**4. miRNA impact on DENV infection**

Studies have demonstrated the importance of miRNAs in viral infections. Mutations in the main catalytic components of the RNA interference pathway led to an increase in DENV replication in mammalian cells (**Figure 2**) [38]. Studies that analyzed the expression of miRNA in the blood of patients with dengue demonstrated a large number of miRNAs expressed differently in response to dengue infections [35]. About 348 miRNAs were described with different expressions in patients with dengue. Interestingly, studies have also identified 17 miRNAs that could use to distinguish between mild and severe dengue with complications [39].

The expressions of miR-24-1-5p, miR-512-5p, and miR-4640-3p were able to distinguish mild dengue from those with liver complications. At the same time, miR-383 was significantly more expressed in dengue with mild clinical status than those diagnosed with severe dengue and accumulation of body fluids [40, 41].

Studies have also shown 12 miRNAs with negative regulation and 41 with positive regulation in the serum of patients infected with DENV-1 when compared to the control group. Among these miRNAs we highlight hsa-miR-21-5p, hsa-miR-146a-5p, hsa-miR-590-5p, hsa-miR-188-5p, and hsa-miR-152-3p that were identified as promising invasive molecular markers for the detection of DENV infection [42, 43].

The microRNAs miR-21-5p and miR146a-5p are involved in inflammation and cell proliferation. They are expressed significantly concerning the control group, indicating their sensitivity and specificity as indicators of DENV infection. Besides, both miRNAs are correlated with the number of leukocytes and neutrophils. These findings suggested that some miRNAs could be used as diagnostic markers for DENV infections [44].

Effective disruption of host RNAi machinery is one of the pathogenic strategies of viruses to mitigate the host's response. Several viruses have reported producing protein suppressors through RNAi to cause silencing in infected cells, thereby

#### **Figure 2.**

*An example of increased miRNA expression after the entry of vesicular stomatitis virus (VSV), Japanese encephalitis virus (JEV), and dengue virus in mammalian cells. miRNA expression increased in a RIG-Idependent manner. The RIG-I protein interacts with viral RNA through its helicase domain, leading to nuclear transcription of the pri-miRNA by NF-kB. The reduction of target mRNAs explains the proviral function of this miRNA as the response of interferon type I (adapted from Bruscella et al.) [45].*

**139**

virus-induced infection [49].

*Dengue Virus and the Relationship with MicroRNAs DOI: http://dx.doi.org/10.5772/intechopen.92453*

interfere with the AGO1 protein [46].

for viral entry [49, 50].

**replication**

**5. miRNAs and the inhibition of viral replication**

interfering with RISC's loading or inhibiting the cutting activity of the AGO protein, a component of RISC and the biogenesis of miRNAs. DENV also has such suppressors that could neutralize the host's RNAi response. NS4B has reported suppressing host RNAi, interfering with the processing of Dicer, a key protein in miRNA biogenesis [38]. It has also reported that NS1 protein can interfere with apoptosis through miRNA-15 and miRNA-16 [5]. The NS3 protein has shown to

The miRNAs generally induce translational repression by binding to target mRNAs. Thus, it is not surprising that most of the miRNAs identified so far have DENV replication. The evidence points to the fact that miRNAs bind complementarily to the DENV 5'UTR or 3'UTR genome and thus inhibit DENV replication. The miR-548 g-3p represented the first evidence that a miRNA suppresses DENV multiplication by directly linking it to the viral genome. In the study, they showed that miR-548 g-3p was able to bind to the stem-loop A (SLA) promoter at 5'UTR, which is a crucial element for DENV RNA synthesis and replication, and uncontrolled replication of DENV-1. This inhibitory effect was proposed to arise from the binding of miR-548 g-3p to SLA, which could make it physically difficult, and thus attenuated the interaction between the SLA promoter and NS5. This DENV protein

contains a C-dependent RNA-terminal RNA polymerase domain [45, 47].

all DENV serotypes and is present in the 3'UTR. The three dengue serotypes, miR-133a, miR-484, and miR-744, are involved in DENV replication, genome circularization, and viral viability. The overexpression of miR-133a, miR-484, and miR-744 in Vero cells had been experimentally validated to show the potencies of these three miRNAs in inhibiting DENV replication [48]. In another study, it found that miR-252 can inhibit DENV-2 replication in cell culture. The identification of protein E as a target for this miRNA is interesting since it has an indispensable role

