Tight junction

Cellular structures that form barriers in tissues

Tight junctions are specialized connections between adjacent epithelial or endothelial cells. They play a crucial role in maintaining the selective permeability of epithelial and endothelial barriers, regulating the passage of ions, molecules, and water between cells. Tight junctions are essential for the function of various organs and tissues, including the intestines, blood-brain barrier, and kidneys.

Structure

Tight junctions are composed of a complex network of proteins that form a seal between adjacent cells. The primary proteins involved in tight junctions include claudins, occludin, and junctional adhesion molecules (JAMs). These proteins interact with the actin cytoskeleton of the cell, providing structural support and maintaining the integrity of the junction.

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Diagram of tight junction structure showing claudins and occludin.

Claudins

Claudins are a family of proteins that are critical for the formation and function of tight junctions. They determine the selectivity and permeability of the junctions by forming ion-selective pores. Different tissues express different claudins, which contribute to the tissue-specific properties of tight junctions.

Occludin

Occludin is another integral membrane protein found in tight junctions. It plays a role in the regulation of junctional permeability and is involved in signaling pathways that control cell proliferation and differentiation.

Junctional Adhesion Molecules (JAMs)

JAMs are members of the immunoglobulin superfamily and contribute to the formation and maintenance of tight junctions. They are involved in cell signaling and the regulation of paracellular permeability.

Function

Tight junctions serve several critical functions in the body:

• Barrier Function: Tight junctions create a barrier that controls the movement of substances between the apical and basolateral surfaces of epithelial cells. This barrier is essential for maintaining the distinct environments on either side of the epithelium.

• Selective Permeability: Tight junctions regulate the passage of ions and small molecules through the paracellular pathway. This selectivity is crucial for processes such as nutrient absorption in the intestines and the maintenance of the blood-brain barrier.

• Cell Polarity: Tight junctions help establish and maintain cell polarity by demarcating the boundary between the apical and basolateral surfaces of epithelial cells.

• Signal Transduction: Tight junctions are involved in signaling pathways that influence cell behavior, including proliferation, differentiation, and apoptosis.

Clinical Significance

Disruption of tight junctions can lead to various pathological conditions. For example, increased permeability of tight junctions in the intestines can result in inflammatory bowel disease and celiac disease. In the blood-brain barrier, compromised tight junctions can contribute to neurological disorders such as multiple sclerosis and Alzheimer's disease.

Related pages

• Adherens junction
• Desmosome
• Gap junction
• Epithelial tissue
• Endothelial cell