Hypoxia-Inducible Factor 1α (HIF1α) Suppresses Virus Replication in Human Cytomegalovirus Infection by Limiting Kynurenine Synthesis

Abstract

Human cytomegalovirus (HCMV) replication depends on the activities of several host regulators of metabolism. Hypoxia-inducible factor 1α (HIF1α) was previously proposed to support virus replication through its metabolic regulatory function. HIF1α protein levels rise in response to HCMV infection in nonhypoxic conditions, but its effect on HCMV replication was not investigated. We addressed the role of HIF1α in HCMV replication by generating primary human cells with HIF1α knocked out using CRISPR/Cas9. When HIF1α was absent, we found that HCMV replication was enhanced, showing that HIF1α suppresses viral replication. We used untargeted metabolomics to determine if HIF1α regulates metabolite concentrations in HCMV-infected cells. We discovered that in HCMV-infected cells, HIF1α suppresses intracellular and extracellular concentrations of kynurenine. HIF1α also suppressed the expression of indoleamine 2,3-dioxygenase 1 (IDO1), the rate-limiting enzyme in kynurenine synthesis. In addition to its role in tryptophan metabolism, kynurenine acts as a signaling messenger by activating aryl hydrocarbon receptor (AhR). Inhibiting AhR reduces HCMV replication, while activating AhR with an exogenous ligand increases virus replication. Moreover, we found that feeding kynurenine to cells promotes HCMV replication. Overall, our findings indicate that HIF1α reduces HCMV replication by regulating metabolism and metabolite signaling. IMPORTANCE Viruses, including human cytomegalovirus (HCMV), reprogram cellular metabolism using host metabolic regulators to support virus replication. Alternatively, in response to infection, the host can use metabolism to limit virus replication. Here, our findings show that the host uses hypoxia-inducible factor 1α (HIF1α) as a metabolic regulator to reduce HCMV replication. Further, we found that HIF1α suppresses kynurenine synthesis, a metabolite that can promote HCMV replication by signaling through the aryl hydrocarbon receptor (AhR). In infected cells, the rate-limiting enzyme in kynurenine synthesis, indoleamine 2,3-dioxygenase 1 (IDO1), is suppressed by a HIF1α-dependent mechanism. Our findings describe a functional connection between HIF1α, IDO1, and AhR that allows HIF1α to limit HCMV replication through metabolic regulation, advancing our understanding of virus-host interactions.

TNFα-induced metabolic reprogramming drives an intrinsic anti-viral state

“…Separately, our data show that cells lacking Hif1α are more permissive to infection ( Fig 4L ), suggesting Hif1α may play a role in limiting the initiation of infection. Consistent with this finding, Hif1α was recently shown to attenuate HCMV replication in human fibroblasts [ 46 ]. The anti-viral phenotype associated with Hif1α-mediated metabolic regulation is intriguing, yet the mechanisms responsible for TNFα-induced glycolysis still require elucidation.…”

“…Kynurenine accumulates in a variety of inflammatory conditions and is induced during Human Immunodeficiency Virus (HIV) infection [ 47 , 48 ]. Others have described pro-viral effects of kynurenine on HCMV replication [ 46 ], suggesting a potentially complex relationship with infection that requires further analysis with respect to its roles in inflammation, intrinsic immunity and during viral infection.…”

Human Cytomegalovirus in breast milk is associated with milk composition, the infant gut microbiome, and infant growth

“…This pathway has previously been implicated in the immune response to CMV in studies of human cells and primary tissues 49,50 , suggesting this association may be a response to mammary CMV reactivation. Additionally, one study found that providing kynurenine to human fibroblasts promoted CMV replication, and blocking IDO1 decreased CMV replication 51 . Given our observational study design, we cannot determine if the association with increased IDO1/kynurenine is a cause or consequence of mammary CMV reactivation.…”

Alteration in Cellular Signaling and Metabolic Reprogramming during Viral Infection

“…Although the exact metabolic consequence remains unclear, the human immunodeficiency virus type 1 (HIV-1) viral protein Vpr induces stabilization of HIF-1α ( 117 ), resulting in the induction of two critical glycolytic enzymes, HK and PKM2 ( 118 ). In HCMV-infected cells, HIF-1α suppresses kynurenine levels and expression of the rate-limiting enzyme of kynurenine synthesis, indoleamine 2,3-dioxygenase 1 ( 119 ). HIF-1α reduces HCMV replication by regulating metabolism and metabolite signaling ( 119 ).…”

“…In HCMV-infected cells, HIF-1α suppresses kynurenine levels and expression of the rate-limiting enzyme of kynurenine synthesis, indoleamine 2,3-dioxygenase 1 ( 119 ). HIF-1α reduces HCMV replication by regulating metabolism and metabolite signaling ( 119 ). Further studies remain necessary to identify viral factors required for HIF-1α induction during HCMV infection.…”