Tachykinins: Neuropeptides That Are Ancient, Diverse, Widespread and Functionally Pleiotropic

Proteome-wide neuropeptide identification using NeuroPeptide-HMMer (NP-HMMer)

Neuropeptides are essential neuronal signaling molecules that orchestrate animal behavior and physiology via actions within the nervous system and on peripheral tissues. Due to the small size of biologically active mature peptides, their identification on a proteome-wide scale poses a significant challenge using existing bioinformatics tools like BLAST. To address this, we have developed NeuroPeptide-HMMer (NP-HMMer), a hidden Markov model (HMM)-based tool to facilitate neuropeptide discovery, especially in underexplored invertebrates. NP-HMMer utilizes manually curated HMMs for 46 neuropeptide families, enabling rapid and accurate identification of neuropeptides. Validation of NP-HMMer on Drosophila melanogaster, Daphnia pulex, Tribolium castaneum and Tenebrio molitor demonstrated its effectiveness in identifying known neuropeptides across diverse arthropods. Additionally, we showcase the utility of NP-HMMer by discovering novel neuropeptides in Priapulida and Rotifera, identifying 22 and 19 new peptides, respectively. This tool represents a significant advancement in neuropeptide research, offering a robust method for annotating neuropeptides across diverse proteomes and providing insights into the evolutionary conservation of neuropeptide signaling pathways.

Neuropeptidergic regulation of neuromuscular signaling in larval zebrafish alters swimming behavior and synaptic transmission

Chemical synaptic transmission is modulated to accommodate different activity levels, thus enabling homeostatic scaling in pre- and postsynaptic compartments. In nematodes, cholinergic neurons use neuropeptide signaling to modulate synaptic vesicle content. To explore if this mechanism is conserved in vertebrates, we studied the involvement of neuropeptides in cholinergic transmission at the neuromuscular junction of larval zebrafish. Optogenetic stimulation by photoactivated adenylyl cyclase evoked locomotion. We generated mutants lacking the neuropeptide-processing enzyme carboxypeptidase E (cpe), and the most abundant neuropeptide precursor in motor neurons, tachykinin (tac1). Both mutants showed exaggerated locomotion after photostimulation. Recording excitatory postsynaptic currents demonstrated overall larger amplitudes in the wild type. Exaggerated locomotion in the mutants thus reflected upscaling of postsynaptic excitability. Both mutant muscles expressed more nicotinic acetylcholine receptors (nAChRs) on their surface; thus, neuropeptide signaling regulates synaptic transmitter output in zebrafish motor neurons, and muscle cells homeostatically regulate nAChR surface expression, compensating reduced presynaptic input.

Drug effects on neuropeptides and their receptors: Big hopes but moderate success in the treatment of chronic pain

Neuropeptides, including tachykinins, CGRP, and somatostatin, are localized in a peptidergic subgroup of nociceptive primary afferent neurons. Tachykinins and CGRP are pronociceptive, somatostatin is an antinociceptive mediator. Intensive drug research has been performed to develop tachykinin and CGRP antagonists, and somatostatin agonists as analgesics. CGRP receptor antagonists are efficacious and well-tolerated drugs in migraine. Monoclonal antibodies against CGRP or its receptor are used for the prophylactic treatment of migraine. Tachykinin NK1 receptor antagonists failed as analgesics but are used for chemotherapy-induced nausea and vomiting. New, orally active somatostatin 4 receptor agonists are promising drug candidates for treating various pain conditions.

Two C-terminal isoforms of Aplysia tachykinin-related peptide receptors exhibit phosphorylation-dependent and phosphorylation-independent desensitization mechanisms

Diversity, a hallmark of G protein-coupled receptor (GPCR) signaling, partly stems from alternative splicing of a single gene generating more than one isoform for a receptor. Additionally, receptor responses to ligands can be attenuated by desensitization upon prolonged or repeated ligand exposure. Both phenomena have been demonstrated and exemplified by the deuterostome tachykinin signaling system, although the role of phosphorylation in desensitization remains a subject of debate. Here, we describe the signaling system for tachykinin-related peptides (TKRPs) in a protostome, mollusk Aplysia. We cloned the Aplysia TKRP precursor, which encodes three TKRPs (apTKRP-1, apTKRP-2a, and apTKRP-2b) containing the FXGXR-amide motif. In situ hybridization and immunohistochemistry showed predominant expression of TKRP mRNA and peptide in the cerebral ganglia. TKRPs and their posttranslational modifications were observed in extracts of central nervous system ganglia using mass spectrometry. We identified two Aplysia TKRP receptors (apTKRPRs), named apTKRPR-A and apTKRPR-B. These receptors are two isoforms generated through alternative splicing of the same gene and differ only in their intracellular C termini. Structure-activity relationship analysis of apTKRP-2b revealed that both C-terminal amidation and conserved residues of the ligand are critical for receptor activation. C-terminal truncates and mutants of apTKRPRs suggested that there is a C-terminal phosphorylation-independent desensitization for both receptors. Moreover, apTKRPR-B also exhibits phosphorylation-dependent desensitization through the phosphorylation of C-terminal Ser/Thr residues. This comprehensive characterization of the Aplysia TKRP signaling system underscores the evolutionary conservation of the TKRP and TK signaling systems, while highlighting the intricacies of receptor regulation through alternative splicing and differential desensitization mechanisms.

Zika virus exists in enterocytes and enteroendocrine cells of the Aedes aegypti midgut

The Aedes aegypti midgut is crucial for blood digestion, nutrition, reproduction, and pathogen interaction. Using single-cell RNA sequencing, we explored virus infection and transcriptomic changes at the cellular level. We identified 12 distinct cell clusters in the Ae. aegypti midgut post-Zika virus infection, including intestinal stem cells, enteroblasts, enteroendocrine cells (EE), and enterocytes (ECs). The virus was found mainly in specific subsets of ECs and EE. Infection altered transcriptional profiles related to metabolism, signaling, and immune responses. Functional studies highlighted three significantly differentially expressed genes in infected cells. Notably, silencing apolipophorin III reduced virus RNA copy number in the midgut, emphasizing the role of specific genes in viral infection. These findings enhance our understanding of mosquito midgut cell processes during Zika virus infection and suggest potential targets for vector control.

Developmental dynamics of the prefrontal cortical SST and PV interneuron networks: Insights from the monkey highlight human-specific features

The primate prefrontal cortex (PFC) is a quintessential hub of cognitive functions. Amidst its intricate neural architecture, the interplay of distinct neuronal subtypes, notably parvalbumin (PV) and somatostatin (SST) interneurons (INs), emerge as a cornerstone in sculpting cortical circuitry and governing cognitive processes. While considerable strides have been made in elucidating the developmental trajectory of these neurons in rodent models, our understanding of their postmigration developmental dynamics in primates still needs to be studied. Disruptions to this developmental trajectory can compromise IN function, impairing signal gating and circuit modulation within cortical networks. This study examined the expression patterns of PV and SST, ion transporter KCC2, and ion channel subtypes Kv3.1b, and Nav1.1 - associated with morphophysiological stages of development in the postnatal marmoset monkey in different frontal cortical regions (granular areas 8aD, 8aV, 9, 46; agranular areas 11, 47L). Our results demonstrate that the maturation of PV+ INs extends into adolescence, characterized by discrete epochs associated with specific expression dynamics of ion channel subtypes. Interestingly, we observed a postnatal decrease in SST interneurons, contrasting with studies in rodents. This endeavor broadens our comprehension of primate cortical development and furnishes invaluable insights into the etiology and pathophysiology of neurodevelopmental disorders characterized by perturbations in PV and SST IN function.

Molecular basis of selective amyloid-β degrading enzymes in Alzheimer's disease

The accumulation of the small 42-residue long peptide amyloid-β (Aβ) has been proposed as a major trigger for the development of Alzheimer's disease (AD). Within the brain, the concentration of Aβ peptide is tightly controlled through production and clearance mechanisms. Substantial experimental evidence now shows that reduced levels of Aβ clearance are present in individuals living with AD. This accumulation of Aβ can lead to the formation of large aggregated amyloid plaques-one of two detectable hallmarks of the disease. Aβ-degrading enzymes (ADEs) are major players in the clearance of Aβ. Stimulating ADE activity or expression, in order to compensate for the decreased clearance in the AD phenotype, provides a promising therapeutic target. It has been reported in mice that upregulation of ADEs can reduce the levels of Aβ peptide and amyloid plaques-in some cases, this led to improved cognitive function. Among several known ADEs, neprilysin (NEP), endothelin-converting enzyme-1 (ECE-1), insulin degrading enzyme (IDE) and angiotensin-1 converting enzyme (ACE) from the zinc metalloprotease family have been identified as important. These ADEs have the capacity to digest soluble Aβ which, in turn, cannot form the toxic oligomeric species. While they are known for their amyloid degradation, they exhibit complexity through promiscuous nature and a broad range of substrates that they can degrade. This review highlights current structural and functional understanding of these key ADEs, giving some insight into the molecular interactions that leads to the hydrolysis of peptide substrates, the crucial tasks performed by them and the potential for therapeutic use in the future.

