Dissecting cellular mechanics: Implications for aging, cancer, and immunity

Viscoelasticity of diverse biological samples quantified by Acoustic Force Microrheology (AFMR)

In the context of soft matter and cellular mechanics, microrheology - the use of micron-sized particles to probe the frequency-dependent viscoelastic response of materials - is widely used to shed light onto the mechanics and dynamics of molecular structures. Here we present the implementation of active microrheology in an Acoustic Force Spectroscopy setup (AFMR), which combines multiplexing with the possibility of probing a wide range of forces ( ~ pN to ~nN) and frequencies (0.01-100 Hz). To demonstrate the potential of this approach, we perform active microrheology on biological samples of increasing complexity and stiffness: collagen gels, red blood cells (RBCs), and human fibroblasts, spanning a viscoelastic modulus range of five orders of magnitude. We show that AFMR can successfully quantify viscoelastic properties by probing many beads with high single-particle precision and reproducibility. Finally, we demonstrate that AFMR to map local sample heterogeneities as well as detect cellular responses to drugs.

Mechanical convergence in mixed populations of mammalian epithelial cells

Tissues consist of cells with different molecular and/or mechanical properties. Measuring the forces and stresses in mixed-cell populations is essential for understanding the mechanisms by which tissue development, homeostasis, and disease emerge from the cooperation of distinct cell types. However, many previous studies have primarily focused their mechanical measurements on dissociated cells or aggregates of a single-cell type, leaving the mechanics of mixed-cell populations largely unexplored. In the present study, we aimed to elucidate the influence of interactions between different cell types on cell mechanics by conducting in situ mechanical measurements on a monolayer of mammalian epithelial cells. Our findings revealed that while individual cell types displayed varying magnitudes of traction and intercellular stress before mixing, these mechanical values shifted in the mixed monolayer, becoming nearly indistinguishable between the cell types. Moreover, by analyzing a mixed-phase model of active tissues, we identified physical conditions under which such mechanical convergence is induced. Overall, the present study underscores the importance of in situ mechanical measurements in mixed-cell populations to deepen our understanding of the mechanics of multicellular systems.

Patient's dermal fibroblasts as disease markers for visceral myopathy

Visceral myopathy (VSCM) is a rare genetic disease, orphan of pharmacological therapy. VSCM diagnosis is not always straightforward due to symptomatology similarities with mitochondrial or neuronal forms of intestinal pseudo-obstruction. The most prevalent form of VSCM is associates with variants in the gene ACTG2, encoding the protein gamma-2 actin. Overall, VSCM is a mechano-biological disorder, in which different genetic variants lead to similar alterations to the contractile phenotype of enteric smooth muscles, resulting in the emergence of life-threatening symptoms. In this work we analyzed the morpho-mechanical phenotype of human dermal fibroblasts from patients affected with VSCM, demonstrating that they retain a clear signature of the disease when compared with different controls. We evaluated several biophysical traits of fibroblasts, and we show that a measure of cellular traction forces can be used as a non-specific biomarker of the disease. We propose that a simple assay based on traction forces could be designed to provide a valuable support for clinical decision or pre-clinical research.

Unravelling cell migration: defining movement from the cell surface

Cell motility is essential for life and development. Unfortunately, cell migration is also linked to several pathological processes, such as cancer metastasis. Cells' ability to migrate relies on many actors. Cells change their migratory strategy based on their phenotype and the properties of the surrounding microenvironment. Cell migration is, therefore, an extremely complex phenomenon. Researchers have investigated cell motility for more than a century. Recent discoveries have uncovered some of the mysteries associated with the mechanisms involved in cell migration, such as intracellular signaling and cell mechanics. These findings involve different players, including transmembrane receptors, adhesive complexes, cytoskeletal components , the nucleus, and the extracellular matrix. This review aims to give a global overview of our current understanding of cell migration.

Possibilities of using T-cell biophysical biomarkers of ageing

Ageing is interrelated with the development of immunosenescence. This article focuses on one of the cell sets of the adaptive immune system, T cells, and provides a review of the known changes in T cells associated with ageing. Such fundamental changes affect both cell molecular content and internal ordering. However, acquiring a complete description of the changes at these levels would require extensive measurements of parameters and, furthermore, important fine details of the internal ordering that may be difficult to detect. Therefore, an alternative approach for the characterisation of cells consists of the performance of physical measurements of the whole cell, such as deformability measurements or migration measurements: the physical parameters, complementing the commonly used chemical biomarkers, may contribute to a better understanding of the evolution of T-cell states during ageing. Mechanical measurements, among other biophysical measurements, have the advantage of their relative simplicity: one single parameter agglutinates the complex effects of the variety of changes that gradually appear in cells during ageing.

