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Cardiac muscle, also called heart muscle or myocardium, is one of three types of vertebrate muscle tissues. Cardiac muscle cells, also known as cardiomyocytes, are surrounded by an extracellular matrix produced by supporting fibroblast cells. Cardiac fibroblasts are vital cells within cardiac muscle that are largely responsible for creating and maintaining the extracellular matrix. The cardiac extracellular matrix (cECM) is composed of proteins and polysaccharides, which provide structural and biochemical support to cardiovascular tissue. The cECM is an essential component of the heart that imparts fundamental cellular processes during organ development and homeostasis.
| Characteristics | Values |
|---|---|
| Type of muscle tissue | Cardiac muscle is one of three types of vertebrate muscle tissues, the others being skeletal muscle and smooth muscle. |
| Description | Cardiac muscle is an involuntary, striated muscle that constitutes the main tissue of the wall of the heart. |
| Composition | Cardiac muscle is composed of individual cardiac muscle cells (cardiomyocytes) joined by intercalated discs, and encased by collagen fibers and other substances that form the extracellular matrix. |
| Function | Cardiac muscle contracts in a similar manner to skeletal muscle, with electrical stimulation triggering the release of calcium from the cell's internal calcium store, the sarcoplasmic reticulum. |
| Role of Extracellular Matrix | The extracellular matrix (ECM) provides structural and biochemical support to cardiovascular tissue, and is essential for the differentiation of cardiac progenitor cells and regulation of cardiomyocyte function. |
| Components of ECM | The ECM is composed of proteins (including collagen, elastin, and laminin) and polysaccharides (glycosaminoglycans). |
| Modification of ECM | Modification of the ECM, such as through injection of ECM components, has been explored as a potential therapeutic approach for cardiac repair and regeneration. |
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What You'll Learn
- Cardiac muscle cells are surrounded by an extracellular matrix
- Fibroblasts are vital supporting cells within cardiac muscle
- The cardiac extracellular matrix is composed of proteins and polysaccharides
- The cardiac extracellular matrix is an essential component of the heart
- The composition of the cardiac extracellular matrix changes significantly after birth
Cardiac muscle cells are surrounded by an extracellular matrix
Cardiac muscle, also known as myocardium or heart muscle, is one of the three types of vertebrate muscle tissues, the other two being skeletal muscle and smooth muscle. Cardiac muscle cells, or cardiomyocytes, are the contractile myocytes of the cardiac muscle. They are striated, branched, and contain many mitochondria. Each myocyte contains a single, centrally located nucleus surrounded by a cell membrane called the sarcolemma. The sarcolemma contains voltage-gated calcium channels, which are specialized ion channels that skeletal muscles do not possess.
The cardiac extracellular matrix is dynamically remodelled according to the loads imposed on it during muscle growth, exercise, and in response to injury. This is particularly important for the properties of cardiac muscle after ischemia. Matrix metalloproteinases (MMPs) are responsible for remodelling the extracellular matrix within the muscle and are secreted by both fibroblasts and muscle cells. The degradation of the cardiac matrix and induction of fibrosis are implicated in the inhibition of survival and differentiation of cardiac stem cells (CSCs).
Cardiac fibroblasts are vital supporting cells within cardiac muscle. They are smaller but more numerous than cardiomyocytes, and they play a crucial role in responding to injuries such as myocardial infarction. Following an injury, fibroblasts can become activated and transform into myofibroblasts, which exhibit characteristics of both fibroblasts and smooth muscle cells. In this state, fibroblasts can repair the injury by generating collagen and contracting to pull the injured area together.
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Fibroblasts are vital supporting cells within cardiac muscle
Cardiac muscle, also known as myocardium, is a type of vertebrate muscle tissue that makes up the main tissue of the heart wall. The myocardium is encased by an extracellular matrix, which is composed of collagen fibres and other substances. Cardiac fibroblasts are vital supporting cells within cardiac muscle that play a crucial role in creating and maintaining this extracellular matrix.
Fibroblasts are the primary cell type responsible for the deposition of the extracellular matrix, which surrounds and supports cardiomyocytes (the contractile myocytes of the cardiac muscle). The matrix is composed of proteins such as collagen and elastin, as well as glycosaminoglycans (GAGs), which are polysaccharides that help to bind water molecules. Together, these substances provide support, strength, and elasticity to the cardiac muscle, while also keeping the muscle cells hydrated.
Cardiac fibroblasts are also important in maintaining normal cardiac function and responding to injury. When the heart is injured, fibroblasts can become activated and turn into myofibroblasts, which exhibit characteristics of both fibroblasts and smooth muscle cells. In this state, fibroblasts can repair damage by generating collagen and contracting to pull the edges of the injured area together. Additionally, fibroblasts can influence the electrical currents passing across the muscle cell's surface membrane through gap junctions and membrane nanotubes, which allow for the exchange of molecules and the propagation of electrical signals between cells.
Recent studies have also highlighted the importance of fibroblasts in blood vessel formation, suggesting their potential role in cardiac therapies. Furthermore, fibroblasts are a major source of new fibroblasts in the adult cardiac valves and other regions of the heart, contributing to the structural, biochemical, mechanical, and electrical properties of the myocardium. While there is still much to learn about fibroblasts, they are undoubtedly vital supporting cells within cardiac muscle, contributing to both its structure and function.
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The cardiac extracellular matrix is composed of proteins and polysaccharides
The cardiac extracellular matrix (ECM) is an essential component of the heart, playing a fundamental role in organ development and homeostasis. It is composed of proteins and polysaccharides, which provide structure and support to the cardiac muscle.
