Borrelia burgdorferi glycosaminoglycan-binding proteins: a potential target for new therapeutics against Lyme disease

Lyme disease and the pursuit of a clinical cure

Lyme disease, caused by the spirochete Borrelia burgdorferi, is the most common vector-borne illness in the United States. Many aspects of the disease are still topics of controversy within the scientific and medical communities. One particular point of debate is the etiology behind antibiotic treatment failure of a significant portion (10-30%) of Lyme disease patients. The condition in which patients with Lyme disease continue to experience a variety of symptoms months to years after the recommended antibiotic treatment is most recently referred to in the literature as post treatment Lyme disease syndrome (PTLDS) or just simply post treatment Lyme disease (PTLD). The most commonly proposed mechanisms behind treatment failure include host autoimmune responses, long-term sequelae from the initial Borrelia infection, and persistence of the spirochete. The aims of this review will focus on the in vitro, in vivo, and clinical evidence that either validates or challenges these mechanisms, particularly with regard to the role of the immune response in disease and resolution of the infection. Next generation treatments and research into identifying biomarkers to predict treatment responses and outcomes for Lyme disease patients are also discussed. It is essential that definitions and guidelines for Lyme disease evolve with the research to translate diagnostic and therapeutic advances to patient care.

Pharmacology of Heparin and Related Drugs: An Update

Heparin has been used extensively as an antithrombotic and anticoagulant for close to 100 years. This anticoagulant activity is attributed mainly to the pentasaccharide sequence, which potentiates the inhibitory action of antithrombin, a major inhibitor of the coagulation cascade. More recently it has been elucidated that heparin exhibits anti-inflammatory effect via interference of the formation of neutrophil extracellular traps and this may also contribute to heparin's antithrombotic activity. This illustrates that heparin interacts with a broad range of biomolecules, exerting both anticoagulant and nonanticoagulant actions. Since our previous review, there has been an increased interest in these nonanticoagulant effects of heparin, with the beneficial role in patients infected with SARS2-coronavirus a highly topical example. This article provides an update on our previous review with more recent developments and observations made for these novel uses of heparin and an overview of the development status of heparin-based drugs. SIGNIFICANCE STATEMENT: This state-of-the-art review covers recent developments in the use of heparin and heparin-like materials as anticoagulant, now including immunothrombosis observations, and as nonanticoagulant including a role in the treatment of SARS-coronavirus and inflammatory conditions.

VlsE, the nexus for antigenic variation of the Lyme disease spirochete, also mediates early bacterial attachment to the host microvasculature under shear force

Hematogenous dissemination is a critical step in the evolution of local infection to systemic disease. The Lyme disease (LD) spirochete, which efficiently disseminates to multiple tissues, has provided a model for this process, in particular for the key early event of pathogen adhesion to the host vasculature. This occurs under shear force mediated by interactions between bacterial adhesins and mammalian cell-surface proteins or extracellular matrix (ECM). Using real-time intravital imaging of the Lyme spirochete in living mice, we previously identified BBK32 as the first LD spirochetal adhesin demonstrated to mediate early vascular adhesion in a living mouse; however, deletion of bbk32 resulted in loss of only about half of the early interactions, suggesting the existence of at least one other adhesin (adhesin-X) that promotes early vascular interactions. VlsE, a surface lipoprotein, was identified long ago by its capacity to undergo rapid antigenic variation, is upregulated in the mammalian host and required for persistent infection in immunocompetent mice. In immunodeficient mice, VlsE shares functional overlap with OspC, a multi-functional protein that displays dermatan sulfate-binding activity and is required for joint invasion and colonization. In this research, using biochemical and genetic approaches as well as intravital imaging, we have identified VlsE as adhesin-X; it is a dermatan sulfate (DS) adhesin that efficiently promotes transient adhesion to the microvasculature under shear force via its DS binding pocket. Intravenous inoculation of mice with a low-passage infectious B. burgdorferi strain lacking both bbk32 and vlsE almost completely eliminated transient microvascular interactions. Comparative analysis of binding parameters of VlsE, BBK32 and OspC provides a possible explanation why these three DS adhesins display different functionality in terms of their ability to promote early microvascular interactions.

