Establishing In Vitro Models to Study Endogenous Neurotoxicants

互联网2014-02-07

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Advances in molecular genetics over the last decade have resulted in the identification of genetic mutations responsible for several inherited neurological diseases. Not only has cloning of these genes led to methods for diagnosis of patients and identification of carriers but also to the establishment of animal and cell culture models to study mechanisms by which mutant proteins induce toxicity in vulnerable cell types. Early neuropathological studies of autopsy tissue from patients with degenerative neurological diseases commonly revealed the presence of inclusion bodies in affected neuronal populations (see Table 1 ; 1 –44 ). These include tangles and plaques in Alzheimer’s disease, Lewy bodies in Parkinson’s disease, and nuclear or cytoplasmic aggregates in the trinucleotide repeat diseases (spinal bulbar muscular atrophy, Huntington’s disease, spinocerebellar ataxia 1 and 3, dentato-pallidoluysian atrophy) and cytoplasmic inclusions in familial and sporadic motor neuron diseases (45 ,46 ). That similar inclusions are observed in both sporadic and hereditary forms of neurological diseases suggested that similar pathways might be involved in pathogenesis whether protein abnormalities result from inherited sequence differences, DNA damage, or posttranslational modifications. The presence in inclusions of ubiquitin, a stress protein required for targeting abnormal proteins for degradation, suggested failure of proteolytic processing to rid cells of aberrant proteins. However, the primary or secondary role of these inclusions in the pathogenesis of disease could not be surmised from studies of postmortem tissue at end-stage disease.

Table 1 Examples of Proteotoxicants Resulting in Genetic Mutations Responsible for Human Neurological Disease

Mutant protein	Human disease	Inclusion bodies	Cells most affected	Ref.
Amyloid precursor protein	Alzheimer’s	Extracellular β-amyloid in plagues, neurofibrillary tangles	Limbic and association cortices, hippocampus	1 –4
Tau	Frontotemporal dementias Multisystem atrophy	Paired helical filaments in neurofibrillary tangles	Frontotemporal cortical neurons	5 –7
Presenilin 1 and 2	Alzheimer’s	Amyloid plaques	Limbic and association cortices, hippocampus	3 ,4 ,8 –10
α -Synuclein	Parkinson’s Lewy body dementia	Lewy bodies	Substantia nigra Cortical pyramidal neurons	6 ,11
Cu/Zn-superoxide dismutase (SOD-1)	Chromosome 21-linked amyotrophic lateral sclerosis (ALS)	Cytoplasmic inclusions	Upper and motor motor neurons, astrocytes	12 –15
High-molecular-weight neurofilament protein (NF-H)	Rare cases of familial ALS	Hyaline and keinlike inclusions, Bunina bodies	Upper and lower motor neurons	16
~undefinedHuntingtin	Huntington’s	Nuclear and cytoplasmic inclusions	Striatum, cerebral cortex	17 –20
~undefinedAndrogen receptor	Kennedy’s disease	Nuclear and cytoplasmic inclusions	Lower motor neurons, dorsal root ganglia	18 –22
~undefinedAtaxin-1	Spinocerebellar ataxia (SCA1)	Eosinophillic spheroids, nuclear inclusion body	Cerebellar Purkinje, dentate nucleus, brainstem	18 –20 ,23
~undefinedAtaxin-2	SCA2	Increased mutant protein, but no inclusions	Cerebellar Purkinje, brain-stem, fronto- temporal lobes	18 –20 , 24 –26
~undefinedAtaxin-3	SCA3 / Machado-Joseph disease	Nuclear inclusions	Cerebellar dentate neurons, basal ganglia, brainstem, spinal cord	18 –20 , 27
8α_1A -subunit of voltage-dependent calcum channel	SCA6	Cytoplasmic inclusions	Cerebellar Purkinje and Granule neurons, dentate nucleus, inferior olive	18 –20 , 28 ,29
~undefinedAtaxin-7	SCA7	Nuclear inclusion	Cerebellum, brainstem, macula, visual cortex	18 –20 , 30
~undefinedAtrophin-1	Dentorubropallidoluysianatrophy	Nuclear inclusion	Cerebellum, cerebral cortex, basal ganglia	18 –20 , 31 ,32
~undefined *Poly(A)binding protein 2	Oculopharyngeal dystrophy	Nuclear inclusion	Skeletal muscle	33
Neuroserpin	Familial dementia/progressive myoclonus epilepsy	Collins bodies	Cortical neurons, subcortical nuclei	34 –36
Prion protein	Creutzfeld-Jacob (CJD), Gerstmann-St�ussler-Scheinker disease	PrP^Sc deposition in plaques	Cortex, basal ganglia Cerebellum, cerebrum, brainstem	2 ,37 – 39
Fatal familial insomnia	Kuru	Multiple	Cerebellum, cerebrum, brainstem
PMP22, P0	Charcot-Marie-Tooth	Accumulation in endoplasmic reticulum	Schwann cells	40 –44