Cholinergic axons regulate type I acini in salivary glands of Ixodes ricinus and Ixodes scapularis ticks

Ferritin1-mediated ferroptosis participates in granular acini degeneration of Haemaphysalis longicornis salivary glands

Ticks (Haemaphysalis longicornis) transmit pathogens to their hosts through their salivary glands during blood-feeding. The salivary glands of adult parthenogenetic H. longicornis undergo degeneration post-engorgement. Clarifying the molecular mechanisms underlying salivary gland degeneration of H. longicornis is conducive to identifying novel targets for preventing and controlling these widespread vectors. In this study, we investigated the salivary glands of adult parthenogenetic H. longicornis to elucidate the relationship between ferroptosis, iron-dependent cell death, H. longicornis ferritin 1 (HlFer1) and salivary gland degeneration post-attachment and post-engorgement. Fluorescence microscopy, revealed increased iron accumulation, reactive oxygen species, lipid peroxidation, and decreased mitochondrial cristae in the granular acini of H. longicornis salivary glands post-engorgement. The results of a qPCR analysis indicated that HlFer1, glutathione peroxidase 4 (GPX4), transferrin (TRF), and high mobility group protein B1 (HMGB1) expression elevated in H. longicornis salivary glands post-attachment and post-engorgement. In vitro culture of H. longicornis salivary glands showed that erastin promotes ferroptosis, while ferrostatin-1 blocks this process. RNA interference (RNAi) targeting HlFer1 promoted ferroptosis in salivary gland granular acini. In conclusion, we demonstrated that HlFer1-induced ferroptosis is a key molecular mechanism underlying the salivary gland granular acini degeneration of H. longicornis. Our findings are important for developing novel preventive measures against H. longicornis as a disease vector.

Distribution of alpha-synuclein in rat salivary glands

Expression of alpha-synuclein (Syn), a presynaptic neuronal protein, was immunohistochemically examined in intact rat submandibular, sublingual, and lingual glands. The submandibular gland contained abundant periductal Syn-immunoreactive (-ir) nerve fibers. Abundant Syn-ir varicosities were present in acini of the sublingual and serous lingual glands. By confocal laser scanning microscopy, Syn-ir nerve fibers around smooth muscle actin (SMA)-ir cells alone were infrequent; however, those around aquaporin-5 (AQP5)-ir cells alone and both SMA- and AQP5-ir cells were abundant in the sublingual and serous lingual glands. SMA-ir cells were occasionally immunoreactive for toll-like receptor 4, a Syn receptor. Syn-ir nerve fibers contained tyrosine hydroxylase (TH) in the submandibular gland and choline acetyltransferase (ChAT) in all examined salivary glands. In the superior cervical (SCG), submandibular, and intralingual ganglia, sympathetic and parasympathetic neurons co-expressed Syn with TH and ChAT, respectively. SCG neurons innervating the submandibular gland contained mostly Syn. In the thoracic spinal cord, 14.7% of ChAT-ir preganglionic sympathetic neurons co-expressed Syn. In the superior salivatory nucleus, preganglionic parasympathetic neurons projecting to the lingual nerve co-expressed Syn and ChAT. The present findings indicate that released Syn acts on myoepithelial cells. Syn in pre- and post-ganglionic neurons may regulate neurotransmitter release and salivary volume and composition.

Hard Ticks as Vectors: The Emerging Threat of Tick-Borne Diseases in India

Hard ticks (Ixodidae) play a critical role in transmitting various tick-borne diseases (TBDs), posing significant global threats to human and animal health. Climatic factors influence the abundance, diversity, and vectorial capacity of tick vectors. It is imperative to have a comprehensive understanding of hard ticks, pathogens, eco-epidemiology, and the impact of climatic changes on the transmission dynamics of TBDs. The distribution and life cycle patterns of hard ticks are influenced by diverse ecological factors that, in turn, can be impacted by changes in climate, leading to the expansion of the tick vector's range and geographical distribution. Vector competence, a pivotal aspect of vectorial capacity, involves the tick's ability to acquire, maintain, and transmit pathogens. Hard ticks, by efficiently feeding on diverse hosts and manipulating their immunity through their saliva, emerge as competent vectors for various pathogens, such as viruses, parasites and bacteria. This ability significantly influences the success of pathogen transmission. Further exploration of genetic diversity, population structure, and hybrid tick vectors is crucial, as they play a substantial role in influencing vector competence and complicating the dynamics of TBDs. This comprehensive review deals with important TBDs in India and delves into a profound understanding of hard ticks as vectors, their biology, and the factors influencing their vector competence. Given that TBDs continue to pose a substantial threat to global health, the review emphasizes the urgency of investigating tick control strategies and advancing vaccine development. Special attention is given to the pivotal role of population genetics in comprehending the genetic diversity of tick populations and providing essential insights into their adaptability to environmental changes.