Target-based discovery of antagonists of the tick (Rhipicephalus microplus) kinin receptor identifies small molecules that inhibit midgut contractions

BACKGROUND

A GPCR (G protein-coupled receptor) target-based approach was applied to identify antagonists of the arthropod-specific tick kinin receptor. These small molecules were expected to reproduce the detrimental phenotypic effects that had been observed in Rhipicephalus microplus females when the kinin receptor was silenced by RNA interference. Rhipicephalus microplus, the southern cattle tick, cattle fever tick, or Asian blue tick, is the vector of pathogenic microorganisms causing the deadly bovine babesiosis and anaplasmosis. The widespread resistance to acaricides in tick populations worldwide emphasizes that exploring novel targets for effective tick control is imperative.

RESULTS

Fifty-three structural analogs of previously identified tick kinin antagonists were screened in a 'dual-addition' calcium fluorescence assay using a CHO-K1 cell line expressing the tick kinin receptor. Seven molecules were validated as non-cytotoxic antagonists, four of which were partial (SACC-0428764, SACC-0428780, SACC-0428800, and SACC-0428803), and three were full antagonists (SACC-0428799, SACC-0428801, and SACC-0428815). Four of these antagonists (SACC-0428764, SACC-0428780, SACC-0428799, and SACC-0428815) also inhibited the tick midgut contractions induced by the myotropic kinin agonist analog 1728, verifying their antagonistic bioactivity. The small molecules were tested on recombinant human neurokinin (NK) receptors, the one most similar to the invertebrate kinin receptors. Most molecules were inhibitors of the NK1 receptor, except SACC-0412066, a previously identified tick kinin receptor antagonist, which inhibited the NK1 receptor only at the highest concentration tested (25 μm). None of the molecules inhibited the NK3 human receptor.

CONCLUSION

Molecules identified through this approach could be useful probes for studying the tick kinin signaling system and midgut physiology. © 2024 The Author(s). Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

Investigating the role of phenylalanine residues for amyloid formation of the neuropeptide neurokinin B

Neurokinin B (NKB) is a tachykinin peptide that has diverse roles in biology, including in human reproductive development. Cellular processing of this peptide is thought to involve formation of a dense core vesicle during transit through the regulated secretory pathway. The ability of NKB to rapidly form an amyloid can contribute to formation of the secretory granule but features that support amyloid formation of NKB are not well understood. NKB contains a diphenylalanine sequence well recognised as an important motif for self-assembly of other peptides including amyloid β. Using mutations of the diphenylalanine motif we show that this motif in NKB is necessary for amyloid formation, and it is the unique combination of aromaticity and hydrophobicity of phenylalanine that is crucial for aggregation. Using disulfide cross-linking we propose that phenylalanine at sequence position 6 is important for stabilising inter-sheet interactions in the NKB amyloid fibril. Although having a highly conserved sequence, the NKB peptide from zebrafish only contains a single phenylalanine and does not fibrillise as extensively as mammalian NKB. Analysis of self-assembly of NKB-like peptides from different species may help in elucidating their biological roles. Taken together, this work shows that mammalian NKB has evolved, within only 10 residues, a sequence optimised for rapid self-assembly, whilst also containing residues for metal-binding, receptor binding and receptor discrimination.

Evolutionary conserved peptide and glycoprotein hormone-like neuroendocrine systems in C. elegans

Peptides and protein hormones form the largest group of secreted signals that mediate intercellular communication and are central regulators of physiology and behavior in all animals. Phylogenetic analyses and biochemical identifications of peptide-receptor systems reveal a broad evolutionary conservation of these signaling systems at the molecular level. Substantial progress has been made in recent years on characterizing the physiological and putative ancestral roles of many peptide systems through comparative studies in invertebrate models. Several peptides and protein hormones are not only molecularly conserved but also have conserved roles across animal phyla. Here, we focus on functional insights gained in the nematode Caenorhabditis elegans that, with its compact and well-described nervous system, provides a powerful model to dissect neuroendocrine signaling networks involved in the control of physiology and behavior. We summarize recent discoveries on the evolutionary conservation and knowledge on the functions of peptide and protein hormone systems in C. elegans.

Molecular characterization, localization, and physiological roles of ITP and ITP-L in the mosquito, Aedes aegypti

The insect ion transport peptide (ITP) and its alternatively spliced variant, ITP-like peptide (ITP-L), belong to the crustacean hyperglycemic hormone family of peptides and are widely conserved among insect species. While limited, studies have characterized the ITP/ITP-L signaling system within insects, and putative functions including regulation of ion and fluid transport, ovarian maturation, and thirst/excretion have been proposed. Herein, we aimed to molecularly investigate Itp and Itp-l expression profiles in the mosquito, Aedes aegypti, examine peptide immunolocalization and distribution within the adult central nervous system, and elucidate physiological roles for these neuropeptides. Transcript expression profiles of both AedaeItp and AedaeItp-l revealed distinct enrichment patterns in adults, with AedaeItp expressed in the brain and AedaeItp-l expression predominantly within the abdominal ganglia. Immunohistochemical analysis within the central nervous system revealed expression of AedaeITP peptide in a number of cells in the brain and in the terminal ganglion. Comparatively, AedaeITP-L peptide was localized solely within the pre-terminal abdominal ganglia of the central nervous system. Interestingly, prolonged desiccation stress caused upregulation of AedaeItp and AedaeItp-l levels in adult mosquitoes, suggesting possible functional roles in water conservation and feeding-related activities. RNAi-mediated knockdown of AedaeItp caused an increase in urine excretion, while knockdown of both AedaeItp and AedaeItp-l reduced blood feeding and egg-laying in females as well as hindered egg viability, suggesting roles in reproductive physiology and behavior. Altogether, this study identifies AedaeITP and AedaeITP-L as key pleiotropic hormones, regulating various critical physiological processes in the disease vector, A. aegypti.

Semi-synthetic nanobody-ligand conjugates exhibit tunable signaling properties and enhanced transcriptional outputs at neurokinin receptor-1

Antibodies have proven highly valuable for therapeutic development; however, they are typically poor candidates for applications that require activation of G protein-coupled receptors (GPCRs), the largest collection of targets for clinically approved drugs. Nanobodies (Nbs), the smallest antibody fragments retaining full antigen-binding capacity, have emerged as promising tools for pharmacologic applications, including GPCR modulation. Past work has shown that conjugation of Nbs with ligands can provide GPCR agonists that exhibit improved activity and selectivity compared to their parent ligands. The neurokinin-1 receptor (NK1R), a GPCR targeted for the treatment of pain, is activated by peptide agonists such as Substance P (SP) and neurokinin A (NKA), which induce signaling through multiple pathways (Gs , Gq and β-arrestin). In this study, we investigated whether conjugating NK1R ligands with Nbs that bind to a separate location on the receptor would provide chimeric compounds with distinctive signaling properties. We employed sortase A-mediated ligation to generate several conjugates consisting of Nbs linked to NK1R ligands. Many of these conjugates exhibited divergent and unexpected signaling properties and transcriptional outputs. For example, some Nb-NKA conjugates showed enhanced receptor binding capacity, high potency partial agonism, prolonged cAMP production, and an increase in transcriptional output associated with Gs signaling; whereas other conjugates were virtually inactive. Nanobody conjugation caused only minor alterations in ligand-induced upstream Gq signaling with unexpected enhancements in transcriptional (downstream) responses. Our findings underscore the potential of nanobody conjugation for providing compounds with advantageous properties such as biased agonism, prolonged duration of action, and enhanced transcriptional responses. These compounds hold promise not only for facilitating fundamental research on GPCR signal transduction mechanisms but also for the development of more potent and enduring therapeutics.

Lessons from lonely flies: Molecular and neuronal mechanisms underlying social isolation

Animals respond to changes in the environment which affect their internal state by adapting their behaviors. Social isolation is a form of passive environmental stressor that alters behaviors across animal kingdom, including humans, rodents, and fruit flies. Social isolation is known to increase violence, disrupt sleep and increase depression leading to poor mental and physical health. Recent evidences from several model organisms suggest that social isolation leads to remodeling of the transcriptional and epigenetic landscape which alters behavioral outcomes. In this review, we explore how manipulating social experience of fruit fly Drosophila melanogaster can shed light on molecular and neuronal mechanisms underlying isolation driven behaviors. We discuss the recent advances made using the powerful genetic toolkit and behavioral assays in Drosophila to uncover role of neuromodulators, sensory modalities, pheromones, neuronal circuits and molecular mechanisms in mediating social isolation. The insights gained from these studies could be crucial for developing effective therapeutic interventions in future.

