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Merz C.N.B.,Cedars Sinai Research Institute | Olson M.B.,University of Pittsburgh | McClure C.,University of Pittsburgh | Yang Y.-C.,Cedars Sinai Research Institute | And 8 more authors.
American Heart Journal | Year: 2010

Background: Compared with men, women have more evidence of myocardial ischemia with no obstructive coronary artery disease. Although low endogenous estrogen levels are associated with endothelial dysfunction, the role of low-dose hormone therapy has not been fully evaluated. We postulate that a 12-week duration of low-dose hormone replacement therapy is associated with myocardial ischemia and endothelial dysfunction. Methods and Results: Using a multicenter, randomized, placebo-controlled design, subjects were randomized to receive either 1 mg norethindrone/10 μg ethinyl estradiol or placebo for 12 weeks. Chest pain and menopausal symptoms, cardiac magnetic resonance spectroscopy, brachial artery reactivity, exercise stress testing, and psychosocial questionnaires were evaluated at baseline and exit. Recruitment was closed prematurely because of failure to recruit after publication of the Women's Health Initiative hormone trial. Of the 35 women who completed the study, there was less frequent chest pain in the treatment group compared with the placebo group (P = .02) at exit. Women taking 1 mg norethindrone/10 μg ethinyl estradiol also had significantly fewer hot flashes/night sweats (P = .003), less avoidance of intimacy (P = .05), and borderline differences in sexual desire and vaginal dryness (P = .06). There were no differences in magnetic resonance spectroscopy, brachial artery reactivity, compliance, or reported adverse events between the groups. Conclusions: These data suggest that low-dose hormone therapy improved chest pain symptoms, menopausal symptoms, and quality of life, but did not improve ischemia or endothelial dysfunction. Given that it was not possible to enroll the prespecified sample size, these results should not be considered definitive. © 2010 Mosby, Inc. All rights reserved. Source


Hamidi S.,Cedars Sinai Research Institute | Hamidi S.,University of California at Los Angeles | Hamidi S.,University of Southern California | Aliesky H.A.,Cedars Sinai Research Institute | And 5 more authors.
Thyroid | Year: 2013

Background: Graves' hyperthyroidism is induced by immunizing mice with adenovirus expressing the human thyrotropin (TSH)-receptor. Using families of recombinant-inbred mice, we previously discovered that genetic susceptibility to induced thyroid-stimulating antibodies and hyperthyroidism are linked to loci on different chromosomes, indicating a fundamental genetic difference in thyroid sensitivity to ligand stimulation. An approach to assess thyroid sensitivity involves challenging genetically diverse lines of mice with TSH and measuring the genotype/strain-specific increase in serum thyroxine (T4). Methods: We investigated genetic susceptibility and genetic control of T4 stimulation by 10 mU bovine TSH in female mice of the CXB, BXH, and AXB/BXA strain families, all previously studied for induced Graves' hyperthyroidism. Results: Before TSH injection, T4 levels must be suppressed by inhibiting endogenous TSH secretion. Three daily intraperitoneal L-triiodothyronine injections efficiently suppressed serum T4 in females of 50 of 51 recombinant inbred strains. T4 stimulation by TSH was more strongly linked in CXB and BXH sets, derived from parental strains with divergent T4 stimulation, than in AXB/BXA strains generated from parents with similar TSH-induced responses. Genetic loci linked to the acute TSH-induced T4 response (hours) were not the same as those linked to induced hyperthyroidism (which develops over months). Conclusions: Genetic susceptibility for thyroid sensitivity to TSH stimulation was distinct for three families of inbred mouse lines. These observations parallel the human situation with multiple genetic loci contributing to the same trait and different loci associated with the same trait in different ethnic groups. Of the genetic loci highlighted in mice, three overlap with, or are located up or downstream, of human TSH-controlling genes. Other studies show that human disease genes can be identified through cross-species gene mapping of evolutionary conserved processes. Consequently, our findings suggest that novel thyroid function genes may yet be revealed in humans. © Copyright 2013, Mary Ann Liebert, Inc. 2013. Source


Chen C.-R.,Cedars Sinai Research Institute | McLachlan S.M.,Cedars Sinai Research Institute | Rapoport B.,Cedars Sinai Research Institute
Journal of Biological Chemistry | Year: 2011

