{'fraction_non_alphanumeric': 0.03827478424973953, 'fraction_numerical': 0.017830112642277223, 'mean_word_length': 5.346057884231537, 'pattern_counts': {'":': 0, '<': 2, '<?xml version=': 0, '>': 1, 'https://': 0, 'lorem ipsum': 0, 'www.': 0, 'xml': 0}, 'pii_count': 0, 'substrings_counts': 0, 'word_list_counts': {'cursed_substrings.json': 2, 'profanity_word_list.json': 0, 'sexual_word_list.json': 0, 'zh_pornsignals.json': 0}}
Non-coding RNA in SARS-CoV-2: Progress toward therapeutic significance

The recently developed pathogenic virus, SARS-CoV-2, was found in the Hubei Province, China. Giving rise to a broad spectrum of symptoms, SARS-CoV-2 rapidly spread across the globe, causing multi-systemic and dangerous complications, with death in extreme cases. Thereby, the number of research cases increases every day on preventing infection and treating its resulting damage. Accumulating evidence suggests noncoding RNAs (ncRNAs) are necessary for modifying virus infection and antiviral immune reaction, along with biological processes regulating SARS-CoV-2 and subsequent disease states. Therefore, understanding these mechanisms might provide a further understanding of the pathogenesis and feasible therapy alternatives against SARS-CoV2. Consequently, the molecular biology of SARS-CoV-2, ncRNA's role in its infection, and various RNA therapy tactics against the virus have been presented in this review section.


Introduction
Beginning in December 2019, the Novel Coronavirus, abbreviated as SARS-CoV-2 (severe acute respiratory syndrome coronavirus 2), has spread worldwide [1]. Coronaviruses can be divided into alpha coronaviruses, beta coronaviruses, gamma coronaviruses, and delta coronaviruses [2]. Beta coronaviruses include the SARS-CoV-2, SARS-CoV, and the Middle East Respiratory Syndrome Coronavirus (MERS-CoV), enveloped RNA viruses (as all kinds of Coronaviruses) that are highly pathogenic to humans [3]. MA Moni et al. examined the phylogenetic tree of identified coronaviruses (SARS-CoV, MERS-CoV and SARS-CoV-2) and pandemic influenza A strains (H1N1, H3N2 and H5N1), which led to the understanding that SARS-CoV-2 closely relates to SARS-CoV and MERS-CoV. Additionally, researchers have confirmed that novel coronaviruses cause particularly contrasting transcriptional feedback in host cells, although there is a close phylogenetic relationship among SARS-CoV-2, SARS-CoV, and MERS-CoV. Correspondingly, the resulting disease from SARS-CoV-2 is an entirely different entity compared to those of previous coronaviruses [4]. This highly infectious virus sets off symptoms associated with flu, such as fever, cough, and dyspnea, that ultimately could advance to acute respiratory distress syndrome (ARDS), pneumonia, renal failure, and death [5]. Presently, there is no specific treatment for SARS-CoV-2 despite the urgency of pandemic outbreaks of the virus and high transmission rates in humans. Mitigation of RNA expression could be a novel and promising therapeutic method, potentially achieved through administration of RNA mimics, restoring down-regulated RNA expression, or RNA inhibitors (anti-RNA), counteracting up-regulation of pathogenic RNAs. Additionally, due to the current deeper understanding of disease-relevant RNAs and advances in in-vivo delivery systems, the administration of RNA-based therapeutics has shown to be viable and safe in humans, with promising efficacy results from early-phase clinical trials [6]. Moreover, these molecules have previously been effective against viruses, and with regard to their considerable superiority (low toxicity, high specificity, and relatively simple and low-cost synthesis), they might provide a reasonable base for nucleic acid-based drugs against SARS-CoV-2. Additionally, further mutations in the SARS-CoV-2 genome might strongly influence the range of hosts, tissue tropism, and virus pathogenicity, as well as the effects of drugs and vaccines on the virus. Therefore, the fact that RNAs could be easily altered to accommodate the genetic mutations of the virus makes the method an attractive approach for therapies against SARS-CoV-2.
The delivery technology could be considered the main issue for establishing and implementing RNA-based drugs. Developing these delivery systems potentially solves the challenges of RNA delivery in vivo as the foundation for higher RNA treatment potency. Lipid nanoparticles (LNPs) delivery of the COVID-19 spike protein-encoding mRNA through lipid nanoparticles (LNPs) is now known to indicate lung protection capability against viral infection [7]. Non-viral nanocarriers other than LNPs, including lipid-based nanoparticles (NPs), polymeric NPs, Nacetyl galactosamine (GalNAc)-siRNA conjugate, and biomimetic nano vectors, are capable of protecting the nucleic acids against nuclease degradation, thereby facilitating their cellular uptake and aiding in the regulated release of encapsulated therapeutics [8][9][10][11]. Collectively, these findings call attention to the therapeutic potential of targeted RNAs for treating and preventing SARS-CoV-2 infection. Consequently, in this review, we discuss the emerging roles of ncRNAs in SARS-CoV-2 molecular pathogenesis and highlight transpiring roles of ncRNAs in SARS-CoV-2 treatment.

Molecular biology of SARS-CoV-2 1.SARS-CoV-2 genome organization
The nucleotide length of SARS-CoV-2 genome is in the range of 26.0 kb to 32.0 kb. 65 to 70 % of the viral genome region, i.e. the first 20 kilobase downstream to the 5 ′ -end, encodes the ORF1ab (open reading frame 1a and ab) or the replicase gene, potentially encoding the NSPs (nonstructural proteins) called pp1a and pp1ab polyproteins, respectively. The pp1a non-structural protein is related to NSP1 to 11 and the pp1ab is related to NSP12 to 16. The 10 kilobase region upstream to the 3 ′ -end contains the genes of various structural proteins, including surface (S), envelope (E), membrane (M), and nucleocapsid (N) proteins. The hemagglutinin-esterase gene is not available in the SARS-CoV-2 genome. However, it is surrounded by untranslated regions (UTRs) at 5 ′ end of 265 and 3 ′ end of 358 nucleotides. Sequence variation among SARS-CoV-2 and SARS-CoV did not reveal any significant difference in ORFs and nsps [8] (Fig. 1).

