L: Cell adhesion and the extracellular matrix

Complete - could add more for clarity

What is the ground substance of the extracellular matrix made up of?

• collagen protein fibres

• Elastic fibres

• Reticular fibres

• Amorphous components (proteoglycans, multi-adhesive glycoproteins and glycosaminoglycans [GAG])

What are the two main divisions of connective tissues?

• loose connective tissues

• Dense connective tissues (regular and irregular)

What cells form the extracellular matrix?

• adipocytes (fat cells)

• Mast cells, macrophages and plasma cells (blood derived)

• Fibroblasts and myofibroblasts

What fibres form the extracellular matrix?

• collagen fibres and fibrils

• elastic fibres

• reticular fibres

• cartilage and bone

What is the ground tissue below the basement membrane of epithelial cells majorly composed of?

Ground substance, more cells and the extracellular matrix

Which components of the ECM constitute the ground substance, more predominantly in loose connective tissues?

Amorphous components

What allows components of the ECM to link to each other and also attach to cells?

Adhesion proteins

What does the ECM mediate?

• the organisation of cells into tissues

• coordination of cellular function through activation of intracellular signalling pathways involved in control of cell growth

• proliferation

• gene expression

What connective tissue has high levels of fibrous proteins?

Tendons

What connective tissue has high levels of polysaccharides?

Cartilage

What is the variation of ECM across different tissue types based on?

Quantitative differences in the types or amounts of ECM and the modifications in organisation

What is the basement membrane an example of?

Extracellular matrix

What is the connective tissue beneath the basement membrane of epithelial cells secreted by?

Fibroblasts

What fibre proteins exist in the extracellular matrix?

• collagen

• elastin

• fibronectin

• laminin

What is an example of a polysaccharide present in the extracellular matrix?

Glycosaminoglycans (GAGs)

What is the function of fibroblasts?

They synthesise and secrete fibrillar proteins - collagen, elastic and reticular fibres

What do fibroblasts secrete along with fibrillar proteins?

Complex carbohydrates

What is the major structural protein of ECM?

Collagen

What are the characteristics of collagen?

Highly flexible with high tensile strength

What is collagen made up of?

A triple helix of polypeptide chains.

What does the helix domain of collagen contain?

Three repeat of amino acid sequence (Gly-X-Y) (Glycine - Proline - Hydroxyproline)

What three amino acids make up the triple helix of collagen?

Glycine, proline (X) and hydroxyproline (Y)

Which structure in the amino acids in collagen provides stability for the helical conformation of the polypeptide chains?

The ring structure

What is associated with the helix molecule of collagen that allows it to be described as a glycoprotein?

Sugar groups

What is proline or lysine modified to create (collagen)?

Hydroxyproline or hydroxylysine

Where are proline or lysine modified to create hydroxyproline or hydroxylysine?

In the rough endoplasmic reticulum

What modifies proline to create hydroxyproline?

Prolyl hydroxylase

What does the hydroxylation of proline or lysine residues require?

Ascorbic Acid (vitamin C)

What is the most abundant form of collagen in the ECM?

Type 1 collagen

What is the first step of collagen biosynthesis?

Procollagen alpha chains are synthesised in the RER and in the RER asparagine-linked oligosaccharides are added to the C-terminal polypeptide

What is the second step of collagen biosynthesis?

Propeptides forms trimers covalently linked by disulfide bonds and selected residues covalently modified in the Gly-X-Y triple repeat (lysine, proline).

What is the third step of collagen biosynthesis?

Modification facilitate zipperlike formation and stabilisation of the triple helices with the attachment of a chaperone protein (Hsp47). The chaperone protein stabilises the helices or inhibit premature aggregation of the trimers.

What is the fourth step of collagen biosynthesis?

Folded procollagen are shuttled off to Golgi complex where they are further modified (lateral association).

What is the fifth step of collagen biosynthesis?

Next, the chains are secreted, N- and C- terminal removed, and trimers assemble into fibrils and crosslinked via covalent bond.

What pattern are collagen fibres laid to create collagen fibrils?

Like bricks, with cross-links between layers

What is type IV collagen?

A network forming collagen, a major constituent of basal laminae

How does type IV collagen differ from type I?

The amino acid repeats (Gly-X-Y) of type IV collagen are disrupted by a non-helical short sequence.