Lipoproteome screening of the Lyme disease agent identifies inhibitors of antibody-mediated complement killing

Spirochetal pathogens, such as the causative agent of Lyme disease, Borrelia burgdorferi sensu lato, encode an abundance of lipoproteins; however, due in part to their evolutionary distance from more well-studied bacteria, such as Proteobacteria and Firmicutes, few spirochetal lipoproteins have assigned functions. Indeed, B. burgdorferi devotes almost 8% of its genome to lipoprotein genes and interacts with its environment primarily through the production of at least 80 surface-exposed lipoproteins throughout its tick vector–vertebrate host lifecycle. Several B. burgdorferi lipoproteins have been shown to serve roles in cellular adherence or immune evasion, but the functions for most B. burgdorferi surface lipoproteins remain unknown. In this study, we developed a B. burgdorferi lipoproteome screening platform utilizing intact spirochetes that enables the identification of previously unrecognized host interactions. As spirochetal survival in the bloodstream is essential for dissemination, we targeted our screen to C1, the first component of the classical (antibody-initiated) complement pathway. We identified two high-affinity C1 interactions by the paralogous lipoproteins, ElpB and ElpQ (also termed ErpB and ErpQ, respectively). Using biochemical, microbiological, and biophysical approaches, we demonstrate that ElpB and ElpQ bind the activated forms of the C1 proteases, C1r and C1s, and represent a distinct mechanistic class of C1 inhibitors that protect the spirochete from antibody-mediated complement killing. In addition to identifying a mode of complement inhibition, our study establishes a lipoproteome screening methodology as a discovery platform for identifying direct host–pathogen interactions that are central to the pathogenesis of spirochetes, such as the Lyme disease agent.

Effect of Invasion of Borrelia burgdorferi in Normal and Neoplastic Mammary Epithelial Cells

Borrelia burgdorferi, the causative agent of Lyme Disease, is known to be able to disseminate and colonize various organs and tissues of its hosts, which is very crucial for its pathogenicity and survival. Recent studies have shown the presence of B. burgdorferi DNA in various breast cancer tissues, in some with poor prognosis, which raises the question about whether B. burgdorferi can interact with mammary epithelial cells and could have any effect on their physiology, including tumorigenic processes. As the model in this study, we have used MCF 10A normal and MDA-MB-231 tumorigenic mammary epithelial cells and infected both cell lines with B. burgdorferi. Our immunofluorescence and confocal microscopy results showed that B. burgdorferi is capable of invading normal epithelial and breast carcinoma cell lines within 24 h; however, the infection rate for the breast carcinoma cell lines was significantly higher. While the infection of epithelial cells with B. burgdorferi did not cause any changes in cell proliferation rates, it showed a significant effect on the invasion and migratory capacity of the breast cancer cells, but not on the normal epithelial cells, as determined by Matrigel invasion and wound healing assays. We have also found that the levels of expression of several epithelial-mesenchymal transition (EMT) markers (fibronectin, vimentin, and Twist1/2) changed, with a significant increase in tissue remodeling marker (MMP-9) in MDA-MB-231 cells demonstrated by quantitative Western blot analyses. This observation further confirmed that B. burgdorferi infection can affect the in vitro migratory and invasive properties of MDA-MB-231 tumorigenic mammary epithelial cells. In summary, our results suggest that B. burgdorferi can invade breast cancer tumor cells and it can increase their tumorigenic phenotype, which urges the need for further studies on whether B. burgdorferi could have any role in breast cancer development.

Conserved lysine residues in decorin binding proteins of Borrelia garinii are critical in adhesion to human brain microvascular endothelial cells

Lyme borreliosis is a tick-borne disease caused by Borrelia burgdorferi sensu lato spirochetes (Lyme borreliae). When the disease affects the central nervous system, it is referred to as neuroborreliosis. In Europe, neuroborreliosis is most often caused by Borrelia garinii. Although it is known that in the host Lyme borreliae spread from the tick bite site to distant tissues via the blood vasculature, the adherence of Lyme borreliae to human brain microvascular endothelial cells has not been studied before. Decorin binding proteins are adhesins expressed on Lyme borreliae. They mediate the adhesion of Lyme borreliae to decorin and biglycan, and the lysine residues located in the binding site of decorin binding proteins are important to the binding activity. In this study, we show that lysine residues located in the canonical binding site can also be found in decorin binding proteins of Borrelia garinii, and that these lysines contribute to biglycan and decorin binding. Most importantly, we show that the lysine residues are crucial for the binding of Lyme borreliae to decorin and biglycan expressing human brain microvascular endothelial cells, which in turn suggests that they are involved in the pathogenesis of neuroborreliosis.

