Neonatal hyper- and hypothyroidism alter the myoglobin gene expression program in adulthood

Abstract

Myoglobin acts as an oxygen store and a reactive oxygen species acceptor in muscles. We examined myoglobin mRNA in rat cardiac ventricle and skeletal muscles during the first 42 days of life and the impact of transient neonatal hypo- and hyperthyroidism on the myoglobin gene expression pattern. Cardiac ventricle and skeletal muscles of Wistar rats at 7-42 days of life were quickly removed, and myoglobin mRNA was determined by Northern blot analysis. Rats were treated with propylthiouracil (5-10 mg/100 g) and triiodothyronine (0.5-50 µg/100 g) for 5, 15, or 30 days after birth to induce hypo- and hyperthyroidism and euthanized either just after treatment or at 90 days. During postnatal (P) days 7-28, the ventricle myoglobin mRNA remained unchanged, but it gradually increased in skeletal muscle (12-fold). Triiodothyronine treatment, from days P0-P5, increased the skeletal muscle myoglobin mRNA 1.5- to 4.5-fold; a 2.5-fold increase was observed in ventricle muscle, but only when triiodothyronine treatment was extended to day P15. Conversely, hypothyroidism at P5 markedly decreased (60%) ventricular myoglobin mRNA. Moreover, transient hyperthyroidism in the neonatal period increased ventricle myoglobin mRNA (2-fold), and decreased heart rate (5%), fast muscle myoglobin mRNA (30%) and body weight (20%) in adulthood. Transient hypothyroidism in the neonatal period also permanently decreased fast muscle myoglobin mRNA (30%) and body weight (14%). These results indicated that changes in triiodothyronine supply in the neonatal period alter the myoglobin expression program in ventricle and skeletal muscle, leading to specific physiological repercussions and alterations in other parameters in adulthood.

Figure 1. Pattern of Mb mRNA expression in ventricular and skeletal muscles of rats throughout the postnatal developmental period. Northern blot analysis of ventricular and skeletal Mb mRNA levels of intact rats from postnatal (P) day 7 through P42 is shown at the top of the figure, and the quantitative results obtained by densitometric analysis of Mb and 18s rRNA transcripts hybridization ratio are shown at the bottom, in arbitrary units (A.U.). Data are reported as means±SE of 12 animals/group. *P<0.05 and **P<0.01 vs P7, P14, and P28; ^#P<0.01 vs all groups except P21; ⁺P<0.01 vs all groups; ⁺⁺P<0.05 vs P7, P14, and P21 (one-way ANOVA).

Figure 2. Influence of thyroid hormone on the pattern of Mb gene expression in ventricular and skeletal muscles of rats during 5 and 15 days of postnatal developmental. Northern blot analysis of ventricle and skeletal muscles Mb mRNA levels of rats subjected to T₃ or PTU treatment from P0 through P5 (A, B, D, and E) or P15 (C and F) is shown at the top of each panel, and the quantitative results obtained by densitometric analysis of Mb and 18s rRNA transcripts hybridization ratio are shown at the bottom, in arbitrary units (A.U.). The effect of increasing doses of T₃, from P0 to P5, on Mb mRNA expression is shown in A and D, and of the PTU treatment [5 mg = Hypo-5 (I), or 10 mg/100 g BW = Hypo-5 (II)] during the same period, is shown in B and E. Panels C and F show the effect of T₃ (4 µg/100 g BW) and PTU (5 mg/100 g BW) treatment during the first 15 days of postnatal life on Mb mRNA expression. Data are reported as means±SE of 12 animals/group. *P<0.05, **P<0.01 and ***P<0.001 vs control-5 and vs control-15 (one-way ANOVA).

Figure 3. Effect of transient postnatal hyper- and hypothyroidism from postnatal (P) day 0 to P30 on molecular programming of myoglobin gene expression in ventricle (A), soleus (B) and extensorum digitalis longus (EDL) (C) muscles of 90-day-old rats. Northern blot analysis of ventricle, soleus, and EDL Mb mRNA levels of rats subjected to vehicle (control-90), T₃ (4 µg/100 g BW, HyperPNT) and PTU (5 mg/100 g BW, HypoPNT) treatment from P0 through P30, and allowed to grow with no further treatment until 90 days of life, is shown at the top of each panel, and the quantitative results obtained by densitometric analysis of Mb and 18s rRNA transcripts hybridization ratio is shown at the bottom, in arbitrary units (A.U). Data are reported as means±SE of 12 animals/group. *P<0.05 vs control-90 (ANOVA).