Atrial natriuretic peptide gene expression and its secretion by pneumocytes derived from neonatal rat lungs

Expression patterns of natriuretic peptides in pre-hibernating and hibernating anatolian ground squirrel (Spermophilus xanthoprymnus) lung

Anatolian ground squirrel (Spermophilus xanthoprymnus) is a true hibernator. This animal transiently reduces pulmonary function during hibernation. Continuance of pulmonary function is very important to survive ground squirrels during the hibernation. Natriuretic peptides may be key players in the modulation of pulmonary hemostasis. However, NPs' role in pulmonary function during hibernation remains unclear. We aimed to investigate the localization and distribution of atrial natriuretic peptide (ANP), brain natriuretic peptide (BNP) and C-type natriuretic peptide (CNP) in squirrel lungs during pre-hibernation and hibernation periods using immunohistochemistry. Our immunohistochemical data indicate that ANP, BNP, and CNP were produced by the mucosal epithelium of terminal and respiratory bronchioles, smooth muscle cells in the lamina propria of terminal bronchioles and vascular smooth muscle cells, alveolar type II cells, and macrophages. ANP immunoreactivity was weaker than BNP and CNP immunoreactivities in these cells. The results also demonstrate that the number of ANP, BNP and CNP positive alveolar type II cells tended to increase, although statistically non-significant, during the hibernation period, but the expression of NPs in other pulmonary cells is unaffected by hibernation. This study firstly investigates ANP, BNP and CNP distribution in the Anatolian ground squirrel lung. However, further studies are required to dissect their functional roles during the hibernation.

Natriuretic peptide C receptor in the developing sheep lung: role in perinatal transition

Background: At birth, the release of surfactant from alveolar type II cells (ATIIs) is stimulated by increased activity of the beta-adrenergic/adenylyl cyclase/cyclic 3'-5' adenosine monophosphate-signaling cascade. Atrial natriuretic peptide (ANP) stimulates surfactant secretion through natriuretic peptide receptor A (NPR-A). ANP inhibits adenylyl cyclase activity through its binding to NPR-C. We wished to further understand the role of the NPR-C in perinatal transition. Methods: We studied ATII expression of NPR-C in fetal and newborn sheep using immunohistochemistry, and surfactant secretion in isolated ATIIs by measuring ³[H] choline release into the media. Results: ANP induced surfactant secretion, and, at higher doses, it inhibits the stimulatory effect of the secretagogue terbutaline. ATII NPR-C expression decreased significantly after birth. Premature delivery also markedly decreased ANP and NPR-C in ATIIs. Co-incubation of terbutaline (10^-4 M) with ANP (10^-6 M) significantly decreased ³[H] choline release from isolated newborn ATII cells when compared with terbutaline alone; this inhibitory effect was mimicked by the specific NPR-C agonist, C-ANP (10^-10 M). Conclusion: ANP may act as an important epithelial-derived inhibitor of surfactant release in the fetal lung, and downregulation of ANP and NPR-C following birth may sensitize ATII cells to the effects of circulating catecholamines, thus facilitating surfactant secretion.

Health risk assessment for air pollutants: alterations in lung and cardiac gene expression in mice exposed to Milano winter fine particulate matter (PM2.5)

Oxidative stress, pulmonary and systemic inflammation, endothelial cell dysfunction, atherosclerosis and cardiac autonomic dysfunction have been linked to urban particulate matter exposure. The chemical composition of airborne pollutants in Milano is similar to those of other European cities though with a higher PM2.5 fraction. Milano winter fine particles (PM2.5win) are characterized by the presence of nitrate, organic carbon fraction, with high amount of polycyclic aromatic hydrocarbons and elements such as Pb, Al, Zn, V, Fe, Cr and others, with a negligible endotoxin presence. In BALB/c mice, we examined, at biochemical and transcriptomic levels, the adverse effects of repeated Milano PM2.5win exposure in lung and heart. We found that ET-1, Hsp70, Cyp1A1, Cyp1B1 and Hsp-70, HO-1, MPO respectively increased within lung and heart of PM2.5win-treated mice. The PM2.5win exposure had a strong impact on global gene expression of heart tissue (181 up-regulated and 178 down-regulated genes) but a lesser impact on lung tissue (14 up-regulated genes and 43 down-regulated genes). Focusing on modulated genes, in lung we found two- to three-fold changes of those genes related to polycyclic aromatic hydrocarbons exposure and calcium signalling. Within heart the most striking aspect is the twofold to threefold increase in collagen and laminin related genes as well as in genes involved in calcium signaling. The current study extends our previous findings, showing that repeated instillations of PM2.5win trigger systemic adverse effects. PM2.5win thus likely poses an acute threat primarily to susceptible people, such as the elderly and those with unrecognized coronary artery or structural heart disease. The study of genomic responses will improve understanding of disease mechanisms and enable future clinical testing of interventions against the toxic effects of air pollutant.