Non-structural protein in SARS-CoV-2 infection
Entry of SARS-CoV-2 into host cells is an essential factor of viral infectivity and pathogenesis. It has been shown that SARS-CoV-2 surface spike protein binds to human ACE2 (hACE2) through its receptorbinding domain (RBD) and mediates SARS-CoV-2 entry into cells. M Ö rd observed that novel coronavirus SARS-CoV-2 carries an insertion, 680 SPRRAR↓SV 687 , forming a cleavage motif RxxR at the boundary of S1/S2 subunits for furin-like enzymes to assist viral entry into target cells [12]. Moreover, A Bayati et al. revealed that SARS-CoV-2 undergoes rapid, clathrin-mediated endocytosis after engagement with the plasma membrane. In this context, they further demonstrated a decreased viral infectivity through siRNA-mediated knockdown of clathrin's heavy chain. Therefore, virus infectibility is significantly dependent on clathrin-mediated endocytosis [13]. Following cell entrance, the replication cycle of SARS-CoV-2 occurs in multiple stages. At the 5 ′ end, the genomic RNA with two large open reading frames (ORFs; ORF1a and ORF1b) occupies two-thirds of the capped and polyadenylated genome ( Fig. 1). ORF1a and ORF1b encode 16 non-structural proteins (NSPs), 15 of which shape the viral replication and transcription complex (RTC). RTC includes RNA-processing and RNA-modifying enzymes in addition to an RNA proofreading function, which is necessary for integrity maintenance of the >30 kb coronavirus genome. Nsp12 functions as an RNA-dependent RNA polymerase (RdRp) by using nsp7 and nsp8 as its additional factors, and nsp13 is a helicase [14]. Furthermore, the RTC complex assembles double-membraned vesicles that are responsible for full-length negative RNA strand template synthesis and, ultimately, genomic RNA. Genomic RNAs are paired with structural proteins from virions into budding Golgi vesicles. Eventually, virion-containing vesicles fuse with host cell membrane, and by exocytosis, mature SARS-CoV-2 is released [15]. In the case of SARS-CoV-2 exocytosis, S Ghosh et al. investigated the egress pathway of β-coronaviruses. They realized these viruses use a lysosomal, Arl8b-dependent exocytic pathway to reach the extracellular environment. They also observed that through this pathway, GRP78/BIP, an ER chaperone facilitating coronavirus infectivity, is co-released with β-coronaviruses [16]. S Angeletti et al. observed a stabilizing mutation in the endosome-associated-protein-like domain of the nsp2 protein using homology modeling and positive selective pressure analysis. It was also revealed that stabilizing mutations could account for the high contagious ability of COVID-2019, while the destabilizing mutation in nsp3 proteins could lead to a potential differentiation mechanism of COVID-2019 and SARS [17].

Structural protein in SARS-CoV-2 infection
Other structural protein-encoding ORFs are contained within onethird of the SARS-CoV-2 genome, which includes spike protein (S), an envelope protein (E protein), nucleocapsid protein (N protein), and membrane protein (M protein). S, E, and M proteins form the viral envelope/surface together, with N proteins carrying the RNA genome. E protein, at around 8-12 kDa, is the smallest among the structural proteins, playing a significant role in the pathogenesis, assembly, and release of the virus. JL Nieto-Torres et al. observed that E proteins form calcium ion-permeable protein-lipid channels in ERGIC/Golgi membranes. In addition, calcium transportation through the E protein ion channels was shown to boost activation of the NLRP3 inflammasome activation leading to the overproduction of IL-1β [18]. The M protein is an O-linked glycoprotein with the rough size of 25-30 kDa, most abundant among various structural proteins. It possesses three distinct transmembrane domains. Although M proteins possess a variety of amino acid compositions, they are structurally preserved across various genera. Except for β-CoVs and δ-CoVs showing O-linked glycosylation, other coronavirus M proteins go through N-linked glycosylation. Glycosylation plays an essential role in organ tropism and IFN signaling. LT Collins et al. suggested the structural role of proteins that bud into the ER-Golgi intermediate compartment (ERGIC) as essential for forming infectious particles. Through a study of molecular dynamic simulation, they observed cooperation of M protein dimers intending to maintain membrane curvature, while E protein pentamers kept the planar structure of the membrane [19]. The N protein is exclusively present in the complex organization of the nucleocapsid structure. The three distinct domains in the N protein, i.e. N-terminal, RNA-binding (linker region), and C-terminal, are incredibly conserved. N proteins help pack viral RNA into nucleocapsids. With the help of these proteins, the viral genomes release into the network of the endoplasmic reticulum-Golgi intermediate compartment (ERGIC). The central core of N proteins has residues of ~140 amino acid-long domains arranged in a 'bead on string' manner that bind to viral RNAs. L Zebin et al. investigated the biological effects of the SARS-CoV-2 nucleocapsid proteins on human-induced pluripotent stem cells (iPSC). They observed the nucleocapsid protein of SARS-CoV-2 suppressing translation of crucial pluripotency genes through binding to particular sites of RNAs and breaking pluripotency maintenance of iPSCs. Thereby, nucleocapsid proteins of SARS-CoV-2 play a crucial role in impairing reproductive and hematopoietic systems in patients dealing with SARS-CoV-2 infection [20]. Viral effects on innate immune recognition and response through evolved enzymes or host cell enzymes were markedly affected by modifications to the RNA of the virus, making it indistinguishable from RNAs of the host cell. M6A, as the most common eukaryotic internal RNA modification, has been observed in several types of viruses, such as Hepatitis C virus (HCV) [21]. Liu et al. conducted the first transcriptome-wide m 6 A methylome characterization of SARS-CoV-2 through a combination of RIP-seq and miCLIP analysis. They observed the wide distribution of m 6 A and its dynamical regulation in the positive-sense genome and negative-sense RNA intermediates [22]. Additionally, N Li performed host cell m6A methyltransferase METTL3 and observed enhanced m 6 A modification in the nucleocapsid (N) domain of viral genome. Further, they revealed that levels of m 6 A in SARS-CoV-2 RNA of METTL3-depleted cells decreased, leading to more binding of RIG-I to SARS-CoV-2 RNA which resulted in activation of IκBα phosphorylation and expression of downstream inflammatory genes [23].