Which is more flexible type IV collagen or fibril forming collagens?

Type IV collagen

What is the principle component of elastic fibres?

Elastin

How are elastin crosslinked?

They are cross linked through covalent bond formation between the residue side chain of lysine.

What gives elastin rubber like properties?

The network of cross linked side chains of elastin

Where can elastin fibres commonly be found?

in organs that stretch, such as the lungs

What makes the gel of the ECM?

Glycosaminoglycans (GAGs)

What repeating unit forms glycosaminoglycans?

Disaccharides

What are the two types of sugar constituents of glycosaminoglycans (GAGs)?

• N-acetylglucosamine or N-acetylegalactosamine

• Glucuronic or iduronic acid

What charge do glycosaminoglycans predominantly have and what does this allow them to do?

Negative charge and they can bind to positive ions and trap water molecules to form hydrated gels

What type of support do GAGs provide to the ECM?

Mechanical

What is the only type of GAG to occur as a single polysaccharide?

Hyaluronan

What are the types of GAG?

• dermatan sulfate

• chondroitin sulfate

• keratan sulfate

• heparan sulfate

• hyaluronan

What does the linkage of GAG to proteins lead to the formation of?

Proteoglycans

What are the functions of proteoglycans?

• matrix support/ cushioning/ hydration

• glue like function

• links between proteins of ECM and ECM and cell surface

How does the extracellular matrix bind to the intracellular cytoskeleton?

Collagen/proteoglycans bind to fibronectin, which links to integrins (transmembrane), which bind via adaptors to the actin cytoskeleton

What ECM components do adhesion proteins interact with?

collagen and proteoglycans - for matrix organisation

What are adhesion proteins the binding sites for?

Cell surface receptors such as integrin

What is fibronectin?

A dimeric glycoprotein made of two polypeptide chains

What is the main adhesion protein in connective tissues?

Fibronectin

Which binding sites of fibronectin provide the cross link?

Binding sites for proteoglycans and collagen

What is the main adhesion protein in basal laminae?

Laminin

What subunits are laminar made from?

heterotrimer subunits (alpha, beta and gamma)

What is a myofibroblast?

A bi-functional cell that secretes collagen (fibroblast like) and synthesises actin, myosin and desmin (smooth muscle like)

What does the myofibroblast do when there is tissue damage?

• proliferate

• secrete collagen

• consolidate damages area (fibrous scarring)

• contract (reduce the size of the damaged area - express focal adhesions and smooth muscle tension

What are the granules of mast cells composed of?

Basophils which store chemical substances

What does mast cell granule content contain?

Heparin and histamine

What are the mediators of inflammation and what two categories are they divided into?

Chemical substances - preformed mediators, newly synthesised mediators

What do B-lymphocytes differentiate into and what are these cells capable of synthesising?

Plasma cells - capable of synthesising immunoglobulin or antibodies.

What is the life span of a plasma cell?

10-30 days

What do macrophages contain high levels of?

Lysosomes

Are macrophages phagocytotic or lymphocytotic?

Phagocytotic

What specific protein do macrophages have on their surface?

Major histocompatibility complex II (MCH II)

What does leptin signal?

To the brain that the body has eaten enough food.

What causes Duchenne’s muscular dystrophy?

A nonsense gene mutation causes the absence of dystrophin (adaptor) due to premature termination of translation

What does Duchenne’s muscular dystrophy cause?

Muscle wasting, muscle weakness, inability to walk

What does carcinoma in situ mean?

That cancer cells have formed but not spread to nearby tissue

What transition do epithelial cells undergo when cancer cells are present?

Epithelial to mesenchymal transition.

what has reduced expression when cells convert to mesenchymal cells?

Cadherins

How does micro invasion of the basement membrane begin (cancer)?

It is aided by actin-based protrusions called invadipodia

What is secreted during microinvasion of the basement membrane by cancer cells?

Metallproteases

What do invading tumours lead cells to express?

Integrins - promotes interaction with ECM and non epithelial cells

What do autocrine motility factors from the tumour do?

They increase the motility of tumour cells and decrease E-cadherin

What do angiogenesis factors promote?

Vascularisation

What is dissemination?

The spreading of cancer cells away from the primary site

What is metastasis?

the growth of a tumour in a secondary location due to the spread of cancer cells