Curved adhesions mediate cell attachment to soft matrix fibres in three dimensions

Engineering the Cellular Microenvironment: Integrating Three-Dimensional Nontopographical and Two-Dimensional Biochemical Cues for Precise Control of Cellular Behavior

The development of biomaterials capable of regulating cellular processes and guiding cell fate decisions has broad implications in tissue engineering, regenerative medicine, and cell-based assays for drug development and disease modeling. Recent studies have shown that three-dimensional (3D) nanoscale physical cues such as nanotopography can modulate various cellular processes like adhesion and endocytosis by inducing nanoscale curvature on the plasma and nuclear membranes. Two-dimensional (2D) biochemical cues such as protein micropatterns can also regulate cell function and fate by controlling cellular geometries. Development of biomaterials with precise control over nanoscale physical and biochemical cues can significantly influence programming cell function and fate. In this study, we utilized a laser-assisted micropatterning technique to manipulate the 2D architectures of cells on 3D nanopillar platforms. We performed a comprehensive analysis of cellular and nuclear morphology and deformation on both nanopillar and flat substrates. Our findings demonstrate the precise engineering of single cell architectures through 2D micropatterning on nanopillar platforms. We show that the coupling between the nuclear and cell shape is disrupted on nanopillar surfaces compared to flat surfaces. Furthermore, our results suggest that cell elongation on nanopillars enhances nanopillar-induced endocytosis. We believe our platform serves as a versatile tool for further explorations into programming cell function and fate through combined physical cues that create nanoscale curvature on cell membranes and biochemical cues that control the geometry of the cell.

Filopodia: integrating cellular functions with theoretical models

Filopodia, widely distributed on cell surfaces, are distinguished by their dynamic extensions, playing pivotal roles in a myriad of biological processes. Their functions span from mechanosensing and guidance to cell-cell communication during cellular organization in the early embryo. Filopodia have significant roles in pathogenic processes, such as cancer invasion and viral dissemination. Molecular mapping of the filopodome has revealed generic components essential for filopodia functions. In parallel, recent insights into biophysical mechanisms governing filopodia dynamics have provided the foundation for broader investigations of filopodia's biological functions. We highlight recent discoveries of engagement of filopodia in various stages of development and pathogenesis and present an overview of intricate molecular and physical features of these cellular structures across a spectrum of cellular activities.

Membrane Curvature Promotes ER-PM Contact Formation via Junctophilin-EHD Interactions

Contact sites between the endoplasmic reticulum (ER) and the plasma membrane (PM) play a crucial role in governing calcium regulation and lipid homeostasis. Despite their significance, the factors regulating their spatial distribution on the PM remain elusive. Inspired by observations in cardiomyocytes, where ER-PM contact sites concentrate on tubular PM invaginations known as transverse tubules (T-tubules), we hypothesize that the PM curvature plays a role in ER-PM contact formation. Through precise control of PM invaginations, we show that PM curvatures locally induce the formation of ER-PM contacts in cardiomyocytes. Intriguingly, the junctophilin family of ER-PM tethering proteins, specifically expressed in excitable cells, is the key player in this process, while the ubiquitously expressed extended synaptotagmin 2 does not show a preference for PM curvature. At the mechanistic level, we find that the low complexity region (LCR) and the MORN motifs of junctophilins can independently bind to the PM, but both the LCR and MORN motifs are required for targeting PM curvatures. By examining the junctophilin interactome, we identify a family of curvature-sensing proteins, Eps15-homology domain containing proteins (EHDs), that interact with the MORN_LCR motifs and facilitate junctophilins' preferential tethering to curved PM. These findings highlight the pivotal role of PM curvature in the formation of ER-PM contacts in cardiomyocytes and unveil a novel mechanism for the spatial regulation of ER-PM contacts through PM curvature modulation.

Coaching ribosome biogenesis from the nuclear periphery

Severe invagination of the nuclear envelope is a hallmark of cancers, aging, neurodegeneration, and infections. However, the outcomes of nuclear invagination remain unclear. This work identified a new function of nuclear invagination: regulating ribosome biogenesis. With expansion microscopy, we observed frequent physical contact between nuclear invaginations and nucleoli. Surprisingly, the higher the invagination curvature, the more ribosomal RNA and pre-ribosomes are made in the contacted nucleolus. By growing cells on nanopillars that generate nuclear invaginations with desired curvatures, we can increase and decrease ribosome biogenesis. Based on this causation, we repressed the ribosome levels in breast cancer and progeria cells by growing cells on low-curvature nanopillars, indicating that overactivated ribosome biogenesis can be rescued by reshaping nuclei. Mechanistically, high-curvature nuclear invaginations reduce heterochromatin and enrich nuclear pore complexes, which promote ribosome biogenesis. We anticipate that our findings will serve as a foundation for further studies on nuclear deformation.

