RT Journal Article SR Electronic T1 PGE2 accounts for bidirectional changes in alveolar macrophage self-renewal with aging and smoking JF Life Science Alliance JO Life Sci. Alliance FD Life Science Alliance LLC SP e202000800 DO 10.26508/lsa.202000800 VO 3 IS 11 A1 Loka R Penke A1 Jennifer M Speth A1 Christina Draijer A1 Zbigniew Zaslona A1 Judy Chen A1 Peter Mancuso A1 Christine M Freeman A1 Jeffrey L Curtis A1 Daniel R Goldstein A1 Marc Peters-Golden YR 2020 UL https://www.life-science-alliance.org/content/3/11/e202000800.abstract AB Alveolar macrophages (AMs) are resident immune cells of the lung that are critical for host defense. AMs are capable of proliferative renewal, yet their numbers are known to decrease with aging and increase with cigarette smoking. The mechanism by which AM proliferation is physiologically restrained, and whether dysregulation of this brake contributes to altered AM numbers in pathologic circumstances, however, remains unknown. Mice of advanced age exhibited diminished basal AM numbers and contained elevated PGE2 levels in their bronchoalveolar lavage fluid (BALF) as compared with young mice. Exogenous PGE2 inhibited AM proliferation in an E prostanoid receptor 2 (EP2)-cyclic AMP-dependent manner. Furthermore, EP2 knockout (EP2 KO) mice exhibited elevated basal AM numbers, and their AMs resisted the ability of PGE2 and aged BALF to inhibit proliferation. In contrast, increased numbers of AMs in mice exposed to cigarette smoking were associated with reduced PGE2 levels in BALF and were further exaggerated in EP2 KO mice. Collectively, our findings demonstrate that PGE2 functions as a tunable brake on AM numbers under physiologic and pathophysiological conditions.