1 INTRODUCTION

Malaria is an infection caused by protozoan pathogens of the Plasmodium spp. It is one of the most prevalent infectious diseases worldwide and according to the World Malaria Report, an estimated 229,000 cases of malaria occurred in 2020 causing ∼65,000 deaths (World Malaria Report, 2020). Of more than 120 Plasmodium species only five are known to infect humans: Plasmodium falciparum (which is responsible for the most severe form of the disease), Plasmodium vivax, Plasmodium malariae, Plasmodium ovale, and Plasmodium knowlesi (Ashley et al., 2018; Miller et al., 1994). P. falciparum and P. vivax are the predominant species infecting humans worldwide (Howes et al., 2016).

Plasmodium spp. have a complex life cycle that alternates between a mosquito vector of the Anopheles genus (the malaria vectors) and a vertebrate host (Pimenta et al., 2015). They are transmitted to humans during a blood meal, when Plasmodium sporozoites are injected by the bite of an infected mosquito female. Sporozoites, carried by the circulatory system to the liver, invade the hepatocytes. In the liver, the sporozoites mature into schizonts, which break and release merozoites into the blood stream (Figure 1).

The Plasmodium life cycle

Merozoites invade erythrocytes (at the beginning of the asexual blood stage) and undergo a trophic period (the trophozoite stage; Cowman et al., 2012; Phillips et al., 2017) at the end of which multiple rounds of nuclear division without cytokinesis lead to the formation of schizonts. The rupture of the schizonts in the blood stream releases merozoites, and the invasion of erythrocytes initiates another round of the blood-stage replicative cycle. A portion of the merozoites differentiate and mature into male and female gametocytes, at this stage they can infect the mosquito host again during another blood meal (Figure 1; Bartoloni & Zammarchi, 2012).

The progression through the complex life cycle of Plasmodium requires tight regulation of gene expression, which occurs at both transcriptional and post-transcriptional levels. Furthermore, as a survival adaptation to hostile variations present in host environments, regulating RNAs and proteins represents a fundamental step in the immune response of the protozoan organism (Hughes et al., 2010). The immunological response against the malaria parasite is complex, and the defense mechanisms are strongly affected by a multitude of antigens presented at different stages of the Plasmodium spp. life cycle. In humans, the immunological response to malaria antigens is mainly regulated through the cooperation of both the innate and adaptive immune systems with the immune attack higher during the erythrocytic stage (Hisaeda et al., 2005; Uchechukwu et al., 2017). Considerable evidence revealed that B cells, antibodies, T cells, cytokines, and their respective receptors, all play crucial roles in the recruitment and activation of different cell types of the immune system thus modulating the complex immunological response against malaria parasites (Deroost et al., 2016; Good et al., 1998). Indeed, the ability of the human organism to fight malaria infection relies on changes in gene expression that culminates in the activation of specific B-cell and T-cell subpopulations as well as cytokine production. Recently, for example, we investigated the effects of an increased production of soluble BAFF and downregulation of the RNA binding protein NF90 in modulating immune cell populations and cytokine production in the presence of malaria antigens (Idda et al., 2019; Lodde et al., 2020). In recent years, ncRNAs emerged as key modulators of gene expression by controlling heterogeneous events such as mRNA transcription, mRNA splicing, and translational efficiency (Pearson & Jones, 2016; Wright & Bruford, 2011).

The ncRNAs can be classified into structural (tRNA and rRNA) and regulatory ncRNAs. Regulatory ncRNAs, including microRNAs (miRNAs) and long non-coding RNAs (lncRNAs), are expressed in specific cell types and in a time-dependent manner to control particular outcomes (Z. Qu & Adelson, 2012; Dai et al., 2019). Interestingly, there is much evidence to suggest that ncRNAs could play a key role in numerous pathways implicated in the pathogenesis of infectious diseases including malaria (Drury et al., 2017; J. Chen et al., 2019; Shirahama et al., 2020; Tribolet et al., 2020). For example, Chakrabarti et al. (2007), Raabe et al. (2009), and Mourier et al. (2008) identified several types of ncRNAs, including miRNAs and lncRNAs with fundamental functions in the regulation of antigenic variation and virulence mechanism during P. falciparum infection. Recently additional evidence also suggests promising applications of ncRNAs in the prognosis and treatment of malaria infection (Rubio et al., 2016).

