Matrix in cell growth
• Matrix is an insoluble, dynamic gel in the
cytoplasm, believed to be involved in cell
shape determination and locomotive
mechanism, across a solid substrate. It
consists of polymeric microtubules, actin
microfilaments and intermediate filaments
interacting with a number of other proteins.
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Extracellular matrix (ECM)
Part of three connective tissue layers
(endomysium, perimysium, and epimysium)
surrounding muscle fibres.
Extracellular matrix is composed of proteins
including collagens and proteoglycans.
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Component of extra cellular matrix
ECM is comprised variously of collagen, laminin,
fibronectin, hyaluronan and proteoglycans such
as beta glycan, decorin, perlecan, and syndecan-
1, some of which bind to growth factors or
cytokines.
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Component of extra cellular matrix
• Proteoglycans in extracellular matrix form a cross-linked meshwork with fibrous
proteins
• Some proteins bind multiple other proteins and glycosaminoglycans (fibronectin).
• Integrin is a family of proteins that mediate signalling between cell interior and
extracellular matrix.
• Mass of interactions between cells and matrix not only anchors cells to matrix but
also provides paths that direct migration of cells in developing tissue and (through
integrin) conveys information in both directions across plasma membrane.
ECMs are composed of proteins such as collagen and elastin that serve as scaffolds for
cells as well as networks of various adhesion ligands and growth factors, which
promote cell signalling. ECM is complex in both structure and composition.
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Role of matrix
Some important roles that matrix play in biological system which is described as
follows.
• Matrixes are generally used for providing support
• It involve in segregating tissues from one another
• It takes part in regulation of intercellular communication
• Extracellular Matrix cells have been found to cause regrowth and healing of tissue.
• Some time it acts as fibrosis
• The use of ECM constituents can be highly beneficial in enhancing cell survival,
proliferation, or differentiation, but unless recombinant molecules are used
• In human foetuses, the extracellular matrix works with stem cells to grow and
regrow all parts of the human body and foetus can regrow anything that gets
damaged in the womb
• In case of injury repair and tissue engineering, the extracellular matrix serves two
main functions a) It prevents the immune system by triggering from the injury and
responding with inflammation and scar tissue b) It facilitates the surrounding cells to
repair the tissue instead of forming scar tissue
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Molecular components
• Components of the ECM are produced
intracellularly by resident cells and secreted
into the ECM through exocytosis.
• Once secreted, they then aggregate with the
existing matrix. The ECM is composed of an
interlocking mesh of fibrous proteins and
glycosaminoglycans (GAGs).
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Proteoglycans
• Glycosaminoglycan (GAGs) are carbohydrate polymers
and are usually attached to extracellular matrix
proteins to form proteoglycans (exception-hyaluronic
acid).
• Proteoglycans have a net negative charge that attracts
positively charged sodium ions (Na+) which attracts
water molecules via osmosis, keeping the ECM and
resident cells hydrated.
• Proteoglycans may also help to trap and store growth
factors within the ECM.
• There are the different types of proteoglycan found
within the extracellular matrix.
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1. Heparin sulphate
• Heparin sulphate (HS) is a linear polysaccharide found in all
animal tissues. It occurs as a proteoglycan (PG) in which
two or three HS chains are attached in close proximity to
cell surface or extracellular matrix proteins.
• HS binds to a variety of protein ligands and involve in
regulation of a wide variety of biological activities, including
developmental processes, angiogenesis, blood coagulation
and tumour metastasis.
• In the extracellular matrix, particularly basement
membranes, the multi-domain proteins perlecan, agrin and
collagen XVIII are the main proteins to which heparin
sulphate is attached.
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2. Chondroitin sulphate
• Chondroitin sulfates help to provide the
tensile strength of cartilage, tendons,
ligaments and walls of the aorta.
• They have also been known to affect
neuroplasticity.
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3. Keratan sulphate
• Keratan sulfates have variable sulfate content
and unlike many other GAGs, do not contain
uronic acid. They are present in the cornea,
cartilage, bones and the horns of animals.
