Figure 4
T3-stimulated proliferative signaling in neonatal cardiomyocytes requires IGF-1 and T3 receptor-α. (A) Schematic showing the location of two potential Igf1 transcription start sites and the two discriminating primer pairs for quantification of distinct transcripts. mRNA quantification by RT-qPCR of Igf1 transcripts showing that T3 enhances the transcription of Igf1 from the proximal promoter. (B) Representative immunoblot and quantitative analyses of neonatal cardiomyocytes lysate showing that T3 increases IGF-1 formation in a dose dependent manner. (C) Knockdown of TRα, and to a lesser extent TRβ, prevents T3-dependent IGF-1 formation. (D) Representative immunoblot and quantitative analyses of neonatal cardiomyocyte lysate showing that knockdown of IGF-1 with siRNA prevents T3-dependent induction of cyclin D1. Error bars indicate SEM. n = 4 biological replicates/group. n.s., nonsignificant; **P < 0.01, ***P < 0.001, compared to controls.