Emerging role of non-coding RNA in SARS-CoV-2 infection
Based on findings from the Human Genome Project (HGP) coupled with the latest high-throughput sequencing technology, it has become apparent that a low portion (<2 %) of the human genome encodes roughly 25,000 proteins. Many noncoding RNAs (noncoding RNA, ncRNA) are transcribed from the rest of the human genome (approximately 98 %). Various forms of ncRNAs are sub-classified according to length. Long non-coding RNAs are transcripts longer than 200 base pairs (bp), and those shorter than 200 bp are small ncRNAs, including microRNAs (miRNAs). CircRNAs are other forms of ncRNAs that, unlike linear RNAs, possess 5 ′ caps and 3 ′ tails. They form covalently closed loop structures without 5 ′ -3 ′ polarities and don't contain polyadenylated tails. Additional evidence shows that both host-and virusderived ncRNAs affect protection from and susceptibility to SARS-CoV-2 in severe cases. Following SARS-CoV-2 infection, it was demonstrated that to achieve successful nucleic acid synthesis cycles, ncRNAs (miRNAs, circRNAs, and lncRNAs) are altered by the virus. Attempts have been made to compare the various research group datasets on altered expressions during infection. Identifying dysregulated or altered ncRNAs possibly leads to a symptom mitigation strategy and limitation of viral genome amplification, enhancing the immune response during SARS-CoV-2 infection. Furthermore, these profiles provide a disease state distinguishing base and act as biomarkers. Identifying dysregulated or altered ncRNAs possibly leads to a symptom mitigation strategy and limitation of viral genome amplification, enhancing the immune response during SARS-CoV-2 infection. Furthermore, these profiles provide a disease state distinguishing base and act as biomarkers. As a result, a concise summary of major contributing ncRNAs in SARS-CoV-2 infection has been described in the following segment to provide therapeutic targets and biomarkers for treatment and risk classification patients with SARS-CoV-2 (Table 1).

MicroRNA in SARS-CoV-2 infection
MicroRNAs (miRNAs) are categorized as small molecules containing 17-24 nucleotides. They are noncoding single-stranded RNAs able to suppress the translation of mature messenger RNA (mRNA). MiRNAs are known to be active during the regulation of various physiological and pathological pathways in animals, including humans [24][25][26][27]. Moreover, miRNAs have been shown to influence viral infections. Q Li et al. discovered three pro-viral and nine antiviral miRNAs interacting with HCV through integrative functional genomics strategies in HCV-infected cells. Moreover, mechanistic studies demonstrated that miR-25, let-7, and miR-130 families repress essential HCV co-factors and, as a result, restrict viral infection at multiple stages [28]. In 2021, considering SARS-CoV-2 infection, Keikha et al. evaluated the expression of four inflammatory miRNAs and their targets in serum samples of COVID-19 patients selected from various severity stages. They observed that the relative expression of hsa-miR-31-3p, hsa-miR-29a-3p, and hsa-miR-126-3p had significantly decreased, and the relative expression of their mRNA targets (ZMYM5, COL5A3, and CAM-SAP1) had increased dramatically in correlation to disease severity. Conversely, the relative expression of hsa-miR-17-3p had significantly increased, and the corresponding mRNA target (DICER1) had significantly decreased with an increase in disease severity. Additionally, they declared that patients nonresponsive to treatment had shown similar miRNA profiles. In COVID-19 patients responsive to treatment, expression of selected miRNAs and their targets were observed to be in normal level ranges [29]. These findings provided crucial insight into the pathophysiological aspects of miRNAs in SARS-CoV-2 infection (Fig. 2).

MiR-146a.
The long arm of chromosome 5 contains the miRNA-146a, which acts as a protective aid in reducing inflammation by targeting inflammation-related genes [26,27,30]. Furthermore, F Zeinali et al. observed negative regulation by miRNA-146a in the  [60] qPCR Peripheral blood CDR1as CDR1as involved in SARS-CoV-2 diseases. [63] (continued on next page) production of IL-6 and TNF-α and a negative correlation with IR (insulin resistance) in type 2 diabetes mellitus (T2DM) through RT-PCR analysis [31]. Consequently, a decrease in miR-146a-5p levels would be expected to stimulate the release of inflammatory cytokines, e.g., IL-6. In the case of SARS-CoV-2, J Sabbatinelli et al. observed increased levels of IL-6 and reduced levels of miR-146a-5p compared to healthy age-matched subjects, suggesting the imbalance of IL-6/miR-146a-5p physiological axis in SARS-CoV-2 pathogenesis. Droplet digital PCR (ddPCR) further indicated that response to tocilizumab (TCZ) is correlated to a significant reduction of plasma IL-6 and increase of miR-146a levels, suggesting TCZ treatment is capable, at least in responder patients, of offsetting the IL-6/miR-146a-5p axis unbalance. As a result, circulation of low miR-146a-5p levels in SARS-CoV-2 patients might predict poor outcomes in cases that develop systemic hyper-inflammation [32]. Moreover, Roganović et al. investigated the upregulation of miR-146a and its relation to type 2 diabetes and the susceptibility of periodontitis patients to infection via expression modulation of SARS-CoV-2 cellular entry agents. They observed that diabetes-and periodontitisinduced increase of microRNA-146a in the oral cavity potentially upregulates angiotensin-converting enzyme 2 expression, essential SARS-CoV-2 entry receptors, and modulates host antiviral response, which is suggesting of increased infection rates in patients with diabetes and periodontitis [33].   luciferase reporter assay, bta-miR-98 was observed to act with Caspase-3. Through overexpression of bta-miR-98, caspase-3 signaling was inhibited, leading to lower apoptosis and suppression of CPIV3 replication [37]. Additionally, X Fei et al. examined regulatory alterations on proliferation, migration, invasion, and apoptosis of hepatitis B virusrelated hepatocellular carcinoma (HBV-HCC) caused by miR-98. They observed that miR-98-5p functions as a secretion inhibitor of HBV, in addition to modulation of proliferation, migration, and invasion of HBV-HCC cells through the use of nuclear factor-κB-inducing kinase (NIK) as targets [38]. Regarding SARS-CoV-2, A Matarese et al. identified hsa-miR-98-5p as a highly conserved miRNA through bioinformatics evaluations, capable of repressing TMPRSS2 mRNA expression. As well, the luciferase assay confirmed the interaction between miR-98-5p and TMPRSS2 3'-UTR in human lung microvascular endothelial cells (HMVEC-L) and human umbilical vein endothelial (HUVEC) cells. In short, SARS-CoV-2 infection is highly influenced by miR-98 as a regulatory agent [39]. and systemic arterial hypertension as independent factors associated with patients of group IV (p < 0.0001). They postulated that independent of COVID-19 risk factors, miR-200c-3p is a determinant of severity, possibly representing a means of SARS-CoV-2 identification in patients [42]. In addition, it has been found that upregulation of miR-200c might increase the susceptibility of obese individuals to SARS-CoV-2, and circulating miR-200c could act as a potential biomarker in the early identification of those at severe SARS-CoV-2 risk. Consequently, miR-200c plays a crucial role in SARS-CoV-2 pathogenesis [43].

