Reactive Center Loop (RCL) Peptides Derived from Serpins Display Independent Coagulation and Immune Modulating Activities

Proteomics of Bacterial and Mouse Extracellular Vesicles Released in the Gastrointestinal Tracts of Nutrient-Stressed Animals Reveals an Interplay Between Microbial Serine Proteases and Mammalian Serine Protease Inhibitors

Bacterial extracellular vesicles (BEVs) produced by members of the intestinal microbiota can not only contribute to digestion but also mediate microbe-host cell communication via the transfer of functional biomolecules to mammalian host cells. An unresolved question is which host factors and conditions influence BEV cargo and how they impact host cell function. To address this question, we analysed and compared the proteomes of BEVs released by the major human gastrointestinal tract (GIT) symbiont Bacteroides thetaiotaomicron (Bt) in vivo in fed versus fasted animals using nano-liquid chromatography with tandem mass spectrometry (LC-MSMS). Among the proteins whose abundance was negatively affected by fasting, nine of ten proteins of the serine protease family, including the regulatory protein dipeptidyl peptidase-4 (DPP-4), were significantly decreased in BEVs produced in the GITs of fasted animals. Strikingly, in extracellular vesicles produced by the intestinal epithelia of the same fasted mice, the proteins with the most increased abundance were serine protease inhibitors (serpins). Together, these findings suggest a dynamic interaction between GI bacteria and the host. Additionally, they indicate a regulatory role for the host in determining the balance between bacterial serine proteases and host serpins exported in bacterial and host extracellular vesicles.

Proteolytic signatures of coagulation identified by plasma peptidomics

BACKGROUND

Coagulation entails sequential proteolytic events in plasma, ultimately leading to fibrin clot formation.

OBJECTIVES

In this study, we employed a mass spectrometry-based peptidomics approach to characterize the molecular events of coagulation-induced limited proteolysis.

METHODS

Citrated plasma from healthy donors was in vitro-coagulated by recalcification combined with the addition of tissue factor (TF) in the absence or presence of hirudin. The formation of endogenous peptide products over time was monitored using a mass spectrometry approach with a de novo algorithm for peptide identification.

RESULTS

Plasma coagulation resulted in a distinct peptidome enriched with activation peptides of prothrombin and FXIIIA, fibrinopeptides A and B, reactive center loops of protease inhibitors, the bait region of α2-macroglobulin, and additional proteolytic hotspots outside the coagulation system. While thrombin inhibition blocked almost all TF-initiated limited proteolysis, most events were TF concentration-independent, with the exception of prothrombin, fibrinogen, FV, FXIIIA, α2-macroglobulin, protein C inhibitor, complement C3, and plexin domain-containing 2. The order of events of fibrinopeptide A and B formation-prothrombin conversion, FXIIIA activation, and protease inhibitor proteolysis-followed the kinetics of thrombin generation.

CONCLUSION

Plasma peptidomics of coagulation-initiated limited proteolysis captures peptide products derived from pro- and anticoagulant events and proteolytic signatures beyond the classical coagulation system. We envision that this peptidomics strategy enables the assessment of functional aspects of coagulation in bleeding and thrombotic disorders at the molecular level.

The role of coagulome in the tumor immune microenvironment

The rising incidence and persistent thrombosis in multiple cancers including those that are immunosuppressive highlight the need for understanding the tumor coagulome system and its role beyond hemostatic complications. Immunotherapy has shown significant benefits in solid organ tumors but has been disappointing in the treatment of hypercoagulable cancers, such as glioblastoma and pancreatic ductal adenocarcinomas. Thus, targeting thrombosis to prevent immunosuppression seems a clinically viable approach in cancer treatment. Hypercoagulable tumors often develop fibrin clots within the tumor microenvironment (TME) that dictates the biophysical characteristics of the tumor tissue. The application of systems biology and single-cell approaches highlight the potential role of coagulome or thrombocytosis in shaping the tumor immune microenvironment (TIME). In-depth knowledge of the tumor coagulome would provide unprecedented opportunities to better predict the hemostatic complications, explore how thrombotic stroma modulates tumor immunity, reexamine the significance of clinical biomarkers, and enable steering the stromal versus systemic immune response for boosting the effectiveness of immune checkpoint inhibitors in cancer treatment. We focus on the role of coagulation factors in priming a suppressive TIME and the huge potential of existing anticoagulant drugs in the clinical settings of cancer immunotherapy.

Review on Extraction, Modification, and Synthesis of Natural Peptides and Their Beneficial Effects on Skin

Peptides, functional nutrients with a size between those of large proteins and small amino acids, are easily absorbed by the human body. Therefore, they are seeing increasing use in clinical medicine and have revealed immunomodulatory and anti-inflammatory properties which could make them effective in healing skin wounds. This review sorted and summarized the relevant literature about peptides during the past decade. Recent works on the extraction, modification and synthesis of peptides were reviewed. Importantly, the unique beneficial effects of peptides on the skin were extensively explored, providing ideas for the development and innovation of peptides and laying a knowledge foundation for the clinical application of peptides.

Pathogen-derived peptides in drug targeting and its therapeutic approach

Peptides, short stretches of amino acids or small proteins that occupy a strategic position between proteins and amino acids, are readily accessible by chemical and biological methods. With ideal properties for forming high-affinity and specific interactions with host target proteins, they have established an important niche in the drug development spectrum complementing small molecule and biological therapeutics. Among the most successful biomedicines in use today, peptide-based drugs show great promise. This, coupled with recent advances in synthetic and nanochemical biology, has led to the creation of tailor-made peptide therapeutics for improved biocompatibility. This review presents an overview of the latest research on pathogen-derived, host-cell-interacting peptides. It also highlights strategies for using peptide-based therapeutics that address cellular transport challenges through the introduction of nanoparticles that serve as platforms to facilitate the delivery of peptide biologics and therapeutics for treating various inflammatory diseases. Finally, this paper describes future perspectives, specific pathogen-based peptides that can enhance specificity, efficiency, and capacity in functional peptide-based therapeutics, which are in the spotlight as new treatment alternatives for various diseases, and also presents verified sequences and targets that can increase chemical and pharmacological value.

