W2L3 Flashcards
What happens if Cell-Matrix junctions are disrupted in the skin?
Detachment of epidermis from dermis = blistering
Blister is loss of cell-to-cell contacts
Top part of blister is ep cell holding on to each other (epidermis has Cell-cell adhesions bear most of the mechanical stress).
- Bottom part of blister is dermis (dermis has Matrix bears most of the mechanical stress, not the cells)
- Between epidermis and dermis is fluid
Weakest link in the entirety of the skin is the junction bw the epidermis and the dermis
- hemidesmosomes are on the bottom layer trying to hang on to the basement membrane, and they rip, resulting in fluid flowing in to fill the gap
- order: epidermis, basement membrane, dermis
- weakest link are hemidesmosomes and focal adhesions that attach the epidermis to the basal lamina, which leads to dermis. Thus this is why we have a splitting of epidermis and dermis
Callous is hyperplasia of cells of cornified tissues
Blister fluid is extracellular fluid that you normally have around your cells
Immunofluorescence microscopy: Focal Adhesions in quiescent (untreated) or migratory lung tumor cells
Focal adhesions are made of proteins such as integrin, paxillin and actin cytoskeleton
Tumor cells also use focal adhesions
- any cell that wants to migrate or move will have focal adhesions
In untreated (quiescent, not migratory) cells, the actin cytoskeleton goes only around the cell periphery.
- if you overlay the immunofluorescent image of actin cytoskeleton and paxillin, the 2 colors do not overlay.
If you stimulate the cells to be migratory,
- focal adhesions become longer and larger
- the actin cytoskeleton also makes actin stress fibers
- you can also see the overlap bw focal adhesion and actin cytoskeleton better than in the quiescent cells
Cell junction
There are 3 types of junctions in cells
- anchoring junctions, occluding junctions and communicating junctions
Anchoring junctions can be cell-matrix as well as cell-cell, whereas occluding and communicating junctions are cell-cell
Anchoring junctions mechanically attach cells to their external surroundings
Occluding junctions block water passage and molecular passage
Communicating junction allows cells to communicate with another cell
Transmission of Information
From outer to inner:
- Extracellular matrix (ECM)
- PM transmembrane proteins
- i.e. integrins, which are part of focal adhesions or hemidesmosomes
- They physically interact with ECM and with proteins on the inside of the cells - Adaptor proteins at cell surface, inside the cell
- i.e. talin, vinculin
- it is like glue
- Scaffolding are complex adaptor proteins that allow multiple things to come together - Cytoskeleton
- i.e. actin filaments - Adaptor proteins on nuclear membrane
- Nuclear structural proteins
- lamina
ECM can be either very spongey or rigid. This information about the ECM is physically transmitted to the nucleus. The nucleus responds to this and changes the proteins that it needs to secrete to take care of how the ECM is. For example, if its too rigid, the cell will want to make some proteins that will chew up some ECM. If it is spongey, the fibroblast will make more collagen for the ECM. Thus there is physical sampling of what is outside of the cell and this info is transmitted to the inside of the cell mechanically. Then, the cell responds and secretes stuff to take care of this.
By mechanical, prof means physical transmission
Another type of signaling that is not mechanical or physical is via tyrosine kinases and phosphorylation cascades
Human Connective Tissue Diseases (most are collagen-based issues)
Arthritis (osteoarthritis)
Scleroderma, which is a form of fibrosis
Vitamin C deficiency (Scurvy)
Osteogenesis Imperfecta
Degenerative disc disease
Collagen - a major component of the ECM
Collagen family
28 types in human genome
Most abundant protein in mammals (about 1/3 of whole body protein content)
Trimeric structure
- Homotrimeric: all 3 chains come from the same gene
- Heterotrimeric: all 3 chains come from different genes
Helical shape bc have 3 aa motifs that repeat itself over and over again: glycine, proline, hydroxyproline or hydroxylysine
- 3 alpha chains come together to make one collagen fiber
- Each alpha chain has 3 things: glycine, proline, and hydroxyproline or hydroxylysine
Made by fibroblasts
- Fibroblasts make collagen and fibroblasts move all over the place. Fibroblasts can also remodel collagen.
Form Insoluble fibers
Collagen Biosynthesis
Multiple forms of collagen: fibrillar (collagen I, II, III), beaded microfilaments (Collagen VI) and network forming (Collagen X, VIII)
- Most collagen in body is fibrillar
- Polypeptide synthesis of collagen occurs in the ER
- Post-translational modifications in the ER
- Proline and lysine hydroxylation
- Hydroxylysine glycosylation
- N-linked glycosylation - Triple helix formation occurs inside the ER, with proline cis-trans isomerization.
