Metabolic cross‐talk between alveolar type 2 cells and resident alveolar macrophages attenuates inflammation in acute lung injury
Authors: Vohwinkel Christine , Roy Rene , Allawzi Ayed , Burns Nana , Tuder Rubin M. , Grayck Eva Nozik 
Published: April 2020

Introduction

Acute lung injury (ALI) is an inflammatory lung disease, which manifests itself in patients as acute respiratory distress syndrome (ARDS). Our lab previously showed that hypoxia inducible transcription factor (HIF) 1A up‐regulates glycolytic capacity in AT II cells during ALI as a compensatory mechanism to dampen inflammation with the mechanism unknown. In tumor associated macrophages, lactate, the end product of glycolysis can shift macrophages to an anti‐inflammatory Arg‐1 + phenotype. We hypothesized that increased glycolysis in AT2 cells would crosstalk and shift AMs towards a pro‐resolving phenotype and thus attenuate inflammation in ALI.

Methods

C57/B6 wild type or AT2 cell‐specific HIF1A knockout (SPC‐ER Hif1a loxp/loxp) animals were utilized. To induce ALI mice received either i.t. LPS or i.t. HCl (acid aspiration). 6 hours after induction of ALI mice received 25 mM Lactate i.t or pH‐controlled PBS in the control group. Resident vs. recruited AMs (CD45+ CD64+) were segregated by expression of Siglec‐F and CD11b respectively by flow cytometry. ALI severity was determined by cytokine expression and histology. Cytokine expression was measured with qPCR. A549 cells (an alveolar epithelial cell line) with stable knockdown of lactate dehydrogenase LDHA (A549 LDHA KD) or controls were co‐cultured with primary human airway macrophages (isolated from deceased donor lungs not suitable for transplantation) and stimulated with LPS.

Results

i.t Lactate significantly attenuated ALI in both models of acute lung injury in C57/B6 mice. The numbers of resident and recruited AMs were not altered by treatment with lactate 6‐hour post‐injury. However, the levels of Arg1, were increased in resident AMs in lactate treated mice. Furthermore, i.t. lactate shifted cytokine expression in murine airway macrophages towards increased IL‐10 but decreased IL‐1b and IL‐6 production. SPC‐ER Hif1a loxp/loxp animals displayed exacerbated injury and inflammation following LPS/Acid ALI. However, i.t. lactate significantly attenuated ALI phenotype in SPC‐ER Hif1a loxp/lox with increased IL‐10 and Arg1 mRNA expression.

Human primary macrophages co‐cultured with A549 had significantly reduced inflammatory responses to LPS than macrophages alone. The protective phenotype of the epithelial cells on macrophages was abrogated when LDHA was genetically suppressed in A549 cells (A549 LDHA KD).

Conclusions

Our data in 2 murine models of ALI and in an in vitro co‐culture model with primary human airway macrophages show that lactate produced by AT2 cells serves as a mediator to dampen macrophage inflammatory responses by shifting the macrophages towards a more anti‐inflammatory phenotype. Epithelial HIF1A is an activator of glycolysis is sufficient to prevent this shift in resident macrophages as SPC‐ER Hif1a loxp/loxp animals have worse ALI but can be “rescued” with i.t. Lactate. This suggests, that modifying the airway macrophage phenotype via metabolic crosstalk with the alveolar epithelium metabolism acts as an innate protective mechanism to dampen excessive airway inflammation in ALI.

Support or Funding Information

NHLBI/NIH, NICHD/NIH and Parker B Francis Foundation

Figure 1