Intestinal proteases of free-living and parasitic astigmatid mites

Scabies

Scabies is one of the most common and highest-burden skin diseases globally. Estimates suggest that >200 million people worldwide have scabies at any one time, with an annual prevalence of 455 million people, with children in impoverished and overcrowded settings being the most affected. Scabies infection is highly contagious and leads to considerable morbidity. Secondary bacterial infections are common and can cause severe health complications, including sepsis or necrotizing soft-tissue infection, renal damage and rheumatic heart disease. There is no vaccine or preventive treatment against scabies and, for the past 30 years, only few broad-spectrum antiparasitic drugs (mainly topical permethrin and oral ivermectin) have been widely available. Treatment failure is common because drugs have short half-lives and do not kill all developmental stages of the scabies parasite. At least two consecutive treatments are needed, which is difficult to achieve in resource-poor and itinerant populations. Another key issue is the lack of a practical, rapid, cheap and accurate diagnostic tool for the timely detection of scabies, which could prevent the cycle of exacerbation and disease persistence in communities. Scabies control will require a multifaceted approach, aided by improved diagnostics and surveillance, new treatments, and increased public awareness.

Cloning, sequencing, expression, and purification of aspartic proteases isolated from two human Demodex species

Aspartic proteases (ASPs) are important hydrolases for parasitic invasion of host tissues or cells. This was the first study on Demodex ASP. First, the complete coding sequence (CDS) was amplified, cloned and sequenced. Then, the protein physical and chemical properties was analysed. Finally, the recombinant plasmid, expression and purification system was established. Results showed that the lengths of CDS of Demodex folliculorum and D. brevis were 1161 and 1173 bp, respectively. The molecular weight of the protein was approximately 40 KDa. It contained an aspartic acid residue, a substrate-binding site and signal peptide, yet lacked a transmembrane domain and was located in the membrane or extracellular matrix. The phylogenetic and conserved motif analyses showed that D. folliculorum and D. brevis clustered separately and then formed a single branch, which finally clustered with other Acariformes species. The prokaryotic expression systems for recombinant ASP with His-tag (rASP-His) and GST-tag (rASP-GST) were constructed. The inclusion bodies of rASP-His were renaturated by gradient urea and purified using NI beads, while those of rASP-GST were renaturated by sarkosyl and Triton X-100 and purified using GST beads. Conclusively, the prokaryotic expression and purification system of Demodex rASP was successfully established for further pathogenic mechanism research.

Transcriptome Analysis of Host Inflammatory Responses to the Ectoparasitic Mite Sarcoptes scabiei var. hominis

Scabies, a human skin infestation caused by the ectoparasitic mite Sarcoptes scabiei var. hominis, affects more than 200 million people globally. The prevailing knowledge of the disease process and host immune response mechanisms is limited. A better understanding of the host-parasite relationship is essential for the identification of novel vaccine and drug targets. Here we aimed to interrogate the transcriptomic profiles of mite-infested human skin biopsies with clinical manifestations of ordinary scabies subjects ("OS"; n = 05) and subjects naive to scabies ("control"; n = 03) using RNASeq data analysis. A combined clustering, network, and pathway mapping approach enabled us to identify key signaling events in the host immune and pro-inflammatory responses to S. scabiei infestation. The clustering patterns showed various differentially expressed genes including inflammatory responses and innate immunity genes (DEFB4A, IL-19, CXCL8, CSF3, SERPINB4, S100A7A, HRNR) and notably upregulation of the JAK-STAT pathway in scabies-infested samples. Mite-infested human skin biopsies (GSE178563) were compared with an ex-vivo porcine infested model (E-MTAB-6433) and human skin equivalents (GSE48459). Marked enrichment of immune response pathways (JAK-STAT signaling, IL-4 and IL-13 pathway, and Toll receptor cascade), chemokine ligands and receptors (CCL17, CCL18, CCL3L1, CCL3L3, CCR7), and cytokines (IL-13 and IL-20) were observed. Additionally, genes known for their role in psoriasis and atopic dermatitis were upregulated, e.g., IL-19. The detailed transcriptomic profile has provided an insight into molecular functions, biological processes, and immunological responses and increased our understanding about transcriptomic regulation of scabies in human.

