Transcriptomic profiling and the first spatial expression analysis of candidate genes in the salivary gland of the East Asian medicinal leech, Hirudo nipponia

Hirudo nipponia, a blood-sucking leech native to East Asia, possesses a rich repertoire of active ingredients in its saliva, showcasing significant medical potential due to its anticoagulant, anti-inflammatory, and antibacterial effects against human diseases. Despite previous studies on the transcriptomic and proteomic characteristics of leech saliva, which have identified medicinal compounds, our knowledge of tissue-specific transcriptomes and their spatial expression patterns remains incomplete. In this study, we conducted an extensive transcriptomic profiling of the salivary gland tissue in H. nipponia based on de novo assemblies of tissue-specific transcriptomes from the salivary gland, teeth, and general head region. Through gene ontology (GO) analysis and hierarchical clustering, we discovered a novel set of anti-coagulant factors-i.e., Hni-Antistasin, Hni-Ghilanten, Hni-Bdellin, Hni-Hirudin-as well as a previously unrecognized immune-related gene, Hni-GLIPR1 and uncharacterized salivary gland specific transcripts. By employing in situ hybridization, we provided the first visualization of gene expression sites within the salivary gland of H. nipponia. Our findings expand on our understanding of transcripts specifically expressed in the salivary gland of blood-sucking leeches, offering valuable resources for the exploration of previously unidentified substances with medicinal applications.

'Pearls' of the nineteenth-century: from therapeutic actors to global commodities medicinal leeches in the Ottoman Empire

Nineteenth-century physicians increasingly favoured leeching - the placing of a live leech onto a patient's skin to stimulate or limit blood flow - as a cure for numerous ailments. As conviction in their therapeutic properties spread, leech therapy dominated European medicine; France imported over fifty million leeches in one year. Demand soon outpaced supply, spawning a lucrative global trade. Over-collection and farming eventually destroyed leech habitats, wreaked environmental havoc and forced European merchants to seek new supply sources. Vast colonies of leeches were found to inhabit the immense wetlands of the Ottoman Empire, which soon became a major exporter of medicinal leeches. Following the Treaty of Balta Liman (1838), the Ottoman state moved to exert control over the lucrative trade, imposing a tax on leech gathering and contracting with tax-farmers (mültezim) to collect the taxes. British diplomats, merchants and other stakeholders protested the imposition of the tax, as had previously happened with the commodification of wildlife; their pursuit of profit led collectors and farmers to over-gather leeches, with catastrophic consequences. By the end of the century, so great had their worth climbed that the leech population faced extinction. This paper situates medicinal leeches as therapeutic actors of history and adopts an interscale approach in formulating the human-leech interaction. It offers a substantive contribution to the history of medicine, in revealing the centrality of leeches to the rise of modern medicine and global trade, but also by making visible their role in shaping imperial diplomacy and worldwide economic markets.

Hirudo verbana as a freshwater invertebrate model to assess the effects of polypropylene micro and nanoplastics dispersion in freshwater