Dietary supplementation with pyrroloquinoline quinone promotes growth, relieves weaning stress, and regulates metabolism of piglets compared with adding zinc oxide

Hindered growth often occurs because of psychological and environmental stress during the weaning period of piglets. This study aimed to compare the effects of growth performance, diarrhea indices, digestibility of nutrients, antioxidant capacity, neurotransmitters levels and metabolism of weaned pigs fed diets supplemented with pyrroloquinoline quinone (PQQ) and zinc oxide (ZnO). Pigs weaned at d 28 (n = 108) were fed with three different diets including: the basal diet (CTRL group), the basal diet supplemented with 3.0 mg/kg PQQ (PQQ group) and the basal diet containing 1,600 mg/kg ZnO (ZNO group). During the first 14 d, weaned pigs fed the diet supplemented with PQQ and ZnO decreased feed to gain ratio and diarrhea rate (P < 0.01). Compared with the CTRL group, average daily gain was increased in weaned pigs in the PQQ group from d 15 to 28 (P = 0.03). Compared with the CTRL group, pigs fed PQQ and ZnO supplemented diets showed improved apparent total tract digestibility (ATTD) of nutrients (P ≤ 0.05). During the overall experimental period, the concentration of malondialdehyde was decreased in plasma of pigs in the PQQ and ZNO groups compared with the CTRL group (P < 0.05). At d 28, the concentration of vasoactive intestinal peptide (VIP) and calcitonin gene-related peptide (CGRP) was lower in plasma of weaned pigs in the PQQ and ZNO groups compared with the CTRL group (P < 0.05). There was no difference between the PQQ and ZNO group in growth performance, ATTD of nutrition, antioxidant capacity and neurotransmitters levels. PQQ increased 3-methoxy-4-hydroxymandelate (P < 0.05) compared with the CTRL group. According to metabolomic analysis, erucamide, formononetin and 3-methyl-L-histidine were up-regulated in the PQQ group (P < 0.05). Compared with the CTRL group, aloesin and dibutyl adipate were down-regulated in the PQQ group (P < 0.05). In conclusion, similar to ZnO, PQQ improves growth performance, digestibility of nutrients, antioxidant capacity, neuromodulation and metabolism of weaned pigs. Thus, like ZnO, PQQ can be effectively applied in weaned pigs.

Neurokinin-2 receptor negatively modulates substance P responses by forming complex with Neurokinin-1 receptor

BACKGROUND

Tachykinins and their cognate receptors, neurokinin receptors (NKs) including NK1, NK2, and NK3 play vital roles in regulating various physiological processes including neurotransmission, nociception, inflammation, smooth muscle contractility, and stimulation of endocrine and exocrine gland secretion. Their abnormal expression has been reported to be associated with neurological disorders, inflammation, and cancer. Even though NKs are expressed in the same cells with their expression being inversely correlated in some conditions, there is no direct evidence to prove their interaction. Understanding the functional crosstalk between NKs in mediated downstream signaling and cellular responses may elucidate the roles of each receptor in pathophysiology.

RESULTS

In this study, we showed that NKs were co-expressed in some cells. However, different from NK3, which only forms homodimerization, we demonstrated a direct interaction between NK1 and NK2 at the protein level using co-immunoprecipitation and NanoBiT-based protein interaction analysis. Through heterodimerization, NK2 downregulated substance P-stimulated NK1 signals, such as intracellular Ca2+ mobilization and ERK phosphorylation, by enhancing β-arrestin recruitment, even at the ligand concentration that could not activate NK2 itself or in the presence of NK1 specific antagonist, aprepitant. In A549 cells with receptors deleted and reconstituted, NK2 exerted a negative effect on substance P/NK1-mediated cell migration.

CONCLUSION

Our study has provided the first direct evidence of an interaction between NK1 and NK2, which highlights the functional relevance of their heterodimerization in cellular responses. Our findings demonstrated that through dimerization, NK2 exerts negative effects on downstream signaling and cellular response mediated by NK1. Moreover, this study has significant implications for understanding the complexity of GPCR dimerization and its effect on downstream signaling and cellular responses. Given the important roles of tachykinins and NKs in pathophysiology, these insights may provide clues for developing NKs-targeting drugs.

The Repurposing of Non-Peptide Neurokinin-1 Receptor Antagonists as Antitumor Drugs: An Urgent Challenge for Aprepitant

The substance P (SP)/neurokinin-1 receptor (NK-1R) system is involved in cancer progression. NK-1R, activated by SP, promotes tumor cell proliferation and migration, angiogenesis, the Warburg effect, and the prevention of apoptosis. Tumor cells overexpress NK-1R, which influences their viability. A typical specific anticancer strategy using NK-1R antagonists, irrespective of the tumor type, is possible because these antagonists block all the effects mentioned above mediated by SP on cancer cells. This review will update the information regarding using NK-1R antagonists, particularly Aprepitant, as an anticancer drug. Aprepitant shows a broad-spectrum anticancer effect against many tumor types. Aprepitant alone or in combination therapy with radiotherapy or chemotherapy could reduce the sequelae and increase the cure rate and quality of life of patients with cancer. Current data open the door to new cancer research aimed at antitumor therapeutic strategies using Aprepitant. To achieve this goal, reprofiling the antiemetic Aprepitant as an anticancer drug is urgently needed.

Spatial transcriptomics reveal basal sex differences in supraoptic nucleus gene expression of adult rats related to cell signaling and ribosomal pathways

BACKGROUND

The supraoptic nucleus (SON) of the hypothalamus contains magnocellular neurosecretory cells that secrete the hormones vasopressin and oxytocin. Sex differences in SON gene expression have been relatively unexplored. Our study used spatially resolved transcriptomics to visualize gene expression profiles in the SON of adult male (n = 4) and female (n = 4) Sprague-Dawley rats using Visium Spatial Gene Expression (10x Genomics).

METHODS

Briefly, 10-μm coronal sections (~ 4 × 4 mm) containing the SON were collected from each rat and processed using Visium slides and recommended protocols. Data were analyzed using 10x Genomics' Space Ranger and Loupe Browser applications and other bioinformatic tools. Two unique differential expression (DE) analysis methods, Loupe Browser and DESeq2, were used.

RESULTS

Loupe Browser DE analysis of the SON identified 116 significant differentially expressed genes (DEGs) common to both sexes (e.g., Avp and Oxt), 31 significant DEGs unique to the males, and 73 significant DEGs unique to the females. DESeq2 analysis revealed 183 significant DEGs between the two groups. Gene Ontology (GO) enrichment and pathway analyses using significant genes identified via Loupe Browser revealed GO terms and pathways related to (1) neurohypophyseal hormone activity, regulation of peptide hormone secretion, and regulation of ion transport for the significant genes common to both males and females, (2) Gi signaling/G-protein mediated events for the significant genes unique to males, and (3) potassium ion transport/voltage-gated potassium channels for the significant genes unique to females, as some examples. GO/pathway analyses using significant genes identified via DESeq2 comparing female vs. male groups revealed GO terms/pathways related to ribosomal structure/function. Ingenuity Pathway Analysis (IPA) identified additional sex differences in canonical pathways (e.g., 'Mitochondrial Dysfunction', 'Oxidative Phosphorylation') and upstream regulators (e.g., CSF3, NFKB complex, TNF, GRIN3A).

CONCLUSION

There was little overlap in the IPA results for the two different DE methods. These results suggest sex differences in SON gene expression that are associated with cell signaling and ribosomal pathways.

Enteroendocrine cells and gut hormones as potential targets in the crossroad of the gut-kidney axis communication

Recent studies suggest that disruptions in intestinal homeostasis, such as changes in gut microbiota composition, infection, and inflammatory-related gut diseases, can be associated with kidney diseases. For instance, genomic investigations highlight how susceptibility genes linked to IgA nephropathy are also correlated with the risk of inflammatory bowel disease. Conversely, investigations demonstrate that the use of short-chain fatty acids, produced through fermentation by intestinal bacteria, protects kidney function in models of acute and chronic kidney diseases. Thus, the dialogue between the gut and kidney seems to be crucial in maintaining their proper function, although the factors governing this crosstalk are still emerging as the field evolves. In recent years, a series of studies have highlighted the significance of enteroendocrine cells (EECs) which are part of the secretory lineage of the gut epithelial cells, as important components in gut-kidney crosstalk. EECs are distributed throughout the epithelial layer and release more than 20 hormones in response to microenvironment stimuli. Interestingly, some of these hormones and/or their pathways such as Glucagon-Like Peptide 1 (GLP-1), GLP-2, gastrin, and somatostatin have been shown to exert renoprotective effects. Therefore, the present review explores the role of EECs and their hormones as regulators of gut-kidney crosstalk and their potential impact on kidney diseases. This comprehensive exploration underscores the substantial contribution of EEC hormones in mediating gut-kidney communication and their promising potential for the treatment of kidney diseases.

Semi-synthetic nanobody-ligand conjugates exhibit tunable signaling properties and enhanced transcriptional outputs at neurokinin receptor-1

Antibodies have proven highly valuable for therapeutic development; however, they are typically poor candidates for applications that require activation of G protein-coupled receptors (GPCRs), the largest collection of targets for clinically approved drugs. Nanobodies (Nbs), the smallest antibody fragments retaining full antigen-binding capacity, have emerged as promising tools for pharmacologic applications, including GPCR modulation. Past work has shown that conjugation of Nbs with ligands can provide GPCR agonists that exhibit improved activity and selectivity compared to their parent ligands. The neurokinin-1 receptor (NK1R), a GPCR targeted for the treatment of pain, is activated by peptide agonists such as Substance P (SP) and neurokinin A (NKA), which induce signaling through multiple pathways (Gs, Gq and β-arrestin). In this study, we investigated whether conjugating NK1R ligands with Nbs that bind to a separate location on the receptor would provide chimeric compounds with distinctive signaling properties. We employed sortase A-mediated ligation to generate several conjugates consisting of Nbs linked to NK1R ligands. Many of these conjugates exhibited divergent and unexpected signaling properties and transcriptional outputs. For example, some Nb-NKA conjugates showed enhanced receptor binding capacity, high potency partial agonism, prolonged cAMP production, and an increase in transcriptional output associated with Gs signaling; whereas other conjugates were virtually inactive. Nanobody conjugation caused only minor alterations in ligand-induced upstream Gq signaling with unexpected enhancements in transcriptional (downstream) responses. Our findings underscore the potential of nanobody conjugation for providing compounds with advantageous properties such as biased agonism, prolonged duration of action, and enhanced transcriptional responses. These compounds hold promise not only for facilitating fundamental research on GPCR signal transduction mechanisms but also for the development of more potent and enduring therapeutics.

