HIF-α Activation Impacts Macrophage Function during Murine Leishmania major Infection

Abstract

Leishmanial skin lesions are characterized by inflammatory hypoxia alongside the activation of hypoxia-inducible factors, HIF-1α and HIF-2α, and subsequent expression of the HIF-α target VEGF-A during Leishmania major infection. However, the factors responsible for HIF-α activation are not known. We hypothesize that hypoxia and proinflammatory stimuli contribute to HIF-α activation during infection. RNA-Seq of leishmanial lesions revealed that transcripts associated with HIF-1α signaling were induced. To determine whether hypoxia contributes to HIF-α activation, we followed the fate of myeloid cells infiltrating from the blood and into hypoxic lesions. Recruited myeloid cells experienced hypoxia when they entered inflamed lesions, and the length of time in lesions increased their hypoxic signature. To determine whether proinflammatory stimuli in the inflamed tissue can also influence HIF-α activation, we subjected macrophages to various proinflammatory stimuli and measured VEGF-A. While parasites alone did not induce VEGF-A, and proinflammatory stimuli only modestly induced VEGF-A, HIF-α stabilization increased VEGF-A during infection. HIF-α stabilization did not impact parasite entry, growth, or killing. Conversely, the absence of ARNT/HIF-α signaling enhanced parasite internalization. Altogether, these findings suggest that HIF-α is active during infection, and while macrophage HIF-α activation promotes lymphatic remodeling through VEGF-A production, HIF-α activation does not impact parasite internalization or control.

Hypoxia-Inducible Factor-1 Alpha Stabilization in Human Macrophages during Leishmania major Infection Is Impaired by Parasite Virulence

“…Our results clearly contrasted to previous study, which reported that infection of murine macrophages with L. major alone was not sufficient to promote HIF-1α accumulation in vitro but required additional exogenous inflammatory signals [33]. Our data should be further confirmed whether HIF-1α inhibits parasite phagocytosis as described elsewhere [34].…”

Regulatory Functions of Hypoxia in Host–Parasite Interactions: A Focus on Enteric, Tissue, and Blood Protozoa

“…Mice deficient in HIF-1α in myeloid cell compartments have a more severe disease outcome and a higher parasitic burden, suggesting that HIF-1α expressed by myeloid cells contributes to the innate immune response against L. major [ 134 ]. Conversely, other reports suggest that HIF-1α activation has no impact on the macrophage phagocytosis of Leishmania , nor on control of parasitic burden [ 66 ]. HIF-1α expression is downregulated in Leishmania- infected hamsters in a species-dependent fashion, suggesting that different Leishmania spp.…”

“…Drugs capable of targeting HIF-1α, such as resveratrol and echinomycin, decrease L. amazonesis survival in macrophages [ 128 ]. Recent studies have also demonstrated that HIF-dependent upregulation of Vegfa results in lymphangiogenesis, a critical step in the resolution of cutaneous lesions during L. major infection [ 66 , 129 , 130 ] ( Figure 2 A). The host cellular hypoxic response may also have leishmanicidal effects.…”