Dysregulation of ncRNAs in association with Neurodegenerative Disorders

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Dysregulation of ncRNAs in association with Neurodegenerative Disorders

January 11, 2021 by Amandeep Kaur

Dysregulation of ncRNAs in association with Neurodegenerative Disorders

Curator: Amandeep Kaur

Research over the years has added evidences to the hypothesis of “RNA world” which explains the evolution of DNA and protein from a simple RNA molecule. Our understanding of RNA biology has dramatically changed over the last 50 years and rendered the scientists with the conclusion that apart from coding for protein synthesis, RNA also plays an important role in regulation of gene expression.

Figure: Overall Taxonomy of ncRNAs
https://www.nature.com/articles/s42256-019-0051-2

The universe of non-coding RNAs (ncRNAs) is transcending the margins of preconception and altered the traditional thought that the coding RNAs or messenger RNAs (mRNAs) are more prevalent in our cells. Research on the potential use of ncRNAs in therapeutic relevance increased greatly after the discovery of RNA interference (RNAi) and provided important insights into our further understanding of etiology of complex disorders.

Figure: Atomic Structure of Non-coding RNA
https://en.wikipedia.org/wiki/Non-coding_RNA

Latest research on neurodegenerative disorders has shown the perturbed expression of ncRNAs which provides the functional association between neurodegeneration and ncRNAs dysfunction. Due to the diversity of functions and abundance of ncRNAs, they are classified into Housekeeping RNAs and Regulatory ncRNAs.

The best known classes of ncRNAs are the microRNAs (miRNAs) which are extensively studied and are of research focus. miRNAs are present in both intronic and exonic regions of matured RNA (mRNA) and are crucial for development of CNS. The reduction of Dicer-1, a miRNA biogenesis-related protein affects neural development and the elimination of Dicer in specifically dopaminergic neurons causes progressive degeneration of these neuronal cells in striatum of mice.

A new class of regulatory ncRNAs, tRNAs-derived fragments (tRFs) is superabundantly present in brain cells. tRFs are considered as risk factors in conditions of neural degeneration because of accumulation with aging. tRFs have heterogenous functions with regulation of gene expression at multiple layers including regulation of mRNA processing and translation, inducing the activity of silencing of target genes, controlling cell growth and differentiation processes.

The existence of long non-coding RNAs (lncRNAs) was comfirmed by the ENCODE project. Numerous studies reported that approximately 40% of lncRNAs are involved in gene expression, imprinting and pluripotency regulation in the CNS. lncRNA H19 is of paramount significance in neural viability and contribute in epilepsy condition by activating glial cells. Other lncRNAs are highly bountiful in neurons including Evf2 and MALAT1 which play important function in regulating neural differentiation and synapse formation and development of dendritic cells respectively.

Recently, a review article in Nature mentioned about the complex mechanisms of ncRNAs contributing to neurodegenerative conditions. The ncRNA-mediated mechanisms of regulation are as follows:

Epigenetic regulation: Various lncRNAs such as BDNF-AS, TUG1, MEG3, NEAT1 and TUNA are differentially expressed in brain tissue and act as epigenetic regulators.
RNAi: RNA interference includes post-transcriptional repression by small-interfering RNAs (siRNAs) and binding of miRNAs to target genes. In a wide spectrum of neurodegenerative diseases such as Alzheimer’s disease, Parkinson disease, Huntington’s disease, Amyotrophic lateral sclerosis, Fragile X syndrome, Frontotemporal dementia, and Spinocerebellar ataxia, have shown perturbed expression of miRNA.
Alternative splicing: Variation in splicing of transcripts of ncRNAs has shown adverse affects in neuropathology of degenerative diseases.
mRNA stability: The stability of mRNA may be affected by RNA-RNA duplex formation which leads to the degradation of sense mRNA or blocking the access to proteins involved in RNA turnover and modify the progression of neurodegenerative disorders.
Translational regulation: Numerous ncRNAs including BC200 directly control the translational process of transcripts of mRNAs and effect human brain of Alzheimer’s disease.
Molecular decoys: Non-coding RNAs (ncRNAs) dilute the expression of other RNAs by molecular trapping, also known as competing endogenous RNAs (ceRNAs) which hinder the normal functioning of RNAs. The ceRNAs proportion must be equivalent to the number of target miRNAs that can be sequestered by each ncRNAs in order to induce consequential de-repression of the target molecules.

Table: ncRNAs and related processes involved in neurodegenerative disorders
https://www.nature.com/articles/nrn.2017.90

The unknown functions of numerous annotated ncRNAs may explain the underlying complexity in neurodegenerative disorders. The profiling of ncRNAs of patients suffering from neurodevelopmental and neurodegenerative conditions are required to outline the changes in ncRNAs and their role in specific regions of brain and cells. Analysis of Large-scale gene expression and functional studies of ncRNAs may contribute to our understanding of these diseases and their remarkable connections. Therefore, targeting ncRNAs may provide effective therapeutic perspective for the treatment of neurodegenerative diseases.

References https://www.nature.com/scitable/topicpage/rna-functions-352/ https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6035743/ https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7695195/ https://link.springer.com/article/10.1007/s13670-012-0023-4 https://www.nature.com/articles/nrn.2017.90