Borrelia burgdorferi (Bb), the causative agent of Lyme disease, modulates the physical forces and immunity signaling in endothelial cells (ECs).
Through videomicroscopy of ECs exposed to Bb and transcriptomics, we discovered that Bb does so by concurrently and actively modulating the EC physical forces and innate immune signaling responses in a time-dependent manner, with ECs exhibiting strong biomechanical alterations at early but not late exposure to pathogens. Video credit to Marie Münkel.
How does differential traction force generation of cells based on matrix stiffness impact the competition between bacterially-infected vs surrounder uninfected cells?
Through computational modeling coupled with in vitro experiments we found that increased matrix stiffness promotes infected cell squeezing by enhancing cell displacements and traction stresses of nearby uninfected cells. Video credit to Marie Münkel.
Listeria monocytogenes infection mound at late infection of MDCK epithelial cells.
Orthogonal views of fixed host Madin-Darby Canine Kidney (MDCK) epithelial cells infected with L. monocytogenes at 24 h post-infection. Host nuclei: red, L. monocytogenes: yellow, host vimentin: magenta. Image is center around a 3D infection mound that results due to mechanical competition between uninfected cells surrounding the mound and infected cells pertaining in the extruding mound. Infected cells at the base of the mound show disruption in vimentin cytoskeleton. Top view is 230 x 230 μm.
Listeria monocytogenes infection of human endothelial cells.
Host cell nuclei are in blue, L. monocytogenes is red and F-actin is shown in green. Samples were fixed and imaged through Structured Illumination Microscopy (SIM). Notice the actin comet tails behind the intracellular bacteria.
Scanning electron microscopy images of Listeria monocytogenes adhering onto host endothelial cells
In collaboration with Yi-Ting Yeh, UCSD
Traction force microscopy on MDCK epithelial cells infected with low multiplicity of Listeria monocytogenes
Panels show: phase contrast image; bacterial fluorescence; magnitude of cell-matrix deformations; radial deformations (positive deformations values indicate deformations pointing away from the center of the infection focus); overlay of radial deformations and bacterial fluorescence; and magnitude of cellular traction stresses (color indicates stress magnitude in Pa). Host cells that are adhering onto soft 3 kPa hydrogel.
Time-lapse movie showing orthogonal views of MDCK epithelial cell nuclei originating from an uninfected or Listeria monocytogenes-infected wells over the course of 20 h.
Host cell nuclei are in yellow and L. monocytogenes in black. Acquisition using confocal microscopy started 24 h post-infection. Times post-infection are indicated. One image from each different plane (i.e. x-y, x-z, and y-z) is shown.
Listeria monocytogenes infection of human endothelial cells through infected macrophages.
Time-lapse of phase contrast images showing a L. monocytogenes-infected macrophage transferring bacteria to underlying endothelial hells. Superimposed is the image of the endothelial cell host nuclei in blue. Video taken by Prathima Radhakrishnan.
Mound formation during in silico infection of cells in monolayer.
Simulations showing the stress distribution (MPa) during cell contraction and the resulting mound formation when uninfected cells (beige) protrude (arrows show cell displacements, μm). Infected cells are shown in brown. Four different cases are considered and shown as different panels. Note that only when passive and/or active contractility of infected cells decreases as compared to surrounding uninfected cells, infection mounds emerge.
Single Borrelia burgdorferi spirochetes within a microscope slide.
Time-lapse recording of Borrelia burgdorferi spirochetes constitutively expressing GFP (Bb1286) within a microscope slide. Bacterial cultures were prepared by Ben Ross.
Timelapse movie of endothelial cells (HMEC-1) in monolayer exposed to high dosage of Borrelia burgdorferi.
Time-lapse videomicroscopy of endothelial cells in monolayer (HMEC-1) exposed to high dosage of Borrelia burgdorferi (causative agent of Lyme disease) over the course of 2-day long recording. Panels show: phase contrast image, host cell nuclei (blue), Borrelia burgdorferi fluorescence and overlay of all three channels.
Large Borrelia burgdorferi aggregates ingested by endothelial cells (HMEC-1).
3D confocal microscopy images of fixed samples of endothelial cells in monolayer (HMEC-1) exposed to high dosage of Borrelia burgdorferi for 24 h. Panels show: image of host cell nuclei (blue) superimposed with phalloidin fluorescence to label F-actin (red), Borrelia burgdorferi fluorescence (green), LAMP1 fluorescence to mark lysosomal structures (white) and overlay of the three out of four channels. Note that endothelial cells have internalized these large Borrelia burgdorferi aggregates that colocalize with LAMP1.