Tissue Engineering - Quiz 2
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What is the extracellular matrix (ECM)?
A complex network of proteins and polysaccharide chains that cells secrete for the architecture of the cells. Allows for organization.
Regulates behavior of cells that touch, inhabit, or crawl through the meshes. Influences their survival, development, migration, proliferation, shape and function.
What type of attachment is performed by cadherins?
Cell to cell attachment and tie cytoskeletons together.
What are the common motives of all biological and tissue engineered systems?
- Interact with the environment (signals, send receive)
- Self assemble
- Extracellular signals guide the internal programs of the cells for development, repair, diseases
- Dynamic systems, Dynamic equilibrium, Feedback
- Continuous controlled remodeling
- Contains basal lamina - where cells are attached to each other by cell-cell adhesions
What type of attachment is performed by integrins?
Cell to matrix attachments
Describe the desire to have the availability of changes in dendritic spine density changes in the brain.
Changes in dendritic spine density underlie many brain functions, including motivation, learning, and memory.
Long-term memory is mediated in part by growth of new dendritic spine or enlargement of pre-existing spines to reinforce a particular neural pathway. This strengthens the connection betweens two neurons and the ability of presynaptic cells to activate postsynaptic cells is enhanced. This is the basis of the synaptic plasticity.
What is a hydrogel?
A network of polymer chains that are water-insoluble, sometimes found as a colloidal gel in which water is the dispersion medium. Hydrogels are superabsorbent (can contain more than 99% water) natural or synthetic polymers.
What are the functions of the extracellular matrix?
- Supports and surrounds cells
- Determines physical properties of tissues
- Reservoir for growth factors
- Role incell adhesion, proliferation, migration
- Role in cell-to-cell communication
- Morphogenesis (creation of shape of tissue)
- Wound healing
- Tumor invasion
What is the basal lamina?
- Organize cell proteins in plasma membrane
- Promote cell survival, proliferation, differentiation
- Serve as highway for cell migration
- Helps determine and coordinate local spatial organization of components
- Structural, filtering roles
- Determine cell polarity
- Influence cell metabolism
What does a biomaterial scaffold provide with a three-dimensional structure and biochemical composition that is attractive to host cell infiltration and conducive to tissue regeneration?
- Neutrients and cells infiltrate from adjacent tissues
- Host cells inviade biomaterial scaffold and begin to signal for capillary ingrowth
- Gradually remodeled by host cells into the appropriate replacement tissue for the damaged site.
What is VEGF?
An angiogenic growth factor for the growth of capillaries.
What is the composition of the ECM?
- Secreted proteins assembled in a network
- Fibrous structural proteins (ie. collagens and elastins)
- Adhesive glycoproteins
- Proteoglycans and hyaluronic acid
- Interstitial matrix
- Basement membrane
(T/F) The basal lamina serves as the permeability barrier determining which molecules will pass into the urine from the blood.
Transmembrane laminin receptors (________ and dystroglycan) in the plasma membrane are thought to organize the assembly of the basal lamina.
What is the protein that gives the ECM elastic properties?
Cross-linked molecules of elastin.
What is a proteoglycan?
- A class of glycoproteins that are heavily glycosylated that serves as the carbohydrate backbone.
- Serves as a filler material in the ECM, movement of molecules in the ECM and signaling.
(T/F) Integrin-ECM mediated function is essential for survival and growth of normal adhering cells, while cancerous cells are able to avoid this requirement.
- Intgrin molecules are used for cell to cell attachments and normal cells undergo apoptosis sshortly after loss of adhesion but cancer cells are able to avoid entering apoptosis.
What is an integrin?
- (Transmembrane proteins)
- Integrins are receptors that mediate attachment between a cell and the tissues surrounding it, which may be either cells or the ECM. They also play a role in cell signaling and thereby regulate cellular shape, motility, and the cell cycle.
Integrins bind cell surface and ECM components such as fibronectin, vitronectin, collagen, and laminin.
What is fibronectin?
Fibronectin is a component of the ECM that binds to integrins and gives matrix strength and resilliance.
Fibronectin plays a major role in cell adhesion, growth, migration and differentiation, and it is important for processes such as wound healing and embryonic development.
What is laminin?
- Component of the basal lamina for cell attachment.
- Laminins critically contribute to cell attachment and differentiation, cell shape and movement, maintenance of tissue phenotype, and promotion of tissue survival.
Sometimes used to coat artifical scaffolds for adhesion.
(T/F) Attachment of tissues cells to ECM protects them against apoptosis (programmed cell death).
- When tissue cells are brought into suspension,t hey become susceptible to self-destruction, even in the presence of sufficient growth and nutrient factors.
What are 6 factors that cell adhesion contributes to?
- Cell proliferation
- Cell differentiation
- Cell motility
- Cellular trafficking
- Tissue architecture
What are the cell adhesion molecules? (6)
- Cadherins (calcium dependent adhesion molecules)
- Selectins (Carbohydrate binding proteins)
- Immunoglobulin (Ig) superfamily
- Mucin-like cell adhesion molecules
- Cartilage link proteins
What are some properties of cadherins?
