Download MBBS (Bachelor of Medicine and Bachelor of Surgery) Latest Extracelular Matrix 3 Lecture PPT
EXTRACELLULAR
MATRIX 3
DR. S. SHEKHAR
ASSOC. PROFESSOR
DEPT. OF BIOCHEMISTRY
PROTEOGLYCAN
? A proteoglycans consists of a core protein bound covalently
to GAGs, and these units form large complexes with other
components of the extracellular matrix, such as hyaluronic
acid or collagen.
? GAGs consist of repeating disaccharide subunits.
? Proteins linked covalently to glycosaminoglycans (GAGs).
Carbohydrates make up about 95% of its weight.
? Proteins bound covalently to GAGs are called core proteins.
? Many have been classified; they vary in tissue of origin,
function, core protein types.
? Examples include aggrecans, syndecan, betaglycan,
serglycan
PROTEOGLYCAN
? The highly negatively charged
sulfated sugars on the
proteoglycan "bristles" recruit
sodium and water to generate
a viscous but compressible
matrix.
? They have diverse role in
regulating connective tissue
structure and permeability (ie
regulates
movement
of
molecules through matrix).
? They also serve as reservoir of growth factors (eg
FGF & HGF), they act as modulators of cell growth
and differentiation.
? In joint cartilage they also provide layer of lubrication
between bony surfaces.
? Some are integral part of cell membrane & have roles
in cell proliferation, migration and adhesion
? Highly hydrated compressible gels that confer
resistance to compressive forces.
Glycoaminoglycans
? Unbranched polysaccharide chains composed of
repeating dissacharide units.
? Negatively charged under physiological conditions (due
to the occurrence of sulfate and uronic acid groups)
? Disaccharide subunits are:
1. Uronic acid
D-glucuronic acid or
L-iduronic acid
2. Aminosugar
N-acetyl glucosamine (GlcNAc) or
N-acetyl galactosamin (GalNAc)
Glycoaminoglycans
? Amino sugars and uronic acids are
the most common building blocks
of the glycosaminoglycans.
? amino sugars -OH at C-2 is
replaced by an amino group. This
amino group is most often
acetylated and sometimes sulfated.
? uronic acids C-6 of the hexose is
oxidized to a carboxyl group.
Linkage of GAGs to protein core by specific
trisaccharide linker
GALACTOSE
GALACTOSE
XYLOSE
Types of GAGs
Seven types of GAGs
1. Hyaluronan
2. Chondroitin sulfate
3. Dermatan sulfate
4. Heparin
5. Heparan sulfate
6. Keratan sulfate I
7. Keratan sulfate II
1. Hyaluronan
? Made up of Unbranched,
repeating units of GlcUA
and GlcNAc
? It tends to have enormous
carbohydrate chain
? Not covalently attached to
a core protein
? The carbohydrates are not sulfated
? Especially high in concentration in highly hydrated
tissues such as skin and umbilical cord, and in bone,
cartilage, joints (synovial fluid) and in vitreous humor in
the eye, as well as in embryonic tissues
Hyaluronan
? permitting cell migration during morphogenesis
? Important in wound healing
? Its ability to attract water into the ECM triggers
loosening of the matrix
? The high concentrations of hyaluronic acid together
with chondroitin sulfates present in cartilage
contribute to its compressibility
? Hyaluronidase an enzyme secreted by some bacteria
helps with their invasion of tissues
2. Chondroitin sulfate
? Repeating unit of GlcUA
and GalNAc
? Attached to a core protein
through xyl-serine
? Sulfated carbohydrates
? Tends to have shorter polymers
Chondroitin sulfate
? They are located at sites of calcification in
endochondral bone and are a major component
of cartilage.
? Provides tensile strength to cartilage, tendons,
ligaments and walls of aorta
? Thought to act as signaling molecules in the
prevention of the repair of nerve endings after
injury.
3.Dermatan sulfate
? Made up of repeating
IdUA and GalNAc.
? May also contain GlcUA
? Attached to a core protein
through xyl-serine
? Widely distributed troughout the body.
Contributes to the pliability of the skin
? Evidence suggests it may play a part in blood
coagulation, wound repair and resistance to
infection
Keratan Sulfate (KS) I and II
? Repeating units of Gal and
GlcNAc
? KS I is attached to core
protein through GlcNAc-Asp
? KS II is attached through
GalNAc-Thr
? Present mainly in cornea,
cartilage, bone
? In the eye, they lie between collagen fibrils and play a
critical role in corneal transparency
Heparin
? Repeating units of GlcN (mostly
sulfated but sometimes acetylated)
and either of the gluconic acids
mostly iduronic acid
? Heparin is linked to its core protein
(mostly glycine and serine) through
a bond with serine
? Heparin is mostly intracellular
unlike rest of GAGs-in mast cells
? Involved in anticoagulation by binding factor factor IX, XI
and Plasma antithrombin III
? Binds lipoprotein lipase in endothelial cell walls and puts
them into circulation
Heparan sulfate
? Made up of GlcN and
uronic acid predominantly
glucoronic acid
? Attached to its core
protein through xyl-serine
? Mainly extracellular
? Associated with the plasma membrane of cells, may
act as receptors and may also participate in the mediation of
the cell growth and cell - cell communication
? This proteoglycan is also found in the basement membrane of
the kidney along with type IV collagen and laminin where it
plays a major role in determining the charge selectiveness of
glomerular filtration.