Tissue Specific Dual RNA-Seq Defines Host-Parasite Interplay in Murine Visceral Leishmaniasis Caused by Leishmania donovani and Leishmania infantum

Visceral leishmaniasis is associated with hepato-splenomegaly and altered immune and hematological parameters in both preclinical animal models and humans. We studied mouse experimental visceral leishmaniasis caused by Leishmania infantum and Leishmania donovani in BALB/c mice using dual RNA-seq to investigate the transcriptional response of host and parasite in liver and spleen. We identified only 4 species-specific parasite expressed genes (SSPEGs; log2FC >1, FDR <0.05) in the infected spleen, and none in the infected liver. For the host transcriptome, we found 789 differentially expressed genes (DEGs; log2FC >1, FDR <0.05) in the spleen that were common to both infections, with IFNγ signaling and complement and coagulation cascade pathways highly enriched, and an additional 286 and 186 DEGs that were selective to L. donovani and L. infantum infection, respectively. Among those, there were network interactions between genes of amino acid metabolism and PPAR signaling in L. donovani infection and increased IL1β and positive regulation of fatty acid transport in L. infantum infection, although no pathway enrichment was observed. In the liver, there were 1,939 DEGs in mice infected with either L. infantum or L. donovani in comparison to uninfected mice, and the most enriched pathways were IFNγ signaling, neutrophil mediated immunity, complement and coagulation, cytokine-chemokine responses, and hemostasis. Additionally, 221 DEGs were selective in L. donovani and 429 DEGs in L. infantum infections. These data show that the host response for these two visceral leishmaniasis infection models is broadly similar, and ∼10% of host DEGs vary in infections with either parasite species. IMPORTANCE Visceral leishmaniasis (VL) is caused by two species of Leishmania parasites, L. donovani in the Old World and L. infantum in the New World and countries bordering the Mediterranean. Although cardinal features such as hepato-splenomegaly and alterations in blood and immune function are evident, clinical presentation may vary by geography, with for example severe bleeding often associated with VL in Brazil. Although animal models of both L. donovani and L. infantum have been widely used to study disease pathogenesis, a direct side-by-side comparison of how these parasites species impact the infected host and/or how they might respond to the stresses of mammalian infection has not been previously reported. Identifying common and distinct pathways to pathogenesis will be important to ensure that new therapeutic or prophylactic approaches will be applicable across all forms of VL.

Neuroserpin: structure, function, physiology and pathology

Neuroserpin is a serine protease inhibitor identified in a search for proteins implicated in neuronal axon growth and synapse formation. Since its discovery over 30 years ago, it has been the focus of active research. Many efforts have concentrated in elucidating its neuroprotective role in brain ischemic lesions, the structural bases of neuroserpin conformational change and the effects of neuroserpin polymers that underlie the neurodegenerative disease FENIB (familial encephalopathy with neuroserpin inclusion bodies), but the investigation of the physiological roles of neuroserpin has increased over the last years. In this review, we present an updated and critical revision of the current literature dealing with neuroserpin, covering all aspects of research including the expression and physiological roles of neuroserpin, both inside and outside the nervous system; its inhibitory and non-inhibitory mechanisms of action; the molecular structure of the monomeric and polymeric conformations of neuroserpin, including a detailed description of the polymerisation mechanism; and the involvement of neuroserpin in human disease, with particular emphasis on FENIB. Finally, we briefly discuss the identification by genome-wide screening of novel neuroserpin variants and their possible pathogenicity.

Therapeutic SERPINs: Improving on Nature

Serine proteases drive important physiological processes such as coagulation, fibrinolysis, inflammation and angiogenesis. These proteases are controlled by serine protease inhibitors (SERPINs) that neutralize their activity. Currently, over 1,500 SERPINs are known in nature, but only 37 SERPINs are found in humans. Thirty of these are functional protease inhibitors. The inhibitory potential of SERPINs is in perfect balance with the proteolytic activities of its targets to enable physiological protease activity. Hence, SERPIN deficiency (either qualitative or quantitative) can lead to disease. Several SERPIN resupplementation strategies have been developed to treat SERPIN deficiencies, including concentrates derived from plasma and recombinant SERPINs. SERPINs usually inhibit multiple proteases, but only in their active state. Over the past decades, considerable insights have been acquired in the identification of SERPIN biological functions, their inhibitory mechanisms and specificity determinants. This paves the way for the development of therapeutic SERPINs. Through rational design, the inhibitory properties (selectivity and inhibitory potential) of SERPINs can be reformed and optimized. This review explores the current state of SERPIN engineering with a focus on reactive center loop modifications and backbone stabilization. We will discuss the lessons learned from these recombinant SERPINs and explore novel techniques and strategies that will be essential for the creation and application of the future generation of therapeutic SERPINs.

Viruses for Landscape-Scale Therapy: Biological Control of Rabbits in Australia

Viral diseases, whether of animals or humans, are normally considered as problems to be managed. However, in Australia, two viruses have been used as landscape-scale therapeutics to control European rabbits (Oryctolagus cuniculus), the preeminent invasive vertebrate pest species. Rabbits have caused major environmental and agricultural losses and contributed to extinction of native species. It was not until the introduction of Myxoma virus that effective control of this pest was obtained at a continental scale. Subsequent coevolution of rabbit and virus saw a gradual reduction in the effectiveness of biological control that was partially ameliorated by the introduction of the European rabbit flea to act as an additional vector for the virus. In 1995, a completely different virus, Rabbit hemorrhagic disease virus (RHDV), escaped from testing and spread through the Australian rabbit population and again significantly reduced rabbit numbers and environmental impacts. The evolutionary pressures on this virus appear to be producing quite different outcomes to those that occurred with myxoma virus and the emergence and invasion of a novel genotype of RHDV in 2014 have further augmented control. Molecular studies on myxoma virus have demonstrated multiple proteins that manipulate the host innate and adaptive immune response; however the molecular basis of virus attenuation and reversion to virulence are not yet understood.

