725 - Molecular neurobiology of disease

1. 725 - Molecular neurobiology of disease • Parkinson’s disease • Schizophrenia • Alzheimer’s disease • Reference List

2. Approaches • epidemiology • genetic • chromosome • gene / protein • pharmacology • anatomical • post-mortem • MRI/PET • animal models

3. Human Brain • cut vertically down midline

4. Parkinson’s disease • Loss of dopaminergic neurons • normal: 4% per decade • Parkinson’s: 70-80% loss Parkinson’s normal substantia nigra

5. Symptoms • Hard to initiate movement • Interaction of substantia nigra with cortex see 746 lecture 6

6. Therapy • L-DOPA • cross blood-brain barrier • dopamine agonists • MAO-B inhibitors (selegiline = deprenyl) • cell replacement • fetal midbrain transplants • pigs • carotid body • stem cells • deep brain [=thalamus] stimulation

7. Animal model • Model with MPTP  MPP+ • Neuronal damage, • activates microglia, • which produce NO (iNOS), • causes further neuronal damage MPTP (1-methyl-4-phenyl -1,2,3,6-tetrahydropyridine)MPP 1-Methyl-4-phenylpyridinium

8. Causation • Inherited disorder • *a-synuclein (folds SNAREs) • Parkin (E3 ubiquitin ligase) • DJ-1 (stress response chaperone) • PINK-1 (mitochondrial protein kinase) • *LRRK2 (another ?mitochondrial kinase) • It is not clear why mutations in a-synuclein, or parkin or [] genes cause nigral dopaminergic cell death in familial PD [Le W & Appel SH (2004)] *dominant – others are recessive

9. Causation • Environmental factors too • Rotenone • fish poison • blocks mitochondrial function • upregulates a-synuclein • oxidises DJ-1 • Paraquat

10. One model inhibitors of parkin

11. Another model

12. Summary • Parkinson’s has • well-defined deficit – loss of dopaminergic cells • well-described pathology & behaviour • variety of therapies • no cure • no known cause

13. Schizophrenia • Positive (hallucinations) & negative symptoms (asociality) • possibly several illnesses • seasonal • highly inherited

14. Developmental disease • genetic cause : • DISC1 or a chromosome translocation • caused by failure of neurons to migrate ? • red shows areas less in Sc

15. Dopamine hypothesis • positive symptoms respond to treatment • negative symptoms do not respond to treatment • DA antagonists • Chlorpromazine • side effects, e.g. Parkinsonism, constipation • Haloperidol • D2 (+D3, D4 +5-HT2A) blocker

16. Newer drugs • e.g. clozapine • dopamine D2 receptors and 5-HT action • D2 receptor block is key point • e.g. mouse model • -ve symptoms from  DA in prefrontal cortex • 5-HT action helps -ve symptoms • NMDA (glutamate) receptors blocked by phencyclidine, relieves many symptoms

17. Depression • 5-HT (=serotonin) • main treatment is with uptake inhibitors • SSRI eg Prozac • Noradrenaline • also selective re-uptake inhibitors PFC: pre-frontal cortex

18. Summary so far • ethical issues “impede” research • animal models hard to interpret • key concept: neural diseases identified with cellular / molecular deficit • disease related to change in specific neurotransmitter • complexity of CNS leads to side effects

19. Dementia • Reduction of brain volume and cells with age • Dementia increases with age • at 65, 11% of USA had dementia • 70% of dementia is Alzheimer’s • 15% from strokes • at 85, 47% affected • Early onset Alzheimer’s inherited • <1% of cases

20. Alois Alzheimer • On November 3, 1906, Alois Alzheimer gave a lecture to the Meeting of the Psychiatrists of South West Germany, presenting the neuropathological and clinical description of the features of one of his cases, Auguste D., who had died of a dementing illness at the age of 55,

21. Alzheimer’s Symptoms • Forgetfulness • untidiness • confusion • less movement • storage of new memory reduced • finally loss of bodily function

22. Neuroanatomy • cortex very reduced normal Alzheimer

23. Neuroanatomy • cortex reduced - note gaps between folds

24. Neurodegeneration • brains feature • plaques(Ab =b-amyloid) • tangles(tau)

25. Neurofibrillary tangles • micrograph drawing by Alois Alzheimer

26. Development of tau

27. Amyloid hypothesis • Down’s syndrome leads to AD by 40 • linked to chromosome 21 • Positional cloning identified: • amyloid-b (Ab) peptide 40-42 amino acids • families with mutations in bAPP • 670 / 692 / 716 & 717 • amyloid b toxic to cultures

28. Presenilins • Familial early onset dominant AD linked to mutations on chromosomes 14 & 1 • presenilin I : mutations lead to onset at age 28 • presenilin II : second homologous gene • mutations • are in regions conserved between PSI and PSII associated with AD • lead to increased Ab production

29. Presenilins • code for two secretases b and g • involved in processing bAPP g b a a secretase now called ADAMb secretase called BACE

30. Proteolysis of APP Normal amyloidogenic APP

31. Proteolysis of Ab • In non-familial AD, plaques caused not by production of Ab but by failure to degrade it • Little evidence for increased production of Ab peptide • maybe normally degraded quickly • half life 1-2 hr • tangles resistant to degradation • enzymes: • neprilysin & insulin-degrading-enzyme

32. Neprilysin • Neprilysin knockout mice have more Ab42

33. Major problem • how does faulty b-amyloid lead to tangles of tau? • tau is hyperphosphorylated • GSK-3 glycogen synthase kinase

34. More direct interaction? • tau and Ab form complexes • GSK-3 phosphorylates tau in complex Ab is extracellular tau Ab in neurons

35. tau v Ab • AD has both tau and Ab • other diseases have just tangles of tau

36. Apolipoprotein E • Another family gene for late onset of AD produces Apolipoprotein E

37. Apolipoprotein E - cont • receptor (LRP) expressed in astrocytes • normal role is in cholesterol transport • may aid in clearance of b-amyloid from brain to blood • mutations disrupt clearance

38. Oxidative stress • main function of b-amyloid may be to protect cells from reactive Oxygen radicals • damage to mitochondria leads to *OH • shortage of energy (or oxygen) increases likelihood of AD • through high [Ca] • metal ions might affect build up of b-amyloid

39. Therapy ?? • cholinergic therapy  • secretase blockers • relief of oxidative stress • Apolipoprotein therapy • stem cells for replacement • vaccination  • ginko biloba

40. Cholinergic hypothesis • cholinergic neurones in basal forebrain project to cortex and hippocampus • muscarinic antagonist, (M1), pirenzipine, causes memory loss in hippocampus • agonists, e.g. physostigmine, improve memory • But other systems interact

41. Cholinergic therapy • Cholinesterase inhibitors – delay symptoms • Tacrine: allosteric – 1993 (toxic in liver) • Donepezil; mixed binding

42. Try Cholinergic agonist • M2 on basal ganglia and intestine • Depletion of M1 receptors? • M1 and M3 receptors in hippocampus • Drug trials discontinued

43. Summary of AD • Full mechanism not known • amyloid hypothesis well – established • role of tau also established • role for glia and neurons • No one effective treatment • cholinotherapy promising ? • Happy Christmas & New Year!