Synthesis of proteoglycans
? Starts with core protein synthesis from ribosomes on
the RER
? The addition of GAGs takes place in the Golgi
Apparatus
? The addtions of the GAGs to their core protein is of
three types:
1. O-glycosidic linkage between xylose and serine
(xyl-gal-gal-glcua)
2. O-glycosidic linkage between GalNAc and serine
eg in Keratan sulfate II
3. N-glycosylsamine bond between GlcNAc and
asparagine
Elongation
Further modifications
? The units in the
? Epimerization
of
saccharide chains are
glucoronic
acid
to
elongated in alternating
iduronic acid catalysed
acidic/amino
sugars,
by epimerases
donated from UDP
derivatives
through
specific
glycosyl
? Sulfation of the amine
transferases
sugars are catalysed by
sulfo-transferases
Function of Proteoglycans
? organize water molecules
- resistent to compression
- return to original shape
- repel negative molecules
? occupy space between cells and collagen
? high viscosity - lubricating fluid in the joints
? specific binding to other macromolecules
Function of Proteoglycans
? link to collagen fibers - form network - in bone
combine with calcium salts (calcium
carbonate, hydroxyapatite)
? cell migration and adhesion - passageways
between cells
? anchoring cells to matrix fibers
Degradation of GAGs and Inborn Errors of
Metabolism
? Inborn
error
of
? GAGs are degraded
metabolism affecting
by
specific
any of these enzymes
lysosomal enzymes
results in accumulation
including exo and
of GAGs in lysosome
endoglycosidases,
mucupolysaccharidoses
sulfatases
Eg.
Hurler's
and
Hunter's syndrome
Causation of a mucopolysaccharidosis
Mutation(s) in a gene encoding a lysosomal hydrolase
involved in the degradation of one or more GAGs
Defective lysosomal hydrolase
Accumulation of substrate in various tissues,
including liver, spleen, bone, skin, and central nervous
system
Mucopolysaccharidoses (MPSs)
? Autosomal recessive (exception Hunter disease, X-
linked recessive
? Hurler and Hunter syndromes (most widely studied)
? Chronic and progressive and affect multiple organs.
Many patients exhibit
? Organomegaly (eg, hepato- and splenomegaly)
? Severe abnormalities in the development of cartilage and
bone
? Abnormal facial appearance
? Mental retardation.
? In addition, defects in hearing, vision and the
cardiovascular system may be present.
MPS I (Hurler)
? Deficiency of -L-iduronidase
? Is a severe, progressive disorder with multiple
organ and tissue involvement that results in
premature death, usually by 10 years of age
Clinical features:
? Corneal clouding ? Dysostosis multiplex
? Hepatosplenomegal y ? Mental retardation
? Cardiomyopathy ? Coarse facial
features
Intraoral picture showing
Corneal clouding
decayed
teeth
and
macroglossia
Short stature
skeletal dysplasia
Large tongue
Joint stiffness
known as dysostosis
multiplex
Hurler Disease
BIOCHEMISTRY OF BONE
? Bone is made up of the
Cellular Part
matrix and the cells
i. Osteoblast
Matrix
ii. Osteoclast
? Bone matrix is made up
iii. Osteocytes
of organic and inorganic
matter.
iv. Osteoprogenitor
? Organic matter makes up
about 20-40%
Inorganic matter - 60%
Water makes about 10%
Matrix
Organic
Inorganic
Collagen Type I - 90-95% Hydroxyapatite ? Ca10(PO4 )6 (OH)2
Collagen Type V
Octacalcium phosphate -
Ca8H2 (PO4 )6 .5H2O
Osteonectin
Brusite ? CaHPO4 .2H2O
Osteocalcin
Amorphouse calcium
Proteoglycans (Biglycan,
phosphates ? Ca9 (PO4 )6
Decorin)
Magnesium
Fluoride
Sodium
Metabolism
? Bone is a dynamic structure
? Undergoes remodelling in form of resorption and
deposition of new bones
? Remodelling is under the influence of hormones
and physical demands (eg weight bearing)
? Resorption of bones is performed by osteoclast
? Deposition of bones is performed by osteoblast
? Approximately 4% of compact bone and 20% of
trabecular gets renewed annually
Osteoblast and bone deposition
Osteocalcin
? Osteoblast
are
Protein with carboxylated
mononucleated
glutamate with help of Vit
K.
