MBC - Extracellular Matrix

Question 1

General

Answer 1

Complex network of proteins and carbs filling spaces between cells, physical support, mechanical and physiochemical properties of tissue, influences growth + adhesion + differentiation statues of cells and tissues with which it interacts, essential for development + tissue function + organogenesis, deposited by cells (notably fibroblasts), fibrillar and non fibrillar components (make and don’t make fibres), connective tissues particularly rich in ECM; collagen (type I, II, III = fibrillar , IV basement membrane), multi-adhesive glycoproteins (fibronectin + fibrinogen), laminins (basement membrane), proteoglycans (aggrecan + versican + decorin, perlecan (basement membrane)), matrix components interact with cell surface receptors, varied properties (tendon and skin = tough and flexible, bone = hard and dense, cartilage = resilient and shock-absorbing, different collagen and arrangement of oriented collages + different ECM components)

Question 2

Gene mutations affecting matrix proteins

Answer 2

Cause osteogenesis imperfecta (type I collagen), Marfan’s syndrome (Fibrillin I), Alpert’s syndrome (Type IV collagen (alpha5 chain)), epidermolysis bullosa (laminin V (all 3 chains)), congenital muscular dystrophy (laminin II (alpha2 chain))

Question 3

Gene mutations affecting ECM catabolism

Answer 3

Aka multipolysaccharides (MPSs), inability to degrade GAGs, Hurler’s syndrome (poor prognosis, death at around 10, L-alpha-iduronidase)

Question 4

Fibrotic disorders due to excessive ECM deposition

Answer 4

Liver fibrosis (cirrhosis), kidney fibrosis (diabetic nephropathy), lung fibrosis (idiopathic pulmonary fibrosis (IPF))

Question 5

Disorders due to excessive ECM loss

Answer 5

Osteoarthritis

Question 6

Collagens - general

Answer 6

Family of fibrous proteins found in all multicellular organisms, major protein in bone + tendon + skin, most abundant protein in mammals (25% of total protein mass), in skin builds up in different orientations (successive layers nearly at right angles to each other (resisting tensile forces in all directions, mature bone and cornea have same arrangement)), 28 collagen types (roman numerals), 42 genes encoding them, 3 alpha chains (triple helix made up of 1 or more different alpha chains), type I has chains from 2 different genes ([alpha1(I)]_2[alpha2(I)]), types II and 3 only have 1 chain type ([alpha1(II)]_3 and [alpha1(III)]_3)

Question 7

Collagen triple helix

Answer 7

fly-x-y (x=often proline, y=often hydroxyproline), each alpha chain = approximately 1000 amino acids forming left-handed helix, 3 alpha chains form stiff triple helical structure (every third position must be glycine), glycine = small enough to occupy interior (hydrogen side chain allow for tight packing)

Question 8

Collagen biosynthesis

Answer 8

All newly synthesised collagen chains have non collagenous domains at N- and C- termini, removed after secretion for fibrillar collagens but remain part of collagen in most types

Question 9

Collagen - Ehlers-Danlos syndrome

Answer 9

Group of inherited connective tissue disorders, stretch skin and loose joints, collagen mutation affects production + structure and processing

Question 10

Fibrin-associated collagens

Answer 10

Ie types IX and XII, associate with fibrillar collagens, regulate organisation collagen fibrils

Question 11

Network-forming collagens

Answer 11

Type IV, all basement membranes, molecular constitution varies between tissues, non-fibrillar, more flexible (helix disordered in several regions)

Question 12

Collagen type IV assembly

Answer 12

N and C terminal domains uncleared after secretion, interact via uncleaved N termini (assemble into flexible multilayer network), rotary shadowing, supermolecular aggregate production at 4 main sites

Question 13

Basement membranes

Answer 13

Surround muscle + peripheral nerve and fat cells, underlie most epithelia, highly specialized ECMs, contain collagens + glycoproteins and proteoglycans

Question 14

Kidney basement membrane

Answer 14

Glomerular basement membrane (GBM), diabetic nephropathy = accumulation of ECM = thickened GBM = restricted renal filtration and can lead to renal failure, Alport syndrome = collagen IV mutations = abnormally split and laminated GMB = progressive loss of hearing and kidney function

