Proteopathic Diseases and Amelogenesis Imperfecta Flashcards
Define Proteopathy
a class of diseases where proteins become structurally abnormal and disrupt the functions of cells, tissues and organs of the body
What happens if the Proteins Mutate and Misfold?
- become toxic and lose normal function
- accumulate in the cell
- damage the tissues
How does Amelogenesis Happen?
- mutation on the amelogenin gene = Y64H
- leads to dysfunctional protein
- aggregation of the protein
What are the Secretory Cells of the Enamel?
ameloblasts
How are Ameloblasts formed? 2 Paths
- gene transcribed onto mRNA
TWO PATHS:
1) attach onto free ribosome in the cytoplasm
- protein constructed and used with the cells
2) attach onto fixed ribosome on the RER
- protein folds into 3D shape
- modified and package into vesicles
- transport to golgi apparatus
- enzymes modify protein and glycoprotein
- released into the extraceullar environment
What are Multiple Vesicles Called?
Cistamae
What are the 3 Different Types of Vesicles?
Lysosome - digestive enzymes
Secretory - empty products outside cell by exocytosis
Membrane - add new lipids and proteins to plasma membrane
What are the Two Different Pathways which Proteins Translocate to the Endoplasmic Reticulum
Co-translational translocation
Post-translational translocation
Describe Co-translational translocation
- during translation
- ribosome attaches onto the ER
- protein is inserted into the ER membrane
- protein gets translated
Describe Post-translational translocation
- after translation
- signal sequence
- protein is released from the ribosome
- protein is inserted and translocated into the rough endoplasmic reticulum
What does a Polypeptide Chain Develop into?
3D structure
- either alpha helices or beta pleated sheets
3 Descriptions of the Folding of Protiens
randomised
occurs in an aqueous solution
depends on the side chains
What is an Important Protein which Reduces the Error of Misfolding?
chaperone = BiP
2 Ways in Which Disrupted Protein Folding can Occur.
Mutation
Faulty Phosphorylated Modification
How can a Misfolded Protein lead to Disease? (5)
- accumulates
- forms inclusion bodies, fibres
- ER stress
- tissue dysfunction
- disease
What happens when you get ER Stress?
= unfolded protein response
- cell activates complementary adaptive mechanisms
- eliminates damaged cells by apoptosis
Why don’t we Constantly get ER Stress?
UPR - unfolded protein response
- identifies the faulty proteins
What is the Mechanism of UPR?
to produce transcription regulatory proteins such as BIP
- receive signal to be induced from transmembrane sensors
How does BIP Help Fold Proteins Correctly?
- regulate transmembrane sensors in the ER membrane and on the cytoplasmic side
Give 3 Transmembrane Sensors, which BIP regulates
IRE1, PERK and ATF6
How does BIP Regulate IRE1
- two protein kinases phosphorylate due to misfolded protein
- induces ribonuclease domain
= splice a specific mRNA - activates specific transcription regulatory proteins
How does BIP Regulate PERK
- two protein kinases phosphorylate due to misfolded protein
- activates translation initiation factors
- forms specific transcription factors - increase genes for folding
What is the Role of Translation Initiation Factors in PERK?
- reduce synthetic rate of protein translocation
- less ER stress
How does BIP Regulate ATF6?
- ATF6 moves to golgi apparatus
- proteolytic cleavage of the cytosolic domain
- activates genes specific to UPR
- reduce ER stress
3 Things Which can Happen After UPR.
ERAD - protein degradation
CHOP - apoptosis
genes activate to increase protein folding capacity
What is the Prevalence of AI?
1/700-1400
Define Genesis Imperfecta, where does it originate
a group of developmental conditions in the genome.
Clinical Phenotypes of AI
- hypoplastic enamel - thin or absent
- hypomaturation - name is normal thickness but white surface - mistaken for fluorosis
- hypermineralized
When do you know you have AI?
when teeth are erupted
Symptoms and Treatment of AI.
- sensitivity
- discolouration
- prone to disintegration
- can only be managed
Describe the 5 Stages of Enamel Formation
Presecretory
Secretory - 30% mineral
- initial mineral and matrix
- complete when full thickness of tissue is layed
- ameloblasts = tall, columnar, densely packed, 7mm height
Transition
- at or during amelogenin secretion
Early Maturation - 40% mineral
Maturation - 90% mineral
- final matrix removal
- final mineral content acquired
- ameloblasts = shorted to half and nucleus at centre
- final mineralisation is considered complete post-eruption
What do we use to Study AI?
mice showing enamel defects
How do we study AI? What is the Project.
Mutagenesis Project
- induce the mutation in male rodent using chemical ‘N-Ethyl-N-Nitrosourea’ (ENU)
- cross bred with healthy mice
- search for abnormalities
What is the Allele for the Phenotype known as?
wild-type
Define Monophyodont
having one set of teeth - lab mice
Describe the Enamel of Mice.
single crystal of hydroxyapatite
- rods within are rhombohedral, 25-50nm
- 10^4 Bundle into larger nanorods
inner enamel - nanorods are arranged in intersecting sections
outer enamel - nanorods are parallel
= makes the edge of enamel detachable and sharp
= resistant to acid wear
In Mice’s genes, where is the Amelogenin allele?
on the X chromosome
women = XX
men = XY
What is the Amelogenin Mutation?
Y64H
In Humans Genes, where is the Amelogenin allele?
on X and Y
women = XX
men = XY
Which gene produces Amelogenin?
Amex
Define Homozygous.
having two identical alleles of the gene
Define Heterozygous.
having two different alleles of a gene
How does Enamel Differ in Beavers?
more iron, more strength
How do Mutations Affect the Stages of Enamel?
Secretory and Maturation
- more secondary ameloblasts
Transition and Maturation
- ameloblast contact with enamel matrix is occasionally lost = blister like structure
What is the Effect of Mutation on the Enamel?
- tomes process is absent
= disorganised vascular pattern - loss of normal ER and golgi structures
- nuclei of ameloblasts become distorted
How can you Measure if Mutant Amelogenins are being Secreted?
Western Blotting Analysis
Describe Western Blotting Analysis
- detect a specific protein
- using gel electrophoresis to separate
When Mutant Amelogenin Accumulates in the ER, does it cause ER Stress and Activation of UPR?
- evidence needs to be found
- perform in-situ-hybridization and quantitive real time PCR
Does ER stress Lead to AI?
Yes
What can be used to Manage ER Stress when it leads to AI?
4-phenylbuturate - used for urea cycle disorders
- shows improvement in incisors and recovery of enamel