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Non-proteoglycan polysaccharide
There are various non-proteoglycan polysaccharides.
1. Hyaluronic acid: Hyaluronic acid (or hyaluronan at physiological
pH) is a polysaccharide containing alternating residues of D-
glucuronic acid and N-acetyl glucosamine. Unlike other
glycosaminoglycan (GAGs) it is not found as a proteoglycan.
2. Like cellulose and chitin, it is synthesized at the plasma membrane
by a transmembrane hyaluronan synthase.
3. Hyaluronan is the only GAG that occurs as a single long
polysaccharide chain.
4. Hyaluronate is also an essential component of the extracellular
matrix of cartilage and tendons, to which it contributes tensile
strength and elasticity as a result of its strong interactions with
other components of the matrix. A number of proteoglycans
interact with hyaluronan to form large complexes in the
extracellular
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• matrix. A well-characterized example is
aggrecan, the major proteoglycan of cartilage.
Hyaluronic acid acts as an environmental sign
that regulates cell behaviour during
embryonic development, healing processes,
inflammation and tumour development. It
interacts with a specific trans-membrane
receptor, CD44.
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2. Matrix Structural Proteins
• Extracellular matrices are composed of tough
fibrous proteins embedded in a gel-like
polysaccharide ground substance-a design
basically similar to that of plant cell walls.
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Collagen
• In ECM of most animals, collagens are the abundantly found
structural protein. In fact, collagen is the most abundant protein in
the human body and accounts for 90% of bone matrix protein
content.
• Collagens are present in the ECM as fibrillar proteins and give
structural support to resident cells.
• Collagens are a large family of proteins containing at least 27
different members. They are characterized by the formation of triple
helices in which three polypeptide chains are wound tightly around
one another in a rope-like structure.
• The different collagen polypeptides can assemble into 42 different
trimers. The triple helix domains of the collagens consist of repeats of
the amino acid sequence Gly-X-Y. A glycine (the smallest amino acid,
with a side chain consisting only of hydrogen) is required in every
third position, so that the polypeptide chains can pack together close
enough to form the collagen triple helix. 15
Collagen
• Proline is frequently found in the X position and hydroxyproline in
the γ position; because of their ring structure these amino acids
stabilize the helical conformations of the polypeptide chains.
• The unusual amino acid hydroxyproline is formed within the
endoplasmic reticulum by modification of proline residues that
have already been incorporated into collagen polypeptide chains.
• Lysine residues in collagen are also frequently converted to
hydroxylysines. The hydroxyl groups of these modified amino acids
are thought to stabilize the collagen triple helix by forming
hydrogen bonds between polypeptide chains.
• These amino acids are rarely found in other proteins although
hydroxyproline is also common in some of the glycoproteins of
plant cell walls.
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The collagen can be divided into several families
according to the types of structure they form:
• Fibril- forming
• Fibril-associated
• Network forming
• Anchoring fibrils
• Transmembrane
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collagen and families
• The most abundant type of collagen (type I collagen) is one
of the fibril forming collagens--the basic structural
components of connective tissues.
• The polypeptide chains of these collagens consist of
approximately a thousand amino acids or 330 Gly-XY
repeats. After being secreted from the cell these collagens
assemble into collagen fibrils in which the triple helical
molecules are associated in regular staggered arrays.
• These fibrils do not form within the cell because the fibril
forming collagens are synthesized as soluble precursors
(procollagens) that contain nonhelical segments at both
ends of the polypeptide chain. Procollagen is cleaved to
collagen after its secretion, so the assembly of collagen into
fibrils take place only outside the cell.
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collagen and families
• The association of collagen molecules in fibrils
is further strengthened by the formation of
covalent crosslinks between the side chains of
lysine and hydroxylysine residues.
• Frequently, the fibrils further associate with
one another to form collagen fibers, which can
be several micrometers in diameter.
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Elastin
• In contrast to collagens, Elastins give elasticity to tissues,
allowing them to stretch when needed and then return to
their original state. This is useful in blood vessels, the lungs, in
skin, and the ligaments.
