Bi / CNS 150 Lecture 24 Monday November 26, 2012 Two neurodegenerative diseases Henry Lester Kandel, Chapters 43 & 58 1

Proposal for Bi/CNS 150 extra credit: a. Enroll for the course. b. If you wish to continue after the first 2 weeks, inform Henry Lester.

c. Pass the course. Should be quite easy.

d. Contribute to the forums with technical and scientific explanations.

e. Contribute to the Caltech Bi/CNS 150 students forum.

Result: at least 1/3 grade (i. e., B+ to A-). Retroactive, will not destroy the curve.

Inspect the “Landing Page”: https://www.coursera.org/#course/drugsandbrain After 12/1: Inspect the “Course Page”: https://class.coursera.org/drugsandbrain-2012-001/class/index Inspect miniLecture 5 Inspect the discussion forums: https://class.coursera.org/drugsandbrain-2012-001/forum/index 2

Parkinson’s disease 1. Clinical description 2. Genetics 3. Pathophysiology 4. Biomarkers and animal models 5. Heterozygote advantage: none known 6. Therapeutic approaches James Parkinson, apothecary surgeon 1817,

An Essay on the Shaking Palsy

, described "paralysis agitans", from observations of 6 individuals during his daily walks in London Parkinson’s disease (tremor at rest 3 5 Hz, “pill-rolling”, slow movements, particularly when starting; short, rapid steps) but most Parkinson patients are either medicated or stimulated 3

Dopaminergic neurons in the human brain: Saggital view Substantia Nigra: Dopaminergic neurons die in PD Ventral tegmental area: Dopaminergic neurons remain healthy Rodent brain section, stained for tyrosine hydroxylase: coronal view 4

like several previous Lectures

Only dopaminergic neurons express the cell membrane dopamine transporter. HO Antidepressants (“SSRIs” = serotonin selective reuptake inhibitors): Prozac Zoloft Paxil Drugs of abuse: MDMA Na + -coupled cell membrane serotonin transporter N H NH 3 + Attention-deficit disorder medications: Ritalin Dexedrine Drugs of abuse: Na + Cocaine Amphetamine -coupled cell membrane dopamine transporter cytosol synaptic cleft HO HO H 2 C C H 2 NH 3 + 5

2.

Parkinsonism in people 1. Most cases are unexplained dopamine HO H 2 C C H 2 NH 3 + HO reactive: oxidative damage?

The “frozen addict”. An impurity in synthetic heroin. Taken up by the dopamine transporter (expressed only in dopaminergic cells). Kills cells.

3.

The influenza pandemic (worldwide epidemic) of 1918, killed 20 million people. The flu specifically killed dopaminergic neurons in many people (“Awakenings”). 4.

Genetics: see next topic 5.

Smoking protects against PD.

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3. Genetics. Familial Parkinson’s Disease Provides a Good Review of Bi 8/9 (~ 10% of patients). Onset 30’s to 50’s (rarely earlier or later) Locus PARK1 & PARK4 PARK2 PARK3 PARK5 PARK6 PARK7 PARK8 PARK9 PARK10 PARK16 Chromosome location 4q21 –q23 6q25.2-q27 2p13 4p14 Gene or protein name a

-synuclein (Unknown function) Parkin E3 Ubiquitin ligase

Unknown

UCH-L1

ubiquitin-C-terminal hydrolase-L1

PINK1,

PTEN-Induced Putative Kinase 1 1p35-p36 1p36 12cen 1p36 Various

DJ-1 LRRK2

leucine-rich repeat kinase 2 ATP13A2 Much less is known Inheritance pattern AD AR AD, IP AD AR AR AD AD various AD, autosomal dominant; AR, autosomal recessive; IP, incomplete penetrance 7

a synuclein has an unknown function; it’s an “intrinsically disordered protein”.

Mutant a -synuclein forms fibrils.

The hallmark of PD pathology: Intracellular “Lewy bodies”, especially in dopamine neurons Improper mitochondrial fission / fusion may be one of the early events (Prof. D. Chan, Caltech) 8

4. Animal Models for Parkinson’s Disease:

Drosophila

that overexpress synuclein 1. The 4 dopaminergic neurons die preferentially!