Fibrinolytic Serine Proteases, Therapeutic Serpins and Inflammation: Fire Dancers and Firestorms

The making and breaking of clots orchestrated by the thrombotic and thrombolytic serine protease cascades are critical determinants of morbidity and mortality during infection and with vascular or tissue injury. Both the clot forming (thrombotic) and the clot dissolving (thrombolytic or fibrinolytic) cascades are composed of a highly sensitive and complex relationship of sequentially activated serine proteases and their regulatory inhibitors in the circulating blood. The proteases and inhibitors interact continuously throughout all branches of the cardiovascular system in the human body, representing one of the most abundant groups of proteins in the blood. There is an intricate interaction of the coagulation cascades with endothelial cell surface receptors lining the vascular tree, circulating immune cells, platelets and connective tissue encasing the arterial layers. Beyond their role in control of bleeding and clotting, the thrombotic and thrombolytic cascades initiate immune cell responses, representing a front line, "off-the-shelf" system for inducing inflammatory responses. These hemostatic pathways are one of the first response systems after injury with the fibrinolytic cascade being one of the earliest to evolve in primordial immune responses. An equally important contributor and parallel ancient component of these thrombotic and thrombolytic serine protease cascades are the serine protease inhibitors, termed serpins. Serpins are metastable suicide inhibitors with ubiquitous roles in coagulation and fibrinolysis as well as multiple central regulatory pathways throughout the body. Serpins are now known to also modulate the immune response, either via control of thrombotic and thrombolytic cascades or via direct effects on cellular phenotypes, among many other functions. Here we review the co-evolution of the thrombolytic cascade and the immune response in disease and in treatment. We will focus on the relevance of these recent advances in the context of the ongoing COVID-19 pandemic. SARS-CoV-2 is a "respiratory" coronavirus that causes extensive cardiovascular pathogenesis, with microthrombi throughout the vascular tree, resulting in severe and potentially fatal coagulopathies.

A Novel Mouse Monoclonal Antibody C42 against C-Terminal Peptide of Alpha-1-Antitrypsin

The C-terminal-fragments of alpha1-antitrypsin (AAT) have been identified and their diverse biological roles have been reported in vitro and in vivo. These findings prompted us to develop a monoclonal antibody that specifically recognizes C-36 peptide (corresponding to residues 359–394) resulting from the protease-associated cleavage of AAT. The C-36-targeting mouse monoclonal Immunoglobulin M (IgM) antibody (containing κ light chains, clone C42) was generated and enzyme-linked immunosorbent assay (ELISA)-tested by Davids Biotechnologie GmbH, Germany. Here, we addressed the effectiveness of the novel C42 antibody in different immunoassay formats, such as dot- and Western blotting, confocal laser microscopy, and flow cytometry. According to the dot-blot results, our novel C42 antibody detects the C-36 peptide at a range of 0.1–0.05 µg and shows no cross-reactivity with native, polymerized, or oxidized forms of full-length AAT, the AAT-elastase complex mixture, as well as with shorter C-terminal fragments of AAT. However, the C42 antibody does not detect denatured peptide in SDS-PAGE/Western blotting assays. On the other hand, our C42 antibody, unconjugated as well as conjugated to DyLight488 fluorophore, when applied for immunofluorescence microscopy and flow cytometry assays, specifically detected the C-36 peptide in human blood cells. Altogether, we demonstrate that our novel C42 antibody successfully recognizes the C-36 peptide of AAT in a number of immunoassays and has potential to become an important tool in AAT-related studies.

Dutomycin Induces Autophagy and Apoptosis by Targeting the Serine Protease Inhibitor SERPINB6

Autophagy plays an important role in maintaining tumor cell progression and survival in response to metabolic stress. Thus, the regulation of autophagy can be used as a strategy for anticancer therapy. Here, we report dutomycin (DTM) as a novel autophagy enhancer that eventually induces apoptosis due to excessive autophagy. Also, human serine protease inhibitor B6 (SERPINB6) was identified as a target protein of DTM, and its novel function which is involved in autophagy was studied for the first time. We show that DTM directly binds SERPINB6 and then activates intracellular serine proteases, resulting in autophagy induction. Inhibitory effects of DTM on the function of SERPINB6 were confirmed through enzyme- and cell-based approaches, and SERPINB6 was validated as a target protein using siRNA-mediated knockdown and an overexpression test. In a zebrafish xenograft model, DTM showed a significant decrease in tumor area. Furthermore, the present findings will be expected to contribute to the expansion of novel basic knowledge about the correlation of cancer and autophagy by promoting active further research on SERPINB6, which was not previously considered the subject of cancer biology.