Comparative transcriptome analysis of two Daphnia galeata genotypes displaying contrasting phenotypic variation induced by fish kairomones in the same environment of the Han River, Korea

BACKGROUND

Phenotypic plasticity is a crucial adaptive mechanism that enables organisms to modify their traits in response to changes in their environment. Predator-induced defenses are an example of phenotypic plasticity observed across a wide range of organisms, from single-celled organisms to vertebrates. In addition to morphology and behavior, these responses also affect life-history traits. The crustacean Daphnia galeata is a suitable model organism for studying predator-induced defenses, as it exhibits life-history traits changes under predation risk. To get a better overview of their phenotypic plasticity under predation stress, we conducted RNA sequencing on the transcriptomes of two Korean Daphnia galeata genotypes, KE1, and KB11, collected in the same environment.

RESULTS

When exposed to fish kairomones, the two genotypes exhibited phenotypic variations related to reproduction and growth, with opposite patterns in growth-related phenotypic variation. From both genotypes, a total of 135,611 unigenes were analyzed, of which 194 differentially expressed transcripts (DETs) were shared among the two genotypes under predation stress, which showed consistent, or inconsistent expression patterns in both genotypes. Prominent DETs were related to digestion and reproduction and consistently up-regulated in both genotypes, thus associated with changes in life-history traits. Among the inconsistent DETs, transcripts encode vinculin (VINC) and protein obstructor-E (OBST-E), which are associated with growth; these may explain the differences in life-history traits between the two genotypes. In addition, genotype-specific DETs could explain the variation in growth-related life-history traits between genotypes, and could be associated with the increased body length of genotype KE1.

CONCLUSIONS

The current study allows for a better understanding of the adaptation mechanisms related to reproduction and growth of two Korean D. galeata genotypes induced by predation stress. However, further research is necessary to better understand the specific mechanisms by which the uncovered DETs are related with the observed phenotypic variation in each genotype. In the future, we aim to unravel the precise adaptive mechanisms underlying predator-induced responses.

Transcriptome analysis reveals salivary gland-specific neuropeptide signaling genes in the predatory stink bug, Picromerus lewisi

Predatory stink bugs derive from phytophagous stink bugs and evolved enhanced predation skills. Neuropeptides are a diverse class of ancient signaling molecules that regulate physiological processes and behavior in animals, including stink bugs. Neuropeptide evolution might be important for the development of predation because neuropeptides can be converted to venoms that impact prey. However, information on neuropeptide signaling genes in predatory stink bugs is lacking. In the present study, neuropeptide signaling genes of Picromerus lewisi, an important predatory stink bug and an effective biological agent, were comprehensively identified by transcriptome analysis, with a total of 59 neuropeptide precursor genes and 58 potential neuropeptide receptor genes found. In addition, several neuropeptides and their receptors enriched in salivary glands of P. lewisi were identified. The present study and subsequent functional research contribute to an in-depth understanding of the biology and behavior of the predatory bugs and can provide basic information for the development of better pest management strategies, possibly including neuropeptide receptors as insecticide targets and salivary gland derived venom toxins as novel killing moleculars.

Involvement of neuronal tachykinin-like receptor at 86C in Drosophila disc repair via regulation of kynurenine metabolism

Neurons contribute to the regeneration of projected tissues; however, it remains unclear whether they are involved in the non-innervated tissue regeneration. Herein, we showed that a neuronal tachykinin-like receptor at 86C (TkR86C) is required for the repair of non-innervated wing discs in Drosophila. Using a genetic tissue repair system in Drosophila larvae, we performed genetic screening for G protein-coupled receptors to search for signal mediatory systems for remote tissue repair. An evolutionarily conserved neuroinflammatory receptor, TkR86C, was identified as the candidate receptor. Neuron-specific knockdown of TkR86C impaired disc repair without affecting normal development. We investigated the humoral metabolites of the kynurenine (Kyn) pathway regulated in the fat body because of their role as tissue repair-mediating factors. Neuronal knockdown of TkR86C hampered injury-dependent changes in the expression of vermillion in the fat body and humoral Kyn metabolites. Our data indicate the involvement of TkR86C neurons upstream of Kyn metabolism in non-autonomous tissue regeneration.

Functional homology of tachykinin signalling: The influence of human substance P on the immune system of the mealworm beetle, Tenebrio molitor L

Tachykinin-related peptides (TRPs) are one of the most prominent families of neuropeptides in the animal kingdom. Insect TRPs display strong structural and functional homology to vertebrate tachykinins (TKs). To study functional homologies between these two neuropeptide families, the influence of human substance P (SP, one of the essential vertebrate TKs) on the immune system of the mealworm beetle, Tenebrio molitor L., was analysed. Human SP influences the phagocytic abilities of T. molitor haemocytes. Peptide injection leads to an increase in the number of haemocytes participating in the phagocytosis of latex beads. In contrast, incubation of haemocytes from non-injected beetles in a solution of physiological saline and SP causes a decrease in phagocytic activity. Treatment with human SP also led to increased adhesion of haemocytes, but no changes in the arrangement of the F-actin cytoskeleton were observed. Interestingly, 6 h after human SP injection, increased DNA integrity in T. molitor haemocytes was reported. The opposite effects were observed 24 h after SP injection. Human SP caused the upregulation of humoral immune responses, such as phenoloxidase (PO) activity in the T. molitor haemolymph, and the downregulation of immune-related genes encoding coleoptericin A, tenecin 3 and Toll receptor. However, genes encoding attacin 2 and cecropin were upregulated. Despite these differences, the antimicrobial activity of T. molitor haemolymph was significantly lower in beetles injected with SP than in control beetles. Moreover, an analysis of the direct influence of SP on lysozyme activity was performed. Our results suggest that SP at a concentration of 10^-6 M can directly inhibit lysozyme activity. However, an opposite effect was reported after the application of SP at a concentration of 10^-4 M. The presented results suggest structural and functional homology between TK signalling in vertebrates and insects. Primarily, this was visible in the context of the humoral response and general antimicrobial activity of T. molitor haemolymph. However, some of the results related to haemocyte function may also indicate the importance of the TK and TRP sequences for evoking immunological effects.

Olfactory detection of viruses shapes brain immunity and behavior in zebrafish

Olfactory sensory neurons (OSNs) are constantly exposed to pathogens, including viruses. However, serious brain infection via the olfactory route rarely occurs. When OSNs detect a virus, they coordinate local antiviral immune responses to stop virus progression to the brain. Despite effective immune control in the olfactory periphery, pathogen-triggered neuronal signals reach the CNS via the olfactory bulb (OB). We hypothesized that neuronal detection of a virus by OSNs initiates neuroimmune responses in the OB that prevent pathogen invasion. Using zebrafish ( Danio rerio ) as a model, we demonstrate viral-specific neuronal activation of OSNs projecting into the OB, indicating that OSNs are electrically activated by viruses. Further, behavioral changes are seen in both adult and larval zebrafish after viral exposure. By profiling the transcription of single cells in the OB after OSNs are exposed to virus, we found that both microglia and neurons enter a protective state. Microglia and macrophage populations in the OB respond within minutes of nasal viral delivery followed decreased expression of neuronal differentiation factors and enrichment of genes in the neuropeptide signaling pathway in neuronal clusters. Pituitary adenylate-cyclase-activating polypeptide ( pacap ), a known antimicrobial, was especially enriched in a neuronal cluster. We confirm that PACAP is antiviral in vitro and that PACAP expression increases in the OB 1 day post-viral treatment. Our work reveals how encounters with viruses in the olfactory periphery shape the vertebrate brain by inducing antimicrobial programs in neurons and by altering host behavior.

Single-cell transcriptome profiles of Drosophila fruitless-expressing neurons from both sexes

Drosophila melanogaster reproductive behaviors are orchestrated by fruitless neurons. We performed single-cell RNA-sequencing on pupal neurons that produce sex-specifically spliced fru transcripts, the fru P1-expressing neurons. Uniform Manifold Approximation and Projection (UMAP) with clustering generates an atlas containing 113 clusters. While the male and female neurons overlap in UMAP space, more than half the clusters have sex differences in neuron number, and nearly all clusters display sex-differential expression. Based on an examination of enriched marker genes, we annotate clusters as circadian clock neurons, mushroom body Kenyon cell neurons, neurotransmitter- and/or neuropeptide-producing, and those that express doublesex. Marker gene analyses also show that genes that encode members of the immunoglobulin superfamily of cell adhesion molecules, transcription factors, neuropeptides, neuropeptide receptors, and Wnts have unique patterns of enriched expression across the clusters. In vivo spatial gene expression links to the clusters are examined. A functional analysis of fru P1 circadian neurons shows they have dimorphic roles in activity and period length. Given that most clusters are comprised of male and female neurons indicates that the sexes have fru P1 neurons with common gene expression programs. Sex-specific expression is overlaid on this program, to build the potential for vastly different sex-specific behaviors.

