Education & Certifications


  • MSc, University Of Oxford, Biomedical Engineering (2014)
  • Diploma, University Of Patras, Physics (2012)

Stanford Advisors


Current Research and Scholarly Interests


Neutrophils are the most abundant circulating leukocytes in humans, comprising the first line of innate immune defense. As neutrophils migrate towards sites of infection and inflammation they encounter a highly heterogeneous environment. Tasked to navigate through microscale obstacles, neutrophils often develop multiple competing fronts, raising the question of how the cell is able to select which front to maintain and which front(s) to abandon. To answer this question, I challenge chemotaxing HL-60 neutrophil-like cells with microfluidic devices containing obstacles and combine quantitative microscopy with sub-cellular optogenetics, statistical learning, and data science.

All Publications


  • Directional reorientation of migrating neutrophils is limited by suppression of receptor input signaling at the cell rear through myosin II activity. Nature communications Hadjitheodorou, A., Bell, G. R., Ellett, F., Shastry, S., Irimia, D., Collins, S. R., Theriot, J. A. 2021; 12 (1): 6619

    Abstract

    To migrate efficiently to target locations, cells must integrate receptor inputs while maintaining polarity: a distinct front that leads and a rear that follows. Here we investigate what is necessary to overwrite pre-existing front-rear polarity in neutrophil-like HL60 cells migrating inside straight microfluidic channels. Using subcellular optogenetic receptor activation, we show that receptor inputs can reorient weakly polarized cells, but the rear of strongly polarized cells is refractory to new inputs. Transient stimulation reveals a multi-step repolarization process, confirming that cell rear sensitivity to receptor input is the primary determinant of large-scale directional reversal. We demonstrate that the RhoA/ROCK/myosin II pathway limits the ability of receptor inputs to signal to Cdc42 and reorient migrating neutrophils. We discover that by tuning the phosphorylation of myosin regulatory light chain we can modulate the activity and localization of myosin II and thus the amenability of the cell rear to 'listen' to receptor inputs and respond to directional reprogramming.

    View details for DOI 10.1038/s41467-021-26622-z

    View details for PubMedID 34785640

  • Quantitative comparison of principal component analysis and unsupervised deep learning using variational autoencoders for shape analysis of motile cells bioRxiv Chan, C. K., Hadjitheodorou, A., Tsai, T. Y., Theriot, J. A. 2020
  • Neutrophil-like HL-60 cells expressing only GFP-tagged β-actin exhibit nearly normal motility. Cytoskeleton (Hoboken, N.J.) Garner, R. M., Skariah, G. n., Hadjitheodorou, A. n., Belliveau, N. M., Savinov, A. n., Footer, M. J., Theriot, J. A. 2020

    Abstract

    Observations of actin dynamics in living cells using fluorescence microscopy have been foundational in the exploration of the mechanisms underlying cell migration. We used CRISPR/Cas9 gene editing to generate neutrophil-like HL-60 cell lines expressing GFP-β-actin from the endogenous locus. In light of many previous reports outlining functional deficiencies of labeled actin, we anticipated that HL-60 cells would only tolerate a monoallelic edit, as biallelic edited cells would produce no normal β-actin. Surprisingly, we recovered viable monoallelic GFP-β-actin cells as well as biallelic edited GFP-β-actin cells, in which one copy of the ACTB gene is silenced and the other contains the GFP tag. Furthermore, the edited cells migrate with similar speeds and persistence as unmodified cells in a variety of motility assays, and have nearly normal cell shapes. These results might partially be explained by our observation that GFP-β-actin incorporates into the F-actin network in biallelic edited cells at similar efficiencies as normal β-actin in unedited cells. Additionally, the edited cells significantly up-regulate γ-actin, perhaps helping to compensate for loss of normal β-actin. Interestingly, biallelic edited cells have only modest changes in global gene expression relative to the monoallelic line, as measured by RNA sequencing. While monoallelic edited cells downregulate expression of the tagged allele and are thus only weakly fluorescent, biallelic edited cells are quite bright and well-suited for live cell microscopy. The non-disruptive phenotype and direct interpretability of this fluorescent tagging approach make it a promising tool for studying actin dynamics in these rapidly migrating and highly phagocytic cells. This article is protected by copyright. All rights reserved.

    View details for DOI 10.1002/cm.21603

    View details for PubMedID 32072765

  • Efficient Front-Rear Coupling in Neutrophil Chemotaxis by Dynamic Myosin II Localization. Developmental cell Tsai, T. Y., Collins, S. R., Chan, C. K., Hadjitheodorou, A. n., Lam, P. Y., Lou, S. S., Yang, H. W., Jorgensen, J. n., Ellett, F. n., Irimia, D. n., Davidson, M. W., Fischer, R. S., Huttenlocher, A. n., Meyer, T. n., Ferrell, J. E., Theriot, J. A. 2019; 49 (2): 189–205.e6

    Abstract

    Efficient chemotaxis requires rapid coordination between different parts of the cell in response to changing directional cues. Here, we investigate the mechanism of front-rear coordination in chemotactic neutrophils. We find that changes in the protrusion rate at the cell front are instantaneously coupled to changes in retraction at the cell rear, while myosin II accumulation at the rear exhibits a reproducible 9-15-s lag. In turning cells, myosin II exhibits dynamic side-to-side relocalization at the cell rear in response to turning of the leading edge and facilitates efficient turning by rapidly re-orienting the rear. These manifestations of front-rear coupling can be explained by a simple quantitative model incorporating reversible actin-myosin interactions with a rearward-flowing actin network. Finally, the system can be tuned by the degree of myosin regulatory light chain (MRLC) phosphorylation, which appears to be set in an optimal range to balance persistence of movement and turning ability.

    View details for PubMedID 31014479

  • Analytical and numerical study of diffusion-controlled drug release from composite spherical matrices MATERIALS SCIENCE & ENGINEERING C-MATERIALS FOR BIOLOGICAL APPLICATIONS Hadjitheodorou, A., Kalosakas, G. 2014; 42: 681-690

    Abstract

    We investigate, both analytically and numerically, diffusion-controlled drug release from composite spherical formulations consisting of an inner core and an outer shell of different drug diffusion coefficients. Theoretically derived analytical results are based on the exact solution of Fick's second law of diffusion for a composite sphere, while numerical data are obtained using Monte Carlo simulations. In both cases, and for the range of matrix parameter values considered in this work, fractional drug release profiles are described accurately by a stretched exponential function. The release kinetics obtained is quantified through a detailed investigation of the dependence of the two stretched exponential release parameters on the device characteristics, namely the geometrical radii of the inner core and outer shell and the corresponding drug diffusion coefficients. Similar behaviors are revealed by both the theoretical results and the numerical simulations, and approximate analytical expressions are presented for the dependencies.

    View details for DOI 10.1016/j.msec.2014.06.009

    View details for Web of Science ID 000340687400086

    View details for PubMedID 25063169

  • Quantifying diffusion-controlled drug release from spherical devices using Monte Carlo simulations MATERIALS SCIENCE & ENGINEERING C-MATERIALS FOR BIOLOGICAL APPLICATIONS Hadjitheodorou, A., Kalosakas, G. 2013; 33 (2): 763-768