Super-Resolution Imaging Approaches for Quantifying F-Actin in Immune Cells

Advanced optical imaging for the rational design of nanomedicines

Despite the enormous potential of nanomedicines to shape the future of medicine, their clinical translation remains suboptimal. Translational challenges are present in every step of the development pipeline, from a lack of understanding of patient heterogeneity to insufficient insights on nanoparticle properties and their impact on material-cell interactions. Here, we discuss how the adoption of advanced optical microscopy techniques, such as super-resolution optical microscopies, correlative techniques, and high-content modalities, could aid the rational design of nanocarriers, by characterizing the cell, the nanomaterial, and their interaction with unprecedented spatial and/or temporal detail. In this nanomedicine arena, we will discuss how the implementation of these techniques, with their versatility and specificity, can yield high volumes of multi-parametric data; and how machine learning can aid the rapid advances in microscopy: from image acquisition to data interpretation.

Filament displacement image analytics tool for use in investigating dynamics of dense microtubule networks

The fate and motion of cells is influenced by a variety of physical characteristics of their microenvironments. Traditionally, mechanobiology focuses on external mechanical phenomena such as cell movement and environmental sensing. However, cells are inherently dynamic, where internal waves and internal oscillations are a hallmark of living cells observed under a microscope. We propose that these internal mechanical rhythms provide valuable information about cell health. Therefore, it is valuable to capture the rhythms inside cells and quantify how drugs or physical interventions affect a cell's internal dynamics. One of the key dynamical entities inside cells is the microtubule network. Typically, microtubule dynamics are measured by end-protein tracking. In contrast, this paper introduces an easy-to-implement approach to measure the lateral motion of the microtubule filaments embedded within dense networks with (at least) confocal resolution image sequences. Our tool couples the computer vision algorithm Optical Flow with an anisotropic, rotating Laplacian of Gaussian filtering to characterize the lateral motion of dense microtubule networks. We then showcase additional image analytics used to understand the effect of microtubule orientation and regional location on lateral motion. We argue that our tool and these additional metrics provide a fuller picture of the active forcing environment within cells.

Roles of the cytoskeleton in human diseases

Recently, researches have revealed the key roles of the cytoskeleton in the occurrence and development of multiple diseases, suggesting that targeting the cytoskeleton is a viable approach for treating numerous refractory diseases. The cytoskeleton is a highly structured and complex network composed of actin filaments, microtubules, and intermediate filaments. In normal cells, these three cytoskeleton components are highly integrated and coordinated. However, the cytoskeleton undergoes drastic remodeling in cytoskeleton-related diseases, causing changes in cell polarity, affecting the cell cycle, leading to senescent diseases, and influencing cell migration to accelerate cancer metastasis. Additionally, mutations or abnormalities in cytoskeletal proteins and their related proteins are closely associated with several congenital diseases. Therefore, this review summarizes the roles of the cytoskeleton in cytoskeleton-related diseases as well as its potential roles in disease treatment to provide insights regarding the physiological functions and pathological roles of the cytoskeleton.

TatA and TatB generate a hydrophobic mismatch important for the function and assembly of the Tat translocon in Escherichia coli

The twin-arginine translocation (Tat) system serves to translocate folded proteins across energy-transducing membranes in bacteria, archaea, plastids, and some mitochondria. In Escherichia coli, TatA, TatB, and TatC constitute functional translocons. TatA and TatB both possess an N-terminal transmembrane helix (TMH) followed by an amphipathic helix. The TMHs of TatA and TatB generate a hydrophobic mismatch with the membrane, as the helices comprise only 12 consecutive hydrophobic residues; however, the purpose of this mismatch is unclear. Here, we shortened or extended this stretch of hydrophobic residues in either TatA, TatB, or both and analyzed effects on translocon function and assembly. We found the WT length helices functioned best, but some variation was clearly tolerated. Defects in function were exacerbated by simultaneous mutations in TatA and TatB, indicating partial compensation of mutations in each by the other. Furthermore, length variation in TatB destabilized TatBC-containing complexes, revealing that the 12-residue-length is important but not essential for this interaction and translocon assembly. To also address potential effects of helix length on TatA interactions, we characterized these interactions by molecular dynamics simulations, after having characterized the TatA assemblies by metal-tagging transmission electron microscopy. In these simulations, we found that interacting short TMHs of larger TatA assemblies were thinning the membrane and—together with laterally-aligned tilted amphipathic helices—generated a deep V-shaped membrane groove. We propose the 12 consecutive hydrophobic residues may thus serve to destabilize the membrane during Tat transport, and their conservation could represent a delicate compromise between functionality and minimization of proton leakage.

Metrics of 2D immunological synapses in human T cells via high-content confocal cell imaging

Immunological synapses (IS) are the privileged site of complex information transfer between T cells and antigen presenting cells. IS are highly structured in terms of actin and tubulin cytoskeleton organization, receptor and proximal signal patterning, and intracellular organelle polarization. The magnitude and quality of T cell responses upon antigen recognition is dependent on IS molecular organization. For that reason, methods to precisely assess IS parameters are crucial to monitor T cell activation and function in health and disease, but also for T cell centered therapeutic intervention. Confocal and super-resolution microscopy approaches have allowed to characterize the complex structure of the T cell IS. However, those approaches suffer from a low-throughput and low-content format precluding multi-parametric classification of IS across large numbers of samples or stimulatory conditions. Here, we present a protocol of high-content confocal cell imaging in a 384-well plate format adapted to the unbiased analysis of primary T cells forming IS over pre-coated stimulatory molecules. The protocol focuses on the staining of F-actin, pericentrin and granzyme B in CD8⁺ T cells, but is transposable to other IS molecular markers and lymphocyte subsets. We discuss potential applications offered by the multi-parametric characterization of T cell IS in a high-throughput format.