Functional characterization of three G protein-coupled acetylcholine receptors in parasitic nematode Trichinella spiralis

The physiological significance of metabotropic acetylcholine receptors in parasitic nematodes remains largely unexplored. Here, three different Trichinella spiralis G protein-coupled acetylcholine receptors (TsGAR-1, -2, and -3) were identified in the genome of T. spiralis. The phylogenetic analyses showed that TsGAR-1 and -2 receptors belong to a distinct clade specific to invertebrates, while TsGAR-3 is closest to the cluster of mammalian-type muscarinic acetylcholine receptors (mAChR). The mRNA of TsGAR-1, -2, and -3 was detected in muscle larvae, newborn larvae, and adults. The functional aequorin-based assay in Chinese hamster ovary cells revealed that all three types of T. spiralis GARs trigger the Gq/11 pathway upon activation of the receptor with the acetylcholine ligand. TsGAR-1 and TsGAR-2 showed atypical affinity with classical muscarinic agonists, while TsGAR-3 was sensitive to all muscarinic agonists tested. High concentrations of propiverine antagonist blocked the activities of all three TsGARs, while atropine and scopolamine antagonists effectively inhibited only TsGAR-3. Our data indicate that the distinct pharmacological profile of TsGAR-1 and -2 receptors, as well as the phylogenetic distance between them and their mammalian orthologs, place them as attractive targets for the development of selective anthelmintic drugs interfering with nematodes' cholinergic system.

Isolation and electrophysiological recording of Ixodes ricinus synganglion neurons

The central nervous system of hard ticks (Ixodidae) consists of a concentrated merged nerve mass known as the synganglion. Although knowledge of tick neurobiology has dramatically improved over the last two decades, this is the first time that isolation and electrophysiological recordings have been carried out on tick neurons from the synganglion. Method: We developed a simple protocol for synganglion neuron isolation and used a whole-cell patch clamp to measure ionic currents induced by acetylcholine, nicotine and muscarine. Relatively large neurons (∼ 25 μm and ∼ 35 μm) were isolated and 1 mM acetylcholine was used to induce strong inward currents of -0.38 ± 0.1 nA and - 1.04 ± 0.1 nA, respectively, with the corresponding cell capacitances being at around 142 pF and 188 pF. In addition, successive application of 1 mM acetylcholine through ∼25 μm and ∼ 35 μm cells for increasing amounts of time resulted in a rapid reduction in current amplitudes. We also found that acetylcholine-evoked currents were associated with a reversible increase in intracellular calcium levels for each neuronal type. In contrast, 1 mM muscarine and nicotine induced a strong and non-reversible increase in intracellular calcium levels. This study serves as a proof of concept for the mechanical isolation of tick synganglion neurons followed by their electrophysiological recording. This approach will aid investigations into the pharmacological properties of tick neurons and provides the tools needed for the identification of drug-targeted sites and effective tick control measures.

Dual SIFamide receptors in Ixodes salivary glands

Salivary glands are vital to tick feeding success and also play a crucial role in tick-borne pathogen transmission. In previous studies of Ixodes scapularis salivary glands, we demonstrated that saliva-producing type II and III acini are innervated by neuropeptidergic axons which release different classes of neuropeptides via their terminals (Šimo et al., 2009b, 2013). Among these, the neuropeptide SIFamide-along with its cognate receptor-were postulated to control the basally located acinar valve via basal epithelial and myoepithelial cells (Vancová et al., 2019). Here, we functionally characterized a second SIFamide receptor (SIFa_R2) from the I. scapularis genome and proved that it senses a low nanomolar level of its corresponding ligand. Insect SIFamide paralogs, SMYamides, also activated the receptor but less effectively compared to SIFamide. Bioinformatic and molecular dynamic analyses suggested that I. scapularis SIFamide receptors are class A GPCRs where the peptide amidated carboxy-terminus is oriented within the receptor binding cavity. The receptor was found to be expressed in Ixodes ricinus salivary glands, synganglia, midguts, trachea, and ovaries, but not in Malpighian tubules. Investigation of the temporal expression patterns suggests that the receptor transcript is highly expressed in unfed I. ricinus female salivary glands and then decreases during feeding. In synganglia, a significant transcript increase was detected in replete ticks. In salivary gland acini, an antibody targeting the second SIFamide receptor recognized basal epithelial cells, myoepithelial cells, and basal granular cells in close proximity to the SIFamide-releasing axon terminals. Immunoreactivity was also detected in specific neurons distributed throughout various I. ricinus synganglion locations. The current findings, alongside previous reports from our group, indicate that the neuropeptide SIFamide acts via two different receptors that regulate distinct or common cell types in the basal region of type II and III acini in I. ricinus salivary glands. The current study investigates the peptidergic regulation of the I. ricinus salivary gland in detail, emphasizing the complexity of this system.

