Probing nanomechanical responses of cell membranes

Autophagy as an Anti-senescent in Aging Neurocytes

Neuron homeostasis is crucial for the organism, and its maintenance is multifactorial, including autophagy. The turnover of aberrant intracellular components is a fundamental pathogenetic mechanism for cell aging. Autophagy is involved in the acceleration of the neurocyte aging process and the modification of cell longevity. Neurocyte aging is a process of loss of cell identity through cellular and subcellular changes that include molecular loss of epigenetics, transcriptomic, proteomic, and autophagy dysfunction. Autophagy dysfunction is the hallmark of neurocyte aging. Cell aging is the credential feature of neurodegenerative diseases. Pathophysiologically, aged neurocytes are characterized by dysregulated autophagy and subsequently neurocyte metabolic stress, resulting in accelerated neurocyte aging. In particular, chaperone- mediated autophagy perturbation results in upregulated expression of aging and apoptosis genes. Aged neurocytes are also characterized by the down-regulation of autophagy-related genes, such as ATG5-ATG12, LC3-II / LC3-I ratio, Beclin-1, and p62. Slowing aging through autophagy targeting is sufficient to improve prognosis in neurodegenerative diseases. Three primary anti-senescent molecules are involved in the aging process: mTOR, AMPK, and Sirtuins. Autophagy therapeutic effects can be applied to reverse and slow aging. This article discusses current advances in the role of autophagy in neurocyte homeostasis, aging, and potential therapeutic strategies to reduce aging and increase cell longevity.

A Review of Continuum Mechanics for Mechanical Deformation of Lipid Membranes

Mechanical deformation of lipid membranes plays important roles in various cellular tasks. Curvature deformation and lateral stretching are two major energy contributions to the mechanical deformation of lipid membranes. In this paper, continuum theories for these two major membrane deformation events were reviewed. Theories based on curvature elasticity and lateral surface tension were introduced. Numerical methods as well as biological applications of the theories were discussed.

Entry of microparticles into giant lipid vesicles by optical tweezers

Entry of micro- or nanosized objects into cells or vesicles made of lipid membranes occurs in many processes such as entry of viruses into host cells, microplastics pollution, drug delivery, or biomedical imaging. Here we investigate the microparticle crossing of lipid membranes in giant unilamellar vesicles in the absence of strong binding interactions (e.g., streptavidin-biotin binding). In these conditions, we observe that organic and inorganic particles can always penetrate inside the vesicles provided an external piconewton force is applied and for relatively low membrane tensions. In the limit of vanishing adhesion, we identify the role of the membrane area reservoir and show that a force minimum exists when the particle size is comparable to the bendocapillary length.

The interplay between membrane topology and mechanical forces in regulating T cell receptor activity

T cells are critically important for host defense against infections. T cell activation is specific because signal initiation requires T cell receptor (TCR) recognition of foreign antigen peptides presented by major histocompatibility complexes (pMHC) on antigen presenting cells (APCs). Recent advances reveal that the TCR acts as a mechanoreceptor, but it remains unclear how pMHC/TCR engagement generates mechanical forces that are converted to intracellular signals. Here we propose a TCR Bending Mechanosignal (TBM) model, in which local bending of the T cell membrane on the nanometer scale allows sustained contact of relatively small pMHC/TCR complexes interspersed among large surface receptors and adhesion molecules on the opposing surfaces of T cells and APCs. Localized T cell membrane bending is suggested to increase accessibility of TCR signaling domains to phosphorylation, facilitate selective recognition of agonists that form catch bonds, and reduce noise signals associated with slip bonds.

A possible molecular mechanism for mechanotransduction at cellular focal adhesion complexes

Mechanotransduction at focal adhesion complexes is key for various cellular events. Theoretical analyses were performed to predict a potential role of lipid membranes in modulating mechanotransduction at focal adhesions. Calculations suggested that the size of nanostructural constraints and mechanical pulling applied on lipid membranes affect the generation of cellular traction forces and signaling transduction at focal adhesions. This work provides predictions on how lipid membranes contribute to mechanotransduction at cellular focal adhesions.

Automated Cell Mechanical Characterization by On-Chip Sequential Squeezing: From Static to Dynamic

The mechanical properties of cells are harmless biomarkers for cell identification and disease diagnosis. Although many systems have been developed to evaluate the static mechanical properties of cells for biomedical research, their robustness, effectiveness, and cost do not meet clinical requirements or the experiments with a large number of cell samples. In this paper, we propose an approach for on-chip cell mechanical characterization by analyzing the dynamic behavior of cells as they pass through multiple constrictions. The proposed serpentine microfluidic channel consisted of 20 constrictions connected in series and divided into five rows for tracking cell dynamic behavior. Assisted by computer vision, the squeezing time of each cell through five rows of constrictions was automatically collected and filtered to evaluate the cell's mechanical deformability. We observed a decreasing passage time and increasing dynamic deformability of the cells as they passed through the multiple constrictions. The deformability increase rate of the HeLa cells was eight times greater than that of MEF cells. Moreover, the weak correlation between the deformability increase rate and the cell size indicated that cell recognition based on measuring the deformability increase rate could hardly be affected by the cell size variation. These findings showed that the deformability increase rate of the cell under on-chip sequential squeezing as a new index has great potential in cancer cell recognition.