Biology subjects

Shim, G.

Publications and source records attributed to Shim, G..

8 recordsLinked to original sources

bioRxiv2025

Electric field intensity modulates keratocyte migration without altering turning dynamics

Cell migration is a cornerstone of biological systems, enabling organisms to adapt to environmental stimuli and maintain homeostasis. Disruptions in this process can lead to functional impairment or system failure. In many cases, cells do not move randomly; instead, they migrate directionally in response to external cues, allowing them to perform essential biological functions. This directed movement is especially important in processes such as morphogenesis, cancer invasion, and wound healing. To unravel the complexities of directional cell migration, investigating natural guiding stimuli is crucial. Among these, electrical fields stand out as precise and physiologically relevant stimulus. Using a platform designed to apply programmable electric fields, the SCHEEPDOG device; we applied controlled electric field of varying intensities to keratocytes and quantitatively analyzed their migratory behavior. Our findings reveal that electric field stimulation not only induces robust directional migration but also enhances migration speed in an intensity-dependent manner. Additionally, cells initially moving in random directions gradually align with the field vector, with higher intensities accelerating the alignment. Intriguingly, while both speed and alignment time can be modulated through stimulation, the overall shape of migration trajectories remains unchanged. In other terms, for cells initially moving to the opposite direction of the field, the alignment is accompanied by making a turn and the size and shape of this turn is not affected by the magnitude of the electrical stimulation. Together, these results demonstrate that electrical stimulation can tune the speed and directional alignment of keratocyte migration without altering turning dynamics. These findings contribute to a deeper understanding of electrotaxis and offers new insights into how biophysical cues regulate cell migration in both physiological and pathological contexts.

biophysics↗

bioRxiv2025

Automated high-throughput patch clamp electrophysiology of hiPSC-derived neuronal models

The advent of human induced pluripotent stem cells (hiPSCs) and their differentiation into neurons and brain organoids has revolutionized our ability to model brain disorders in a human context. However, current technologies to assay the electrophysiological properties of human neurons in these models remain limited by throughput, as single-cell manual patch clamp is laborious and resource intensive. Here, we provide methods to perform high-throughput automated patch-clamp (APC) on hiPSC-derived neurons. We describe how to dissociate and perform voltage-clamp recordings on human neurons from three well-established protocols - 2D directed differentiation of cortical neurons, NGN2-induced neurons, and 3D cortical organoids - using the Nanion Syncropatch 384, a commercially available high-throughput APC system. Using this approach, we investigated the biophysical properties of voltage-gated sodium channels (VGSCs) and provide direct comparisons between manual and APC recordings across all three hiPSC-derived model systems. We demonstrate the capability of this automated system for pharmacological analysis of native human VGSC isoforms, which will enable compound screening approaches. Lastly, we provide methods to sort specific cellular populations within these hiPSC models using fluorescence-activated cell sorting (FACS) followed by APC. These methods and results provide a transformative and novel high-throughput technique for quantifying passive and active membrane properties in cell-type specific and/or genetically modified hiPSC-derived neurons.

neuroscience↗

bioRxiv2023

TCF4 mutations disrupt synaptic function through dysregulation of RIMBP2 in patient-derived cortical neurons

Genetic variation in the transcription factor 4 (TCF4) gene is associated with risk for a variety of developmental and psychiatric conditions, which includes a syndromic form of ASD called Pitt Hopkins Syndrome (PTHS). TCF4 encodes an activity-dependent transcription factor that is highly expressed during cortical development and in animal models is shown to regulate various aspects of neuronal development and function. However, our understanding of how disease-causing mutations in TCF4 confer pathophysiology in a human context is lacking. Here we show that cortical neurons derived from patients with TCF4 mutations have deficits in spontaneous synaptic transmission, network excitability and homeostatic plasticity. Transcriptomic analysis indicates these phenotypes result from altered expression of genes involved in presynaptic neurotransmission and identifies the presynaptic binding protein, RIMBP2 as the most differentially expressed gene in PTHS neurons. Remarkably, TCF4-dependent deficits in spontaneous synaptic transmission and network excitability were rescued by increasing RIMBP2 expression in presynaptic neurons. Together, these results identify TCF4 as a critical transcriptional regulator of human synaptic development and plasticity and specifically identifies dysregulation of presynaptic function as an early pathophysiology in PTHS.

neuroscience↗

bioRxiv2022

Pump it up: bioelectric stimulation controls tissue hydrostatic pressure and water transport via electro-inflation

Epithelial tissues sheath many organs, separating outside from inside and exquisitely regulating ion and water transport electromechanically to maintain homeostatic balance and tissue hydrostatic pressure. While it is increasingly clear that the ionic microenvironment and external electric stimuli can affect epithelial function and behavior, the coupling between electrical perturbation and tissue form remain unclear. We investigated this by combining electrical stimulation with three-dimensional epithelial tissues with hollow lumens--both kidney cysts and complex intestinal stem cell organoids. Our core finding is that physiological strength electrical stimulation of order 1-3 V/cm (with both direct and alternating currents) can drive powerful and rapid inflation of hollow tissues through a process we call electro-inflation, inducing up to a threefold increase in tissue volume and striking asymmetries in tissue form. Electro-inflation is primarily driven by field-induced ion crowding on the outer surface of the hollow tissue that creates an ion gradient across the epithelial shell, which drives increased ionic flux mediated by ion channels/transporters and subsequent osmotic water flow into the lumen. This influx generates hydrostatic pressure, and inflation results from a competition between this pressure and cell cytoskeletal tension. We validated these interpretations with computational models connecting ion crowding around tissues to tissue mechanics. Electrically stimulated cysts and organoids also exhibited pronounced asymmetry, where the epithelial shell thickened on the cathode-facing side and thinned on the anode-facing side of the tissue. We discovered that this process is the result of 3D electrotaxis-directed migration of cells in an electric field-causing a redistribution of cells around the shell. The ability of electrical cues to dramatically regulate tissue size and shape highlight the key role of the electrical micro-environment and the potential offered by manipulating these signals.