? Descendants
of
mesenchymal marrow
Acts as a dock for Ca2+
cells
which finally reacts with
phosphates
to
form
? Lays down bone matrix
hydroxyapatite
(osteoid) - collagen,
osteocalcin, osteonectin.
Osteonectin
Collagen type I and V
osteoid protein that makes
contact collagen I and
hydroxyapatite
Schematic illustration of the major cells present in the membranous bone.
Osteoblasts are synthesizing type I collagen, which forms a matrix that traps
cells. As this occurs, osteoblasts gradually differentiate to become osteocytes.
? Osteoblast synthesize
most of the proteins found in
bones as well as growth factors and cytokines
needed for mineralization.
? Osteoblast synthesize the new bone matrix called
osteoid and cause its mineralization.
? They contain alkaline phosphatase in their apical
surface which releases phosphates from organic
phosphates.
? Bone proteins such as bone sialoproteins (e.g.
tyrosin rich acid matrix proteins or TRAMP) and
osteopontin bind calcium through their structural
motiffs rich in aspartate and glutamate.
? These proteins provide the initial side of nucleation
for mineralization which is facilitated by localized
high calcium and phosphate concentration
? Ionic product of Ca+2 and PO -3
4 of 70 or more
(average = 40) stimulate mineralization.
? Osteoblast
subsequently
differentiate
into
osteocytes to maintain matrix.
OSTEOCLAST AND BONE RESORPTION
? Multinucleated cells, interspersed between osteoblast
? Cause resorption of bones
? These cells have ruffled border in their apical membrane
which is in contact with bone matrix.
? Protons and lysosomal enzymes such as acid proteinase
released into this area create a micro environment of low
pH (below 4.0)
? The hydroxyapatite crystal solubilizes in this environment
and bone proteins in matrix are degraded leading to bone
resorption.
? Products of the bone resorption are taken up in the
cytoplasm of osteoclasts for further digestion and
transferred into capillaries
? Osteoclast seals off matrix
to be resorbed
? H/K ATPase pump- pumps H+ into the matrix (pH=4)
increasing the solubility of hydroxyapatite
? Lysosomal acid hydrolases
(acid
phosphatases,
collagenases,
sulfatases,
Cathepsin K) exocytosed
into the matrix to hydrolyse
the matrix
? HCO3 - is extruded out of
the cell to maintain
intracellular pH
Regulation of bone metabolism
? Many factors are involved in the regulation of
bone metabolism.
? Glucocorticoids ? inhibition of bone formation.
? Growth hormone (GH) ? stimulation of bone
formation through somatomedins (growth factors
IGF-1 and IGF-2).
? Insulin ? stimulation of synthetic activity of
osteoblasts.
? Thyroid hormones ? stimulation of osteoclasts,
activation of bone remodelation.
Regulation of bone metabolism
? Estrogens ? inhibition of bone resorption
(inhibition of osteoclastic activity through
specific local factors).
? Catecholamines ? antagonists of calcitonin.
? Prostaglandins ? different classes of
prostaglandins have different effect, which is
dependent on concentration (10-9 ? 10-7 mol/l
stimulates synthesei of collagen, 10-6 inhibits
collagen synthesis.
Calcium homeostasis
A. Parathyroid hormone (parathyroid)
? Released by low plasma calcium.
? Stimulates bone resorption.
? Prevents calcium excretion by kidneys.
? Stimulates calcitriol synthesis.
B. Calcitriol (1,25-diOH-Vit. D)
? 25-hydroxylation in liver
? 1-hydroxylation in kidney
? Stimulates bone resorption.
? Stimulates intestinal calcium absorption
Calcium homeostasis
C. Calcitonin (thyroid)
? Is released by high plasma calcium.
? Acts on bone osteoclasts to reduce bone
resorption.
? Net result of its action is a decline in plasma
calcium & phosphate.
CARTILAGE
1. Hyaline
- Flexible and resilient
? Chondrocytes appear
spherical
? Lacuna ? cavity in matrix
holding chondrocyte
? Collagen the only fiber
2. Elastic
3. Fibrous
- highly- bendable
-resists compression and
- Matrix with elastin as
tension
well as collagen fibers
- Rows of thick collagen
- Epiglottis, larynx and
fibers alternating with
outer ear
rows of chondrocytes
(in matrix)
- Knee menisci and
annunulus fibrosis of
intervertebral discs
The Principal Proteins Found in Cartilage
Schematic representation of the molecular organization in the cartilage
matrix.
