NADPH oxidase 4 (NOX4) and the NOX4-related redox signaling are implicated in
cardiac hypertrophy. NOX4 is interrelated with endoplasmic reticulum stress (ERS). Spliced
X-box binding protein 1 (Xbp1s) is a key mediator of ERS while its role in
cardiac hypertrophy is still poorly understood. Recently, receptor interacting
protein kinase 1(RIPK1) has been increasingly reported to be associated with ERS. Therefore, we aimed to test the hypothesis that Xbp1s mediates NOX4-triggered
cardiac hypertrophy via RIPK1 signaling. In the heart tissue of transverse aortic constriction (TAC) rats and in primary cultured neonatal cardiomyocytes(NCMs) treated with angiotensinII(AngII) or
isoproterenol (ISO), NOX4 expression and
reactive oxygen species (ROS) generation, and expression of Xbp1s as well as RIPK1-related phosphorylation of P65 subunit of NF-κB were elevated. Gene silencing of NOX4 by specific
small interfering RNA (
siRNA) significantly blocked the upregulation of NOX4, generation of ROS, splicing of Xbp1 and activation of the RIPK1-related NF-κB signaling, meanwhile attenuated cardiomyocyte
hypertrophy. In addition, ROS scavenger (
N-acetyl-L-cysteine, NAC) and NOX4 inhibitor
GKT137831 reduced ROS generation and alleviated activation of Xbp1 and RIPK1-related NF-κB signaling. Furthermore, splicing of Xbp1 was responsible for the increase in RIPK1 expression in AngII or ISO-treated NCMs. Upregulated RIPK1 in turn activates NF-κB signaling in a
kinase activity-independent manner. These findings suggest that Xbp1s plays an important role in NOX4-triggered cardiomyocyte
hypertrophy via activating its downstream effector RIPK1, which may prove significant for the development of future therapeutic strategies.