Amyloid Diseases, Alzheimers and Parkinsons

What is an Amyloid Plaque formed of?

Naturally occurring protein unfolds, aggregates, and collects in fibrous plaques

In what secondary structure are plaques always formed?

Beta-pleated sheets

What do Plaques look like under an X-ray?

• A ‘cross’ Indicating repeated structure

• every 4.7A in one direction and 10A at right angles

• Caused by parallel beta-strands ,running at right angles to the direction of the fibre (cross-beta)

What happens as a result of excessive amounts of antibody light chains?

• They accumulate as amyloid deposits

• Particularly in the Kidneys

• Also builds up in the heart, leading to heart failure

What acute phase protein is produced by the body to deal with inflammation, and how does it lead to amyloid deposits in the Kidneys?

• Serum Amyloid A

• requites immune cells and transports cholesterol to the liver

• Upregulated in chronic inflammatory diseases, such as rheumatoid arthritis

• Builds up in Kidneys, leading to amyloid deposits

What used to be a problem with Dialysis?

• External Dialysis does not remove proteins (they’re too big)

• Beta2microglobin being one of them

• This would then build up in organs or joints: dialysis-related amyloidogenesis

How does Amyloid build up occur as a result of Type-2 Diabetes?

• The body increases expression of insulin due to the body building a resistance to it

• A hormone called Islet amyloid polypeptide (IAPP) is expressed at the same time as insulin (100x)

• This can lead to build-up of IAPP in islet cells

What are symptoms of Alzheimers?

• First - loss of short-term memory

• Later - disorientation, mood swings, delusions and apathy, leading to withdrawal

What is the life expectancy of Alzheimer’s?

3-9 years

What are the trends of Alzheimer’s?

• Incidence increases dramatically with age

• As western populations age, this makes it a rapidly growing disease

• Leading cause of death for women in the UK

• Over a million people in UK with it in 2024

Why are plaque build-ups called Amyloids?

When they were first discovered in 1850s, they stained with iodine, so amyloid (starch-like)

What is the source of Amyloid-beta plaques in the brain in Alzheimer’s?

A-beta peptides are produced by sequential cleavage of amyloid precursor protein (APP) by beta-secratase and Y-secratase.

How do beta/Y-Secretase cleaved APP products aggregate?

• (40 and 42 length products - 42 much more prone to aggregation)

• Miss folding and oligomerisation, forms soluble oligomers and then insoluble extracellular amyloid plaques

What are the effects of soluble A-beta plaques?

• Impair synaptic function, disrupt signalling and trigger neuro-inflammation

• Dense plaques are a hallmark on pathology but soluble oligomers correlate better with cognitive impairment

What are Nurofibrillary Tangles (NFTs) composed of?

• Intracellular aggregates of hyper-phosphorlyated tau protein

• Normal tau stabilises microtubules, when phosphorylated it detaches and aggregates into paired helical filaments that from tangles

What genetic element is associated with early onset Alzheimer’s and what hypothesis was generated because of this?

• Mutations in the gene for APP or genes presenilins 1 and 2 (Y-secretase)

• Led to the Amyloid cascade hypothesis: It is caused by the overproduction of A-beta, which collects in plaques

What 2 bit of genetic evidence (other than preslins mutations) support the Amyloid cascade hypothesis?

• App gene is on chromosome 21, Downs patients typically have early onset Alzheimer’s, Downs with distal chromosome 21 trisomy do not get early onset disease

• Allele APoE4, increase risk 3x in heterozygotes and 15x in homozygotes, EPoE transports cholesterol to neurons. Most likely association is that EPoE helps to remove or break down A-beta (and E4 is the worst at this)

What happens if you make Transgenic Mice, with a mutant form of human APP that predisposes humans towards Alzheimer’s?

• The mice have plaques and ‘have Alzheimer’s’

• They run slower and were worse at finding a submerged platform in a pool of water

• However they did not explore their surroundings less, or fall of a beam less

What are the problems with Animal models of Alzheimer’s?

• In humans 60 years to start, in mice 16 months

• How reliably can we say that behaviour in a mouse is ‘Alzheimer’s’

Why is it hard to study Plaques?

• It is hard to know what about the plaques is casing the disease:

  • Is it the plaques simply blocking the transmission of nerve impulses?

  • Plaques also case inflammation (They are recognised as foreign by the body and so the body attacks its own neurons)

  • They also stimulate the production of ROS, also leading to inflammation and tissue damage

What are the two forms of A-beta fibres?

• Fibres

• Oligomers (blobs)

(Oligomers may be ‘on-pathway’ to fibres, as in they may eventually become them)

Why is the current theory that oligomers are more toxic than fibres of A-beta?

Oligomers have ‘more ends to build on’, as they are smaller

What is the possible relation between tau and A-beta?

Tau phosphorylation is governed by a balance between kinases and phosphatases. It may be that A-beta alters the activity of these enzymes, in particular phosphatases

What is the standardised drug trail progression?

• Preclinical - Show that it affects the biochemistry in the way expected

• Clinical:

  • Phase 1 - Small scale on healthy volunteers, is it toxic?, appropriate doses in humans?

  • Phase 2 - Fairly small scale on patients, does it work? is it safe in patients?

  • Phase 3 - Large scale on lots more patients, does it really work and what are the side effects?