Deriving Immune-Modulating Peptides from Viral Serine Protease Inhibitors (Serpins)

Viruses have devised highly effective approaches that modulate the host immune response, blocking immune responses that are designed to eradicate viral infections. Over millions of years of evolution, virus-derived immune-modulating proteins have become extraordinarily potent, in some cases working at picomolar concentrations when expressed into surrounding tissues and effectively blocking host defenses against viral invasion and replication. The marked efficiency of these immune-modulating proteins is postulated to be due to viral engineering of host immune modulators as well as design and development of new strategies (i.e., some derived from host proteins and some entirely unique). Two key characteristics of viral immune modulators confer both adaptive advantages and desirable functions for therapeutic translation. First, many virus-derived immune modulators have evolved structures that are not readily recognized or regulated by mammalian immune pathways, ensuring little to no neutralizing antibody responses or proteasome-mediated degradation. Second, these immune modulators tend to target early steps in central immune responses, producing a powerful downstream inhibitory "domino effect" which may alter cell activation and gene expression.We have proposed that peptide metabolites of these immune-modulating proteins can enhance and extend protein function. Active immunomodulating peptides have been derived from both mammalian and viral proteins. We previously demonstrated that peptides derived from computationally predicted cleavage sites in the reactive center loop (RCL) of a viral serine proteinase inhibitor (serpin ) from myxoma virus, Serp-1 , can modify immune response activation. We have also demonstrated modulation of host gut microbiota produced by Serp-1 and RCL-derived peptide , S7, in a vascular inflammation model. Of interest, generation of derived peptides that maintain therapeutic function from a serpin can act by a different mechanism. Whereas Serp-1 has canonical serpin-like function to inhibit serine proteases, S7 instead targets mammalian serpins. Here we describe the derivation of active Serp- RCL peptides and their testing in inflammatory vasculitis models.

Recombinant Myxoma Virus-Derived Immune Modulator M-T7 Accelerates Cutaneous Wound Healing and Improves Tissue Remodeling

Complex dermal wounds represent major medical and financial burdens, especially in the context of comorbidities such as diabetes, infection and advanced age. New approaches to accelerate and improve, or "fine tune" the healing process, so as to improve the quality of cutaneous wound healing and management, are the focus of intense investigation. Here, we investigate the topical application of a recombinant immune modulating protein which inhibits the interactions of chemokines with glycosaminoglycans, reducing damaging or excess inflammation responses in a splinted full-thickness excisional wound model in mice. M-T7 is a 37 kDa-secreted, virus-derived glycoprotein that has demonstrated therapeutic efficacy in numerous animal models of inflammatory immunopathology. Topical treatment with recombinant M-T7 significantly accelerated wound healing when compared to saline treatment alone. Healed wounds exhibited properties of improved tissue remodeling, as determined by collagen maturation. M-T7 treatment accelerated the rate of peri-wound angiogenesis in the healing wounds with increased levels of TNF, VEGF and CD31. The immune cell response after M-T7 treatment was associated with a retention of CCL2 levels, and increased abundances of arginase-1-expressing M2 macrophages and CD4 T cells. Thus, topical treatment with recombinant M-T7 promotes a pro-resolution environment in healing wounds, and has potential as a novel treatment approach for cutaneous tissue repair.

Repertoire of Structure-Activity-Based Novel Modified Peptides Elicits Enhanced Osteogenic Potential

Biologically active peptides in milk proteins can be used as effective dietary supplements for management of bone-associated issues including osteoporosis. A bioactive peptide derived from milk, viz. VLPVPQK/PepC, has been validated previously from our lab for its osteoanabolic action. In this study, we report 14 novel variants of PepC, designed in silico, based on the structure-activity relationship, aiming to enhance its osteogenic effect that holds tremendous therapeutic utility for bone-related injuries. PepC was computationally modified at seven positions of its original sequence, resulting in 14 modified synthetic peptides for functional predictions and in vitro assessment by comparative analysis of modified peptides by PepC for improved ability in osteogenic functional assays (proliferation potential, antioxidant ability, gene and protein expression, cytotoxic effect, bone mineralization) using calvarial osteoblasts. For most peptides with the highest Peptide7 response relative to PepC (p < 0.05), enhanced osteoanabolic response was observed. Further observations on Peptide7 have therefore been investigated in depth (qPCR, immunoblotting, LCMS/MS, and PCA analysis). Peptide7 displayed a rise in the expression of osteogenes (Osterix, Opg, Bmp2, and Runx2, p < 0.05) and protein (Runx2 and Bmp2, p < 0.05). Besides, LCMS/MS findings suggest Peptide7 escapes intestinal peptidases degradation. Experimental evidence supports an improved osteological reaction to newly modified peptides and hence exploitation in the preparation of functional foods or supplements.

Peptides based on the reactive center loop of Manduca sexta serpin-3 block its protease inhibitory function

One innate immune response in insects is the proteolytic activation of hemolymph prophenoloxidase (proPO), regulated by protease inhibitors called serpins. In the inhibition reaction of serpins, a protease cleaves a peptide bond in a solvent-exposed reactive center loop (RCL) of the serpin, and the serpin undergoes a conformational change, incorporating the amino-terminal segment of the RCL into serpin β-sheet A as a new strand. This results in an irreversible inhibitory complex of the serpin with the protease. We synthesized four peptides with sequences from the hinge region in the RCL of Manduca sexta serpin-3 and found they were able to block serpin-3 inhibitory activity, resulting in suppression of inhibitory protease-serpin complex formation. An RCL-derived peptide with the sequence Ser-Val-Ala-Phe-Ser (SVAFS) displayed robust blocking activity against serpin-3. Addition of acetyl-SVAFS-amide to hemolymph led to unregulated proPO activation. Serpin-3 associated with Ac-SVAFS-COO⁻ had an altered circular dichroism spectrum and enhanced thermal resistance to change in secondary structure, indicating that these two molecules formed a binary complex, most likely by insertion of the peptide into β-sheet A. The interference of RCL-derived peptides with serpin activity may lead to new possibilities of “silencing” arthropod serpins with unknown functions for investigation of their physiological roles.