We don’t know why.

(2. The cells show dense structures like Lewy bodies) 3. The flies show a “movement disorder” 9

4. More Animal Models for Parkinson’s Disease

a. Toxin-treated mice, rats, and moneys; b. Mice with altered PARK genes c. Stem cells from people carrying PD mutations Induced pluripotent stem cells, “disease in a dish”. But there are still major technical issues in generating dopaminergic neurons.

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like previous lectures

Deep brain stimulation for Parkinson’s Disease Tremor arises in a malfunctioning feedback loop: substantia nigra, striatum, and other structures in basal ganglia.

Implanted stimulating electrodes retune this loop.

PPTg

Axons passing through

Cortex ACh INs INs ?

INs ACh MSN D2R MSN D1R dorsal striatum

Indirect pathway

ACh SNc =

Direct Pathway

GPe STN ?

Transmitters GABA Glu GPi SNr + DA Thalamus Excitation (Regardless of color) Inhibition

1. Meta-analysis of 45 studies 3 Inadvertent neuroprotective effect: tobacco use Pools case cohort all 2 Relative risks 1 0 Hernan, 2002 individual studies: case-control cohort 2. Tanner, 2002: 33 discordant identical twins including at least one smoker. The twins without PD smoked more than their brothers smoked (37.1 vs 25.3 pack-years,

p=0.077)

http://en.wikipedia.org/wiki/Case-control_study 12

Mechanistic hypotheses about the neuroprotective effects of tobacco use in PD Goal: intervene in early-stage PD with drug taken from that point.

1. Circuit-based: Cell-selective upregulation of α4β2 nicotinic receptors (pharmacological deep brain stimulation) 2. Presynaptic: Selective upregulation in nerve terminals of dopaminergic neurons 3. Cell-delimited: Pharmacological chaperoning of intracellular receptors → reprogram cell physiology (Lester research group) 13

Transplantation of stem cells induced to release dopamine No reproducible success to date.

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Alzheimer’s disease 1. Clinical description 2. Genetics 3. Pathophysiology 4. Biomarkers and animal models 5. Heterozygote advantage: none known 6. Therapeutic approaches

1.

1. Symptoms of Alzheimer’s Disease AD begins with a “pure” impairment of cognitive function.

2.

A.

B.

C.

Progression

AD begins slowly. At first, the only symptom may be mild forgetfulness.

In this stage, people may have trouble remembering recent events, activities, or the names of familiar people or things. They may not be able to solve simple math problems. They may begin to repeat themselves every few minutes in conversation. In the middle stages of AD, individuals may forget how to do simple tasks, like brushing their teeth or combing their hair. They can no longer think clearly. They begin to have problems speaking, understanding, reading, or writing. Late stage: AD patients may become anxious or aggressive, or wander away from home. Eventually, patients need total care.

Incidence and public health costs of Alzheimer’s disease

AD is the most common degenerative brain disease (est. 4.5 million Americans) Risk Factors: age 65-74 ~5% 75 ~10% 80 ~20% >85 ~50% (However, AD is not considered a normal part of aging).

The more common form of AD, known as late-onset or sporadic AD , occurs later in life, with no obvious inheritance pattern.

However, several risk factor genes may interact with each other to cause the disease. Most common risk factor gene identified so far for late-onset AD, is a gene that makes one form of apolipoprotein E (apoE). ApoE4 is the risk factor gene.

Familial AD , a rare form, usually starts at age 30 - 60.

Estimated public health cost of AD: ~ $90 billion / yr in medical care & lost productivity.

The Anatomical Hallmark of Alzheimer’s Pathology: Amyloid Plaques and Neurofibrillary Tangles in Brain

Amyloid Plaques contain large amounts of a 42 amino acid peptide termed “ b -amyloid ”, or A b 42 The best present hypothesis: b -amyloid itself is the initial cause of the pathophysiology that leads Amyloid to plaques dementia.

probably contribute to the later stages of pathology Neurofibrillary tangles: rich in cytoskeletal proteins, especially the microtubule-associated protein named “ tau ”. In the tangles: heavily phosphorylated proteins, which may cause aggregation and precipitation of the cytoskeleton,

