Proinflammatory Effects of Respiratory Syncytial Virus–Induced Epithelial HMGB1 on Human Innate Immune Cell Activation

Abstract

High mobility group box 1 (HMGB1) is a multifunctional nuclear protein that translocates to the cytoplasm, and is subsequently released to the extracellular space during infection and injury. Once released it acts as a damage-associated molecular pattern and regulates immune and inflammatory responses. Respiratory syncytial virus (RSV) is a major cause of acute lower respiratory tract infections in infants and elderly, for which no effective treatment or vaccine is currently available. This study investigated the effects of HMGB1 on cytokine secretion, as well as the involvement of NF-κB and TLR4 pathways in RSV-induced HMGB1 release in human airway epithelial cells (AECs) and its proinflammatory effects on several human primary immune cells. Purified HMGB1 was incubated with AECs (A549 and small alveolar epithelial cells) and various immune cells, and measured the release of proinflammatory mediators, and the activation of NF-κB and p38 MAPK. HMGB1 treatment significantly increased the phosphorylation of NF-κB and p38 MAPK but did not induce the release of cytokines/chemokines from AECs. However, addition of HMGB1 to immune cells did significantly induce the release of cytokines/chemokines and activated the NF-κB and p38 MAPK pathways. We found that activation of NF-κB accounted for RSV-induced HMGB1 secretion in AECs in a TLR4-dependent manner. These results indicated that HMGB1 secreted from AECs can facilitate the secretion of proinflammatory mediators from immune cells in a paracrine mechanism, thus promoting the inflammatory response that contributes to RSV pathogenesis. Therefore, blocking the proinflammatory function of HMGB1 may be an effective approach for developing novel therapeutics.

Glycyrrhetinic acid alleviates hepatic inflammation injury in viral hepatitis disease via a HMGB1-TLR4 signaling pathway

“…3G and 6H). In fact, pretreatment with a TLR4 blocking agent decreased the HMGB1 levels from virus-infected cells via the TLR4-NFκB pathway, and the inactivation of NFκB resulted in a decreased release of various pro-inflammatory cytokines, including IL-1β, IL-6, TNF-α and HMGB1 [37,54]. Furthermore, reduced HMGB1 levels led to the inhibition of NFκB pathway in various immune cells, and the inflammation response was alleviated significantly.…”

“…It has been reported that TLR4 is key receptor of innate immune signaling responses to influenza virus and other respiratory viruses [51]. Although host HMGB1 and RAGE interaction is also a major mechanism driving serious liver injury, the TLR4 pathway has recently been demonstrated to be more involved in respiratory syncytial virus and human papilloma virus (HPV) infection [52][53][54]. Previously, the expression of TLR3, TLR4, TLR7, TLR9 and TLR10 genes from hepatic tissue was shown to be significantly upregulated in some viral infection models [32,55].…”

Extracellular HMGB1: a therapeutic target in severe pulmonary inflammation including COVID-19?

“…The biological implications of this mechanism may be of tremendous importance for the pathogenesis of severe pulmonary inflammation because the high constitutive cell surface RAGE expression. It has been demonstrated in preclinical and clinical studies that severe respiratory infections including influenza and human respiratory syncytial virus (HRSV) generate substantial extracellular HMGB1 release in pulmonary inflammation and that HMGB1-specific antagonists ameliorate these conditions (Ito et al 2011;Nosaka et al 2015;Nosaka et al 2018;Hatayama et al 2019;Manti et al 2018;Rayavara et al 2018;Rallabhandi et al 2012;Simpson et al 2020). Extracellular HMGB1 accumulates locally due to passive release from dying cells and active secretion from innate immunity cells and additional cell types.…”

RSV Reprograms the CDK9•BRD4 Chromatin Remodeling Complex to Couple Innate Inflammation to Airway Remodeling

“…Interestingly, many of these secreted proteins do not contain classic signal peptides, suggesting novel and incompletely understood mechanisms for innate signaling. For example, we have demonstrated that the nuclear damage-associated molecular patterns (DAMPs), HMGB1, and histone H3 undergo nuclear export and extracellular secretion in response to RSV; these DAMPs controlling mononuclear inflammation [38,41]. Informatics analysis indicated that RSV infected Scgb1a1-expressing bronchiolar cells selectively secrete 103 unique proteins and exosomal contents (Cluster 3 in Figure 1C).…”

“…Epithelial type I and III IFNs play an important role in anti-viral response of neighboring epithelial cells. Damage-associated HMGB1 is important in monocyte recruitment and activation [41]. Epithelial B-cell activating factor (BAFF) is responsible for T-cell independent B-cell activation mediating the pulmonary antibody response [42].…”