Plastics are a heterogeneous class of synthetic compounds that, due to their unique characteristics find numerous applications both in industrial and civil fields. However, despite the great advantages that these materials brought in everyday life, the plastic wastes resulting from their massive use represent one of the main environmental problems at the global level. Once released, plastics persist for a long time and are subjected both to biotic and abiotic processes leading to the formation of small particles, known as micro and to nanoplastics, that interact with organisms, accumulating inside tissues and risking to enter in the trophic chain. Among the different types of plastic, polypropylene (PP) is one of the diffused, widely exploited in food and textile industries for disposable packaging and to produce surgical masks. Owing to the huge distribution and the resultant abundant presence of PP waste products, it results necessary investigate the possible toxicity on living organisms. For these reasons, here we analyzed the effects of PP micro and nanoplastics dispersed in freshwater, using the medicinal leech Hirudo verbana as invertebrate model. To better follow the plastics fate, fluorescent particles, labeled with a fluorophore, have been used. Animals were examined at various timings after plastics exposure and results were analyzed by means of microscopy, immunofluorescent and molecular biology analyses. After assessing the entrance of PP fragments into leech tissues, the activation of the innate immune response was evaluated. The results show that the presence of micro and nanoplastics induces an initial physical protection that consists in the secretion of mucus, followed by an increase of blood vessels and the recruitment of immune cells, in particular macrophages. Moreover, macrophages were directly involved in both phagocytic and encapsulation processes, as demonstrated by acid phosphatase (ACP) histoenzymatic and Thioflavin-T assays, expressing specific pro-inflammatory factors, such as HvRNASET2 and HmAIF-1, as demonstrated by immunolocalization and qPCR experiments. Finally, the expression levels of genes related to oxidative stress-induced enzymes have been investigated, in order to evaluate the possible increase in reactive oxygen species (ROS), due to the entry into the leech tissues of PP micro and nanoplastics. This work allows deepening the current knowledge of the possible harmful effects on human health deriving from micro and nanoplastics dispersion, leading new insight about freshwater ecosystems that often represent the first environments interested in plastic pollution.

Recombinant HvRNASET2 protein induces marked connective tissue remodelling in the invertebrate model Hirudo verbana

The RNASET2 ribonuclease, belonging to the highly conserved RH/T2/s RNase gene family, has been recently shown to modulate inflammatory processes in both vertebrates and invertebrates. Indeed, the RNASET2 protein acts as a chemoattractor for macrophages in both in vitro and in vivo experimental settings and its expression significantly increases following bacterial infections. Moreover, we recently observed that injection of human recombinant RNASET2 protein in the body wall of the medicinal leech (a consolidated invertebrate model for both immune response and tissue regeneration) not only induced immune cell recruitment but also apparently triggered massive connective tissue remodelling as well. Based on these data, we evaluate here a possible role of leech recombinant RNASET2 protein (rHvRNASET2) in connective tissue remodelling by characterizing the cell types involved in this process through histochemical, morphological and immunofluorescent assays. Moreover, a time-course expression analysis of newly synthesized pro-collagen1α1 (COL1α1) and basic FGF receptor (bFGFR, a known fibroblast marker) following rHvRNASET2 injection in the leech body wall further supported the occurrence of rHvRNASET2-mediated matrix remodelling. Human MRC-5 fibroblast cells were also investigated in order to evaluate their pattern of collagen neosynthesis driven by rHvRNASET2 injection.Taken together, the data reported in this work provide compelling evidence in support of a pleiotropic role for RNASET2 in orchestrating an evolutionarily conserved crosstalk between inflammatory response and regenerative process, based on macrophage recruitment and fibroblast activation, coupled to a massive extracellular reorganization.

Concentrations of some heavy metal and macroelements in sediment, water, macrophyte species, and leech (Hirudo sulukii n. sp.) from the Kara Lake, Adiyaman, Turkey

Content of some heavy metals (Cd, Cr, Cu, Fe, Mn, Ni, Pb, and Zn) and macroelements (Ca, Mg, Na, and K) were determined in samples of water, sediment, macrophytes (Potamogeton crispus, Potamogeton perfoliatus, Myriophyllum spicatum, and Chara vulgaris), and leech (Hirudo sulukii n. sp.) collected from Kara Lake Adiyaman, Turkey at four distinct seasons using inductively coupled plasma optical emission spectrometer (ICP-OES). It was found that the studied heavy metals were completely below the detection limit of ICP-OES for water samples. The results showed that most heavy metals (Ni, Cr, Zn, Fe, and Pb) and macroelements (Mg and Na) had their highest values in sediment samples in August. Increases of heavy metals and macroelements may be due to evaporation because of summer stagnation at this period. The average content of studied elements was in the order of Mn>Ni>Cr>Zn>Fe>Pb>Cu in sediment samples. As a non-essential heavy metal, Cr was the most accumulated in all the macrophytes studied. The average Cr concentration was in the order of P. crispus > P. perfoliatus > M. spicatum > C. vulgaris. In C. vulgaris, the accumulation of Ca was the highest compared with other macrophytes. The accumulation of heavy metal was in the order of Fe>Zn>Cu>Pb>Mn>Cr>Ni>Cd in H. sulukii n. sp. The obtained results showed that the heavy metal and macroelement (Na, Ca, Mg, and K) concentrations in water, sediment, macrophytes, and leech are below the risk values according to the aquatic life pollutant data provided by the U.S. Environmental Protection Agency. Overall, the element contents can be attributable to the geological sources because of the general absence of serious pollution in Kara Lake, Adiyaman, Turkey.

