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Glucocorticoids inhibit notch target gene expression in osteoblasts.

ABSTRACT: Glucocorticoids in excess suppress osteoblast function and cause osteoporosis. We demonstrated that cortisol induces the expression of selected Notch receptors in osteoblasts, revealing a potential mechanism for the skeletal effects of glucocorticoids. However, it remains to be determined whether increased expression of Notch receptors results into enhanced signaling. Following activation of Notch, its intracellular domain (NICD) binds to the DNA-associated protein recombination signal binding protein for immunoglobulin kappa-J region (RBPJ) and induces the expression of target genes such as Hey1, Hey2, and HeyL. To determine whether glucocorticoids modulate Notch signaling in the skeleton, 1 month old wild-type mice were administered prednisolone or placebo and sacrificed after 72?h, and gene expression was analyzed in femoral bone. Prednisolone induced Tsc22d3, a glucocorticoid target gene, and suppressed Hey1 and HeyL expression, which is indicative of inhibited Notch receptor activity or direct Hey downregulation. To determine the mechanisms of Hey suppression, wild-type osteoblast-enriched cells were seeded on the Notch cognate ligand Delta-like (DLL)1 or transfected with constructs expressing the NOTCH1 NICD fragment and exposed to either cortisol or vehicle. Cortisol opposed the induction of mRNA and heterogeneous nuclear RNA for Hey1, Hey2, and HeyL by DLL1, but had no effect on mRNA stability, indicating that glucocorticoids inhibit Hey expression by transcriptional mechanisms. Transactivation studies and electrophoretic mobility shift assays revealed that cortisol did not oppose RBPJ-mediated transcription or RBPJ/DNA interactions, respectively. In conclusion, glucocorticoids suppress expression of Hey1, Hey2, and HeyL in osteoblasts by RBPJ-independent transcriptional mechanisms.

SUBMITTER: Zanotti S

PROVIDER: S-EPMC6830575 | biostudies-literature | 2018 Jul

REPOSITORIES: biostudies-literature

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Glucocorticoids inhibit notch target gene expression in osteoblasts.

Zanotti Stefano S Yu Jungeun J Adhikari Suyash S Canalis Ernesto E

Journal of cellular biochemistry 20180325 7

Glucocorticoids in excess suppress osteoblast function and cause osteoporosis. We demonstrated that cortisol induces the expression of selected Notch receptors in osteoblasts, revealing a potential mechanism for the skeletal effects of glucocorticoids. However, it remains to be determined whether increased expression of Notch receptors results into enhanced signaling. Following activation of Notch, its intracellular domain (NICD) binds to the DNA-associated protein recombination signal binding p ...[more]

PMID: 29575203

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Project description:Background and objectiveCementum and bone are similar mineralized tissues, but cementum accumulates much more slowly than bone, does not have vasculature or innervation and does not undergo remodeling. Despite these differences, there are no well-established markers to distinguish cementoblasts from other mature mineralizing cells such as osteoblasts and odontoblasts. The purpose of this study was to assess differences in gene expression between cementoblasts and osteoblasts using gene profiling of cell populations isolated directly from osteocalcin-green fluorescent protein (OC-GFP) transgenic mice.Material and methodsOC-GFP reporter mice were used as they show labeling of cementoblasts, osteoblasts and odontoblasts, but not of periodontal ligament fibroblasts, within the periodontium. We sorted cells digested from the molar root surface to isolate OC-GFP(+) cementoblasts. Osteoblasts were isolated from calvarial digests. Microarray analysis was performed, and selected results were confirmed by real-time PCR and immunostaining or in situ hybridization.ResultsMicroarray analysis identified 95 genes that were expressed at least two-fold higher in cementoblasts than in osteoblasts. Our analysis indicated that the Wnt signaling pathway was differentially regulated, as were genes related to skeletal development. Real-time PCR confirmed that expression of the Wnt inhibitors Wnt inhibitory factor 1 (Wif1) and secreted frizzled-related protein 1 (Sfrp1) was elevated in cementoblasts compared with osteoblasts, and Wif1 expression was localized to the apical root region. In addition, the transcription factor BARX homeobox 1 (Barx1) was expressed at higher levels in cementoblasts, and immunohistochemistry indicated that BARX1 was expressed in apical cementoblasts and cementocytes, but not in osteoblasts or odontoblasts.ConclusionThe OC-GFP mouse provides a good model for selectively isolating cementoblasts, and allowed for identification of differentially expressed genes between cementoblasts and osteoblasts.

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Glucocorticoids inhibit notch target gene expression in osteoblasts.

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Glucocorticoids inhibit notch target gene expression in osteoblasts.

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