| Summary: | O objetivo deste estudo foi investigar os efeitos do T3 e do seu análogo GC-24, agonista TR<font face=\"symbol\">b seletivo, na proteólise muscular mediada pela via ubiquitina-proteassoma. Avaliamos o efeito do T3 e GC-24 no trofismo radial de fibras musculares, no nível de ubiquitinação e na expressão de genes envolvidos na via ubiquitina-proteassoma. Para tanto foram utilizados, ratos Wistar divididos em 4 grupos (Controle, 12 horas, 1 e 7 dias) e tratados com T3 e GC-24. Determinou-se a área de secção transversa dos cortes histológicos através do programa \"Image Pro-Plus\". O nível de ubiquitinação foi determinado através de Western Blot para proteína ubiquitinada e a expressão gênica por PCR em Tempo real. T3 e GC-24 promoveram redução do diâmetro das fibras musculares e aumentaram o nível de proteínas ubiquitinadas em ambos os músculos. Com relação à expressão gênica, T3 e GC-24 modularam a expressão dos genes analisados de maneira diferenciada, demonstrando que GC-24 é capaz de modular genes pouco ou não responsivos ao T3.
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Triiodothyronine (T3) is known to play a key role in the function of several tissues/organs via the thyroid hormone receptor isoforms a/pha (TRa) and beta (TRI3). Abnormalities in skeletal muscle function have been associated with increased leveis of T3, which is a major sarcopenia (Ioss of sarcomeres). Although the phenomenon of sarcopenia induced by T3 has been widely reported, little is known about the molecular mechanisms invo/ved in proteolysis induced by T3. In this study we have investigated the effects of T3 and GC-24, a novel synthetic TRI3¬selective compound, on the ubiquitin proteasome pathway. We analyzed the effect of T3 and GC-24 on the radial trophism, ubiquitination leveis and gene expression of the ubiquitin-proteasome pathway, which are important regulators of muscle proteolysis in the skeletal muscle. We have addressed the ubiquitin ligases (Atrogin¬1, MuRF-1 and E3a) and the deubiquitinating enzymes (UBP45, UBP69 and USP28). Wistar male rats (170-200g) were divided in 4 groups (Control, 12, 1 and 7 days). Rats received T3 (30l-\'g/100g) and GC-24 (16 I-\'g/1 OOg). After decapitation, EDL and soleus muscles were removed for histological ana/ysis, protein expression and gene expression. Cross sectional area was determined in histological sections through the software \"Image-Pro Plus. The ubiquitination leveis was determined by Western Blot and gene expression determined by Real Time PCR analysis. T3 and GC-24 reduced the diameter of the muscle fibers vs control group. Both T3 and GC-24 incresed the ubiquitination leveis, in the soleus and EDL. Regarding gene expression analysis, T3 and GC-24 modulate the gene expression in a differential manner. In the soleus, T3 increased Atrogin-1 and E3 alpha gene expression, while did not alter Murf-1 gene expression. On the other hand, in EDL Atrogin-1 gene expression is not altered, while E3 alpha and Murf-1 are elevated by T3. In the soleus and EDL deubiquitinating gene expression is mostly not altered, exception made for UBP 45, which is reduced by T3 in soleus muscle. GC-24, increased gene expression of E3a and MuRF-1 in the soleus, while did not alter Atrogin-1 gene expression. However, in EDL muscle, GC-24 increased Atrogin-1 and E3a mRNA, while did not alter MuRF-1. Finally, GC-24 decreased UBP 45 gene expression in EDL muscle and USP 28 gene expression was robustly elevated by GC-24 in both muscles analyzed. This data shows that GC-24 is able to strongly modulate genes that are less responsive or even unresponsive to T3, pointing that the GC-24-TRb complex might trans-activate differently target genes. However, both T3 and GC-24 are able to modulate the muscle proteolysis.
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