The recent major implications of ncRNAs in gene regulation prompted us to provide an overview of the latest studies analyzing the role of ncRNAs, miRNAs, lncRNAs, and circular RNAs (circRNAs), in the regulation of gene expression during Plasmodium infection in humans. Specifically, we investigate the possibility of using these molecules as biomarkers to monitor disease status as well as the surprising capacity of ncRNAs in mediating the interaction between human host and malaria parasite.

2 miRNAS IN MALARIA INFECTION

The miRNAs are small ncRNAs (21–24 nts) that regulate gene expression in diverse biological processes. The miRNAs are initially transcribed as long primary (pri)microRNA transcripts and afterward, cleaved into 70–100 nucleotide long precursor miRNA (pre-miRNA) (Gregory et al., 2004; Lee et al., 2003). The pre-miRNA is exported from the nucleus to the cytoplasm by Exportin-5/RanGTP. In the cytoplasm the endonuclease Dicer digests the pre-miRNA into a 21–25 nucleotide miRNA duplex thus generating the mature miRNAs (Lund et al., 2004). The mature miRNAs are then selectively attached to a large complex of proteins termed the RNA-induced silencing complex (RISC) which brings together the miRNA and its target on the mRNA through sequence-specific interactions. The miRNA directs the RISC complex to target sites mainly located at the 3′-untranslated regions (UTRs) leading to regulation of post-transcriptional events such as RNA degradation and translational repression (Figure 2; Fabian & Sonenberg, 2012; Tang, 2005).

miRNAs biogenesis and function in response to malaria infection. miRNAs are transcribed by RNA PolII to produce pri-miRNAs which are cleaved to generate pre-miRNA that is transported to the cytoplasm to form mature miRNAs. After that, the single mature strand of miRNA is uploaded to the RISC complex, which contains Ago-2 protein. During malaria infection miRNAs can regulate mRNA target or be secreted becoming possible biomarker or are imported by P. falciparum to modulate the expression of its own genes

The miRNAs have been implicated in many cellular processes, such as cellular proliferation and differentiation, apoptosis, cytokine and chemokine production, inflammation, and immune response (Bueno & Malumbres, 2011; Chen et al., 2004; Munk et al., 2018; O'Connell et al., 2012; Rajman & Schratt, 2017; Salvi et al., 2019; Su et al., 2015).

Much evidence suggests that Plasmodium parasites are unable to produce miRNAs (Rathjen et al., 2006; Xue et al., 2008) and that both miRNA and human Argonaute 2 (hAgo2), a component of the RISC, are imported by P. falciparum to modulate the expression of its own genes. Indeed, in the parasite, hAgo2 exists as a complex with specific human miRNAs including let-7a and miR15a which can, for example, target the Plasmodium gene Rad54 (Dandewad et al., 2019). On the other hand, malaria antigens can affect the production of organ-specific host miRNAs, pointing toward the potential of these small molecules as biomarkers that can be used to reveal malaria associated immune responses and, in the worst cases, organ injury (Figure 2; Rubio et al., 2016). Thus, the content of miRNAs in the host cells and body fluids is influenced by host-pathogen interactions (Hakimi & Cannella, 2011). For example, sequestration of P. vivax gametocytes in bone marrow has been associated with transcriptional changes of miRNAs involved in erythropoiesis, that in turn alter the expression of target mRNAs (Baro et al., 2017). A complete list of the miRNAs discussed in this manuscript is show in Table 1.

