Cytosolic Sensors of Viral RNA Are Involved in the Production of Interleukin-6 via Toll-Like Receptor 3 Signaling in Human Glomerular Endothelial Cells

Abstract

Background/Aims: Dysregulation of interleukin-6 (IL-6) production in residual renal cells may play a pivotal role in the development of glomerulonephritis (GN). Given that Toll-like receptor 3 (TLR3) signaling has been implicated in the pathogenesis of some forms of GN, we examined activated TLR3-mediated IL-6 signaling in cultured normal human glomerular endothelial cells (GECs). Methods: We treated GECs with polyinosinic-polycytidylic acid (poly IC), an authentic double-stranded RNA, and analyzed the expression of IL-6 and the cytosolic viral RNA sensors retinoic acid-inducible gene-I (RIG-I) and melanoma differentiation associated gene 5 (MDA5) using reverse transcription quantitative real-time polymerase chain reaction, western blotting, and enzyme-linked immunosorbent assays. To further elucidate the effects of poly IC on this signaling pathway, we subjected the cells to small interfering RNA (siRNA) against TLR3, interferon (IFN)-β, RIG-I, and MDA5. Results: We found that poly IC induced the expression of RIG-I, MDA5 and IL-6 via TLR3/IFN-β signaling in GECs. siRNA experiments revealed that both MDA5 and RIG-I were involved in the poly IC-induced expression of IL-6, with MDA5 being upstream of RIG-I. Conclusion: Interestingly, cytosolic sensors of viral RNA were found to be involved in IL-6 production via TLR3 signaling in GECs. Regional activation of TLR3/IFN-β/ MDA5/RIG-I/IL-6 axis due to viral and “pseudoviral” infections is involved in innate immunity and inflammatory reactions in GECs. We believe this signaling pathway also plays a pivotal role in the development of some forms of GN.

The microbiome and cytosolic innate immune receptors

“…It has been recently shown that RLRs drive inflammatory macrophage polarization and suppress wound healing macrophages against West Nile virus infection 165 . MDA5 and RIG‐I are involved in the TLR3‐mediated IL‐6 signaling in human glomerular endothelial cells 166 . More interestingly, in vivo delivery of therapeutically active RIG‐I mimetics leads to RIG‐I activation in breast cancer, triggering apoptosis and pyroptosis for immunogenic killing of tumor cells 167 .…”

Interleukin-6 via Toll-Like Receptor 3 Signaling Attenuates the Expression of Proinflammatory Chemokines in Human Podocytes

“…ELISA kits for IFN-α and IFN-β were purchased from PBL Assay Science (Piscataway, NJ, USA). siRNA against IFN-β is previously described [7][8][9][10][11][12]. Primer sequences are listed in Table 1.…”

“…Since the expression of TLR3 in resident glomerular cells is confirmed in biopsy specimens from patients with CKD [4,5], regional antiviral host defenses via the activation of TLR3 signaling in the intrinsic glomerular cells have been postulated to be involved in the pathogenesis of some CKD types [4][5][6]. To date, considering the implications of TLR3 signaling in the pathogenesis of CKD, we treated cultured human mesangial cells (MCs) and glomerular endothelial cells (GECs) with polyinosinic-polycytidylic acid (poly IC), an authentic viral doublestranded RNA, and thereafter examined the expressions of representative proinflammatory chemokines and cytokines [6][7][8][9][10][11][12]. Notably, podocytes themselves also reportedly express TLR3 and its downstream signaling pathways, and these axes are presumed to be involved in the pathogenesis of certain CKD forms [13,14].…”

“…Among the TLR3 signaling-induced functional molecules in resident glomerular cells, we recently reported that TLR3 signaling can induce IL-6 expression in GECs [11]. IL-6, a representative proinflammatory mediator, is known as a pleiotropic cytokine that regulates pro-and anti-inflammatory reactions in numerous cell types, including resident glomerular cells [15][16][17].…”

Coagulopathy in COVID-19: Connecting the Dots Together

“…IL-6 is produced by activated leukocytes and endothelial cells and acts on multiple cells and tissues. 9,10 Furthermore, IL-6 is also involved in the pathogenesis of the cytokine release syndrome (CRS), which is an acute systemic inflammatory syndrome characterized by fever and multiple organ dysfunction.…”