Effects of dexamethasone exposure on rat metanephric development: in vitro and in vivo studies

Abstract

Effects of dexamethasone exposure on rat metanephric development: in vitro and in vivo studies. Am J Physiol Renal Physiol 293: F548-F554, 2007. First published May 30, 2007; doi:10.1152/ajprenal.00156.2007.-Maternal administration of dexamethasone (DEX) for 48 h early in rat kidney development results in offspring with a reduced nephron endowment. However, the mechanism through which DEX inhibits nephrogenesis is unknown. In this study, we hypothesized that DEX may indirectly inhibit nephrogenesis by inhibiting ureteric branching morphogenesis. Whole metanephroi from embryonic day 14.5 (E14.5) rat embryos were cultured in the presence of DEX. DEX (10 Ϫ5 M) exposure for 2 days significantly inhibited ureteric branching compared with metanephroi grown in control media or DEX (10 Ϫ7 M). Culturing metanephroi for a further 3 days (in control media only) reduced total glomerular number in metanephroi previously exposed to DEX (10 Ϫ5 M) or (10 Ϫ7 M) compared with control cultures. Expression of genes known to regulate ureteric branching morphogenesis was determined by real-time PCR in metanephroi after 2 days in culture. DEX exposure in vitro decreased expression of glial cell line-derived neurotrophic factor (GDNF) and increased expression of bone morphogenetic protein-4 (BMP-4) and transforming growth factor-␤1 (TGF-␤1). Similar gene expression changes were found in E16.5 metanephroi in which the dam had been exposed to 2 days of DEX (0.2 mg ⅐ kg Ϫ1 ⅐ day Ϫ1 ) at E14.5/15.5 in vivo. However, in kidneys collected at E20.5 after in vivo exposure for 2 days, GDNF expression was increased and BMP-4 and TGF-␤1 expression decreased suggesting a biphasic response in gene expression to DEX exposure. These results show for the first time that inhibition of ureteric branching morphogenesis may be a key mechanism through which DEX exposure results in a reduced nephron endowment.hypertension; reduced nephron endowment PREDISPOSITION TO MANY adult-onset diseases, including hypertension, is thought to be a result of poor fetal and early postnatal development (1). Maternal glucocorticoid exposure during pregnancy has been used as an animal model to induce a poor in utero environment. Animal models in which the developing fetus is exposed to elevated levels of circulating maternal glucocorticoids result in offspring with a permanent nephron deficit. This reduction in nephron complement is thought to contribute to the onset of hypertension that is also observed in these offspring (12-14, 20, 21). Studies with dexamethasone (DEX), a synthetic glucocorticoid that readily crosses the placental barrier, revealed that the severity of these phenotypes is dependent on the timing and duration of glucocorticoid exposure. Interestingly, just 2 days of exposure is able to produce a decrease in nephron endowment. In the rat, maternal administration of DEX (0.2 mg⅐kg Ϫ1 ⅐day Ϫ1) over 2 days results in adult hypertension and a reduced glomerular (nephron) number in both male and female offspring when administered on embryonic days 15/16 (E15/1...

Maternal nutrient restriction inhibits ureteric bud branching but does not affect the duration of nephrogenesis in rats

“…In support of this hypothesis, Ki67 expression and TUNEL staining were more intense in the nephrogenic zone of NR kidneys than that in controls at E18. Similar compensatory response has been reported in dexamethasone and maternal LPD models (1,5,24). In maternal LPD, glomerular number of kidneys was even higher than controls at E20 (24).…”

“…At E14, however, ureteric bud tip numbers in NR kidneys were approximately half of CON. Decreased ureteric branching has been reported in metanephroi treated with dexamethasone, ethanol, and gentamicin in an organ culture (5,7,18).In a similar manner to ureteric branching, body weight and metanephros size of NR fetuses were not different from controls at E13. At E14, weight and kidney size became smaller in NR fetuses.…”

“…At E14, however, ureteric bud tip numbers in NR kidneys were approximately half of CON. Decreased ureteric branching has been reported in metanephroi treated with dexamethasone, ethanol, and gentamicin in an organ culture (5,7,18).…”

“…With respect to the kidney, low birth weight is associated with a risk for hypertension and renal disease, and reduced nephron number is considered to be the cause. In animals, maternal protein or global nutrient restriction, uterine artery ligation, hyperglycemia, and exposure to various agents such as glucocorticoids or alcohol produce offspring with fewer nephrons (1)(2)(3)(4)(5)(6). Depletion of stem cells by increased apoptosis has been suggested to be responsible for the decreased nephron formation (1,3).…”

“…On the other hand, ureteric bud branching is a fundamental step in determining nephron number. The mechanism of reduced nephron endowment in dexamethasone or ethanol exposure has been suggested to be inhibited branching morphogenesis in an organ culture study (5,7). Reduced ureteric branching has recently been reported in a model of maternal hyperglycemia in vivo (8).…”