incompletely understood. Here, we report that current locomotor state directly modulates the activity of BAG CO₂ sensory neurons in Caenorhabditis elegans. By recording neuronal activity in animals freely navigating CO₂ landscapes, we found that during reverse crawling states, BAG activity is suppressed by tyraminergic corollary discharge signaling. We provide genetic evidence that tyramine released from the RIM reversal interneurons extrasynaptically activates the inhibitory chloride channel LGC-55 in BAG. Disrupting this pathway genetically leads to excessive behavioral responses to CO₂ stimuli. Moreover, we find that LGC-55 signaling cancels out perception of self-produced CO₂ and O₂ stimuli when animals reverse into their own gas plume in ethologically relevant aqueous environments. Our results show that sensorimotor integration involves corollary discharge signals directly modulating chemosensory neurons.

Kidins220/ARMS modulates brain morphology and anxiety-like traits in adult mice

Kinase D interacting substrate of 220 kDa (Kidins220), also known as ankyrin repeat-rich membrane spanning (ARMS), is a transmembrane scaffold protein that participates in fundamental aspects of neuronal physiology including cell survival, differentiation, and synaptic plasticity. The Kidins220 constitutive knockout line displays developmental defects in the nervous and cardiovascular systems that lead to embryonic lethality, which has so far precluded the study of this protein in the adult. Moreover, Kidins220 mRNA is tightly regulated by alternative splicing, whose impact on nervous system physiology has not yet been addressed in vivo. Here, we have asked to what extent the absence of Kidins220 splicing and the selective knockout of Kidins220 impact on adult brain homeostasis. To answer this question, we used a floxed line that expresses only the full-length, non-spliced Kidins220 mRNA, and a forebrain-specific, CaMKII-Cre driven Kidins220 conditional knockout (cKO) line. Kidins220 cKO brains are characterized by enlarged ventricles in the absence of cell death, and by deficient dendritic arborization in several cortical regions. The deletion of Kidins220 leads to behavioral changes, such as reduced anxiety-like traits linked to alterations in TrkB-BDNF signaling and sex-dependent alterations of hippocampal-dependent spatial memory. Kidins220 floxed mice present similarly enlarged brain ventricles and increased associative memory. Thus, both the absolute levels of Kidins220 expression and its splicing pattern are required for the correct brain development and related expression of behavioral phenotypes. These findings are relevant in light of the increasing evidence linking mutations in the human KIDINS220 gene to the onset of severe neurodevelopmental disorders.

A global phosphoproteomics analysis of adult Fasciola gigantica by LC-MS/MS

Protein phosphorylation plays key roles in a variety of essential cellular processes. Fasciola gigantica is a tropical liver fluke causing hepatobiliary disease fascioliasis, leading to human health threats and heavy economic losses. Although the genome and protein kinases of F. gigantica provided new insights to understand the molecular biology and etiology of this parasite, there is scant knowledge of protein phosphorylation events in F. gigantica. In this study, we characterized the global phosphoproteomics of adult F. gigantica by phosphopeptide enrichment-based LC–MS/MS, a high-throughput analysis to maximize the detection of a large repertoire of phosphoproteins and phosphosites. A total of 1030 phosphopeptides with 1244 phosphosites representing 635 F. gigantica phosphoproteins were identified. The phosphoproteins were involved in a wide variety of biological processes including cellular, metabolic, and single-organism processes. Meanwhile, these proteins were found predominantly in cellular components like membranes and organelles with molecular functions of binding (51.3%) and catalytic activity (40.6%). The KEGG annotation inferred that the most enriched pathways of the phosphoproteins included tight junction, spliceosome, and RNA transport (each one contains 15 identified proteins). Combining the reports in other protozoa and helminths, the phosphoproteins identified in this work play roles in metabolic regulation and signal transduction. To our knowledge, this work performed the first global phosphoproteomics analysis of adult F. gigantica, which provides valuable information for development of intervention strategies for fascioliasis.

Regulation of longevity by depolarization-induced activation of PLC-β-IP3R signaling in neurons

Mitochondrial ATP production is a well-known regulator of neuronal excitability. The reciprocal influence of plasma-membrane potential on ATP production, however, remains poorly understood. Here, we describe a mechanism by which depolarized neurons elevate the somatic ATP/ADP ratio in Drosophila glutamatergic neurons. We show that depolarization increased phospholipase-Cβ (PLC-β) activity by promoting the association of the enzyme with its phosphoinositide substrate. Augmented PLC-β activity led to greater release of endoplasmic reticulum Ca2+ via the inositol trisphosphate receptor (IP3R), increased mitochondrial Ca2+ uptake, and promoted ATP synthesis. Perturbations that decoupled membrane potential from this mode of ATP synthesis led to untrammeled PLC-β-IP3R activation and a dramatic shortening of Drosophila lifespan. Upon investigating the underlying mechanisms, we found that increased sequestration of Ca2+ into endolysosomes was an intermediary in the regulation of lifespan by IP3Rs. Manipulations that either lowered PLC-β/IP3R abundance or attenuated endolysosomal Ca2+ overload restored animal longevity. Collectively, our findings demonstrate that depolarization-dependent regulation of PLC-β-IP3R signaling is required for modulation of the ATP/ADP ratio in healthy glutamatergic neurons, whereas hyperactivation of this axis in chronically depolarized glutamatergic neurons shortens animal lifespan by promoting endolysosomal Ca2+ overload.