Amyloidosis Flashcards
What is amyloid?
Abnormal extracellular protein deposit composed of amyloid fibrils, Glycosaminoglycans and serum Amyloid P Component.
It is similar to what is found on the cell surface of many bacteria
Describe amyloid structure
Different globular precursor proteins can form fibrils which are rigid, non-branching and insoluble
~50-100Å diameter
Pathognomonic cross-β core structure
Why is in vivo amyloid clearance so low?
Because cells like macrophages ‘ignore’ it
What are the components of amyloid fibrils?
Fibrilar proteins
Heparan/dermatan sulphate
Serum amyloid P component (SAP)
What are the two general classes of amyloidosis?
Local (one organ) and Systemic (many organs)
Describe systemic amyloidosis (prevalence and severity)
Rare (incidence 0.4/100,000)
Usually fatal ~ 1 per 1,000-1,500 deaths
Why is amyloidosis often diagnosed late?
It is so rare that it is not well known to doctors
How is the current state of amyloidosis treatment?
Treatment is very challenging and it is still an important unmet medical need.
Major recent advances and better outcomes in specialist centres
What is the most common type of amyloidosis?
AL Amyloidosis
Inheritance of amyloidosis
Can be hereditary or it can be acquired
Give examples of acquired and hereditary amyloidoses
AL is acquired. It is associated with myelomas which make many immunoglobulin light chains and fragments. Can eventually lead to beta-sheet and then amyloid fibril formation.
Familial amyloid polineuropathy or cardiopathy is hereditary and is related to transthyretin variants (mutation) and fragments.
With amyloid fibrils there is a large heterogeneity in what?
Concentration of protein and protein type
What is the most common genetic amyloidosis?
Familial amyloid polyneuropathy or cardiopathy
How is the location of the disease determined?
By the location of the amyloid deposits
Why is it hard to figure out which organs will be affected by AL amyloidosis?
Because light chains which form the amyloid fibrils have high heterogeneity and thus can target different organs
What dictates survival in amyloidosis?
The protein precursor
What is an important determinant of amyloidosis prognosis?
Type of organ involved in deposition is important in prognosis
Cardiac involvement is worse
Describe amyloid structure at a molecular level
Structure is considered a cross-beta structure because the angles are consistent with beta sheet
Make multiple hydrogen bonds among the aggregates.
At the end you have the most stable form of the protein found in nature.
In addition to the one amyloidogenic protein which generate the structure, other proteins provide additional stability to the structure
What is the structure of the serum amyloid P component?
Pentamer
How do the pathogenic variants of the precursour proteins differ from the wild type form?
They are partially denatured
What would happen if the precursor protein was fully denatured?
It would not form amyloid
What do all the amyloid precursors have in common?
All lose thermodynamic stability
Is amyloidosis a gain of function or loss of function disease, explain?
Gain-of-function
Normally proteins with decreased stability would be detected and broken down
Instead, these are not and go on to form amyloid.
What is the genotype of most patients?
Heterozygous = dominant
When is amyloidosis onset and why is it at this stage in life?
Middle age
Partially folded proteins will be broken down
At some point there is a high enough concentration for nucleation and after this elongation occurs.
What is nucleation?
It is a term for aggregate formation
How does amyloidosis progress?
Lag phase –> nucleation–> elongation.
After nucleation you can have a strong acceleration in 2-3 years
(You use different drugs pre- and post-nucleation)
What are synonyms for nuclei?
Seeds and template
What can reduce the lag phase of amyloid fibril formation and what does this suggest?
When seeds are added, the lag phase decreases suggesting that seeds have a key role in amyloid fibril formation
Why do the monomers in the amyloid fibril not have the same structure as the precursor?
The fibril can be made up of variant and WT protein
The variant protein first forms the fibril
The variant for then converts the WT protein so that it can elongate
When can wild type monomers be found in the fibrils?
If there is not too much destabilization of the variant compared to the wild type
Give an exmaple of how amyloidosis was studied
The structure of the precursor (beta2-microglobulin) was found–> mutation behind it was found–> fibril formation was modeled with biomechanical conditions found in the human body –> showed that forces in the body provided the energy to change from native state to partially folded one
What can hydrophobic/hydrophilic interface and turbulent fluid flow do?
They can generate forces in the range of 20-50 pN sufficient to cause protein unfolding
What is the mechanism of amyloid toxicity?
Oligomeric state is considered by many as the source of toxicity
Oligomers can associate with membranes and make holes messing with the separation between the intracellular and extracellular space - can activate apoptotic pathways
In vivo though we don’t have disease without amyloid
What is an oligomer?
An intermediate between precursor and fibres
What is the relevance of amyloid in in vivo toxicity of amyloidosis?
Histology shows the tissue is completely remodelled
Amyloid can greatly affect glucose diffusion, oxygen gradient etc
Once fibrils are formed, molecular crowding significantly increases: COLLOIDAL STABILITY IS REDUCED and OLIGOMERISATION IS FAVOURED
There is still a gap in the investigation of toxicity in vivo and in vitro models
Protein cleavage with and without mechanical forces was studied in a family with a transthyretin mutation. What was found?
Showed that shear stress/mechanical forces can act as a cofactor to protein cleavage (a mechanoenzymatic mechanism)
