The medicinal leech as a valuable model for better understanding the role of a TLR4-like receptor in the inflammatory process

Therapeutic Potentials of Medicinal Leech in Chinese Medicine

The use of medicinal leeches in clinical therapy has been employed for a long time, as it was originally recognized for exerting antithrombin effects. These effects were due to the ability of the leech to continuously suck blood while attached to human skin. According to Chinese Pharmacopoei, leeches used in traditional Chinese medicine mainly consist of Whitmania pigra Whitman, Hirudo nipponia Whitman, and Whitmania acranulata, but the latter two species are relatively scarce. The main constituents of leeches are protein and peptide macromolecules. They can be categorized into two categories based on their pharmacological effects. One group consists of active ingredients that directly target the coagulation system, such as hirudin, heparin, and histamine, which are widely known. The other group comprises protease inhibitor components like Decorsin and Hementin. Among these, hirudin secreted by the salivary glands of the leech is the most potent thrombin inhibitor and served as the sole remedy for preventing blood clotting until the discovery of heparin. Additionally, leeches play a significant role in various traditional Chinese medicine formulations. In recent decades, medicinal leeches have been applied in fields including anti-inflammatory treatment, cardiovascular disease management, antitumor treatment, and many other medical conditions. In this review, we present a comprehensive overview of the historical journey and medicinal applications of leeches in various medical conditions, emphasizing their pharmaceutical significance within traditional Chinese medicine. This review offers valuable insights for exploring additional therapeutic opportunities involving the use of leeches in various diseases and elucidating their underlying mechanisms for future research.

Multiple toll-like receptors (TLRs) display differential bacterial and ligand specificity in the earthworm, Eisenia andrei

Toll-like receptors (TLRs), an ancient and well-conserved group of pattern recognition receptors (PRRs), recognize conserved pathogen-associated molecular patterns. TLRs consist of three domains: the extracellular N-terminal domain, containing one or more leucine-rich repeats (LRRs), responsible for the recognizing and binding of antigens; the type-I transmembrane domain; and the intracellular domain known as the Toll/Interleukin-1 receptor (TIR) domain required for the downstream signaling pathway. We identified six new full-length complementary DNA (cDNA) sequences, Ean-TLR1/2/3/4/5/6. The deduced amino acid sequences indicate that Ean-TLRs consist of one signal peptide, one LRR N-terminal domain (Ean-TLR4/5), varying numbers of LRRs, one (Ean-TLR1/2/3/4/5) or two (Ean-TLR6) LRR C-terminal domains, one type-I transmembrane domain, and a TIR domain. In addition, a TIR domain alignment revealed that three conserved motifs, designated as Box 1, Box 2, and Box 3, contain essential amino acid residues for downstream signaling activity. Phylogenetic analysis of earthworm TLRs generated two separate evolutionary branches representing single (sccTLR) and multiple (mccTLR) cysteine cluster TLRs. Ean-TLR1/2/3/4 (sccTLR type) and Ean-TLR6 (mccTLR type) were clustered with corresponding types of previously reported earthworm TLRs as well as TLRs from Clitellata and Polychaete. As PRRs, earthworm TLRs should be capable of sensing a diverse range of pathogens. Except for Ean-TLR3, which was not responsive to any bacteria, earthworm TLR expression was significantly induced by Gram-positive but not Gram-negative bacteria. Moreover, it is likely that earthworms can differentiate between different species of Gram-positive bacteria via their TLR responses. The ligand specificity of earthworm TLRs suggests that their pathogenic ligand recognition is likely to be as specific and diverse as the mammalian TLR pathogen-sensing system.

AIF-1 and RNASET2 are involved in the inflammatory response in the Mediterranean mussel Mytilus galloprovincialis following Vibrio infection

Filter-feeding bivalves, such as the Mytilus species, are exposed to different types of bacteria in the surrounding waters, in particular of the Vibrio genus. Mussels lack an adaptive immune system and hemocytes can recognize pathogen-associated molecular patterns (PAMPs) via pattern recognition receptors (PRRs) to activate intracellular signaling pathways to trigger the antimicrobial effectors synthesis. Among the areas of bivalve immunity that deserve study include the role of hemocyte subpopulations. Since little information are available on immune responses at the tissue level to human pathogenic vibrios commonly detected in coastal waters involved in seafood-borne diseases, in this work, immunological parameters of the hemocytes from the Mediterranean mussel M. galloprovincialis were evaluated in response to in vivo challenge with Vibrio splendidus. The histological approach has been first used in order to identify the hemocytes recruitment at the infection site and the morphological change of muscular fibers. In addition, using immunolabeling with specific antibody we detected the production of molecules involved in the inflammatory activated cascade: Toll-like receptors 4 (TLR4), the myeloid differentiation factor 88 (MyD88), the Allograft inflammatory factor-1 (AIF-1) and the ribonucleases RNASET2, belonging to the T2 family, that in vertebrates are involved in the recruitment and activation of macrophages. Our results indicate the activation of TLR4 during bacterial infection preparatory to the recruitment of the MyD88 adapter with a putative role in recognition and intracellular signalling. Furthermore, the data presented in this work suggest that challenging with Gram-negative bacteria causes a massive migration of AIF-1⁺ hemocytes and that the ribonuclease RNASET2 could play a key role in the recruitment of these activated hemocytes. Our approach is useful for further understanding the complex molecular defence mechanisms of the host in invertebrates, especially in relation to the need to develop methods to evaluate the immunological response of bivalve molluscs used in aquaculture.

Antimicrobial Role of RNASET2 Protein During Innate Immune Response in the Medicinal Leech Hirudo verbana

The innate immune response represents a first-line defense against pathogen infection that has been widely conserved throughout evolution. Using the invertebrate Hirudo verbana (Annelida, Hirudinea) as an experimental model, we show here that the RNASET2 ribonuclease is directly involved in the immune response against Gram-positive bacteria. Injection of lipoteichoic acid (LTA), a key component of Gram-positive bacteria cell wall, into the leech body wall induced a massive migration of granulocytes and macrophages expressing TLR2 (the key receptor involved in the response to Gram-positive bacteria) toward the challenged/inoculated area. We hypothesized that the endogenous leech RNASET2 protein (HvRNASET2) might be involved in the antimicrobial response, as already described for other vertebrate ribonucleases, such as RNase3 and RNase7. In support of our hypothesis, HvRNASET2 was mainly localized in the granules of granulocytes, and its release in the extracellular matrix triggered the recruitment of macrophages toward the area stimulated with LTA. The activity of HvRNASET2 was also evaluated on Staphylococcus aureus living cells by means of light, transmission, and scanning electron microscopy analysis. HvRNASET2 injection triggered the formation of S. aureus clumps following a direct interaction with the bacterial cell wall, as demonstrated by immunogold assay. Taken together, our data support the notion that, during the early phase of leech immune response, granulocyte-released HvRNASET2 triggers bacterial clumps formation and, at the same time, actively recruits phagocytic macrophages in order to elicit a rapid and effective eradication of the infecting microorganisms from inoculated area.

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.