Ontogeny of atrial natriuretic peptide and its receptor in the lung: effects on perinatal surfactant release

During the transition at birth to air breathing, regulation of surfactant release from alveolar type II (ATII) cells is critical. Atrial natriuretic peptide (ANP) stimulates natriuretic peptide receptor-A (NPR-A) and increases intracellular cGMP. We examined the changes in ANP and NPR-A in respiratory epithelium during the perinatal period using immunohistochemistry and studied the effect of ANP on surfactant release from ATII cells isolated from fetal and newborn lambs. NPR-A mRNA was detected in the fetal lung by Northern Blot and RT-PCR. At 100 d gestation (term 145 d), ANP staining was absent and NPR-A staining was weak in cuboidal epithelial cells. ANP and NPR-A staining was prominent in ATII cells at 136 d gestation and was undetectable postnatally. ANP stimulated (maximal effect at 10(-10)M) surfactant release from both late gestation fetal and neonatal ATII cells. Protein kinase G inhibition significantly blocked this release. We conclude that ANP stimulates surfactant release in isolated perinatal ATII cells by a cGMP-dependent mechanism. ANP and NPR-A expression in ATII cells is greatest in late gestation and declines sharply postnatally. We speculate that increased activity of the ANP/NPR-A pathway in late gestation may prime the surfactant system, preparing the lung for air breathing.

Ectopic expression of active processed form of atrial natriuretic peptide in skeletal myoblasts

Atrial natriuretic peptide (ANP) is a cardiac hormone that elicits a profound diuresis, natriuresis, and hypotension. As a preliminary study toward ANP gene therapy of cardiovascular disorders, we have cloned a cDNA for mouse preproANP and carried out expression studies in muscle cells. The expression cassette, which was flanked by ITRs from AAV-2, consisted of HCMV IE enhancer/promoter, preproANP gene, and polyadenylation signal from bovine growth hormone. We transfected this expression vector into primary skeletal myoblasts and examined the following points: (1) secretion of immunoreactive ANP, (2) biological activity, and (3) nature of secreted ANP(s). The conditioned media from cells transfected with ANP vector had significantly higher levels of irANP in comparison to mock control. The secreted irANP had biological activity as confirmed by the elevated level of intracellular cGMP in human umbilical vein endothelial cells. Reverse-phase HPLC analysis showed that the processed form of ANP was the predominant form. These results demonstrate that preproANP gene could be ectopically expressed and correctly processed in skeletal myoblasts, which has implications for development of muscle-based ANP gene therapy.

Cloning, sequence analysis, tissue-specific expression, and prohormone isolation of Eel atrial natriuretic peptide

A complementary DNA (cDNA) encoding eel atrial natriuretic peptide (ANP) precursor was specifically amplified from eel atrial mRNAs by rapid-amplification polymerase chain reaction. The sequence analysis of the cDNA using multiple clones revealed that the preproANP consists of 140 amino acid residues carrying a signal sequence at its N-terminus and a mature ANP at its C-terminus. An additional glycine residue was attached to the C-terminus of previously isolated eel ANP. The glycine residue may be used for amidation of the C-terminus or removed after processing. The cleavage site of a signal peptide with 22 amino acid residues was confirmed by isolation of proANP protein from eel atria. The proANP sequence deduced from the cDNA was also confirmed for 71% of the isolated protein. Sequence comparison with other natriuretic peptides revealed that eel ANP is more similar to mammalian ANP than to B-type natriuretic peptide (BNP) at both amino acid and nucleotide sequence levels. The eel ANP gene was a single copy gene as shown by Southern blot analysis. Northern blot analysis showed that eel ANP mRNA is approximately 0.8 kb in size and exclusively detected in the atrium. Thus, eel ANP is a true atrial hormone judging from both the sequence and the site of production. However, reverse transcription-polymerase chain reaction detected ANP message in the brain, gill, cardiac ventricle, red body of swim bladder (rete mirabilis), intestine, head kidney (including interrenal and chromaffin tissues) and kidney. Most of these tissues are involved in ion and/or gas exchange in fishes.

Increased production of atrial natriuretic peptide in the rat thymus after irradiation

The rat thymus involutes when exposed to dexamethasone, and this phenomenon is accompanied by a striking increase of ANP localized in thymic macrophages. This study was designed to investigate whether a stimulus, that is X-rays, well known to also cause involution of the thymus, is followed by an elevation of ANP-expression. Rats were irradiated with 4, 6 and 8 Gy, and after 4 days we found a dose-dependent increase (3-, 30- and 40-fold) of mRNA coding for ANP. The corresponding ANP precursor (ANP1-126) has been found elevated 4-, 10-, and 13-fold, respectively. Immunohistochemical analysis of irradiated (6 Gy) tissue revealed heavily IR-ANP positive cells in the cortex, which, due to their morphological and enzyme-histochemical characteristics, were identified as highly phagocytising macrophages. We suggest, thus, that regardless of the stimulus applied (DEX or X-rays) causing the vast cell death in the thymus, the increased ANP-expression is linked to the highly activated phagocytic system of the thymus under these conditions.