Local Serpin Treatment via Chitosan-Collagen Hydrogel after Spinal Cord Injury Reduces Tissue Damage and Improves Neurologic Function

Spinal cord injury (SCI) results in massive secondary damage characterized by a prolonged inflammation with phagocytic macrophage invasion and tissue destruction. In prior work, sustained subdural infusion of anti-inflammatory compounds reduced neurological deficits and reduced pro-inflammatory cell invasion at the site of injury leading to improved outcomes. We hypothesized that implantation of a hydrogel loaded with an immune modulating biologic drug, Serp-1, for sustained delivery after crush-induced SCI would have an effective anti-inflammatory and neuroprotective effect. Rats with dorsal column SCI crush injury, implanted with physical chitosan-collagen hydrogels (CCH) had severe granulomatous infiltration at the site of the dorsal column injury, which accumulated excess edema at 28 days post-surgery. More pronounced neuroprotective changes were observed with high dose (100 µg/50 µL) Serp-1 CCH implanted rats, but not with low dose (10 µg/50 µL) Serp-1 CCH. Rats treated with Serp-1 CCH implants also had improved motor function up to 20 days with recovery of neurological deficits attributed to inhibition of inflammation-associated tissue damage. In contrast, prolonged low dose Serp-1 infusion with chitosan did not improve recovery. Intralesional implantation of hydrogel for sustained delivery of the Serp-1 immune modulating biologic offers a neuroprotective treatment of acute SCI.

Deriving Immune Modulating Drugs from Viruses-A New Class of Biologics

Viruses are widely used as a platform for the production of therapeutics. Vaccines containing live, dead and components of viruses, gene therapy vectors and oncolytic viruses are key examples of clinically-approved therapeutic uses for viruses. Despite this, the use of virus-derived proteins as natural sources for immune modulators remains in the early stages of development. Viruses have evolved complex, highly effective approaches for immune evasion. Originally developed for protection against host immune responses, viral immune-modulating proteins are extraordinarily potent, often functioning at picomolar concentrations. These complex viral intracellular parasites have "performed the R&D", developing highly effective immune evasive strategies over millions of years. These proteins provide a new and natural source for immune-modulating therapeutics, similar in many ways to penicillin being developed from mold or streptokinase from bacteria. Virus-derived serine proteinase inhibitors (serpins), chemokine modulating proteins, complement control, inflammasome inhibition, growth factors (e.g., viral vascular endothelial growth factor) and cytokine mimics (e.g., viral interleukin 10) and/or inhibitors (e.g., tumor necrosis factor) have now been identified that target central immunological response pathways. We review here current development of virus-derived immune-modulating biologics with efficacy demonstrated in pre-clinical or clinical studies, focusing on pox and herpesviruses-derived immune-modulating therapeutics.

Immune protection is dependent on the gut microbiome in a lethal mouse gammaherpesviral infection

Immunopathogenesis in systemic viral infections can induce a septic state with leaky capillary syndrome, disseminated coagulopathy, and high mortality with limited treatment options. Murine gammaherpesvirus-68 (MHV-68) intraperitoneal infection is a gammaherpesvirus model for producing severe vasculitis, colitis and lethal hemorrhagic pneumonia in interferon gamma receptor-deficient (IFNγR-/-) mice. In prior work, treatment with myxomavirus-derived Serp-1 or a derivative peptide S-7 (G305TTASSDTAITLIPR319) induced immune protection, reduced disease severity and improved survival after MHV-68 infection. Here, we investigate the gut bacterial microbiome in MHV-68 infection. Antibiotic suppression markedly accelerated MHV-68 pathology causing pulmonary consolidation and hemorrhage, increased mortality and specific modification of gut microbiota. Serp-1 and S-7 reduced pulmonary pathology and detectable MHV-68 with increased CD3 and CD8 cells. Treatment efficacy was lost after antibiotic treatments with associated specific changes in the gut bacterial microbiota. In summary, transkingdom host-virus-microbiome interactions in gammaherpesvirus infection influences gammaherpesviral infection severity and reduces immune modulating therapeutic efficacy.

Enterococcus faecalis exploits the human fibrinolytic system to drive excess collagenolysis: implications in gut healing and identification of druggable targets

Perforations, anastomotic leak, and subsequent intra-abdominal sepsis are among the most common and feared complications of invasive interventions in the colon and remaining intestinal tract. During physiological healing, tissue protease activity is finely orchestrated to maintain the strength and integrity of the submucosa collagen layer in the wound. We (Shogan, BD et al. Sci Trans Med 7: 286ra68, 2015.) have previously demonstrated in both mice and humans that the commensal microbe Enterococcus faecalis selectively colonizes wounded colonic tissues and disrupts the healing process by amplifying collagenolytic matrix-metalloprotease activity toward excessive degradation. Here, we demonstrate for the first time, to our knowledge, a novel collagenolytic virulence mechanism by which E. faecalis is able to bind and locally activate the human fibrinolytic protease plasminogen (PLG), a protein present in high concentrations in healing colonic tissue. E. faecalis-mediated PLG activation leads to supraphysiological collagen degradation; in this study, we demonstrate this concept both in vitro and in vivo. This pathoadaptive response can be mitigated with the PLG inhibitor tranexamic acid (TXA) in a fashion that prevents clinically significant complications in validated murine models of both E. faecalis- and Pseudomonas aeruginosa-mediated colonic perforation. TXA has a proven clinical safety record and is Food and Drug Administration approved for topical application in invasive procedures, albeit for the prevention of bleeding rather than infection. As such, the novel pharmacological effect described in this study may be translatable to clinical trials for the prevention of infectious complications in colonic healing.NEW & NOTEWORTHY This paper presents a novel mechanism for virulence in a commensal gut microbe that exploits the human fibrinolytic system and its principle protease, plasminogen. This mechanism is targetable by safe and effective nonantibiotic small molecules for the prevention of infectious complications in the healing gut.

Prevention of Anastomotic Leak Via Local Application of Tranexamic Acid to Target Bacterial-mediated Plasminogen Activation: A Practical Solution to a Complex Problem

OBJECTIVE

To investigate the role of bacterial- mediated plasminogen (PLG) activation in the pathogenesis of anastomotic leak (AL) and its mitigation by tranexamic acid (TXA).

BACKGROUND

AL is the most feared complication of colorectal resections. The pathobiology of AL in the setting of a technically optimal procedure involves excessive submucosal collagen degradation by resident microbes. We hypothesized that activation of the host PLG system by pathogens is a central and targetable pathway in AL.

