Cadherin and integrin regulation of epithelial cell migration

Thymosin β4 Regulates the Differentiation of Thymocytes by Controlling the Cytoskeletal Rearrangement and Mitochondrial Transfer of Thymus Epithelial Cells

The thymus is one of the most crucial immunological organs, undergoing visible age-related shrinkage. Thymic epithelial cells (TECs) play a vital role in maintaining the normal function of the thymus, and their degeneration is the primary cause of age-induced thymic devolution. Thymosin β4 (Tβ4) serves as a significant important G-actin sequestering peptide. The objective of this study was to explore whether Tβ4 influences thymocyte differentiation by regulating the cytoskeletal rearrangement and mitochondrial transfer of TECs. A combination of H&E staining, immunofluorescence, transmission electron microscopy, RT-qPCR, flow cytometry, cytoskeletal immunolabeling, and mitochondrial immunolabeling were employed to observe the effects of Tβ4 on TECs' skeleton rearrangement, mitochondrial transfer, and thymocyte differentiation. The study revealed that the Tβ4 primarily regulates the formation of microfilaments and the mitochondrial transfer of TECs, along with the formation and maturation of double-negative cells (CD4-CD8-) and CD4 single-positive cells (CD3+TCRβ+CD4+CD8-) thymocytes. This study suggests that Tβ4 plays a crucial role in thymocyte differentiation by influencing the cytoskeletal rearrangement and mitochondrial transfer of TECs. These effects may be associated with Tβ4's impact on the aggregation of F-actin. This finding opens up new avenues for research in the field of immune aging.

The Interaction of Mechanics and the Hippo Pathway in Drosophila melanogaster

Drosophila melanogaster has emerged as an ideal system for studying the networks that control tissue development and homeostasis and, given the similarity of the pathways involved, controlled and uncontrolled growth in mammalian systems. The signaling pathways used in patterning the Drosophila wing disc are well known and result in the emergence of interaction of these pathways with the Hippo signaling pathway, which plays a central role in controlling cell proliferation and apoptosis. Mechanical effects are another major factor in the control of growth, but far less is known about how they exert their control. Herein, we develop a mathematical model that integrates the mechanical interactions between cells, which occur via adherens and tight junctions, with the intracellular actin network and the Hippo pathway so as to better understand cell-autonomous and non-autonomous control of growth in response to mechanical forces.

Long-term adherent cell dynamics emerging from energetic and frictional interactions at the interface

Cell adhesion plays an important role in a wide range of biological situations, including embryonic development, cancer invasion, and wound healing. Although several computational models describing adhesion dynamics have been proposed, models applicable to long-term, large-length-scale cell dynamics are lacking. In this study we investigated possible states of long-term adherent cell dynamics in three-dimensional space by constructing a continuum model of interfacial interactions between adhesive surfaces. In this model a pseudointerface is supposed between each pair of triangular elements that discretize cell surfaces. By introducing a distance between each pair of elements, the physical properties of the interface are given by interfacial energy and friction. The proposed model was implemented into the model of a nonconservative fluid cell membrane where the cell membrane dynamically flows with turnover. Using the implemented model, numerical simulations of adherent cell dynamics on a substrate under flow were performed. The simulations not only reproduced the previously reported dynamics of adherent cells, such as detachment, rolling, and fixation on the substrate, but also discovered other dynamic states, including cell slipping and membrane flow patterns, corresponding to behaviors that occur on much longer timescales than the dissociation of adhesion molecules. These results illustrate the variety of long-term adherent cell dynamics, which are more diverse than the short-term ones. The proposed model can be extended to arbitrarily shaped membranes, thus being useful for the mechanical analysis of a wide range of long-term cell dynamics where adhesion is essential.

Mucosal healing and inflammatory bowel disease: Therapeutic implications and new targets

Mucosal healing (MH) is vital in maintaining homeostasis within the gut and protecting against injury and infections. Multiple factors and signaling pathways contribute in a dynamic and coordinated manner to maintain intestinal homeostasis and mucosal regeneration/repair. However, when intestinal homeostasis becomes chronically disturbed and an inflammatory immune response is constitutively active due to impairment of the intestinal epithelial barrier autoimmune disease results, particularly inflammatory bowel disease (IBD). Many proteins and signaling pathways become dysregulated or impaired during these pathological conditions, with the mechanisms of regulation just beginning to be understood. Consequently, there remains a relative lack of broadly effective therapeutics that can restore MH due to the complexity of both the disease and healing processes, so tissue damage in the gastrointestinal tract of patients, even those in clinical remission, persists. With increased understanding of the molecular mechanisms of IBD and MH, tissue damage from autoimmune disease may in the future be ameliorated by developing therapeutics that enhance the body’s own healing response. In this review, we introduce the concept of mucosal healing and its relevance in IBD as well as discuss the mechanisms of IBD and potential strategies for altering these processes and inducing MH.

