strand 2 Flashcards
tissues function
specialization
distribution of workload/ mechanical stress
4 types of animal tissues
epithelial
muscular
nervous
connective
epithelial tissue cells to ECM ratio
^ cells
less ECM contact
cell junctions
link individual cells
cytoskeletal filaments
transmit mechanical forces
basal lamina
point of cell attachment
connective tissue
characteristics of epithelial cells
assymetric/ polarized
4 types of cell junctions in tissues
adherins junctions
desmosomes
tight
junctions
gap junctions
cadherin
superfamily of Ca2+ dependent molecules
E-cadherin/ N cadherin/ P cadherin
classical/ non-classical
components of adherens junctions
flexible hinge region separates 5 copies of extracellular domain
N-terminal cadherin domains
Ca2+
adherens junctions
homophilic cadherin binding
E-cadherin-N-cadherin
intracellular domain interacts w actin via catenins / adaptor proteins > reducing tension as myosin II pulls on actin
Ca2+ function in adherens junctions
prevents flexing
promotes homophilic binding to another cadherin
macro-assembly allowing adherens junctions to withstand mechanical force
membrane protrusions initiate cell-cell contact
actin/ cadherin recruitment expands junction
actin remodelling/ myosin recruitment further expands
desmosomes
specialized cadherins connecting w intermediate filaments for strength at junctions
tight junctions
selective permeability barrier of epithelial
sealing strands of occludin and claudin proteins
differential transporter molecules expressed in apical/ basal PM
selective transport
gap junctions
connexin/ innexin channels
similarities w epithelial/ muscle/ nervous tissue
4 junction types
^ cell-cell interaction
basal lamina interaction
ECM function
strength and support
cell communication
polarity
shape
cell migration
basal lamina
thin layer of ECM
produced by cells above and below
evolutionarily conserved
maintains epithelial
laminin/ typeIV/ XVIII/ collagen / nidogen/ perlecan/ fibronectin
connective tissue
reduced cellular content/ cell-cell contact
^ECM content
ECM
main stress-bearing component of connective tissue
indirect means of cell-cell contact
2 types of connecive tissue
indigenous
immigrant (immune cells)
connective tissue ECM composition
^MW ^charged polysaccharides
fibrous proteins
glycoproteins
(all self-associate)
» Can become calcified/ transparent
polysaccharides in ECM of connective tissue
GAGs cov. attached to proteins (repeating sulphated disaccharide
bind much water
fibrous proteins in ECM of connective tissue
stiff, triple stranded, helical for tensile strength
collagen family
glycoproteins in ECM of connective tissue
elastins/ fibronectins
types of proteoglycans
simple
complex
(can self-aggregate)
connective tissue
decreased cellular content/ ^ECM content
main stress-bearing component for indirect cell-cell contact
types of cartilage
hyaline
fibro
elastic
hyaline collagen
chondrocyte articular joints
fibro collagen
joint capsules/ ligaments
elastic collagen
ear/ larynx
articular cartilage
TII collagen and aggrecan for strength and support
collagen bio-synthesis
synthesized in ER and processed in golgi, exocytosis release
pre-synthesized with pro-peptides that are removed to enable auto-aggregation
Ehlers Danlos syndrome
defective collagen deposition
hyperextensible joints
aggrecan
large proteoglycan
- attracts water for hydrated gel
- high charge (GAG)
- hyaluronan links aggregates
hydrated gel of aggrecan function
compression resistance
swelling pressure (turgor)
strength and support
chondrocyte
-only found in adult cartilage
-5-10% ECM vol
-RER/ golgi rich
-secrete type II collagen and aggrecan
-highly specialized indigenous cell
chondrocyte differentiation
during embryonic development from MSC
MSC
mesenchymal stem cells
MSC that differentiate into chondrocytes signatures
Sox-9 expression
Col2A expression
chondrocyte proliferation and ECM synthesis
Sox-9
HMG-box DNA binding txn factor
COL2A
produces collagen type II (cartilage precursor)
what does chondrocyte proliferation require?
TGF-beta
fibroblast growth factor
insulin-like growth factor
parathyroid hormone related protein
ECM
network of fibrous proteins and hydrated proteoglycans that surround cells in tissues
- maintained by synthesis and breakdown of matrix molecules
proteinases
break down/ cleave proteins
intracellular e.g. threonine/ cysteine
extracel e.g. serine/ metallo
degradome
570 genes in a genome encoding proteinases
collagenase
break down collagen
metalloproteinase family 3 minimal domains
catalytic (binds ZN2+)
PRE/pro (removed during secretion and activated)
haemopoxin (substrate specificity)
3 types of metalloproteinase family
- matrix metalloproteinases
- ADAM
-ADAMTS
matrix metalloproteinases
key ECM modifier
- mediate catabolism and release/ activation of growth factors/hormones/cytokines in ECM
-Zn2+ binding catalytic
-ECM secretion as inactive pro-enzymes
- activated by pro region removal by kinases
^specificity
ADAM
A disintegrin-like and metalloproteinase
(Most membrane bound)
ADAMTS
ADAM with thrombospondin motifs
- secreted into ECM like MMPs
involved in catabolism of ECM
what are metalloproteinases inhibited by?
- alpha 2 macroglobulin
-tissue inhibitors of metalloproteinases (TIMPs) > slot into active sites
whats cleaved from ECM?
Why?
specific catabolic fragments and neo-epitopes
> allows for ECM breakdown monitoring
Loading stress effect on ECM homeostasis
produces ECM fragments and ^ECM synthesis
ECM remodelling functions
-embryonic development
-wound healing (angiogenesis and immune cell migration)
-metalloproteinase activity control]
-tumour prevention
ECM breakdown product recognition
homeostatic control> integrin recognition/ signalling and inflam cytokines ^ECM synthesis
PRR recognition expressed in ECM cells
healthy ECM maintenance
-ECM secretion of metalloproteinase
-ECM fragment recog (integrin/PRR)> feedback
-inflammation upon matrix damagee
excessive ECM breakdown outcome
tumour migration
types of ossification
intramembranous
endochondrial
intramembranous ossification
conversion of mesenchymal tissue into bone
endochondral ossification
conversion of cartilage to bone
(foetal development)
ossification initiation
MSC-differentiated osteoblasts (chondrocytes die and cavities form)
osteoblasts
cells forming bone
what controls spatial patterning of ossification
morphogens (secreted signalling molecules)
via inductive signalling (m pass between cells via developing ECM)
hedgehog protein family
sonic (SHH)
desert (DHH)
indian (IHH)
positive feedback loops of hedgehog protein family
loops of IHH and PTHrp (skeletal morphogen)
> maintains spatial chondrocyte proliferation
where’s PTHrp secreted
DHH
Where’s PTHrP produced?
chondrocytes
smoothened and patched interaction in presence of hedgehog
Hh binding to Ptch reverses inhibition of Smo> moves to nucleus and activates gene expression
Cubitus interruptus (Ci) switched off
smoothened and patched interaction in presence of hedgehog
Ci cleaved and bound to repressor
genes switched off responsive to hedgehog
long bone formation
cartilage catabolized and osteoid ECM calcified, trapping osteoblasts
PTHrp role in long bone formation
maintains chondro proliferation/ cartilage production
prevents terminal differentiation
IHH and PTHrP feedback in long bone formation
less PTHrp received further from central, therefore less IHH, therefore less PTHrP produced, therefore ^ossification
articular cartilage
only chondrocytes
ECM connective tissue directs bone development in embryogenesis (permits mechanical load/art bone movement)
osteoarthritis
progressive loss of ECM/ “chondrogenic phenotype” in articular cartilage without obvious cause
osteoarthritis symptoms
limited joint movement/ deformity/ inflammation/ severe pain and reduced QOL
ass. w new bone formation
gene expression in OA
reduced sox9 expression
ECM homeostasis
loading stress > ECM fragments >ECM synthesis
integrins mediate signalling (FAK recruitment for altered gene exp)
aggrecan stain
saffronin-o
destabilisation of medial miniscus
miniscus cut to destabilize joints
aggrecan breakdown
ADAMTS-S breaks down and ^neo-epitopes identifed w diagnostic antibodies
aggrecanase
ADAMTSS
collagenase
MMP-13
genes behind OA
GDF5
RUNX2
PTHLH
SMAD3
GDF5
growth factor of TGF beta fam in ECM
RUNX2
master txn factor driving endochondrial ossification
PTHLH
PTHrP chondrocyte growth factor
IHH secretion driven
SMAD3
intracellular signalling protein in TGF beta production
OA therapies
surgery
NSAIDs
identify/ target key proteinases (ADAMTS-4/5/ MMP-13)
genetic screening
TIMP3
inhibits MMP-13
common patients w RA
young female
rheumatoid arthritis
progressive ECM/ chondrogenic phenotype loss in articular cartilage from immune cell-mediated damage
Rheumatoid factor
IgM autoantibodies against IgG structural antigens (reacting w citrullinated epitopes)
arginine PTM
citrulline
ACPA
anti-citrullinated peptide antibodies
60% RA patients possess
RA mediation
B and CD4 T cell mediated autoimmunity
RA characteristics
synovium inflammation > leukocytes into tissues
autoreactive T cells activate macrophages> pro-inflam cytokines > ^MMP/ RANK ligand by fibroblasts
MMP attack tissues > osteoblast bone destroying/ joint destruction
autoantigens recognized by CD4+ T cells in RA
collagen (CIA collagen induced antigen)
aggrecan (proteoglycan induced arthritis PGIA)
RA therapies
NSAID
TNF-alpha target for infliximab
rituximab (kills B cells)
ACPA screening