Link proteins noncovalently bind the core protein (red) of proteoglycans
to the linear hyaluronic acid molecules (gray). The chondroitin sulfate
side chains of the proteoglycan bind to the collagen fibrils, forming a
cross-linked matrix
CHONDROCYTES
? Progenitor cells arise in marrow
? Progenitor cells differentiate into chondroblast
? Chondroblast-secrete chondrin the primary substance in
cartilage for building and repairing cartilage
? When chondroblast get completely surrounded by matrix-
chondrocytes
? Chondrocytes in gaps called lacunae
? Functions to produce and maintain the extracellular
matrix
? CHONDRONECTIN is involved in the attachment of type II
collagen to chondrocytes (the cells in cartilage)
? Cartilage is an avascular tissue and obtains most of its
nutrients from synovial fluid.
? It exhibits slow but continuous turnover.
? Various proteases (eg, collagenases and stromelysin)
synthesized by chondrocytes can degrade collagen
and the other proteins found in cartilage.
? Interleukin-1 (IL-1) and tumor necrosis factor
(TNF) stimulate the production of such proteases.
? Whereas transforming growth factor (TGF) and
insulin-like growth factor 1 (IGF-I) generally exert an
anabolic influence on the cartilage.
Cartilage Matrix
AGGRECAN
Composition
? Collagen ?Type II (main matrix
collagen) and I
? Elastin and fibrous cartilages
contain elastin and type II
collagen respectively
? Proteoglycans-
Aggrecan is the main one.
Others include chondronectin.
Attaches to Collagen type II
Clinical Correlation-Bone and Cartilage
Osteogenesis imperfecta
? Mutations in gene encoding type I collagen
? Leads to increased bone fragility
? scleras are often abnormally thin and translucent and may
appear blue
? Severe forms-babies born with multiple fractures-mostly
fatal
? Eight types (I-VIII) of this condition have been
recognized.
? Types I to IV are caused by mutations in the COL1A1 or
COL1A2 genes or both
? Mutation causes replacement of glycine by another
bulkier amino acid, affecting formation of the triple helix.
Osteogenesis imperfecta
? These mutations result in decreased expression of
collagen or in structurally abnormal pro chains that
assemble into abnormal fibrils, weakening the overall
structure of bone
? When one abnormal chain is present, it may interact
with two normal chains, but folding may be prevented,
resulting in enzymatic degradation of all of the chains.
This is called "procollagen suicide
? Types V to VIII are less common and are caused by
mutations in the genes for proteins involved in bone
mineralization other than collagen
BRITTLE BONE DISEASE
Osteopetrosis (marble bone disease)
? Decreased ability to resorb bones
? Increased density of the bones
? Due to mutation in gene encoding carbonic anhydrase
II.
? Deficiency of CA II in osteoclat prevent normal bone
resorption, and osteopetrosis results.
BONE MODELLING AND REMODELLING
? MODELLING- during growth, skeleton increases in
size by apposition of new bone tissue on outer surface
of cortex.
? REMODELLING- It is a cellular process of bone
activity by which both cortical and cancellous bone are
maintained.
? Bone remodelling has two main functions-
1. To repair micro damage within skeleton to maintain
skeletal strength.
2. To supply calcium to maintain serum calcium levels
? OSTEOPOROSIS results from bone loss due to age
related changes in bone remodelling as well as extrinsic
and intrinsic factors that exagerate this process.
Osteoporosis
? Generalized progressive reduction in bone tissue mass per
unit volume (densimetric studies) causing skeletal
weakness.
? weak bones prone to fracture
? Resorption>deposition
? Primary- age related. Women>men
1. Decrease in estrogen and androgen concentrations
2. Reduced physical activity
3. Insufficient vitamin D and calcium intake
4. Reduced UV exposure, resulting in lower endogenous
production of vitamin D
5. Reduced renal function secondary to diabetes,
arteriosclerosis, or analgesics abuse, resulting in
insufficient 1-hydroxylation necessary to activate vitamin
D
Dual-energy X-ray
absorptiometry (DEXA)
? Gold standard method
to determine bone
mineral density.
Advantages
1. Rapid and non invasive
technique
2. Radiation exposure is
minimal
Dwarfism - Achondroplasia
Achondroplasia
? Affected individuals have short limbs, normal
trunk size, macrocephaly, and a variety of
other skeletal abnormalities.
? often inherited as an autosomal dominant trait,
Rickets
Osteomalacia
Lack of vitamin D in
Lack of vitamin D in
children
adults
1. Bones of children are 1. Bones are inadequately
inadequately
mineralized
causing
mineralized
causing
softened,
weakened
softened,
weakened
bones
bones
2. Main symptom is pain
2. Bowed
legs
and
when weight is put on
deformities of the
the affected bone
pelvis, skull, and rib
cage are common
?
This post was last modified on 30 November 2021