Novel tools to study cell-ECM interactions, cell adhesion dynamics and migration

Integrin-mediated cell adhesion is essential for cell migration, mechanotransduction and tissue integrity. In vivo, these processes are regulated by complex physicochemical signals from the extracellular matrix (ECM). These nuanced cues, including molecular composition, rigidity and topology, call for sophisticated systems to faithfully explore cell behaviour. Here, we discuss recent methodological advances in cell-ECM adhesion research and compile a toolbox of techniques that we expect to shape this field in future. We outline methodological breakthroughs facilitating the transition from rigid 2D substrates to more complex and dynamic 3D systems, as well as advances in super-resolution imaging for an in-depth understanding of adhesion nanostructure. Selected methods are exemplified with relevant biological findings to underscore their applicability in cell adhesion research. We expect this new "toolbox" of methods will allow for a closer approximation of in vitro experimental setups to in vivo conditions, providing deeper insights into physiological and pathophysiological processes associated with cell-ECM adhesion.

Single molecule imaging unveils cellular architecture, dynamics and mechanobiology

The biomechanical regulation of the cytoskeleton and cell adhesions underlies various essential cellular functions. Studying them requires visualizing their nanostructure and molecular dynamics with evermore precise spatio-temporal resolution. In this review we will focus on the recent advances in single molecule fluorescence imaging techniques and discuss how they improve our understanding of mechanically sensitive cellular structures such as adhesions and the cytoskeleton. We will also discuss future directions for research, emphasizing on the 3D nature of cellular structures and tissues, their mechanical regulation at the molecule level, as well as how super-resolution microscopy will enhance our knowledge on protein structure and conformational changes in the cellular context.

Protein-membrane interactions: sensing and generating curvature

Biological membranes are integral cellular structures that can be curved into various geometries. These curved structures are abundant in cells as they are essential for various physiological processes. However, curved membranes are inherently unstable, especially on nanometer length scales. To stabilize curved membranes, cells can utilize proteins that sense and generate membrane curvature. In this review, we summarize recent research that has advanced our understanding of interactions between proteins and curved membrane surfaces, as well as work that has expanded our ability to study curvature sensing and generation. Additionally, we look at specific examples of cellular processes that require membrane curvature, such as neurotransmission, clathrin-mediated endocytosis (CME), and organelle biogenesis.

Curvature-induced clustering of cell adhesion proteins

Cell adhesion proteins typically form stable clusters that anchor the cell membrane to its environment. Several works have suggested that cell membrane protein clusters can emerge from a local feedback between the membrane curvature and the density of proteins. Here, we investigate the effect of such a curvature-sensing mechanism in the context of cell adhesion proteins. We show how clustering emerges in an intermediate range of adhesion and curvature-sensing strengths. We identify key differences with the tilt-induced gradient sensing mechanism we previously proposed (Lin et al., arXiv:2307.03670).

All the small things: Nanoscale matrix alterations in aging tissues

Cellular aging stems from multifaceted intra- and extracellular molecular changes that lead to the gradual deterioration of biological function. Altered extracellular matrix (ECM) properties that include biochemical, structural, and mechanical perturbations direct cellular- and tissue-level dysfunction. With recent advancements in high-resolution imaging modalities and nanomaterial strategies, the importance of nanoscale ECM features has come into focus. Here, we provide an updated window into micro- to nano-scale ECM properties that are altered with age and in age-related disease, and the impact these altered small-scale ECM properties have on cellular function. We anticipate future impactful research will incorporate nanoscale ECM features in the design of new biomaterials and call on the tissue biology field to work collaboratively with the nanomaterials community.

Reduced PaxillinB localization to cell-substrate adhesions promotes cell migration in Dictyostelium

Many cells adhere to extracellular matrix for efficient cell migration. This adhesion is mediated by focal adhesions, a protein complex linking the extracellular matrix to the intracellular cytoskeleton. Focal adhesions have been studied extensively in mesenchymal cells, but recent research in physiological contexts and amoeboid cells suggest focal adhesion regulation differs from the mesenchymal focal adhesion paradigm. We used Dictyostelium discoideum to uncover new mechanisms of focal adhesion regulation, as Dictyostelium are amoeboid cells that form focal adhesion-like structures for migration. We show that PaxillinB, the Dictyostelium homologue of Paxillin, localizes to dynamic focal adhesion-like structures during Dictyostelium migration. Unexpectedly, reduced PaxillinB recruitment to these structures increases Dictyostelium cell migration. Quantitative analysis of focal adhesion size and dynamics show that lack of PaxillinB recruitment to focal adhesions does not alter focal adhesion size, but rather increases focal adhesion turnover. These findings are in direct contrast to Paxillin function at focal adhesions during mesenchymal migration, challenging the established focal adhesion model.