Insecticidal efficacy and risk assessment of different neuropeptide analog combinations against the peach-potato aphid following topical exposure

BACKGROUND

Insect neuropeptides control essential physiological metabolic activities. In our previous studies, Capability/CAP2b (PK/CAPA) analog 1895 applied alone or as a combination of CAPA analogs (1895 + 2315) was reported to decrease aphid fitness. While this was obtained with the combination of two peptide analogs of the same neuropeptide class, the effect of combining peptide analogs of different neuropeptide classes has not been explored so far.

RESULTS

In this study, we assessed the effect of combinations of the PK/CAPA analog 1895 with neuropeptide analogs of four different classes [adipokinetic hormone (AKH) analog: 2271; myosuppressin analog: 2434; kinin analog: 2460; tachykinin-related peptide analog: 2463] on the fitness of aphids. We found that the combination of 1895 and AKH analog 2271 was the most effective one to control Myzus persicae. The triple combination 1895 + 2271 + 2315 provided a synergistic effect by further increasing aphid mortality and reducing reproduction relative to 1895 + 2315. Additionally, a biosafety assessment of the combination 1895 + 2271 + 2315 showed no significant lethal nor sub-lethal effects on survival rates and food intake for the pollinator (Bombus terrestris) and the two representative natural enemies (Harmonia axyridis and Nasonia vitripennis).

CONCLUSION

These results could facilitate establishment of the triple combination 1895 + 2271 + 2315, and/or inclusion of second generation analogs, as alternatives to broad spectrum and less friendly insecticides. © 2022 Society of Chemical Industry.

Tachykinin-related peptides modulate immune-gene expression in the mealworm beetle Tenebrio molitor L

Tachykinins (TKs) are a group of conserved neuropeptides. In insects, tachykinin-related peptides (TRPs) are important modulators of several functions such as nociception and lipid metabolism. Recently, it has become clear that TRPs also play a role in regulating the insect immune system. Here, we report a transcriptomic analysis of changes in the expression levels of immune-related genes in the storage pest Tenebrio molitor after treatment with Tenmo-TRP-7. We tested two concentrations (10^-8 and 10^-6 M) at two time points, 6 and 24 h post-injection. We found significant changes in the transcript levels of a wide spectrum of immune-related genes. Some changes were observed 6 h after the injection of Tenmo-TRP-7, especially in relation to its putative anti-apoptotic action. Interestingly, 24 h after the injection of 10^-8 M Tenmo-TRP-7, most changes were related to the regulation of the cellular response. Applying 10^-6 M Tenmo-TRP-7 resulted in the downregulation of genes associated with humoral responses. Injecting Tenmo-TRP-7 did not affect beetle survival but led to a reduction in haemolymph lysozyme-like antibacterial activity, consistent with the transcriptomic data. The results confirmed the immunomodulatory role of TRP and shed new light on the functional homology between TRPs and TKs.

Review: The evolution of peptidergic signaling in Cnidaria and Placozoa, including a comparison with Bilateria

Bilateria have bilateral symmetry and are subdivided into Deuterostomia (animals like vertebrates) and Protostomia (animals like insects and mollusks). Neuropeptides occur in both Proto- and Deuterostomia and they are frequently structurally related across these two lineages. For example, peptides belonging to the oxytocin/vasopressin family exist in both clades. The same is true for the G protein-coupled receptors (GPCRs) of these peptides. These observations suggest that these neuropeptides and their GPCRs were already present in the common ancestor of Proto- and Deuterostomia, which lived about 700 million years ago (MYA). Furthermore, neuropeptides and their GPCRs occur in two early-branching phyla that diverged before the emergence of Bilateria: Cnidaria (animals like corals and sea anemones), and Placozoa (small disk-like animals, feeding on algae). The sequences of these neuropeptides and their GPCRs, however, are not closely related to those from Bilateria. In addition, cnidarian neuropeptides and their receptors are not closely related to those from Placozoa. We propose that the divergence times between Cnidaria, Placozoa, and Bilateria might be too long for recognizing sequence identities. Leucine-rich repeats-containing GPCRs (LGRs) are a special class of GPCRs that are characterized by a long N-terminus containing 10-20 leucine-rich domains, which are used for ligand binding. Among the ligands for LGRs are dimeric glycoprotein hormones, and insulin-like peptides, such as relaxin. LGRs have been found not only in Proto- and Deuterostomia, but also in early emerging phyla, such as Cnidaria and Placozoa. Humans have eight LGRs. In our current review, we have revisited the annotations of LGRs from the sea anemone Nematostella vectensis and the placozoan Trichoplax adhaerens. We identified 13 sea anemone LGRs and no less than 46 LGRs from T. adhaerens. All eight human LGRs appear to have orthologues in sea anemones and placozoans. LGRs and their ligands, therefore, have a long evolutionary history, going back to the common ancestor of Cnidaria and Placozoa.

Reduced Ca2+ transient amplitudes may signify increased or decreased depolarization depending on the neuromodulatory signaling pathway

Neuromodulators regulate neuronal excitability and bias neural circuit outputs. Optical recording of neuronal Ca²⁺ transients is a powerful approach to study the impact of neuromodulators on neural circuit dynamics. We are investigating the polymodal nociceptor ASH in Caenorhabditis elegans to better understand the relationship between neuronal excitability and optically recorded Ca²⁺ transients. ASHs depolarize in response to the aversive olfactory stimulus 1-octanol (1-oct) with a concomitant rise in somal Ca²⁺, stimulating an aversive locomotory response. Serotonin (5-HT) potentiates 1-oct avoidance through Gα_q signaling, which inhibits L-type voltage-gated Ca²⁺ channels in ASH. Although Ca²⁺ signals in the ASH soma decrease, depolarization amplitudes increase because Ca²⁺ mediates inhibitory feedback control of membrane potential in this context. Here, we investigate octopamine (OA) signaling in ASH to assess whether this negative correlation between somal Ca²⁺ and depolarization amplitudes is a general phenomenon, or characteristic of certain neuromodulatory pathways. Like 5-HT, OA reduces somal Ca²⁺ transient amplitudes in ASH neurons. However, OA antagonizes 5-HT modulation of 1-oct avoidance behavior, suggesting that OA may signal through a different pathway. We further show that the pathway for OA diminution of ASH somal Ca²⁺ consists of the OCTR-1 receptor, the G_o heterotrimeric G-protein, and the G-protein activated inwardly rectifying channels IRK-2 and IRK-3, and this pathway reduces depolarization amplitudes in parallel with somal Ca²⁺ transient amplitudes. Therefore, even within a single neuron, somal Ca²⁺ signal reduction may indicate either increased or decreased depolarization amplitude, depending on which neuromodulatory signaling pathways are activated, underscoring the need for careful interpretation of Ca²⁺ imaging data in neuromodulatory studies.

Descending control of nociception in insects?

Modulation of nociception allows animals to optimize chances of survival by adapting their behaviour in different contexts. In mammals, this is executed by neurons from the brain and is referred to as the descending control of nociception. Whether insects have such control, or the neural circuits allowing it, has rarely been explored. Based on behavioural, neuroscientific and molecular evidence, we argue that insects probably have descending controls for nociception. Behavioural work shows that insects can modulate nocifensive behaviour. Such modulation is at least in part controlled by the central nervous system since the information mediating such prioritization is processed by the brain. Central nervous system control of nociception is further supported by neuroanatomical and neurobiological evidence showing that the insect brain can facilitate or suppress nocifensive behaviour, and by molecular studies revealing pathways involved in the inhibition of nocifensive behaviour both peripherally and centrally. Insects lack the endogenous opioid peptides and their receptors that contribute to mammalian descending nociception controls, so we discuss likely alternative molecular mechanisms for the insect descending nociception controls. We discuss what the existence of descending control of nociception in insects may reveal about pain perception in insects and finally consider the ethical implications of these novel findings.

Endocrine cybernetics: neuropeptides as molecular switches in behavioural decisions

Plasticity in animal behaviour relies on the ability to integrate external and internal cues from the changing environment and hence modulate activity in synaptic circuits of the brain. This context-dependent neuromodulation is largely based on non-synaptic signalling with neuropeptides. Here, we describe select peptidergic systems in the Drosophila brain that act at different levels of a hierarchy to modulate behaviour and associated physiology. These systems modulate circuits in brain regions, such as the central complex and the mushroom bodies, which supervise specific behaviours. At the top level of the hierarchy there are small numbers of large peptidergic neurons that arborize widely in multiple areas of the brain to orchestrate or modulate global activity in a state and context-dependent manner. At the bottom level local peptidergic neurons provide executive neuromodulation of sensory gain and intrinsically in restricted parts of specific neuronal circuits. The orchestrating neurons receive interoceptive signals that mediate energy and sleep homeostasis, metabolic state and circadian timing, as well as external cues that affect food search, aggression or mating. Some of these cues can be triggers of conflicting behaviours such as mating versus aggression, or sleep versus feeding, and peptidergic neurons participate in circuits, enabling behaviour choices and switches.