• Elastins are synthesized by fibroblasts and smooth muscle
cells.
• Elastins are highly insoluble, and tropoelastins are secreted
inside a chaperone molecule, which releases the precursor
molecule upon contact with a fiber of mature elastin.
Tropoelastins are then deaminated to become incorporated
into the elastin strand.
• Diseases such as cutis laxa and Williams syndrome are
associated with deficient or absence of elastin fibers in the
ECM. 20
Matrix adhesion proteins:
• Matrix adhesion proteins, the final class of
extracellular matrix constituents are
responsible for linking the components of the
matrix to one another and to the surfaces of
cells.
• They interact with collagen and proteoglycans
to specify matrix organization and are the
major binding sites for integrins.
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1. Fibronectin
• Fibronectin is the principal adhesion protein of connective tissues.
Fibronectin is a dimeric glycoprotein consisting of two polypeptide chains,
each containing nearly 2500 amino acids.
• Fibronectin are proteins that connect cells with collagen fibers in the ECM,
allowing cells to move through the ECM.
• Within the extracellular matrix, fibronectin is often cross-linked into fibrils.
Fibronectin has binding sites for both collagen and GAGs so it cross-links
these matrix components.
• Fibronectins bind collagen and cell surface integrins, causing a
reorganization of the cell's cytoskeleton and facilitating cell movement.
• Fibronectin are secreted by cells in an unfolded, inactive form. Binding to
integrins unfolds fibronectin molecules, allowing them to form dimers so
that they can function properly. Fibronectins also help at the site of tissue
injury by binding to platelets during blood clotting and facilitating cell
movement to the affected areas during wound healing.
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2. Laminin
• In almost all animals, Basal laminae contain distinct adhesion proteins of
the laminin family.
• Laminins are heterotrimers of α, β and γ subunits which are the products
of five α genes, four β genes, and three γ genes.
• Like type IV collagen, laminins can self-assemble into meshlike polymers.
Such laminin networks are the major structural components of the basal
laminae synthesized in very early embryos, which do not contain collagen.
• The laminins also have binding sites for cell surface receptors such as
integrins, type IV collagen, and the heparan sulfate proteoglycan,
perlecan.
• In addition, laminins are tightly associated with another adhesion protein,
called entactin, which also binds to type IV collagen. As a result of these
multiple interactions, laminin, entactin, type IV collagen, and perlecan
form cross-linked networks in the basal lamina. They also support in cell
adhesion.
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Cell adhesion to the ECM
• Many cells bind to components of the extracellular matrix.
• Cell adhesion can occur in two ways by focal adhesions,
connecting the ECM to actin filaments of the cell, and
hemi-desmosomes, connecting the ECM to intermediate
filaments such as keratin.
• This cell-to-ECM adhesion is regulated by specific cell
surface cellular adhesion molecules (CAM) known as
integrins.
• The integrins are a family of transmembrane proteins
consisting of two subunits, designated α and β. Integrins
are cell surface proteins that bind cells to ECM structures
such as fibronectin and laminin, and also to integrin
proteins on the surface of other cells.
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Cell adhesion to the ECM
• Fibronectins bind to ECM macromolecules and
facilitate their binding to transmembrane
integrins.
• The attachment of fibronectin to the
extracellular domain initiates intracellular
signaling pathways as well as association with
the cellular cytoskeleton via a set of adaptor
molecules such as actin.
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Interesting facts:
• 1. Collagens are abundantly found structural protein in
the human body and accounts for 90% of bone matrix
protein content.
• 2. Elastins give elasticity to tissues, allowing them to
stretch when needed and then return to their original
state.
• 3. Fibronectins bind to ECM macromolecules and
facilitate their binding to transmembrane integrins.
• 4. Basal laminae contain distinct adhesion proteins of
the laminin family in almost all animals.
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Questions
1. Explain the role of matrix in cell culture?
2. Give the detail about matrix material that are
generally used?
3. What is the difference between proteoglycan
and non-proteoglycan polysaccharide and how
can they involve in formation of matrix?
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