Diabetes-induced alterations in atrial natriuretic peptide gene expression in Wistar-Kyoto and spontaneously hypertensive rats

We investigated the effects of streptozotocin-induced diabetes on atrial natriuretic peptide (ANP) synthesis, hemodynamic parameters, blood volume, and histopathology, as well as the reversibility of such effects with insulin therapy in Wistar-Kyoto (WKY) rats and spontaneously hypertensive rats (SHRs). The biatrial ANP messenger RNA (mRNA) levels in the diabetic WKY rats increased by 16-17% compared with those in the age-matched WKY rats at 12 weeks after the onset of diabetes, whereas their ventricular ANP mRNA levels showed increases of 190% in left ventricles and 160% in right ventricles at 8 weeks. In the diabetic SHRs, the left atrial ANP mRNA levels increased by 36% compared with those in the age-matched SHRs, as early as 4 weeks after diabetes onset. Their ventricular ANP mRNA levels also showed 80-82% increases in left and right ventricles at 4 weeks. In proportion to changes in cardiac ANP synthesis, the biventricular end-diastolic pressures were significantly elevated at 8 weeks in the diabetic WKY rats and at 4 weeks in the diabetic SHRs. The blood volume significantly increased at 8 weeks in the diabetic WKY rats and remained higher thereafter, whereas it did not change in the diabetic SHRs throughout the experimental period. The left ventricular peak dP/dt was depressed in the 8-week diabetic SHRs, whereas in the diabetic WKY rats, its depression was observed at 12 weeks after diabetes onset. Histopathological studies showed that diabetic changes in ANP synthesis and hemodynamic parameters described above occurred before the cardiomyopathic histological changes. Cardiac ANP synthesis in the diabetic rats completely reverted to control levels after insulin therapy, accompanied by normalization of hemodynamic parameters. The present study indicates that 1) ANP synthesis is significantly augmented in the streptozotocin-induced diabetic rat compared with that in the normal rat, and the combination of diabetes and hypertension produces an earlier and greater effect in stimulating cardiac ANP synthesis than does either disease alone; 2) an elevation in the intraventricular filling pressure that occurs before observable cardiomyopathic histopathological alterations might be involved partially in the augmented ANP synthesis; and 3) the reversibility with insulin therapy suggests that the streptozotocin-induced alterations observed in cardiac ANP synthesis and hemodynamics result from insulin-deficient diabetes mellitus, not from cardiac toxicity of streptozotocin.

Atrial natriuretic peptide in peripheral organs other than the heart

The heart atria represent the major site of synthesis of atrial natriuretic peptide (ANP) in mammals including man, and its function as a regulator of water and salt homeostasis has been repeatedly suggested. However, more recently ANP has been located in organs not intimately related to cardiovascular physiology, e.g. the adrenals, lungs, and gut, as well as tissues belonging to the lymphatic, reproductive or endocrine systems. Thus, ANP might serve many more physiological roles than originally thought, but the functional significance of ANP in these non-cardiac tissues is presently poorly understood.

Changes of atrial natriuretic peptide and its messenger RNA with development and regression of cardiac hypertrophy in renovascular hypertensive rats

We assessed the changes in atrial natriuretic peptide (ANP) and its messenger RNA (mRNA) levels in atria and ventricles in relation to hemodynamic factors during antihypertensive treatments in two-kidney, one-clip renovascular hypertensive rats (RHRs). Hypertension of 10-week duration caused a twofold increase in the left ventricular weight/body weight ratio, a significant increase in left ventricular end-diastolic pressure, and an eightfold increase in left ventricular ANP mRNA levels in RHRs, as compared with the levels in control rats. Uninephrectomy or 4 weeks of treatment with the converting enzyme inhibitor enalapril reduced the blood pressure to the control level, with the complete reversal of left ventricular hypertrophy, left ventricular end-diastolic pressure, and ANP mRNA levels. Four weeks of treatment with the arterial vasodilator hydralazine significantly, but not completely, reduced the high blood pressure, but it did not influence left ventricular hypertrophy, end-diastolic pressure, and ANP mRNA levels. The increased ANP synthesis observed in the right ventricles of RHRs also reverted to the control level by uninephrectomy or enalapril treatment, but not by hydralazine, with a time course similar to that of left ventricular ANP. In addition, uninephrectomy caused the left and right ventricular ANP and ANP mRNA levels of RHRs to fall to the levels of control rats as early as 1 week, despite persistent left ventricular hypertrophy.(ABSTRACT TRUNCATED AT 250 WORDS)