The accumulation of α‐synuclein gives rise to the formation of a nucleus for the accumulation of other proteins, which ultimately leads to the formation of Lewy bodies (within the dopamine secreting cells).
PD is a proteinopathy characterized by the misfolding and aggregation of α‐synuclein synucleinopathy, which leads to the destruction of dopaminergic neurons within substantia nigra pars compacta.
By linking to the 3′‐UTR sequence of Hsp70 mRNA, miR‐16‐1 configures Hsp70. Its increase reduces the Hsp70, which in turn boosts the aggregation of α‐synuclein protein, and this increases the incidence of PD.
miR‐16‐1 is a case in point that has been seen in some patients with PD.It has been shown to decrease the expression of Hsp70 by increasing the aggregation of the α‐synuclein protein
lncRNAs have been reported to cause apoptosis in the brain
For example, EBF3‐AS is a lncRNA that increases significantly in the hippocampus of the mice whose neurons had undergone apoptosis (Figure 1)
This protein is commonly found in the presynaptic terminus and is a factor in the transmission of synaptic dopaminergic neurons.
It is interesting to note that miR‐124 has a target sequence on BACE1 mRNA, and by binding to it, it inhibits mRNA.
Moreover, inhibition of miR‐124 significantly increases the level of BACE1 in neurons. On the other hand, its overexpression significantly suppresses the expression of BACE1.
For instance, measuring lncRNA BACE1 within the cytoplasm of the patients showed that its level in patients with Alzheimer’s was significantly higher than that in the control group
BACE1‐AS can increase the expression of BACE1 mRNA by increasing its stability, which gives rise to AD
By attaching to the 3′‐UTR sequence, the miR‐153 reduces the expression of the APP
Downregulation of miR‐153 increases the expression of APP and eventually, the production of β‐ameloid is promoted, increasing the risk of AD
Two miRNAs that play an important role in regulating α‐synuclein expression are miR‐153 and miR‐7
That is, in the event that miRNAs regulating α‐synuclein that reduce its accumulation (including miR‐153, miR‐7, miR‐132, and miR‐133‐b) are decreased, the progression of PD will be accelerated.
These two miRNAs downregulate the α‐synuclein by binding to the 3′‐UTR portion in the mRNA transcribed from SNCA.
In an experiment conducted to investigate this, pre‐miR‐34b and premiR‐ 34c were introduced into human dopaminergic SH‐SY5S cells and it was found that the amount of α‐synuclein protein had decreased significantly.
It has been shown that miR‐7 inhibition increases the expression of α‐synuclein
The experiments conducted on SH‐SY5Y cells show that computational analyses on the miR‐15b binding site 3′‐UTR can be proven in practice, and miR‐15b expression can reduce BACE1 by binding to this sequence
For example, miR‐339‐5p, having two binding sites on BCAE1 mRNA, can downregulate the expression of the BACE1 protein
In addition, miR‐34‐b and miR‐34‐c have been shown to experience a significant reduction in patients with Parkinson’s compared with controls, and this reduction is accompanied by a decrease in the expression of DJ‐1 protein
It was found that miR‐384, by binding to the 3′‐UTR sequence on BACE1 mRNA, could not only reduce expression in SH‐SY5Y cells but also attach to the 3′‐UTR sequence of the mRNA APP and reduce its expression, and this highlights the importance of miR‐384 in AD
On the other hand, miR‐101, by downregulating RanBP9, can indirectly reduce the production of APP
Besides, by directly affecting APP, miR‐101 can cause its downregulation, which ultimately provides the basis for AD
Given the important role of miR‐101 in preventing AD, miR‐101 reduction can play a role in AD development
As regards, the MAPKK2 pathway, miR‐9 has been shown to inhibit tangles neurofibrillary by inhibiting this pathway and to play an important role in preventing AD.
miR‐132 is another miRNA that has a regulatory effect on α‐synuclein. The downregulation of this miRNA results in the accumulation of α‐synuclein protein
However, this is part of the role that miR‐132 plays in the regulation of PD.