bioengineering↗

bioRxiv2022

Clemastine fumarate enhances myelination and promotes functional recovery in a syndromic ASD mouse model of Pitt-Hopkins Syndrome

Pitt-Hopkins syndrome (PTHS) is an autism spectrum disorder (ASD) caused by autosomal dominant mutations in the Transcription Factor 4 gene (TCF4). One pathobiological process caused by Tcf4 mutation is a cell autonomous reduction in oligodendrocytes (OLs) and myelination. In this study, we show that clemastine is effective at restoring myelination defects in a PTHS mouse model. In vitro, clemastine treatment reduced excess oligodendrocyte precursor cells (OPCs) and normalized OL density. In vivo, two-week intraperitoneal administration of clemastine also normalized OPC and OL density in the cortex of Tcf4 mutant mice and appeared to increase the number of axons undergoing myelination, as EM imaging of the corpus callosum showed a significant increase in uncompacted myelin. Importantly, this treatment paradigm resulted in functional rescue by improving electrophysiology and behavior. Together, these results provide preclinical evidence that remyelination therapies may be beneficial in PTHS and potentially other neurodevelopmental disorders characterized by demyelination.

neuroscience↗

bioRxiv2021

Cellular crowd control: overriding endogenous cell coordination makes cell migration more susceptible to external programming

As collective cell migration is essential in biological processes spanning development, healing, and cancer progression, methods to externally program cell migration are of great value. However, problems can arise if the external commands compete with strong, pre-existing collective behaviors in the tissue or system. We investigate this problem by applying a potent external migratory cue--electrical stimulation and electrotaxis--to primary mouse skin monolayers where we can tune cell-cell adhesion strength to modulate endogenous collectivity. Monolayers with high cell-cell adhesion showed strong natural coordination and resisted electrotactic control, with this conflict actively damaging the leading edge of the tissue. However, reducing pre-existing coordination in the tissue by specifically inhibiting E-cadherin-dependent cell-cell adhesion, either by disrupting the formation of cell-cell junctions with E-cadherin specific antibodies or rapidly dismantling E-cadherin junctions with calcium chelators, significantly improved controllability. Finally, we applied this paradigm of weakening existing coordination to improve control to demonstrate accelerated wound closure in vitro. These results are in keeping with those from diverse, non-cellular systems, and confirm that endogenous collectivity should be considered as a key, quantitative design variable when optimizing external control of collective migration.

bioengineering↗

bioRxiv2020

Come together: bioelectric healing-on-a-chip

There is a growing interest in bioelectric wound treatment and electrotaxis, the process by which cells detect an electric field and orient their migration along its direction, has emerged as a potential cornerstone of the endogenous wound healing response. Despite recognition of the importance of electrotaxis in wound healing, no experimental system to date demonstrates that the actual closing of a wound can be accelerated solely by the electrotaxis response itself, and in vivo systems are too complex to resolve cell migration from other healing stages such as proliferation and inflammation. This uncertainty has led to a lack of standardization between stimulation methods, model systems, and electrode technology required for device development. In this paper, we present a healing-on-chip approach that is a standardized, low-cost, model for investigating electrically accelerated wound healing. Our device provides the first convergent field geometry used in a stimulation device. We validate this device by using electrical stimulation to close a 1.5 mm gap between two large (30 mm2) primary skin keratinocyte layers to double the rate of healing over an unstimulated tissue. This proves that convergent electrotaxis is both possible and can accelerate healing, and offers a new healing-on-a-chip platform to explore future bioelectric interfaces.

bioengineering↗

bioRxiv2019

On-demand spatiotemporal programming of collective cell migration via bioelectric stimulation

Directed cell migration is critical across biological processes spanning healing to cancer invasion, yet no existing tools allow real-time interactive guidance over such migration. We present a new bioreactor that harnesses electrotaxis--directed cell migration along electric field gradients--by integrating four independent electrodes under computer control to dynamically program electric field patterns, and hence steer cell migration. Using this platform, we programmed and characterized multiple precise, two-dimensional collective migration maneuvers in renal epithelia and primary skin keratinocyte ensembles. First, we demonstrated on-demand, 90-degree collective turning. Next, we developed a universal electrical stimulation scheme capable of programming arbitrary 2D migration maneuvers such as precise angular turns and migration in a complete circle. Our stimulation scheme proves that cells effectively time-average electric field cues, helping to elucidate the transduction time scales in electrotaxis. Together, this work represents an enabling platform for controlling cell migration with broad utility across many cell types.

bioengineering↗