What is the Difference Between Focal Adhesion and Hemidesmosomes

The key difference between focal adhesion and hemidesmosomes is that focal adhesion mediates the adhesion between cells and the extracellular matrix while hemidesmosomes mediate anchoring of the epidermal keratin filament cytoskeleton to the extracellular matrix.

Focal adhesion and hemidesmosomes are two types of adhesive interactions. They are very important for the mechanical integrity of the skin. Focal adhesion and hemidesmosomes extend from the cell rear to the cell front. Moreover, they also play important roles in keratinocyte migration. Epidermal keratinocyte migration is linked to the wound healing process of re-epithelialization, which helps close the wounds.

CONTENTS

1. Overview and Key Difference
2. What is Focal Adhesion (Cell-Matrix Adhesion)
3. What are Hemidesmosomes
4. Similarities – Focal Adhesion and Hemidesmosomes
5. Focal Adhesion vs Hemidesmosomes in Tabular Form
6. Summary – Focal Adhesion vs Hemidesmosomes

What is Focal Adhesion (Cell-Matrix Adhesion)?

Focal adhesion is an adhesive site where the cells connect to the extracellular matrix. It contains clusters of transmembrane integrin receptors tethered at one end to the extracellular matrix and the other to actin stress fibers. Focal adhesion is responsible for cell traction and extracellular matrix reorganization. It mediates the tight connection between the cells and the extracellular matrix, enabling cells to communicate with the external environment. It also helps cell adhesion, migration, diffusion, differentiation, and apoptosis.

Focal adhesion is usually called cell-matrix adhesion. The integrin receptors are the core of focal adhesions. Integrins span the plasma membrane and connect different extracellular matrix components to the cell. The integrins form heterodimers containing alpha and beta subunits. This heterodimer binds to the extracellular matrix at its extracellular ligand-binding domain and anchors to the actin cytoskeleton at its cytosolic domain. Other proteins such as talin, alpha-actinin, vinculin, paxillin, and focal adhesion kinase are also later recruited to stabilize the focal adhesion. Furthermore, the changes in the focal adhesion that lack tone regulation can lead to cancer progression and metastasis.

What are Hemidesmosomes?

Hemidesmosomes mediate the anchoring of the epidermal keratin filament cytoskeleton to the extracellular matrix. Normally, hemidesmosomes are very small stud-like structures found in keratinocytes of the epidermis of the skin that attaches to the extracellular matrix. Hemidesmosomes are of two types: type 1 and 2. Type 1 hemidesmosomes are found in the stratified and pseudo-stratified epithelium. Type 1 hemidesmosomes have five main elements: integrin α6β4, plectin 1a, tetraspanin protein CD151, BPAG1e, and BPAG2. Type 2 hemidesmosomes contain integrin α6β4 and plectin without Bp antigens.

Genetic or acquired diseases cause disruption of hemidesmosome components, leading to skin blistering disorders between different layers of the skin. They are collectively called epidermolysis bullosa (EB). The typical symptoms of this disease include fragile skin, blister development, and erosion from minor physical stress. Mutations in 12 different genes that code for parts of the hemidesmosomes have led to epidermolysis bullosa. Based on different mutational causes, epidermolysis bullosa is divided into three types: EB simplex, dystrophic EB, and junctional EB.

What are the Similarities Between Focal Adhesion and Hemidesmosomes?

• Focal adhesion and hemidesmosomes are two types of adhesive interactions.
• They are very important for the mechanical integrity of the skin
• Both play a vital role in cellular signalling.
• They play important roles in the keratinocyte migration.
• Both are very important for skin homeostasis.
• Integrins are included in the structures of both.
• Changes in both adhesive interactions can cause different diseases.

What is the Difference Between Focal Adhesion and Hemidesmosomes?

Focal adhesion mediates the adhesion between cells and the extracellular matrix while hemidesmosomes mediate anchoring of the epidermal keratin filament cytoskeleton to the extracellular matrix. This is the key difference between focal adhesion and hemidesmosomes. Furthermore, focal adhesion is made up of integrins heterodimers containing alpha and beta subunits, talin, alpha-actinin, vinculin, paxillin, and focal adhesion kinase. On the other hand, hemidesmosomes are made up of integrin α6β4, plectin 1a, tetraspanin protein CD151, BPAG1e and BPAG2.

The following table presents the difference between focal adhesion and hemidesmosomes.

Summary – Focal Adhesion vs Hemidesmosomes

Focal adhesion and hemidesmosomes are two types of adhesive interactions that are very important for skin homeostasis. Focal adhesion mediates the adhesion between cells and the extracellular matrix, while hemidesmosomes mediate anchoring of the epidermal keratin filament cytoskeleton to the extracellular matrix. This is the key difference between focal adhesion and hemidesmosomes

Reference:

1. “Focal Adhesion.” An Overview | ScienceDirect Topics.
2. “Hemidesmosome.” An Overview | ScienceDirect Topics.

Image Courtesy:

1. “Focal Adhesions in Human Mesenchymal Stem Cells” By NIH Image Gallery (CC BY-NC 2.0) via Flickr
2. “Hemidesmosomes showing interaction between integrins and laminin” By lu.qianhe – Own work (CC BY-SA 4.0) via Commons Wikimedia