Links of Cytoskeletal Integrity with Disease and Aging

Aging is a complex feature and involves loss of multiple functions and nonreversible phenotypes. However, several studies suggest it is possible to protect against aging and promote rejuvenation. Aging is associated with many factors, such as telomere shortening, DNA damage, mitochondrial dysfunction, and loss of homeostasis. The integrity of the cytoskeleton is associated with several cellular functions, such as migration, proliferation, degeneration, and mitochondrial bioenergy production, and chronic disorders, including neuronal degeneration and premature aging. Cytoskeletal integrity is closely related with several functional activities of cells, such as aging, proliferation, degeneration, and mitochondrial bioenergy production. Therefore, regulation of cytoskeletal integrity may be useful to elicit antiaging effects and to treat degenerative diseases, such as dementia. The actin cytoskeleton is dynamic because its assembly and disassembly change depending on the cellular status. Aged cells exhibit loss of cytoskeletal stability and decline in functional activities linked to longevity. Several studies reported that improvement of cytoskeletal stability can recover functional activities. In particular, microtubule stabilizers can be used to treat dementia. Furthermore, studies of the quality of aged oocytes and embryos revealed a relationship between cytoskeletal integrity and mitochondrial activity. This review summarizes the links of cytoskeletal properties with aging and degenerative diseases and how cytoskeletal integrity can be modulated to elicit antiaging and therapeutic effects.

Biophysics involved in the process of tumor immune escape

Much of the current research into immune escape from cancer is focused on molecular and cellular biology, an area of biophysics that is easily overlooked. A large number of immune drugs entering the clinic are not effective for all patients. Apart from the molecular heterogeneity of tumors, the biggest reason for this may be that knowledge of biophysics has not been considered, and therefore an exploration of biophysics may help to address this challenge. To help researchers better investigate the relationship between tumor immune escape and biophysics, this paper provides a brief overview on recent advances and challenges of the biophysical factors and strategies by which tumors acquire immune escape and a comprehensive analysis of the relevant forces acting on tumor cells during immune escape. These include tumor and stromal stiffness, fluid interstitial pressure, shear stress, and viscoelasticity. In addition, advances in biophysics cannot be made without the development of detection tools, and this paper also provides a comprehensive summary of the important detection tools available at this stage in the field of biophysics.

Regulatory mechanisms of the early phase of white adipocyte differentiation: an overview

The adipose organ comprises two main fat depots termed white and brown adipose tissues. Adipogenesis is a process leading to newly differentiated adipocytes starting from precursor cells, which requires the contribution of many cellular activities at the genome, transcriptome, proteome, and metabolome levels. The adipogenic program is accomplished through two sequential phases; the first includes events favoring the commitment of adipose tissue stem cells/precursors to preadipocytes, while the second involves mechanisms that allow the achievement of full adipocyte differentiation. While there is a very large literature about the mechanisms involved in terminal adipogenesis, little is known about the first stage of this process. Growing interest in this field is due to the recent identification of adipose tissue precursors, which include a heterogenous cell population within different types of adipose tissue as well as within the same fat depot. In addition, the alteration of the heterogeneity of adipose tissue stem cells and of the mechanisms involved in their commitment have been linked to adipose tissue development defects and hence to the onset/progression of metabolic diseases, such as obesity. For this reason, the characterization of early adipogenic events is crucial to understand the etiology and the evolution of adipogenesis-related pathologies, and to explore the adipose tissue precursors’ potential as future tools for precision medicine.

Pancreatic Ductal Adenocarcinoma Cortical Mechanics and Clinical Implications

Pancreatic ductal adenocarcinoma (PDAC) remains one of the deadliest cancers due to low therapeutic response rates and poor prognoses. Majority of patients present with symptoms post metastatic spread, which contributes to its overall lethality as the 4th leading cause of cancer-related deaths. Therapeutic approaches thus far target only one or two of the cancer specific hallmarks, such as high proliferation rate, apoptotic evasion, or immune evasion. Recent genomic discoveries reveal that genetic heterogeneity, early micrometastases, and an immunosuppressive tumor microenvironment contribute to the inefficacy of current standard treatments and specific molecular-targeted therapies. To effectively combat cancers like PDAC, we need an innovative approach that can simultaneously impact the multiple hallmarks driving cancer progression. Here, we present the mechanical properties generated by the cell’s cortical cytoskeleton, with a spotlight on PDAC, as an ideal therapeutic target that can concurrently attack multiple systems driving cancer. We start with an introduction to cancer cell mechanics and PDAC followed by a compilation of studies connecting the cortical cytoskeleton and mechanical properties to proliferation, metastasis, immune cell interactions, cancer cell stemness, and/or metabolism. We further elaborate on the implications of these findings in disease progression, therapeutic resistance, and clinical relapse. Manipulation of the cancer cell’s mechanical system has already been shown to prevent metastasis in preclinical models, but it has greater potential for target exploration since it is a foundational property of the cell that regulates various oncogenic behaviors.

