Lecture 11 - ECM stiffness, fibrosis and cancer Flashcards
The extracellular matrix
The mechanical properties of most tissues are defined by their matrix
Matrisome: what is it made of, what two types are there, and what features define its mechanical properties?
Matrisome proteins - proteins that compose or associate with the ECM - are classified as:
- Core Matrisome - structural components: collagens, glycoproteins and proteoglycans
- Matrisome-Associated - secreted proteins that associate with or modify the ECM
The following features of the matrix define its mechanical properties:
* Identity of matrix proteins
* Concentration of matrix proteins
* How proteins are organized
* Whether matrix proteins are crosslinked together
* Some tissues also contain mineral deposits (e.g., bone)
Mass spec
- Disrupting and solubilising tissues to get proteins
- Using trypsin to digest the protein
- Using liquid chromatography coupled tandem mass spectrometry (LC-MS/MS)
- Obtaining bioinformatics
Core matrisome: how much of it is composed of proteins, what do collagens, proteoglycans, and glycoproteins do?
20% mass is proteins
Collagens - structural components of connective tissues, using a repeating sequence of amino acids allows the formation of triple-helical structures, that assemble into fibrils
Proteoglycans (e.g., perlecan, biglycan, lumican):
Proteins functionalized with glycosaminoglycans (GAGs; repeating polymers of disaccharides) bind to water, salts and soluble factors; fill space in the ECM and provide lubrication
Glycoproteins (e.g., fibronectin, laminins):
Proteins functionalized with complex oligosaccharide chains, provide a range of functions: ECM assembly; cell adhesion; signalling; binding growth factors etc.
The matrisome can be studied in different tissues and resolved spatially and by time and is affected by disease
Matrix proteins
Many matrix proteins behave as “biological polymers” - Higher concentrations increase stiffness, strength highest when along a length (ie, a tendon)
Assembly and orientation therefore influence the strength
Cross-linking can bind ECM molecules together, increasing the stiffness of tissues
hallmarks of cancer
Although the specific mutations and affected pathways may differ, most cancers acquire the same functional capabilities - the ‘hallmarks of cancer’
The matrices of healthy tissues, cancers and sites of metastasis are different - although there are many shared proteins, they all have many differences too
- Sustaining proliferative signalling
- Evading growth suppressors
- Avoiding immune destruction
- Enabling replicative immortality
- Tumour-promoting inflammation
- Activating invasion and metastasis
- Inducing angiogenesis
- Genome instability and mutation
- Resisting cell death
- Deregulating cellular energetics
ECM protein receptors: what examples are there, and what do they do?
DDR, integrin receptors, etc
Bind to ECM proteins and activate several pathways
What types of cell behaviours can be influenced by mechanical signals?
The following cell behaviours can be influenced by mechanical signals:
* Cell morphology (e.g., spreading and shape)
* Contractility (how hard cells pull on their surroundings)
* Propagation rate and apoptosis
* Cell movement
* Differentiation (commitment to lineage)
Matrix-regulated pathways: FAK, MAPK/ERK, VEGF, Rho/ROCK/Rac.
Focal adhesion kinase (FAK) signalling limits sensitivity to growth inhibitors and apoptosis
Mitogen-activated protein kinase (MAPK) and extracellular-signal-regulated kinase (ERK) signalling promotes cell proliferation
Vascular endothelial growth factor (VEGF) signalling induces angiogenesis
Rho/ROCK and Rac signalling drive invasion and metastasis
Immune cell activity can be modulated by extracellular matrix
Breast cancer: what is it, how frequent is it, what are the statistics, and how does diagnosis work?
Breast cancer is one of the most prevalent tumour types
Lifetime risk is 1-in-8 for women.
55,000 diagnoses per year in the UK, and 1.5 million worldwide.
Results in death in 1-in-5 cases in the UK, 1-in-3 worldwide
Mammography uses low-intensity X-rays to look for characteristic masses in breast tissue - tumours are seen as regions of very high mammographic density (MD) - High MD is the most significant risk factor for breast cancer after ageing
High MD: what is it, what is it the most significant risk factor for, and what do elevated MD levels correlate with?
High MD tissue is stiffer
High MD is the most significant risk factor for breast cancer after ageing
Areas of elevated MD correlate with increased fibrillar collagen & higher fibre organization
What occurs in the ECM as a tumour develops
Epithelial cell begins uncontrolled cell proliferation
Increased matrix production - e.g., by fibroblasts
Increased crosslinking - ie, by enzyme lysyl oxidase, LOX
Reorganisation of matrix - e.g., by proteases
Cancer cells invade ECM
CAFs: what are they, what relation to cancer do they have, and what physiological effects do they cause?
Cancer-associated fibroblasts
Solid tumour formation can be considered as a fibrotic process
- Growth of tumour
- Recruitment of fibroblasts.
- Excessive matrix
- Tissue stiffening
- inflammation
- Metastasis
- Organ failure
Metastasis: what does it require and what limits does it have?
- Enzymatic matrix remodelling
- Cell deformation
Invasion into surrounding tissue is limited by the cell’s ability to degrade the matrix, or to squeeze through small gaps - typically the nucleus
The nucleus: what is its size as an organelle, how is it attached to the cytoskeleton, what determines its stiffness, and what is its role in metastasis?
Typically the largest and stiffest organelle
Attached to the cytoskeleton by IF, MT, and actin
Stiffness is determined by lamin proteins in the nuclear envelope - Lamin A (viscous), lamin B (elastic)
More lamin: metastasis inhibited
