Human neuroglial cells internalize Borrelia burgdorferi by coiling phagocytosis mediated by Daam1

PLoS One. 2018 May 10;13(5):e0197413. doi: 10.1371/journal.pone.0197413. eCollection 2018.

Abstract

Borrelia burgdorferi, the agent of Lyme borreliosis, can elude hosts' innate and adaptive immunity as part of the course of infection. The ability of B. burgdorferi to invade or be internalized by host cells in vitro has been proposed as a mechanism for the pathogen to evade immune responses or antimicrobials. We have previously shown that B. burgdorferi can be internalized by human neuroglial cells. In this study we demonstrate that these cells take up B. burgdorferi via coiling phagocytosis mediated by the formin, Daam1, a process similarly described for human macrophages. Following coincubation with glial cells, B. burgdorferi was enwrapped by Daam1-enriched coiling pseudopods. Coiling of B. burgdorferi was significantly reduced when neuroglial cells were pretreated with anti-Daam1 antibody indicating the requirement for Daam1 for borrelial phagocytosis. Confocal microscopy showed Daam1 colocalizing to the B. burgdorferi surface suggesting interaction with borrelial membrane protein(s). Using the yeast 2-hybrid system for identifying protein-protein binding, we found that the B. burgdorferi surface lipoprotein, BBA66, bound the FH2 subunit domain of Daam1. Recombinant proteins were used to validate binding by ELISA, pull-down, and co-immunoprecipitation. Evidence for native Daam1 and BBA66 interaction was suggested by colocalization of the proteins in the course of borrelial capture by the Daam1-enriched pseudopodia. Additionally, we found a striking reduction in coiling for a BBA66-deficient mutant strain compared to BBA66-expressing strains. These results show that coiling phagocytosis is a mechanism for borrelial internalization by neuroglial cells mediated by Daam1.

Publication types

  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • Adaptive Immunity
  • Adaptor Proteins, Signal Transducing / genetics*
  • Borrelia burgdorferi*
  • Brain Neoplasms / metabolism
  • Brain Neoplasms / pathology
  • Cell Line, Tumor
  • Glioma / metabolism
  • Glioma / pathology
  • Humans
  • Immunity, Innate
  • Lipoproteins / chemistry
  • Lyme Disease / immunology*
  • Macrophages / metabolism
  • Microfilament Proteins
  • Neuroglia / metabolism
  • Neuroglia / microbiology
  • Neurons / microbiology*
  • Neutrophils / metabolism*
  • Phagocytosis*
  • Protein Binding
  • Protein Domains
  • Recombinant Proteins / chemistry
  • Two-Hybrid System Techniques
  • rho GTP-Binding Proteins

Substances

  • Adaptor Proteins, Signal Transducing
  • DAAM1 protein, human
  • Lipoproteins
  • Microfilament Proteins
  • Recombinant Proteins
  • rho GTP-Binding Proteins

Grants and funding

Funded by Centers for Disease Control and Prevention US Govt as part of official duties.