OC 19.5 - PHD2D4E;C127S Tibetan mutations protect viral diseases in hypoxia, but predispose to infections in normoxia

Background: We described that the Tibetan specific gain-of-function mutation of prolylhydroxylase-2 (PHD2)_D4E/C127S protects highlanders from hypoxia-triggered clinical events. Having higher affinity to O2, PHD2_D4E;C127S variant is capable of hydroxylating proline-residues of its substrate, hypoxia inducible factor(HIF)-1α, in turn inhibiting hypoxia-triggered maladies at high-altitudes. A recent study described that elevated HIF1α in hypoxia negatively regulates the interferon(IFN)-regulating factor(IRF)-3, and suppresses IFN-α/β synthesis in monocytes.

Aims: We herein examined the role of PHD2_D4E/C127S mutations on the HIF1α:IFN-α/β axis in viral infections.

Methods: We recruited Tibetans from high-altitude and sea-level, and identified their genotypes. Used their monocytes for infection with Dengue virus(DENV) and SARS-CoV-2. We also used cells engineered with PHD2_D4E/C127S or PHD2_WT for infection. We measured the viral load and interferon response in monocytes in hypoxia/normoxia.

Results: The PHD2_D4E/C127S monocytes protected DENV2 infection by suppressing HIF1α, in turn promoting IRF-3/7/9 and IFN-α/β in hypoxic environment(1%O2) in vitro. Other hand, PHD2_WT monocytes showed elevated HIF1α and suppressed IRFs and IFN-α/β along with higher infection in hypoxia. Interestingly, the PHD2_D4E/C127S monocytes showed increased HIF1α and suppressed IRFs and IFN-α/β, and higher infection in normoxia(21%O2). The treatment with HIF1α-inhibitor significantly rescued the DENV2 infection. Furthermore, infection with SARS-CoV-2 also yielded similar observations. PHD2_D4E/C127S engineered-HUH7 cells showed an increased viral infection alongside elevated HIF1α and less IRF-3/7/9 and IFN-α/β under normoxia. Also, an increased Akt-phosphorylation and ACE2 expression correlated with high SARS-CoV-2 infection. The above infection was inhibited by either HIF1α and/or Akt-inhibitor. Most importantly, the CD4/CD8T-cells of PHD2_D4E/C127S individuals, either vaccinated or exposed to prior infection, showed elevated expression of IFN-α/β upon exposure to SARS-CoV-2-RBD peptides under hypoxia in vitro as compared to PHD2_WT.

Conclusion(s): Our findings thus suggest a unique crosstalk of PHD2_D4E/C127S mutations with environmental hypoxic cues in protection or predisposition to viral infections.