The Nanomechanical Properties of CLL Cells Are Linked to the Actin Cytoskeleton and Are a Potential Target of BTK Inhibitors

Shear flow deformability cytometry: A microfluidic method advancing towards clinical use - A review

BACKGROUND

Shear flow deformability cytometry is an emerging microfluidic technique that has undergone significant advances in the last few years and offers considerable potential for clinical diagnostics and disease monitoring. By simultaneously measuring mechanical and morphological parameters of single cells, it offers a comprehensive extension of traditional cell analysis, delivering unique insight into cell deformability, which is gaining recognition as a novel biomarker for health and disease. Due to its operating principle, the method is particularly suitable for the clinical analysis of blood samples.

RESULTS

This review focuses on the recent developments in shear flow deformability cytometry, which is a widely adopted variant of deformability cytometry. It has a strong potential for applications in clinical practice due to its robust and simple operation, demonstrated applications with whole blood samples, as well as its high throughput, which can reach approximately 1000 cells per second. We begin by discussing some basic factors that influence the mechanical properties of cells and give an overview of deformability cytometry and its operational principles for samples from blood, cultured cells and tissues. Next, we review recent clinically relevant applications in analysis of blood and cancer cells. Finally, we address key challenges to clinical adoption, such as regulatory approval, scalable manufacturing, and workflow integration, emphasizing the need for further validation studies to facilitate clinical implementation.

SIGNIFICANCE

This article uniquely emphasizes the clinical relevance of microfluidic shear flow deformability cytometry, by giving an overview of mechanical and morphological biomarkers studied in clinically significant samples. In addition, it addresses critical barriers to clinical translation. By identifying these obstacles, this article aims to demonstrate the potential of deformability cytometry to bridge the gap between the research and the routine medical practice.

Elastic properties of leukemic cells linked to maturation stage and integrin activation

Acute myeloid leukemia (AML) remains challenging to cure. In addition to mutations that alter cell functioning, biophysical properties are modulated by external cues. In particular, membrane proteins that interact with the bone marrow niche can induce cellular changes. Here, we develop an atomic force microscopy (AFM) approach to measure non-adherent AML cell mechanical properties. The Young's modulus of the AML cell line, THP-1, increased in response to retronectin, whereas knock-out of the adhesion protein ITGB1 resulted in no response to retronectin. Confocal microscopy revealed different actin cytoskeleton morphologies for wild-type and ITGB1 knock-out cells exposed to retronectin. These results indicate that ITGB1 mediates stimuli-induced cellular mechanoresponses through cytoskeletal changes. We next used AFM to investigate the elastic properties of primary AML cells and found that more committed cells had lower Young's moduli than immature AMLs. Overall, this provides a platform for investigating the molecular mechanisms involved in leukemic cell mechanoresponse.

The cytoskeletal control of B cell receptor and integrin signaling in normal B cells and chronic lymphocytic leukemia

B cells migrate within lymphoid organs during maturation and activation, processes orchestrated by the interplay between B cell receptor (BCR) signaling and microenvironmental cues. Integrins act as mechanoreceptors, linking BCR activation to cytoskeletal remodeling, facilitating immune synapse formation, antigen recognition, and extraction. BCR activation models describe receptor clustering and mechanical changes within the antigen-BCR complex. Upon activation, immune synapses form, enabling antigen extraction and downstream signaling. Integrins stabilize these synapses, amplify BCR signaling, and modulate BCR positioning via actin reorganization. In chronic lymphocytic leukemia (CLL), aberrant BCR signaling and integrins are major players in leukemic cell homing, prognosis, and therapy resistance. In this review, we summarize the current understanding of the interplay of BCR mechanics and B cell localization, with a particular focus on communication between BCR signaling and integrin-mediated processes via actin dynamics. We give insights into normal B cell biology and then outline aspects typical to CLL.

Production of AFM wedged cantilevers for stress-relaxation experiments: Uniaxial loading of soft, spherical cells

The fabrication of wedge-shaped cantilevers for Atomic Force Microscopy (AFM) remains a critical yet challenging task, particularly when precision and efficiency are required. In this study, we present a streamlined protocol for producing these wedges using NOA63 UV-curing polymer, which simplifies the process and eliminates the need for dedicated equipment. Our method reduces preparation time while maintaining the mechanical properties of the cantilevers, in line with the manufacturer's specifications. We demonstrate the effectiveness of our wedged cantilevers in stress-relaxation experiments performed by means of AFM and confocal microscopy on primary Chronic Lymphocytic Leukemia cells and the MEC1 cell line. These experiments highlight the effectiveness of using modified cantilevers to consistently apply precise uniaxial loading to soft, spherical cells. This technique offers a marked improvement in fabrication speed and operational ease compared to traditional methods, without compromising the accuracy or performance of the measurements. This protocol is not only time-saving, but also adaptable for use in a wide range of biological applications, making it a valuable tool for AFM-based research in cellular mechanics.

Bruton's tyrosine kinase-bearing B cells and microglia in neuromyelitis optica spectrum disorder

BACKGROUND

Neuromyelitis optica spectrum disorder (NMOSD) is an inflammatory autoimmune disease of the central nervous system that involves B-cell receptor signaling as well as astrocyte-microglia interaction, which both contribute to evolution of NMOSD lesions.

MAIN BODY

Through transcriptomic and flow cytometry analyses, we found that Bruton's tyrosine kinase (BTK), a crucial protein of B-cell receptor was upregulated both in the blood and cerebrospinal fluid of NMOSD patients. Blockade of BTK with zanubrutinib, a highly specific BTK inhibitor, mitigated the activation and maturation of B cells and reduced production of causal aquaporin-4 (AQP4) autoantibodies. In a mouse model of NMO, we found that both BTK and pBTK expression were significantly increased in microglia. Transmission electron microscope scan demonstrated that BTK inhibitor ameliorated demyelination, edema, and axonal injury in NMO mice. In the same mice colocalization of GFAP and Iba-1 immunofluorescence indicated a noticeable increase of astrocytes-microglia interaction, which was alleviated by zanubrutinib. The smart-seq analysis demonstrated that treatment with BTK inhibitor instigated microglial transcriptome changes including downregulation of chemokine-related genes and genes involved in the top 5 biological processes related to cell adhesion and migration, which are likely responsible for the reduced crosstalk of microglia and astrocytes.

CONCLUSIONS

Our results show that BTK activity is enhanced both in B cells and microglia and BTK inhibition contributes to the amelioration of NMOSD pathology. These data collectively reveal the mechanism of action of BTK inhibition and corroborate BTK as a viable therapeutic target.