Glucocorticoid effects on vitamin K-dependent carboxylase activity and matrix Gla protein expression in rat lung

Abstract

The role of glucocorticoids in the regulation of vitamin K-dependent carboxylase activity was investigated in fetal and adult lung. Glucocorticoid deficiency induced by adrenalectomy (ADX) stimulated adult lung growth and reduced carboxylation in a tissue-specific manner. Type II epithelial cells were enriched in carboxylase activity, where ADX-induced downregulation was retained in freshly isolated cells. Carboxylase activity in fetal type II cells was one-half that found in fetal fibroblasts isolated from the same lungs, and both populations increased activity with time in culture. Both carboxylase activity and formation of gamma-carboxyglutamate (Gla)-containing proteins were stimulated by dexamethasone (Dex) in fetal type II cells. Matrix Gla protein (MGP), a vitamin K-dependent protein known to be synthesized in type II cells, was also found in fetal fibroblasts, where its expression was stimulated by Dex. These combined results suggested an important role for glucocorticoids and MGP in the developing lung, where both epithelial and mesenchymal cells coordinate precise control of branching morphogenesis. We investigated MGP expression and its regulation by Dex in the fetal lung explant model. MGP mRNA and protein were increased in parallel with the formation of highly branched lungs, and this increase was stimulated twofold by Dex at each day of culture. Dex-treated explants were characterized by large, dilated, conducting airways and a peripheral rim of highly branched saccules compared with uniformly branched controls. We propose that glucocorticoids are important regulators of vitamin K function in the developing and adult lung.

EPAS1, a Dexamethasone-Inducible Gene in Osteoblasts, Inhibits Osteoblastic Differentiation

“…MGP is one of the noncollagenous bone matrix proteins. In addition to our findings, GC-dependent MGP upregulation has also been reported in rat lung cells [30]. A previous study of MGP knockout mice suggests that MGP is an inhibitor of bone mineralization, as MGP-deficient mice exhibit inappropriate calcification of various cartilages and ectopic vascular calcification [20].…”

Osteoblasts mediate the adverse effects of glucocorticoids on fuel metabolism

“…This mimics observations in humans treated with glucocorticoids (52). It has also been reported that both the vitamin K-dependent carboxylase activity and the biosynthesis of its substrates are enhanced by glucocorticoids (53,54). This was not seen in Tg mice, in which glucocorticoid signaling was disrupted in osteoblasts.…”

Matrix GLA protein modulates branching morphogenesis in fetal rat lung

“…This model provides an ideal system in which to examine specific regulators of lung growth and differentiation by using reagentaddition protocols. Increased MGP mRNA expression over the culture interval mimics the early embryonic in vivo time course (17). A stereotypic morphological pattern of explant growth was observed in control cultures, characterized by a high degree of distal epithelial branching (Fig.…”

“…Total RNA (0.1-1 g) was reverse-transcribed for 1 h at 42°C by using poly(dT) primers, 500 M deoxynucleotides, 10 mM dithiothreitol, 1ϫ RT buffer, and an RNase H Ϫ reverse transcriptase (Superscript H Ϫ ; Invitrogen) in a total volume of 20 l. After RT, samples were variably diluted for subsequent PCR amplification; dilutions were empirically based on relative abundance of the respective gene product in fetal lung. MGP mRNA expression was quantified by competitive PCR, as described previously (17). Both endogenous MGP and an MGP cDNA mimic amplified with equal efficiency by using the same set of primers that included forward primer 5Ј-CGGAGAAATGCCAACACCTT-3Ј and reverse primer 5Ј-GCAACGAACAATCTGTG-3Ј.…”