TUDCA decreases ER stress in HOX neonatal rat lungs.

(A) The expression levels of ER stress markers (P-PERK 0.6±0.1-fold, p<0.001, n = 5; PERK 0.7±0.1-fold, p = 0.00364, n = 5; P-IRE1α 0.6±0.0-fold, p<0.001, n = 5; IRE1α 0.6±0.1-fold, p<0.001, n = 5; GRP78 0.8±0.1-fold, p<0.001, n = 5; cleaved ATF6 0.1±0.0-fold, p<0.001, n = 5; spliced XBP1 0.3±0.0-fold, p<0.001, n = 5; 2 males and 3 females) are all decreased while the N-glycosylated VEGFR2 is increased (3.5±0.2-fold, p<0.001, n = 5) in HOX neonatal lungs at P10 indicating TUDCA can attenuate hyperoxia-induced ER stress. (B) TUDCA also decreases ER stress-mediated apoptosis as evidenced by the decreased CHOP (0.6±0.1-fold, p = 0.002001, n = 5), caspase-12 (0.7±0.1-fold, p<0.001, n = 5), cleaved caspase-12 (0.6±0.1-fold, p<0.001, n = 5), and BAX/BCl₂ ratio (0.2±0.0-fold, p<0.001, n = 5). (C) In IHC stain, P-IRE1α levels are decreased (40.8±3.5 A.U. vs 53.1±5.0 A.U., p<0.001, n = 6, 3 for each sex) in chronic hyperoxia exposed neonatal rat lungs by TUDCA. (D) The dilated ER structure, ER-mitochondria separation, and mitochondrial fission are seen both in AT2 (20,000x magnification) and EC (30,000x magnification) while TUDCA partially reverses the structural changes under the electron microscope. LB: lamellar body in AT2. M: mitochondria. Scale bar = 100 μm for light microscope and = 500 nm for electron microscope. *: p<0.05.