Scabies itch: an update on neuroimmune interactions and novel targets

Frequently described as 'the worst itch' one can ever experience scabies itch is the hallmark of Sarcoptes scabiei mite infestation. Notably, the itchiness often persists for weeks despite scabicides therapy. The mechanism of scabies itch is not yet fully understood, and effective treatment modalities are still missing which can severely affect the quality of life. The aim of this review is to provide an overview of the scope of itch in scabies and highlight candidate mechanisms underlying this itch. We herein discuss scabies itch, with a focus on the nature, candidate underlying mechanisms and treatment options. We also synthesize this information with current understanding of the mechanisms contributing to non-histaminergic itch in other conditions. Itch is a major problem in scabies and can lead to grave consequences. We provide the latest insights on host-mite interaction, secondary microbial infection and neural sensitization with special emphasis on keratinocytes and mast cells to better understand the mechanism of itch in scabies. Also, the most relevant current modalities remaining under investigation that possess promising perspectives for scabies itch (i.e. protease-activated receptor-2 (PAR-2) inhibitor, Mas-related G protein-coupled receptor X2 (MRGPRX2) antagonist) are discussed. Greater understanding of these diverse mechanisms may provide a rational basis for the development of improved and targeted approaches to control itch in individuals with scabies.

Proteases and pseudoproteases in parasitic arthropods of clinical importance

Parasitic arthropods feed on blood or skin tissue and share comparable repertoires of proteases involved in haematophagy, digestion, egg development and immunity. While proteolytically active proteases of multiple classes dominate, an increasing number of pseudoproteases have been discovered that have no proteolytic function but are pharmacologically active biomolecules, evolved to carry out alternative functions as regulatory, antihaemostatic, anti-inflammatory or immunomodulatory compounds. In this review, we provide an overview of proteases and pseudoproteases from clinically important arthropod parasites. Many of these act in central biological pathways of parasite survival and host-parasite interaction and may be potential targets for therapeutic interventions.

The gut epithelium from feeding to fasting in the predatory soil mite Pergamasus longicornis (Mesostigmata: Parasitidae): one tissue, two roles

A review of acarine gut physiology based on published narratives dispersed over the historical international literature is given. Then, in an experimental study of the free-living predatory soil mite Pergamasus longicornis (Berlese), quantitative micro-anatomical changes in the gut epithelium are critically assessed from a temporal series of histological sections during and after feeding on larval dipteran prey. An argued functional synthesis based upon comparative kinetics is offered for verification in other mesostigmatids. Mid- and hind-gut epithelia cell types interconvert in a rational way dependent upon the physical consequences of ingestion, absorption and egestion. The fasted transitional pseudo-stratified epithelium rapidly becomes first squamous on prey ingestion (by stretching), then columnar during digestion before confirmed partial disintegration (gut 'lumenation') during egestion back to a pseudo-stratified state. Exponential processes within the mid- and endodermic hind-gut exhibit 'stiff' dynamics. Cells expand rapidly ([Formula: see text] 22.9-49.5 min) and vacuolate quickly ([Formula: see text] 1.1 h). Cells shrink very slowly ([Formula: see text] 4.9 days) and devacuolate gently ([Formula: see text] 1.0-1.7 days). Egestive cellular degeneration has an initial [Formula: see text] 7.7 h. Digestion appears to be triggered by maximum gut expansion-estimated at 10 min post start of feeding. Synchrony with changes in gut lumen contents suggests common changes in physiological function over time for the cells as a whole tightly-coupled epithelium. Distinct in architecture as a tissue over time the various constituent cell types appear functionally the same. Functional phases are: early fluid transportation (0-1 h) and extracellular activity (10-90 min); through rising food absorption (10 min to [Formula: see text] day); to slow intracellular meal processing and degenerative egestive waste material production (1 to [Formula: see text] days) much as in ticks. The same epithelium is both absorptive and degenerative in role. The switch in predominant physiology begins 4 h after the start of feeding. Two separate pulses of clavate cells appear to be a mechanism to facilitate transport by increasing epithelial surface area in contact with the lumen. Free-floating cells may augment early extracellular lumenal digestion. Possible evidence for salivary enzyme alkaline-related extra-corporeal digestion was found. Giant mycetome-like cells were found embedded in the mid-gut wall. Anteriorly, the mid-gut behaves like a temporally expendable food processing tissue and minor long-term resistive store. Posteriorly the mid-gut behaves like a major assimilative/catabolic tissue and 'last-out' food depot (i.e., a 'hepatopancreas' function) allowing the mite to resist starvation for up to 3.5 weeks after a single meal. A 'conveyor-belt' wave of physiology (i.e., feeding and digestion, then egestion and excretion) sweeps posteriorly but not necessarily pygidially over time. Assimilation efficiency is estimated at 82%. The total feeding cycle time histologically from a single meal allowing for the bulk of intracellular digestion and egestive release is not 52.5 h but of the order of 6 days ([Formula: see text] total gut emptyings per day), plus typically a further 3 days for subsequent excretion to occur. Final complete gut system clearance in this cryptozooid may take much longer ([Formula: see text] days). A common physiology across the anactinotrichid acarines is proposed. A look to the future of this field is included.