TABLE 1. miRNAs and lncRNAs in malaria ncRNA name Regulation Biological sample References miRNA let-7a n.d. RBCs Dandewad et al. (2019) miR-15a n.d. RBCs Dandewad et al. (2019) miR-16-5p Upregulated WB Dieng et al. (2020) miR-15a-5p Upregulated WB Dieng et al. (2020) miR-181c-5p Upregulated WB Dieng et al. (2020) miR-598-3p Upregulated WB Dieng et al. (2020) miR-146a n.d. WB Van Loon et al. (2019) miR-451 Up and downregulated Hbs, RBCs, plasma Chamnanchanunt et al. (2015); Lamonte et al. (2012); Wang et al. (2017) let-7i Upregulated RBCs, mice brain Chamnanchanunt et al. (2015); Lamonte et al. (2012); Wang et al. (2017) miR-221 Downregulated Bone marrow Baro et al. (2017) miR-222 Downregulated Bone marrow Baro et al. (2017) miR-24 Downregulated Bone marrow Baro et al. (2017) miR-191 Downregulated Bone marrow Baro et al., 2017 miR-144 Upregulated Bone marrow Baro et al. (2017) miR-140 Upregulated RBCs Wang et al. (2017) miR-16 Downregulated Plasma Chamnanchanunt et al. (2015) miR-223 No change/UP Plasma, RBCs Chamnanchanunt et al. (2015); Lamonte et al. (2012) miR-226-3p No changes Plasma Chamnanchanunt et al. (2015) miR-7977 Upregulated WB Kaur et al. (2018) miR-28-3p Upregulated WB Kaur et al. (2018) miR-378-5p Upregulated WB Kaur et al. (2018) miR-194-5p Upregulated WB Kaur et al. (2018) miR-3667-5p Upregulated WB Kaur et al. (2018) miR-150-5p Upregulated EV Ketprasit et al. (2020) miR-15b-5p Upregulated EV Ketprasit et al. (2020) Let-7a-5p Upregulated EV Ketprasit et al. (2020) miR-3135b Upregulated WB Li et al. (2018) miR-6780b-5p Upregulated WB Li et al. (2018) miR-1246 Upregulated WB Li et al. (2018) miR-6126 Upregulated WB Li et al. (2018) miR-3613-5p Upregulated WB Li et al. (2018) miR-4497 Upregulated Plasma Gupta et al. (2021) let-7i Upregulated Mouse brain El-Assaad et al. (2011) miR-150 Upregulated Mouse brain El-Assaad et al. (2011) miR-27a Upregulated Mouse brain El-Assaad et al. (2011) miR-155 Upregulated Mouse brain Barker et al. (2017) miR-19a-3p Upregulated Mouse brain Martin-Alonso et al. (2018) miR-19b-3p Upregulated Mouse brain Martin-Alonso et al. (2018) miR-142-3p Upregulated Mouse brain Martin-Alonso et al. (2018) miR-223-3p Upregulated Mouse brain Martin-Alonso et al. (2018) lncRNA TARE-3 n.d. P.f. Sierra-Miranda et al. (2012) TARE-6 n.d. P.f. Sierra-Miranda et al. (2012) Abbreviations: EV, extracellular vesicle; Hbs, hemoglobin; n.d., no define; P.f., Plasmodium falciparum; RBCs, red blood cells; WB, whole blood.

In the next sections we analyze two topics: (a) the modulation of miRNA expression in the human host induced by the presence of malaria antigens and (b) the ability of Plasmodium falciparum and Plasmodium vivax to import and embed the host miRNA machinery with the aim of modulating its own gene expression.

2.1 Modulation of human miRNA expression induced by Plasmodium infection

The clinical responses to infection and the development of effective responses to antimalarial drugs are marked by an interindividual variability also modulated by miRNA and post-transcriptional events. To better understand these differences, Burel et al. used a controlled human infection model to study early immune events following primary infection of healthy human volunteers with blood-stage P. falciparum malaria. They observed a dichotomous pattern of either high or low expression of a defined set of miRNAs that correlated with variations in parasite growth rate: 50% of individuals upregulated a set of miRNAs involved in immune responses (high-miRNA responders), whereas the remaining volunteers downregulated the same miRNAs (low-miRNA responders). The high-miRNA responders had higher numbers of activated CD4+ T cells and developed a significantly enhanced antimalarial antibody response. Furthermore, prior to infection, in the whole blood of low-miRNA responders, a set of 17 miRNAs was identified that differentiated them from high-miRNA responders (Burel et al., 2017). A few years later, Dieng et al. performed an integrative genomic profiling and longitudinal study in a pediatric cohort from Burkina Faso. The authors reported a strong miRNA signature expression of a subset of miRNA during P. falciparum infection which correlate with infection and parasitemia. Over one-third (127 out of 320) of the analyzed miRNAs, were significantly differentially expressed following P. falciparum infection in non-infected children: integrative miRNA–mRNA analysis identified several infection-responsive miRNAs including miR-16-5p, miR-15a-5p, and miR-181c-5p, promoting lymphocyte cell death. Furthermore, human miRNA cis-eQTL analysis using whole-genome sequencing data, identified 1376 genetic variants associated with the expression of 34 miRNAs. Specifically, they reported a protective effect of rs114136945 minor allele on parasitemia mediated by miR-598-3p expression (Dieng et al., 2020). Accordingly, a common miRNA-146a polymorphism (rs2910164) increased the chances of P. falciparum malaria in pregnant African women (Van Loon et al., 2019). However, the same polymorphism was not associated with the odds ratio of malaria, irrespective of parasite species. These results also underline the importance of the genetic background relating to the complexity of clinical manifestations and the role of miRNAs during malaria infection (Van Loon et al., 2020).