- Dependence on calcium - calcium binding site
- Removal of Ca causes adhesion to be adrift
- Bind in a homophilic pattern (one cadherin to another)
- Highly selective recognition
- Regulate intercellular recognition
- Fundamental to animal morphogenesis
cadherins generally mediate homotypic cell-cell adhesion and they are present in what type of cell-cell binding sites?
- Cell-cell junctions
- Adherens junctions
What are the key regulators of cell adhesion? Their pivotal role for the molecules in synaptic assembly, remodeling, and plasticity has been revealed.
What are selectins?
- Caldium dependent cell to cell surface carbohydrate binding proteins.
- Binds to oligosaccharides.
- Heterophilic cell adhesion (binding protein binds to another type of site on a cell.
- Binding is relatively weak.
(T/F) Selectins can facilitate carcinoma metastasis (cancer disease?) and heparin can prevent them.
Heparin can prevent the binding of the activated platelets from carcinoma cells?
(T/F) Integrins are transmembrane binding glycoproteins that usually bind cells to matrix but may also bind cells to cells.
Cells can be influenced heavily by the _______, such as the matrix proteins, because of the presence of transmembrane glycoproteins called integrins.
(T/F) Immunoglobulin is a calcium dependent cell to cell binding molecule.
- Immunoglobulin (Ig) superfamily is non-calcium dependent cell to cell binding.
- The bind may be homophilic or heterophilic.
- Single pass, transmembrane proteins which bind to the cytoskeletal system inside the cells.
What is an example of a cartilage link protein?
- a high molecular weight glycosaminoglycan polysaccacharide that is is present in the tissue matrix and body fluids of all vertebrates. It plays a fundamental role in the regulation of cell migration and differentiation.
- The majority of hyaluronon binding proteins belong to the cartilage link-proteins superfamily.
(T/F) Different substrates or surface modifcations have large effects on cell morhpology.
What is the function of radial glia in the cortex?
Allows for migration of neurons in the developing cortex.
What determines cell migration?
What are two basic principles for axons to find their targets?
- Intermediate targets - Stepping stones to approach by relatively linear growth and make a choice at the stepping stones on the next direction.
- Selective fasciculation - Follow existing neuron axons anf thereby forming axon bundles (fascicles) with the ability to switch from one fascicle to another at a given choice point.
What are intermediate targets in axon migration?
- Growing axons can use intermediate targets (stepping-stones) which they approach by relatively simple linear growth. Once they have reached the intermediate target, they have to "make a choice" before aiming for the next intermediate target.
- This breaks the entire path into shorter more manageable segments.
The alternative principle is selective fasciculation
What is selective fasciculation in axon migration?
Most growing axons face an environment already full of other neuronal processes which they can simply follow thereby forming axon bundles (fascicles). A developing axon can also switch from one fascicle to another at a given choice point(s). This selective fasciculation simplifies the navigation problems a growing axon faces.
The alternative principle is intermediate targets.
What are the two categories for axon guidance signals present in the embryo? How are these further classified? What section of the growing axon is used to interpret the signals?
- Repulsive (chemorepulsive, contact repulsive) and attractive (chemoattractive, contact attractive) signals.
- Based on how easily they can diffuse through tissue, a further distinction is made: long range and short range signals.
Long range signals tend to be diffusible molecules secreted by cells.
Short range cells tend to be non-diffusible and bound to cell surfaces or the extracellular matrix (ECM)
- The "growth cone" on the growing tip of the axon is the key structure necessary for interpreting the different signals. It is shaped like a hand and "feels" its way through the embryo.
- Consists of a celtral area (c-region), filopodia and lamellopodia while being highly mobile.
(T/F) Two different cues such as surface chemistry and topography (sudden step down) are important factors for axon migration.
True. If the step is too deep, the axon will not be able to cross the step and fill follow the edge of the step.
What are four types of neuronal implants?
- Direct cell implantation.
- Encapsulated cell implants.
- Controlled release implants
- Axonal guidance implants.
In the case that implanted cells are dying without appropriate oxygen supply, what are possible solutions for this?
- "thin" implants
- tissue engineered construct in a place with good blood supply
- Implants with engineered blood access
- Oxygen generation in or near implants
- Attacting blood vessels around the implant
- Revascularization of the implant (growth factors, cell types)
- Engineered blood vessels
(T/F) Endothelial cells can form tubes in vitro with dependence on scaffold composition and culture conditions for vasculation.
(T/F) Adding fibroblasts can produce VEGF and will increase revascularization.
What are three methods of releasing VEGF?
- Release from scaffold (controlled and 'on demand' or constant)
- Release from genetically modified cells.
What are some factors inducing vascularization?
- VEGF - Vascular endothelial growth factor
- bFGF - Basic fibroblast growth factor
- Fibronectin (integrin receptor activation)
- PDGF - Platelet-derived growth factor
- Transforming growth factor -beta
- Hyaluronic acid
What are factors inhibiting vascularization?
- Monoclonal antibodies (against VEGF)
- Platelet factor-4
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