METHODS

We employed kinetic analysis of binding and activation of human PLG by microbes known to cause AL, and collagen degradation assays to test the impact of PLG on bacterial collagenolysis. Further, we measured the ability of the antifibrinolytic drug TXA to inhibit this process. Finally, using mouse models of pathogen-induced AL, we locally applied TXA via enema and measured its ability to prevent a clinically relevant AL.

RESULTS

PLG is deposited rapidly and specifically at the site of colorectal anastomoses. TXA inhibited PLG activation and downstream collagenolysis by pathogens known to have a causal role in AL. TXA enema reduced collagenolytic bacteria counts and PLG deposition at anastomotic sites. Postoperative PLG inhibition with TXA enema prevented clinically and pathologically apparent pathogen-mediated AL in mice.

CONCLUSIONS

Bacterial activation of host PLG is central to collagenolysis and pathogen-mediated AL. TXA inhibits this process both in vitro and in vivo. TXA enema represents a promising method to prevent AL in high-risk sites such as the colorectal anastomoses.

The immunosuppressive functions of two novel tick serpins, HlSerpin-a and HlSerpin-b, from Haemaphysalis longicornis

Serpins are evolutionarily conserved serine protease inhibitors that are widely distributed in animals, plants and microbes. In this study, we reported the cloning and functional characterizations of two novel serpin genes, HlSerpin-a and HlSerpin-b, from the hard tick Haemaphysalis longicornis of China. Recombinant HlSerpin-a and HlSerpin-b displayed protease inhibitory activities against multiple mammalian proteases. Similar to other tick serpins, HlSerpin-a and HlSerpin-b suppressed the expression of inflammatory cytokines such as TNF-α, interleukin (IL)-6 and IL-1β from lipopolysaccharide-stimulated mouse bone-marrow-derived macrophages (BMDMs) or mouse bone-marrow-derived dendritic cells (BMDCs). The minimum active region (reaction centre loop) of HlSerpin-a, named SA-RCL, showed similar biological activities as HlSerpin-a in the protease inhibition and immune suppression assays. The immunosuppressive activities of full-length HlSerpin-a and SA-RCL are impaired in Cathepsin G or Cathepsin B knockout mouse macrophages, suggesting that the immunomodulation functions of SA and SA-RCL are dependent on their protease inhibitory activity. Finally, we showed that both full-length HlSerpins and SA-RCL can relieve the joint swelling and inflammatory response in collagen-induced mouse arthritis models. These results suggested that HlSerpin-a and HlSerpin-b are two functional arthropod serpins, and the minimal reactive peptide SA-RCL is a potential candidate for drug development against inflammatory diseases.

Serp-2, a virus-derived apoptosis and inflammasome inhibitor, attenuates liver ischemia-reperfusion injury in mice

BACKGROUND

Ischemia-reperfusion injury (IRI) is an antigen-independent, innate immune response to arterial occlusion and ischemia with subsequent paradoxical exacerbation after reperfusion. IRI remains a critical problem after vessel occlusion and infarction or during harvest and surgery in transplants. After transplant, liver IRI (LIRI) contributes to increased acute and chronic rejection and graft loss. Tissue loss during LIRI has been attributed to local macrophage activation and invasion with excessive inflammation together with hepatocyte apoptosis and necrosis. Inflammatory and apoptotic signaling are key targets for reducing post-ischemic liver injury.Myxomavirus is a rabbit-specific leporipoxvirus that encodes a suite of immune suppressing proteins, often with extensive function in other mammalian species. Serp-2 is a cross-class serine protease inhibitor (serpin) which inhibits the inflammasome effector protease caspase-1 as well as the apoptotic proteases granzyme B and caspases 8 and 10. In prior work, Serp-2 reduced inflammatory cell invasion after angioplasty injury and after aortic transplantation in rodents. In this report, we explore the potential for therapeutic treatment with Serp-2 in a mouse model of LIRI.

METHODS

Wildtype (C57BL/6 J) mice were subjected to warm, partial (70%) hepatic ischemia for 90 min followed by treatment with saline or Serp-2 or M-T7, 100 ng/g/day given by intraperitoneal injection on alternate days for 5 days. M-T7 is a Myxomavirus-derived inhibitor of chemokine-GAG interactions and was used in this study for comparative analysis of an unrelated viral protein with an alternative immunomodulating mechanism of action. Survival, serum ALT levels and histopathology were assessed 24 h and 10 days post-LIRI.

RESULTS

Serp-2 treatment significantly improved survival to 85.7% percent versus saline-treated wildtype mice (p = 0.0135), while M-T7 treatment did not significantly improve survival (p = 0.2584). Liver viability was preserved by Serp-2 treatment with a significant reduction in serum ALT levels (p = 0.0343) and infarct scar thickness (p = 0.0016), but with no significant improvement with M-T7 treatment. Suzuki scoring by pathologists blinded with respect to treatment group indicated that Serp-2 significantly reduced hepatocyte necrosis (p = 0.0057) and improved overall pathology score (p = 0.0046) compared to saline. Immunohistochemistry revealed that Serp-2 treatment reduced macrophage infiltration into the infarcted liver tissue (p = 0.0197).

CONCLUSIONS

Treatment with Serp-2, a virus-derived inflammasome and apoptotic pathway inhibitor, improves survival after liver ischemia-reperfusion injury in mouse models. Treatment with a cross-class immune modulator provides a promising new approach designed to reduce ischemia-reperfusion injury, improving survival and reducing chronic transplant damage.

Modulation of Host Immunity by Helminths: The Expanding Repertoire of Parasite Effector Molecules

Helminths are extraordinarily successful parasites due to their ability to modulate the host immune response. They have evolved a spectrum of immunomodulatory molecules that are now beginning to be defined, heralding a molecular revolution in parasite immunology. These discoveries have the potential both to transform our understanding of parasite adaptation to the host and to develop possible therapies for immune-mediated disease. In this review we will summarize the current state of the art in parasite immunomodulation and discuss perspectives on future areas for research and discovery.

