3.
Extra Cellular: outside the cell
Matrix: structure made from a network of
interacting components
The ECM is composed of an interlocking
mesh of
fibrous proteins and glycosaminoglycans
(GAGs).
Components of the ECM are produced
intracellularly by resident cells, and
secreted into the ECM via exocytosis.
3
5.
Act as structural support to maintain cell organization and
integrity (epithelial tubes; mucosal lining of gut; skeletal
muscle fiber integrity)
Compartmentalize tissues (pancreas: islets vs. exocrine
component; skin: epidermis vs. dermis)
Provide hardness to bone and teeth (collagen fibrils
become mineralized)
Present information to adjacent cells:
◦ Inherent signals (e.g., RGD motif in fibronectin)
◦ Bound signals (BMP7, TGF , FGF, SHH)
Serve as a highway for cell migration during development
(neural crest migration), in normal tissue maintenance
(intestinal mucosa), and in injury or disease (wound
healing; cancer)
5
9.
Collagens
Proteoglycans
◦ Perlecan, aggrecan, agrin, collagen XVIII
Hyaluronan (no protein core)
Large Glycoproteins
◦ Laminins, nidogens, fibronectin, vitronectin
Fibrillins, elastin, LTBPs, MAGPs, fibulins
“Matricellular” Proteins
◦ SPARC, Thrombospondins, Osteopontin,
tenascins
9
10.
Most ECM proteins are large, modular,
multidomain glycosylated or glycanated
proteins
Some domains recur in
different ECM proteins
◦ Fibronectin type III repeats
◦ Immunoglobulin repeats
◦ EGF-like repeats
Perlecan
10
11.
Specialized layers of extracellular matrix
surrounding or adjacent to all epithelia,
endothelia, peripheral nerves, muscle cells,
and fat cells
Originally defined by electron microscopy
as ribbon-like extracellular structures
beneath epithelial cells
11
14.
In general, basement membranes appear very
similar to each other by EM.
But all are not alike!
There is a wealth of molecular and functional
heterogeneity among basement membranes,
due primarily to isoform variations of
basement membrane components.
14
16.
Collagen IV 6 chains form α chain
heterotrimers
Laminin 12 chains form several α-β-γ
heterotrimers
Entactin/Nidogen 2 isoforms
Sulfated proteoglycans Perlecan and Agrin are
the major ones; Collagen XVIII is another
16
17.
A family of fibrous proteins found in all
multicellular animals
They are secreted by connective tissue cells,
as well as by a variety of other cell types
They are the most abundant proteins in
mammals, constituting 25% of the total
protein mass in these animals
17
20.
Collagen is highly cross-linked in tissues
where tensile strength is required such as
Achilles tendon
If cross-linking is inhibited, the tensile
strength of fibers is greatly reduced,
collagenous tissues become fragile, and
structures tend to tear (skin, tendon, and
blood vessels)
20
22.
Collagen I
◦ Osteogenesis imperfecta
◦ Ehlers-Danlos syndrome type VII
Collagen II
◦ Multiple diseases of cartilage
Collagen III
◦ Ehlers-Danlos syndrome type IV
Collagen IV
◦ Alport syndrome, stroke, hemorrhage, porencephaly
Collagen VII
◦ Dystrophic epidermolysis bullosa (skin blistering)
22
25. Collagen Crosslinking
If crosslinking is
inhibited (Lysyl
hydroxylase mutations;
vitamin C deficiency),
collagenous tissues
become fragile, and
structures such as
skin, tendons, and
blood vessels tend to
tear. There are also
many bone
manifestations of
under-crosslinked
collagen.
25
26.
Liver spots on skin, spongy
gums, bleeding from mucous
membranes, depression,
immobility
Vitamin C deficiency
Ascorbate is required for
prolyl hydroxylase and lysyl
hydroxylase activities
Acquired disease of fibrillar
collagen
Illustration from Man-of-War by Stephen Biesty (Dorling-Kindersley, NY, 1993)
26
27.
At least four types of osteogenesis imperfecta
Type I osteogenesis imperfecta is the mildest
form of the condition
Type II is the most severe results in death in
utero or shortly after birth
Milder forms generate a severe crippling
disease
27
28. Clinical:
Ranges in severity from mild to perinatal lethal
bone fragility, short stature, bone deformities, teeth
abnormalities, gray-blue sclerae, hearing loss
Biochemical:
reduced and/or abnormal type I collagen
Molecular:
mutations in either type I collagen gene, COL1A1 or
COL1A2, resulting in haploinsufficiency or disruption of
the triple helical domain (dominant negative: glycine
substitutions most common)
28
29. •
Mutations in the COL1A1 and COL1A2 genes
cause OI
•
These mutations typically interfere with the
assembly of type I collagen molecules
•
•
A defect in the structure of type I collagen
weakens connective tissues, particularly
bone, resulting in the characteristic features
of OI
OI types I, II, and IV have an autosomal
dominant pattern of inheritance, which
means one copy of the altered gene in each
cell is sufficient to cause the condition
29
31. Heterotrimers are composed of
one , one , and one chain.
400 to 800 kDa cruciform, Y, or rodshaped macromolecules.
Major glycoprotein of basement
membranes—it’s required!
Chains are evolutionarily related.
5 alpha, 4 beta, and 3 gamma chains
are known. They assemble with each
other non-randomly.
15 heterotrimers described to date.
LM-521
31
32.
Laminin chains assemble
into trimers in the ER and
are secreted as trimers
into the extracellular
space.
Full-sized laminin trimers
can self-polymerize into a
macromolecular network
through short arm-short
arm interactions.
The chain LG domain is
left free for interactions
with cellular receptors.
32
33. Involves LG domains and receptors on the surface of cells.
Results in laminin polymerization and signal transduction.
33
37.
Caused by dominant
Fibrillin-1 (FBN1)
mutations
◦ Haploinsufficiency is the
culprit
Skeletal, ocular, and
cardiovascular defects
Deficiency of elastinassociated microfibrils
Syndrome may result from
alterations in TGF
signaling, rather than
purely structural changes
in microfibrils
37
38.
Damage to the lung air sacs
(alveoli) that affects breathing
Macrophages induced to
“ingest” particles in smoke also
secrete proteases that degrade
elastic fibers
Loss of lung elasticity makes
exhalation difficult
Increased alveolar size reduces
the surface area for gas
exchange
38