Gut neuroendocrine signaling regulates synaptic assembly in C. elegans

Synaptic connections are essential to build a functional brain. How synapses are formed during development is a fundamental question in neuroscience. Recent studies provided evidence that the gut plays an important role in neuronal development through processing signals derived from gut microbes or nutrients. Defects in gut-brain communication can lead to various neurological disorders. Although the roles of the gut in communicating signals from its internal environment to the brain are well known, it remains unclear whether the gut plays a genetically encoded role in neuronal development. Using C. elegans as a model, we uncover that a Wnt-endocrine signaling pathway in the gut regulates synaptic development in the brain. A canonical Wnt signaling pathway promotes synapse formation through regulating the expression of the neuropeptides encoding gene nlp-40 in the gut, which functions through the neuronally expressed GPCR/AEX-2 receptor during development. Wnt-NLP-40-AEX-2 signaling likely acts to modulate neuronal activity. Our study reveals a genetic role of the gut in synaptic development and identifies a novel contribution of the gut-brain axis.

Mosquito saliva enhances virus infection through sialokinin-dependent vascular leakage

Viruses transmitted by Aedes mosquitoes are an increasingly important global cause of disease. Defining common determinants of host susceptibility to this large group of heterogenous pathogens is key for informing the rational design of panviral medicines. Infection of the vertebrate host with these viruses is enhanced by mosquito saliva, a complex mixture of salivary-gland-derived factors and microbiota. We show that the enhancement of infection by saliva was dependent on vascular function and was independent of most antisaliva immune responses, including salivary microbiota. Instead, the Aedes gene product sialokinin mediated the enhancement of virus infection through a rapid reduction in endothelial barrier integrity. Sialokinin is unique within the insect world as having a vertebrate-like tachykinin sequence and is absent from Anopheles mosquitoes, which are incompetent for most arthropod-borne viruses, whose saliva was not proviral and did not induce similar vascular permeability. Therapeutic strategies targeting sialokinin have the potential to limit disease severity following infection with Aedes-mosquito-borne viruses.

G Protein-Coupled Receptors as Potential Intercellular Communication Mediators in Trypanosomatidae

Detection and transduction of environmental signals, constitute a prerequisite for successful parasite invasion; i.e., Leishmania transmission, survival, pathogenesis and disease manifestation and dissemination, with diverse molecules functioning as inter-cellular signaling ligands. Receptors [i.e., G protein-coupled receptors (GPCRs)] and their associated transduction mechanisms, well conserved through evolution, specialize in this function. However, canonical GPCR-related signal transduction systems have not been described in Leishmania, although orthologs, with reduced domains and function, have been identified in Trypanosomatidae. These inter-cellular communication means seem to be essential for multicellular and unicellular organism’s survival. GPCRs are flexible in their molecular architecture and may interact with the so-called receptor activity-modifying proteins (RAMPs), which modulate their function, changing GPCRs pharmacology, acting as chaperones and regulating signaling and/or trafficking in a receptor-dependent manner. In the skin, vasoactive- and neuro- peptides released in response to the noxious stimuli represented by the insect bite may trigger parasite physiological responses, for example, chemotaxis. For instance, in Leishmania (V.) braziliensis, sensory [Substance P, SP, chemoattractant] and autonomic [Vasoactive Intestinal Peptide, VIP, and Neuropeptide Y, NPY, chemorepellent] neuropeptides at physiological levels stimulate in vitro effects on parasite taxis. VIP and NPY chemotactic effects are impaired by their corresponding receptor antagonists, suggesting that the stimulated responses might be mediated by putative GPCRs (with essential conserved receptor domains); the effect of SP is blocked by [(D-Pro 2, D-Trp7,9]-Substance P (10^-6 M)] suggesting that it might be mediated by neurokinin-1 transmembrane receptors. Additionally, vasoactive molecules like Calcitonin Gene-Related Peptide [CGRP] and Adrenomedullin [AM], exert a chemorepellent effect and increase the expression of a 24 kDa band recognized in western blot analysis by (human-)-RAMP-2 antibodies. In-silico search oriented towards GPCRs-like receptors and signaling cascades detected a RAMP-2-aligned sequence corresponding to Leishmania folylpolyglutamate synthase and a RAMP-3 aligned protein, a hypothetical Leishmania protein with yet unknown function, suggesting that in Leishmania, CGRP and AM activities may be modulated by RAMP- (-2) and (-3) homologs. The possible presence of proteins and molecules potentially involved in GPCRs cascades, i.e., RAMPs, signpost conservation of ancient signaling systems associated with responses, fundamental for cell survival, (i.e., taxis and migration) and may constitute an open field for description of pharmacophores against Leishmania parasites.

The Neuromodulatory Basis of Aggression: Lessons From the Humble Fruit Fly

Aggression is an intrinsic trait that organisms of almost all species, humans included, use to get access to food, shelter, and mating partners. To maximize fitness in the wild, an organism must vary the intensity of aggression toward the same or different stimuli. How much of this variation is genetic and how much is externally induced, is largely unknown but is likely to be a combination of both. Irrespective of the source, one of the principal physiological mechanisms altering the aggression intensity involves neuromodulation. Any change or variation in aggression intensity is most likely governed by a complex interaction of several neuromodulators acting via a meshwork of neural circuits. Resolving aggression-specific neural circuits in a mammalian model has proven challenging due to the highly complex nature of the mammalian brain. In that regard, the fruit fly model Drosophila melanogaster has provided insights into the circuit-driven mechanisms of aggression regulation and its underlying neuromodulatory basis. Despite morphological dissimilarities, the fly brain shares striking similarities with the mammalian brain in genes, neuromodulatory systems, and circuit-organization, making the findings from the fly model extremely valuable for understanding the fundamental circuit logic of human aggression. This review discusses our current understanding of how neuromodulators regulate aggression based on findings from the fruit fly model. We specifically focus on the roles of Serotonin (5-HT), Dopamine (DA), Octopamine (OA), Acetylcholine (ACTH), Sex Peptides (SP), Tachykinin (TK), Neuropeptide F (NPF), and Drosulfakinin (Dsk) in fruit fly male and female aggression.

Pyrroloquinoline Quinone Regulates Enteric Neurochemical Plasticity of Weaned Rats Challenged With Lipopolysaccharide

The enteric nervous system (ENS) is important for the intestinal barrier to defend and regulate inflammation in the intestine. The aim of this study was to investigate the effect of pyrroloquinoline quinone (PQQ) on regulating neuropeptide secretion by ENS neurons of rats challenged with lipopolysaccharide (LPS) to create enteritis. Thirty Sprague Dawley rats were divided into five groups, namely, basal (CTRL), basal plus LPS challenge (LPS), basal with 2.5 mg/kg b.w./day of PQQ plus challenge with LPS (PQQ 2.5), basal with 5.0 mg/kg b.w./day PQQ plus challenge with LPS (PQQ 5), and basal with 10.0 mg/kg b.w./day PQQ plus challenge with LPS (PQQ 10). After treatment with basal diet or PQQ for 14 days, rats were challenged with LPS except for the CTRL group. Rats were euthanized 6 h after the LPS challenge. Rats showed an increased average daily gain in PQQ treatment groups (P &lt; 0.05). Compared with the LPS group, PQQ 5 and PQQ 10 rats showed increased villus height and villus height/crypt depth of jejunum (P &lt; 0.05). In PQQ treatment groups, concentrations of IL-1β and TNF-α in serum and intestine of rats were decreased, and IL-10 concentration was increased in serum compared with the LPS group (P &lt; 0.05). Compared with the LPS group, the concentration of neuropeptide Y (NPY), nerve growth factor (NGF), vasoactive intestinal peptide (VIP), substance P (SP), calcitonin gene-related peptide (CGRP), and brain-derived neurotropic factor (BDNF) in serum were decreased in PQQ treatment groups (P &lt; 0.05). Compared with the LPS group, ileal mRNA levels of BDNF, NPY, and NGF were decreased in PQQ treatment groups (P &lt; 0.05). Jejunal concentrations of SP, CGRP, VIP, BDNF, NPY, and NGF were decreased in PQQ treatment groups compared with the LPS group (P &lt; 0.05). Compared with the LPS group, phosphor-protein kinase B (p-Akt)/Akt levels in jejunum and colon were decreased in PQQ treatment groups (P &lt; 0.05). In conclusion, daily treatment with PQQ improved daily gain, jejunal morphology, immune responses. PQQ-regulated enteric neurochemical plasticity of ENS via the Akt signaling pathway of weaned rats suffering from enteritis.

