title: Pituitary-thyroid setpoint and thyrotropin receptor expression in consomic rats.
abstract: The genetic basis for differences in TSH sensitivity between two rat strains was examined using consomic rats generated from original strains salt-sensitive Dahl (SS) (TSH 1.8 +/- 0.1 ng/ml; free T(4) index 4.9 +/- 0.4) and Brown Norwegian (BN) (TSH 5.5 +/- 0.6 ng/ml, P < 0.05; free T(4) index 4.3 +/- 0.1, P not significant). Consomic rats SSBN6 [BN chromosome (CH) 6 placed in SS rat] and SSBN2 (BN CH 2 placed in SS rat) have TSH concentrations intermediate between pure SS and BN strains (2.9 +/- 0.3 and 3.1 +/- 0.3 ng/ml, respectively; P < 0.05). Candidate genes on rat CH 2 included TSH beta-subunit and on CH 6 the TSH receptor (TSHR). TSH from sera of BN, SS, SSBN6, and SSBN2 strains had similar in vitro bioactivity suggesting that the cause for the variable TSH concentrations was not due to an altered TSH. Physiological response to TSH was measured by changes in serum T(4) concentrations upon administration of bovine TSH (bTSH). Rat strain SS had a greater T(4) response to bTSH than BN (change in T(4), 1.3 +/- 0.1 vs. 0.4 +/- 0.1 microg/dl, P < 0.005), suggesting reduced thyrocyte sensitivity to TSH in BN. Sequencing of the TSHR coding region revealed an amino acid difference in BN (Q46R). This substitution is unlikely to contribute to the strain difference in serum TSH because both TSHR variants were equally expressed at the cell surface of transfected cells and responsive to bTSH. Given similar TSH activity and similar TSHR structure, TSHR mRNA expression in thyroid tissue was quantitated by real-time PCR. BN had 54 +/- 5% the total TSHR expression compared to SS (100 +/- 7%, P < 0.0001), when corrected for GAPDH expression, a difference confirmed at the protein level. Therefore, the higher TSH level in the BN strain appears to reflect an adjustment of the feedback loop to reduced thyrocyte sensitivity to TSH secondary to reduced TSHR expression. These strains of rat provide a model to study the cis- and trans-acting factors underlying the difference in TSHR expression.
authors.affiliation: Department of Medicine, The University of Chicago, Chicago, IL 60637, USA.
authors.forename: Lars C
authors.initials: LC
authors.lastname: Moeller
authors.forename: Manuela
authors.initials: M
authors.lastname: Alonso
authors.forename: Xiaohui
authors.initials: X
authors.lastname: Liao
authors.forename: Vance
authors.initials: V
authors.lastname: Broach
authors.forename: Alexandra
authors.initials: A
authors.lastname: Dumitrescu
authors.forename: Jacqueline
authors.initials: J
authors.lastname: Van Sande
authors.forename: Lucia
authors.initials: L
authors.lastname: Montanelli
authors.forename: Stephen
authors.initials: S
authors.lastname: Skjei
authors.forename: Charles
authors.initials: C
authors.lastname: Goodwin
authors.forename: Helmut
authors.initials: H
authors.lastname: Grasberger
authors.forename: Samuel
authors.initials: S
authors.lastname: Refetoff
authors.forename: Roy E
authors.initials: RE
authors.lastname: Weiss
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D030801:Animals, Genetically Modified; D002417:Cattle; D002874:Chromosome Mapping; D002875:Chromosomes / Q000502:physiology; D025461:Feedback, Physiological / Q000502:physiology*; D007438:Introns; D009994:Osmolar Concentration; D010902:Pituitary Gland / Q000378:metabolism*; D011401:Promoter Regions, Genetic / Q000502:physiology; D012333:RNA, Messenger / Q000378:metabolism; D051381:Rats; D011914:Rats, Inbred BN; D020303:Rats, Inbred Dahl; D011989:Receptors, Thyrotropin / Q000235:genetics / Q000378:metabolism*; D013960:Thyroid Function Tests; D013961:Thyroid Gland / Q000378:metabolism*; D013972:Thyrotropin / Q000235:genetics / Q000494:pharmacology / Q000502:physiology; D037322:Thyrotropin, beta Subunit / Q000235:genetics; D013974:Thyroxine / Q000097:blood
chemical_list: D012333:RNA, Messenger; D011989:Receptors, Thyrotropin; D037322:Thyrotropin, beta Subunit; D013972:Thyrotropin; D013974:Thyroxine