Advanced Cell Bio Exam 2: ECM Article Review

Definition of ECM according to what is given in the intro?

- A dynamic 3-dimensional network of macromolecules that provides structural support for the cells and tissues.

What is the purpose of the manuscript?

- To give a broad overview of the matrisome, the major ECM macromolecules, and their interaction networks within the ECM and with the cell surface.
- Summarize their main structural features and their roles in tissue organizations and cell functions.
- Emphasize the importance of specific ECM constituents in disease development and progression as well as the advances in molecular targeting of ECM to design new therapeutic strategies.

What are the major functions of the ECM?

- Operate as communication liaisons between the cells in organs and tissues by coordinating multiple signaling inside-out or outside-in commands.
1. Functions as a communication liaison
a. Guide tissue morphogenesis
b. Development and homeostasis
c. Growth, survival, differentiation and adhesion

Is the ECM tissue specific?

Yes, but it is also adaptive

What are the major components of the ECM?

Collagens, Proteoglycans, Glycosaminoglycans, Elastin, Laminins, Fribronectin, and other glycoproteins

What are the characteristics of Collagens?

Over 30% of ECMs
-Type I, II, III make up 80-90% of body collagen
-Triple-helix of homo or hetero trimeric α-chains
-Supportive, elastic and bring stability
-IX abundant in connective tissue
-Possess a triple-helix morphology consisting of homo- or hetero-trimeric alpha-chains.

What are the characteristics of the Proteoglycans?

Protein core with (-) GAGs
-Structural: can compress
-Biological roles: draws water for RXN and traps GFs
-Degraded by MMPS
-Consist of a protein core with negatively charged GAGs including heparan sulfate (HS), heparin (Hep), chondroitin sulfate (CS), keratan sulfate (KS), and dermatan sulfate (DS).
-Hold structural and biological roles. For example, they are responsible for the mechanical resistance to compression and hydration of the tissues and serve to trap growth factors (GFs) in the ECM.

How are the four groups of proteoglycans divided?

They are divided into these groups depending on their localization and homology.

What are the functions of the small leucine-rich PG's (SLRPs)?

Control the tissue spatial properties in development and homeostasis since they immobilize GFs in the ECM and regulate collagen fibrillogenesis.

What is the function of the hyalectan versican?

Bind to HA and regulate numerous signaling pathways and cellular functions

What is the function of the pericellular PGs?

Interact with various cellular receptors and can modulate the cardiovascular and musculoskeletal system.

What is the function of serglycin (SRGN)?

Participates in the storage and bioavailability of important molecules, and in plethora of functions such as maturation of granules and apoptosis of mast cells and immune regulation.

What are the characteristics of the proteoglycans?

o Protein core with negative GAG’s
o Responsible for mechanical resistance to compression and hydration of tissues, traps growth factors in the ECM
o Hyaluronan (HA)
o Lectin-binding
o Hyalectans: bind to HA and regulate signaling pathways
o Leucine- rich (SLRP)
• Control the tissue special properties in development and homeostasis

What are the characteristics of the glycosaminoglycans?

negative portion of proteoglycans
-Important in differentiating proteoglycans
-Hyaluronan (HA)
-Contributes to water retention in tissues and to their structural integrity. Plays a pivotal role in embryogenesis and tissue repair, regeneration, and homeostasis

What are the characteristics of elastin?

Shaped during development and childhood
-elastin derived peptides manipulate signal transduction and change physiology
-abundant in arteries, lungs and skin

How does tropoelastin create the elastin meshwork?

By cross-linking upon a scaffold of fibrillins and other microfibrils proteins.

When is elastin shaped and decomposed?

Shaped: during development and childhood
Decomposes: during adulthood and aging

What do fibrillins do?

• Aid binding proteins to harbor elastin and participate in cell signaling through interaction with syndecans and integrins

What do elastases do?

break apart elastin and products can affect skin maintenance, arteries, and veins

What does lysl oxidase do?

act as a signaling manipulator and participate in repair and remodeling

What are the characteristics of the laminins?

16 members each with α, β, and γ subunits
Important in development

What are the characteristics of fibronectin?

Regulates tension
-Interacts with integrins: regulating adhesion and cytokines (with GFs).

What are the confromational changes of fibronectin?

Active-stretching
Relaxed fibronectin fibers

What is tenascin?

matricellular proteins and comprise of four members

What are the four members of tenascin?

TN-C
TN-R
TN-W
TN-X

What is TN-C's function?

involved in tissue morphogenisis

What is TN-R's function?

expressed in the central nervous system and is mostly connected to neurogenisis

What is TN-W's function?

implicated in osteogenisis and abundant in specific stem cell niches and dense CT

What is TN-X's function?

Involved in organogensis

What do each of the TNs include?

o EGF-like domains
o Fibronectin-type III domains
o Fibrinogen-like globe

TNs modulate cell adhesion through their interaction with?

