HEMIDESMOSOMES: DESCRIPTION, STRUCTURE AND FUNCTIONS - BIOLOGY - 2025

The hemidesmososmas are asymmetrical appearance structures that connect epithelial cells. The basal domains of the cell are linked to the underlying basal lamina. They are particularly important in tissues that are in constant mechanical tension.

These epithelial junctions are responsible for increasing the overall stability of the epithelial tissues due to the participation of the intermediate filaments of the cytoskeleton and the different components of the basal lamina. That is, they promote stable adhesions in connective tissue.

Scheme of a cell and its unions. 1. Basement membrane, 2. Cell nucleus, 3. Cytoplasm, 4. Desmosome, 5. Hemidesmosome.

Source Possible2006

The term hemidesmosome can be misleading. Although it is true that a hemidesmosome resembles a “half” desmosome (another type of structure associated with adhesion between neighboring cells), few of the biochemical components coincide between both structures, so the similarity is totally superficial.

In the classification of cell junctions, hemidesmosomes are considered anchor junctions, and are grouped together with tight junctions, belt desmosomes, and point desmosomes.

Anchor junctions are responsible for holding cells together, while the opposite category (gap junctions) have communication functions between adjacent cells.

Description

Cells are the building blocks of living things. However, the analogy with a brick or a structural block fails in some respects. Unlike the bricks of a building, adjacent cells do have a series of connections and communicate with each other.

Between cells, there are various structures that connect them and allow both contact and communication. One of these anchoring structures are desmosomes.

Hemidesmosomes are cell junctions found in different epithelia and are exposed to constant abrasion and mechanical forces.

In these regions, there is a potential separation between epithelial cells from the underlying connective tissue, thanks to mechanical stress. The term hemidesmosome comes from the apparent similarity to half desmosomes.

They are common in the skin, the cornea (a structure located in the eye), different mucous membranes of the oral cavity, the esophagus and the vagina.

They are located on the basal cell surface and provide an increase in the adhesion of the basal lamina.

Structure

A desmosome is an asymmetric connecting structure that is made up of two main parts:

• An internal cytoplasmic lamina found in association with intermediate filaments - the latter are also known as keratins or tonofilaments.
• The second component of hemidesmosomes is the outer membrane plate that is responsible for connecting the hemidesmosome with the basal lamina. The anchor filaments (made up of laminin 5) and integrin participate in this association.

Proteins that make up the hemidesmosome

In the plaque of hemidesmosomes there are the following main proteins:

Plectin

Plectin is responsible for forming cross-links between the intermediate filaments and the adhesion plate of the desmosome.

This protein has been shown to have the ability to interact with other structures, such as microtubules, actin filaments, among others. Therefore, they are crucial in the interaction with the cytoskeleton.

BP 230

Its function is to fix the intermediate filaments to the intracellular adhesion plate. It is called 230, since its size is 230 kDa.

The BP 230 protein has been linked to various diseases. The lack of a properly functioning BP 230 causes a condition called bullous pemphigoid, which causes the appearance of blisters.

In patients suffering from this disease, it has been possible to detect a high level of antibodies against the components of hemidesmosomes.

Erbina

It is a protein with a molecular weight of 180 kDa. It is involved with the connection between BP 230 and the integrins.

Integrins

Unlike desmosomes that are rich in cadherins, hemidesmosomes have high amounts of a type of protein called integrins.

Specifically, we found the α ₆ β ₄ integrin protein. It is a heterodimer formed by two polypeptide chains. There is an extracellular domain that enters the basal lamina and establishes interactions with laminins (laminin 5).

The anchoring filaments are molecules formed by laminin 5 that are located in the extracellular region of hemidesmosomes. The filaments extend from the integrin molecules to the basement membrane.

This interaction between laminin 5 and the mentioned integrin is crucial for the formation of the hemidesmosome and maintaining adhesion in the epithelium.

Like BP 230, the incorrect functionality of the integrins has been linked to certain pathologies. One of them is bullous epidermolysis, a hereditary skin condition. Patients suffering from this disease have mutations in the gene that codes for integrins.

Type XVII collagen

They are proteins that cross membranes and have a weight of 180 kDa. They are related to the expression and function of laminin 5.

Biochemical and medical studies of this important protein have elucidated its role in inhibiting the migration of cells located in the endothelium during the process of angiogenesis (formation of blood vessels). In addition, it regulates the movements of keratinocytes in the skin.

CD151

It is a 32 kDa glycoprotein and plays an indispensable role in the accumulation of integrin receptor proteins. This fact makes it possible to facilitate interactions between cells and the extracellular matrix.

It is important to avoid confusing the terms anchor filaments and anchor fibrils, as both are used quite frequently in cell biology. The anchor filaments are made up of laminin 5 and type XVII collagen.

In contrast, the anchoring fibrils are made up of type VII collagen. Both structures have different roles in cell adhesion.

Features

The main function of hemidesmosomes is the attachment of cells to the basal lamina. The latter is a thin layer of extracellular matrix whose function is to separate epithelial tissue and cells. As its name implies, the extracellular matrix is ​​not made up of cells, but of external protein molecules.

In simpler words; Hemidesmosomes are molecular structures that make sure to hold our skin together and work like a kind of screw.

They are located in regions (mucosa, eyes, among others) that are constantly under mechanical stress and their presence helps to maintain the union between the cell and the lamina.

References

1. Freinkel, RK, & Woodley, DT (Eds.). (2001). The biology of the skin. CRC Press.
2. Kanitakis, J. (2002). Anatomy, histology and immunohistochemistry of normal human skin. European journal of dermatology, 12 (4), 390-401.
3. Kierszenbaum, AL (2012). Histology and cell biology. Elsevier Brazil.
4. Ross, MH, & Pawlina, W. (2006). Histology. Lippincott Williams & Wilkins.
5. Welsch, U., & Sobotta, J. (2008). Histology. Panamerican Medical Ed.