Name: tight junction proteins and cell barriers
Uploaded: 2023-04-30T11:55:38.000Z
Duration: 1 min 29 s
Channel: JoVE

Dans des organes tels que les reins et les intestins, les cellules épithéliales sont scellées par des jonctions serrées pour empêcher le flux de macromolécules, d’ions et de petits solutés dans l’espace paracellulaire.
Les jonctions serrées comprennent principalement des protéines transmembranaires claudine et occludine, chacune avec quatre hélices alpha couvrant la membrane.
Des rangées de claudines et d’occludines polymérisent sur la membrane, formant un réseau de brins d’étanchéité.
Ces brins se fixent à des brins similaires de protéines sur la cellule adjacente par leurs boucles extracellulaires, maintenant ainsi les deux membranes ensemble.
Du côté cytoplasmique, les queues C-terminales de ces protéines s’associent aux domaines PDZ de grandes protéines d’échafaudage appelées zonula occludens ou ZO.
Les protéines ZO ont plusieurs domaines de liaison aux protéines et peuvent donc se lier aux claudines, aux occludines, à l’actine et à d’autres protéines ZO, formant un maillage qui organise et stabilise ces brins de scellement.
En plus de sceller l’espace paracellulaire, les jonctions serrées empêchent également le mouvement latéral des protéines, telles que les transporteurs de glucose, le long de la membrane. Cela aide à localiser ces protéines à la surface apicale de l’épithélium intestinal pour l’absorption du glucose.

<ol>
	<li>Sawada, Norimasa. « Maladies humaines liées aux jonctions serrées. » Pathology international 63.1 (2013) : 1-12. <a href="https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7168075/">Lien</a></li>
	<li>Anderson, James M., et Christina M. Van Itallie. « Physiologie et fonction de la jonction serrée. » Cold Spring Harbor perspectives in biology 1.2 (2009) : a002584. <a href="https://cshperspectives.cshlp.org/content/1/2/a002584.full">Lien</a></li>
	<li>Mariano, Cibelle et al. « Un regard sur la tricelluline et son rôle dans la formation et le maintien des jonctions serrées. » Revue européenne de biologie cellulaire 90.10 (2011) : 787-796. <a href=" https://d1wqtxts1xzle7.cloudfront.net/52322075/A_look_at_tricellulin_and_its_role_in_ti20170327-17112-1qhpwe8-libre.pdf?1490608194=&response-content-disposition=inline%3B+filename%3DA_look_at_tricellulin_and_its_role_in_ti.pdf&Expires=1654205963&Signature=IelR0FUZCC6ZcqAcJvs1JTGe6liRDBX6aqaYzcw4sMZ2yqyhu5BuZ9DDbujaDRUN9SwX20yuCRLRyzxl6MWAa4QfY2cZ1wtZb4qfoi5otW~z0rhB3ba231uB1~pdP0rZpdHB4~snYhLr-~nZRsoaUqTFJmJaJXpxtHnoBGC4HFP29Q8D3q0rNHNDJGq9Qx9SfcLWmDISH7n8IfsUozT6rdpn421eOVufn5lNVunpqMX6iiRAT4D7p8bJEPpfd2~3cygJP7Ltc32RiIm2RHGvp9CRUoXs015y2aR4A7--dka7UzL97Aa~DDZ8ES90wX9D58qA~jX24DnmzNeNwlAayg__&Key-Pair-Id=APKAJLOHF5GGSLRBV4ZA">Lien</a></li>
</ol>

jonctions serrées

Tight Junctions

Les jonctions serrées sont des joints moléculaires entre les cellules qui empêchent la fuite de fluides, d'ions et d'autres petits solutés à travers les cavités et les compartiments des organismes multicellulaires. Ils sont principalement composés de protéines transmembranaires claudine et occludine, ainsi que d'autres protéines telles que la tricelluline et la MAJ(molécule d'adhésion jonctionnelle). Toutes ces protéines sont des protéines transmembranaires à 4 passages, à l'exception de MAJ, qui est une protéine transmembranaire à un seul passage appartenant à la superfamille des immunoglobulines. Les domaines extracellulaires de ces protéines à jonction serrée interagissent avec ceux de la membrane cellulaire adjacente, réunissant et scellant ainsi les deux cellules adjacentes.

