Living Neural Network Dynamics

• Coupled Biomechanical and Ionic Excitability in Developing Neural Cell Networks

Sylvester Gates, PhD Student, Biology
with Prof. Kan Cao (Brain & Behavior Institute, UMD)

Waves and oscillations play a key role in the flow and processing of information in the brain. Recent work has demonstrated that in addition to electrical activity, biomechanical signaling can also be excitable and thus capable of self-sustaining oscillations and waves. Here we measured the biomechanical dynamics of actin polymerization in neural precursor cells throughout their differentiation into populations of neurons and astrocytes. Fluorescence-based live-cell imaging allowed us to analyze the dynamics of actin in conjunction with the dynamics of calcium signals. Actin dynamics throughout differentiation showed a rhythmic character, localized mostly in processes, with changes in scale associated with differentiation. Furthermore, actin dynamics impact ionic dynamics, with an increase in the frequency of calcium bursts accompanied by a decrease in cell-cell correlations when actin dynamics is inhibited. This impact of cytoskeletal dynamics on cell-cell coupling and ionic neural cell signaling suggests that information flow in the brain may be able to harness both biomechanical and electrical/ionic excitability.

Publications:
Gates S, Alvarez P, Cao K, O’Neill KM, Losert W, bioRxiv 2023

• Collective Information and Communication in Morphologically Distinct Astrocytes

Nick Mennona, PhD Student, Physics
with Dr. Valentina Benfenati (National Research Council of Italy)
with Dr. Grazia Paola Nicchia (University of Bari Aldo Moro)

Collective activity patterns in astrocytic networks are of considerable importance, given the recent finding that astrocytes actively contribute to cognition. This work analyzes collective information capacity and information flow of calcium signals within morphologically distinct in vitro astrocyte networks, building on prior high-resolution studies of Ca2+ dynamics within individual astrocytes. We investigate group Ca2+ dynamics in several astrocytic phenotypes – polygonal, stellate, and reactive – which represent distinct cytoskeletal architectures with differences in cell-cell coupling that may affect information flow within astrocyte networks. All morphologies are present in the brain to varying degrees at different physiological states.

• Large scale collective neural network dynamics

Anna Emenheiser, PhD Student, Biophysics
with Prof. Kan Cao (Brain & Behavior Institute, UMD)

We record the activity of a self-assembled network of thousands of neural cells in one field of view via calcium imaging. Since synapses between neurons and other cell-cell junctions are also mechanical in nature, we also image dynamic changes in one major mechanical element of the cell scaffolding, the actin cytoskeleton using a novel multiscale microscope system. With this biological model and multiscale imaging, we then investigate how the collective calcium and biomechanical activity changes in neural models for neurodegenerative diseases such as Alzheimer’s Disease.

• Astrocytes use dynamic actin waves and reoriented actin filaments to respond to chemophysical cues

Kate O'Neill, Research Scientist and Nick Mennona, PhD Student, Physics
with Dr. Valentina Benfenati (National Research Council of Italy)
with Dr. Grazia Paola Nicchia (University of Bari Aldo Moro)

Astrocytes are the most abundant glial cell and are considered non-excitable brain cells because they do not fire action potentials like neurons. Instead, astrocytes play key roles in regulating various aspects of brain homeostasis, which is essential for proper cognitive function. Our work explores a less traditional aspect of excitability in the form of intracellular actin waves, and we reveal that the homeostatic regulation of the brain by astrocytes may be more active than previously thought. In collaboration with the National Research Council of Italy and the University of Bari Aldo Moro, we use live imaging and novel dynamics analyses to show that astrocytes use actin dynamics near the boundary to sense chemical and mechanical cues. Superresolution imaging also reveals that orientation of actin filaments near the boundary may contribute to the unique dynamics observed after specific mechanical cues.

Using superresolution imaging coupled with LoG (Laplacian of Gaussian), we demonstrate that astrocytic actin organizes differently near the boundary depending upon the differentiated state of the astrocyte. Astrocytes grown on HTlc (a nanotopography which induces a stellate morphology) have actin with clusters perpendicular relative to cell boundary; astrocytes grown on PDL have parallel actin clusters relative to their closest boundaries. These results demonstrates that organization of actin can predict functional states in astrocytes.

Publications:
O’Neill KM, Saracino E, Barile B, Mennona NJ, et al., Advanced Biology 2022

• Actin Dynamics as a Multiscale Integrator of Cellular Guidance Cues

Abby Bull, PhD Student, Physics
with Prof. Min Zhao (UC Davis) and Prof. Quan Qing (ASU)

Migrating cells must integrate multiple, competing external guidance cues. However, it is not well understood how cells prioritize among these cues. We investigate external cue integration by monitoring the response of wave-like, actin-polymerization dynamics, the driver of cell motility, to combinations of nanotopographies and electric fields in neutrophil-like cells. The electric fields provide a global guidance cue, and approximate conditions at wound sites in vivo. The nanotopographies have dimensions similar to those of collagen fibers, and act as a local esotactic guidance cue. We find that cells prioritize guidance cues, with electric fields dominating long-term motility by introducing a unidirectional bias in the locations at which actin waves nucleate. That bias competes successfully with the wave guidance provided by the bidirectional nanotopographies.