Phylogenetic relationships, stage-specific expression and localisation of a unique family of inactive cysteine proteases in Sarcoptes scabiei

Background

Scabies is worldwide one of the most common, yet neglected, parasitic skin infections, affecting a wide range of mammals including humans. Limited treatment options and evidence of emerging mite resistance against the currently used drugs drive our research to explore new therapeutic candidates. Previously, we discovered a multicopy family of genes encoding cysteine proteases with their catalytic sites inactivated by mutation (SMIPP-Cs). This protein family is unique in parasitic scabies mites and is absent in related non-burrowing mites. We postulated that the SMIPP-Cs have evolved as an adaptation to the parasitic lifestyle of the scabies mite. To formulate testable hypotheses for their functions and to propose possible strategies for translational research we investigated whether the SMIPP-Cs are common to all scabies mite varieties and where within the mite body as well as when throughout the parasitic life-cycle they are expressed.

Results

SMIPP-C sequences from human, pig and dog mites were analysed bioinformatically and the phylogenetic relationships between the SMIPP-C multi-copy gene families of human, pig and dog mites were established. Results suggest that amplification of the SMIPP-C genes occurred in a common ancestor and individual genes evolved independently in the different mite varieties. Recombinant human mite SMIPP-C proteins were produced and used for murine polyclonal antibody production. Immunohistology on skin sections from human patients localised the SMIPP-Cs in the mite gut and in mite faeces within in the epidermal skin burrows. SMIPP-C transcription into mRNA in different life stages was assessed in human and pig mites by reverse transcription followed by droplet digital PCR (ddPCR). High transcription levels of SMIPP-C genes were detected in the adult female life stage in comparison to all other life stages.

Conclusions

The fact that the SMIPP-Cs are unique to three Sarcoptes varieties, present in all burrowing life stages and highly expressed in the digestive system of the infective adult female life stage may highlight an essential role in parasitism. As they are excreted from the gut in scybala they presumably are able to interact or interfere with host proteins present in the epidermis.

Electronic supplementary material

The online version of this article (10.1186/s13071-018-2862-0) contains supplementary material, which is available to authorized users.

Molecular characteristics and serodiagnostic potential of chitinase-like protein from Sarcoptes scabiei

Scabies, caused by the mite Sarcoptes scabiei, is an allergic skin disease that affects millions of people and other mammals worldwide. This highly contagious parasitic disease is among the top 50 epidemic disease and is regarded as a neglected tropical disease. Diagnosis of scabies is difficult in the early stage, and the pathogenesis of scabies is not currently clear. Here, we expressed, identified and located the chitinase-like protein of S. scabiei (SsCLP), and evaluated its potential as an early-stage diagnostic antigen for rabbit scabies. Indirect ELISA using recombinant SsCLP (rSsCLP) exhibited diagnostic sensitivity of 94.4% (17/18) and specificity of 86.7% (26/30). Early diagnostic test after artificial infection of rabbits with S. scabiei for 1 week showed a positive detection rate of 96.7% (29/30). Immunolocalization assays showed that fluorescence signals were localized on the surface of mites and, in infected rabbits, were observed in keratinized skin and embedded mites. Intradermal skin tests of rabbits by injecting rSsCLP showed a wheal, flare and erythema reaction. These results suggest that S. scabiei chitinase-like protein is conducive to host invasion, participates in inducing the allergic response of the host, and is an effective antigen for the diagnosis of S. scabiei.

