SAT010 Role Of Glucocorticoids In Induction Of Autophagy During Fetal Lung Development

Abstract

Abstract Disclosure: R. Mishra: None. Development of the fetal lung and production of pulmonary surfactant is a complex process that involves crosstalk between the mesenchyme and epithelium, branching morphogenesis, thinning of the bronchi alveolar ducts and alveolar septa, differentiation of alveolar type II cells, increased synthesis of surfactant lipids and proteins and their trafficking to lamellar bodies (LBs). The regulation of these processes is incompletely understood. Autophagy has recently been shown to be critical for lung morphogenesis and lamellar body biogenesis. In studies of global and lung epithelial cell-specific knockout of a number of autophagy-related genes in mice, there was found to be neonatal respiratory distress and lethality at birth. Interestingly, the lung phenotype of mice with an epithelial cell-specific knockout of the autophagy gene, Beclin 1 (Becn1), was very similar to that of mice with a targeted deletion of the glucocorticoid receptor (GR) gene (GRKO). Moreover, this phenotype was also observed in mice double-deficient in steroid receptor coactivators (Src)-1 and 2 (Src-1/-2dKO), which serve an essential role in GR transcriptional activity in fetal lung. Therefore we were interested to determine whether GCs acting through the GR regulate autophagy gene expression in fetal lung. In preliminary studies, we made the exciting discovery that nuclear levels of phospho (p)-GRS220 increased markedly in mouse fetal lung (MFL) at 16.5 dpc (compared to 15.5 dpc) and continued to increase toward term (18.5 dpc). Importantly, nuclear levels of total GR remained unchanged from 15.5 -18.5 dpc. Moreover, we observed that treatment of cultured MFL epithelial cells with the synthetic glucocorticoid, dexamethasone (Dex), upregulated expression of the autophagy genes, Becn1, Atg7 and Lc3b. Dex Induction of autophagy genes was prevented by co-incubation with the potent small-molecule inhibitor, SI-2, which selectively reduces cellular protein levels of the SRC family of GR coactivators. The importance of SRC-1 and SRC-2 in the regulation of autophagy gene expression is further emphasized by our finding that Becn1 and Atg7 expression was significantly reduced in lungs of Src-1/-2 dKO fetal mice at term. Previously, we found that glucocorticoids increase expression of transcription factor, C/EBPβ in an SRC-1/SRC-2-dependent manner which further upregulates C/EBPα in MFL epithelial cells. In ChIP-qPCR studies, we observed an increased binding of p- GRS220 and C/EBPα to the promoter regions of autophagy genes in MFL with advancing gestation. We also observed that siRNA-mediated knockdown of C/EBPα prevented Dex induction of autophagy gene expression. These exciting collective findings suggest that glucocorticoids together with SRC-1 and SRC-2 enhance autophagic flux in fetal lung via the C/EBP signaling pathway. Presentation: Saturday, June 17, 2023