Integrins

What does lysyl oxidase and LOX-like proteins do?

o Initiate the covalent cross-linking of tropoelastin (TE) and collagen fibrils, which stabilizes the corresponding networks.

Define Matrisome

- The ECM databases and interaction networks, a modern field with significant impact to understand the matrix components interactomes

What does figure 1 show in the article?

- Shows the composition and structure of the ECMs specialized connective tissues such as cartilage, bone, and cornea.
A) Connective Tissue is used for connection, support, and nourishment
B) Cartilage is used for mechanical support, viscoelasticity, and lubrication
C) Bone is a durable, strong, stiff structure with low elasticity for shock absorption
D) Cornea is transparent and plays a role in refraction

What is basement membrane rich in?

laminins and collagen 4

What are laminin's purpose?

scaffolding and signaling
o Tissue and cell specific, different combinations make it more specific
o N-terminal interact with basement membrane biomacromolecules
o C-terminal bind to cell surface receptors; creates a bridge between the outside ECM and the inside cytoskeleton which affects cell signaling

What is the underlying basement membrane made of?

connective tissue

What boosts tissue mechanochemical properties?

Proteoglycans and proteins

What is the function of the pericellular matrix?

enhancing cellular attachment
o Tightly organized network in contact with the cells creating cross-junctions via integrins, and PG’s such as sydecans

What is the function of interstitial connective tissue?

providing tissue integrity
o Supports, encloses, separates tissues

What do integrins do?

create a bridge between the outside of the ECM and the inside of the actin cytoskeleton

Define bone?

- Type of CT that is mainly composed of ECM, characterized by organic biomacromolecules and inorganic compounds

________ is the main collagen found in bone, but collagen III and V are also present?

Collagen 1

Altogether what does the collagens contribute to?

- Act as a scaffold and contribute to the bone and biomechanical properties

How do the different types of PGs play a role in bone?

- Maintain bone homeostasis through promotion of collagen assembly and help retain water (for bone toughness).

What is osteonectin's role in bone?

affects collagen mineralization

What are THBS's role in bone?

differentiation of the cellular bone components and the regulation of bone metabolism.

What are R-spondin's role in bone?

regulators of pathway controlling bone development in embryos and bone remodeling in adults.

How do specialized proteins containing gamma-carboxyglutamic acid contribute to bone formation?

Through regulation of mineralization and fibrillogenisis

Why is bone ECM continuously changing?

Due to aging and disease

What overseas the remodeling of bone ECM?

Several MMPs and cathepsin K

The cooperation of MMP-9 and MMP-14 play a crucial role in _____________________?

Bone catabolism

What makes the cornea so unique?

Its opacity

What is the name of the cornea’s BM that separated the middle and inner layers?

Descemet's membrane

What is the cornea structure?

- Cornea consists of the outer epithelium and its DM, which is contacting the Bowman’s layer.
- The middle layer: stroma
- The inner layer: the endothelium

What is the function of the epithelium of the cornea?

multilayer of cells that facilitates the flow of tears and acts as a barrier to bacteria/viruses

What is the function of the corneal epithelial BM?

Allows continuous refraction because it is very thin

What is mainly responsible for the cornea's transparency?

- The corneal stroma occupying 80% of the tissue thickness.

What gives the cornea biomechanical stability and shape?

Being rich in collagen 1

____________ are residents cells of the stroma and are responsible for the homeostasis of its components, either by synthesizing them or by controlling their proteolytic degradation due to MMP production.

Keratocytes

What is the function of the crystallins in the stroma ECM?

Help reinforce refraction

What does the thickness of the Descemet's membrane depend on?

The age and composition of the ECM molecules

What are the functions of the corneal endothelium?

- Supports homeostasis, hydration, and nutritional supply of the stroma.

__________ is an avascular tissue, and this property is controlled by the expression of anti-angiogenic and the inhibition of pro-angiogenic molecules.

Cornea

Define matrisome

- The ensemble of genes encoding ECM and ECM-associated proteins.

What has been used to determine the matrisome of various species using automated machine learning-based algorithms?

- Specific features of ECM proteins (signal peptide, presence of protein domains, motifs, or repeats).

Describe the two ways the matrisome definition is very useful.

- To identify matrisome components in datasets collected in normal and diseased cells/tissues. Further analyze ECM organization, functions, and physiological process and diseases using bioinformatic tools and dedicated databases.
- To design new therapeutic strategies.

What lab technique was used to experimentally characterize the matrisome?

Mass Spectrometry

__________ are rapidly emerging as dynamic modulators of normal states (ECM hydration, homeostasis, wound healing, etc.) and pathobiological conditions (inflammation, fibrosis, cancer, etc.).