Long-noncoding RNA in SARS-CoV-2 infection
Transcribed and spliced products of RNA polymerase II or III, or LncRNAs, are 5'capped and sometimes contain a polyadenylated 3'end tail. Recent assessments have observed lncRNAs as crucial molecules of biological and pathological process regulation, while their subcellular location represents their function to a high degree [44,45]. Recent indepth studies have suggested a close correlation between viral infections and host cell transcriptome alternations in segments such as lncRNAs. In this regard, Q Zhang et al. outlined mRNA and lncRNA expressions in THP-1 cells through emerging RNA-seq to characterize transcriptional changes during human CMV latent infection [46]. They found a multitude of dysregulated lncRNAs resulting from latent human cytomegalovirus (CMV) infection. Furthermore, E Carnero observed lncRNA EGOT, through antagonizing antiviral response, negatively affecting antiviral response and aiding in hepatitis C virus (HCV) replication [47]. Regarding SARS-CoV-2, H Shaath et al. utilized computational and transcriptome analyses of publicly available PBMC datasets from four groups of individuals: ICU-admitted COVID-19 patients, COVID-19 not admitted to ICU, ICU-admitted non-COVID-19 patients, and non-COVID-19 patients not admitted to ICU. In ICUadmitted patients with COVID-19, they observed upregulation of LINC02207, AC020636.1, AC243967.2, LINC01127, AC00727.1, and AC092746.1, while the patients with COVID-19 that were not ICUadmitted showed upregulation of LINC02084, LINC02446, LINC00861, AC015911.3, LINC01871, and ANKRD44-AS1. Consequently, the results suggested lncRNA-based biomarkers as being correlated with SARS-CoV-2 severity [48]. Additionally, long noncoding RNA analysis could be used as an effective risk assessment tool in SARS-CoV-2 patients. In this context, J Cheng et al.  [52]. In viral infections, M Mohyeldeen et al. studied serum detectability and diagnostic association of NEAT1 in viral hepatitis C (HCV) and HCVassociated hepatocellular carcinoma (HCC). They identified significant alterations in the serum expression of NEAT1 in HCV and HCC patients, suggesting diminished NEAT1 possibly leading to the progression of HCV infection and ultimate HCC [53]. Furthermore, an in silico analysis of altered lncRNA expression in SARS-CoV-2 infected cells has been recently conducted by S laha et al. [54]. They observed higher rates of NEAT1 expression in the lungs of SARS-CoV-2 patients. Additionally, via the ChIPBase database, they proposed transcription factors IRF1, IRF4, STAT1, STAT3, STAT5A, and MYC are capable of binding to putative promoters of NEAT1, resulting in modified host gene expression. Therefore, NEAT1, mainly by regulating host gene expression, contribute to the antiviral response to SARS-CoV-2 infection (Fig. 3).

