Biology subjects

Bausch, A. R.

Publications and source records attributed to Bausch, A. R..

5 recordsLinked to original sources

bioRxiv2025

Phase separation strength controls actin filament treadmilling

Cellular motility relies on the dynamic turnover of actin filaments, which treadmill through continuous polymerization at the barbed end and disassembly at the pointed end. Yet, the underlying physical principles remain poorly understood. A long-standing challenge has been experimentally reconstituting stable, persistent treadmilling leading to higher-order actin organization. Here, we reconstitute a minimal in vitro system, in which liquid-liquid phase-separated condensates of zyxin and VASP balance cofilin-driven disassembly to enable persistent treadmilling-like movement of actin bundles. The condensates crosslink filaments into dynamic bundles while promoting barbed-end polymerization. The localized stabilization based on condensate-mediated bundling competes against the activity of cofilin and CAP1, enabling selective disassembly at pointed ends and recycling of monomers. To elucidate the physical basis underlying this emergent behavior, we complement our experiments with agent-based simulations that quantitatively recapitulate key experimental findings. This combined approach demonstrates that an intermediate range of zyxin-VASP self-affinity, driving the phase separation, enables robust treadmilling-like movement. A weakened zyxin-VASP self-affinity fails to stabilize the bundles, whereas an excessive affinity impedes filament dynamics. Experimental reconstitution and theoretical modeling together reveal a physical mechanism by which the material properties of multivalent protein condensates govern cytoskeletal turnover, and suggest a general design principle by which biomolecular condensates can spatiotemporally organize cytoskeletal structures.

biophysics↗

bioRxiv2024

Flow-Induced Vascular Remodeling On-Chip: Implications for Anti-VEGF Therapy

Impaired vascular remodeling is linked to tumor progression, impacting the efficacy of anti-vascular therapies. However, the interplay between blood flow and vascular endothelial growth factor (VEGF) in driving vascular remodeling remains unclear. We optimized a human vasculature-on-chip system for long-term perfusion to quantify vascular remodeling under physiologically low and tumor-mimicking high VEGF conditions. Live imaging shows that at low VEGF levels, flow-conditioned vascular networks remodeled like animal models, en-hancing flow velocities. Conversely, static networks lacking flow exhibited continuous growth, loss of network hierarchy, and decreased flow velocities. At tumor-mimicking high VEGF levels, flow-conditioned vessels showed aberrant overgrowth, which was blocked by the anti-VEGF tumor drug bevacizumab, restoring flow-induced remodeling. Without flow, however, high VEGF slowed vessel growth compared to low VEGF, while anti-VEGF treatment restored continuous growth. These findings provide valuable insights into optimizing anti-angiogenic therapies by exploiting VEGF modulation and flow conditions for vascular remodeling and improved tumor treatment.

biophysics↗

bioRxiv2022

Utilization of an Artery-on-a-chip to unravel novel regulators and therapeutic targets in vascular diseases

IntroductionOrgans-on-chips represent novel in vitro models that have the capacity to emulate aspects of human physiology and pathophysiology by incorporating features like tissue-multicellularity and exposure to organ-relevant physical environment. We developed an artery-on-a-chip with the objective to recapitulate the structure of the arterial wall composed of intimal and medial layers and the relevant hemodynamic forces that affect luminal cells. ResultsBy comparing arteries-on-chips exposed either to in vivo-like shear stress values or kept in static conditions, we identified a panel of novel genes modulated by shear stress. We next measured the expression pattern of shear stress-modulated genes in areas of the vascular tree affected by atherosclerotic plaques and aortic aneurysms, where disease development and progression are induced by alterations of shear stress. We obtained biopsies from patients affected by carotid artery disease (CAD), comprising the atherosclerotic plaque (diseased artery) and the adjacent region (non-diseased artery). From patients with abdominal aortic aneurysms (AAA), we obtained the aneurysmal portion (diseased aorta) and non-dilated adjacent segment (non-diseased aorta). Genes modulated by shear stress followed the same expression pattern in non-diseased segments of human vessels and were expressed by endothelial and smooth muscle cells as evidenced by immunofluorescence analysis and single cell RNA sequencing. Using mice and porcine models of vascular CAD and AAA, we confirmed that shear stress mediated targets are important in discriminating diseased and non-diseased vessel portions in vivo. Furthermore, we showed that our artery-on-a-chip can serve as a platform for drug-testing. We were able to reproduce the effects of a therapeutic agent previously used in AAA animal models in artery-on-a-chip systems and extend our understanding of its therapeutic effect through a multicellular structure. ConclusionsOur novel in vitro model is capable of mimicking important physiological aspects of human arteries, such as the response to shear stress, and can further shed light on the mechanism of action of potential therapeutics before they enter the clinical stage. TeaserThe artery-on-a-chip is a novel in vitro platform that enables the mimicry of human arteries and can be used to gain insights into the development and therapeutic targeting of vascular diseases.

cell biology↗

bioRxiv2021

In vivo photocontrol of microtubule dynamics and integrity, migration and mitosis, by the potent GFP-imaging-compatible photoswitchable reagents SBTubA4P and SBTub2M

Photoswitchable reagents to modulate microtubule stability and dynamics are an exciting tool approach towards micron- and millisecond-scale control over endogenous cytoskeleton-dependent processes. When these reagents are globally administered yet locally photoactivated in 2D cell culture, they can exert precise biological control that would have great potential for in vivo translation across a variety of research fields and for all eukaryotes. However, photopharmacologys reliance on the azobenzene photoswitch scaffold has been accompanied by a failure to translate this temporally- and cellularly-resolved control to 3D models or to in vivo applications in multi-organ animals, which we attribute substantially to the metabolic liabilities of azobenzenes. Here, we optimised the potency and solubility of metabolically stable, druglike colchicinoid microtubule inhibitors based instead on the styrylbenzothiazole (SBT) photoswitch scaffold, that are non-responsive to the major fluorescent protein imaging channels and so enable multiplexed imaging studies. We applied these reagents to 3D systems (organoids, tissue explants) and classic model organisms (zebrafish, clawed frog) with one- and two-protein imaging experiments. We successfully used systemic treatment plus spatiotemporally-localised illuminations in vivo to photocontrol microtubule dynamics, network architecture, and microtubule-dependent processes in these systems with cellular precision and second-level resolution. These nanomolar, in vivo-capable photoswitchable reagents can prove a game-changer for high-precision cytoskeleton research in cargo transport, cell motility, cell division and development. More broadly, their straightforward design can also inspire the development of similarly capable optical reagents for a range of protein targets, so bringing general in vivo photopharmacology one step closer to productive realisation.

cell biology↗

bioRxiv2021

A strategy to address dissociation-induced compositional and transcriptional bias for single-cell analysis of the human mammary gland

Single-cell transcriptomics provide insights into cellular heterogeneity and lineage dynamics that are key to better understanding normal mammary gland function as well as breast cancer initiation and progression. In contrast to murine tissue, human mammary glands require laborious dissociation protocols to isolate single cells. This leads to unavoidable procedure-induced compositional and transcriptional bias. Here, we present a new strategy on how to identify and minimize systematic error by combining different tissue dissociation strategies and then directly comparing composition and transcriptome of isolated cells using single-cell RNA sequencing and flow cytometry. Depending on the tissue isolation strategy, we found dramatic differences in abundance and heterogeneity of certain stromal cells types. Moreover, we identified lineage-specific dissociation-induced gene expression changes that, if left unchecked, could lead to misinterpretation of cellular heterogeneity and, since the basal epithelial population is particularly affected by this, wrongful assignment of putative stem cell populations.

cell biology↗