**6. miRNAs that modulate host factors to inhibit or facilitate DENV** 

and it is not surprising that several miRNAs have shown to indirectly regulate DENV replication through modulation of host factors or the immune response. These indirect effects included modulation of the expression of a cell transcript that encodes a host factor necessary for one or a few stages of the viral cycle. The modulation of receptor expression can regulate virus entry, tropism, and essential cofactors for replication or translation that can impair or increase viral replication and the production of viral proteins. Also, miRNAs can increase or restrict cellular responses to viral infection, such as immune response or defense mechanisms [51]. The miRNA let-7c is highly expressed in Huh-7 cells and may be related to the protection of infected cells from oxidative stress and the response to inflammation after DENV infection. Let-7c has shown to bind directly to the basic transcription factor-1 of the leucine zipper (BACH1), a potent repressor of the anti-inflammatory and antioxidant protein heme oxygenase-1 (HO-1), and to dysregulate infection by DENV-2 and DENV-4. In this way, let-7c is probably able to protect the host from

The DENV virus depends on its host's machinery for replication and infection,

Their hypothesis suggests that a functional miRNA has been preserved among

*Dengue Virus and the Relationship with MicroRNAs DOI: http://dx.doi.org/10.5772/intechopen.92453*

*Dengue Fever in a One Health Perspective*

DENV infection [42, 43].

DENV infections [44].

**4. miRNA impact on DENV infection**

Studies have demonstrated the importance of miRNAs in viral infections. Mutations in the main catalytic components of the RNA interference pathway led to an increase in DENV replication in mammalian cells (**Figure 2**) [38]. Studies that analyzed the expression of miRNA in the blood of patients with dengue demonstrated a large number of miRNAs expressed differently in response to dengue infections [35]. About 348 miRNAs were described with different expressions in patients with dengue. Interestingly, studies have also identified 17 miRNAs that could use to distinguish between mild and severe dengue with complications [39]. The expressions of miR-24-1-5p, miR-512-5p, and miR-4640-3p were able to distinguish mild dengue from those with liver complications. At the same time, miR-383 was significantly more expressed in dengue with mild clinical status than those diagnosed with severe dengue and accumulation of body fluids [40, 41]. Studies have also shown 12 miRNAs with negative regulation and 41 with positive regulation in the serum of patients infected with DENV-1 when compared to the control group. Among these miRNAs we highlight hsa-miR-21-5p, hsa-miR-146a-5p, hsa-miR-590-5p, hsa-miR-188-5p, and hsa-miR-152-3p that were identified as promising invasive molecular markers for the detection of

The microRNAs miR-21-5p and miR146a-5p are involved in inflammation and cell proliferation. They are expressed significantly concerning the control group, indicating their sensitivity and specificity as indicators of DENV infection. Besides, both miRNAs are correlated with the number of leukocytes and neutrophils. These findings suggested that some miRNAs could be used as diagnostic markers for

Effective disruption of host RNAi machinery is one of the pathogenic strategies of viruses to mitigate the host's response. Several viruses have reported producing protein suppressors through RNAi to cause silencing in infected cells, thereby

*An example of increased miRNA expression after the entry of vesicular stomatitis virus (VSV), Japanese encephalitis virus (JEV), and dengue virus in mammalian cells. miRNA expression increased in a RIG-Idependent manner. The RIG-I protein interacts with viral RNA through its helicase domain, leading to nuclear transcription of the pri-miRNA by NF-kB. The reduction of target mRNAs explains the proviral function of* 

*this miRNA as the response of interferon type I (adapted from Bruscella et al.) [45].*

**138**

**Figure 2.**

interfering with RISC's loading or inhibiting the cutting activity of the AGO protein, a component of RISC and the biogenesis of miRNAs. DENV also has such suppressors that could neutralize the host's RNAi response. NS4B has reported suppressing host RNAi, interfering with the processing of Dicer, a key protein in miRNA biogenesis [38]. It has also reported that NS1 protein can interfere with apoptosis through miRNA-15 and miRNA-16 [5]. The NS3 protein has shown to interfere with the AGO1 protein [46].
