NADPH oxidase-4 promotes eccentric cardiac hypertrophy in response to volume overload.

Chronic pressure or volume overload induce concentric versus eccentric left ventricular (LV) remodelling, respectively. Previous studies suggest that distinct signalling pathways are involved in these responses. NADPH oxidase-4 (Nox4) is a reactive oxygen species (ROS)-generating enzyme that can limit detrimental cardiac remodelling in response to pressure overload. This study aimed to assess its role in volume overload-induced remodelling.We compared the responses to creation of an aortocaval fistula (Shunt) to induce volume overload in Nox4-null mice (Nox4-/-) versus wild-type (WT) littermates. Induction of Shunt resulted in a significant increase in cardiac Nox4 mRNA and protein levels in WT mice as compared to Sham controls. Nox4-/- mice developed less eccentric LV remodelling than WT mice (echocardiographic relative wall thickness: 0.30 vs 0.27, p < 0.05), with less LV hypertrophy at organ level (increase in LV weight/tibia length ratio of 25% vs 43%, p < 0.01) and cellular level (cardiomyocyte cross-sectional area: 323 µm2 vs 379 μm2, p < 0.01). LV ejection fraction, foetal gene expression, interstitial fibrosis, myocardial capillary density and levels of myocyte apoptosis after Shunt were similar in the two genotypes. Myocardial phospho-Akt levels were increased after induction of Shunt in WT mice whereas levels decreased in Nox4-/- mice (+29% vs -21%, p < 0.05), associated with a higher level of phosphorylation of the S6 ribosomal protein (S6) and the eIF4E-binding protein 1 (4E-BP1) in WT compared to Nox4-/- mice. We identified that Akt activation in cardiac cells is augmented by Nox4 via a Src kinase-dependent inactivation of protein phosphatase 2A (PP2A).Endogenous Nox4 is required for the full development of eccentric cardiac hypertrophy and remodelling during chronic volume overload. Nox4-dependent activation of Akt and its downstream targets S6 and 4E-BP1 may be involved in this effect.Cardiac volume overload resulting, for example, from aortic or mitral regurgitation contributes to the development of heart failure. Its underlying pathophysiology differs from that of cardiac pressure overload. Our study identifies the reactive oxygen species generating enzyme NADPH oxidase-4 (Nox4) as an important regulator of volume overload-induced cardiac remodelling by promoting eccentric LV hypertrophy, an adaptive response to the increased volume. As Nox inhibition is currently being developed as a potential therapeutic approach for several human diseases (e.g. lung fibrosis), our findings highlight the importance of assessing the potential impact on cardiac function in patients with co-existent valvular regurgitation.