Peroxisome proliferator-activated receptor γ is essential for secretion of ANP induced by prostaglandin D2 in the beating rat atrium

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production, and the upregulation of NOX4 and CAT expressions was augmented but the SOD expression induced by CCK-8s was repealed.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.

Comparison of ANP and BNP Granular Density in Atria of Rats After Physiological and Pathological Hypertrophy

Atrial natriuretic peptide (ANP) and brain natriuretic peptide (BNP) are cardiac hormones located in atria granules. Both peptides respond to cardiac pressure and volume dynamics and accordingly serve as translation biomarkers for the clinical treatment of heart failure. Serum ANP and BNP play central secretary roles in blood pressure and cardiac output regulation and have proven utility as differential biomarkers of cardiovascular proficiency and drug-induced maladaptation, yet both peptides are impervious to exercise-induced hypertrophy. We employed immunoelectron microscopy to examine the effects of 28 days of chronic swim exercise or administration of a PPARγ agonist on atrial granules and their stored natriuretic peptides in Sprague Dawley rats. Chronic swimming and drug treatment both resulted in a 15% increase in heart weight compared with controls, with no treatment effects on perinuclear granule area in the left atria (LAs). Drug treatment resulted in larger size granules with greater BNP density in the right atria. Comparing swimming and PPARγ agonist treatment effects on ANP:BNP granule density ratios between atrial chambers revealed a shift toward a greater proportion of ANP than BNP in LAs of swim-trained rats. These data suggest a distinction in the population of ANP and BNP after chronic swim or PPARγ that makes it a novel metric for the differentiation of pathological and physiological hypertrophy.

Endogenous ET-1 promotes ANP secretion through activation of COX2-L-PGDS-PPARγ signaling in hypoxic beating rat atria

Endothelin-1 (ET-1) is a potent stimulus for the secretion of atrial natriuretic peptide (ANP) and hypoxia stimulates the release of ET-1, which is involved in the regulation of atrial ANP secretion. However, the precise mechanism of endogenous ET-1 in the regulation of hypoxia-induced ANP secretion is unclear. Therefore, this study aimed to investigate the mechanism of hypoxia-induced endogenous ET-1 regulation of ANP secretion in isolated perfused hypoxic beating rat atria. The results of this study showed that acute hypoxia significantly stimulated ET-1 release and upregulated the expression of its type A as well as type B receptors (ETA and ETB receptors). Endogenous ET-1 induced by hypoxia markedly upregulated the expression of cyclooxygenase 2 (COX2) through activation of its two receptors, leading to an increase in lipocalin-type prostaglandin D synthase (L-PGDS) expression and prostaglandin D2 (PGD2) production. L-PGDS-derived PGD2 activated peroxisome proliferator-activated receptor γ (PPARγ), ultimately promoting hypoxia-induced ANP secretion. Conversely, L-PGDS-derived PGD2 may in turn regulate L-PGDS expression by a nuclear factor erythroid-2-related factor 2 (NRF2)-mediated feedback mechanism. These results indicate that endogenous ET-1 induced by hypoxia promotes hypoxia-induced ANP secretion by activation of COX2-L-PGDS-PPARγ signaling in beating rat atria. In addition, the positive feedback loop between L-PGDS-derived PGD2 and L-PGDS expression induced by hypoxia is part of the mechanism of hypoxia-induced ANP secretion by endogenous ET-1.

Prostaglandin FP receptor antagonists: discovery, pharmacological characterization and therapeutic utility

In contrast to the availability of potent and selective antagonists of several prostaglandin receptor types (including DP₁ , DP₂ , EP and TP receptors), there has been a paucity of well-characterized, selective FP receptor antagonists. The earliest ones included dimethyl amide and dimethyl amine derivatives of PGF_2α , but these have failed to gain prominence. The fluorinated PGF_2α analogues, AL-8810 and AL-3138, were subsequently discovered as competitive and non-competitive FP receptor antagonists respectively. Non-prostanoid structures, such as the thiazolidinone AS604872, the D-amino acid-based oligopeptide PDC31 and its peptidomimic analogue PDC113.824 came next, but the latter two are allosteric inhibitors of FP receptor signalling. AL-8810 has a sub-micromolar in vitro potency and ≥2 log unit selectivity against most other PG receptors when tested in several cell- and tissue-based functional assays. Additionally, AL-8810 has demonstrated therapeutic efficacy as an FP receptor antagonist in animal models of stroke, traumatic brain injury, multiple sclerosis, allodynia and endometriosis. Consequently, it appears that AL-8810 has become the FP receptor antagonist of choice. LINKED ARTICLES: This article is part of a themed section on Eicosanoids 35 years from the 1982 Nobel: where are we now? To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v176.8/issuetoc.

HIF-1α-l-PGDS-PPARγ regulates hypoxia-induced ANP secretion in beating rat atria

Lipocalin-type prostaglandin D synthase (L-PGDS) and peroxisome proliferator activated receptor γ (PPARγ) play important roles in cardiovascular diseases. Nevertheless, effects of hypoxia-inducible factor 1α (HIF-1α) on L-PGDS and PPARγ protein levels and its role in hypoxia-induced atrial natriuretic peptide (ANP) secretion are unclear. In perfused beating rat atria, we observed that hypoxia significantly increased HIF-1α protein levels and stimulated ANP secretion, while upregulating L-PGDS. Hypoxia-induced ANP secretion was clearly attenuated by HIF-1α antagonist 2-methoxyestradiol, downregulating both HIF-1α and L-PGDS protein levels. It was also attenuated by L-PGDS antagonists, AT-56 and HQL-49, downregulating L-PGDS protein levels. In addition, hypoxia-induced ANP secretion was accompanied by increased PPARγ protein levels and was strongly attenuated by PPARγ antagonist GW9662. Hypoxia-induced increase in atrial PPARγ protein levels were dramatically inhibited by both 2-methoxyestradiol and AT-56. These results indicated that hypoxia promotes ANP secretion, at least in part, by activating HIF-1α-l-PGDS-PPARγ signaling in beating rat atria.