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Thyroid hormone upregulates MDM 2 in rat type I fibre: Implications for skeletal muscle mass regulation
Author(s) -
Ramos G. V.,
Cruz A.,
Silva W. J.,
Rozanski A.,
Baptista I. L.,
Silvestre J. G.,
Moriscot A. S.
Publication year - 2018
Publication title -
acta physiologica
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.591
H-Index - 116
eISSN - 1748-1716
pISSN - 1748-1708
DOI - 10.1111/apha.13003
Subject(s) - myogenesis , skeletal muscle , triiodothyronine , downregulation and upregulation , endocrinology , medicine , chemistry , messenger rna , thyroid , gene expression , stimulation , c2c12 , biology , gene , biochemistry
Aim Based upon a microarray assay, we have identified that triiodothyronine (T3) upregulates MDM 2 gene expression in the rat skeletal muscle. As MDM 2 protein is an E3 ligase, we hypothesized that this enzyme could play a role in T3 effects on skeletal muscle mass control. Methods To test our hypothesis, male rats (2 months old) were randomly assigned into the following groups: intact controls, treated with 20 physiological doses of T3 for 0.5, 1 and 7 days, or with 5, 20 and 50 physiological doses of T3 for 7 days. For in vitro experiments, myotubes and C2C12 cells were treated with T3 for 3 days. Results After validation of the microarray finding throughout RT ‐ PCR and confirmation that T3 induces increases in MDM 2 protein expression in a dose‐dependent manner, we observed that MDM 2 was upregulated by T3 exclusively in fibre type I. Moreover, detailed histological evaluation showed that MDM 2 overexpression distributes punctiformily along the cross section of the fibre and also inside nuclei. MDM 2 colocalizes with PAX 7 in control muscle and T3 downregulates this myogenic factor. Pharmacological inhibition of MDM 2 in cultured myotubes caused a severe decrease in their diameter (~35%, P < .001 vs Control), enhancing the effect of T3 (from ~12% to ~35%, P < .001) alone upon myotube diameter and mRNA levels of atrogenes. Finally, we observed that FOXO 3 ( MDM 2 target) is kept outside the nucleus under T3 stimulation. Conclusion Our results indicate that MDM 2 might be involved in the pro‐trophic effects of T3 in skeletal muscle.