Identification of a tachykinin receptor and its implication in carbohydrate and lipid homeostasis in Rhodnius prolixus, a chagas disease vector

Neuropeptides and their receptors are fundamentally important in regulating many physiological and behavioural processes in insects. In this work, we have identified, cloned, and sequenced the tachykinin receptor (Rhopr-TKR) from Rhodnius prolixus, a vector of Chagas disease. The receptor is a G protein-coupled receptor belonging to the Rhodopsin Family A. The total length of the open reading frame of the Rhopr-TKR transcript is 1110 bp, which translates into a receptor of 338 amino acids. Fluorescent in-situ RNA-hybridization (FISH) for the Rhopr-TKR transcript shows a signal in a group of six bilaterally paired neurons in the protocerebrum of the brain, localized in a similar region as the insulin producing cells. To examine the role of tachykinin signaling in lipid and carbohydrate homeostasis we used RNA interference. Downregulation of the Rhopr-TKR transcript led to a decrease in the size of blood meal consumed and a significant increase in circulating carbohydrate and lipid levels. Further investigation revealed a close relationship between tachykinin and insulin signaling since the downregulation of the Rhopr-TKR transcript negatively affected the transcript expression for insulin-like peptide 1 (Rhopr-ILP1), insulin-like growth factor (Rhopr-IGF) and insulin receptor 1 (Rhopr-InR1) in both the central nervous system and fat body. Taken together, these findings suggest that tachykinin signaling regulates lipid and carbohydrate homeostasis via the insulin signaling pathway.

Reductive site-selective atypical C,Z-type/N2-C2 cleavage allows C-terminal protein amidation

Biomolecule environments can enhance chemistries with the potential to mediate and modulate self-modification (e.g., self-cleavage). While these enhanced modes are found in certain biomolecules (e.g., RNA ribozymes), it is more rare in proteins. Targeted proteolytic cleavage is vital to physiology, biotechnology, and even emerging therapy. Yet, purely chemically induced methods for the site-selective cleavage of proteins remain scarce. Here, as a proof of principle, we designed and tested a system intended to combine protein-enhanced chemistry with tag modification to enable synthetic reductive protein chemistries promoted by diboron. This reductively driven, single-electron chemistry now enables an operationally simple, site-selective cleavage protocol for proteins directed to readily accessible dehydroalanine (Dha) residues as tags under aqueous conditions and in cell lysates. In this way, a mild, efficient, enzyme-free method now allows not only precise chemical proteolysis but also simultaneous use in the removal of affinity tags and/or protein-terminus editing to create altered N- and C-termini such as protein amidation (─CONH₂).

SP protects Nile tilapia (Oreochromis niloticus) against acute Streptococcus agalatiae infection

Substance P (SP) is a neuropeptide that involves in a wide variety of physiological and pathological events, mainly exerts its roles by neurokinin 1 receptor (NK1R), also modulates immune function. However, the roles of SP during immune response to acute bacterial infection of Nile tilapia (Oreochromis niloticus) remain unclear. In this study, the gene of SP precursor (tachykinin precursor 1, TAC1) and the gene of SP receptor (NK1R) from Nile tilapia were identified, and the roles of SP during an acute bacterial infection in a warm water environment were investigated. On-TAC1(Oreochromis niloticus-TAC1) contains conservative SP & NKA peptide sequences and On-NK1R contains seven conservative transmembrane domains. Their transcriptional levels were most abundant in brain and the On-TAC1 transcripts can be induced in the tilapia challenged with Streptococcus agalactiae. Furthermore, the experimental results revealed that On-SP could promote pyroptosis, suppress inflammation, and improve survival rate during acute bacterial infection. The present data lays a theoretical foundation to further elucidate the mechanism of SP protecting fish against pathogens.

Prevention of tick-borne diseases: challenge to recent medicine

Abstract

Ticks represent important vectors and reservoirs of pathogens, causing a number of diseases in humans and animals, and significant damage to livestock every year. Modern research into protection against ticks and tick-borne diseases focuses mainly on the feeding stage, i.e. the period when ticks take their blood meal from their hosts during which pathogens are transmitted. Physiological functions in ticks, such as food intake, saliva production, reproduction, development, and others are under control of neuropeptides and peptide hormones which may be involved in pathogen transmission that cause Lyme borreliosis or tick-borne encephalitis. According to current knowledge, ticks are not reservoirs or vectors for the spread of COVID-19 disease. The search for new vaccination methods to protect against ticks and their transmissible pathogens is a challenge for current science in view of global changes, including the increasing migration of the human population.

Highlights

• Tick-borne diseases have an increasing incidence due to climate change and increased human migration

• To date, there is no evidence of transmission of coronavirus COVID-19 by tick as a vector

• To date, there are only a few modern, effective, and actively- used vaccines against ticks or tick-borne diseases

• Neuropeptides and their receptors expressed in ticks may be potentially used for vaccine design

Neuropeptidergic regulation of compulsive ethanol seeking in C. elegans

Despite the catastrophic consequences of alcohol abuse, alcohol use disorders (AUD) and comorbidities continue to strain the healthcare system, largely due to the effects of alcohol-seeking behavior. An improved understanding of the molecular basis of alcohol seeking will lead to enriched treatments for these disorders. Compulsive alcohol seeking is characterized by an imbalance between the superior drive to consume alcohol and the disruption or erosion in control of alcohol use. To model the development of compulsive engagement in alcohol seeking, we simultaneously exploited two distinct and conflicting Caenorhabditis elegans behavioral programs, ethanol preference and avoidance of aversive stimulus. We demonstrate that the C. elegans model recapitulated the pivotal features of compulsive alcohol seeking in mammals, specifically repeated attempts, endurance, and finally aversion-resistant alcohol seeking. We found that neuropeptide signaling via SEB-3, a CRF receptor-like GPCR, facilitates the development of ethanol preference and compels animals to seek ethanol compulsively. Furthermore, our functional genomic approach and behavioral elucidation suggest that the SEB-3 regulates another neuropeptidergic signaling, the neurokinin receptor orthologue TKR-1, to facilitate compulsive ethanol-seeking behavior.

Social touch-like tactile stimulation activates a tachykinin 1-oxytocin pathway to promote social interactions

It is well known that affective and pleasant touch promotes individual well-being and facilitates affiliative social communication, although the neural circuit that mediates this process is largely unknown. Here, we show that social-touch-like tactile stimulation (ST) enhances firing of oxytocin neurons in the mouse paraventricular hypothalamus (PVH) and promotes social interactions and positively reinforcing place preference. These results link pleasant somatosensory stimulation to increased social interactions and positive affective valence. We further show that tachykinin 1 (Tac1⁺) neurons in the lateral and ventrolateral periaqueductal gray (l/vlPAG) send monosynaptic excitatory projections to PVH oxytocin neurons. Functionally, activation of PVH-projecting Tac1⁺ neurons increases firing of oxytocin neurons, promotes social interactions, and increases preference for the social touch context, whereas reducing activity of Tac1⁺ neurons abolishes ST-induced oxytocin neuronal firing. Together, these results identify a dipeptidergic pathway from l/vlPAG Tac1⁺ neurons to PVH oxytocin neurons, through which pleasant sensory experience promotes social behavior.

Tachykinins, new players in the control of reproduction and food intake: A comparative review in mammals and teleosts

In vertebrates, the tachykinin system includes tachykinin genes, which encode one or two peptides each, and tachykinin receptors. The complexity of this system is reinforced by the massive conservation of gene duplicates after the whole-genome duplication events that occurred in vertebrates and furthermore in teleosts. Added to this, the expression of the tachykinin system is more widespread than first thought, being found beyond the brain and gut. The discovery of the co-expression of neurokinin B, encoded by the tachykinin 3 gene, and kisspeptin/dynorphin in neurons involved in the generation of GnRH pulse, in mammals, put a spotlight on the tachykinin system in vertebrate reproductive physiology. As food intake and reproduction are linked processes, and considering that hypothalamic hormones classically involved in the control of reproduction are reported to regulate also appetite and energy homeostasis, it is of interest to look at the potential involvement of tachykinins in these two major physiological functions. The purpose of this review is thus to provide first a general overview of the tachykinin system in mammals and teleosts, before giving a state of the art on the different levels of action of tachykinins in the control of reproduction and food intake. This work has been conducted with a comparative point of view, highlighting the major similarities and differences of tachykinin systems and actions between mammals and teleosts.

Multiple tachykinins and their receptors characterized in the gastropod mollusk Pacific abalone: Expression, signaling cascades, and potential role in regulating lipid metabolism

Tachykinin (TK) families, including the first neuropeptide substance P, have been intensively explored in bilaterians. Knowledge of signaling of TK receptors (TKRs) has enabled the comprehension of diverse physiological processes. However, TK signaling systems are largely unknown in Lophotrochozoa. This study identified two TK precursors and two TKR isoforms in the Pacific abalone Haliotis discus hannai (Hdh), and characterized Hdh-TK signaling. Hdh-TK peptides harbored protostomian TK-specific FXGXRamide or unique YXGXRamide motifs at the C-termini. A phylogenetic analysis showed that lophotrochozoan TKRs, including Hdh-TKRs, form a monophyletic group distinct from arthropod TKRs and natalisin receptor groups. Although reporter assays demonstrated that all examined Hdh-TK peptides activate intracellular cAMP accumulation and Ca²⁺ mobilization in Hdh-TKR-expressing mammalian cells, Hdh-TK peptides with N-terminal aromatic residues and C-terminal FXGXRamide motifs were more active than shorter or less aromatic Hdh-TK peptides with a C-terminal YXGXRamide. In addition, we showed that ligand-stimulated Hdh-TKRs mediate ERK1/2 phosphorylation in HEK293 cells and that ERK1/2 phosphorylation is inhibited by PKA and PKC inhibitors. In three-dimensional in silico Hdh-TKR binding modeling, higher docking scores of Hdh-TK peptides were consistent with the lower EC50 values in the reporter assays. The transcripts for Hdh-TK precursors and Hdh-TKR were highly expressed in the neural ganglia, with lower expression levels in peripheral tissues. When abalone were starved for 3 weeks, Hdh-TK1 transcript levels, but not Hdh-TK2, were increased in the cerebral ganglia (CG), intestine, and hepatopancreas, contrasting with the decreased lipid content and transcript levels of sterol regulatory element-binding protein (SREBP). At 24 h post-injection in vivo, the lower dose of Hdh-TK1 mixture increased SREBP transcript levels in the CG and hepatopancreas and accumulative food consumption of abalone. Higher doses of Hdh-TK1 and Hdh-TK2 mixtures decreased the SREBP levels in the CG. When Hdh-TK2-specific siRNA was injected into abalone, intestinal SREBP levels were significantly increased, whereas administration of both Hdh-TK1 and Hdh-TK2 siRNA led to decreased SREBP expression in the CG. Collectively, our results demonstrate the first TK signaling system in gastropod mollusks and suggest a possible role for TK peptides in regulating lipid metabolism in the neural and peripheral tissues of abalone.