The ECM is a noncellular component of the heart's tissue, formed by the interaction of filamentous proteins, proteoglycans, and glycosaminoglycans (polysaccharides). Collagens I and III are key constituents of the ECM, providing structural and mechanical support to the tissue. The ECM also contains collagen fibers that encase the cardiac muscle cells, contributing to the overall strength and elasticity of the muscle.
The composition of the ECM is dynamic and can change rapidly after birth, coinciding with the loss of the heart's regenerative capacity. These changes in ECM composition can lead to the development of cardiovascular diseases, as the formation of fibrotic tissue impairs organ function. Therefore, understanding the composition and function of the ECM is crucial for developing effective therapies for heart conditions.
Cardiac fibroblasts (cFBs) are primarily responsible for producing and remodelling the ECM. They play a vital role in responding to cardiac injuries, such as myocardial infarction, by activating and transforming into myofibroblasts. This transformation allows fibroblasts to repair the injury by generating collagen and contracting to bring the injured area together.
The cardiac ECM, with its protein and polysaccharide composition, provides essential support, strength, and elasticity to the cardiac muscle cells. It also helps maintain hydration in the muscle cells by binding water molecules. The dynamic nature of the ECM allows it to adapt to the changing needs of the heart during growth, exercise, and injury response.
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The cardiac extracellular matrix is an essential component of the heart
The cardiac extracellular matrix (ECM) is a complex architectural network of structural and non-structural proteins, creating strength and plasticity. It is an essential component of the heart, playing a fundamental role in cardiac development, homeostasis, and remodelling. The ECM surrounds the cardiomyocyte and fibroblasts, providing support and strength to the muscle cells, creating elasticity in cardiac muscle, and keeping the muscle cells hydrated by binding water molecules.
The ECM is composed of proteins, including collagen and elastin, along with polysaccharides (sugar chains) known as glycosaminoglycans. The common denominator for these groups is glycosylation, which refers to the decoration of proteins or lipids with sugars. This process is one of the most prominent and complex forms of post-translational modification in biology, allowing for enormous diversity in both structure and function. Over 50% of proteins in vertebrates are predicted to be glycosylated, and sugars are one of the four basic components of eukaryotic cells.
The cardiac ECM is dynamically remodelled according to the loads imposed on it during muscle growth, exercise, and in response to damage. This is particularly relevant to the properties of cardiac muscle after ischemia. The atrioventricular valves in the heart are a special type of connective tissue structure well adapted to their function. Collagen fibre orientation in the cusps of these valves reinforces them against predominant haemodynamic stresses.
The ECM is essential for the differentiation of cardiac progenitor cells (CPC) into specific lineages and regulates myocyte contractility by E-M coupling and calcium transients. It also directs miRNAs required for precise regulation of continuous and synchronized beating of cardiomyocytes, which is indispensable for survival. Alterations in the matrix homeostasis due to induction of MMPs, altered expression of specific miRNAs, or impaired signalling for contractility of cardiomyocytes can lead to catastrophic effects.
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The composition of the cardiac extracellular matrix changes significantly after birth
The extracellular matrix (ECM) is an essential component of the heart, playing a role in fundamental cellular processes during organ development and homeostasis. The ECM is composed of proteins such as collagen and elastin, as well as polysaccharides (sugar chains) called glycosaminoglycans. These substances provide support and strength to the muscle cells, create elasticity in the cardiac muscle, and keep the muscle cells hydrated by binding water molecules.
The composition of the cardiac ECM changes significantly in a short period after birth, coinciding with the loss of the heart's regenerative capacity. This change in composition is associated with a decrease in the expression of the dystrophin complex protein agrin, which is an important regulator of cardiomyocyte division during the transient neonatal regenerative period. The reduction in agrin expression leads to a decrease in cardiomyocyte division and impaired cardiac regeneration.
Additionally, biomechanical alterations at the ECM around the time of birth may influence cardiomyocyte cycling activity, further impacting the heart's regenerative capacity. These changes contribute to the accumulation of defective molecules and organelles in the cytoplasm, characteristic of cellular aging. As a result, cardiomyocytes accumulate dysfunctional mitochondria, oxidized proteins, and lipofuscin particles, leading to a decline in their reparative abilities.
The understanding of these ECM alterations and their impact on cardiac cells is crucial for the development of more effective therapies and regenerative strategies. By mimicking the fetal-neonatal extracellular environment, researchers can explore tissue engineering and regenerative medicine approaches to promote cardiac regeneration and improve cardiovascular health in newborns and adults.
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Frequently asked questions
Yes, cardiac muscle has an extracellular matrix (ECM) composed of proteins and polysaccharides secreted by cardiac cell types.
The cardiac matrix is made of fibrillary and non-fibrillary components. Fibrillary components include fibrillar collagens, while non-fibrillary components are made up of the basement membrane, proteoglycans, and glycoproteins.
The cardiac matrix provides structural and biochemical support to the cardiovascular tissue. It is essential for the differentiation of cardiac progenitor cells (CPC) into specific lineages. The matrix also regulates myocyte contractility and directs miRNAs required for the continuous and synchronized beating of cardiomyocytes.
Following an injury, cardiac fibroblasts can become activated and turn into myofibroblasts, which exhibit behaviour somewhere between a fibroblast and a smooth muscle cell. Fibroblasts can repair an injury by creating collagen while gently contracting to pull the edges of the injured area together.
