Dominic Stone
Desmosomes are intercellular junctions that play a vital role in maintaining the structural integrity of stratified epithelia. They are particularly important in cardiac tissue, where they help to maintain the coordination of cardiac myocytes. Cardiac muscle tissue is only found in the heart, and its highly coordinated contractions are responsible for pumping blood into the vessels of the circulatory system. Intercalated discs, which are part of the sarcolemma, contain two structures that are essential for cardiac muscle contraction: gap junctions and desmosomes. The gap junctions form channels between adjacent cardiac muscle fibres, allowing for the quick transmission of action potentials and the coordinated contraction of the entire heart. The remainder of the intercalated disc is composed of desmosomes, which are responsible for mechanically coupling myocytes in the heart.
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What You'll Learn
- Intercalated discs contain desmosomes and are vital for cardiac muscle contraction
- Desmosomes are intercellular junctions that maintain the structural integrity of cardiac tissue
- Desmosomal alterations can drive calcium-mediated arrhythmogenic mechanisms
- Desmosomal mutations can lead to blistering disorders
- Desmosomes and adherens junctions intermingle to form a hybrid area composita
Intercalated discs contain desmosomes and are vital for cardiac muscle contraction
Cardiac muscle tissue is only found in the heart. The highly coordinated contractions of cardiac muscle pump blood into the vessels of the circulatory system. Cardiac muscle fibres are shorter than skeletal muscle fibres and usually contain only one nucleus, which is located in the central region of the cell. Cardiac muscle fibres are also extensively branched and are connected to one another at their ends by intercalated discs.
Intercalated discs are part of the sarcolemma and contain two structures important in cardiac muscle contraction: gap junctions and desmosomes. A gap junction forms channels between adjacent cardiac muscle fibres that allow the depolarising current produced by cations to flow from one cardiac muscle cell to the next. This joining is called electric coupling, and in cardiac muscle, it allows the quick transmission of action potentials and the coordinated contraction of the entire heart. This network of electrically connected cardiac muscle cells creates a functional unit of contraction called a syncytium. The remainder of the intercalated disc is composed of desmosomes.
Desmosomes have long been appreciated as intercellular junctions that are vital for maintaining the structural integrity of stratified epithelia. More recent clinical investigations of patients with diseases such as arrhythmogenic cardiomyopathy have further highlighted the importance of desmosomes in cardiac tissue, where they help to maintain coordination of cardiac myocytes.
Studies have shown the involvement of connexins, calcium handling machinery, and sodium channels as early drivers of arrhythmias, suggesting these may be distinct pathways regulating electrical function from the desmosome. Recent studies have also implicated complex interactions between CSN subunits and desmosomal proteins.
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Desmosomes are intercellular junctions that maintain the structural integrity of cardiac tissue
Cardiac muscle cells are connected via intercalated discs, which contain gap junctions and desmosomes. These junctions allow cardiomyocytes to contract together in a synchronous manner, enabling the heart to work as a pump. Desmosomes are intercellular junctions that maintain the structural integrity of cardiac tissue. They are major cell adhesion junctions that anchor cell membranes to the intermediate filament network, particularly in tissues that are under constant physical stress, such as the heart.
Desmosomes are composed of tissue-specific desmosomal cadherins (desmogleins and desmocollins), armadillo proteins (plakoglobin and plakophilins), and plakins (desmoplakins). Desmogleins and desmocollins are transmembrane proteins that form Ca2+-dependent heterophilic cell-to-cell adhesive interactions. Plakoglobin and plakophilins are cytoplasmic cadherin binding partners that signal and regulate cadherin adhesive activity. Desmoplakins link to intermediate filaments such as desmin.
The importance of desmosomes in maintaining the structural integrity of the heart is evident in diseases such as arrhythmogenic cardiomyopathy. Studies have shown that mutations or loss of desmosomal proteins can lead to cardiomyopathies and arrhythmias. For example, human genetic studies have identified human DSP variants with an affinity for intermittent myocardial inflammatory episodes similar to myocarditis but with distinct cardiomyopathy. Additionally, studies in PKP2cKO mice and PKP2 mutant-induced pluripotent stem cell-derived cardiomyocytes have shown abnormal calcium handling and dysregulation of calcium-handling gene expression, highlighting the role of desmosomal alterations in driving calcium-mediated arrhythmogenic mechanisms.
Furthermore, the stability of desmosomes is dependent on the fascia adherens junction protein, N-cadherin. The loss of fascia adherens and desmosomal proteins can lead to gap junction instability, suggesting cross-talk between mechanical and electrical junctional components. Overall, desmosomes play a crucial role in maintaining the structural integrity of cardiac tissue and proper heart function.
