Protein Misfolding Can Have Deadly Consequences 992328 992334

Protein Misfolding Can Have Deadly Consequences 992328張謹淳 992334林思慧 992504曹紋寧 992539鄭翰群 1

• In April 1996 a paper was published in the medical journal Lancet that generated widespread alarm in the populations of Europe. • The paper described a study of 10 persons afflicted with Creutzfeldt-Jakob disease (CJD), a rare, fatal disorder that attacks the brain, causing a loss of motor coordination and dementia. 2

CJD • CJD can occur as an inherited disease. • CJD can also be acquired. 3

• The cases described in the 1996 Lancet paper had also been acquire, but the apparent source of the disease was contaminated beef. • The contaminated beef was derived from cattle raised that had contracted a neurodegenerative disease that caused the animals to lose motor coordination and develop demented behavior. • Mad cow disease! 4

• A disease that runs in families can invariably be traced to a faulty gene, whereas diseases that are acquired from a contaminated source can invariably be traced to an infectious agent. 5

• How can the same disease be both inherited and infectious? 6

In 1960, D. Carleton Gajdusek showed that the Islanders were contracting a fatal neurodegenerative disease. They called it”kuru”. Autopsies of the brain of patient who had died of kuru showed a distinct pathology , referred to as spongiform encephalopathy. 7

• It was soon shown that the brains of islanders suffering from kuru were strikingly similar in microscopic appearance to the brains of persons afflicted with CJD. • This observation raised an important question: Did the brain of a person suffering from CJD, which was known to be an inherited disease, contain an infectious agent? 8

• In 1968, Gajdusek showed that when extracts prepared from a biopsy of the brain of a person who had died from CJD were injected into a suitable lab animal, that animal did indeed develop a spongiform encephalopathy similar to that of kuru or CJD 9

• Clearly, the extracts contained an infectious agent, which at the time was presumed to be a virus. 10

• In 1982, Stanley Prusiner published a paper suggesting that, unlike viruses, the infectious agent responsible for CJD lacked nucleic acid and instead was composed solely of protein. He called the protein a prion. 11

• It was presumed initially that the prion protein was an external agent, some type of virus-like particle lacking nucleic acid. • Contrary to this expectation, the prion protein was soon shown to be encoded by a gene (called PRNP) within the cell’s own chromosomes. 12

• The gene is expressed within normal brain tissue and encodes a protein designated Pr. PC (standing for prion protein cellular) that resides at the surface of nerve cells. • A modified version of the protein(Pr. PSc) is present in the brains of humans with CJD. • Unlike the normal Pr. PC , the modified version of the protein accumulates within nerve cells, forming aggregates that kill the cells. 13

• In the purified states, Pr. PC and Pr. PSc have very differentphysical properties. Pr. PC Pr. PSc Monomeric molecule fibrils Soluble in salt solutions Insoluble in salt solutions Readily destroyed by protein-digesting enzymes Resistant to enzymatic digestion 14

Pr. PC Pr. PSc 15

How Pr. PSc act an infectious agent? • Pr. PSc bind to normal protein(Pr. PC) can convert Pr. PC into Pr. PSc • Appearance of the abnormal protein in the body starts a chain reaction →Normal protein molecules gradually converted to the abnormal prion form. 16

Pr. PC Pr. PSc converted Pr. PSc Bind again 17

Alzheimer’s disease (AD) • Memory loss • 10% individuals at least 65 years of age 40% are 80 years or older • The brain contains fibrillar deposits of an insoluble material referred to as amyloid. 18

Alzheimer’s disease (AD) 19 © 2000 - 2012 American Health Assistance Foundation http: //www. ahaf. org/alzheimers/about/understanding/plaques-and-tangles. html

CJD v. s AD-same • Fetal neurodegenerative disease • Occur in an inherited or sporadic form • Fibrillar deposits result from self-association of a polypeptide 20

CJD v. s AD-differences • Proteins that form the disease-causing aggregates are unrelated. • Affected parts of the brain are different. • AD is nontransmissible. 21

AD-amyloid hypothesis • Amyloid β–peptide (Aβ): part of amyloid precursor protein(APP) • Aβ is cut by Β-secretase and γ-secretase from APP • Two species of Aβ: Aβ 40 & Aβ 42 • Misfold Aβ 42 has the potential to cause damage to the brain, the soluble oligomers are toxic to nerve cells 22

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AD-Aβ 42 • Refold into a different conformation (contains β–pleated sheet) • Tend to self-associate to large aggregates (visible fibrils) • Oligomers appear to attack the synapses and lead to the dead of nerve cell • Inherited AD leads to increased Aβ 42 production, by mutations in the APP gene 24

drugs • Management of symptoms • Three strategies : – Prevent formation of Aβ 42 – Remove the Aβ 42 – Prevent interaction between Aβ 25

• One of the best approached to the development of treatments for human diseases is to find laboratory animal, particularly mice, that develop similar diseases. • Animals that exhibit a disease that mimics a human disease are termed animal model 26

• For whatever reason, the brain of aging mice show no evidence of the amyloid deposits found in humans, and there was no animal model for AD. • Until 1995, the researchers create a strain of mice by genetically engineering the mice to carry a mutant human APP gene. 27

• This strain develop amyloid plaques in their brain and performed poorly at tasks that required memory. • We can use these investigations to illustrate some of the steps required in the development of a new drug. 28

• In 1999, Dale Schenk and his colleagues published an extraordinary finding. • Repeatedly injecting the animals with the very same substance that causes the problem, the aggregated Aβ 42 peptide. 29

• The researcher had immunized (i. e. , vaccinated) the mice against the disease. • When young (6 -week-old) mice were immunized with Aβ 42, they failed to develop the amyloid brain deposits as they grow older. • When older (13 -mounth-ole) mice whose brains already contained extensive amyloid deposits were immunized with the Aβ 42. 30

• The immunized mice performed better than their nonimmunized littermates on memorybase tests. 31

Phase I clinical trial • A Phase I clinical trial is the first step in testing a new drug or procedure in humans. • Phase I tests are designed to monitor the safety of the procedure rather than its effectiveness against the disease. 32

• No one showed any ill-effects due to injection of the amyloid peptide. As the result, the investigators were allowed to proceed to a Phase II clinical trial. 33

Phase II clinical trial • Phase II: 1. the patients are randomly divided into two groups that are treated similarly except that one group is given the curative factor being investigated and the other group is given a placebo. 2. The study is double-blinded, which means that neither the researchers nor patients know who is receiving treatment and who is receiving the plcebo. 34

• The Phase II trial for the Aβ vaccine began in 2001 and enrolled more than 350 individuals in the United States and Europe who had been diagnosed with mild to moderate AD. 35

• Most of these patients were successfully treated with steroids, but the trial was discontinued. • 2001 was reported in 2008, analysis of this patient group indicates that Aβ 42 vaccination had no effect on preventing disease progression 36

Two interpretation • Amyloid deposits are not the cause of the symptoms of dementia. • Irreversible toxic effect the deposits had already occurred by the time immunization had begun. 37

• These treatments had stared earlier, the symptoms of the disease might never have appeared. • It may be possible to begin preventive treatments in persons who are at very haigh risk of developing AD before they develop symptoms. 38

Drugs develop • Alzhemed: small molecular designed to bind to Aβ peptide and block certain interactions, thereby stopping molecular aggregation and fibril formation • Flurizan: a nonsteroidal anti-innammatory drug, or NSAID, like ibuprofen. 39

• The drug was found to reduce mental decline over a period of one year by an average of 81 percent compared to patient receiving a placebo. • The drug is now being test in larger Phase III study 40

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