What difficulties are there surrounding AD in clinical trials?

• Getting volunteers is hard

• AD requires measure of ‘severity’, cognitive performances (standardised scores), needs a ‘significant improvement’, sensitive measure

• Who decides what a ‘significant improvement’ is?

• What if it merely slows onset?

What do the only current drugs of AD affect?

Neurotransmitters

• Cholinergic (use of inhibitor to prolong signal)

• These only affect the symptoms and cannot cure

How good is alpha secretase as a drug target for AD?

• no link to AD

• Need to increase its activity, not decrease

• There are some drugs in trial

Are there any drugs that use beta-secretase as a target?

Not yet

How good is Y-secratase as a drug target?

• Also cleaves the signalling receptor Notch, involved in neural development, heart development, and maturation of cells in various tissues

• So an inhibitor would have effects all over the body, unless you can deliver it specifically to the brain

What is an example of active immunisation, targetting the end of amyloid cassette?

• Immunise using A-beta(1-42) and get the immune system to do the work

• 6% of patients develop meningoencephalitis

What target offers the most success in clinical trials for treating AD so far?

Antibodies against A-beta plaques

What is adcanumab?

A antibody targeting amyloid aggregates of A-beta and not A-beta monomers

What were the outcome of the trials for adcanumab?

• 2015: most halted for no effect or harmful effect (there was some suggestion that antibodies could slow down neurological decline)

• 2016: Halted a trial in phase 3 because of lack of effect

• 2017: Another trial was halted

• 2019: Withdrew, but then brought back again

• 2021: Approved by FDA (controversial, some people resigned) (not approved in UK or Europe)

• 2024: Withdrawn for ‘financial reasons’

What antibody was approved in 2023 by FDA?

Lecanamab, It was designed to bind to protofibrils (not oligomers). (not approved in UK or Europe)

What is passive immunisation for AD?

• Antibodies targeting the A-beta plaques (Lecanamab,adcanumab)

• passive as it doesn’t stop them from forming

What did S Linse et al 2020, find from analyses of monoclonal antibodies?

• different antibodies work in different ways

• They target different epitopes and behave in different ways

• Adcanumab was the best

Why was Adcanumab the best in the S Linse et al 2020 antibody comparison study?

• It was the most specific for fibrils

• Best at preventing secondary nucleation (The formation of new fibres using old ones as catalysts)

How does Parkinson’s differ from Alzheimer’s?

Parkinson’s affects dopamine neurotransmitters where Alzheimer’s mainy affects acetyl choline

What is the Amyloid protein in Parkinson’s and where does it collect?

• alpha-synuclein

• Collects in neurons ‘Lewy bodies’

What are the two main genetic factors form Parkinson’s?

• Gene for alpha-synuclein, function not clear - organisation of pre-synaptic vesicles?

• Gene for leucine-rich repeat kinase (LRRK2) (aka dardarin or PARK8), function unclear but something to do with maintenance of dendrite structure (neurite outgrowth). No clear connection to Parkinson’s

What kind of structure is alpha-synuclein?

Intrinsically Disordered

Why are Intrinsically Disordered proteins more likely to form Amyloids?

They do not need to unfold first - lower energy barrier to forming amyloid

What are some other potential causes of Parkinson’s?

• Environmental factors (pesticides, head-injury, metals) (evidence not convincing)

• Some chemicals seem to protect? (coffee, smoking?)

• Epigenetic link with DNA methylation

• Some connections to mitochondrial damage?

In what way are drugs for Parkinson’s similar to Drugs for Alzheimer’s

No cure, just drugs that improve synaptic signalling e.g. L-DOPA, biosynthetic precursor of dopamine that can pass the blood brain barrier, unlike Dopamine

What is Kuru and why was it only women that got it?

• Rare disease in Papua New Guinea

• Women and children ate the brain as part of ritualistic cannibalism, (men ate other organs e.g. heart, so unaffected)

What was the spread and mortality of Kuru, what did it lead to?

2% mortality rate

• from 1900 onwards till cannibalism was banned, very strong selection pressure, some villages had almost no young women

• Led to a selective sweep

What is a Selective sweep?

Strong evolutionary pressure leading to certain alleles becoming highly enriched

How is Lactose Intolerance an example of a selective sweep?

• As babies everyone has ability to breakdown lactose, but loose it when become adult

• Majority of the worlds population are lactose intolerant, at some point everyone was

• In populations that herd cattle the lactase gene is found however, It is rare in Asian populations

How do host-pathogen interactions drive selective sweeps?

• Host and pathogen are in an evolutionary arms race, each exerting selective pressure on the other

• Beneficial alleles that increase resistance (or virluence) can readily rise in frequency

• Examples in humans include Toll-like receptor variants likely driven by Yersinia pestis after the Black Death (1347-1351)

What is an eample of a pathogen-driven selective sweep?

• Toxoplasma gondii: a single clonal strain emerged in Europe and North America within the last ~10,000 years and has spread into South America

• Similar selective events in pathogens or after pandemics can shape host genomes (e.g. immune genes)

• Such past selection may partly explain population differences in susceptibility to disease (e.g., possible contributions to COVID-19 resistance)

Why was the Selective sweep of Kuru particularly remarkable?

• Led to almost complete change of G127 to V in local populations

• Remarkable because it happened over only 60 years or 3 generations