Short-term maintenance on a high-sucrose diet alleviates aging-induced sleep fragmentation in drosophila

Sleep is a fundamental behavior in an animal’s life influenced by many internal and external factors, such as aging and diet. Critically, poor sleep quality places people at risk of serious medical conditions. Because aging impairs quality of sleep, measures to improve sleep quality for elderly people are needed. Given that diet can influence many aspects of sleep, we investigated whether a high-sucrose diet (HSD) affected aging-induced sleep fragmentation using the fruit fly, Drosophila melanogaster. Drosophila is a valuable model for studying sleep due to its genetic tractability and many similarities with mammalian sleep. Total sleep duration, sleep bout numbers (SBN), and average sleep bout length (ABL) were compared between young and old flies on a normal sucrose diet (NSD) or HSD. On the NSD, old flies slept slightly more and showed increased SBN and reduced ABL, indicating increased sleep fragmentation. Short-term maintenance of flies in HSD (up to 8 days), but not long-term maintenance (up to 35 days), suppressed aging-induced sleep fragmentation. Our study provides meaningful strategies for preventing the deterioration of sleep quality in the elderly.

Insects as a New Complex Model in Hormonal Basis of Obesity

Nowadays, one of the biggest problems in healthcare is an obesity epidemic. Consumption of cheap and low-quality energy-rich diets, low physical activity, and sedentary work favor an increase in the number of obesity cases within many populations/nations. This is a burden on society, public health, and the economy with many deleterious consequences. Thus, studies concerning this disorder are extremely needed, including searching for new, effective, and fitting models. Obesity may be related, among other factors, to disrupting adipocytes activity, disturbance of metabolic homeostasis, dysregulation of hormonal balance, cardiovascular problems, or disorders in nutrition which may lead to death. Because of the high complexity of obesity, it is not easy to find an ideal model for its studies which will be suitable for genetic and physiological analysis including specification of different compounds’ (hormones, neuropeptides) functions, as well as for signaling pathways analysis. In recent times, in search of new models for human diseases there has been more and more attention paid to insects, especially in neuro-endocrine regulation. It seems that this group of animals might also be a new model for human obesity. There are many arguments that insects are a good, multidirectional, and complex model for this disease. For example, insect models can have similar conservative signaling pathways (e.g., JAK-STAT signaling pathway), the presence of similar hormonal axis (e.g., brain–gut axis), or occurrence of structural and functional homologues between neuropeptides (e.g., neuropeptide F and human neuropeptide Y, insulin-like peptides, and human insulin) compared to humans. Here we give a hint to use insects as a model for obesity that can be used in multiple ways: as a source of genetic and peptidomic data about etiology and development correlated with obesity occurrence as well as a model for novel hormonal-based drug activity and their impact on mechanism of disease occurrence.

Metabolic control of daily locomotor activity mediated by tachykinin in Drosophila

Metabolism influences locomotor behaviors, but the understanding of neural curcuit control for that is limited. Under standard light-dark cycles, Drosophila exhibits bimodal morning (M) and evening (E) locomotor activities that are controlled by clock neurons. Here, we showed that a high-nutrient diet progressively extended M activity but not E activity. Drosophila tachykinin (DTk) and Tachykinin-like receptor at 86C (TkR86C)-mediated signaling was required for the extension of M activity. DTk neurons were anatomically and functionally connected to the posterior dorsal neuron 1s (DN1_ps) in the clock neuronal network. The activation of DTk neurons reduced intracellular Ca²⁺ levels in DN1_ps suggesting an inhibitory connection. The contacts between DN1_ps and DTk neurons increased gradually over time in flies fed a high-sucrose diet, consistent with the locomotor behavior. DN1_ps have been implicated in integrating environmental sensory inputs (e.g., light and temperature) to control daily locomotor behavior. This study revealed that DN1_ps also coordinated nutrient information through DTk signaling to shape daily locomotor behavior.

Lee and colleagues report the effect of a high-sucrose diet on Drosophila locomotor activity via DTk-TkR86C neuropeptide signalling. This signalling pattern appears to involve a circadian element, with pacemaker neuron involvement having a possible time-of-day effect on locomotor behaviour.

Characterization of putative tachykinin peptides in Caenorhabditis elegans

Tachykinin-like peptides, such as substance P, neurokinin A, and neurokinin B, are among the earliest discovered and best-studied neuropeptide families, and research on them has contributed greatly to our understanding of the endocrine control of many physiological processes. However, there are still many orphan tachykinin receptor homologs for which cognate ligands have not yet been identified, especially in small invertebrates, such as the nematode Caenorhabditis elegans (C. elegans). We here show that the C. elegans nlp-58 gene encodes putative ligands for the orphan G protein-coupled receptor (GPCR) TKR-1, which is a worm ortholog of tachykinin receptors. We first determine, through an unbiased biochemical screen, that a peptide derived from the NLP-58 preprotein stimulates TKR-1. Three mature peptides that are predicted to be generated from NLP-58 show potent agonist activity against TKR-1. We designate these peptides as C. elegans tachykinin (CeTK)-1, -2, and -3. The CeTK peptides contain the C-terminal sequence GLR-amide, which is shared by tachykinin-like peptides in other invertebrate species. nlp-58 exhibits a strongly restricted expression pattern in several neurons, implying that CeTKs behave as neuropeptides. The discovery of CeTKs provides important information to aid our understanding of tachykinin-like peptides and their functional interaction with GPCRs.

The Effect of SP/NK1R on the Expression and Activity of Catalase and Superoxide Dismutase in Glioblastoma Cancer Cells

Introduction

Glioblastoma is the most malignant brain tumor with different therapeutic protocols, including surgery, radiotherapy, and chemotherapy. Substance P (SP), a peptide released by sensory nerves, increases cellular excitability by activating the neurokinin-1 receptor (NK1R) in several human tumor cells. Aprepitant is a potent and long-lasting NK1R antagonist, considered a new agent for inhibiting proliferation and induction of apoptosis in malignant cells. This study aimed to evaluate the effects of the SP/NK1R system on the expression and activity of catalase and superoxide dismutase (SOD) in the glioblastoma U87 cancer cell line.

Methods

Cytotoxicity was measured by the resazurin test, 24 hours after treatment, with increasing aprepitant concentrations. The production of reactive oxygen species (ROS) was also measured 24 hours after treatment with SP and aprepitant. Enzymes activity of catalase and SOD was measured using the corresponding assay kits. Real-time PCR also measured their expression.

Results

Aprepitant significantly reduced the viability of U87 cells in a concentration-dependent manner. ROS production was significantly reduced, and the activity of catalase and SOD increased after treatment with aprepitant. The expression of catalase and SOD enzymes also increased significantly in the presence of aprepitant.

Conclusion

The present study showed that aprepitant inhibited SP's oxidizing effects via inducing the antioxidant effects of catalase and SOD in the U87 cell line. Therefore, this drug might be introduced as a potential candidate for controlling glioblastoma cancer in animal models and clinical trials.

Neuropeptides: Roles and Activities as Metal Chelators in Neurodegenerative Diseases

Neurodegenerative diseases, such as Alzheimer's disease (AD) and Parkinson's disease (PD), are characterized by deposits of amyloid proteins. The homeostasis of metal ions is crucial for the normal biological functions in the brain. However, in AD and PD, the imbalance of metal ions leads to formation of amyloid deposits. In the past four decades, there has been extensive effort to design compound agents than can chelate metal ions with the aim of preventing the formation of the amyloid deposits. Unfortunately, the compounds to date that were designed were not successful candidates to be used in clinical trials. Neuropeptides are small molecules that are produced and released by neurons. It has been shown that neuropeptides have neuroprotective effects in the brain and reduce the formation of amyloid deposits. This Review Article is focused on the function of neuropeptides as metal chelators. Experimental and computational studies demonstrated that neuropeptides could bind metal ions, such as Cu²⁺ and Zn²⁺. This Review Article provides perspectives and initiates future studies to investigate the role of neuropeptides as metal chelators in neurodegenerative diseases.