Circular RNA in COVID-19 infection
Circular RNAs (circRNAs/circ) are the most common eukaryotic noncoding RNAs. CircRNAs can be divided into three classes exonic (ecircRNA), exon-intron (EIcircRNA), or intronic (ciRNA) circRNAs. CircRNAs, mostly being ecircRNAs, are mainly cytoplasmic. Pre-RNA back-splicing is catalyzed by RNA polymerase II (RNA Pol II) and is a prerequisite for the formation of circRNAs. A circularized RNA is formed by connecting a downstream 5 ′ splice donor site and an upstream 3 ′ splice acceptor site. Opposed to linear RNAs, circRNAs are continuous, consist of covalent structures that lack both ends (5 ′ and 3 ′ ends), and are stable, ultimately protected against degradation by exonucleases [55]. Additionally, circRNAs primarily operate based on specific tissue and cells while being observed in biological material to steadily express, i.e. saliva, tissue, blood, and exosomes. Consequently, potential biomarkers for diagnosis and prognosis in various diseases could include circRNAs [56]. CircRNAs have been detected as biomarkers to be highly expressed in viral and infectious diseases with the rapid development of bioinformatics and high-throughput sequencing. In this regard, it has been suggested that circ-10,156, through the miR-149-3p/Akt1 pathway, operates as a molecular sponge for miR-149-3p, regulating the proliferation of HBV-related liver cancer cells. Additionally, through miR-1287-5p inhibition, circ-0004812 endorses FSTL1 expression, thereby controlling the HBV-induced immune suppression [57]. Furthermore, circ-FNDC3B and circ-CNOT1 are correlated to the MERS-CoV load in Mers-CoV-infected lung adenocarcinoma, and their knockout will cause a decrease in the viral content of cells [58]. Therefore, circRNAs play vital regulatory roles in infection and the resulting host antiviral responses. Regarding the COVID-19 virus, Y Wu et al. sequenced the blood of COVID-19 patients and those of healthy individuals. Through comparison, they found differentially expressed circRNAs, indicating circRNAs possibly play an essential role in COVID-19 infection. Through exhaustive comparison, they observed 570 different circRNAs, among which 155 were up-regulated, and 415 were down-regulated. Additionally, functional enrichment analysis proposed these differentially expressed circRNAs as predominantly involved in maintaining the host cell immunity and inflammation, substance and energy metabolism, cell cycle, and cell apoptosis [59]. Furthermore, M Yang et al. carried out a genome-wide dynamic analysis of circRNAs in lung epithelial human cells affected by Covid-19 at four intervals. They observed some circRNAs, including hsa_circ_0000566, hsa_-circ_0080941, hsa_circ_0001681, hsa_circ_04769, hsa_circ_0080942, hsa_circ_0005630, and hsa_circ_0060927 exhibiting higher degrees of difference in RPM expression value in comparison to others, suggesting their connection to virus infection regulation. Using GO and KEGG function enrichment analysis, they suggested that genes connected to early inflammatory and immune responses, as well as those of cell signal transduction, acting as parental genes of circRNAs, function biologically during infection with COVID-19. Systematically, production of type III interferon, positive interferon-beta regulation, antigens processing, and presence of exogenous peptide antigens were enriched in the studies conducted in later infection stages (12-24 hpi). Notably, in early viral infection stages (0 and 7 hpi), signaling pathways of chemokines, MAPK, and RIG-I-like receptors were enriched [60].

CDR1as.
CDR1as, or ciRS-7, operated as the in vivo miR-7 sponge or inhibitor. Unprecedentedly, H Xu outlined the expression of CDR1as in islet cells and a significant increase in insulin mRNA level and granule secretion in β cells as a result of its overexpression [61]. Moreover, it was found that circRNA-CDR1as via sponging miR-641 modulate inflammation in osteoarthritis [62]. Regarding long-COVID syndrome, J Mester-Tonczar assessed the expression of circRNA-CDR1as in 12 healthy (seronegativity to SARS-CoV-2 antigen) and 5 post-COVID volunteers. They observed a significant upregulation of CDR1as (p = 0.019) in post-COVID volunteers and found that CDR1as expression functions as a molecular biomarker for the prediction of long-COVID [63] (Fig. 4).

Therapeutic potency of ncRNA
Targeted therapeutic factors have traditionally been based on small synthetic molecules or large proteins like monoclonal antibodies. These agents leave many therapeutic targets resistant to drugs as they lack active sites and/or pockets or possess inaccessible ones in their threedimensional structure capable of chemically engaged [78]. Conversely, RNAs present an attractive, transformative chance to access genetic targets with therapeutic intent. The therapeutic design of RNA is responsive to modularity and adaptability and is based on the computational blueprint of the genetic code. In this regard, RNA-based therapy is a promising and potential strategy for disease treatment with the introduction of exogenous nucleic acids for gene expression modulation in specific cells [78]. Many RNA-based methods have been developed, including lncRNAs, small interfering RNAs (siRNAs), miRNA mimics, therapeutic circular RNAs (circRNAs), gene editing based on CRISP-R-Cas9, and extra ncRNA-containing vesicles. A growing number of studies on specific miRNAs regarding their gain or loss of function, along with existing data on pharmacologically modulated families of miRNA or individual miRNAs of animal disease models, presents miRNAs as viable therapeutic targets. There are benefits to miRNA-based therapies. First, miRNAs develop naturally in human cells; therefore, they operate based on their intrinsic modification and mechanisms of downstream target selection. Second, miRNA function depends on multiple genes in one pathway as a target, causing a broader yet specific response. Regarding lncRNAs, a diverse functioning supply of lncRNAs reveals numerous chances as therapeutic targets, which need to be functionally modified based on the lncRNA principle of action. Transcriptional and post-transcriptional inhibition, steric secondary structure or protein interaction hindering, synthetic lncRNA introduction (for example, circular), and expression patterns by CRISPR-C+as9 and CRISPR-Cas13, respectively, are all possible constituents of lncRNA targeting [79]. Inhibition of lncRNAs-induced cytokine storm could be achieved by a posttranscriptional breakdown of the lncRNA with short hairpin RNAs (shRNAs), antisense oligonucleotides (ASOs), or siRNAs. Improved design of altered siRNA and ASOs has resulted in higher functionality and stability, while off-target effects are reduced. Also, gene editing with CRISPR-Cas or promoter blockade can inhibit lncRNA transcription. Since lncRNAs function and secondary structures contain proteins and nucleic acids, a diverse collection of RNA decoys, nanobodies, small molecules, and aptamers are being assessed further to promote steric hindrance. Most of the present means of therapy are focused on the inhibition of pathogenic lncRNAs by delivering synthetically made lncRNAs. A feasible approach for lncRNA delivery is using an adenoassociated virus, herpes virus, ncRNA sponges, modified chemical ncRNAs, non-viral vectors, computed tomography-guided injections, and endoscopic ultrasound [9]. Furthermore, the question of whether circRNAs are capable as therapeutic agents and targets or not has been raised due to recent studies that show the stability of circRNAs against exonucleolytic decay. Two methods could therapeutically utilize CircRNAs. One is the therapeutic knockdown or ectopic expression of native circRNAs linked to diseases. Lipid-based polymers carrying siRNA and shRNAs are recently the most convenient method to knock down circRNAs in vivo. CRISPR/Cas9 and CRISPR/Cas13 can knock out or knock down particular circRNAs and are possible clinical applications in the future. Second, non-native (artificial) circRNA engineering possesses specific molecular effects. Single-stranded linear RNAs could be transcribed in vitro or synthesized, then cyclized using splint ligation, producing purified circRNA molecules ready for delivery into target cells [80]. However, the successful application of ncRNA-based therapeutics depends on an exceptional interdisciplinary approach, such as developments in molecular biology, immunology, pharmacology, chemistry and nanotechnology. A practical RNA-based therapy should be tested based on immunogenicity, and needs to be chemically altered for refined pharmacokinetics and pharmacodynamics, delivered based on patterns of biodistribution and mechanisms of intracellular escape, interact precisely and dynamically with the target, and be optimally dosed to lead the excellent effect. Results suggest that ncRNAs are preferable means of therapeutic development considering careful assessments of toxicities and improved delivery methods. Accordingly, in the following section therapeutic ability of ncRNAs in SARS-CoV-2 is presented, and their capability to be used as SARS-CoV-2 therapeutics.

