Regulation of Gene Expression by Thyroid Hormone in Primary Astrocytes: Factors Influencing the Genomic Response.

Astrocytes mediate the action of thyroid hormone in the brain on other neural cells through the production of the active hormone triiodothyronine (T3) from its precursor thyroxine. T3 has also many effects on the astrocytes in vivo and in culture, but whether these actions are directly mediated by transcriptional regulation is not clear. In this work, we have analyzed the genomic response to T3 of cultured astrocytes isolated from the postnatal mouse cerebral cortex using RNA sequencing. Cultured astrocytes express relevant genes of thyroid hormone metabolism and action encoding type 2 deiodinase (Dio2), Mct8 transporter (Slc16a2), T3 receptors (Thra1 and Thrb), and nuclear corepressor (Ncor1) and coactivator (Ncoa1). T3 changed the expression of 668 genes (4.5% of expressed genes), of which 117 were responsive to T3 in the presence of cycloheximide. The Wnt and Notch pathways were downregulated at the posttranscriptional level. Comparison with the effect of T3 on astrocyte-enriched genes in mixed cerebrocortical cultures isolated from fetal cortex revealed that the response to T3 is influenced by the degree of astrocyte maturation and that, in agreement with its physiological effects, T3 promotes the transition between the fetal and adult patterns of gene expression.

Hormone replacement therapy and messenger RNA expression of estrogen receptor coregulators after exercise in postmenopausal women.

UNLABELLED: The use of hormone replacement therapy (HRT) is a potential treatment to relieve symptoms of menopause in postmenopausal women; however, the effects on skeletal muscle are unclear. Specifically, it is unknown if HRT enhances estrogen receptor (ER) transcriptional activation in skeletal muscle at rest and after resistance exercise. PURPOSE: To evaluate changes in the messenger RNA (mRNA) expression of ER coregulators (steroid receptor coactivator-1 (SRC-1) and silencing mediator of retinoid and thyroid receptors (SMRT)) in postmenopausal women after a maximal eccentric exercise bout. METHODS: Fourteen postmenopausal women were divided into two groups: control, women not using HRT (n = 6, 59.2 +/- 4.2 yr, 63.1 +/- 17.4 kg); or HRT, women using traditional HRT (n = 8, 58.5 +/- 3.7 yr, 89.5 +/- 23.7 kg). Participants performed 10 sets of 10 maximal eccentric repetitions of single-leg extension on the Cybex dynamometer at 60 degrees .s with 20-s rest periods between sets. Muscle biopsies of the vastus lateralis were obtained from the exercised leg at baseline and 4 h after the exercise bout. mRNA expression was determined using real-time polymerase chain reaction for SRC-1 and SMRT. RESULTS: mRNA expression of SRC-1 significantly increased (P < or = 0.01; 2.4- to 5.2-fold change) and mRNA expression of SMRT significantly decreased (P < or = 0.01; -1.3- to -4.3-fold change) after the exercise bout in both groups. We observed significantly greater changes in mRNA expression of SRC-1 and SMRT (P < or = 0.01) in the HRT group compared with controls after exercise. CONCLUSIONS: A single bout of maximal eccentric exercise enhances ER transcriptional activity with a greater response present in postmenopausal women using HRT.

Oestradiol and SERM treatments influence oestrogen receptor coregulator gene expression in human skeletal muscle cells.

AIM: Oestrogen receptors (ER) are present in human skeletal muscle (hSkM) cells; however, the function of the receptor is currently unknown. We investigated the influence of oestradiol and selective ER modulators [tamoxifen (TAM), raloxifene (RAL)] on ER coregulator mRNA expression in hSkM. METHODS: Human skeletal muscle cells were treated with 10 nm oestradiol, 5 microm TAM and 10 microm RAL over a 24-h period. Following the treatment period, mRNA expression was quantified using real-time PCR to detect changes in ER-alpha, ER-beta, steroid receptor coactivator (SRC), silencing mediator for retinoid and thyroid hormone receptors (SMRT), MyoD, GLUT4 and c-fos. RESULTS: ER-alpha mRNA expression increased with all three drug treatments (P < 0.05) while there was no change in mRNA expression of ER-beta in hSkM cells. mRNA expression of SRC increased and SMRT decreased with oestradiol, TAM and RAL in hSkM cells (P < 0.05). Importantly, mRNA expression of MyoD increased with oestradiol and decreased with TAM and RAL in hSkM cells (P < 0.05). mRNA expression of GLUT4 increased with oestradiol and RAL and decreased with TAM in hSkM cells (P < 0.05). CONCLUSIONS: These findings are novel in that they provide the first evidence that oestradiol and selective ER modulators influence ER-alpha function in hSkM cells. This demonstrates the importance of the ER and alterations in its coregulators, to potentially prevent sarcopenia and promote muscle growth in postmenopausal women using these forms of hormone replacement therapy.