Electrophysiology and transcriptomics reveal two photoreceptor classes and complex visual integration in Hirudo verbana

Among animals with visual processing mechanisms, the leech Hirudo verbana is a rare example in which all neurons can be identified. However, little is known about its visual system, which is composed of several pigmented head eyes and photosensitive non-pigmented sensilla that are distributed across its entire body. Although several interneurons are known to respond to visual stimuli, their response properties are poorly understood. Among these, the S-cell system is especially intriguing: it is multimodal, spans the entire body of the leech and is thought to be involved in sensory integration. To improve our understanding of the role of this system, we tested its spectral sensitivity, spatial integration and adaptation properties. The response of the S-cell system to visual stimuli was found to be strongly dependent on the size of the area stimulated, and adaptation was local. Furthermore, an adaptation experiment demonstrated that at least two color channels contributed to the response, and that their contribution was dependent on the adaptation to the background. The existence of at least two color channels was further supported by transcriptomic evidence, which indicated the existence of at least two distinct groups of putative opsins for leeches. Taken together, our results show that the S-cell system has response properties that could be involved in the processing of spatial and color information of visual stimuli. We propose the leech as a novel system to understand visual processing mechanisms with many practical advantages.

Medicinal leech antimicrobial peptides lacking toxicity represent a promising alternative strategy to combat antibiotic-resistant pathogens

The rise of antibiotic resistance has necessitated the development of alternative strategies for the treatment of infectious diseases. Antimicrobial peptides (AMPs), components of the innate immune response in various organisms, are promising next-generation drugs against bacterial infections. The ability of the medicinal leech Hirudo medicinalis to store blood for months with little change has attracted interest regarding the identification of novel AMPs in this organism. In this study, we employed computational algorithms to the medicinal leech genome assembly to identify amino acid sequences encoding potential AMPs. Then, we synthesized twelve candidate AMPs identified by the algorithms, determined their secondary structures, measured minimal inhibitory concentrations against three bacterial species (Escherichia coli, Bacillus subtilis, and Chlamydia thrachomatis), and assayed cytotoxic and haemolytic activities. Eight of twelve candidate AMPs possessed antimicrobial activity, and only two of them, 3967 (FRIMRILRVLKL) and 536-1 (RWRLVCFLCRRKKV), exhibited inhibition of growth of all tested bacterial species at a minimal inhibitory concentration of 10 μmol. Thus, we evidence the utility of the developed computational algorithms for the identification of AMPs with low toxicity and haemolytic activity in the medicinal leech genome assembly.

Bacterial Community of the Digestive Tract of the European Medicinal Leech (Hirudo verbana) from the Danube River