An interesting aspect of malaria infection is the ability of red blood cells (RBCs) carrying the HbS variant in the hemoglobin gene (the molecular cause of sickle cell disease) to confer malaria resistance (Aidoo et al., 2002; Friedman, 1978). Indeed, La Monte et al. have investigated if miRNAs play a role in establishing this pattern. Remarkably, they found that, during the intraerythrocytic lifecycle of P. falciparum, a subset of erythrocyte miRNAs translocated into the parasite. In particular, the miRNAs miR-451 and let-7i are highly enriched in HbS erythrocytes and can regulate parasite growth. Surprisingly, they found that miR-451 and let-7i interact with crucial parasite mRNAs and induce translation inhibition through impaired ribosomal loading. Thus, modulation of miRNA expression in erythrocytes can influence the cell-intrinsic resistance to malaria of sickle cell erythrocytes, representing a unique host defense strategy against complex eukaryotic pathogens (Lamonte et al., 2012).

To gain insights into P. vivax infection during the bone marrow phase, Baro et al. performed a morphological and molecular study on cells expressing CD71, a marker for bone marrow erythroid precursors, (Marsee et al., 2010) from bone marrow aspirated from a man diagnosed with P. vivax infection, before and after treatment (Baro et al., 2017). To identify possible bone marrow transcriptional changes related to erythropoiesis during infection, the expression profiles of small RNAs both during the acute attack and at convalescence were determined. Analysis of miRNAs related to erythropoiesis revealed a distinct series of differentially expressed miRNAs during P. vivax infection. For example, miR-221/222, miR-24, and miR-191, which are normally downregulated during erythroid maturation, were decreased during P. vivax infection compared with convalescence. In contrast, miR-144, which is upregulated during erythropoiesis, was found to be increased. These results indicate an altered miRNA profile in bone marrow erythropoiesis pathway during the acute P. vivax infection in the analyzed patient (Baro et al., 2017).

2.2 Extracellular vesicle-derived miRNAs

Extracellular vesicles (EVs) are membranous cell-derived vesicles originating from the endosomal system (exosomes) or by the outward budding and fission of the plasma membrane into the extracellular spaces (microvesicles) (Raposo & Stoorvogel, 2013). EVs (exosomes and microvesicles) transport proteins, nucleic acids (including ncRNAs), lipids, and so on from the host cells (Figure 2) (Zhang et al., 2019).

EVs have been extensively studied in malaria (Tsamesidis et al., 2020). Studies of circulating EVs from various cellular sources during Plasmodium spp. infection demonstrated an upregulation in EV secretion, thus demonstrating a key role of EVs in disease pathogenesis and prognosis. For example, RBC-derived EVs concentrations in patients infected with either P. vivax, P. malariae, or P. falciparum are higher in patients affected by P. falciparum severe malaria (SM) (Pankoui Mfonkeu et al., 2010). Furthermore, it has been demonstrated that the EVs released during malaria infections generate a proinflammatory environment contributing to both SM and cerebral malaria (CM) onset, while genetic or pharmacological blockage of EV production reduces the development of CM in a mouse model (Babatunde et al., 2020; Cohen et al., 2018; Combes et al., 2005; Couper et al., 2010). Also, several studies reported that miRNAs can be transferred from one species to another through EVs, inducing species-to-species signaling, even in a cross-kingdom manner. In general, these vescicles play important roles for intercellular communication and could potentially serve as biomarkers for different aspects of a specific disease (Tkach & Théry, 2016).

In line with these general considerations, in 2016 Mantel et al. demonstrated that inflammatory responses, during Plasmodium infection, are triggered in part by bioactive parasite products including infected RBC-derived EVs. EVs contain functional miRNA–Argonaute 2 complexes that are derived from the host RBC. Moreover, they demonstrated that EVs are efficiently internalized by endothelial cells, and that the miRNA–Argonaute 2 complexes modulate target gene expression and barrier properties thus providing a mechanistic link between EVs and vascular dysfunction during malaria infection (Mantel et al., 2016).

