Cytokine storm in the pathophysiology of COVID-19: Possible functional disturbances of miRNAs

Abstract

SARS-CoV-2, as the causative agent of COVID-19, is an enveloped positives-sense single-stranded RNA virus that belongs to the Beta-CoVs sub-family. A sophisticated hyper-inflammatory reaction named cytokine storm is occurred in patients with severe/critical COVID-19, following an imbalance in immune-inflammatory processes and inhibition of antiviral responses by SARS-CoV-2, which leads to pulmonary failure, ARDS, and death. The miRNAs are small non-coding RNAs with an average length of 22 nucleotides which play various roles as one of the main modulators of genes expression and maintenance of immune system homeostasis. Recent evidence has shown that Homo sapiens (hsa)-miRNAs have the potential to work in three pivotal areas including targeting the virus genome, regulating the inflammatory signaling pathways, and reinforcing the production/signaling of IFNs-I. However, it seems that several SARS-CoV-2-induced interfering agents such as viral (v)-miRNAs, cytokine content, competing endogenous RNAs (ceRNAs), etc. preclude efficient function of hsa-miRNAs in severe/critical COVID-19. This subsequently leads to increased virus replication, intense inflammatory processes, and secondary complications development. In this review article, we provide an overview of hsa-miRNAs roles in viral genome targeting, inflammatory pathways modulation, and IFNs responses amplification in severe/critical COVID-19 accompanied by probable interventional factors and their function. Identification and monitoring of these interventional elements can help us in designing the miRNAs-based therapy for the reduction of complications/mortality rate in patients with severe/critical forms of the disease.

Keywords: COVID-19; Cytokine storm; Gene regulators; SARS-CoV-2; miRNAs; miRNAs-based therapy.

Fig. 1

The most effective pro-inflammatory pathways on cytokine storm development in severe/critical COVID-19. a) Following the SARS-CoV-2 entry, its genome is recognized by endosomal TLRs and cytosolic sensors. Multiple adaptor proteins are then recruited. These lead to the nuclear translocation of IRF3, IRF7, and NF-κB transcription factors accompanied by the production of IFNs-I, pro-inflammatory mediators, and miRNAs. A group of proteins, encoded by the virus or host, impede the activation of IFNs-I generation pathways. Among them, viral nsp13 and 6 inhibit the TANK-binding kinase 1 (TBK1) and IRF3, respectively. SARS-CoV-2 ORF6 and host PGE2 also prevent the nuclear translocation of IRF3 and IRF7. Moreover, viral nsp15 hinders the identification of this pathogen genome by cytosolic sensors, and its N protein inhibits them. Ang II/AT1R interaction underlies the activation of pro-inflammatory pathways, nuclear translocation of NF-κB as well as AP-1 transcription factors, and ultimately high-level production of pro-inflammatory mediators on the one hand, and causes activation of ADAM17 molecule, conversion of the mIL-6R into sIL-6R, and induction of this receptor trans-signaling process on the other. Several pro-inflammatory pathways are also activated downstream of IL-6R resulting in the excessive production of the pro-inflammatory mediators and IL-6 Amp cycle. The cPLA2 produces arachidonic acid (AA) and LPLs via decomposition of membrane phospholipids and the latter are predisposing factors for virus increased replication. The enzymes COX-I, -II, mPGES-1, lipoxygenases (LOXs), etc. participate in the generation pathways of eicosanoids and these lipid mediators intensify the pro-inflammatory reactions. It seems that Apelin/APJ axis undergoes some disruptions in this infection, in a way that it does not respectively induce the elevated and reduced expression of ACE2 and AT1R leading to the cytokine storm progression. b) Produced IFNs-I bind to the related receptors and launching their signaling pathways results in the nuclear translocation of STAT1/STAT2 heterodimers, expression of ISGs and some miRNAs. However, several viral proteins including nsp1, 6, 13, ORF3a, 7a, and M inhibit STAT1 and 2 transcription factors and decrease the activity of this pivotal antiviral pathway. In addition, SARS-CoV-2 ORF6 impedes the nuclear translocation of STAT1/STAT2 heterodimers and host PGE2 hampers the ISGs. Activation of multiple pathways and molecules including activity of nicotinamide adenine dinucleotide phosphate (NADPH) oxidases (NOXs) in the endosome, the enzymes involved in the eicosanoids generation pathway, in the downstream of RAGE, NF-κB and AP-1 ones, and also as a consequence of mitochondrial membrane depolarization by elevated Ang II provides the basis for high-level production of ROS. This molecule provokes the activity of the NLRP3-Inflammasome complex and NF-κB pathway, both of which lead to the production of pro-inflammatory mediators and pyroptosis. The host PGE2 also stimulates the activity of the mentioned complex. The Ang II/AT1R interaction causes trans-activation of the cytoplasmic tail of RAGE and launching its downstream pathway on the one hand and activates ADAM17 on the other. This molecule underlies the accumulation of Ang II through ACE2 cleavage. Furthermore, ADAM17 activity is followed by high-level procreation of MMP-9 and consequently more complications. Production of mature TNF-α is the other result of ADAM17 activation. Ligation of RAGE, TNFR and TLR4 with their correspondent ligands (e.g. advanced glycation end products (AGEs), TNF-α, and lipopolysaccharide (LPS)) also contributes to the generation of pro-inflammatory mediators. Nuclear translocation of IRF3 and gene transcription of IFNs-I occur in the MyD88-independent pathway of TLR4 signaling. Nevertheless, SARS-CoV-2 nsp13 and 6 respectively inhibit the TBK1 and IRF3. Its ORF6 and host PGE2 also impede the IRF3 nuclear translocation resulting in the limitation of IFNs-I production in this pathway.

