title: M-protein is down-regulated in cardiac hypertrophy driven by thyroid hormone in rats.
abstract: Although it is well known that the thyroid hormone (T3) is an important positive regulator of cardiac function over a short term and that it also promotes deleterious effects over a long term, the molecular mechanisms for such effects are not yet well understood. Because most alterations in cardiac function are associated with changes in sarcomeric machinery, the present work was undertaken to find novel sarcomeric hot spots driven by T3 in the heart. A microarray analysis indicated that the M-band is a major hot spot, and the structural sarcomeric gene coding for the M-protein is severely down-regulated by T3. Real-time quantitative PCR-based measurements confirmed that T3 (1, 5, 50, and 100 physiological doses for 2 days) sharply decreased the M-protein gene and protein expression in vivo in a dose-dependent manner. Furthermore, the M-protein gene expression was elevated 3.4-fold in hypothyroid rats. Accordingly, T3 was able to rapidly and strongly reduce the M-protein gene expression in neonatal cardiomyocytes. Deletions at the M-protein promoter and bioinformatics approach suggested an area responsive to T3, which was confirmed by chromatin immunoprecipitation assay. Functional assays in cultured neonatal cardiomyocytes revealed that depletion of M-protein (by small interfering RNA) drives a severe decrease in speed of contraction. Interestingly, mRNA and protein levels of other M-band components, myomesin and embryonic-heart myomesin, were not altered by T3. We concluded that the M-protein expression is strongly and rapidly repressed by T3 in cardiomyocytes, which represents an important aspect for the basis of T3-dependent sarcomeric deleterious effects in the heart.
authors.affiliation: Department of Anatomy, Institute of Biomedical Sciences, University of São Paulo, 2415 Lineu Prestes Av ICB 3, Cidade Universitária, CEP 05508-900, São Paulo, Brazil. moriscot@usp.br.
authors.forename: Andrei
authors.initials: A
authors.lastname: Rozanski
authors.forename: Ana Paula C
authors.initials: AP
authors.lastname: Takano
authors.forename: Patricia N
authors.initials: PN
authors.lastname: Kato
authors.forename: Antonio G
authors.initials: AG
authors.lastname: Soares
authors.forename: Camilo
authors.initials: C
authors.lastname: Lellis-Santos
authors.forename: Juliane Cruz
authors.initials: JC
authors.lastname: Campos
authors.forename: Julio Cesar Batista
authors.initials: JC
authors.lastname: Ferreira
authors.forename: Maria Luiza M
authors.initials: ML
authors.lastname: Barreto-Chaves
authors.forename: Anselmo S
authors.initials: AS
authors.lastname: Moriscot
mesh_terms: D000818:Animals; D000831:Animals, Newborn; D001483:Base Sequence; D006332:Cardiomegaly / Q000209:etiology / Q000235:genetics* / Q000503:physiopathology; D002460:Cell Line; D002478:Cells, Cultured; D064211:Connectin / Q000235:genetics* / Q000378:metabolism; D015536:Down-Regulation / Q000187:drug effects / Q000235:genetics*; D007037:Hypothyroidism / Q000235:genetics; D008297:Male; D051379:Mice; D008969:Molecular Sequence Data; D009200:Myocardial Contraction / Q000187:drug effects / Q000235:genetics; D032383:Myocytes, Cardiac / Q000187:drug effects / Q000378:metabolism; D020411:Oligonucleotide Array Sequence Analysis; D011401:Promoter Regions, Genetic / Q000235:genetics; D011485:Protein Binding / Q000187:drug effects / Q000235:genetics; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D051381:Rats; D017208:Rats, Wistar; D011988:Receptors, Thyroid Hormone / Q000378:metabolism; D012518:Sarcomeres / Q000378:metabolism; D013963:Thyroid Hormones / Q000494:pharmacology*; D013971:Thyrotoxicosis / Q000150:complications; D014284:Triiodothyronine / Q000494:pharmacology; D015854:Up-Regulation / Q000187:drug effects / Q000235:genetics
chemical_list: D064211:Connectin; C577289:Myom2 protein, rat; D012333:RNA, Messenger; D011988:Receptors, Thyroid Hormone; D013963:Thyroid Hormones; D014284:Triiodothyronine