Recent studies have also reported significant production of extracellular vesicles (microparticles, MPs) in the blood circulation of malaria patients, with RBCs being the major source of EV production. Wang et al. isolated the MPs from a culture medium of normal RBCs and malaria parasite-infected RBCs (iRBCs), compared their quantity and origins and profiled miRNAs by RNA seq analysis. They observed a larger production of MPs in the culture media of iRBCs as compared with RBCs. Further investigation indicated that, in these MPs, hAgo2 associated with hundreds of miRNAs. These hAgo2–miRNA complexes were transferred into the parasites, and the expression of an essential malaria antigen PfEMP1, was downregulated by miR-451/140. This report revealed, for the first time, that the malaria parasite can use human post-transcriptional elements and mechanisms to modulate its own gene expression and underline the possibility of using miRNAs as potential drugs to treat malaria patients (Wang et al., 2017). Along the same line, Babatunde et al. isolated EVs from cultured iRBCs to study the content of regulatory RNAs. They found that miRNAs and tRNA-derived fragments are the most abundant human RNAs. They also identified approximately 120 plasmodial RNAs, including mRNAs coding for exported proteins and proteins involved in drug resistance, as well as ncRNAs. These data demonstrated that iRBC-EVs carry small regulatory RNAs and suggest their use as biomarkers for disease diagnosis and progression (Babatunde et al., 2020).

2.3 Extracellular miRNAs as biomarkers for malaria

Extracellular miRNAs, including plasma miRNAs, are highly stable (Reid et al., 2011) and the levels of some plasma miRNAs change as an effect of infectious diseases and organ damage (Chen et al., 2008; Mitchell et al., 2008) Thus, plasma miRNAs can be considered as possible non-invasive biomarkers (Figure 2). One of the first studies on this topic was published by Chamnanchanun et al. (2015). To identify new biomarkers for malaria infection, they analyzed plasma miRNAs from 19 malaria patients and 19 normal subjects, using reverse transcription-based quantitative polymerase chain reaction (RT-qPCR). They showed that the plasma levels of miR-451 and miR-16 were downregulated in patients with P. vivax infection, and suggested a correlation with the severity of parasitemia (Chamnanchanunt et al., 2015). By contrast, the levels of other abundant miRNAs in plasma (miR-223, miR-226-3p) did not change significantly in malaria patients. More recently, Kaur et al., investigated the expression of miRNAs from total RNA extracted from whole blood samples of healthy controls, which were negative for P. vivax, and P. vivax complicated and uncomplicated malaria using Affymetrix miRNA array. The authors identified a total of 276 miRNAs differentially expressed, out of which five miRNAs (miR-7977, miR-28-3p, miR-378-5p, miR-194-5p, and miR-3667-5p) were found to be significantly upregulated in complicated P. vivax malaria patients. MiR-7977, which was the most upregulated in complicated P. vivax, may have a role in the infection pathology, probably through regulation of the TGFβ signaling pathway. It was also postulated that miR-7977 may be used as a potential biomarker to distinguish between complicated versus uncomplicated P. vivax infection (Kaur et al., 2018).

More recently, Ketprasit et al. analyzed miRNA expression in EVs purified from the plasma of Thai P. vivax-infected patients, P. falciparum-infected patients and uninfected individuals. In their experimental conditions the relative expression of miR-150-5p and miR-15b-5p was higher in P. vivax-infected patients as compared with uninfected individuals, while let-7a-5p was upregulated in both P. vivax-infected and P. falciparum-infected patients. Using bioinformatic tools they also observed that these miRNAs may regulate key genes involved in the malaria pathway such as the adherent junctions and the transforming growth factor-β pathways. The identified miRNAs could potentially be used as disease biomarkers but further investigation is required to validate sensitivity and specificity (Ketprasit et al., 2020).

Malaria remains the most significant imported parasitic infection in North America and Europe (Mali et al., 2012; Odolini et al., 2012), of which P. falciparum is both the most common and the most severe. Correlating altered miRNA expression during the blood stage of imported malaria is required to better understand the in vivo biological and molecular processes involved in the response to P. falciparum infection and to find new biomarkers and diagnosis tools. To this end, Li et al. used a parallel microarray-based approach to obtain an integrated view of how the host miRNAs expression profile changes in response to P. falciparum infection. Whole blood from six subjects with adult imported P. falciparum malaria (AIFM) was compared with six normal subjects. They identified five upregulated miRNAs (miR-3135b, miR-6780b-5p, miR-1246, miR-6126, and miR-3613-5p), which can act as potential blood biomarkers of immunopathological status and prediction of early host responses, disease prognosis, and severe outcomes in AIFM (Li et al., 2018).

2.4 Severe malaria and cerebral malaria

SM and CM, two key complications of malaria infection, are injurious health problems in endemic areas, especially when considering the widespread issue of malarial drug resistance and the lack of an effective vaccine (Postels & Birbeck, 2013; WHO, 2014).

2.4.1 Severe malaria

SM occurs when infections are complicated by vital organ dysfunctions or aberrant metabolism (WHO, 2014). During infection, P. falciparum infected erythrocytes can be sequestrated in vital organs which leads to inflammation and possible organ impairment. These events correlate with a rapid release of miRNAs into the host fluids that can be detected as promising biomarkers for the prognosis of SM. Recently, using next-generation sequencing, Gupta et al. evaluated the differential expression of miRNAs in SM and in uncomplicated malaria (UM) in children living in Mozambique. They identified six miRNAs associated with in vitro P. falciparum cytoadhesion, severity, and P. falciparum biomass. Among them, levels of miR-4497 were higher in the plasma of children affected by SM as compared with UM and correlated with P. falciparum biomass. These findings suggest that different physio-pathological processes in SM and UM lead to differential expression of miRNAs suggesting a way for assessing their prognostic value (Gupta et al., 2021).

2.4.2 Cerebral malaria

CM is the most severe neurological complication of malaria, whose hallmark is impaired consciousness, with coma being the most severe manifestation (Idro et al., 2010). CM onset is a complex event involving multiple alterations, including aberrant levels of proinflammatory cytokine interferon-γ (IFN-γ) and tumor necrosis factor alpha (TNF-α), aggregation of inflammatory cells in the cerebral blood vessels, tissue sequestration of infected RBCs, and apoptosis. As stated above, a relevant function of miRNAs in malaria pathogenesis has been identified, and a contribution in CM onset recently demonstrated. Unfortunately, the study of miRNA in human CM is still on its infancy, thus, we decided to focus on mouse studies for this section.

To deeply understand the role of miRNA in the immune response to Plasmodium during CM El-Assaad et al. used brain tissue of Plasmodium infected mice: they have shown a significant upregulation in the expression of let-7i, miR-150, and miR-27a suggesting their critical involvement in the severity of CM (El-Assaad et al., 2011). The family of let-7 miRNAs is described as controlling cellular proliferation and the innate immune response. miR-150 is highly expressed in monocytes and has a role in cell proliferation and apoptosis, while miR-27a is involved in apoptosis induction, regulation of T cell proliferation, and activation of the NF-κB signaling pathway (Chhabra et al., 2009; O'Hara et al., 2010; Tourneur & Chiocchia, 2010). The upregulation of these miRNAs and modulation of their potential targets during malaria infection may be crucial for CM development.

Ex vivo endothelial microvessel and mouse models have been used by Barker et al, to describe the potential role of miR-155 in CM. miR-155 is a negative regulator of endothelial and blood–brain barrier (BBB) integrity during SM. miR-155 targets ANXA2 mRNA that binds VE-cadherin which is required for endothelial barrier function. Interestingly, in this study, deletion of miR-155 resulted in decreased endothelial activation, increased BBB integrity, and increased T cell function, improving clinical outcomes during CM (Barker et al., 2017). These results point to new therapeutic strategies inhibiting miR-155; further investigations are need to deeply investigate this possibility.

In another mouse model of CM, the expression of miRNAs was studied following infection with Plasmodium berghei (causing CM) or Plasmodium yoelii (causing severe but non-cerebral malaria [NCM]). Using microarray analysis, miRNA expression was analyzed in the brains of non-infected (NI), NCM, and CM mice. Four dysregulated miRNAs were identified and validated in CM mice as compared with NCM, miR-19a-3p, miR-19b-3p, miR-142-3p, and miR-223-3p. These miRNAs are involved in key pathways implicated in CM onset, including the TGF-β and endocytosis pathways, vitally involved in the neurological syndrome. This data implies that, at least in the mouse model, miRNAs may play a regulatory role in CM pathogenesis (Martin-Alonso et al., 2018).

All together, these results demonstrated the relevance of miRNAs for SM and CM onset, diagnosis, and prognosis while providing further incentive to deeply study the potential role of miRNAs in human CM.

3 lncRNAS AND circRNAS IN MALARIA INFECTION

The lncRNAs and circRNAs are classes of ncRNAs longer than 200 nts, usually characterized by the absence of protein-coding capabilities. Both lncRNAs an