L-PGDS Attenuates Acute Lung Injury by Prostaglandin D₂ in Both Dependent and Independent Ways

Lipocalin-type PG D synthase (L-PGDS) has two roles: it can be a PGD synthase, or it can be a carrier protein of hydrophobic small molecules. In this study, we investigated the dual roles of L-PGDS in acute lung injury by using L-PGDS-deficient and point-mutated mice, which lack PGD₂ producibility but maintain lipocalin ability. Hydrochloride (HCl) administration (0.1 M intratracheally for 6 h) caused hemorrhage and dysfunction in the wild-type (WT) mouse lung. These symptoms were accompanied by an increase in PGD₂ production. Both deficiency and point mutation of L-PGDS aggravated the HCl-induced hemorrhage and dysfunction. Although both the gene modifications decreased PGD₂ production, only L-PGDS-deficient mice, but not point mutation mice, lacked protein expressions of L-PGDS in the lungs. In the WT mice, HCl administration caused pulmonary edema, indexed as an increase in lung water content and protein leakage in bronchoalveolar lavage fluid. L-PGDS deficiency and point mutation similarly aggravated edema formation. HCl administration also stimulated mucin production and bronchoalveolar lavage fluid leukocyte infiltration in the WT mouse lungs. Of interest, L-PGDS deficiency, but not point mutation, exacerbated these manifestations. Consistently, only L-PGDS deficiency increased the mRNA expression of IL-33, which stimulates mucin production in the inflamed lung. These results show that L-PGDS attenuated HCl-induced acute lung injury progresses in two different ways: L-PGDS produced PGD₂, which inhibited pulmonary edema formation, whereas its lipocalin ability decreased mucin formation and inflammatory cell infiltration in the inflamed lung.