The tetrapartite synapse in neuropsychiatric disorders: Matrix metalloproteinases (MMPs) as promising targets for treatment and rational drug design

Inflammation and an exacerbated immune response are widely accepted contributing mechanisms to the genesis and progression of major neuropsychiatric disorders. However, despite the impressive advances in understanding the neurobiology of these disorders, there is still no approved drug directly linked to the regulation of inflammation or brain immune responses. Importantly, matrix metalloproteinases (MMPs) comprise a group of structurally related endopeptidases primarily involved in remodeling extracellular matrix (ECM). In the central nervous system (CNS), these proteases control synaptic plasticity and strength, patency of the blood-brain barrier, and glia-neuron interactions through cleaved and non-cleaved mediators. Several pieces of evidence have pointed to a complex scenario of MMPs dysregulation triggered by neuroinflammation. Furthermore, major psychiatric disorders' affective symptoms and neurocognitive abnormalities are related to MMPs-mediated ECM changes and neuroglia activation. In the past decade, research efforts have been directed to broad-spectrum MMPs inhibitors with frustrating clinical results. However, in the light of recent advances in combinatorial chemistry and drug design technologies, specific and CNS-oriented MMPs modulators have been proposed as a new frontier of therapy for regulating ECM properties in the CNS. Therefore, here we aim to discuss the state of the art of MMPs and ECM abnormalities in major neuropsychiatric disorders, namely depression, bipolar disorder, and schizophrenia, the possible neuro-immune interactions involved in this complex scenario of MMPs dysregulation and propose these endopeptidases as promising targets for rational drug design.

A new role for Notch in the control of polarity and asymmetric cell division of developing T cells

A fundamental question in biology is how single cells can reliably produce progeny of different cell types. Notch signalling frequently facilitates fate determination. Asymmetric cell division (ACD) often controls segregation of Notch signalling by imposing unequal inheritance of regulators of Notch. Here, we assessed the functional relationship between Notch and ACD in mouse T cell development. To attain immunological specificity, developing T cells must pass through a pivotal stage termed β-selection, which involves Notch signalling and ACD. We assessed functional interactions between Notch1 and ACD during β-selection using direct presentation of Notch ligands, DL1 and DL4, and pharmacological inhibition of Notch signalling. Contrary to prevailing models, we demonstrate that Notch controls the distribution of Notch1 itself and cell fate determinants, α-Adaptin and Numb. Further, Notch and CXCR4 signalling cooperated to drive polarity during division. Thus, Notch signalling directly orchestrates ACD, and Notch1 is differentially inherited by sibling cells.

Astrocytes in Migration

Cell migration is a fundamental phenomenon that underlies tissue morphogenesis, wound healing, immune response, and cancer metastasis. Great progresses have been made in research methodologies, with cell migration identified as a highly orchestrated process. Brain is considered the most complex organ in the human body, containing many types of neural cells with astrocytes playing crucial roles in monitoring normal functions of the central nervous system. Astrocytes are mostly quiescent under normal physiological conditions in the adult brain but become migratory after injury. Under most known pathological conditions in the brain, spinal cord and retina, astrocytes are activated and become hypertrophic, hyperplastic, and up-regulating GFAP based on the grades of severity. These three observations are the hallmark in glia scar formation-astrogliosis. The reactivation process is initiated with structural changes involving cell process migration and ended with cell migration. Detailed mechanisms in astrocyte migration have not been studied extensively and remain largely unknown. Here, we therefore attempt to review the mechanisms in migration of astrocytes.

