From the Guidelines
Cellular junctions are crucial for maintaining tissue integrity and intercellular communication, with tight junctions, adherens junctions, and gap junctions being the primary types, each serving distinct functions such as sealing intercellular spaces, providing mechanical strength, and facilitating direct cell-to-cell communication. These junctions are essential for various physiological processes and are composed of different proteins and structures. For instance, tight junctions are formed by the interaction of transmembrane proteins such as occludins, claudins, and junctional adhesion molecules, which seal the intercellular space and regulate the passage of molecules and ions between cells 1. Adherens junctions, on the other hand, are characterized by the presence of cadherin proteins that mediate cell-to-cell adhesion and are linked to the actin cytoskeleton, providing mechanical strength to tissues 1. Gap junctions form channels between adjacent cells, allowing for the direct exchange of small molecules and ions, which is vital for coordinated cellular activities in tissues like the heart 1. Additionally, desmosomes and hemidesmosomes provide strong adhesion between cells and to the basement membrane, respectively, and are particularly important in tissues that experience mechanical stress, such as the skin. The specific combination and arrangement of these junctions vary among different tissues, reflecting their unique physiological requirements and functions. In the context of drug delivery, the presence of tight junctions in barriers such as the blood-brain barrier (BBB) and the blood-retinal barrier (BRB) poses a significant challenge, as these junctions restrict the passage of molecules and ions, limiting the accessibility of therapeutic agents to target sites 1. Understanding the structure and function of cellular junctions is essential for developing effective strategies to overcome these barriers and improve drug delivery to specific tissues and organs. The most recent and highest quality study on this topic, published in 2023, highlights the importance of considering the physico-chemical properties of drugs and the role of transporters in facilitating their passage across cellular barriers 1. This knowledge can be applied to design drugs that can effectively cross these barriers, improving their therapeutic efficacy and reducing potential side effects. Overall, the study of cellular junctions is crucial for understanding tissue biology and for the development of novel therapeutic strategies.
From the Research
Types of Cellular Junctions
- Tight junctions: regulate tissue barrier function, cell proliferation, and migration 2, 3
- Adherens junctions: provide essential adhesive and mechanical properties, and play a role in vascular permeability 4, 5
- Desmosomes: couple the intermediate filament cytoskeleton at points of strong cell-cell adhesion, and confer new mechanical and signaling properties to vertebrate cells and tissues 4, 6
- Gap junctions: provide for intercellular communication 3, 6
Functions of Cellular Junctions
- Regulate tissue homeostasis and barrier function 2, 5
- Control cell proliferation, migration, and survival 2, 3, 5
- Integrate mechanical and chemical pathways to coordinate tissue architecture with behavior 4
- Play a role in gene transcription, tumor suppression, and cell polarity 3
Importance of Cellular Junctions
- Defects in cell-cell junctions can give rise to a wide range of tissue abnormalities and are common in genetic abnormalities and cancers 2
- Cellular junctions are essential for the development of embryonic layers and organs, as well as adult tissue homeostasis 6
- Dysregulation of cellular junctions can lead to diseases such as organ injuries 5