It is well known that genes play a major role in the pathogenesis of neurodegenerative diseases. There have been major efforts in biomedical research to learn about disease-related genes, which has led to highly targeted therapeutics for several diseases that were previously untreatable.
In this article, we review the functionality of SNCA and explore its role in targeted gene therapy for neurodegenerative diseases, presenting brief technical insights on the state of SNCA gene research.
Background Information – SNCA Gene
|
Species |
Human |
Mouse |
Rat |
|
Chromosome |
4 |
6 |
4 |
|
Full Length (bp) |
114,226 |
98,283 |
100,825 |
|
mRNA (nt) |
3,177 |
1,304 |
1,145 |
|
Numbers of exons |
13 |
7 |
8 |
|
Numbers of amino acids |
140 |
140 |
14 |
|
Gene Family |
SNCB, SNCG |
||
|
Cyagen Mouse Models |
|||
|
Status |
Custom |
Catalog Models |
Live Mice |
|
Knockout (KO) |
√ |
√ |
|
|
Conditional Knockout (cKO) |
√ |
√ |
|
Note: the mark ‘√’represents the corresponding models that available from Cyagen Knockout Catalog Models.
Overview of SNCA Gene Research
The SNCA gene encodes α-synuclein, a member of the synuclein family which also includes β-and γ-synuclein. The α-synuclein protein is highly expressed in brain tissue, it can selectively inhibit phospholipase D2 and bind to calcium ion channels. α-synuclein also plays a role in integration of presynaptic signals and membrane transport. Its specific function is to regulate the synaptic vesicle transport and control the release of neurotransmitters in vesicles. However, α- synuclein can also form plaques (Lewy bodies) due to the abnormality self-aggregation in the brain environment, affecting the normal function of neurons and brain tissue. The defect of this gene is closely related to the pathogenesis of Parkinson's disease (PD). In addition, there may be excessive accumulation of this protein found in patients with Alzheimer's disease (AD).
Figure 1: The Pathogenicity hypothesis of α-Synuclein. Aggregated α-synuclein may form a pathway that can alter the permeability of cell membrane. On the other hand, it may enter the mitochondria or endoplasmic reticulum and affect their normal functions. α-synuclein may also have an adverse effect on the degradation pathway of cell contents, such as the formation of lysosomes and autophagosomes.
doi: 10.3389/fnins.2016.00408.
|
Model Name |
A30P/A53T(Tg) |
A53T (Tg) |
A53T (Tg) on SNCA KO |
KO |
KO (Conditional) |
Thyl-aSyn "Line 61" |
E46K Rat (BAC Tg) |
|---|---|---|---|---|---|---|---|
|
Genetic background |
C57/BL6 |
C57BL6/J |
129S6/SvEvTac |
129/SvEvTac |
C57BL/6J |
(C57BL/6 x DBA/2) F1 |
Sprague-Dawley |
|
Details of gene modification |
SNCA: Tg Contains two mutations: A30P and A53T, and the length of the rat tyrosine hydroxylase promoter used was 9 kb. |
SNCA: Tg Human α-synuclein containing A53T. The promoter was mouse PrP. |
SNCA: Tg & KO The introduced PAC contained human SNCA with A53T mutation and its upstream 34kb sequence. Exon 4 and exon 5 on SNCA genes in knockout mice were replaced by neomycin resistant elements. |
SNCA: KO Exon 4 and exon 5 on SNCA genes in knockout mice are replaced by neomycin resistant elements. |
SNCA: CKO Two LoxP sites were located on both sides of Exon 2, and there was a neomycin resistance element in the downstream of LoxP at the End 3 |
SNCA: Tg Expression of human wild-type SNCA induced by mouse Thy1 promoter |
SNCA: Tg BAC introduced SNCA with E46K mutation |
|
Pathological Phenotype |
8 months later, progressive death of dopaminergic neurons in the substantia nigra pars compacta was observed. There was no α-nucleoprotein inclusion. The morphology of the dopaminergic system was abnormal, including abnormality of axons and dendrites. The concentration of dopamine in the striatum decreased. |
There was no obvious neuron loss. There were changes of dopamine-related proteins in striatum, substantia nigra and nucleus accumbens septi. There were specific neuronal accumulations in the regions of original fibrillation- nucleoprotein, ubiquitin, and neurofilament H, accompanied by astrocytosis. |
18 months later, no loss of dopaminergic neurons was observed in the substantia nigra. Rare dystrophic synapses were found in the aged hippocampus, but no Lewy body-like lesion or stimulus-synaptic aggregation was observed in the brain. Dopamine concentration remained unchanged in the striatum. |
