Positive feedback of hepatic angiotensinogen expression in silver sea bream (Sparus sarba)

Investigating the RAS can be a fishy business: interdisciplinary opportunities using Zebrafish

The renin-angiotensin system (RAS) is highly conserved, and components of the RAS are present in all vertebrates to some degree. Although the RAS has been studied since the discovery of renin, its biological role continues to broaden with the identification and characterization of new peptides. The evolutionarily distant zebrafish is a remarkable model for studying the kidney due to its genetic tractability and accessibility for in vivo imaging. The zebrafish pronephros is an especially useful kidney model due to its structural simplicity yet complex functionality, including capacity for glomerular and tubular filtration. Both the pronephros and mesonephros contain renin-expressing perivascular cells, which respond to RAS inhibition, making the zebrafish an excellent model for studying the RAS. This review summarizes the physiological and genetic tools currently available for studying the zebrafish kidney with regards to functionality of the RAS, using novel imaging techniques such as SPIM microscopy coupled with targeted single cell ablation and synthesis of vasoactive RAS peptides.

Changes in plasma angiotensin subtypes in Japanese eel acclimated to various salinities from deionized water to double-strength seawater

Our knowledge of complexity of the renin-angiotensin system (RAS) has grown in recent years and various angiotensin peptides including Ang II, Ang III, Ang IV, and Ang (1-7) were found to have specific functions. Using a combination of HPLC and radioimmunoassay (RIA), we established a high resolution method to quantify various angiotensin subtypes in the plasma of eel acclimated to deionized water (dW), freshwater (FW), seawater (SW), and double-strength seawater (DSW). [Asn(1), Val(5)]-Ang II, [Asp(1), Val(5)]-Ang II, [Val(4)]-Ang III, and [Val(3)]-Ang IV are all present in the circulation and both Ang II subtypes were significantly higher in DSW eel. When the eel was transferred from FW to SW, plasma immunoreactive (ir) Ang II concentration increased and its levels were highly correlated to plasma osmolality, suggesting that the elevated plasma osmolality is the major stimulus for activating the RAS during high salinity transfer. To examine the conversion of [Asn(1)] to [Asp(1)] residue in vivo and in vitro, synthetic [Asn(1), Val(5)]-Ang II was injected into the circulation or incubated with plasma, but the production of [Asp(1), Val(5)]-Ang II was insignificant, which implies that the conversion may occur at the angiotensinogen level. An asparaginase assay was further developed for measuring asparaginase activity and the highest activity was in liver in both FW and SW eel. This new method of analysis can be extended to study the endogenous angiotensin ligands in the local RAS. The potential significance of [Asn(1)] to [Asp(1)] conversion on Ang II metabolism and function is discussed.

A teleostean angiotensinogen from Oplegnathus fasciatus responses to immune and injury challenges

Angiotensinogen (AGT) is the precursor of the renin-angiotensin system and contributes to osmoregulation, acute-phase and immune responses. A full-length cDNA of the AGT (2004 bp with a 1389 bp coding region) was isolated from rock bream (Rb), Oplegnathus fasciatus. The encoded polypeptide of 463 amino acids had a predicted molecular mass of 51.6 kDa. RbAGT possessed a deduced signal peptide of 22 residues upstream of a putative angiotensin I sequence ((23)NRVYVHPFHL(32)). RbAGT possessed a specific domain profile and a signature motif which are characteristics of the serpin family. Sequence homology and phylogenetic analysis indicated that RbAGT was evolutionarily closest to AGT of Rhabdosargus sarba. The mRNA expression profile of RbAGT was determined by quantitative RT-PCR and it demonstrated a constitutive and tissue-specific expression with the highest transcript level in the liver. Significantly up-regulated RbAGT expression was elicited by systemic injection of a lipopolysaccharide, rock bream iridovirus (RBIV) and bacteria (Edwardsiella tarda and Streptococcus iniae), revealing its pathogen inducibility. RbAGT manifested a down-regulated response to systemic injury, contemporaneously with two other serpins, protease nexin-1 (PN-1), and heparin cofactor II (HCII). In addition, a synchronized expression pattern was elicited by RbAGT and RbTNF-α in response to injury, suggesting that TNF-α might be a potential modulator of AGT transcription.

One-week antihypertensive effect of Ile-Gln-Pro in spontaneously hypertensive rats

The antihypertensive effect of an angiotensin I-converting enzyme (ACE) inhibitory peptide Ile-Gln-Pro (IQP), whose sequence was derived from Spirulina platensis , was investigated in spontaneously hypertensive rats (SHRs) for 1 week. The weighted systolic blood pressure (SBP) and diastolic blood pressure (DBP) of the peptide IQP-treated group were significantly lower than those of the negative control group from the third and fourth days, respectively. Accompanying the blood pressure reduction, a significant regulation of the expression of major components of the renin-angiotensin system (RAS) was found in the treatment group, including downregulation of the mRNA levels of renin, ACE, and the angiotensin II type 1 (AT1) receptor in the kidney, as well as serum angiotensinogen (Ang), ACE, and angiotensin II (Ang II) concentrations. The treatment group also showed upregulation of mRNA expression of the angiotensin II type 2 (AT2) receptor in the kidney. Our findings suggested that IQP might be of potential use in the treatment of hypertension.

