# Tibetan PHD2D4E;C127S variant protects from viral diseases in hypoxia, but predispose to infections in normoxia via HIFα:IFN axis

## TL;DR

A Tibetan genetic variant protects against viral infections in low oxygen but increases risk in normal oxygen due to changes in immune response.

## Contribution

First study showing how the PHD2D4E;C127S variant affects immune response to viral infections under different oxygen levels.

## Key findings

- PHD2D4E;C127S variant suppresses DENV2 infection in hypoxia by promoting IFN synthesis.
- Under normoxia, the variant increases ROS and reduces IFN synthesis, worsening DENV2 infection.
- Tibetan T-cells with the variant show higher IFN-γ in response to SARS-CoV-2 under hypoxia.

## Abstract

We previously reported that Tibetan-specific variant of prolyl-hydroxylase-2 (PHD2)D4E;C127S protects highlanders from hypoxia-triggered pathologies by destabilizing hypoxia-inducible factor (HIF)-1α. Others have reported that stabilized HIF1α negatively regulates interferon (IFN)-regulating factor (IRF)-3 under hypoxia. We examined the role of PHD2D4E;C127S variant in IFN synthesis in immune cells during viral infections. Primary monocytes and cells engineered to express the PHD2D4E;C127S variant displayed protection against dengue virus (DENV)-2 infection by suppressing HIF1α, in turn promoting IRF-3 and IFNα/β synthesis in hypoxia (3% O2) in vitro. However, under normoxia (21% O2), these mutant cells increased reactive oxygen species (ROS) generation following DENV2 infection. Increased ROS then suppressed PHD2D4E;C127S activity, reflected by reduced hydroxylation and concomitant stabilization of HIF1α, resulting in suppressed IFN synthesis and higher DENV2 replication. The PHD2WT cells demonstrated the opposite trend. Our data further confirmed the inverse correlation between HIF1α and IFN pathways. CAY10585, a HIF1α-inhibitor, decreased the DENV2 infection by increasing IFN-A/B and IRF-3/7/9 expression. HIF1α-depleted monocytes also showed a similar response to the infection. We extended our findings to COVID-19 infection. The CD4/CD8 T-cells collected from Tibetans with PHD2D4E;C127S variant and exposed to SARS-CoV-2 infection showed elevated expression of IFN-γ in response to exposure to SARS-CoV-2 receptor-binding domain (RBD) peptide under hypoxia, and a lesser expression under normoxia. The study thus highlights a unique crosstalk of PHD2D4E;C127S variant with HIF1α-IFN axis under environmental pO2 in protecting or predisposing Tibetans to viral infections.

Approximately 400 million people permanently reside in high mountain ranges. One such highlander population, Tibetans, who developed genetic adaptation against hypobaric hypoxia and mountain maladies. Earlier we have described that the Tibetan carrying PHD2D4E;C127S variant are protected from hypoxia induced clinical symptoms like polycythemia and edema. The PHD2D4E;C127S variant has significantly higher affinity for oxygen, in turn degrades HIF1α/ HIF2α more efficiently than the PHD2WT. We describe in this study for the first time that the immune response of PHD2D4E;C127S or PHD2WT monocytes/T cells against viral infections under hypoxia vs normoxia. Study describes a unique crosstalk of PHD2D4E;C127S variant with HIF1α under environmental pO2 in regulating the anti-viral interferon (IFN) response against the viral infections including dengue and COVID-19. Tibetan PHD2D4E;C127S variant protects both viral diseases in hypoxia, but predisposes to infections in normoxia.