HIF-1α and HIF-2α transcription factors differentially regulate lung alveolar macrophage function
Alveolar Macrophages (AMs) reside in the alveoli, where oxygen pressure is high, therefore maintaining an active degradation of hypoxia-inducible transcription factors (HIF) mediated by the Von Hippel-Lindau protein (pVHL) ubiquitin ligase complex. We previously found that Vhl-deficient AMs not sensing high oxygen pressure are immature and functionally impaired. Here we investigated the specific roles of HIF-1 and HIF-2 isoforms in the regulation of AM functions. With this aim, we combined deletion of Vhl with single or double deletion of Hif1a and/or Hif2a in AMs under the control of the CD11c promoter using a Cre-Lox system. Our work demonstrates that in Vhl-deficient macrophages, both HIF-1 and HIF-2 contribute to AM defective self-renewal, while HIF-2 plays a central role in regulating the impaired AM maturation associated with pVHL loss. HIF-1 promotes a glycolytic shift in alveolar macrophages, while HIF-2 hinders lipid oxidation and surfactant clearance. Thus, HIF-2 raises as a selective critical factor restraining the therapeutic potential of AMs to degrade surfactant excess in mice that have developed pulmonary alveolar proteinosis (PAP). Overall, regulation of both HIF-1 and HIF-2 isoforms is required for an optimal AM function, highlighting HIF-2 as a potential pharmacological target for secondary PAP.