Extracellular Matrix

Question 1

What is the ECM and what is it’s function?

Answer 1

It is structure outside of the cell, it allows the cell to become part of a tissue and provides support of the cell.
Different amounts of ECM in different types of tissue (e.g. a lot in connective tissue but little in epithelium of the gut as it gets its strength from cytoskeleton)
Cells secrete ECM around themselves.
Mostly collagen (high tensile strength) - 20 different types. Also includes elastin.

Question 2

Describe the ECM in connective tissue.

Answer 2

Lots of ECM in connective tissue as it provides support in the skin, tendons, ligaments, blood vessels and bones.
Different types of ECM within connective tissue - tough and flexible tendons, or hard and dense bone.
Mutations in the ECM (collagen) of connective tissue can lead to Ehlers-Danlos syndrome (stretchy skin).

Question 3

How is collagen organised in the ECM?

Answer 3

3 collagen polypeptides form a superhelix. they interchain with proteins and AA (glycine) at its core. This forms a collagen fibril.
Collagen is secreted by fibroblasts (osteoblasts in the bone), a spindle shaped cell.
On the skin the fibres crosslink to provide extra strength.

Question 4

How does collagen move through the matrix and why?

Answer 4

Collagen needs to remodelled in growth, repair and renewal. Macrophages need to move through ECM to find bacteria, so needs to be able to move. Fibroblasts rearrange collagen. The cell will secrete collagenases.
They use collagen associated proteins to move through the matrix - Fibronectin and Integrin.
Fibronectin binds to the collagen fibril.
Integrin is anchored to the cell plasma membrane by actin at an anchoring junction. Integrin will then anchor fibronectin.
Fibronectin can attach and detach from collagen suing ATP, allowing the cell to crawl through the matrix.

Question 5

How is elastin organised and what is its function?

Answer 5

Loose and unstructured polypeptide interwoven with collagen.
It recoils spontaneously.
Fibrillin, a glycoprotein, is essential for the formation of elastin fibres, it is secreted into the ECM by fibroblasts and becomes incorporated in microfibrils.

Question 6

How do tissues resist compression?

Answer 6

Glycosaminoglycans found in the ECM. GAGs are negatively charges polysaccharides, that links to proteins to form proteoglycans. The negative charge will attract Na+ ions which will draw water in with them. So GAGs draw fluid into the matrix to resist compression