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

Abstract

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.

Choreography of Lyme Disease Spirochete Adhesins To Promote Vascular Escape

“…In addition, extrapolation of our results in the knee joint microvasculature to other dissemination sites requires experimental testing due to the existence of organotypic vasculature ( 49 ), which may impose a requirement for different pathogen proteins for extravasation at different sites. Nonetheless, our model is the only experimental system in which to study the mechanistic properties of spirochete transmigration during animal infection and has resulted in unique insights into the tissue colonization process by B. burgdorferi ( 11 – 14 , 16 , 21 , 31 , 46 , 48 ), including the demonstration of a role for the adhesins P66 and OspC in vascular transmigration and the discovery that distinct stages of the extravasation process could be temporally separated.…”

“…The steps at which five B. burgdorferi adhesins function are shown. The adhesins BBK32 ( 13 , 14 , 57 , 58 ) and VlsE ( 21 ) contain potent adhesive properties that mediate early interactions between the vascular endothelium and B. burgdorferi spirochetes. Subsequently, three adhesins whose functional absence blocks vascular escape (P66 [ 30 ], DbpA/B [see Fig.…”

“…To generate the fluorescent B31 5A4 dbpA/B KO strain (GCB4032), we transformed GCB4433 with 55 μg of DNA from the previously described pTM61 kan , gfp ( 12 , 21 ). Transformants were selected as kanamycin resistant and screened for GFP fluorescence and for the presence of the kan cassette with oligonucleotides B70 and B71 ( 55 ).…”

“…Adhesins are multifunctional proteins and are a touchpoint for interaction of B. burgdorferi with the host, potentially promoting binding to various accessible host components such as the extracellular matrix (ECM), as well as inducing signaling in host cells ( 1 , 17 – 20 ). Our earlier studies have shown a role for the fibronectin and glycosaminoglycan (GAG) binding adhesin BBK32 ( 13 , 14 ) and the dermatan sulfate binding adhesin VlsE in early vascular interactions ( 21 ). In this work, we focus on the role in vascular transmigration of three important B. burgdorferi adhesins, P66, outer surface protein C (OspC), and decorin binding proteins A and B (DbpA/B).…”

Pathogenicity and virulence of Borrelia burgdorferi

“…BBK32 and P66 borrelial proteins are key players mediating the stabilizing interactions and the adhesion to the cells lining the vascular lumen [ 103 , 224 , 225 ]. Recently, it was suggested that VlsE also promotes transient binding to the vasculature under flow via binding to dermatan sulphate and that a complex temporal choreography of P66, DbpA/B and OspC is required for the escape process from postcapillary venules [ 226 , 227 ]. Blood circulation is not the only mechanical stress that B. burgdorferi needs to overcome in order to infect the target tissues.…”