The digestive tract of medicinal leeches from commercial suppliers has been investigated previously and comprises of a relatively simple bacterial community. However, the microbiome of medicinal leeches collected directly from the natural habitat has not been examined. In this study, we characterized the bacterial community in the digestive tract (anterior crop, posterior crop, and intestine) of the European medicinal leech, Hirudo verbana, collected from the Danube river using culture-independent and culture-dependent approaches. Culture-independent approach confirmed that the digestive tract of H. verbana carries a relatively simple bacterial community with species richness in the individual samples ranging from 43 to164. The dominant bacterial taxon was Mucinivorans sp. (49.7% of total reads), followed by Aeromonas sp. (18.7% of total reads). Several low abundance taxa, new for H. verbana, such as Phreatobacter, Taibaiella, Fluviicola, Aquabacterium, Burkholderia, Hydrogenophaga, Wolinella, and unidentified Chitinophagia, were also detected. The aerobic culturing approach showed Aeromonas veronii (Proteobacteria), the known leech symbiont, as the most dominant taxon followed by several Pseudomonas and Acidovorax spp. No significant differences in the bacterial community composition were detected among different parts of the digestive tract of individual leeches. However, the overall composition of the bacterial community among individual specimen varied significantly and this is possibly due to differences in leech age, feeding status, and blood source. Our results showed that the core bacterial community of H. verbana collected from the natural habitat is similar to that reported from the digestive tract of commercially supplied leeches maintained in the laboratory.

Entrapped by the uneven central and Middle Eastern terrains: Genetic status of populations of Hirudo orientalis (Annelida, Clitellata, Hirudinida) with a phylogenetic review of the genus Hirudo

Phylogenetic relationships between species of the genus Hirudo plus genetic variation in the entire distribution range of Hirudo orientalis were investigated based on mitochondrial (COI and 12S rDNA) and nuclear (ITS1+5.8S+ITS2) genome regions. The sister relationship of Hirudo orientalis and H. medicinalis was revealed with a high posterior probability. A broad and patchy distribution with minor genetic differences was observed in populations of H. orientalis along the central and Middle Eastern parts of Asia. The known distribution range occurred in topographically heterogeneous landscapes around the Caspian Sea. The demographic analysis suggests the selection of the COI locus under unfavourable respiratory conditions, but population size expansion cannot be fully rejected. The genetic variation trend indicated northward dispersal. Higher haplotype diversity in the South Caspian region potentially suggests the area as a historical refugium for the species. The vast dispersal is assumed to occur after the Pleistocene glaciations via vertebrate hosts.

Intrinsic frequency response patterns in mechano-sensory neurons of the leech

Animals employ mechano-sensory systems to detect and explore their environment. Mechano-sensation encompasses stimuli such as constant pressure, surface movement or vibrations at various intensities that need to be segregated in the central nervous system. Besides different receptor structures, sensory filtering via intrinsic response properties could provide a convenient way to solve this problem. In leech, three major mechano-sensory cell types can be distinguished, according to their stimulus sensitivity, as nociceptive, pressure and touch cells. Using intracellular recordings, we show that the different mechano-sensory neuron classes in Hirudo medicinalis differentially respond supra-threshold to distinct frequencies of sinusoidal current injections between 0.2 and 20 Hz. Nociceptive cells responded with a low-pass filter characteristic, pressure cells as high-pass filters and touch cells as an intermediate band-pass filter. Each class of mechano-sensory neurons is thus intrinsically tuned to a specific frequency range of voltage oscillation that could help segregate mechano-sensory information centrally.

Summary: Mechano-sensitive neurons of leech are intrinsically tuned to generate somatic input-output functions with distinct filter properties.

On exploration of geometrically constrained space by medicinal leeches Hirudo verbana

Leeches are fascinating creatures: they have simple modular nervous circuitry yet exhibit a rich spectrum of behavioural modes. Leeches could be ideal blue-prints for designing flexible soft robots which are modular, multi-functional, fault-tolerant, easy to control, capable for navigating using optical, mechanical and chemical sensorial inputs, have autonomous inter-segmental coordination and adaptive decision-making. With future designs of leech-robots in mind we study how leeches behave in geometrically constrained spaces. Core results of the paper deal with leeches exploring a row of rooms arranged along a narrow corridor. In laboratory experiments we find that rooms closer to ends of the corridor are explored by leeches more often than rooms in the middle of the corridor. Also, in series of scoping experiments, we evaluate leeches capabilities to navigating in mazes towards sources of vibration and chemo-attraction. We believe our results lay foundation for future developments of robots mimicking behaviour of leeches.