1B Cell Adhesion Part 2
Tissue Engineering
Introduction and Cell Adhesion
Location: Gilman Hall, Johns Hopkins, Whiting School of Engineering.
Quantitative Measures of Cell Adhesion
Key Concept: The underlying equation
τdetachment = Fadhesion
System variables:
Q: volume flow rate
a: half-channel height
b: channel width
x: distance from mid-line
Goal: To determine adhesion forces based on these parameters.
Effects of Cell Adhesion
Cell adhesion impacts several cellular functions:
Survival
Migration
Proliferation
Extracellular matrix (ECM) formation and organization
Cell and nuclear morphology
Gene expression
Metabolism
Structure of the Cell (To an Engineer)
Key components include:
Glycoproteins
Glycocalyx
Transmembrane proteins
Cytoplasm
Nucleus
Cytoskeletal filaments
Lipid bilayer
Types of Cell Adhesions
Homotypic binding: Adhesion between similar cell types.
Heterotypic binding: Adhesion between different cell types.
Binding mediated by soluble linkers: Facilitating interactions via other molecules.
Binding to extracellular matrix: Involves cell-matrix interactions.
Classes of Cell Adhesion Receptors
Ig-like CAMs: e.g., NCAM, Ca++ independent; signals for cell organization.
Cadherins: Cell-cell adhesion, Ca++ dependent, important for embryo development.
Selectins: Carbohydrate-binding, transient during inflammatory responses.
Integrins
Structure: Hetero-dimeric, transmembrane proteins with alpha (α) and beta (β) subunits.
Binding Specificity:
α2β1 binds collagen I
α5β1 binds fibronectin
β2 binds various cell surface ligands
Binding Mechanism: Ca++ dependent.
Integrins and the Cytoskeleton
Function: Integrins couple the cytoskeleton to ECM via adhesion complexes.
Components include talin, vinculin, α-actinin, actin filaments.
Focal Adhesion Complexes
Composition: Multiple proteins; not required to memorize all.
Key Proteins:
Tensin
Talin
Vinculin
Paxillin (integral component)
Focal adhesion kinase (FAK) for signal transduction.
Focal Contact
Fibroblasts grown on culture dish vs. focal contact site: separation and gap specifics.
Focal Adhesion Formation
Key Steps:
Binding of ECM proteins initiates focal adhesion assembly.
Clustered integrins at contact sites strengthen adhesion.
Assembly and Maturation of Focal Adhesions
Key processes involve:
Receptor-matrix binding.
Linkage to actin cytoskeleton.
Signal transduction leading to actin polymerization.
Growing adhesions increase traction and stability.
Dynamic Nature of FA Maturation
Phases of Maturation:
Nascent to mature adhesion transition.
Myosin II involvement and actin dynamics.
Summary of Cell Structure
Key components of cell structure, including cell membrane, cytoskeleton, nucleus, and integrin-related proteins.
Concept 1: Environmental Cues
Cells receive cues from their environment (integrins facilitate this).
Outside-In Signaling
Sequence of molecular events:
Integrin-ECM engagement triggers phosphorylation of focal adhesion proteins.
Clustering and reinforcement of connections.
Regulation of downstream signaling pathways.
Concept 2: ECM Remodeling
Cells alter their environment through restructuring ECM.
Inside-Out Signaling
ECM remodeling affects cellular behavior and interactions with other signaling molecules.
Bidirectional Signaling in Tissue Formation
Cells integrate into pre-existing tissue by sensing ECM alignment and producing matching matrix.
Classic Experiment by Mina Bissell
Examined how cancer cells interact with their microenvironment.
Spatial Organization: 2D vs. 3D Culture
Comparison of cell behavior on two-dimensional surfaces vs. three-dimensional environments.
Mimicking Cellular 3D Architecture
Visual representation of how cells and ECM fibers are arranged spatially.
Review Concepts
Thermodynamic equilibrium in cell aggregation.
Characteristics of adhesion-dependent cells.
Mechanisms of cell attachment to substrates.
Strength measurement of cell attachment.
Types of cell adhesion molecules: Calcium dependency highlighted.
Integrin roles and mechanisms in signaling.
Structure and dynamics of adhesion complexes in 3D environments.