The dengue virus NS1 protein conveys pro-inflammatory signals by docking onto human high-density lipoproteins

Abstract

The nonstructural NS1 protein is a virulence factor secreted by dengue virus (DENV)-infected cells. NS1 is known to alter the complement system, activate immune cells and perturb endothelial barriers. Here we show that pro-inflammatory signals are triggered by a high affinity complex formed between NS1 and human high-density lipoproteins (HDL). Electron microscopy images of the NS1-HDL complexes show spherical HDL particles with rod-shaped NS1 protrusions on their surface. These complexes are readily detectable in the plasma of hospitalized dengue patients using anti-apolipoprotein A-I (ApoA-I) antibodies specific of the HDL moiety. The functional reprogramming of HDL particles by the NS1 protein as a means to exacerbate systemic inflammation during DENV infection provides a new paradigm linking the human lipoprotein network to dengue pathogenesis.

Secreted dengue virus NS1 from infection is predominantly dimeric and in complex with high-density lipoprotein

“…This suggests that there could be a dynamic equilibrium between the HDL-bound NS1 and free NS1, regulated by the interplay between NS1 secretion and circulating HDL. Additionally, our cryoEM structures are in agreement with a recent report of a reconstituted DENV NS1:HDL complex that showed NS1 dimers anchored at the surface of HDL particles (15). .…”

“…This suggests that there could be a dynamic equilibrium between the HDL-bound NS1 and free NS1, regulated by the interplay between NS1 secretion and circulating HDL. Additionally, our cryoEM structures are in agreement with a recent report of a reconstituted DENV NS1:HDL complex that showed NS1 dimers anchored at the surface of HDL particles ( 15 ).. Finally, the detection and quantification of NS1 from a ApoA1 pull-down using commercial antibodies in DENV1-infected patient serum ( 33 ) provides indirect evidence that HDL-bound NS1 complexes are also clinically relevant (Fig.…”

“…While earlier studies used cross-linkers to demonstrate the hexamer conformation, it remains unclear how the hexameric form is biologically meaningful from its assembly to the disruption of endothelial glycocalyx at the membrane milieu. The hexamer model is based on several untested assumptions and low resolution EM data that were challenged by recent evidence that suggests that NS1 may be associated with HDL ( 14, 15 ) and uses scavenger receptor B1 as a cell receptor in cultured cells ( 16 ). To reconcile the findings related to the functional forms of sNS1 and better understand its biological roles, we obtain the native form of sNS1 from the cell-based virus infection system and determine its structures with an antibody.…”

Dengue NS1 interaction with lipids alters its pathogenic effects on monocyte derived macrophages

“…It was recently shown that NS1 binds to HDL and with a lower affinity to LDL, and NS1-HDL complexes induced proinflammatory cytokine production from monocyte-derived macrophages in vitro [5]. While many early studies have suggested that secretory NS1 circulates as a hexamer, with a lipid core, more recent studies suggest that secretory NS1 circulates predominantly as a tetramer associated with HDL [11].…”

“…While many early studies have suggested that secretory NS1 circulates as a hexamer, with a lipid core, more recent studies suggest that secretory NS1 circulates predominantly as a tetramer associated with HDL [11]. During the course of the illness, the apolipoproteins that associate with NS1 have shown to change, with ApoAI and ApoB interacting with NS1 during acute illness but replaced by ApoE towards the recovery phase of illness [5]. Therefore, the lipid composition of the NS1 hexamer/tetramer or lipids that interact with NS1, could also contribute to the virulence of NS1 and potentially help explain some of the variability in previous studies [40].…”