Question 15

Elastic fibres

Answer 15

Elasticity of tissues (ie skin + blood vessels and lungs), interwoven with collagen fibres to limit stretching extent, elastin core + microfibrils (rich in fibrillin)

Question 16

Fibrillin

Answer 16

Mutations in Fibrillin-1 = Marfan’s syndrome (diverse manifestations, mainly skeletal + ocular + cardiovascular systems, individuals predisposed with to aortic ruptures, arachnodactyly (spider-like fingers))

Question 17

Elastin

Answer 17

2 segments that alternate along polypeptide chain (hydrophobic regions and alpha-helical regions rich in alanine + lysine (many cross-linked))

Question 18

Multi-adhesive glycoproteins

Answer 18

Laminins (associated with basement membranes and fibronectin), ECM proteins = very large + modular architecture (characteristic protein domains of 50-200 amino acids, multifunctionality), many multiadhesive (bind various matrix components and cell-surface receptors)

Question 19

Laminins

Answer 19

heterotrimeric proteins made up of alpha chain + beta chain + gamma chain, cross-shaped molecules, very large proteins (each chain = molecular weight between 160 and 400 kDa), multi adhesive, can interact with integrins and dystroglycan cell surface receptors, can self-associate as part of basement membrane matrix, can also interact with other matrix components ie type IV collagen + nidogen + proteoglycans, mutations in specific chains = inherited diseases ie muscular dystrophy and epidermolysis bullosa), congenital muscular dystrophy = absence of alpha2 chain in laminin2 leading to hypotonia + generalised weakness + joint deformities

Question 20

Fibronectins

Answer 20

family of closely related glycoproteins of ECM, can exist as insoluble fibrillar matrix/soluble plasma protein, derived from single gene with alternate splicing of mRNA giving rise to different types, multi-adhesive, large multidomain molecule linked together by disulphide bonds, regulate cell adhesion and migration in embryogenesis and tissue repair, important for wound healing, form mechanical continuum with actin cytoskeleton (integrin receptors at cell surface provide linkage)

Question 21

Proteoglycans

Answer 21

Core proteins to which one or more glusomaminoglycan (GAG) chains attach, GAG chains = repeating disaccharide units with one of 2 sugars being an amino acid sugar (1 OH group replaced with amine group), many sulfated/carboxylated (carry high negative charge which attracts cloud of cations (Na+ included) resulting in large H2O amounts being sucked into ECM), basement membrane proteoglycans (ie perlecan), aggregating proteoglycans (interact with hyaluronan and aggrecan), small leucine-rich proteoglycans (decorin), cell surface proteoglycans (syndecans 1-4)

Question 22

Cartilage

Answer 22

Matrix rich in collagen, large GAGs trapped within mesh work, balance of swelling pressure negated by tension in collagen fibres (tensile strength (synovial cartilage)), up to 100 GAG chains (grouped based on repeating disaccharide into hyaluronan + chondroitin sulfate and dermatan sulfate + heparin and keratan sulfate)

Question 23

Hyaluronan

Answer 23

Aka hyaluronan acid, spun out directly from enzyme embedded in plasma membrane, ECM of soft connective tissues, carbohydrate chain with no core protein, unsulfated, repeating disaccharides (up to 25000 sugars), can undergo very high degree of polymerization (occupy relatively large volume, typically viscous (ie eye vitreous humor and joint synovial fluid (protect cartilaginous surface from damage))

Question 24

GAGs

Answer 24

all except hyaluronan synthesized and attached to their core proteins in ER + Golgi apparatus

Question 25

Aggrecan

Answer 25

Cartilage ECM, highly sulfated GAGs (more negative charge also with negatively charged carboxyl groups which attract osmotically active cations (ie sodium) = large quantities of retained water that resists compressive forces)

Question 26

Osteoarthritis

Answer 26

Erosive, excessive ECM degradation, cartilage cushioning properties =lost, with increasing age aggrecan is cleaved by aggrecanases and metalloproteinases = aggrecan fragments to synovial fluid

Question 27

Fibrotic diseases

Answer 27

Excessive production of fibrous connective tissue = excessive blue staining