Thyroid-stimulating hormone (TSH)-induced reduction in ligand binding affinity (negative cooperativity) requires TSH receptor (TSHR) homodimerization, the latter involving primarily the transmembrane domain (TMD) but with the extracellular domain (ECD) also contributing to this association. To test the role of theTMDin negative cooperativity, we studied the TSHR ECD tethered to the cell surface by a glycosylphosphatidylinositol (GPI) anchor that multimerizes despite the absence of the TMD. Using the infinite ligand dilution approach, we confirmed that TSH increased the rate of dissociation (koff) of prebound 125ITSH from CHO cells expressing the TSH holoreceptor. Such negative cooperativity did not occur with TSHR ECD-GPI-expressing cells. However, even in the absence of added TSH, 125I-TSH dissociated much more rapidly from the TSHR ECD-GPI than from the TSH holoreceptor. This phenomenon, suggesting a lower TSH affinity for the former, was surprising because both the TSHR ECD and TSH holoreceptor contain the entire TSH-binding site, and the TSH binding affinities for both receptor forms should, theoretically, be identical. In ligand competition studies, we observed that the TSH binding affinity for the TSHR ECDGPI was significantly lower than that for the TSH holoreceptor. Further evidence for a difference in ligand binding kinetics for the TSH holoreceptor and TSHR ECD-GPI was obtained upon comparison of the TSH Kd values for these two receptor forms at 4 °C versus room temperature. Our data provide the first evidence that the wild-type TSHRTMDinfluences ligand binding affinity for the ECD, possibly by altering the conformation of the closely associated hinge region that contributes to the TSH-binding site. © 2011 by The American Society for Biochemistry and Molecular Biology, Inc. Source


Hamidi S.,Cedars Sinai Research Institute | Hamidi S.,University of California at Los Angeles | Chen C.-R.,Cedars Sinai Research Institute | Chen C.-R.,University of California at Los Angeles | And 4 more authors.
Thyroid | Year: 2011

Background: Thyroid-stimulating autoantibodies (TSAb) bind to the thyrotropin receptor (TSHR) extracellular domain, or ectodomain (ECD), comprising a leucine-rich repeat domain (LRD) linked by a hinge region to the transmembrane domain (TMD). The LRD (residues 22-260; signal peptide 1-21) contains two disulfide-bonded loops at its N-terminus. In the crystal structure of the isolated LRD complexed with human TSAb monoclonal antibody (mAb) M22, N-terminal disulfide loop 1 (residues 22-30) could not be determined because of crystal disorder. Nevertheless, present crystal structure data are interpreted to exclude a role for the LRD N-terminal disulfide loops in the TSAb epitope(s), contradicting prior functional evidence of a role for these loops in TSAb function. Materials and Methods: To re-examine this issue we studied two cell types expressing the TSHR with the extreme N-terminal loop 1 (residues 22-30) deleted: the TSHR ECD lacking the TMD and tethered to the plasma membrane by a glycosyl-phosphatidylinositol (GPI) anchor, and the TSH holoreceptor containing the TMD. Because TSAb including M22 "see" the holoreceptor poorly relative to the TSHR ECD-GPI, we used the latter to examine the effect of deleting residues 22-30 on M22 binding by flow cytometry and the holoreceptor to test the effect of this deletion on the functional response to M22. Results: Deletion of TSHR N-terminal loop 1 (residues 22-30) reduced the number of TSHR-ECD-GPI recognized by M22 relative to two TSHR mAb with epitopes far downstream of the LRD N-terminal loops. Relative to control mAb 2C11, M22 recognized only 60.4% of cell surface receptors (p=0.02). In contrast to M22 binding to TSHR-ECD-GPI, in functional studies with the TSH holoreceptor, M22 stimulation of cAMP generation was unaltered by the loop 1 deletion. Conclusions: Our data support the concept that TSAb interact with the cysteine-rich N-terminus of the TSHR. Comparison of crystal structures of the same TSHR LRD in complex with TSAb M22 or blocking antibody K1-70 helps reconcile contradictory viewpoints. A difference between M22 interaction with the identical TSHR N-terminus expressed on the TSHR-ECD-GPI and holoreceptor suggests that crystallization of the TSHR LRD-M22 complex may not provide a complete understanding of the functional TSAb epitope(s) in Graves' disease. © Copyright 2011, Mary Ann Liebert, Inc. Source

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