Exploring mechanisms through which glucocorticoids regulate kidney development
Background: Maternal administration of dexamethasone (DEX, synthetic glucocorticoid) for 48hrs results in offspring with a reduced nephron endowment. The mechanism through which DEX inhibits nephron formation is unknown. During kidney development, new nephrons only arise adjacent to ureteric branch tips. We hypothesised that: (1) DEX may decrease glomerular number (GN) by inhibiting ureteric branching (UB) morphogenesis; and (2) DEX may inhibit UB morphogenesis by altering expression levels of specific kidney developmental genes.
Aims: (1) To determine the effect of DEX on UB morphogenesis and glomerulogenesis and (2) To determine the effect of DEX on expression of Bone Morphogenetic Protein 4 (BMP4) and Transforming Growth Factor βeta-1 (TGFβ1), in cultured rat metanephroi.
Methods: Embryonic day 14.5(E14.5) metanephroi from time-mated Sprague Dawley rat embryos were cultured in control media, or media containing (DEX 10-7M, 10-5M) or vehicle for 48 hrs. After 48 hrs in culture quantification of UB points and tips was performed by immunostaining metanephroi with monoclonal anti-pan cytokeratin. Kidneys were also collected at 48 hours for real-time PCR quantitation of BMP4 and TGFβ1 mRNA levels. GN was determined in kidneys at 5 days following lectin histochemistry.
Results: Culture in DEX (10-5M) resulted in formation of fewer UB points and tips;DEX(10-5M)=39±2, compared to control=54±3,p<0.001. Culture in both concentrations of DEX inhibited GN;DEX(10-5M)=44±4, DEX(10-7M)=54±1, compared to control=68±1,p<0.001. DEX treatment resulted in upregulated expression of BMP4 and TGFβ1.
Conclusion: DEX inhibits UB morphogenesis and leads to a decrease in nephron number in cultured metanephroi. DEX may inhibit UB by upregulating BMP4 and TGFβ1 expression.