Methods for Determining and Understanding Serpin Structure and Function: X-Ray Crystallography

Deciphering the X-ray crystal structures of serine protease inhibitors (serpins) and serpin complexes has been an integral part of understanding serpin function and inhibitory mechanisms. In addition, high-resolution structural information of serpins derived from the three domains of life (bacteria, archaea, and eukaryotic) and viruses has provided valuable insights into the hereditary and evolutionary history of this unique superfamily of proteins. This chapter will provide an overview of the predominant biophysical method that has yielded this information, X-ray crystallography. In addition, details of up-and-coming methods, such as neutron crystallography, cryo-electron microscopy, and small- and wide-angle solution scattering, and their potential applications to serpin structural biology will be briefly discussed. As serpins remain important both biologically and medicinally, the information provided in this chapter will aid in future experiments to expand our knowledge of this family of proteins.

Serpin functions in host-pathogen interactions

Serpins are a broadly distributed superfamily of protease inhibitors that are present in all kingdoms of life. The acronym, serpin, is derived from their function as potent serine proteases inhibitors. Early studies of serpins focused on their functions in haemostasis since modulating serine proteases activities are essential for coagulation. Additional research has revealed that serpins function in infection and inflammation, by modulating serine and cysteine proteases activities. The aim of this review is to summarize the accumulating findings and current understanding of the functions of serpins in host-pathogen interactions, serving as host defense proteins as well as pathogenic factors. We also discuss the potential crosstalk between host and pathogen serpins. We anticipate that future research will elucidate the therapeutic value of this novel target.

Crystal Structure of Cleaved Serp-1, a Myxomavirus-Derived Immune Modulating Serpin: Structural Design of Serpin Reactive Center Loop Peptides with Improved Therapeutic Function

The Myxomavirus-derived protein Serp-1 has potent anti-inflammatory activity in models of vasculitis, lupus, viral sepsis, and transplant. Serp-1 has also been tested successfully in a Phase IIa clinical trial in unstable angina, representing a "first-in-class" therapeutic. Recently, peptides derived from the reactive center loop (RCL) have been developed as stand-alone therapeutics for reducing vasculitis and improving survival in MHV68-infected mice. However, both Serp-1 and the RCL peptides lose activity in MHV68-infected mice after antibiotic suppression of intestinal microbiota. Here, we utilize a structure-guided approach to design and test a series of next-generation RCL peptides with improved therapeutic potential that is not reduced when the peptides are combined with antibiotic treatments. The crystal structure of cleaved Serp-1 was determined to 2.5 Å resolution and reveals a classical serpin structure with potential for serpin-derived RCL peptides to bind and inhibit mammalian serpins, plasminogen activator inhibitor 1 (PAI-1), anti-thrombin III (ATIII), and α-1 antitrypsin (A1AT), and target proteases. Using in silico modeling of the Serp-1 RCL peptide, S-7, we designed several modified RCL peptides that were predicted to have stronger interactions with human serpins because of the larger number of stabilizing hydrogen bonds. Two of these peptides (MPS7-8 and -9) displayed extended activity, improving survival where activity was previously lost in antibiotic-treated MHV68-infected mice (P < 0.0001). Mass spectrometry and kinetic assays suggest interaction of the peptides with ATIII, A1AT, and target proteases in mouse and human plasma. In summary, we present the next step toward the development of a promising new class of anti-inflammatory serpin-based therapeutics.

Serpins: Development for Therapeutic Applications

Serine protease inhibitors, or serpins, function as central regulators for many vital processes in the mammalian body, maintaining homeostasis for clot formation and breakdown, immune responses, lung function, and hormone or central nervous system activity, among many others. When serine protease activity or serpin-mediated regulation becomes unbalanced or dysfunctional, then severe disease states and pathogenesis can ensue. With serpinopathies, genetic mutations lead to inactive serpins or protein aggregation with loss of function. With other disorders, such as sepsis, atherosclerosis, cancer, obesity, and the metabolic syndrome, the thrombotic and thrombolytic cascades and/or inflammatory responses become unbalanced, with excess bleeding and clotting and upregulation of adverse immune responses. Returning overall balance can be engineered through introduction of a beneficial serpin replacement as a therapeutic or through blockade of serpins that are detrimental. Several drugs have been developed and are currently in use and/or in development both to replace dysfunctional serpins and to block adverse effects induced by aberrant protease or serpin actions.With this chapter, we provide a general overview of the development of a virus-derived serpin, Serp-1, and serpin reactive center loop (RCL) peptides, as therapeutics. Serp-1 is a virus-derived serpin developed as a new class of immune modulator. We will use the development of Serp-1 as a general introduction to serpin-based drug development.

Analysis of In Vivo Serpin Functions in Models of Inflammatory Vascular Disease

Serpins have a wide range of functions in regulation of serine proteases in the thrombotic cascade and in immune responses, representing up to 2-10% of circulating proteins in the blood. Selected serpins also have cross-class inhibitory actions for cysteine proteases in inflammasome and apoptosis pathways. The arterial and venous systems transport blood throughout the mammalian body representing a central site for interactions between coagulation proteases and circulating blood cells (immune cells) and target tissues, a very extensive and complex interaction. While analysis of serpin functions in vitro in kinetics or gel shift assays or in tissue culture provides very necessary information on molecular mechanisms, the penultimate assessment of biological or physiological functions and efficacy for serpins as therapeutics requires study in vivo in whole animal models (some also consider cell culture to be an in vivo approach).Mouse models of arterial transplant with immune rejection as well as models of inflammatory vasculitis induced by infection have been used to study the interplay between the coagulation and immune response pathways. We describe here three in vivo vasculitis models that are used to study the roles of serpins in disease and as therapeutics. The models described include (1) mouse aortic allograft transplantation, (2) human temporal artery (TA) xenograft into immunodeficient mouse aorta, and (3) mouse herpes virus (MHV68)-induced inflammatory vasculitis in interferon-gamma receptor (IFNγR) knockout mice.