Microfluidic generation of gradient hydrogels to modulate hematopoietic stem cell culture environment

The bone marrow provides spatially and temporally variable signals that impact the behavior of hematopoietic stem cells (HSCs). While multiple biomolecular signals and bone marrow cell populations have been proposed as key regulators of HSC fate, new tools are required to probe their importance and mechanisms of action. Here, a novel method based on a microfluidic mixing platform to create small volume, 3D hydrogel constructs containing overlapping patterns of cell and matrix constituents inspired by the HSC niche is described. This approach is used to generate hydrogels containing opposing gradients of fluorescent microspheres, MC3T3-E1 osteoblasts, primary murine hematopoietic stem and progenitor cells (HSPCs), and combinations thereof in a manner independent of hydrogel density and cell/particle size. Three different analytical methods are described to characterize local properties of these hydrogels at multiple scales: 1) whole construct fluorescent analysis; 2) multi-photon imaging of individual cells within the construct; 3) retrieval of discrete sub-regions from the hydrogel post-culture. The approach reported here allows the creation of stable gradients of cell and material cues within a single, optically translucent 3D biomaterial to enable a range of investigations regarding how microenvironmental signals impact cell fate.

Topographical control of multiple cell adhesion molecules for traction force microscopy

Cellular traction forces are important quantitative measures in cell biology as they have provided much insight into cell behavior in contexts such as cellular migration, differentiation, and disease progression. However, the complex environment in vivo permits application of cell traction forces through multiple types of cell adhesion molecules. Currently available approaches to differentiate traction forces among multiple cell adhesion molecules are limited to specialized approaches to decouple cell-cell from cell-extracellular matrix (ECM) tractions. Here, we present a technique which uses indirect micropatterning onto a polyacrylamide gel to pattern multiple, spatially distinct fluorescently labeled ECM proteins, specifically gelatin and fibronectin (Fn), and confine the area to which cells can adhere. We found that cells interacting with both gelatin and Fn altered their traction forces significantly in comparison to cells on Fn-only substrates. This crosstalk interaction resulted in a decrease in overall traction forces on dual-patterned substrates as compared to cells on Fn-only substrates. This illustrates the unique need to study such interactions and demonstrates great potential in future studies in multi-ligand environments. Current micropatterning techniques on glass can easily be adapted to present other protein classes, such as cadherins, while maintaining control of adhesion spacing, cell spread area, and stiffness, each of which are important regulators of cell mechanobiology.

The study of polarisation in single cells using model cell membranes

The apicobasal polarisation of epithelial cells within an epithelium is critical for its function as a selective barrier. Microenvironmental parameters, including cell-matrix and cell-cell interactions, contribute to the initiation and orientation of this polarity. However, it is often non-trivial to decipher the differential effects of these parameters in a controlled manner using traditional in vitro platforms. A reductionist platform, consisting of E-cadherin coupled onto laterally mobile supported lipid bilayers, was utilised to mimic E-cadherin presentation in the cell membrane. These functionalised bilayers were generated either on flat 2D surfaces or the interior surfaces of round microwells. This platform enabled the study of E-cadherin adhesion and the initiation of polarisation in a controlled environment, where the dimensionality of the microenvironment, type of protein coating and cell shape could be independently studied. A high proportion of single epithelial cells interacted with and clustered cellular E-cadherin in the presence of E-cadherin functionalised bilayers, which was reduced in the presence of integrin-mediated adhesion. The differential response in E-cadherin clustering correlated with the polarisation of E-cadherin and Na,K-ATPase, a reporter for the induction of basolateral polarity. Neither the three-dimensional presentation of E-cadherin nor the cell shape affected E-cadherin clustering or polarisation in single cells. Thus, the mobile presentation of E-cadherin was sufficient to mimic a cell-cell contact and induce basolateral polarisation in single cells.

Innovative method for quantification of cell-cell adhesion in 96-well plates

Cell adhesion is an important part of many complex biological processes. It plays crucial roles in cancer, development, and maintenance of stem cell compartment. The measurement of adhesion under experimental conditions might provide important information for cell biology. There are several protocols to measure adhesion, usually based on washing or shaking to remove non-adherent cells. Here, we describe a quantification method based on gravitational force to measure adhesion in a 96-well format. Non-adherent cells are separated and only vital cells are quantified with a colorimetric assay. As example we provide the quantification of cell-cell interaction with blocking function antibodies for CD44, an N-cadherin antagonists and the stromal cell derived factor-1 alpha (SDF-1). This method facilitates fast and reliable measurement of cell adhesion in multiwell format for screening assays.