The Mechanical Interplay Between Differentiating Mesenchymal Stem Cells and Gelatin-Based Substrates Measured by Atomic Force Microscopy

Traditional methods to assess hMSCs differentiation typically require long-term culture until cells show marked expression of histological markers such as lipid accumulation inside the cytoplasm or mineral deposition onto the surrounding matrix. In parallel, stem cell differentiation has been shown to involve the reorganization of the cell’s cytoskeleton shortly after differentiation induced by soluble factors. Given the cytoskeleton’s role in determining the mechanical properties of adherent cells, the mechanical characterization of stem cells could thus be a potential tool to assess cellular commitment at much earlier time points. In this study, we measured the mechanical properties of hMSCs cultured on soft gelatin-based hydrogels at multiple time points after differentiation induction toward adipogenic or osteogenic lineages. Our results show that the mechanical properties of cells (stiffness and viscosity) and the organization of the actin cytoskeleton are highly correlated with lineage commitment. Most importantly, we also found that the mechanical properties and the topography of the gelatin substrate in the vicinity of the cells are also altered as differentiation progresses toward the osteogenic lineage, but not on the adipogenic case. Together, these results confirm the biophysical changes associated with stem cell differentiation and suggest a mechanical interplay between the differentiating stem cells and their surrounding extracellular matrix.

Protean Regulation of Leukocyte Function by Nuclear Lamins

The leukocyte nucleus must be sufficiently elastic to squeeze through tissue barriers during migration, but not so collapsible as to risk damaging chromatin. The proper balance is struck in part by the composition of the nuclear lamina, a flexible meshwork composed mainly of intermediate filaments woven from type A and type B lamin proteins, that is located subjacent to the inner nuclear membrane. There is now increasing evidence that, in addition to influencing nuclear shape and stiffness and cell migration, lamins and lamin-interacting proteins may also interact functionally with chromatin to influence leukocyte gene expression, differentiation, and effector function, including T cell differentiation, B cell somatic hypermutation, and the formation of neutrophil extracellular traps (NETosis).

Applications of atomic force microscopy in immunology

Cellular mechanics, a major regulating factor of cellular architecture and biological functions, responds to intrinsic stresses and extrinsic forces exerted by other cells and the extracellular matrix in the microenvironment. Cellular mechanics also acts as a fundamental mediator in complicated immune responses, such as cell migration, immune cell activation, and pathogen clearance. The principle of atomic force microscopy (AFM) and its three running modes are introduced for the mechanical characterization of living cells. The peak force tapping mode provides the most delicate and desirable virtues to collect high-resolution images of morphology and force curves. For a concrete description of AFM capabilities, three AFM applications are discussed. These applications include the dynamic progress of a neutrophil-extracellular-trap release by neutrophils, the immunological functions of macrophages, and the membrane pore formation mediated by perforin, streptolysin O, gasdermin D, or membrane attack complex.

Development of label-free biophysical markers in osteogenic maturation

The spatial and temporal changes of morphological and mechanical properties of living cells reflect complex functionally-associated processes. Monitoring these modifications could provide a direct information on the cellular functional state. Here we present an integrated biophysical approach to the quantification of the morphological and mechanical phenotype of single cells along a maturation pathway. Specifically, quantitative phase microscopy and single cell biomechanical testing were applied to the characterization of the maturation of human foetal osteoblasts, demonstrating the ability to identify effective label-free biomarkers along this fundamental biological process.

Changes in the physicochemical properties of fish cell membranes during cellular senescence

Fish cell lines are widely used for the studies of developmental biology, virology, biology of aging, and nutrition physiology. However, little is known about their physicochemical properties. Here, we report the phospholipid compositions and mechanical properties of cell membranes derived from freshwater, anadromous and marine fish species. Biophysical analyses revealed that fish cell lines have highly deformable cell membranes with significantly low membrane tensions and Young's moduli compared with those of mammalian cell lines. The induction of cellular senescence by DNA demethylation using 5-Aza-2'-deoxycytidine significantly reduced the deformability of fish cell membrane, but hydrogen peroxide-induced oxidative stress did not affect the deformability. Mass spectrometry analysis of phospholipids revealed that the level of phosphatidylethanolamine molecules containing polyunsaturated fatty acids significantly increased during the 5-Aza-2'-deoxycytidine-induced cellular senescence. Fish cell lines provide a useful model system for studying the changes in the physicochemical properties of cell membranes during cellular senescence.Abbreviations: 2D-TLC: two-dimensional thin layer chromatography; 5-Aza-dC: 5-Aza-2'-deoxycytidine; DHA: docosahexaenoic acid; EPA: eicosapentaenoic acid; FBS: fetal bovine serum; PC: phosphatidylcholine; PE: phosphatidylethanolamine; PI: phosphatidylinositol; PS: phosphatidylserine; PUFA: polyunsaturated fatty acid; SA-β-gal: senescence-associated beta-galactosidase; SM: sphingomyelin.