TIEG and estrogen modulate SOST expression in the murine skeleton

• Published in: Journal of cellular physiology Vol. 233; no. 4; pp. 3540 - 3551
• Main Authors: Subramaniam, Malayannan, Pitel, Kevin S., Bruinsma, Elizabeth S., Monroe, David G., Hawse, John R.
• Format: Journal Article
• Language: English
• Published: United States Wiley Subscription Services, Inc 01.04.2018
• Subjects: Animals; Biocompatibility; Biomedical materials; bone; Bone and Bones - metabolism; Bone Density - drug effects; Bone Density - physiology; Bone Morphogenetic Proteins - metabolism; Bones; Cancellous bone; Chromatin; Clonal deletion; Compartments; Cortical bone; CRISPR; DNA-Binding Proteins - deficiency; estrogen; Estrogen replacement therapy; Estrogens; Estrogens - pharmacology; Female; Gene deletion; Gene expression; Gene sequencing; Genetic Markers - physiology; Genotypes; Glycoproteins - metabolism; Hormone replacement therapy; Immunoprecipitation; KLF10; Mice; Mice, Knockout; Mimicry; Mineralization; miRNA; Osteocytes - drug effects; Osteocytes - metabolism; Osteoporosis; Ovariectomy; Ovariectomy - methods; Regulatory sequences; Ribonucleic acid; RNA; Rodents; sclerostin; Skeleton; Skeleton - drug effects; Skeleton - metabolism; SOST; SOST protein; TIEG; Transcription Factors - deficiency; KLF10; TIEG; estrogen; bone; SOST; sclerostin
• ISSN: 0021-9541; 1097-4652
• DOI: 10.1002/jcp.26211

TIEG knockout (KO) mice exhibit a female‐specific osteopenic phenotype and altered expression of TIEG in humans is associated with osteoporosis. Gene expression profiling studies identified sclerostin as one of the most highly up‐regulated transcripts in the long bones of TIEG KO mice relative to WT littermates suggesting that TIEG may regulate SOST expression. TIEG was shown to substantially suppress SOST promoter activity and the regulatory elements through which TIEG functions were identified using promoter deletion and chromatin immunoprecipitation assays. Knockdown of TIEG in IDG‐SW3 osteocyte cells using shRNA and CRISPR‐Cas9 technology resulted in increased SOST expression and delayed mineralization, mimicking the results obtained from TIEG KO mouse bones. Given that TIEG is an estrogen regulated gene, and as changes in the hormonal milieu affect SOST expression, we performed ovariectomy (OVX) and estrogen replacement therapy (ERT) studies in WT and TIEG KO mice followed by miRNA and mRNA sequencing of cortical and trabecular compartments of femurs. SOST expression levels were considerably higher in cortical bone compared to trabecular bone. In cortical bone, SOST expression was increased following OVX only in WT mice and was suppressed following ERT in both genotypes. In contrast, SOST expression in trabecular bone was decreased following OVX and significantly increased following ERT. Interestingly, a number of miRNAs that are predicted to target sclerostin exhibited inverse expression levels in response to OVX and ERT. These data implicate important roles for TIEG and estrogen‐regulated miRNAs in modulating SOST expression in bone. In this manuscript, we demonstrate that TIEG directly suppresses the expression of the SOST gene in the mouse skeleton and in osteocyte cell lines. We also elucidate the impact of ovariectomy and estrogen replacement therapy on the expression patterns of SOST in mouse trabecular and cortical bone compartments. Finally, a role for specific miRNAs in mediating the effects of estrogen on SOST expression are indicated.