Gene expression responses in male fathead minnows exposed to binary mixtures of an estrogen and antiestrogen

Background

Aquatic organisms are continuously exposed to complex mixtures of chemicals, many of which can interfere with their endocrine system, resulting in impaired reproduction, development or survival, among others. In order to analyze the effects and mechanisms of action of estrogen/anti-estrogen mixtures, we exposed male fathead minnows (Pimephales promelas) for 48 hours via the water to 2, 5, 10, and 50 ng 17α-ethinylestradiol (EE₂)/L, 100 ng ZM 189,154/L (a potent antiestrogen known to block activity of estrogen receptors) or mixtures of 5 or 50 ng EE₂/L with 100 ng ZM 189,154/L. We analyzed gene expression changes in the gonad, as well as hormone and vitellogenin plasma levels.

Results

Steroidogenesis was down-regulated by EE₂ as reflected by the reduced plasma levels of testosterone in the exposed fish and down-regulation of genes in the steroidogenic pathway. Microarray analysis of testis of fathead minnows treated with 5 ng EE₂/L or with the mixture of 5 ng EE₂/L and 100 ng ZM 189,154/L indicated that some of the genes whose expression was changed by EE₂ were blocked by ZM 189,154, while others were either not blocked or enhanced by the mixture, generating two distinct expression patterns. Gene ontology and pathway analysis programs were used to determine categories of genes for each expression pattern.

Conclusion

Our results suggest that response to estrogens occurs via multiple mechanisms, including canonical binding to soluble estrogen receptors, membrane estrogen receptors, and other mechanisms that are not blocked by pure antiestrogens.

Identification of angiotensinogen genes with unique and variable angiotensin sequences in chondrichthyans

The renin-angiotensin system is an enzyme-linked hormonal cascade that plays an important role in body fluid and cardiovascular regulation. The system is initiated by the action of renin on the precursor protein, angiotensinogen (AGT), whose sequence information is scarce because of its high variability among species. In the present study, we cloned AGT in chondrichthyans (elasmobranchs: Triakis scyllium, Dasyatis akajei,Leucoraja erinacea and a holocephalan: Callorhinchus milii). Homology was low among AGTs thus far identified; 25-28% between elasmobranchs and tetrapods and 33-61% even within chondrichthyans. All chondrichthyan angiotensin (ANG) II's have a unique Pro3 instead of Val3 as seen in all other species. In addition, holocephalan ANG II has an unusual His4 instead of Tyr4. In addition, and the N-terminal amino acid, which is usually Asp1 in tetrapods and Asn1 in fishes, was highly variable (Asp, Asn or Tyr) in chondrichthyans. Molecular phylogenetic analysis showed that chondrichthyan AGT precursors are clustered into a group separated from those of tetrapods and teleosts. The AGT gene was most abundantly expressed in the liver, followed by the kidney, interrenal tissue and rectal gland of Triakis where biological actions of ANG II have been demonstrated. Collectively, we identified diversified AGT genes for the first time in chondrichthyes and showed that their ANG II's have unique amino acid residues at positions 1, 3 and 4. High variability of ANG II sequences in chondrichthyans is discussed in relation to their unique regulatory mechanisms such as urea-based osmoregulation.

Losartan, an Angiotensin type I receptor, restores erectile function by downregulation of cavernous renin-angiotensin system in streptozocin-induced diabetic rats

INTRODUCTION

The high incidence of erectile dysfunction (ED) in diabetes highlights the need for good treatment strategies. Recent evidence indicates that blockade of the angiotensin type I receptor (AT1) may reverse ED from various diseases.

AIM

To explore the role of cavernous renin-angiotensin system (RAS) in the pathogenesis of diabetic ED and the role of losartan in the treatment of diabetic ED.

METHODS

The AT1 blocker (ARB) losartan (30 mg/kg/d) was administered to rats with streptozocin (65 mg/kg)-induced diabetes. Erectile function, cavernous structure, and tissue gene and protein expression of RAS in the corpora cavernosa were studied.

MAIN OUTCOME MEASURE

We sought to determine the changes of cavernous RAS in the condition of diabetes and after treatment with losartan.

RESULTS

RAS components (angiotensinogen, [pro]renin receptor, angiotensin-converting enzyme [ACE], and AT1) were expressed in cavernosal tissue. In diabetic rats, RAS components were upregulated, resulting in the increased concentration of angiotensin II (Ang II) in the corpora. A positive feedback loop for Ang II formation in cavernosum was also identified, which could contribute to overactivity of cavernous RAS in diabetic rats. Administration of losartan blocked the effect of Ang II, downregulated the expression of AT1 and Ang II generated locally, and partially restored erectile function (losartan-treated group revealed an improved intracavernous pressure/mean systemic arterial pressure ratio as compared with the diabetic group (0.480 +/- 0.031 vs. 0.329 +/- 0.020, P < 0.01). However, losartan could not elevate the reduced smooth muscle/collagen ratio in diabetic rats.

CONCLUSIONS

The cavernous RAS plays a role in modulating erectile function in corpora cavernosa and is involved in the pathogenesis of diabetic ED. ARB can restore diabetic ED through downregulating cavernous RAS.

Intraspecific variation in expression of candidate genes for osmoregulation, heme biosynthesis and stress resistance suggests local adaptation in European flounder (Platichthys flesus)

Despite the recent discovery of significant genetic structuring in a large number of marine organisms, the evolutionary significance of these often minute genetic differences are still poorly understood. To elucidate the adaptive relevance of low genetic differentiation among marine fish populations, we studied expression differences of osmoregulatory and stress genes in genetically weakly differentiated populations of the European flounder (Platichthys flesus), distributed across a natural salinity gradient. Flounders were maintained in a long-term reciprocal transplantation experiment mimicking natural salinities in the North Sea and the Baltic Sea. