Remodelling Flashcards
how can cells behave as communities?
- different cell types interact
- make larger structures tissues and then organs
- allows/enables organisms
- ECM allows tissues to form
what is the ECM?
- extracellular matrix
- forms a home for cells
- fibres surround cells
- interact with ECM through integrins
- eg collagens, fibronectin, iaminium, proteoglycans
what are tissues composed of?
- cells and often ECM
- epithelial doesnt have it
what is the ECM composed of?
different proteins and proteoglycans
what does the composition of ECM determine?
determines the physical properties from hard structures
what is the role of the ECM?
- not just an inert scaffold, its dynamic
- helps to define the phenotype and behaviour of the cell
- acts as a storage compartment for signalling molecules
- regulates what signals are presented
what are some features of collagen?
around 25% of the total mammalian proteins
- vitamin c is an essential cofactor for collagen synthesis
- around 30 different types
what is the strutcure of collagen?
- composed of homo or heterodimers of alpha chains to form a triple helical based structure
- amino acid sequence consists of Gly-x-4
- divided into fibrillary or non-fibrillar
what are fibrillar collagens?
organised into fibres and provide tensile strength
what are non-fibrillar collagens?
collagens form networks and sheet like structurs
how is collagen organised?
- amino acid chain
- alpha chain
- assembled into triple helices
- assembled into collagen fibrils
- finally into collagen fibres
why does collagen need gly in the amino acid chain?
- ensures every third residue can twist to form the alpha helix
what is the triple helix?
assembly end to end to make an elongated structure and join through covalent bonds
how is collagen synthesised?
- initally in the cell but then outside
- ribosome = synthesis of alpha chains (has a pro-peptide domain that can be later cleaved off)
- vitamin C interacts and enables hydroxylation of selected prolines and lysines
- glycosylation events occur in the ER
- assemble into the triple helices aided by disulphide bonds
- packaged into a vesicle and secreted out of the cell
- pro-callgen contains the pro-peptide domain
- cleavage of pro-peptides through pro-collagen peptidases
- get collagen allowing assembly into a collagen fibril
- then aggregates into the fibre
what is brittle bone disease?
- osteogenesis imperfecta
- mutations in alpha1 or alpha2 genes
- clearest symptom is bone fragility
what is dermatosparaxis?
- proteolytic processing of procollagen is require for correct assembly into fibrils
- fragile and loose skin with substantial bruising and bleeding
- caused by mutation in the N terminal pro-peptides
how do glycosaminoglycans and proteoglycans interact?
glycosaminoglycans (GAGs) are covalently attached to a core protein to form proteoglycans (except hylauronan)
what do glycosaminoglycans and proteoglycans?
provide hydrated, space-filling functions and compressive strength
what are GAGs?
- 4 classes
- formed by polymerisation of specific disaccharides and modification
- chrondroiton sulfate, hepara sulfate and keratan sulfate (attach to core proteins)
what are hyaluronans?
can attach to the proteoglycan aggrecan or exists as its own disaccharide polymer
what are some examples of proteoglycans?
aggrecan (CS KS), Decorin (CS DS), Perlecan, Syndecan
what is the process of assembly of GAGs and proteoglycan?
- a core protein to which GAGs attach
- sequential addition of GAGs and linking sugars
- have repeating disaccharide repeats
GAGs –> Sugars –> Core protein
how does hyaluronan bind?
- bind to the aggrecan
- does that through its N terminal hyraluronan binding domain and links proteins
how are GAGs and proteoglycans involved into cell signalling?
- proteoglycans can regulate cell signalling events
- have a major role in signalling between various secreted signalling molecules
- can inhibit or enhance the signalling activity of growth factors
what is FGF signalling?
- fibroblast growth factor
- syndecan is a heparan sulfate proteoglycan (HSPG) that helps to control FGF signalling strneght - membrane bound
- Free FGF can bind heparin sulfate side chains
- syndecan can determine the concentration of FGF at the cell surface
- can have free heparin sulfate proteoglycans
what is the role of elastin?
- maintains the elasticity in the skin
- provides elasticity to help regulate tissue function
- allows stretching
- consists of covalently linked monomers
- when relaxed has a coiled sturcture
- found in the lungs and elastic ligaments
what is curtix laxa?
- mutations that effect how elastic is produced or organised
- rare inherited disorder
- skin inelastic and hangs loosely, hypermobility of the joints may also feature
what is fibronectin?
- large glycoprotein that helps matrix organisation
what is the role of fibronectin?
helps matrix organisation
- has a specific binding domains that can link thing together
what is the structure of fibronectin?
- has a very specific binding domain
- homodimer has binding motifs for proteoglycans, cells and collagen
how can you see cells grown on different fibronectin shapes?
- determines how cells adhere to structures by presenting one surface to ahere to
- a teardrop FN
- when the cell is on the FN it occupies the space available
- a lemellipodium forms
- produces structure for migration
- can grow on different shapes
- from this can determine how structures in the cell are organised
what is the basement membrane?
- specific ECM barrier
- separates the epidermis and the dermis
- above = has keratinocytes
- bellow = collagen network in underlying dermis
- a flat, sheet structure
what is the basement membrane composed of?
- entactin, perlecan, laminin, IV collagen
what is entactin?
multi-adhesive matrix protein
what is type IV collagen?
- non-fibrillar collagen
what is the structure of Type IV collagen?
- triple helical with a C terminal globular domain and N terminal domain
- assemble end to end and laterally
- globular heads come together to form alpha helices
- organise into the alpha helix
- collagen dimerisation through C-Nc trimers
- head to head interactions
what does the basement membrane act as?
a selective barrier for cell molecules
what are the properties of a stem cell?
to renew and differentiate
what is self-renew?
- asymmetric cell division
- one becomes a differentiated cell
- one becomes a stem cell
- maintains the stem cell pool
what is the telomerase activity like in stem cells?
- high levels in stem cell
- telomerase added back on the chromosome so its not shortening
- especially in pluripotent
what is totipotent?
- have the ability to develop into an entire organism
- very early days of embryogenesis
- fertilised egg up until around day 4 (when the blastocyst is formed)
what is pluripotent?
- have the ability to develop into virtually every cell type
- do norm form a placenta and supporting tissues
- ES cell of the inner cell mass (ICM) in the blastocyst are pluripotent
what does a teratoma assay determine?
the pluripotency
how does a teratoma assay work?
- inject into the back of mice
- remove an look for a teratoma which should include all 3 germ layers
what are the 3 germ layers?
- endoderm
- mesoderm
- ectoderm
what transcription factors is pluripotency controlled by?
- Oct-4
- Nanog
- Sox2
what are the roles of Oct-4, Nanog and Sox2?
- act collectively to regulate ESC pluripotency
- can activate promoters of self-renewal genes
- silent promoters of developmental genes
- different genes can drive different specific lineage commitment pathways
what is the therapeutic potential of stem cells?
- generation of specific cell types and tissue structures to replace worm or disease body parts
- eg neurodegenerative, disease, diabetes corneal defects, cardiovascular disease, musculoskeletal disorders
what are the potential difficulties of stem cells as a therapy?
- understanding how specialisation takes place
- directing differentiation to generate specific tissue types
how stem cells been used in experimental therapies for Parkinson’s disease?
- directed differentiation of dopaminergic neurons
- NURR1, FGF8 and shh are all required in the normal brain
- look at markers to see if shh and FGF8 have the same markers as DA neurons (this doesnt tell you about functionality)
- then did an in vivo model in a mice model
- DA neurons killed
- test if functions are recovered by transplanted cells
how could ES cells be used to treat paralysis?
- differentiated into cells in the spinal cord
- rat recovered to some extent
- some ability to walk
what is SCNT?
- somatic cell nuclear transfer
- fusion of a somatic cell nucleus with an egg emptied of its genetic material
how can SCNT be used in therapies?
- therapeutic cloning, generate a blastocyst where pluripotent cells are expanded in vitro
- used to create dolly the sheep
what are adult stem cells?
- they are multipotent
- many tissues in the adult can undergo repair and remodelling
- enabled by the presence of stem cells
what is multipotent?
differentiate into more than one cell type
- much more restricted
- generates cells of the tissue in which it resides
how can multipotent stem cells be used therapetuically?
- patients own cells can be used
- fewer ethical concerns as not using embryos
- fewer safety concerns as a teratoma wont be formed
what are heamatopeoitic stem cells used in?
- bone marrow transplants and blood transplants
- the rate of these kind of transplants are generally increasing
what are mesenchymal stem cells?
- found in the bone marrow
- differentiate to bone, fat and cartilage
(make osteoblasts, chondrocytes, adipocytes and stromal cells)
where are mesenchymal stem cells targeted>
- at disorders that affect the muscoskeletal system
- can make bone and cartilage
- theoretically be used to regrow
- studies have been successful to some degree
how can cornea and limbal stem cells be used?
treat the epithelial structure on the outer surface
- eg when theres a limbal cell deficiency or a chemically burnt eye
what is the limbus?
- round the outside of the cornea
- stem cell niche
- migrate to the epithelial layer which is essential for protecting the cornea
how would loss of corneal function be treated with stem cells?
- limbal harvest
- limbal stem cell culture (explant culture or suspension culture)
- culture limbal epithelium on a scaffold
what are iPS cells?
induced pluripotent stem cells
- can express telomerase, ESC surface markers and differentiate into the 3 germ layers
how can iPS cells be used?
- introduction of genes associated with ESC pluripotency
- can reprogramme somatic cells to pluripotent stem cells
- introduction of just four factors appear to be sufficient
what are the issues with iPS cells?
- reprogramming somatic cells to iPS is inefficient
- use of viral delivery systems
- use of oncogenes (potentially cancer forming)
- epigenetic memory of parent cells
- teratoma risk
what are the potential of iPS cells?
- differentiate cells into whatever we need
- personalised medicine
- transplants