Viral Serpin Reactive Center Loop (RCL) Peptides: Design and Testing

Serpins function as a trap for serine proteases, presenting the reactive center loop (RCL) as a target for individual proteases. When the protease cleaves the RCL, the serpin and protease become covalently linked leading to a loss of function of both the protease and the serpin; this suicide inhibition is often referred to as a "mouse trap." When the RCL P1-P1' scissile bond is cut by the protease, the resulting bond between the protease and the RCL leads to insertion of the cleaved RCL into the β-sheet A and relocation of the protease to the opposite pole of the serpin, forming a suicide complex. Only a relatively small part of the serpin molecule can be removed in deletion mutations before the serpin RCL inhibitory function is lost. Serpin RCL peptides have been developed to block formation of serpin aggregates in serpinopathies, genetic serpin mutations wherein the abnormal serpins insert their RCL into adjacent serpins forming aggregates of inactive serpins.We have further posited that this natural cleavage site in the serpin RCL may form active serpin metabolites with potential to add to the serpin's inhibitory functions. We have developed RCL peptides based upon predicted serpin RCL cleavage (or metabolism) sites and tested these serpins for inhibitory function. In this chapter we describe the development of RCL-derived peptides, peptides derived based upon the RCL sequences of two myxomaviral serpins. Methods used to develop peptides are described for RCL-derived peptides from Serp-1, a thrombotic and thrombolytic serine protease inhibitor, and Serp-2, a cross class serine and cysteine protease inhibitor (Subheadings 2.1 and 3.1). Approaches to testing RCL peptide functions, in vitro by molecular assays and in vivo in models of cell migration, MHV-68 infection, and aortic allograft transplant are described (Subheadings 2.2 and 3.2).

Plasminogen Activator Inhibitor Type-1 as a Regulator of Fibrosis

Fibrosis is known as a frequent and irreversible pathological condition which is associated with organ failure. Tissue fibrosis is a central process in a variety of chronic progressive diseases such as diabetes, hypertension, and persistent inflammation. This state could contribute to chronic injury and the initiation of tissue repair. Fibrotic disorders represent abnormal wound healing with defective matrix turnover and clearance that lead to excessive accumulation of extracellular matrix components. A variety of identified growth factors, cytokines, and persistently activated myofibroblasts have critical roles in the pathogenesis of fibrosis. Irrespective of etiology, the transforming growth factor-β pathway is the major driver of fibrotic response. Plasminogen activator inhibitor-1 (PAI-1) is a crucial downstream target of this pathway. Transforming growth factor-β positively regulates PAI-1 gene expression via two main pathways including Smad-mediated canonical and non-canonical pathways. Overexpression of PAI-1 reduces extracellular matrix degradation via perturbing the plasminogen activation system. Indeed, elevated PAI-1 levels inhibit proteolytic activity of tissue plasminogen activator and urokinase plasminogen activator which could contribute to a variety of inflammatory elements in the injury site and to excessive matrix deposition. This review summarizes the current knowledge of critical pathways that regulate PAI-1 gene expression and suggests effective approaches for the treatment of fibrotic disease. J. Cell. Biochem. 119: 17-27, 2018. © 2017 Wiley Periodicals, Inc.

Physiological and pathological functions of neuroserpin: Regulation of cellular responses through multiple mechanisms

It is 27 years since neuroserpin was first discovered in the nervous system and identified as a member of the serpin superfamily. Since that time potential roles for this serine protease inhibitor have been identified in neuronal and non-neuronal systems. Many are linked to inhibition of neuroserpin's principal enzyme target, tissue plasminogen activator (tPA), although some have been suggested to involve alternate non-inhibitory mechanisms. This review focuses mainly on the inhibitory roles of neuroserpin and discusses the evidence supporting tPA as the physiological target. While the major sites of neuroserpin expression are neural, endocrine and immune tissues, most progress on characterizing functional roles for neuroserpin have been in the brain. Roles in emotional behaviour, synaptic plasticity and neuroprotection in stroke and excitotoxicity models are discussed. Current knowledge on three neurological diseases associated with neuroserpin mutation or activity, Familial Encephalopathy with Neuroserpin Inclusion Bodies (FENIB), Alzheimer's disease and brain metastasis is presented. Finally, we consider mechanistic studies that have revealed a distinct inhibitory mechanism for neuroserpin and its possible implications for neuroserpin function.

Identification of novel peptide motifs in the serpin maspin that affect vascular smooth muscle cell function

Maspin is a non-inhibitory member of the serpin family that affects cell behaviours related to migration and survival. We have previously shown that peptides of the isolated G α-helix (G-helix) domain of maspin show bioactivity. Migration, invasion, adhesion and proliferation of vascular smooth muscle cells (VSMC) are important processes that contribute to the build-up of atherosclerotic plaques. Here we report the use of functional assays of these behaviours to investigate whether other maspin-derived peptides impact directly on VSMC; focusing on potential anti-atherogenic properties. We designed 18 new peptides from the structural moieties of maspin above ten amino acid residues in length and considered them beside the existing G-helix peptides. Of the novel peptides screened those with the sequences of maspin strand 4 and 5 of beta sheet B (S4B and S5B) reduced VSMC migration, invasion and proliferation, as well as increasing cell adhesion. A longer peptide combining these consecutive sequences showed a potentiation of responses, and a 7-mer contained all essential elements for functionality. This is the first time that these parts of maspin have been highlighted as having key roles affecting cell function. We present evidence for a mechanism whereby S4B and S5B act through ERK1/2 and AMP-activated protein kinase (AMPK) to influence VSMC responses.