Structural Characterization of a Eukaryotic Cyanase from Tetranychus urticae

The two-spotted spider mite Tetranychus urticae is a polyphagous agricultural pest and poses a high risk to global crop production as it is rapidly developing pesticide resistance. Genomic and transcriptomic analysis has revealed the presence of a remarkable cyanase gene in T. urticae and related mite species within the Acariformes lineage. Cyanase catalyzes the detoxification of cyanate and is potentially an attractive protein target for the development of new acaricides. Phylogenetic analysis indicates that within the Acariformes, the cyanase gene originates from a single horizontal gene transfer event, which precedes subsequent speciation. Our structural studies presented here compare and contrast prokaryotic cyanases to T. urticae cyanase, which all form homodecamers and have conserved active site residues, but display different surface areas between homodimers in the overall decameric structure.

Gene silencing by RNA interference in Sarcoptes scabiei: a molecular tool to identify novel therapeutic targets

BACKGROUND

Scabies is one of the most common and widespread parasitic skin infections globally, affecting a large range of mammals including humans, yet the molecular biology of Sarcoptes scabiei is astonishingly understudied. Research has been hampered primarily due to the difficulty of sampling or culturing these obligatory parasitic mites. A further and major impediment to identify and functionally analyse potential therapeutic targets from the recently emerging molecular databases is the lack of appropriate molecular tools.

METHODS

We performed standard BLAST based searches of the existing S. scabiei genome databases using sequences of genes described to be involved in RNA interference in Drosophila and the mite model organism Tetranychus urticae. Experimenting with the S. scabiei mu-class glutathione S-transferase (SsGST-mu1) as a candidate gene we explored the feasibility of gene knockdown in S. scabiei by double-stranded RNA-interference (dsRNAi).

RESULTS

We provide here an analysis of the existing S. scabiei draft genomes, confirming the presence of a double stranded RNA (dsRNA) - mediated silencing machinery. We report for the first time experimental gene silencing by RNA interference (RNAi) in S. scabiei. Non-invasive immersion of S. scabiei in dsRNA encoding an S. scabiei glutathione S-transferase mu-class 1 enzyme (SsGST-mu1) resulted in a 35% reduction in the transcription of the target gene compared to controls.

CONCLUSIONS

A series of experiments identified the optimal conditions allowing systemic experimental RNAi without detrimental side effects on mite viability. This technique can now be used to address the key questions on the fundamental aspects of mite biology and pathogenesis, and to assess the potential therapeutic benefits of silencing S. scabiei target genes.

Transcriptome-microRNA analysis of Sarcoptes scabiei and host immune response

Scabies is a parasitic disease, caused by the mite Sarcoptes scabiei, and is considered one of the top 50 epidemic diseases and one the most common human skin disease, worldwide. Allergic dermatitis, including an intense itch, is a common symptom, however diagnosis is difficult and there is currently no effective vaccine. The goal of this study was to examine the immune interaction mechanism of both S. scabiei and infected hosts. mRNA-seq and microRNA-seq were conducted on the S. scabiei mite and on infected and uninfected hosts. We focused on differential expression of unigenes and microRNAs, as well as the real targets of unigenes in enriched immune signaling pathways. S. scabiei enhanced host immune function and decreased metabolism after infection, while the immune response of the host inhibited S. scabiei proliferation and metabolism signaling pathways. Differentially expressed unigenes of S. scabiei were enriched in the JAK-STAT signaling pathway and the Toll-like receptor signaling pathway. The differential expression analysis indicated that microRNAs of S. scabiei and hosts have major roles in regulating immune interactions between parasites and hosts.

Characterization of Sarcoptes scabiei cofilin gene and assessment of recombinant cofilin protein as an antigen in indirect-ELISA for diagnosis

Background

Scabies impairs the health of humans and animals and causes heavy economic losses. Traditional diagnostic methods for scabies are inefficient and ineffective, and so far there is no commercial immunodiagnostic or molecular based test for scabies.

