4.14
The Extracellular Matrix
In order to maintain tissue organization, many animal cells are surrounded by structural molecules that make up the extracellular matrix (ECM). Togeth…
The extracellular matrix, or ECM, is a network of fibrous proteins like collagen and elastin and a ground substance that surrounds cells and fills the spaces between them.
The ground substance is a hydrated gel made up of glycosaminoglycans, proteoglycans, glycoproteins, and interstitial fluid, which is mainly water with dissolved ions and gases.
Local cells, especially fibroblasts, secrete most ECM components. Macrophages and other cells also help remodel the matrix.
The ECM contains glycosaminoglycans, or GAGs, which bind water. When attached to core proteins, GAGs form proteoglycans.
In cartilage, hyaluronic acid forms large proteoglycan aggregates. Proteoglycans that contain chondroitin sulfate bind to hyaluronic acid and help the tissue resist compression. Loss of these proteoglycans in cartilage can contribute to osteoarthritis.
Collagens provide rigidity and are especially important in tendons, which join muscles to bones.
Fibronectin acts like a molecular glue and helps cells attach to collagen and GAGs. Cells bind to fibronectin through integrins, which connect the ECM to the cell interior and support signaling.
During migration, cells use these attachments to pull themselves forward across the ECM, which also acts as a support network that guides their movement and behavior.
View the full transcript and gain access to JoVE Core videos
Q1: What is the extracellular matrix and what does it do?
The extracellular matrix (ECM) is a network of fibrous proteins like collagen and elastin surrounding cells and filling spaces between them. It maintains tissue structural integrity, provides support for cell attachment and migration, and guides cell behavior. The ECM also acts as a reservoir for signaling molecules that regulate cellular responses and tissue organization.
Q2: What are the main components of the extracellular matrix?
The ECM contains ground substance, a hydrated gel made of glycosaminoglycans (GAGs), proteoglycans, glycoproteins, and interstitial fluid. Fibrous proteins include collagen, which provides rigidity, and elastin, which enables stretching. Fibronectin acts as a molecular glue connecting cells to the matrix through integrin proteins.
Q3: How do glycosaminoglycans and proteoglycans function in the extracellular matrix?
Glycosaminoglycans (GAGs) bind water molecules, creating a hydrated gel that allows the ECM to withstand compression forces. When GAGs attach to core proteins, they form proteoglycans. In cartilage, proteoglycans containing chondroitin sulfate bind to hyaluronic acid, helping tissue resist compression and preventing osteoarthritis.
Q4: What role do integrins play in connecting cells to the extracellular matrix?
Integrins are transmembrane proteins that bind to fibronectin and collagen in the ECM, linking the matrix to the cell interior. This connection enables cells to attach to the ECM and use these attachments to migrate across the matrix. Integrin engagement also triggers intracellular signaling cascades that influence gene expression and cell behavior.
Q5: How does extracellular matrix composition vary between different tissues?
ECM composition depends on tissue location, physiological function, and neighboring cell types, creating a unique local microenvironment. Cells in each tissue secrete specific ECM molecules; for example, intestinal cells synthesize matrix components for their tissue, while osteoblasts generate the rigid ECM of bone. This diversity in molecular makeup produces tissue-specific properties.
Q6: Why is extracellular matrix remodeling important for tissues?
ECM remodeling is essential for tissue repair, growth, and blood vessel branching. Cells produce matrix metalloproteases (MMPs) and other enzymes that degrade collagen and fibronectin, allowing tissue to adapt and regenerate. However, excessive ECM remodeling also enables cancer cell metastasis, making this process critical for both healthy and pathological outcomes.
Q7: How does the extracellular matrix communicate with cells?
Forces on integrin molecules trigger activation of the intracellular actomyosin network, promoting cell migration, division, and other responses including changes in gene expression. The ECM also binds signaling molecules that are released during matrix degradation. This bidirectional communication between cells and ECM coordinates tissue organization and cellular behavior.