Heparan Sulfate Glycosaminoglycans: (Un)Expected Allies in Cancer Clinical Management

In an era when cancer glycobiology research is exponentially growing, we are witnessing a progressive translation of the major scientific findings to the clinical practice with the overarching aim of improving cancer patients' management. Many mechanistic cell biology studies have demonstrated that heparan sulfate (HS) glycosaminoglycans are key molecules responsible for several molecular and biochemical processes, impacting extracellular matrix properties and cellular functions. HS can interact with a myriad of different ligands, and therefore, hold a pleiotropic role in regulating the activity of important cellular receptors and downstream signalling pathways. The aberrant expression of HS glycan chains in tumours determines main malignant features, such as cancer cell proliferation, angiogenesis, invasion and metastasis. In this review, we devote particular attention to HS biological activities, its expression profile and modulation in cancer. Moreover, we highlight HS clinical potential to improve both diagnosis and prognosis of cancer, either as HS-based biomarkers or as therapeutic targets.

Glycosaminoglycans

Glycosaminoglycans (GAGs) are important constituents of human glycome. They are negatively charged unbranched polysaccharides that are usually covalently attached to proteins, forming glycan-protein conjugates, called proteoglycans. Glycosaminoglycans play critical roles in numerous biological processes throughout individual development and are also involved in the pathological processes of various diseases. Based on their remarkable bioactivities and their universal involvement in disease progression, GAGs are applied as therapeutics or are being targeted or used in treating diseases. In this chapter, we introduce the characteristics of the four classes of GAGs that constitute the glycosaminoglycan family. The pathological roles of glycosaminoglycans in major diseases including innate disease, infectious disease, and cancer are discussed. The application of GAGs and their mimetics as therapeutics is introduced, as well as those therapeutic methods developed based on GAGs' role in pathogenesis. In addition, we provide a brief and overall lookback at the history of GAG research and sort out some critical techniques that facilitated GAG and glycomics studies.

Integrative Transcriptome and Proteome Analyses Provide New Insights Into the Interaction Between Live Borrelia burgdorferi and Frontal Cortex Explants of the Rhesus Brain

Borrelia burgdorferi (Bb), which is neurotropic, can attack the central nervous system (CNS), leading to the development of various neurologic symptoms. The pathogenesis of Lyme neuroborreliosis (LNB) remains poorly understood. Presently, there is a lack of knowledge of the changes in mRNA and proteins in the CNS following early disseminated Lyme disease. Explants from the frontal cortex of 3 rhesus brains were incubated with medium alone or with medium containing live Bb for 6, 12, or 24 hours. Then, we analyzed identified mRNA and proteins in the frontal cortex tissues, allowing for an in-depth view of the transcriptome and proteome for a macroscopic and unbiased understanding of early disseminated Lyme disease in the brain. Through bioinformatics analysis, a complex network of enriched pathways that were mobilized during the progression of Lyme spirochete infection was described. Furthermore, based on the analysis of omics data, translational regulation, glycosaminoglycan/proteoglycan-binding activity in colonization and dissemination to tissues, disease-associated genes, and synaptic function were enriched, which potentially play a role in pathogenesis during the interaction between frontal cortex tissues and spirochetes. These integrated omics results provide unbiased and comprehensive information for the further understanding of the molecular mechanisms of LNB.

The Platelet Fraction Is a Novel Reservoir to Detect Lyme Borrelia in Blood

Simple Summary

To diagnose Lyme disease, a patient’s blood is tested for antibodies that develop as part of the immune response. This can lead to cases being missed or inadequately treated. An ideal test would directly detect the Lyme disease bacteria, Borrelia, to provide better clinical guidance. In this study, we aimed to improve the methods currently used to find Borrelia in human blood, and identified two opportunities for optimization. We demonstrate that the container most commonly used to collect blood (EDTA) decreases Borrelia’s ability to grow, and we identify a superior alternative (citrate). Additionally, using experimentally infected blood, we show that Borrelia is highly concentrated in the platelet fraction, making it an ideal candidate for direct detection. These results lay the foundation for diagnostic test development, which could improve patient outcomes in Lyme disease.