RNA-based therapy in SARS-CoV-2
As mentioned, ncRNAs play a part in multiple complex mechanisms during infection with SARS-CoV-2. Furthermore, ncRNA-based therapies are appropriate for therapeutic progress, possibly resulting in a fast pace expansion of various drugs that could transform into clinical applications. These results offer researchers an understanding of the ncRNA-based therapy approach toward SARS-CoV-2. In this context, Gasparello et al. outlined evidence that the release of critical proteins of the SARS-CoV-2"cytokine storm" can be inhibited by mimicking the biological activity of miRNAs. Their finding demonstrated that treatment with SARS-CoV-2 spike protein on bronchial epithelial IB3-1 cells leads to the production of IL-8 protein and extracellular release and synthesis of IL-8 is possible to be noticeably reduced due to an agomiR molecule that mimics miR-93-5p. They suggested delivery of miR-93-5p agomiRs as possible anti-COVID-19 means of therapy [81]. Furthermore, Pfafenrot et al. assessed the antiviral capacity of circRNAs as a premise for antisense-RNA sequences, using the uncommon metabolic stability of circRNAs to expand new RNA-based antiviral therapeutics. They aimed to obstruct genome expression and viral proliferation of SARS-Cov-2 through particular targeting of conserved 5 ′ -UTR complexes of SARS-CoV-2. For the first time, they combined the standard antisense (AS)-RNA approach and short circRNAs, integrating them into a circular backbone of RNA. They identified an exceptionally accessible subregion of the 5 ′ -leader of SARS-CoV-2 based on structure-guided design and systematic identification of various AS-circRNAs that could be targeted efficiently to reduce the viral replication by 90 % in cell culture. Additionally, comparing the production of antisense sequence within a circRNA to its production within a linear RNA, functional antisense activity was persistently higher with a circRNA backbone. Furthermore, unmodified antisense-circRNA was observed to be prevailing in activity compared to 2 ′ -OMe-and 2 ′ -MOE-modified antisense oligonucleotides and ultimately, it was remarkably resilient to point mutations in target sequences. As a result of their work, AS-circRNAs are established as suitable and novel molecular methods for targeting and functional regulation of distinct RNAs, thereby developing precise, flexible, and potent strategies for molecular virology and medicinal means of therapy [82]. Such encouraging establishments put RNA-based therapeutics forward into clinical trials regarding SARS-CoV-2. Additionally, current assessments of nanoparticle/CRISPR/EV-mediated ncRNA therapies are being considered to pinpoint the importance and effectiveness of SARS-CoV-2 treatment through ncRNAs (Fig. 5).

SARS-CoV-2 therapy mediated by extra vesicle (EV)
As lipid bilayer-delimited particles, EVs naturally release from nearly all cell types and, in contrast to a cell, cannot replicate. It is possible to classify EVs as exosomes, nano-sized vesicles with 30 to 120 nm in diameter, originating from endocytic compartments of cells by forming multivesicular bodies (MVBs), microvesicles with a maximum diameter of 1 μm that is released through membrane budding, or apoptotic bodies with platelet-like dimensions that derive from blebbing of dying cells. Recent studies have indicated that MSCs exert immunomodulation with aid from secreting EVs, which delivers parent cell cargo to recipient cells without oncogenicity or variability. Compared to MSCs, MSC-derived EVs are inherently safer to be administered intravenously to patients, and the risk of tumor formation is much lower. In general, as MSCderived EVs are not carriers of MHC 1 and 2 class antigens, they are less immunogenic [83]. Extracellular vesicles carry a wide range of RNA sequences representing RNA biotypes [84]. The MSCs-derived EVs can have various macromolecules, including proteins, messenger RNAs, small and long ncRNAs, DNAs, lipids, and carbohydrates from parental cells inside their lipid bilayer, which could alter target cell behavior that contributes to angiogenic, immunomodulatory, and regenerative effects. Recent investigations have led to a crucial therapeutic role for MSCsecreted extracellular vesicles (EV). In this regard, intravenous infusion of MSCs was observed as a safe and efficient treatment method for patients with SARS-CoV-2 pneumonia, including elderly patients displaying severe pneumonia [85]. Furthermore, by bioinformatics prediction analysis, IC Schultz et al. suggested MSC-derived EV miRNA inner cargo possibly impairing excessive production of inflammatory cytokines and chemokines, causing coagulation cascade, and promoting cell death by simultaneous targeting of 3'UTR regions of several mRNAs. Additionally, through analysis of the GSE12243 dataset, they identified low expression rates of two receptors used by the SARS-CoV-2 to enter the host cell, TLR4 and Angiotensin-Converting enzyme 2 (ACE2) inside the EVs. Therefore, MSC-derived EVs, unlike their parental cells, are not participants in the spread of SARS-CoV-2 and wouldn't increase COVID-19 development. In conclusion, MSC-derived EVs and their intrinsic cargo from healthy donors manifest anti-inflammatory and anticoagulant function and decrease SARS-CoV-2 death rates [86].