• Nanotopography modulates intracellular excitable systems through cytoskeleton actuation

Qixin Yang, PhD Student, Physics
with Prof. Peter Devreotes (Johns Hopkins University)
with Prof. John Fourkas (University of Maryland)

Cellular sensing of most environmental cues involves receptors that affect a signal-transduction excitable network (STEN), which is coupled to a cytoskeletal excitable network (CEN). We show that the mechanism of sensing of nanoridges is fundamentally different. CEN activity occurs preferentially on nanoridges, whereas STEN activity is constrained between nanoridges. In the absence of STEN, waves disappear, but long-lasting F-actin puncta persist along the ridges. When CEN is suppressed, wave propagation is no longer constrained by nanoridges. A computational model reproduces these experimental observations. Our findings indicate that nanotopography is sensed directly by CEN, whereas STEN is only indirectly affected due to a CEN-STEN feedback loop. These results explain why texture sensing is robust and acts cooperatively with multiple other guidance cues in complex, in vivo microenvironments.

• Excitable Systems perspective on the cellular impact of Elongate Mineral Particles (Asbestos)

Cathy Gu, PhD Student, Physics
with Prof. Ann G. Wylie (University of Maryland)
with Prof. John Fourkas (University of Maryland)

We investigate how the geometry of elongate mineral particles (EMPs) may be sensed by cells based on “esotaxis”, a recently discovered mechanism of texture sensing. Esotaxis is based on cytoskeletal waves and oscillations that are nucleated, shaped, and steered by the texture of the surrounding. We find that EMPs trigger an esotactic response in macrophages, and that the EMP response dominates cytoskeletal activity in these immune cells, while epithelial cells show little to no esotactic response. This result is consistent with the distinct interaction of both cell types with ridge topographies of dimensions comparable to asbestiform EMPs. Our findings raise the question of whether narrow EMPs may also dominate cytoskeletal activity in other immune cell types that exhibit similar esotaxis effects. These findings together with prior studies of esotaxis lead us to the hypothesis that asbestiform EMPs suppress the migration of immune cells and activate immune signaling, lowering the ability of the immune system from reaching nearby tissue.

Publications:
Gu S, Bull A, Perry J, et al., Environmental Research 2023

• Analysis of Actin Waves using Computer Vision Algorithms

Leonard Campanello, PhD Student, Physics
Spandan Pathak, PhD Student, Biophysics
Matthew J. Hourwitz, PhD Student, Chemistry
with Prof. John Fourkas (University of Maryland)

Quantify the spatiotemporal dynamics of objects in biological systems often requires the analysis of diffuse concentration fields, such as fluorescent actin. In this project, we utilize a computer vision algorithm called “optical flow” to capture and coarse grain the dynamics of amorphous actin intensity fields to measure physical properties such as velocity and persistence. We use this analysis to determine the effect of surface topographies on actin dynamics, the effect of electric fields on neutrophil migration, and the ways that actin waves in Dictyostelium Discoidium cells change in response to different physical and chemical perturbations.

Publication:
R.M. Lee, L. Campanello, M.J. Hourwitz, P. Alvarez, A. Omidvar, J.T. Fourkas, W. Losert, Molecular Biology of the Cell 2020

HL60 cell with fluorescently labeled actin, overlaid with clustering of optical flow vectors to quantify mesoscale actin dynamics.

• Neurotransmitter regulated macroscale tissue rhythms

Spandan Pathak, PhD Student, Biophysics
with Dr. Jens Herberholz (University of Maryland)

To study the regulatory effect of the Central Nervous System (CNS) on intestinal functions, we study motility patterns in crayfish hind-gut upon neurogenic and chemical excitations. Using Calcium imaging, we also intend to identify the exact nature of bidirectional communication channels between CNS and ENS (Enteric Nervous System) and in the process, focus deeper on the gut-brain axis.

Movement of isolated hindgut with nerve N7 attached demonstrates spatio-temporal waves across different scales.

• AI-enabled quantification of Collective Dynamics

Cathy Gu, PhD Student, Physics
with Dr. Joe Chalfoun (NIST)

Collective cell migration is an umbrella term for a rich variety of cell behaviors, whose distinct character is important for biological function, notably for cancer metastasis. One essential feature of collective behavior is the motion of cells relative to their immediate neighbors. We introduce an AI-based pipeline to segment and track cell nuclei from phase-contrast images.

Publication:
S. Gu, R.M. Lee, Z. Benson, C. Ling, M.I. Vitolo, S.S. Martin, J. Chalfoun, W. Losert, iScience, iScience 2022

• Modeling Shape Dynamics on nanostructured surfaces

Corey Herr, PhD Student, Physics
with Dr. John Fourkas (UMD)

Asymmetric nanotopography with sub-cellular dimensions has demonstrated the ability to provide a unidirectional bias in cell migration. We use a three-dimensional, physics-based model to study cell guidance on nanotopography. This model can give qualitative predictions of how cells behave on nanostructured surfaces such as sawteeth. Motivated by this model, an analysis of previously reported experimental data indicates that the degree of guidance by asymmetric nanosawteeth increases with the cell velocity.

Publication:
C. Herr, B. Winkler, F. Ziebert, I.S. Aranson, J.T. Fourkas, W. Losert, , Communications Physics 2022

Maryland Day: Welcome to Cells in Motion!

Lab Outreach

As part of the 2023 Maryland Day event, the Losert Lab created an interactive demonstration of our cell tracking software where participants were able to track their motion while playing games such as follow the leader. An acoustic leviation device was also demonstrated to trap styrofoam beads in air. To watch our video or to learn more, visit our Maryland Day page!