Perméabilité Sélective des Jonctions Serrées

Il existe plusieurs isoformes de la claudine transmembranaire, avec jusqu'à 24 types différents exprimés chez l'homme. La diversité de la protéine claudine confère une perméabilité sélective aux différentes jonctions serrées. Par exemple, la claudine-16, exprimée dans l’épithélium rénal, augmente la perméabilité aux ions magnésium, permettant ainsi leur réabsorption du sang lors de la filtration. En revanche, la claudine-5 exprimée dans les cellules endothéliales des capillaires cérébraux diminue sélectivement la perméabilité ionique à travers la barrière hémato-encéphalique.

Jonctions Tricellulaires

En plus de sceller les espaces entre deux cellules, les jonctions serrées scellent également les espaces formés à la jonction de trois cellules - une jonction tricellulaire. La structure des jonctions tricellulaires a été observée pour la première fois dans les années 1970 par microscopie électronique à congélation. Au niveau de ces jonctions, les brins de scellement sont orientés perpendiculairement aux brins des jonctions serrées bicellulaires. Le point de contact tricellulaire forme ainsi un tube vertical étroit d’environ 10 nm de diamètre, qui contrôle le mouvement paracellulaire des molécules.

La tricelluline a été la première protéine identifiée à se concentrer au niveau de ces jonctions tricellulaires. Il partage une homologie de séquence avec les protéines occludines et présente quatre isoformes chez l'homme. Il est intéressant de noter que des mutations dans le gène de la tricelluline, TRIC, provoquent une déficience auditive, démontrant ainsi son importance dans le maintien de jonctions étanches tels que ceux requis dans l'organe de Corti, une structure de l'oreille interne.

Jonctions Serrées

Les jonctions serrées sont des scellements moléculaires entre les cellules qui empêchent la fuite de fluides, d’ions et d’autres petits solutés à travers les cavités et les compartiments dans ...

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tight junction proteins and cell barriers

Tight junction proteins form seals between neighboring cells. These molecular barriers help stop fluids, ions, and other small solutes from leaking across body cavities and tissue compartments in multicellular organisms. They are an important part of cell barriers in places where controlled movement matters.

The main tight junction proteins are claudin and occludin. Other proteins include tricellulin and JAM, which stands for junctional adhesion molecule. Most of these proteins are 4-pass transmembrane proteins, meaning they cross the cell membrane four times. JAM is different because it is a single-pass transmembrane protein in the immunoglobulin superfamily. The extracellular parts of these proteins interact with matching parts on the nearby cell membrane. This brings two adjacent cells together and helps seal them.

Claudin proteins are especially important because there are many isoforms, or forms, of claudin. Humans express up to 24 different types. This diversity gives tight junctions selective permeability, which means some substances pass more easily than others. For example, claudin-16 in kidney epithelium increases permeability to magnesium ions. This helps magnesium move back into the body during filtration. In contrast, claudin-5 in endothelial cells of brain capillaries lowers ion permeability across the blood-brain barrier.

Tight junctions also seal tricellular junctions, which are the gaps where three cells meet. These junctions were first seen in the 1970s with freeze-fracture electron microscopy. At these contact points, the sealing strands run perpendicular to the strands in bicellular tight junctions. The center of the tricellular contact forms a narrow vertical tube about 10 nm wide. This structure helps control paracellular movement, which is movement between cells.

Tricellulin is the first protein known to concentrate at tricellular junctions. It is related in sequence to occludin and has four isoforms in humans. Mutations in the tricellulin gene, TRIC, can cause hearing impairment. This shows how important tight seals are in the organ of Corti, a structure in the inner ear.

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tight junctions

Tight junction proteins form seals between neighboring cells. These molecular barriers help stop fluids, ions, and other small solutes from leaking across body cavities and tissue compartments in multicellular organisms. They are an important part of cell barriers in places where controlled movement matters. The main tight junction proteins are claudin and occludin. Other proteins include tricellulin and JAM, which stands for junctional adhesion molecule. Most of these proteins are 4-pass...

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key terms and concepts

Learn how claudin, occludin, tricellulin, and JAM seal cells, control selective permeability, and support barriers like the blood-brain barrier.

Tight Junction Proteins and Cell Barriers | JoVE K12

cell biology

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Tight Junction Proteins and Cell Barriers

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