As depicted in Fig. 1F, protein levels of the ER chaperone GRP78 and UPR transcription factor XBP1 were increased as early as 1 week and continue to rise at 2 weeks after ISO infusion (Fig. 1F), suggesting that ISO infusion caused aberrant ER stress in the early phase of cardiac hypertrophy. Here, XBP1 is linked to cardiac hypertrophy.