Chromo some

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Gene defect

β-APP mutations 19 14 1 6

2. All known genetic risk factors predisposing to Alzheimer’s disease increase accumulation of A β peptides

ApoE4 polymorphism ( ε4 allele) Presenilin 1 mutation Presenilin 2 mutation TREM2

Phenotype

↑All Aβ peptides, or Aβ40 peptides A673T↓ Aβ peptides, AD, cognitive decline ↑Density of Aβ plaques & vascular deposits ↑Production of Aβ42 peptides ↑Production of Aβ42 peptides ↑Density of Aβ plaques β-APP = amyloid precursor protein = APP

More on the latest genomic hit, TREM2

TREM2, odds ratio 2.9; frequency 0.5% in controls.

TREM2, single-pass membrane protein, expressed in immune cells including microglia. Decreased and increased TREM2 leads to lower and greater phagocytosis, respectively, of apoptotic neurons. Increased TREM2 leads to lower innate immune response. TREM2 malfunction leads to Nasu–Hakola disease, rare recessive disease that is with painful bone cysts in wrists and ankles, psychotic symptoms, and progressive presenile dementia with onset in the fourth decade of life.

Johnsson et al New Eng J Med 2012 Guerreiro et al New Eng J Med 2012

3. Pathophysiology. A β40 and Aβ42 are proteolytic products formed from APP APP proteins: 110 to 140 kDal. APP expressed by most tissues, especially neurons; reaches axon terminals and dendrites. APP is also found in glial cells. Overproduction of A b 40 and A b 42 results from altered ratio of proteolytic cleavages at sites termed a , b , and g .

Fig. 58-6

Red circles: presenilin 1 and

APP

mutations associated with familial AD

presenilin 1 is part of g -secretase, a membrane-associated protease Hardy and Selkoe, 2002, Science

Normal function of presenilin’s g -secretase activity: Notch signaling?

APP cleavage would be a “side effect”

Soluble Oligomers of A β42

A β42 peptides form soluble oligomers of ~4 to 40 peptides. These oligomers interact with other proteins and precipitate to form amyloid plaques.

Soluble oligomers of A β42 (containing ~12 to 40 peptides) are toxic to neurons.

The 12-mer is the most significant toxic form.

Soluble oligomers block induction of LTP (Injected into ventricles 10 min before high frequency stimulation of the rat Schaffer collateral pathway).

Wild Type CM CM + A β oligomers CM = “conditioned medium” from a cell line engineered to express A β CM + nonspecific “control” antibody CM + Antibody against A β Walsh et al., Nature 2002

Hypothetical pathophysiological sequence: APP or presinilin → familial AD

Sporadic Alzheimer’s appears to result from gradual failure of clearance of A β . From Selkoe, 2002, Science

4.

Biomarkers for AD: none established. Only an autopsy is conclusive Some progress in two areas: 1. CSF analyses of tau, phospho-tau at position181, and A β42.

Individual values, or ratios among these.

2. A positron emission tomography (PET) marker, [ 18 F]Florbetapir, binds to plaques containing β-APP.

Animal models: mice overexpressing APP, especially with AD-associated mutations. 27

5. Heterozygote advantage: none known 6. Therapeutic approaches Acetylcholinesterase inhibitors (because cholinergic basal forebrain neurons are among the first to die in AD) Aricept, Exelon, Reminyl NMDA inhibitors Memantine Failed therapeutics: Anti-APP or A β antibodies; γ-secretase inhibitors Still in development β-secretase inhibitors 28

Henry Lester’s “office” hours, Monday this week 1:15-2 Red Door End of lecture 29

APP and its human mutations that lead to increased A

b

peptides

Selkoe, Physiol. Rev., 2001

QuickTime™ and a TIFF (Uncompressed) decompressor are needed to see this picture.

One Current Hypothesis 1.

a) b) Soluble oligomers of A b bind to synaptic sites ADDL’s A b *56 (12-mer and below) (12 mer) 2.

Binding leads to internalization of AMPA and NMDA receptors.

3. Activity increases amount of APP and A b . Are these events part of a normal homeostatic mechanism that becomes deranged in AD?

From J. Neurosci. (2007) 27: 11832