Abstract

Serological diagnosis of Lyme disease suffers from considerable limitations. Yet, the technique cannot currently be replaced by direct detection methods, such as bacterial culture or molecular analysis, due to their inadequate sensitivity. The low bacterial burden in vasculature and lack of consensus around blood-based isolation of the causative pathogen, Borrelia burgdorferi, are central to this challenge. We therefore addressed methodological optimization of Borrelia recovery from blood, first by analyzing existing protocols, and then by using experimentally infected human blood to identify the processing conditions and fractions that increase Borrelia yield. In this proof-of-concept study, we now report two opportunities to improve recovery and detection of Borrelia from clinical samples. To enhance pathogen viability and cultivability during whole blood collection, citrate anticoagulant is superior to more commonly used EDTA. Despite the widespread reliance on serum and plasma as analytes, we found that the platelet fraction of blood concentrates Borrelia, providing an enriched resource for direct pathogen detection by microscopy, laboratory culture, Western blot, and PCR. The potential for platelets to serve as a reservoir for Borrelia and its diagnostic targets may transform direct clinical detection of this pathogen.

Non-anticoagulant Heparin as a Pre-exposure Prophylaxis Prevents Lyme Disease Infection

Lyme disease (LD) is caused by the spirochete Borrelia burgdorferi sensu lato (Bbsl). After transmission to humans by ticks, Bbsl spreads to multiple organs, leading to arthritis, carditis, and neuroborreliosis. No effective prophylaxis against human LD prior to tick exposure is currently available. Thus, a pre-exposure prophylaxis (PrEP) against LD is needed. The establishment of LD bacteria at diverse sites is dictated partly by the binding of Bbsl to proteoglycans (PGs) and glycosaminoglycans (GAGs) in tissues. The drug heparin is structurally similar to these GAGs and inhibits Bbsl attachment to PGs, GAGs, cells, and tissues, suggesting its potential to prevent LD. However, the anticoagulant activity of heparin often results in hemorrhage, hampering the development of this compound as LD PrEP. We have previously synthesized a non-anticoagulant version of heparin (NACH), which was verified for safety in mice and humans. Here, we showed that NACH blocks Bbsl attachment to PGs, GAGs, and mammalian cells. We also found that treating mice with NACH prior to the exposure of ticks carrying Bbsl followed by continuous administration of this compound prevents tissue colonization by Bbsl. Furthermore, NACH-treated mice develop greater levels of IgG and IgM against Bbsl at early stages of infection, suggesting that the upregulation of antibody immune responses may be one of the mechanisms for NACH-mediated LD prevention. This is one of the first studies examining the ability of a heparin-based compound to prevent LD prior to tick exposure. The information presented might also be extended to prevent other infectious diseases agents.

Lyme Disease Frontiers: Reconciling Borrelia Biology and Clinical Conundrums

Lyme disease is a complex tick-borne zoonosis that poses an escalating public health threat in several parts of the world, despite sophisticated healthcare infrastructure and decades of effort to address the problem. Concepts like the true burden of the illness, from incidence rates to longstanding consequences of infection, and optimal case management, also remain shrouded in controversy. At the heart of this multidisciplinary issue are the causative spirochetal pathogens belonging to the Borrelia Lyme complex. Their unusual physiology and versatile lifestyle have challenged microbiologists, and may also hold the key to unlocking mysteries of the disease. The goal of this review is therefore to integrate established and emerging concepts of Borrelia biology and pathogenesis, and position them in the broader context of biomedical research and clinical practice. We begin by considering the conventions around diagnosing and characterizing Lyme disease that have served as a conceptual framework for the discipline. We then explore virulence from the perspective of both host (genetic and environmental predispositions) and pathogen (serotypes, dissemination, and immune modulation), as well as considering antimicrobial strategies (lab methodology, resistance, persistence, and clinical application), and borrelial adaptations of hypothesized medical significance (phenotypic plasticity or pleomorphy).

