Negative Regulation of Antioxidant Enzyme Gene Expression in the Developing Fetal Rat Lung by Prenatal Hormonal Treatments

Abstract

administration of thyrotropin-releasing hormone (TRH) or T R H plus dexamethasone (DEX) to pregnant rats accelerates lung surfactant system development in late gestation, but paradoxically depresses the normal late gestational elevation in fetal lung antioxidant enzyme (AOE) activities (Pediatr Res 30522, 1991). In these present studies, we tested whether both prenatal hormonal treatments act to depress normal fetal lung AOE development by negative regulation of AOE gene expression. We used solution hybridization to quantitate the concentration of AOE mRNA. Results of the developmental studies revealed significantly decreased lung mRNA concentrations of copper-zinc superoxide dismutase, manganese superoxide dismutase, catalase, and glutathione peroxidase in late gestation a s a result of prenatal TRH treatment. The addition of DEX administration did not reverse the lowered expression of lung AOE genes due to T R H treatment, but instead resulted in significant additional decreases in pulmonary AOE mRNA levels a t both 21 and 22 d of gestation.The tested AOE mRNA half-lives (stabilities) revealed no significant differences between controls (8.0-10.5 h) and TRH-treated (8.2-9.5 h) and TRH-plus-DEX treatment (7.8-10.7 h) groups. These findings suggest that prenatal treatment with T R H and with T R H plus DEX acts to depress the normal late fetal lung AOE activity elevations by (direct) negative regulation of AOE gene expression, and the decreased AOE expression is likely regulated at the level of gene transcription rather than posttranscriptionally. (Pediatr Res 33: 171-176, 1993) Abbreviations AOE, antioxidant enzyme CuZnSOD, copper-zinc superoxide dismutase SOD, superoxide dismutase MnSOD, manganese superoxide dismutase CAT, catalase GP, glutathione peroxidase TRH, thyrotropin-releasing hormone T3, triiodothyronine DEX, dexamethasone cRNA, complementary RNA 2). It has been demonstrated in each of the five different species examined to date-the rat, rabbit, guinea pig, hamster. and sheep-that development of the surfactant system and the lung AOE system share a chronologically similar late gestational pattern of development, and that the developing lung markedly increases both its surfactant content and its AOE activity levels during the final I0 to 15% of gestation (3-6). The late gestational rise in AOE (SOD. CAT. and GP) activities is considered to be a normal "preparation for birth" phenomenon that is required to assure safe respiratory functioning of the newborn's lung when it is suddenly exposed to several-fold-higher O2 tension immediately after birth than the O2 tension experienced in We have previously demonstrated that. although prenatal administration of either T3 or T, plus DEX to pregnant rats accelerated surfactant system development in the late fetal lung, both of these hormonal treatments significantly delayed or decreased pulmonary AOE system development (8). Further studies were done recently using the same hormonal agents (TRH instead of T3) that are currently being tested clinically to try...

Differential Gene Expression of Antioxidant Enzymes in the Perinatal Rat Lung

“…cRNA preparation. The rat cRNA for Cu,ZnSOD, CAT, and GP were prepared as previously described (7,8). A pGEM-Blue construct a-actin cDNA (7) was used to synthesize a-actin [3H] cRNA for use as an mRNA recovery marker.…”

Failure of Premature Rabbits to Increase Lung Antioxidant Enzyme Activities after Hyperoxic Exposure: Antioxidant Enzyme Gene Expression and Pharmacologic Intervention with Endotoxin and Dexamethasone

“…Preparation of cRNA was performed as described previously (11,12). Total nucleic acids portionately with added mRNA.…”

Positive Regulation of Pulmonary Antioxidant Enzyme Gene Expression by Prenatal Thyrotropin Releasing Hormone Plus Dexamethasone Treatment in Premature Rats Exposed to Hyperoxia

“…Our findings suggest that the regulation of lung AOE gene expression is complex under hyperoxic conditions. The prematurely delivered rats pretreated with TRH + DEX were previously found to have lowered lung AOE gene expression (depressed AOE activities and AOE mRNA levels) at preterm delivery at d 21 (4,5). Similarly, when examined at 2 d postnatal age after room air exposure, their pulmonary AOE mRNA levels remained lower in the premature TRH + DEX group compared with the shamtreated group.…”

“…It has been previously demonstrated by our laboratories that although prenatal administration of TRH +DEX to pregnant rats accelerates surfactant system development in the late fetal lung, this same hormonal treatment significantly decreases the normal fetal lung AOE (SOD, CAT, and GP) activity elevations in late gestation (4). This hormonal effect appears to depend on a pretranslational/ transcriptional mechanism involving decreased AOE mRNA levels (5). When full-term newborn rats prenatally treated with TRH +DEX were exposed to prolonged hyperoxia, results showed that although these newborns manifested lower baseline AOE activities at birth than control term newborns, the 612 CHEN ETAL.…”

“…The rat complementary RNA for CuZnSOD, MnSOD, CAT, and GP were prepared as previously described (5,8,9). Total nucleic acids were extracted by phenol-chloroform extraction of the left lung tissue homogenate (9).…”