SARS-CoV-2 therapy mediated by CRISPR system
As a mechanism of bacterial adaptive immune defence, the clustered regularly interspaced short palindromic repeats (CRISPR)/CRISPRassociated system (CRISPR/Cas9) has been studied for a long time. This highly flexible RNA-guided system is now being adapted for genome editing. Knockout of protein-coding genes is relatively easy since a small deletion or insertion can disrupt the open reading frame and end the production of functional gene products. In contrast, non-coding genes are vastly different. Particularly concerning lncRNAs, small deletions or insertions cannot effectively knock out functionally. However, Compared to lncRNAs, microRNAs are relatively straightforward. Additionally, TT Ho et al. constructed a dual-guided RNA vector capable of simultaneous cuts at two particular sites to delete large fragments [87]. These approaches could successfully generate knockouts for miR-21, miR-29a, lncRNA-21A, UCA1, and AK023948 in multiple human cell lines. Furthermore, they show that the HR-mediated targeting efficiency can be further improved by suppressing the non-homologous end joining pathway. As a result, the CRISPR/Cas system could be utilized as a powerful means for non-coding gene knockout. This report pinpoints the potential of CRISPR/Cas9 systems as an effective antiviral to manage the upregulation of ncRNAs during SARS-CoV-2 infection. Additionally, it's crucial to mention CRISPR/Cas13d as an RNA-guided, RNA-targeting CRISPR system. An advantage of the CRISPR/Cas13d system is the design flexibility of guide RNAs as a result of Cas13d cleavage activity in RNA targeting not being dependent on the presence of specific sequences like the NGG motif for the DNA-editing effector, Cas9. Recently, Nguyen et al. used this system to particularly chew up 2019-nCov (SARS-CoV-2) RNA genome with crRNAs designed to target the viral ORF1ab (replicase-transcriptase) and S (spike) genes, limiting its reproduction as a result [88]. In addition, TR Abbott et al. established a prophylactic antiviral CRISPR in human cells (PAC-MAN) strategy to genetically intervene with infections with SARS-CoV-2, IAV, and potentially all coronaviruses. They primarily defined regions across numerous genomes of SARS-Cov-2 that were highly conserved, targeting them for viral degradation using CRISPR-Cas13d. Bioinformatics analysis pointed to a group of six crRNAs possibly targeting 91 % of sequenced coronaviruses and 22 other crRNAs capable of targeting all sequenced coronaviruses. Therefore, PAC-MAN has the potential to become a vital method of pan-coronavirus inhibition [89].

SARS-CoV-2 therapy mediated by nanoparticles
In recent decades, NPs have been used to alter the limits of free drug molecules, getting around biological barriers (systemic and cellular) and leading to various new therapy means [90,91]. Small volume, large surface area, simplicity of being targeted, and stimulus-responsive characteristics result in the effectiveness of the NPs as antiviral vectors. During the COVID-19 pandemic, researchers have made use of a multitude of nanoparticle-based carriers of antiviral solutions: gold or silica inorganic nanoparticles, lipid nanoparticles (LNPs) with a lipid bilayer containing cholesterol and surface polyethylene glycol (PEG) for stabilization, self-assembled co-polymeric nanoparticles, virus-like nanoparticles (VLPs) carrying protein structures that mimic wild type viruses without viral genome or infectious abilities, and cell membranecoated nanoparticles constituent of natural cell membranes that surround a solid nanoparticle core [92,93]. Iron oxide, zinc oxide, silver, AVNP2, and carbon-based NPs could act as potential factors capable of alteration in the viral infection process [94,95]. Metal NPs could be used as theranostic factors for diagnostic and therapeutic methods based on their localized surface plasmon resonance (LSPR) effect. In contrast, the LSPR effect is not present in polymeric NPs [96,97]. Nitric oxide (NO) nanoparticles have been shown to prevent SARS-CoV infection and virulence by providing NO for endothelial cells and inhibiting RNA replication with peroxynitrite residue derived from NO [98]. AuNPs and other similar nanomaterials could be used to bind to coronavirus and, through infrared light emission, obstruct its structure, resulting in the deactivation of the virus [99,100]. Along with the antiviral properties, NPs offer a stable delivery system for unstable therapeutics such as microRNAs (miR, miRNA) that are otherwise unstable. Furthermore, concerning their potential advantages, including refined safety, high delivery capability, and economic viability, NPs have been substantially considered to act as RNA molecule carriers [101]. Cerium oxide nanoparticles (CNP) are promising nanocarrier molecules considering local treatment. It has been evident that miRNA-conjugated CNP is capable of protecting the miRNA from oxidative damage as well as cellular uptake promotion by neutralization of its negative charge. SM Niemiec et al. examined the practicality of radical scavenging CNPs conjugated to microRNA-146a, or CNP-miR146a, in acute lung injury (ALI) prevention. They observed increasing pulmonary levels of mir-146a through intratracheal delivery of CNP-miR146a without systemic increase and prevention of ALI as a result of leukocyte recruitment, reducing inflammation and oxidative stress, and decreasing collagen deposition, ultimately improving pulmonary biomechanics. Hence, this method could alleviate mechanical ventilation, ICU admission, and long-term pulmonary rehabilitation in SARS-CoV-2 patients [102]. Similarly, CM Bobba et al. revealed an endogenous increase in miR-146a after injurious ventilation as not being adequate for lung injury prevention during mechanical ventilation. They observed increased miR-146a expression with the use of miR-loaded nanoparticles in the lung in vivo (~1000-10,000-fold), which dampened physiologic lung injury, pulmonary edema, and inflammation during injurious mechanical ventilation. Consequently, nanoparticle-based means of delivery could potentially be used to increase miR-146a levels in vitro and in vivo, ultimately reducing lung injury during mechanical ventilation in SARS-CoV-2 patients [103]. RNA interference (RNAi) provides the means for alternative antiviral therapy. Delivery of RNAi as short interfering RNA (siRNA), short hairpin RNA (shRNA) and miRNA have shown to be efficient in therapeutic gene silencing against viral diseases. In this regard, A Idris et al. presented a highly productive therapy method against SARS-CoV-2, utilizing small interfering RNA (siRNA) coupled with a novel lipid nanoparticle (LNP) delivery system. They primarily screened multiple siRNAs by targeting highly conserved sections of the SARS-CoV-2. They located three candidate siRNAs functionally inhibiting the virus by a higher than 90 % rate, either individually or coupled with other siRNAs. They identified robust repression of the virus in the lungs and a pronounced survival rate following in vivo injection of LNP-siRNA. They conclude that the siRNA-LNP therapeutic approach is beneficial in treating SARS-CoV-2 disease [104]. Additionally, ribozymes are hybrid RNA molecules capable of diminishing specifically targeted RNA. The main superiority of ribozymes is recognition and specific binding to multiple target mRNAs in contrast to the other antisense molecules in RNAi systems [105]. B. DÖNMÜŞ et al. studied the ribozyme capability toward SARS-CoV-2. Based on genome similarity between SARS-CoV and SARS-CoV-2, they recommended hammerhead ribozymes on targeted nanocarriers against SARS-CoV, possibly also effective against SARS-CoV-2. Second, synthesizing and classifying specific ribozymes against SARS-CoV-2 RNA gene loci is possible through a bioinformatics software application. As a result, nanocarriers containing ribozymes could be a significant means of RNAbased pharmaceutical methods in future implementations against SARS-CoV-2 [106].