There was no obvious abnormality of brain. Electron microscopy image showed abnormality of synaptic vesicles in hippocampal neurons, i.e. reduced reserve vesicles. |
|
|
There was no obvious abnormality of brain. Electron microscopy image showed abnormality of synaptic vesicles in hippocampal neurons. There was no obvious loss of neurons. Mutant- polynucleoprotein aggregating in the form of diffuse staining and intracellular aggregation existed in the brain. The aggregates were mainly confined to dopaminergic neurons in the substantia nigra and ventral tegmental area. Nitrotyrosine is elevated in dopaminergic neurons. |
|
Behavior/cognition |
More active than the wild type during the early adulthood, and then gradually became less active than the wild type. The touch screen experiment showed that the coordination of movement in these animals decreased with age. |
Hyperactivity was observed in early age. With the increase of age, severe dyskinesia began to develop, along with the manifestations of wagging, posturing, decreased spontaneous movement, paralysis, and, ultimately, death. According to the evaluation with Barnes' circular maze, the spatial memory was impaired at the age of 11-12 months. |
Impairment of exercise capacity was found during the wheel running test. In the open field test, it was manifested as decreased spontaneous movement. |
The behavior was basically normal. There were slight differences in physical motor activities (e.g., a decrease in nurturing behavior) in the wheel running test. But the behaviors were normal in general. Learning and memory abilities were intact. Some subjects seemed to be anxious. |
|
|
There was no obvious behavioral change. Low dose of rotenone could lead to rats to exhibit such phenomena as movement retardation, postural instability and rigidity. |
|
Other phenotypes |
No difference in body weight was observed compared with the wild type. |
Death before sexual maturity, synaptic dysfunction in the hippocampus. |
Decreased fecal amount, less colonic peristalsis, and extended intestinal transit time; no difference in weight, no olfactory disturbance, and no difference in the autonomous regulation of heart rate. |
Abnormality in microglia: decreased amount of cardiolipin in the brain, and mitochondrial abnormalities. Viable and fertile. |
|
|
Likely to survive and reproduce. |
|
First published papers |
Richfield et al.. 2002 |
Lee et al.. 2002 |
Cabin et al.. 2002 |
Cabin et al.. 2002 |
Ninkina et al., 2015 |
Rockenstein et al., 2002 |
Cannon et al., 2013 |
Table 1: Commonly used SNCA animal models. Notable SNCA models above include 6 mouse models and 1 rat model; 5 transgenic (Tg) models, and 2 KO or cKO models; One of the transgenic (Tg) models was generated from original SNCA knockout (KO) mice.
Expression of SNCA Gene in Human Tissues
Figure 2: Relative expression of mRNA of SNCA gene in humans and mice. The expression of this gene in brain tissue is much higher than that of other tissues. In mice, the expression level of spleen was the second, but only accounts 1/4 of that of brain; in humans, the expression level of ovary was the second, but only accounts 1/4 of that of brain; the expression levels in other organs were lower (such comparison is only limited to the same species rather than in between mice and human). Source: NCBI.
Neurodegenerative Disease Related Resource:
>> Advancing Neurodegenerative Disease Research with Animal Models
>> TARDBP: A Pathogenic Gene of Neurodegenerative Diseases
References:
1. Deng H, Yuan L. Genetic variants and animal models in SNCA and Parkinson disease. Ageing Res Rev. 2014 May;15:161-76. doi: 10.1016/j.arr.2014.04.002. Epub 2014 Apr 21. PMID: 24768741.
2. Vekrellis K, Xilouri M, Emmanouilidou E, Rideout HJ, Stefanis L. Pathological roles of α-synuclein in neurological disorders. Lancet Neurol. 2011 Nov;10(11):1015-25.doi: 10.1016/S1474-4422(11)70213-7. Erratum in: Lancet Neurol. 2011 Dec;10(12):1041. PMID: 22014436.
3. Auluck PK, Caraveo G, Lindquist S. α-Synuclein: membrane interactions and toxicity in Parkinson's disease. Annu Rev Cell Dev Biol. 2010;26:211-33. doi: 10.1146/annurev.cellbio.042308.113313. PMID: 20500090.
