NIH Training Grant Fellow: Katherine Harker

Katherine Harker

Katherine Harker is a Ph.D. candidate in the Lodoen Lab in the department of Molecular Biology and Biochemistry at UC Irvine. She began her research career as an undergraduate studying co-infection models of human immunodeficiency virus-1 (HIV-1), human hepatitis C virus (HCV) and human herpesvirus-6 (HHV-6) in human T cells under the direction of Dr. Dennis Revie at California Lutheran University and Dr. S Zaki Salahuddin at the California Institute of Molecular Medicine. Her thesis work in the Lodoen lab is focused on investigating the molecular mechanisms that mediate Toxoplasma gondii interactions with vascular endothelium using human cell microfluidics and intravital two-photon imaging of the blood-brain barrier (BBB) in mice. T. gondii is a highly successful intracellular parasite that infects approximately one-third of the global population. Systemic parasite dissemination is a critical step in disease pathogenesis; however, little is known about the molecular mechanisms required for T. gondii to cross biological barriers, such as the blood-brain barrier, and cause disease. In the circulation T. gondii are found both as extracellular parasites as well as within blood leukocytes. How these extracellular parasites and infected leukocytes interact with vascular endothelium prior to transmigration remains poorly characterized.

To investigate these interactions, she worked in collaboration with the Liu lab in the department of Biomedical Engineering at UC Irvine to develop a microfluidic system combined with time-lapse fluorescence microscopy. Using this approach, she showed that T. gondii infection profoundly altered primary human monocyte adhesion dynamics (J Leukoc Biol 93(5): 789-800, 2013). T. gondii-infected primary human monocytes exhibited altered adhesion dynamics compared with uninfected monocytes: infected cells rolled at significantly higher velocities (2.5-fold) and over greater distances (2.6-fold) than uninfected monocytes, before firmly adhering. As infected monocytes appeared delayed in their transition to firm adhesion, she examined the effects of infection on integrin expression and function. She found that T. gondii infection impaired LFA-1 and VLA-4 clustering and pseudopod extension in response to integrin ligands. This work has established a system for studying pathogen modulation of human leukocyte adhesion, which has since been used by other members of the Lodoen lab to further investigate the molecular basis for the transendothelial migration of T. gondii-infected monocytes (Ueno et al., Cell Microbiol 16(4): 580-595, 2014).

In addition to examining infected leukocytes, she has extended her investigation to extracellular parasite interactions with vascular endothelium. She showed that shear force influenced parasite adhesion and motility dynamics and the outcome of parasite interactions with endothelium (mBio 5(2), doi:10.1128/mBio.01111-13, 2014). Parasites were capable of adhesion to primary human endothelium in shear stress conditions, and interestingly, shear stress enhanced T. gondii helical gliding, resulting in a significantly greater displacement. In addition, shear stress increased the percentage of parasites that invaded or migrated across the endothelium. In an effort to identify parasite adhesins participating in these processes she examined T. gondii deficient in the adhesion protein MIC2 and found that MIC2 contributed to initial adhesion but was not required for adhesion strengthening. These data suggest that in fluidic conditions, T. gondii adhesion to endothelium may be mediated by a multistep cascade of interactions that is governed by unique combinations of adhesion molecules.

Kathy’s current research interests include using intravital, two-photon microscopy of the brain in mice to address how T. gondii crosses the blood-brain barrier in an infected host and to investigate the role of specific parasite adhesins and host cell integrins in these processes. Outside of lab Kathy is an active participant in her local Graduate Women in Science chapter and she enjoys reading, traveling, hiking with her husband and Labrador retriever, and visiting family and friends.  

Awards:

1. NIH NIAID T32 Immunology Research Training Program (5T32 AI 060573), UC Irvine (2013-2014)

2. Graduate Fellow Award, HHMI-UCI Teaching Fellows Program (2013)

3. Best talk award for oral presentation: Toxoplasma gondii modulates the dynamics of human monocyte adhesion to vascular endothelium under fluidic shear stress. 17th Annual Woods Hole Immunoparasitology meeting (2013)

4. UC Irvine Brython-Davis Fellowship (in recognition of outstanding academic achievement) (2013)

5. First place award for oral presentation: Toxoplasma gondii modulates the dynamics of human monocyte adhesion to vascular endothelium under fluidic shear stress. 10th UC Irvine Immunology Fair (2012)

Publications:

Harker KS, Jivian E, McWhorter FY, Liu W, Lodoen MB. (2014). Shear forces enhance Toxoplasma gondii tachyzoite motility on vascular endothelium. mBio, 5(2), e01111–13–e01111–13. doi:10.1128/mBio.01111-13.

Morgado P, Sudarshana D, Gov L, Harker KS, Lam T, Casali P, Lodoen MB. (2014) CD40 induction by Toxoplasma gondii amplifies inflammatory cytokine responses during infection. Infect Immune. In Revision.

Ueno N, Harker KS, Clarke E, McWhorter FY, Liu W, Tenner AJ, Lodoen MB. (2014). Real-time dynamic imaging reveals Mac-1-mediated transmigration of Toxoplasma gondii-infected human monocytes across endothelial barriers. Cell Microbiol. 16(4): 580-595.

Harker KS*, Ueno N*, Wang T, Bonhomme C, Liu W, Lodoen MB. (2013) Toxoplasma gondii modulates the dynamics of human monocyte adhesion to vascular endothelium under fluidic shear stress. J Leukocyte Biol. 93(5): 789-800. *Equal contributors.                                                                                        

Salahuddin SZ, Snyder KA, Godwin A, Grewal R, Prichard JG, Kelley AS, Revie D (2007) The simultaneous presence and expression of human hepatitis C virus (HCV), human herpesvirus-6 (HHV-6), and human immunodeficiency virus-1 (HIV-1) in a single human T-cell. Virol J. 4:106.