Conclusion and future prospective
SARS-CoV-2 is a devastating primary health concern, particularly for the elderly. Hyper-inflammatory reactions named cytokine storm are among its characteristics, leading to pulmonary failure, ARDS, and death. It was found that ncRNAs, through numerous mechanisms including activation of the inflammatory cascade, viral entrance play a crucial role in the pathogenesis of SARS-CoV-2. Biotechnological advances like high-throughput sequencing, bioinformatics analysis, genome editing, modeling of mice with pharmaceutical chemistry, and ncRNA functional studies can present us with novel viewpoints on viral diseases, including SARS-CoV-2. Today, RNA-based medicine is receiving increasing attention for its diverse use cases and potential therapeutic capacity, while active research continues to develop ncRNAbased drugs. Moreover, ncRNAs and their modifiers could act as target therapy response estimation, contributing to personal treatment plans. Nonetheless, RNA-targeted therapy development is hindered by numerous obstacles. For instance, due to length variation in ncRNA and disparity in its modes of action, in addition to the complex roles of ncRNAs, choosing the proper, specific target among the candidates is exhaustive. So, it requires further advanced knowledge and evaluation of genomic and functional methods of basic and translational research. Moreover, the effectiveness of the delivery method is necessary for stability and uptake improvement, resulting in higher efficacy. Therefore, research in drug delivery of RNA therapeutics is also fast-moving. Despite the usual modification of the viral vectors for lower immunogenicity, non-viral vectors are preferred since significant antigenic response and cytotoxicity can still be observed in some cases. Recent advances in the synthetic development of RNA-encapsulating material, including polymers, lipids, and LNPs (lipid nanoparticles), have guided research toward non-viral-based delivery systems. Furthermore, exosomes offer a novel delivery system, including antiviral drugs and their intrinsic cargo components. Due to their natural function in intercellular communication and immunogenicity, and cytotoxicity, exosomes can act as novel means of drug delivery and natural therapeutics. Although they were not the first, RNA-based therapeutics demonstrated their tremendous success with the SARS-CoV-2 mRNA vaccine. In the past 30 years, a wide range of MRNA therapeutics have been investigated, from immunization to cancer treatment and protein substitution. In the early stages of development, various issues, including administration, translational regulation, stability, and immunogenicity, have hindered the development of functional mRNA therapeutics; however, progress in RNA modifications, transfection techniques, and expression regulatory systems has eliminated chiefly these obstacles. This is why several mRNA-based therapeutics are currently being tested in clinical trials. In addition to the mRNA-based approaches, Nucleic acid aptamers have revolutionized the field of molecular therapy. Nucleic acid aptamers are short sequences of nucleic acid ligands that show a specific ability to attach to a particular target molecule. Experimentally, aptamers are identified through a well-designed method called SELEX (systematic evolution of ligands by exponential enrichment). A large portion of recent research has been dedicated to designing a new method for diagnosing and blocking SARS-CoV-2 based on a G-quadruplex aptamer. Aptamers were developed against spike protein's receptor-binding domain (RBD). The researchers intended ten quadruplex DNA aptamers, labelled AP1, AP2, AP3, AP4, AP5, AP6, AP7, AP8, AP9, and AP10, in silico and selected AP1 based on its interaction with SARS-CoV-2's RBD. They demonstrated that AP1 aptamer could serve as a diagnostic and therapeutic agent for SARS-CoV-2 infection [107]. Importantly, bioengineering is concerned with applying engineering principles to improve bio-molecular applications aimed at addressing critical medical and biological challenges. NcRNA bioengineering can use nanoparticlebased functionalization or engineering nucleoside chemistry to improve theirs in vitro and in vivo delivery and pharmacological properties. Consequently, bioengineering of ncRNAs represents an exciting field of research that is expected to revolutionize nucleic acid therapeutics for a wide range of human diseases, including SARS-CoV-2. Exosomes can be engineered with different surface targeting/therapeutic molecules, incorporating hydrophobic compounds in the bilayer membrane and carrying hydrophilic compounds, RNA molecules, or other macromolecules in their aqueous core. Exosome engineering could be possible through modifications on parental cells, leading them to the secretion of exosomes that carry specific therapeutics or by direct modification of isolated exosomes. The approaches to parental cells could be (A) DNAencoded active compounds that are transfected/infected into parental cells, which will then be released by exosomes, or (B) drug therapy of parental cells that will lead to the release of preferred exosomes. Therefore, engineered exosomes can be a potential drug delivery system for viral diseases such as SARS-CoV-2.

Declaration of competing interest
None.

Data availability
No data was used for the research described in the article.