C107-17 Alveolar Macrophage HIF-1α Drives Lactate Dehydrogenase A Mediated Alveolar Type II Cell Proliferation After Acute Lung Injury

Rationale Alveolar macrophages (AMs) play a critical role in repair after acute lung injury. We have previously demonstrated that a subset of AMs upregulate hypoxia inducible factor-1α (HIF-1α), an important regulator of tissue regeneration. The function of AMs HIF-1α after injury remains unclear, particularly its involvement mediating crosstalk between alveolar type II (ATII) cells, key progenitors of the lung, to proliferate and initiate repair. We hypothesize that AMs HIF-1α promotes the production of soluble mediators that stimulate ATII proliferation thereby initiating repair. Using a complementary and orthogonal approach, we identified AMs-derived lactate dehydrogenase A (LDHA) initiates alveolar regeneration. Methods To test whether HIF-1α promotes reparative programming of AMs, Csf1RCre conditional KOs (cKOs) and wild type (WT) littermate controls were challenged with intratracheal LPS. ATII proliferation and bronchoalveolar lavage (BAL) was assessed 6 days later. Direct effects of AMs on ATII cell proliferation were assessed in vitro. ATII cells were isolated from WT mice via digestion, antibody negative selection, and cultured on rat tail collagen-Matrigel. ATII cultures were treated with conditioned media generated from AMs isolated from LPS-challenged WT and cKOs mice. Unbiased proteomics with mass spectrometry was used to identify soluble factors in conditioned media from WT versus cKO AMs. This was followed by factor addition-depletion in monolayer cultures. Results In vivo, LPS treated WT mice displayed maximum proliferation at day 6 with cKOs showing reduced proliferation. Additionally, BAL from day 6 demonstrated AMs as the predominate cell type in both strains. In vitro, conditioned media from WT mice significantly enhanced ATII proliferation, whereas conditioned media from cKOs displayed an attenuated response. Mass spectrometry-based proteomics revealed that LDHA was upregulated in conditioned media from WT AMs compared to cKO AMs. The addition of recombinant LDHA augmented proliferation while its depletion from conditioned media attenuated ATII proliferation. Conclusion In this study we demonstrate that AMs predominate in the alveolus and that this coincides with maximum ATII proliferative capacity after injury. Crucially, cKO mice exhibit attenuated ATII cell proliferation in vivo. Mechanistically, we uncovered that AMs drive ATII proliferation through HIF-1α-dependent release of LDHA. To our knowledge, LDHA release by AMs has not previously been reported as pro-reparative factor. Taken as a whole, our studies identify the HIF-1α-LDHA axis as novel pathway in alveolar repair. This study lays the groundwork for human studies to define the relevance of the HIF-1α-LDHA axis in lung injury, opening new directions toward targeted therapeutics. This abstract is funded by: T32: HL007085