Proteoglycans

PGs not only regulate matrix structural organization and mechanics, but they also act as what?

- Integrators of major signaling cascades governing cell behavior.

How are PGs attributed with peculiar features in cell behavior and signaling?

- Acting as coreceptors for GFs, facilitating chemokine signaling through GPCRs, interacting with matrix remodeling and ECM effectors.

Integral cell properties including adhesion, migration, proliferation, angiogenesis, and survival are closely correlated with PG expression, while altered PG expression and post-translational modifications in cancer cells and tumor stroma critically affect what?

- Cancer progression and response to therapeutics.

List the 4 major PG classes that mammalian genome decoding has disclosed.

1) Extracellular
2) Pericellular
3) Cell surface associated
4) Intracellular

Describe how PG classification is based.

- On their cellular and subcellular localization.

True or False: PG classifications cannot be further classified into categories.

- False, the can.

Name the one intracellular PG and give its function.

- Serglycin (SRGN)
- Promotes the secretion of inflammatory regulators, tumor growth, and development.

List the extracellular PGs and give their overall function.

- Hyalectans and SLRPs
- Interact with several ECM components and stabilize interactions between HA and other PGs through HA binding in their C-terminal domain.

Hyalectans consist of four members. What are they and what are their functions?

- Versican
- Aggrecan
- Brevican
- Neurocan

What designate the largest class of PGs?

- Small leucine-rich proteoglycans

What family of PGs interact with GFs, cytokines, receptor tyrosine kinases (RTKs) and TLRs, thereby regulating vital processes as embryonic development, homeostasis, migration, proliferation, angiogenesis, innate immunity, apoptosis, and autophagy?

- Small leucine-rich proteoglycans

SLRPs are ubiquitously expressed in all interstitial matrices and may act both as ___________ and as _________, especially during ECM remodeling in cancer, diabetes, inflammation, and atherosclerosis.

- Structural constituents
- Signaling molecules

The third class of extracellular PGs includes _________. What are they associated with?

- SPOCK/testican family
- Various neuronal mechanisms in the CNS

The subfamily of __________ include the modular PGs perlecan and agrin, and collagens XVIII and XV.

- Pericellular/BM PGs

Describe the structure of pericellular/BM PGs

- Contains a large protein core with diverse structural motifs.

Both collagens XVIII and XV have a wide tissue distribution but the highest expression is detected in BM zones, so what is their function?

- To adhere BMs to the underlying CT stroma.

List the two main subfamilies of cell surface PGs.

- HS/CS PGs syndecans
- GPCs

Describe the structure of syndecans.

o C-terminal cytoplasmic domain
o N-terminal polypeptide (where GAGs are attached to serine residues of the protein core)
o TM domain

How can cell surface PGs be altered? How does it relate to cancer?

- By ectodomain shedding, which converts the membrane-bound coreceptors into soluble paracrine effectors that in the case of tumor has a huge impact on cancer cells and their surrounding stroma.

__________ are modified with HS chains near the juxtamembrane region and are anchored to the plasma membrane through C-terminal GPI linkage.

Glypicans (GPCs)

How are GPCs involved in cell signaling and the control of tumor growth, angiogenesis, and metastasis?

- Have been characterized as putative cell surface coreceptors for GFs and matrix modifying enzymes through their HS chains in many cancer cells.

__________ expression is detected in skin, colon, esophagus, smooth muscle, and adipose tissue, as regulates cell proliferation and migration which stimulates endothelial cell motility during microvascular morphogenesis and is involved in the origin and progression of human gliomas.

- CSPG4/NG2

Describe the structure of betaglycan/TGF-beta type III receptor.

- Contains several potential GAG attachment sites and protease-sensitive sequences near the plasma membrane.

__________ is exclusively expressed in the cerebral cortex of the brain. It has been proposed that it is involved in the regulation of specific developmental processes in the CNS, it is required for normal differentiation and has antiapoptotic role.

- Phosphacan/receptor-type protein tyrosine phosphatase beta

Describe the structural level of PGs.

- Have a core protein that one to more than a hundred GAG chains are covalently attached

Variations in the structure of disaccharide unit and sulfonylation degree define ________ GAG members.

Six

Describe GAGs.

- Unbranched, negatively charged, linear heteropolysaccharides with a repeating disaccharide structure.

What is the simplest GAG in nature?

HA

What explains the extreme structural and functional diversity of PGs?

- The unique structure of each GAG chain risen from differences in saccharide, the positions in which the sulfonylation takes place in both disaccharides of the repeating unit, and the numerous combinations that GAGs are attached to the core proteins.

How does GAGs regulate various signaling pathways in normal and pathological processes?

- Through their interactions with different classes of matrix proteins.

What is tightly regulated by the actions of heparanases (HPSE), sulfotransferases, and sulfatases?

- The effects of HS on GF signaling.