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Desmosomal alterations can drive calcium-mediated arrhythmogenic mechanisms
Cardiac muscle tissue is only found in the heart. Intercalated discs are part of the sarcolemma and contain two structures important to cardiac muscle contraction: gap junctions and desmosomes. Desmosomes are intercellular junctions that are vital for maintaining the structural integrity of stratified epithelia.
Desmosomes have been implicated in cardiac arrhythmias and disease. For example, studies have shown the involvement of connexins, calcium handling machinery, and sodium channels as early drivers of arrhythmias. More recent studies have also shed light on the role of desmosomal alterations in driving calcium-mediated arrhythmogenic mechanisms.
Arrhythmogenic cardiomyopathy (ACM) is an inherited cardiac disease characterized by fibrofatty replacement of the myocardium. Deleterious variants in desmosomal genes are the main cause of ACM and lead to common and gene-specific molecular alterations. Molecular and functional alterations in calcium handling were also characterized. For example, a slower calcium re-uptake was observed in the absence of PKP2, DSG2, and DSC2.
Desmosomal loss triggers early connexin channel remodeling, which prevents proper electrical coupling between adjacent cardiomyocytes. PKP2 loss causes calcium dysfunction through multiple mechanisms impacting connexin hemichannel permeability and PKC-driven increase in RYR2 activity (Ca2+ release from the sarcoplasmic reticulum). Interestingly, recent studies have drawn a connection between the desmosomal protein, DSG2, and mitochondrial-mediated calcium overload in ARVC in exercise settings. These studies reveal the possibility that mitochondrial calcium overload-induced cell death may generate arrhythmogenic substrates and further contribute to arrhythmias.
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Desmosomal mutations can lead to blistering disorders
Desmosomes are specialized cell structures that facilitate cell-to-cell adhesion, forming strong connections between adjacent cells. They are particularly important in tissues that experience high mechanical stress, such as cardiac muscle tissue, where they help maintain the structural integrity of the heart. Cardiac muscle cells are connected by intercalated discs, which contain two crucial structures for cardiac function: gap junctions and desmosomes.
Desmosomes play a critical role in maintaining the normal architecture of tissues, and their alterations can lead to various diseases and disorders. For instance, desmosomal mutations have been implicated in arrhythmogenic cardiomyopathy (ACM), a life-threatening condition that can cause sudden death, especially in young athletes. These mutations usually occur in the desmoglein 2 gene but sometimes in the desmocollin 2 gene.
Desmosomal mutations can also lead to blistering disorders, particularly in the skin. Pemphigus, for example, is a class of autoimmune blistering skin diseases characterized by painful lesions in the skin and oral mucosa. Pemphigus vulgaris (PV) and pemphigus foliaceus (PF) are two such diseases where auto-antibodies target desmogleins, causing a loss of cell adhesion and subsequent blistering. Hailey–Hailey disease is another blistering disorder caused by a haploinsufficiency in the ATP2C1 gene, which results in malformation of the desmosomes.
Furthermore, studies using genetically engineered mouse models have provided valuable insights into the pathological mechanisms of blistering skin disorders caused by impaired desmosome function. These models have helped establish causal links between specific mutations and disease phenotypes, such as the DSC3 mutation associated with hair loss and recurrent skin blistering in a family in Afghanistan. Thus, desmosomal mutations can indeed lead to blistering disorders, highlighting the essential role of desmosomes in maintaining tissue integrity and function.
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Desmosomes and adherens junctions intermingle to form a hybrid area composita
Cardiac muscle tissue is only found in the heart and is responsible for pumping blood into the vessels of the circulatory system. Intercalated discs, which are part of the sarcolemma, contain two structures that are important in cardiac muscle contraction: gap junctions and desmosomes. Desmosomes are intercellular junctions that are vital for maintaining the structural integrity of stratified epithelia.
The identification of the area composita occurred in parallel with the recognition of a cardiac disorder called arrhythmogenic cardiomyopathy (AC), which is associated with mutations in DSM molecules. Studies have shown the involvement of connexins, calcium handling machinery, and sodium channels as early drivers of arrhythmias, suggesting distinct pathways regulating electrical function from the desmosome. In cardiac myocytes, contractile units called sarcomeres are stabilized by interwoven desmin intermediate filaments. Actin fibers and intermediate filaments are anchored at hybrid junctions called area composita, containing desmosome and adherens junction components.
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Frequently asked questions
Yes, cardiac muscles have desmosomes.
Desmosomes are intercellular junctions that are vital for maintaining the structural integrity of stratified epithelia.
Desmosomes help maintain the coordination of cardiac myocytes. They are responsible for mechanically coupling myocytes in the heart.
Desmosomal alterations can lead to calcium-mediated arrhythmogenic mechanisms and cardiac arrhythmias.
Desmosomal mutations have been associated with arrhythmogenic cardiomyopathy, myocarditis, and dilated cardiomyopathy (DCM).