In fact, by directly affecting the expression of Nurr1, this miRNA can play a significant role in the development of PD
Let‐7 and miR‐184 have an inhibitory effect on the performance and expression of two transcription factors, namely E2F1 and DP
A case in point is miR‐196a that affects HD
It has also been shown that miR‐205 can regulate LRRK2 and that PD is associated with a significant reduction in the level of miR‐205 in the frontal cortex and striatum
Expression of miR‐205 affects the level of LRRK2 expression, and LRRK2, in turn, affects two miRNAs called let‐7 and miR‐184. This effect is associated with decreased activity and level of let‐7 and miR‐184 within the cell
Also, a significant relationship has been found between the number of copies of CAG and some miRNAs in the striatum and cortex of mice with Huntington. These miRNAs include miR‐206, miR‐301b, miR‐92b, miR‐378b, miR‐208b, and miR‐449a.
For example, miR‐22 with its neuroprotective function prevents the death of neurons by apoptosis.
Activation of the CAMMK2 pathway has been shown to cause tau proteins to be phosphorylated
By activating the CAMMK2 pathway, the β‐ameloid can aid in the phosphorylation of tau proteins and eventually trigger tangles neurofibrillary.
This disease is inherited by autosomal dominant alleles due to a mutation in the huntingtin gene (HTT).
One of the most important proteins involved in PD is the LRRK2 protein
The expression of LRRK2 mutants can cause apoptosis of neuronal and neuroblastoma cells
One of the most important mutations in LRRK2 is the Gly2019- Ser mutant, the most common cause of familial PD.
The PARK 7 gene on chromosome 1 is responsible for coding the DJ‐1 protein. This protein acts as chaperon in the neurons, thus preventing the aggregation of the α‐synuclein protein
It also inhibits apoptosis and prevents the death of neuron
One of these factors is Ran‐binding protein 9 (RanBP9) that can increase the amount of APP in the cell by its effects
The mutation in the SNCA gene causes PD.
BACE1‐AS is transcribed by opposite strand BACE1. Its upregulation in patients with Alzheimer’s can be used as a new biomarker for the diagnosis of this disease.
Comparing miR‐9 in patients with AD against healthy individuals shows a significant decrease of miR‐9 in patients with AD
Dysphagia, dysphasia, and seizures are common symptoms in HD
HD is a neurodegenerative disease characterized by an insidious onset and subsequent progression of chorea and dementia, which usually presents at the ages of 30 to 50, and its symptoms increase with age.
Currently, miR‐10b‐5p, miR‐196a‐5p, miR‐196b‐ 5p, miR‐615‐3p, and miR‐1247‐5p increase in HD, and studies have shown that miR‐196a‐5p, miR‐196b‐5p, and miR‐615‐3p have been almost zero in the control group
These experiments show that in apes, miR‐128a levels at birth and during the disease (either in the presymptomatic or postsymptomatic stage) show a significant reduction of this miRNA
In 12‐month‐old HD transgenic mice, downregulation was observed in the expression of the following miRNAs: miR‐ 22, miR‐29c, miR‐128, miR‐132, miR‐138, miR‐218, miR‐ 222, miR‐344, and miR‐674
It has been shown that DJ‐1 protein levels in patients with PD are significantly lower compared with the healthy subjects
It has also been shown that miR‐494 in patients with PD increases significantly in comparison with healthy subjects.
It has been reported that downregulation of BACE1‐AS reduces the amount of β‐ameloid and plaques
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If you find BEL Commons useful in your work, please consider citing: Hoyt, C. T., Domingo-Fernández, D., & Hofmann-Apitius, M. (2018). BEL Commons: an environment for exploration and analysis of networks encoded in Biological Expression Language. Database, 2018(3), 1–11.