- Higher order assembly in the ER
- Then it goes to the golgi apparatus where there is more N-linked oligosaccharide modifications
- Then it is secreted from intracellular to extracellular
- Procollagen processing
- C and N-terminal propeptide cleavage, which allows you to pack the collagen together and cross-link even further
- Fibrilogenesis, which is crosslinking
- ECM suprastructure formation occurs, which is multiple collagen fibrils cross linked together to make the fibrillar collagen
What happens if you cannot chop off the C and N terminal propeptide? AKA what happens if you do not have the procollagen processing enzymes for diff types of collagen?
- This is a procollagen processing defect called Ehlers-Danlos, this is super double-jointed people because joints are malleable and flexible. Shoulders may also pop out often
- This means they do not get chopped off, meaning that fibrils will be of lower-quality. Fibrils may still be made but cannot pack as well during the procollagen processing step
Post-translational modification in ER is dependent on VitC
- If you do not have VitC, you get scurvy where your teeth will fall out bc you have loose collagen in your gums
If you have procollagen assembly defect during the triple helix formation stage in ER, it means you have osteogenesis imperfecta. This is brittle bone disease. You cannot put the three alpha helices together to make a nice procollagen.
Differences between Collagen Types
of helix repeats, i.e. length of the triple helix portion, gets built into what kind of collagen will be produced
shape of the globular C and N domains
covalent modification differences to the triple helix (i.e. can it be glycosylated or cross linked)
Characteristics of Collagens
- Fibril-forming (fibrillar)
- majority of collagen in the body
- Type I: bone, skin, tendon, ligaments, cornea
- Type II: Cartilage, vitreous humour in the eyes - Fibril-associated
- are not fibrils but collagen that attach themselves to fibrils
- Type VII: bladder, dermis - Network-forming
- Type IV: basement membrane
- Type VI: muscle, dermis, cornea, cartilage - Membrane-associated
- help with focal adhesions and hemidesmosomes attach cells to ECM; a lot of this collagen types are transmembrane
- Type XIII: dermis, eyes, endothelial cells
Collagen types - structural feature, tissue and gene(s)
Type I
- fibrillar, heterotrimeric
- 90% of collagen in body
- skin, bone, ligaments
- COL 1 A1, COL 1 A2
Type II
- fibrillar, homotrimeric
- cartilage, vitreous humour
- COL 2 A1
Type IV
- sheet-forming, Heterotrimeric
- Basal lamina
- COL 4 A1 - COL 4 A6
Type VI
- beaded microfilaments, heterotrimeric
- Skeletal muscle
- COL 6 A1, A2, A3 A5
Type VII
- Fibril-associated (anchoring), Homotrimeric
- dermis
- COL 7A1
Type XIII
- Transmembrane, Homotrimeric
- Hemidesmosomes in skin
- COL 13 A1
Collagen Disease: Type I Collagen
Osteogenesis Imperfecta, aka “brittle bone” disease
Autosomal dominant genetic disorder (COL1A1 and COL1A2 genes)
Improper helix formation (imperfections) due to glycine substitution to other amino acids
Impaired pro-collagen transport to Golgi apparatus, therefore low collagen
Fibril failure during stress
- collagen fibrils go through the bone, the bone is not just hydroxyapatite
- the collagen that goes through the bone allows the bone to be less brittle, to accommodate fluctuations in bending
Proteoglycans
Glycoprotein vs proteoglycan: Difference is the ratio of sugar to proteins
Glycoprotein - proteins that have sugar(s) attached to a protein core. Majority is protein
Proteoglycan - specialized repeating sugars attached to a protein core: Glycosaminoglycans (GAGs)
- form large complexes with other proteoglycans and matrix proteins (such as collagen)
- bind cations and water, regulate the movement of molecules through the matrix, cushioning (for e.g., Perlecan in basal lamina, and Aggrecan in joints and intervertebral discs), etc.
- GAGs are long, linear carbohydrate polymers
- Most common proteoglycans: Perlecan and Aggrecan
Proteoglycan Synthesis
Protein core is made in the rough ER
Glycosaminoglycans (xylose with repetitive structure of disaccharides) are added to the protein core in the Golgi apparatus
Multi-step enzymatic reaction (first step is to add xylose onto serine residues, and serine is part of the consensus site located on the protein core)
- xylose is connected to repetitive structure of disaccharides
Consensus site located on core protein: Ser-Gly-X-Gly, (X can be any amino acid, except proline)
- not proline because it has a kink into the peptide backbone, making it difficult for xylose to recognize the consensus site if proline is there