The role of heparin/heparan sulphate in the IFN-γ-led Arena

IFN-γ (Interferon-gamma) is a pleiotropic cytokine. It is often involved in a variety of physiological processes by binding to the cell surface transmembrane receptor (IFN-γR) to initiate a series of signalling pathways that transmit external signals from cell surface receptors to the cell nucleus. Heparan sulphate (HS), a highly sulphated linear polysaccharide, is ubiquitous on the mammalian cell surface and extracellular matrix. Electrostatic interactions can be generated between the highly sulphated HS region and specific basic amino acid residues in the IFN-γ structure, thereby detaining IFN-γ on the cell surface, and the concentration of IFN-γ on the cell surface is thus, changed. IFN-γ retained on the cell surface will optimize the binding of IFN-γ to the transmembrane receptor resulting in high efficiency signalling. Heparin is a glycosaminoglycan with a structure similar to HS. The structural similarity provides a basis for modelling exogenous heparin dependence for interference with IFN-γ function. This model can be summarized as follows: First, the competitive binding effect; heparin bound to cytokines by competing with membrane-associated HS, causes a decrease in cytokine concentration on the cell surface. Second, the principle of priority occupancy; heparin can occupy the receptor binding site on cytokines, partially preventing the IFN-γ-IFN-γR interaction. These two models interfere with IFN-γ signal transmission. To decipher the mechanism by which heparin influences IFN-γ activity, studies of the structure-activity relationship are in progress. This paper summarizes research progress on the IFN-γ signalling pathway, heparin interference with IFN-γ activity and the structure-activity relationship between heparin and IFN-γ.

Galactosaminoglycans: Medical Applications and Drawbacks

Galactosaminoglycans (GalAGs) are sulfated glycans composed of alternating N-acetylgalactosamine and uronic acid units. Uronic acid epimerization, sulfation patterns and fucosylation are modifications observed on these molecules. GalAGs have been extensively studied and exploited because of their multiple biomedical functions. Chondroitin sulfates (CSs), the main representative family of GalAGs, have been used in alternative therapy of joint pain/inflammation and osteoarthritis. The relatively novel fucosylated chondroitin sulfate (FCS), commonly found in sea cucumbers, has been screened in multiple systems in addition to its widely studied anticoagulant action. Biomedical properties of GalAGs are directly dependent on the sugar composition, presence or lack of fucose branches, as well as sulfation patterns. Although research interest in GalAGs has increased considerably over the three last decades, perhaps motivated by the parallel progress of glycomics, serious questions concerning the effectiveness and potential side effects of GalAGs have recently been raised. Doubts have centered particularly on the beneficial functions of CS-based therapeutic supplements and the potential harmful effects of FCS as similarly observed for oversulfated chondroitin sulfate, as a contaminant of heparin. Unexpected components were also detected in CS-based pharmaceutical preparations. This review therefore aims to offer a discussion on (1) the current and potential therapeutic applications of GalAGs, including those of unique features extracted from marine sources, and (2) the potential drawbacks of this class of molecules when applied to medicine.

Outer surface protein polymorphisms linked to host-spirochete association in Lyme borreliae

Lyme borreliosis is caused by multiple species of the spirochete bacteria Borrelia burgdorferi sensu lato. The spirochetes are transmitted by ticks to vertebrate hosts, including small- and medium-sized mammals, birds, reptiles, and humans. Strain-to-strain variation in host-specific infectivity has been documented, but the molecular basis that drives this differentiation is still unclear. Spirochetes possess the ability to evade host immune responses and colonize host tissues to establish infection in vertebrate hosts. In turn, hosts have developed distinct levels of immune responses when invaded by different species/strains of Lyme borreliae. Similarly, the ability of Lyme borreliae to colonize host tissues varies among different spirochete species/strains. One potential mechanism that drives this strain-to-strain variation of immune evasion and colonization is the polymorphic outer surface proteins produced by Lyme borreliae. In this review, we summarize research on strain-to-strain variation in host competence and discuss the evidence that supports the role of spirochete-produced protein polymorphisms in driving this variation in host specialization. Such information will provide greater insights into the adaptive mechanisms driving host and Lyme borreliae association, which will lead to the development of interventions to block pathogen spread and eventually reduce Lyme borreliosis health burden.

Sequencing the Dermatan Sulfate Chain of Decorin

Glycomics represents one of the last frontiers and most challenging in omic analysis. Glycosylation occurs in the endoplasmic reticulum and the Golgi organelle and its control is neither well-understood nor predictable based on proteomic or genomic analysis. One of the most structurally complex classes of glycoconjugates is the proteoglycans (PGs) and their glycosaminoglycan (GAG) side chains. Previously, our laboratory solved the structure of the chondroitin sulfate chain of the bikunin PG. The current study examines the much more complex structure of the dermatan sulfate GAG chain of decorin PG. By utilizing sophisticated separation methods followed by compositional analysis, domain mapping, and tandem mass spectrometry coupled with analysis by a modified genetic algorithm approach, the structural motif for the decorin dermatan sulfate chain was determined. This represents the second example of a GAG with a prominent structural motif, suggesting that the structural variability of this class of glycoconjugates is somewhat simpler than had been expected.