Nature's contribution lasted for 5 years | The "sheriff" in the brain: Natural antisense transcripts can participate in the regulation of disordered protein stability related to neurodegeneration

Written | Qi human genome expresses thousands of natural antisense transcripts (NAT), which can regulate epigenetic state, transcription, RNA stability or the translation of overlapping genes [1].

Tau protein is a kind of intrinsically disordered protein (IDP) inherent in neurons that stabilize axon microtubules.
Hyperphosphorylated and easily aggregated tau will form the hallmark inclusion bodies of tau protein disease [2].

In addition, studies have reported that mutations in MAPT (tau protein coding gene) lead to familial frontotemporal dementia.
Common mutations in the MAPT H1 haplotype are important risk factors for many tau diseases and Parkinson's disease.

Whether and how MAPT-AS1, a kind of NAT rich in the brain, participates in the process of neurodegenerative diseases such as tau protein disease is still unknown.

On May 19, 2021, the team of Rohan de Silva and Roberto Simone from the UCL Queen’s Square Neurology Institute in the United Kingdom published an article entitled MIR-NATs repress MAPT translation and aid proteostasis in neurodegeneration in the journal Nature.
Studies have reported that MAPT-AS1 contains an embedded mammalian-wide interspersed repeat (MIR), which can compete with the ribosomal entry site of MAPT mRNA to compete for ribosomal RNA pairing to inhibit tau protein translation, indicating MAPT-AS1 plays a key role in tau proteinopathy and reveals the potential broad contribution of MIR-NATs to the strict control of translation of IDPs, especially related to protein stability in neurodegeneration.Human brain RNA-seq data show that the tissue distribution of MAPT-AS1 is similar to that of MAPT mRNA, and the two are positively correlated.

In order to evaluate the role of MAPT-AS1 in the disease, the author first analyzed several recent multi-omics data from other studies [3, 4] and found that the severity of tau pathology was negatively correlated with the level of MAPT-AS1.

Subsequently, the author used two methods of siRNA and lentiviral infection to silence MAPT-AS1 to detect its effect on MAPT expression.
The results both resulted in a significant increase in tau protein levels without affecting MAPT mRNA levels.

So in this process, which part of the sequence of MAPT-AS1 is playing a role? To this end, the authors stably expressed full-length MAPT-AS1 or targeted deletion truncations in SH-SY5Y cells to verify the translational inhibition of tau by different domains.

The results showed that MAPT-AS1 functions in a modular manner, requiring the 5'region to confer target specificity and the 3'MIR CORE-SINE region to mediate translational inhibition.

Previous studies have shown that Tau translation can occur through a cap-dependent and internal ribosome entry site (internal ribosome entry site, IRES)-mediated mechanism [5, 6].

Next, the author wants to know the necessary motifs of MAPT-AS1 that can directly interfere with the recruitment of ribosomes to the 5'UTR of MAPT.

So the author used the 7-nt window to BLAST the similarity between MAPT-AS1, 18s rRNA and MAPT-5'UTR, and found that there are two 7-mer motifs in MIR, one of which interacts with 18s rRNA.
The tau-IRES sequence is the same, and the other is complementary, indicating that MIR competes with the first IRES motif for rRNA binding, and directly blocks the second IRES motif, thereby affecting the recruitment of ribosomes.

Figure 1.
Schematic diagram of two MIR motifs for MAPT-AS1-mediated tau translation inhibition.
The above experiments were done at the cellular level.
Next, the author would like to know the in vivo effect of MAPT translation inhibition. It has been previously reported that the htau transgenic mouse model containing the human MAPT gene can show age-dependent tau pathology and delayed-onset behavioral disorders.
Therefore, the authors have combined MAPT-AS1-FL, MAPT-AS1-ΔMIR, MAPT-AS1- MiniNAT (fully capable of inhibiting tau translation) and eGFP adeno-associated virus were injected unilaterally into the hippocampus of mice.
Compared with the control, mice injected with adenovirus expressing MAPT-AS1-FL or MAPT-AS1-miniNAT The brain showed a significant decrease in overall and phosphorylated tau levels.

Combined with the information provided by the previous database, the authors believe that the reduction of MAPT-AS1 levels and the presence of H1 haplotypes can jointly promote the high activity of tau-IRES and increase the risk of Parkinson's disease by disrupting the stability of tau protein.

In addition to the translational regulation of tau by MAPT-AS1, are there similar antisense transcripts that can also play a similar regulatory role? Based on the similar topology as MAPT-AS1, the author chose PLCG1-AS (PLCG1 is a gene that is dysregulated in Alzheimer’s disease) for verification, which contains a reverse MIRb of the 9-mer motif, The 5'UTR and 18S rRNA complementary to PLCG1 can also compete for ribosome recruitment to achieve translational inhibition.

Therefore, the translational regulation of neurodegeneration-related genes by MIR-NATs in the brain is not an isolated case.
In order to understand the broader relationship between MIR-NATs and diseases, the author analyzed three brains from the brains of Alzheimer’s patients after death.
Transcriptomics meta-analysis was performed on a large data set.

Interestingly, compared with healthy controls, 446 differentially expressed MIR-NATS-AS pairs were identified in AD patients.

More than 40% of the genes are paired with genes encoding high IDPs, and they are significantly enriched in neurodegenerative disease (NDD)-related genes, suggesting that MIR-NATs are involved in the post-transcriptional regulation and neuronal protein stabilization of many IDPs, especially The role in NDD-related genes has broad potential.

In general, in the nervous system, IDPs have the characteristics of metastable, easy to aggregate, and dose-sensitive, and are usually associated with neurodegeneration.
In order to avoid the long-term existence and accumulation of redundant IDPs, their expression is at multiple levels It is strictly regulated, including the enrichment of microRNA binding sites [7].

This study shows that MIR-NATs is another level of regulation, which helps to strictly control the translation of IDPs, and may be used as a potential therapeutic target to control the process of neurodegeneration.

It is worth mentioning that the official website information shows that the work lasted 5 years from submission to publication, which is relatively rare.

Original link: https://doi.
org/10.
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