NADPH oxidase 4 as a source of hydrogen peroxide can regulate norepinephrine levels and vascular contraction

The adrenal glands play a pivotal role in maintaining physiological homeostasis, and disturbance in their function can lead to significant clinical disorders, including hypertension, and adrenal insufficiency. Reactive oxygen species (ROS), once considered merely byproducts of cellular metabolism, are now recognized as critical signaling molecules within the adrenal cortex and medulla. Among the major enzymatic sources of ROS are NADPH oxidases (Nox). Dysregulation of Nox-derived ROS has been linked to altered steroidogenesis, oxidative stress- mediated adrenal damage, and tumorigenic processes. We aimed to elucidate the role of Nox4 on adrenal function under healthy conditions.

Using Nox4-knockout mouse model, adrenal effects were assessed by histological analysis, real-time PCR, and cathecholamine quantification using HPLC-ECD and LC-MS/MS. Cardiovascular function was evaluated by echocardiography, blood pressure measurements, and ex vivo vascular function analysis.

Here, we demonstrated that Nox4 is expressed in the mouse adrenal gland, and its deletion led to decreased hydrogen peroxide production, diminished dopamine beta-hydroxylase mRNA expression, and reduced norepinephrine levels. In chromaffin cells, treatment with hydrogen peroxide stimulated catecholamine release and increased dopamine beta-hydroxylase expression, indicating a regulatory role of hydrogen peroxide in catecholamine synthesis and secretion. Further analysis of the physiological consequences of reduced norepinephrine levels in Nox4^-/- mice revealed decreased alpha-1 adrenergic receptor expression and impaired adrenergic vascular contraction, while cardiac function remained unaffected. In a model of physical activity, Nox4 depletion resulted in smaller adrenal glands and lower urinary norepinephrine concentrations, further explaining diminished physical activity of Nox4^-/- mice.

Our findings provide evidence that Nox4-derived H₂O₂ plays a role in norepinephrine release and norepinephrine-mediated functions. Hence, loss of Nox4 impairs vascular contractility and reduces physical activity performance, highlighting the physiological importance of Nox4 in adrenal function.