Fig. 1

The most effective pro-inflammatory pathways on cytokine storm development in severe/critical COVID-19. a) Following the SARS-CoV-2 entry, its genome is recognized by endosomal TLRs and cytosolic sensors. Multiple adaptor proteins are then recruited. These lead to the nuclear translocation of IRF3, IRF7, and NF-κB transcription factors accompanied by the production of IFNs-I, pro-inflammatory mediators, and miRNAs. A group of proteins, encoded by the virus or host, impede the activation of IFNs-I generation pathways. Among them, viral nsp13 and 6 inhibit the TANK-binding kinase 1 (TBK1) and IRF3, respectively. SARS-CoV-2 ORF6 and host PGE2 also prevent the nuclear translocation of IRF3 and IRF7. Moreover, viral nsp15 hinders the identification of this pathogen genome by cytosolic sensors, and its N protein inhibits them. Ang II/AT1R interaction underlies the activation of pro-inflammatory pathways, nuclear translocation of NF-κB as well as AP-1 transcription factors, and ultimately high-level production of pro-inflammatory mediators on the one hand, and causes activation of ADAM17 molecule, conversion of the mIL-6R into sIL-6R, and induction of this receptor trans-signaling process on the other. Several pro-inflammatory pathways are also activated downstream of IL-6R resulting in the excessive production of the pro-inflammatory mediators and IL-6 Amp cycle. The cPLA2 produces arachidonic acid (AA) and LPLs via decomposition of membrane phospholipids and the latter are predisposing factors for virus increased replication. The enzymes COX-I, -II, mPGES-1, lipoxygenases (LOXs), etc. participate in the generation pathways of eicosanoids and these lipid mediators intensify the pro-inflammatory reactions. It seems that Apelin/APJ axis undergoes some disruptions in this infection, in a way that it does not respectively induce the elevated and reduced expression of ACE2 and AT1R leading to the cytokine storm progression. b) Produced IFNs-I bind to the related receptors and launching their signaling pathways results in the nuclear translocation of STAT1/STAT2 heterodimers, expression of ISGs and some miRNAs. However, several viral proteins including nsp1, 6, 13, ORF3a, 7a, and M inhibit STAT1 and 2 transcription factors and decrease the activity of this pivotal antiviral pathway. In addition, SARS-CoV-2 ORF6 impedes the nuclear translocation of STAT1/STAT2 heterodimers and host PGE2 hampers the ISGs. Activation of multiple pathways and molecules including activity of nicotinamide adenine dinucleotide phosphate (NADPH) oxidases (NOXs) in the endosome, the enzymes involved in the eicosanoids generation pathway, in the downstream of RAGE, NF-κB and AP-1 ones, and also as a consequence of mitochondrial membrane depolarization by elevated Ang II provides the basis for high-level production of ROS. This molecule provokes the activity of the NLRP3-Inflammasome complex and NF-κB pathway, both of which lead to the production of pro-inflammatory mediators and pyroptosis. The host PGE2 also stimulates the activity of the mentioned complex. The Ang II/AT1R interaction causes trans-activation of the cytoplasmic tail of RAGE and launching its downstream pathway on the one hand and activates ADAM17 on the other. This molecule underlies the accumulation of Ang II through ACE2 cleavage. Furthermore, ADAM17 activity is followed by high-level procreation of MMP-9 and consequently more complications. Production of mature TNF-α is the other result of ADAM17 activation. Ligation of RAGE, TNFR and TLR4 with their correspondent ligands (e.g. advanced glycation end products (AGEs), TNF-α, and lipopolysaccharide (LPS)) also contributes to the generation of pro-inflammatory mediators. Nuclear translocation of IRF3 and gene transcription of IFNs-I occur in the MyD88-independent pathway of TLR4 signaling. Nevertheless, SARS-CoV-2 nsp13 and 6 respectively inhibit the TBK1 and IRF3. Its ORF6 and host PGE2 also impede the IRF3 nuclear translocation resulting in the limitation of IFNs-I production in this pathway.