Infestation of mice with ixodid ticks in forests of Belgorod region

Rodents are one of the largest groups of existing mammals and number more than 2,270 known species, which is almost 42 % of the total biodiversity of worldwide-distributed mammals (except Antarctica and some islands). They are well adapted to various habitats and are known to live alongside people and livestock complexes. The purpose of the study was to study infestation of mice with ixodid ticks in forests of the Belgorod region adjacent to livestock and poultry farms. The study was carried out in 2019-2022. The extensiveness of mice infestation was observed in Sylvaemus sylvaticus species, which was 13.26 % higher (P 0.05) than in Sylvimus flavicollis , and 24.33 % higher (P 0.01) than in Apodemus agrarius . The intensity of infestation with preimaginal (larvae and nymphs) stages of Ixodes ricinus ticks had wide fluctuations depending on the type of synanthropic rodent. Thus, the highest intensity was noted in Sylvaemus sylvaticus mice, which was 8.73 and 13.56 % higher (P 0.001) compared to Sylvimus flavicollis and Apodemus agrarius mice, respectively. The maximum infestation of male synanthropic mouse species was 31 ticks in Sylvaemus sylvaticus , 19 ticks in Sylvimus flavicollis , and 9 ticks in Apodemus agrarius . The intensity of infestation in synanthropic mice was the highest in the summer months (from July to August) and decreased slightly in autumn. In autumn, 41.2 % of the examined rodents were infested with ticks, the predominant species was Ixodes ricinus (larvae). Larvae and nymphs of Ixodes ricinus ticks were more often attached to rodents in the head area (mainly on the ears) - 82 %, less often on other parts of the body - 1 8 %. A smaller number of ticks were present on neck, body, legs, sometimes parasites were found on tail.

Choline Oxidase-Integrated Copper Metal-Organic Frameworks as Cascade Nanozymes for One-Step Colorimetric Choline Detection

Choline is an important factor for regulating human health and is widely present in various foods. In this work, a sensor strategy based on a choline oxidase-integrated copper(II) metal-organic framework with peroxidase-like activity is constructed for one-step cascade detection of choline. The one-step cascade strategy can avoid intermediate product transferring in general multi-step reactions, and the multi-enzyme activities can be well exerted under one condition, thus exhibiting excellent catalytic activity and enhanced stability. In the integrated system, choline is catalyzed by ChO_x to produce betaine and H₂O₂, which eventually got converted to hydroxyl radicals by the peroxidase nanozyme, oxidized the chromogenic substrate ABTS, and produced an observable absorption peak at 420 nm. A new choline detection method was thus established and showed a satisfactory linear relationship at 6-300 μM, which has been used for the choline analysis in milk.

Concise Synthesis of Both Enantiomers of Pilocarpine

Furan-2-carboxylic acid was used as a starting material for the synthesis of dehydro-homopilopic acid. Esterification, hydrogenation and enzymatic hydrolysis followed by the reduction of Weinreb amides and a single-step attachment of a 1-methyl-imidazole residue allowed for the concise synthesis of both enantiomers of pilocarpine.

Enlisting the Ixodes scapularis Embryonic ISE6 Cell Line to Investigate the Neuronal Basis of Tick-Pathogen Interactions

Neuropeptides are small signaling molecules expressed in the tick central nervous system, i.e., the synganglion. The neuronal-like Ixodes scapularis embryonic cell line, ISE6, is an effective tool frequently used for examining tick–pathogen interactions. We detected 37 neuropeptide transcripts in the I. scapularis ISE6 cell line using in silico methods, and six of these neuropeptide genes were used for experimental validation. Among these six neuropeptide genes, the tachykinin-related peptide (TRP) of ISE6 cells varied in transcript expression depending on the infection strain of the tick-borne pathogen, Anaplasma phagocytophilum. The immunocytochemistry of TRP revealed cytoplasmic expression in a prominent ISE6 cell subpopulation. The presence of TRP was also confirmed in A. phagocytophilum-infected ISE6 cells. The in situ hybridization and immunohistochemistry of TRP of I. scapularis synganglion revealed expression in distinct neuronal cells. In addition, TRP immunoreaction was detected in axons exiting the synganglion via peripheral nerves as well as in hemal nerve-associated lateral segmental organs. The characterization of a complete Ixodes neuropeptidome in ISE6 cells may serve as an effective in vitro tool to study how tick-borne pathogens interact with synganglion components that are vital to tick physiology. Therefore, our current study is a potential stepping stone for in vivo experiments to further examine the neuronal basis of tick–pathogen interactions.