Defining Mechanisms that Influence Dengue Virus Viremia

PROJECT SUMMARY Dengue virus (DENV) is a major global health challenge, causing more infections worldwide than any other arthropod-borne virus. Key determinants of efficient DENV transmission and disease severity are the magnitude and duration of DENV viremia in human hosts. Moreover, patient specific factors increase disease severity, including pre-existing metabolic dysfunction-associated steatotic liver disease (MASLD) and single nucleotide polymorphisms (SNPs) in the opsonin and complement component, mannose-binding lectin (MBL). 32% of the world has MASLD, a condition of liver fat deposition commonly due to obesity and metabolic syndrome; and DENV infection causes a similar pattern of liver injury to MASLD, highlighting a large population susceptible to severe illness for which the mechanistic basis is unknown. Our laboratory developed a murine model of DENV vascular clearance used to define cellular and molecular mediators of DENV viremia, and thus transmission and disease severity, during both healthy and liver disease states. Using this model, we identified liver tissue-resident macrophages, Kupffer cells (KCs), as necessary for efficient DENV clearance. KCs are lost and dysfunctional during MASLD and in mice with diet-induced MASLD, DENV clearance is impaired. Upon KC loss, monocyte derived macrophages (MoMs) infiltrate the liver and repopulate KCs within days. However, one week following KC depletion and repopulation by MoMs, DENV clearance remains impaired, suggesting that functional differences between tissue-resident KCs and infiltrating MoMs may contribute. In terms of molecular mediators, we identified MBL and a scavenger receptor (SR) to be involved in DENV clearance. Interestingly, there is an established interplay between KCs, MBL, and SRs in the literature. KCs facilitate clearance of many circulating pathogens through SR-mediated phagocytosis; and MBL interacts with the DENV virion and with many SRs, particularly those expressed on KCs, as a soluble recognition molecule for SR-mediated microbe scavenging. Thus, I hypothesize that a KC-expressed SR mediates phagocytic uptake of DENV for clearance and this interaction is facilitated by MBL. Specific MBL SNPs impair DENV clearance by disrupting the DENV- MBL interaction, and liver infiltrating MoMs, in the presence of MASLD-induced KC loss, are unable to efficiently clear DENV due to impaired phagocytic capacity. In Aim 1, I will identify the SR involved in mediating DENV clearance from circulation and evaluate the impact of a group of clinically relevant MBL SNPs on DENV binding and clearance from circulation. In Aim 2, I will identify the spectrum of MASLD disease states that impair DENV clearance from circulation and elucidate the functional differences between KCs and MoMs that contribute to this impairment. Overall, this work will define mechanisms driving risk factors for severe disease and in doing so, allow clinicians to better tailor treatment plans to reduce overall morbidity and mortality from DENV infection. It will also expand our knowledge of the innate immune system and liver immunology to identify therapeutic targets to mitigate severe DENV disease and outbreaks.