**4. miRNAs in acute HSV infection and latency**

Encephalitis due to acute HSV-1 or − 2 infection could arise as a direct effect of the HSV invasion of the host or due to the heightened host responses to the virus which causes host damage in the process of virus destruction. Although the incidence of Herpes Simplex Encephalitis (HSE) cases is low, 20% of those affected face neurological after-effects [23]. The inflammation associated with encephalitis often involve the miRNAs, which is also the situation in HSE. miRNAs also contribute to the susceptibility of the cells to HSV infection. This may be the reason for the discovery of a number of cellular miRNAs in HSE. miRNAs miR-155, miR-146a and miR-15b were found to be upregulated in the mouse brain post-HSE [33] and have been associated with neuroinflammation (**Figure 3**) [34]. HSV-1 encoded miR-H28 and miR-H29 were identified to be expressed late during the infection and are exported out of the infected cells in exosomes, thus indicating a role of these miRNAs in viral spread [35]. Also, miR-200 family and miR-182 are the miRNAs identified to be involved in HSE as they target Syndecan-2 (sdc2) which contributes to the biosynthesis of the heparan sulphate required for the attachment and entry of HSV into the cells. Therefore, downregulation of sdc2 by miRNAs is a strategy maneuvered by the host to resist the spread of the virus [33]. This also depicts that mutations in the miRNA sequence or the mRNA target are key players in varied susceptibility to the HSV infection of the central nervous system.

The opposite of excessive HSV pathogenesis is HSV latency, a phase of HSV infection characterized by minimum genome replication. HSV uses neurons as the hideaway for escaping the spotlight for the immune responses while sheltering itself within the host. Since the discovery of HSV- miRNAs in 2006, many miRNAs have been identified to participate in the different stages of viral latency [36] miR-LAT (Latency associated transcript), a miRNA generated from the exon 1 of

#### **Figure 3.**

*miRNAs in HSV latency: Majorly, the LAT-associated v-miRNAs participate in the induction, establishment and maintenance of latency of the HSV in the cells. HSV-miR-I and miR-II suppress the ICP34.5 expression to restrict HSV replication and promotion of the HSV latency. HSV-miR-H2 and miR-III inhibit the ICP0 expression to suppress the HSV replication. HSV-miR-LAT inhibits apoptosis to allow the infected cell and the virus to survive and establish a latent infection. There are two cellular miRNAs that contribute to the latency. miR-138 promotes latency by preventing ICP0-triggered viral replication whereas miR-155 contribute to the maintenance of latency via the induction of the CD8+ responses.*

the HSV1-LAT gene, is responsible for the TGF-β mediated anti-apoptotic effects on the cells during latency. HSV-miR-H2 has been found to suppress the immediate early protein ICP0, therefore, inhibiting the replication to promote HSV latency (**Figure 3**) [37]. On the other hand, HSV2-miR-H6, a miRNA associated with HSV2-LAT, contributes to the reactivation of the virus from latency [38]. Mutation studies on both these miRNAs confirm their effects. miR-I, is another HSV2-LAT associated miRNA which reduces the expression of ICP34.5, a neurovirulence factor, to establish latency in the dorsal root ganglia [39]. A similar study by the same group identified miR-II and miR-III miRNAs from the HSV2-LAT, with miR-II targeting ICP34.5 and miR-III targeting ICP0, to maintain latency (**Figure 3**) [40]. Furthermore, the cellular miRNAs also engage in the events of HSV latency. miR-155 is involved in the maintenance of latency via the elicitation of CD8 responses [41]. Similarly, enhanced expression of miR-138 in the neurons, to target ICP0 for suppression (**Figure 3**), is crucial in maintaining the HSV-1 latency and survival of the hosts [42]. The crosstalk between the viral/cellular miRNAs, amongst themselves, and with the host transcriptome decides for the maintenance of latency which may be for the lifetime, or trigger the reactivation of the virus.