Methods

Here, we used recombinant Sarcoptes scabiei cofilin protein as an antigen to establish indirect ELISA. S. scabiei cofilin is highly homologous to Dermatophagoides farinae Der f 31 allergen (90 % identity). The S. scabiei cofilin gene was cloned and expressed in Escherichia coli to obtain recombinant protein. Western blotting and fluorescence immunohistochemistry were carried out, and we established an indirect ELISA method and detected 33 serum samples from scabies infected rabbits and 30 serum samples from naïve rabbits.

Results

Western blotting demonstrated that S. scabiei cofilin possessed good immunogenicity and fluorescence immunohistochemistry showed the S. scabiei cofilin is widespread in the splanchnic area of mites. In ELISA, a cut-off value of 0.188 was determined to judge experimental positive and negative serum values. Specificity and sensitivity of the ELISA were 87.9 and 83.33 %, respectively.

Conclusions

Recombinant S. scabiei cofilin showed potential value as a diagnostic antigen. The ELISA method established could be used in clinical diagnosis and provide experimental information in minimal or asymptomatic infection.

Parasitic mites of medical and veterinary importance--is there a common research agenda?

There are an estimated 0.5-1 million mite species on earth. Among the many mites that are known to affect humans and animals, only a subset are parasitic but these can cause significant disease. We aim here to provide an overview of the most recent work in this field in order to identify common biological features of these parasites and to inform common strategies for future research. There is a critical need for diagnostic tools to allow for better surveillance and for drugs tailored specifically to the respective parasites. Multi-'omics' approaches represent a logical and timely strategy to identify the appropriate mite molecules. Recent advances in sequencing technology enable us to generate de novo genome sequence data, even from limited DNA resources. Consequently, the field of mite genomics has recently emerged and will now rapidly expand, which is a particular advantage for parasitic mites that cannot be cultured in vitro. Investigations of the microbiota associated with mites will elucidate the link between parasites and pathogens, and define the role of the mite in transmission and pathogenesis. The databases generated will provide the crucial knowledge essential to design novel diagnostic tools, control measures, prophylaxes, drugs and immunotherapies against the mites and associated secondary infections.

An aspartic protease of the scabies mite Sarcoptes scabiei is involved in the digestion of host skin and blood macromolecules

Background

Scabies is a disease of worldwide significance, causing considerable morbidity in both humans and other animals. The scabies mite Sarcoptes scabiei burrows into the skin of its host, obtaining nutrition from host skin and blood. Aspartic proteases mediate a range of diverse and essential physiological functions such as tissue invasion and migration, digestion, moulting and reproduction in a number of parasitic organisms. We investigated whether aspartic proteases may play role in scabies mite digestive processes.

Methodology/Principle Findings

We demonstrated the presence of aspartic protease activity in whole scabies mite extract. We then identified a scabies mite aspartic protease gene sequence and produced recombinant active enzyme. The recombinant scabies mite aspartic protease was capable of digesting human haemoglobin, serum albumin, fibrinogen and fibronectin, but not collagen III or laminin. This is consistent with the location of the scabies mites in the upper epidermis of human skin.

Conclusions/Significance

The development of novel therapeutics for scabies is of increasing importance given the evidence of emerging resistance to current treatments. We have shown that a scabies mite aspartic protease plays a role in the digestion of host skin and serum molecules, raising the possibility that interference with the function of the enzyme may impact on mite survival.

Scabies is an infectious disease of the skin caused by infestation with the parasitic mite Sarcoptes scabiei. It is a disease that has a considerable impact on humans and other animals, including livestock, wildlife and companion animals. Scabies mites burrow into the skin of their host, consuming host skin and blood molecules. Aspartic proteases play a key role in invasion and digestion processes in many parasitic organisms. We have identified a scabies mite aspartic protease and have shown that it is capable of digesting human haemoglobin, serum albumin, fibrinogen and fibronectin in vitro, indicating that it plays a role in mite digestive processes. This raises the possibility that interfering with the function of this digestive enzyme may impact on mite survival.