Fig. 2

Potential of hsa-miRNAs in targeting the SARS-CoV-2 genome, modulating the pro-inflammatory pathways, and reinforcing the IFNs-I-related ones. a) Based on the bioinformatics assessments, multiple hsa-miRNAs can preclude the generation of the viral proteins including nsps, ORFs, and structural ones through targeting the SARS-CoV-2 genome leading to the removal of their inhibitory effects on IFNs-I production pathways and augmentation of antiviral defence. Moreover, the ability of a wide spectrum of these molecules has been confirmed in binding to the pro-inflammatory mRNAs. Targeting the proteins with a central role in cytokine storm development such as ADAM17, AT1R, IL-6, IL-6R, gp130, STAT3, NF-κB, etc. by hsa-miRNAs is followed by progression reduction of pro-inflammatory events and cessation of IL-6 Amp cycle. In addition, cPLA2, COX-I, -II, and mPGES-1 can be targeted by hsa-miRNAs contributing to the reduction of pro-inflammatory responses and virus replication. Most importantly, some hsa-miRNAs can reinforce the IFNs-I generation and antiviral defence through phosphorylation induction and nuclear translocation facilitation of IRF3 and IRF7. b) Targeting the SARS-CoV-2 proteins-coding genes by hsa-miRNAs leads to the elimination of their inhibitory effects on IFNs-I signaling pathways, higher expression of ISGs, and subsequently strengthening the antiviral defence. Moreover, the hsa-miRNAs with the capability of targeting the enzymes, involved in the eicosanoids production pathways, cause upregulation of ISGs expression and downregulation of ROS procreation resulting in the elevated efficiency of antiviral responses. Targeting each of pivotal pro-inflammatory molecules such as NLRP3, NF-κB, ADAM17, AT1R, TAB2 and 3, RhoB, MMP-9, etc. by hsa-miRNAs also provides the basis for abrogating the vicious cycle of pro-inflammatory reactions. Furthermore, the MyD88-independent pathway in TLR4 signaling and the production of IFNs-I are augmented following the neutralizing of the SARS-CoV-2 genome by hsa-miRNAs leading to the limitation of cytokine storm development.

Fig. 2

Potential of hsa-miRNAs in targeting the SARS-CoV-2 genome, modulating the pro-inflammatory pathways, and reinforcing the IFNs-I-related ones. a) Based on the bioinformatics assessments, multiple hsa-miRNAs can preclude the generation of the viral proteins including nsps, ORFs, and structural ones through targeting the SARS-CoV-2 genome leading to the removal of their inhibitory effects on IFNs-I production pathways and augmentation of antiviral defence. Moreover, the ability of a wide spectrum of these molecules has been confirmed in binding to the pro-inflammatory mRNAs. Targeting the proteins with a central role in cytokine storm development such as ADAM17, AT1R, IL-6, IL-6R, gp130, STAT3, NF-κB, etc. by hsa-miRNAs is followed by progression reduction of pro-inflammatory events and cessation of IL-6 Amp cycle. In addition, cPLA2, COX-I, -II, and mPGES-1 can be targeted by hsa-miRNAs contributing to the reduction of pro-inflammatory responses and virus replication. Most importantly, some hsa-miRNAs can reinforce the IFNs-I generation and antiviral defence through phosphorylation induction and nuclear translocation facilitation of IRF3 and IRF7. b) Targeting the SARS-CoV-2 proteins-coding genes by hsa-miRNAs leads to the elimination of their inhibitory effects on IFNs-I signaling pathways, higher expression of ISGs, and subsequently strengthening the antiviral defence. Moreover, the hsa-miRNAs with the capability of targeting the enzymes, involved in the eicosanoids production pathways, cause upregulation of ISGs expression and downregulation of ROS procreation resulting in the elevated efficiency of antiviral responses. Targeting each of pivotal pro-inflammatory molecules such as NLRP3, NF-κB, ADAM17, AT1R, TAB2 and 3, RhoB, MMP-9, etc. by hsa-miRNAs also provides the basis for abrogating the vicious cycle of pro-inflammatory reactions. Furthermore, the MyD88-independent pathway in TLR4 signaling and the production of IFNs-I are augmented following the neutralizing of the SARS-CoV-2 genome by hsa-miRNAs leading to the limitation of cytokine storm development.