NOX4/Src regulates ANP secretion through activating ERK1/2 and Akt/GATA4 signaling in beating rat hypoxic atria

Cholecystokinin regulates atrial natriuretic peptide secretion through activation of NOX4-Sirt1-LEF1 signaling in beating rat hypoxic atria

The mammalian cardiac myocytes not only synthesize and secrete atrial natriuretic peptide (ANP), but also express cholecystokinin (CCK) and its receptors (CCK1R and CCK2R). However, atrial CCK expression patterns and its effects on ANP secretion during hypoxia are unclear. Therefore, this study is aimed to investigate the effect of hypoxia on the expression levels of CCK and its receptors, as well as the underlying mechanisms involved in regulating hypoxia-induced ANP secretion in isolated beating atria. The results of this study showed that acute hypoxia significantly upregulated expression of CCK and CCK1R as well as CCK2R through activation of hypoxia-inducible factor 1α-apelin signaling. Endogenous CCK induced by hypoxia markedly upregulated the expression of silent information regulator factor 2-related enzyme 1 (Sirt1) and its downstream nuclear factor erythroid‑2‑related factor 2 (Nrf2) via the activation of nicotinamide adenine dinucleotide phosphate oxidase 4 (NOX4), leading to increase of activating T cell factor (TCF) 3 and TCF4/ lymphoid enhancer factor (LEF) 1, ultimately promoting hypoxia-induced ANP secretion. In addition, siRNA-mediated knockdown of LEF1 dramatically attenuated hypoxia-induced increase of ANP expression in HL-1 atrial myocytes. These results indicated endogenous CCK induced by hypoxia promoted hypoxia-induced ANP secretion by activation of NOX4-Sirt1-TCF3/4-LEF1 signaling pathway.

Modulation of NOX2 causes obesity-mediated atrial fibrillation

Obesity is linked to an increased risk of atrial fibrillation (AF) via increased oxidative stress. While NADPH oxidase 2 (NOX2), a major source of oxidative stress and reactive oxygen species (ROS) in the heart, predisposes to AF, the underlying mechanisms remain unclear. Here, we studied NOX2-mediated ROS production in obesity-mediated AF using Nox2-knockout mice and mature human induced pluripotent stem cell-derived atrial cardiomyocytes (hiPSC-aCMs). Diet-induced obesity (DIO) mice and hiPSC-aCMs treated with palmitic acid (PA) were infused with a NOX blocker (apocynin) and a NOX2-specific inhibitor, respectively. We showed that NOX2 inhibition normalized atrial action potential duration and abrogated obesity-mediated ion channel remodeling with reduced AF burden. Unbiased transcriptomics analysis revealed that NOX2 mediates atrial remodeling in obesity-mediated AF in DIO mice, PA-treated hiPSC-aCMs, and human atrial tissue from obese individuals by upregulation of paired-like homeodomain transcription factor 2 (PITX2). Furthermore, hiPSC-aCMs treated with hydrogen peroxide, a NOX2 surrogate, displayed increased PITX2 expression, establishing a mechanistic link between increased NOX2-mediated ROS production and modulation of PITX2. Our findings offer insights into possible mechanisms through which obesity triggers AF and support NOX2 inhibition as a potential novel prophylactic or adjunctive therapy for patients with obesity-mediated AF.

Cholecystokinin Octapeptide Promotes ANP Secretion through Activation of NOX4-PGC-1α-PPARα/PPARγ Signaling in Isolated Beating Rat Atria

Atrial natriuretic peptide (ANP), a canonical cardiac hormone, is mainly secreted from atrial myocytes and is involved in the regulation of body fluid, blood pressure homeostasis, and antioxidants. Cholecystokinin (CCK) is also found in cardiomyocytes as a novel cardiac hormone and induces multiple cardiovascular regulations. However, the direct role of CCK on the atrial mechanical dynamics and ANP secretion is unclear. The current study was to investigate the effect of CCK octapeptide (CCK-8) on the regulation of atrial dynamics and ANP secretion. Experiments were performed in isolated perfused beating rat atria. ANP was measured using radioimmunoassay. The levels of hydrogen peroxide (H₂O₂) and arachidonic acid (AA) were determined using ELISA Kits. The levels of relative proteins and mRNA were detected by Western blot and RT-qPCR. The results showed that sulfated CCK-8 (CCK-8s) rather than desulfated CCK-8 increased the levels of phosphorylated cytosolic phospholipase A2 and AA release through activation of CCK receptors. This led to the upregulation of NADPH oxidase 4 (NOX4) expression levels and H₂O₂ production and played a negative inotropic effect on atrial mechanical dynamics via activation of ATP-sensitive potassium channels and large-conductance calcium-activated potassium channels. In addition, CCK-8s-induced NOX4 subsequently upregulated peroxisome proliferator-activated receptor γ (PPARγ) coactivator-1α (PGC-1α) expression levels through activation of p38 mitogen-activated protein kinase as well as the serine/threonine kinase signaling, ultimately promoting the secretion of ANP via activation of PPARα and PPARγ. In the presence of the ANP receptor inhibitor, the CCK-8-induced increase of AA release, H₂O₂ production, and the upregulation of NOX4 and CAT expressions was augmented but the SOD expression induced by CCK-8s was repealed. These findings indicate that CCK-8s promotes the secretion of ANP through activation of NOX4-PGC-1α-PPARα/PPARγ signaling, in which ANP is involved in resistance for NOX4 expression and ROS production and regulation of SOD expression.

NOX4 stimulates ANF secretion via activation of the Sirt1/Nrf2/ATF3/4 axis in hypoxic beating rat atria

Silent information regulator factor 2-related enzyme 1 (Sirt1) is involved in the regulation of cell senescence, gene transcription, energy balance and oxidative stress. However, the effect of Sirt1 on atrial natriuretic factor (ANF) secretion, especially under hypoxic conditions is unclear. The present study aimed to investigate the effect of Sirt1, regulated by NADPH oxidase 4 (NOX4), on ANF secretion in isolated beating rat atria during hypoxia. ANF secretion was analyzed using radioimmunoassays and protein expression levels were determined by western blotting and immunofluorescence staining. Intra-atrial pressure was recorded using a physiograph. Hypoxia significantly upregulated Sirt1 and nuclear factor erythroid-2-related factor 2 (Nrf2) protein expression levels, together with significantly increased ANF secretion. Hypoxia-induced protein expression of Sirt1 was significantly blocked by a NOX4 inhibitor, GLX351322, and Nrf2 protein expression levels were significantly abolished using the Sirt1 inhibitor, EX527. Hypoxia also significantly elevated the protein expression levels of phosphorylated-Akt and sequestosome 1 and significantly downregulated Kelch-like ECH-associated protein 1 protein expression levels. These effects were significantly blocked by EX527, preventing hypoxia-induced Nrf2 expression. An Nrf2 inhibitor, ML385, significantly abolished the hypoxia-induced upregulation of activating transcription factor (ATF)3, ATF4, T cell factor (TCF)3 and TCF4/lymphoid enhancer factor 1 (LEF1) protein expression levels, and significantly attenuated hypoxia-induced ANF secretion. These results indicated that Sirt1 and Nrf2, regulated by NOX4, can potentially stimulate TCF3 and TCF4/LEF1 signaling via ATF3 and ATF4 activation, thereby potentially participating in the regulation of ANF secretion in beating rat atria during hypoxia. In conclusion, intervening with the Sirt1/Nrf2/ATF signaling pathway may be an effective strategy for resisting oxidative stress damage in the heart during hypoxia.