Chikungunya virus (CHIKV) infection has been associated with severe cardiac manifestations, yet, how CHIKV infection leads to heart disease remains unknown. Here, we leveraged both mouse models and human primary cardiac cells to define the mechanisms of CHIKV heart infection. Using an immunocompetent mouse model of CHIKV infection as well as human primary cardiac cells, we demonstrate that CHIKV directly infects and actively replicates in cardiac fibroblasts. In immunocompetent mice, CHIKV is cleared from cardiac tissue without significant damage through the induction of a local type I interferon response from both infected and non-infected cardiac cells. Using mice deficient in major innate immunity signaling components, we found that signaling through the mitochondrial antiviral-signaling protein (MAVS) is required for viral clearance from the heart. In the absence of MAVS signaling, persistent infection leads to focal myocarditis and vasculitis of the large vessels attached to the base of the heart. Large vessel vasculitis was observed for up to 60 days post infection, suggesting CHIKV can lead to vascular inflammation and potential long-lasting cardiovascular complications. This study provides a model of CHIKV cardiac infection and mechanistic insight into CHIKV-induced heart disease, underscoring the importance of monitoring cardiac function in patients with CHIKV infections.

Arthropod-borne viruses (arboviruses) are an emerging and evolving global public health threat, with limited antiviral treatments or vaccines available. La Crosse virus (LACV) from the Bunyavirales order is responsible for pediatric encephalitis cases in the United States, yet little is known about the infectivity of LACV. Given the structural similarities between class II fusion glycoproteins of LACV and chikungunya virus (CHIKV), an alphavirus from the Togaviridae family, we hypothesized that LACV would share similar entry mechanisms with CHIKV. To test this hypothesis, we performed cholesterol-depletion and repletion assays and used cholesterol-modulating compounds to study LACV entry and replication. We found that LACV entry was cholesterol dependent, while replication was less affected by cholesterol manipulation. In addition, we generated single-point mutants in the LACV Gc ij loop that corresponded to known CHIKV residues important for virus entry. We found that a conserved histidine and alanine residue in the Gc ij loop impaired virus infectivity and attenuated LACV replication in vitro and in vivo . Finally, we took an evolution-based approach to explore how the LACV glycoprotein evolves in mosquitoes and mice. We found multiple variants that cluster in the Gc glycoprotein head domain, providing evidence for the Gc glycoprotein as a contributor to LACV adaptation. Together, these results begin to characterize the mechanisms of LACV infectivity and how the LACV glycoprotein contributes to replication and pathogenesis. IMPORTANCE Vector-borne viruses are significant health threats that lead to devastating disease worldwide. The emergence of arboviruses, in addition to the lack of effective antivirals or vaccines, highlights the need to study how arboviruses replicate at the molecular level. One potential antiviral target is the class II fusion glycoprotein. Alphaviruses, flaviviruses, and bunyaviruses encode a class II fusion glycoprotein that contains strong structural similarities at the tip of domain II. Here, we show that the bunyavirus La Crosse virus uses a cholesterol-dependent entry pathway similar to the alphavirus chikungunya virus, and residues in the ij loop are important for virus infectivity in vitro and replication in mice. These studies show that genetically diverse viruses may use similar pathways through conserved structure domains, suggesting that these viruses may be targets for broad-spectrum antivirals in multiple arboviral families.

Arthropod-borne viruses (arboviruses) are an emerging and evolving global public health threat with little to no antiviral treatments. La Crosse virus (LACV) from the Bunyavirales order is responsible for pediatric encephalitis cases in the United States, yet little is known about the infectivity of LACV. Given the structural similarities between class II fusion glycoproteins of LACV and chikungunya virus (CHIKV), an alphavirus from the Togaviridae family, we hypothesized that LACV would share similar entry mechanisms to CHIKV. To test this hypothesis, we performed cholesterol-depletion and repletion assays and used cholesterol modulating compounds to study LACV entry and replication. We found that LACV entry was cholesterol-dependent while replication was less affected by cholesterol manipulation. In addition, we generated single point mutants in the LACV ij loop that corresponded to known CHIKV residues important for virus entry. We found that a conserved histidine and alanine residue in the Gc ij loop impaired virus infectivity and attenuate LACV in vitro and in vivo. Finally, we took an evolution-based approach to explore how the LACV glycoprotein evolution in mosquitoes and mice. We found multiple variants that cluster in the Gc glycoprotein head domain, supporting the Gc glycoprotein as a target for LACV adaptation. Together, these results begin to characterize the mechanisms of LACV infectivity and how the LACV glycoprotein contributes to infectivity and pathogenesis.

Chikungunya virus (CHIKV) infection has been associated with severe cardiac manifestations. However, how CHIKV infection leads to heart disease remains unknown. Using C57BL/6 mice, we show that cardiac fibroblasts are the main target of CHIKV infection in the heart, and that cardiac tissue infection induces a local and robust type I interferon (IFN-I) response in both infected and non-infected cardiac cells. The loss of IFN-I signaling results in increased CHIKV infection, virus spreading, and apoptosis in cardiac tissue. Importantly, signaling through the mitochondrial antiviral-signaling protein (MAVS) is essential for efficient CHIKV clearance from the heart. Indeed, persistent infection in cardiac tissue of MAVS-deficient mice leads to cardiac damage characterized by focal myocarditis and major vessel vasculitis. This study provides a new mouse model of CHIKV cardiac infection and mechanistic insight on how CHIKV can lead to cardiac damage, underscoring the importance of monitoring cardiac function in patients with CHIKV infections.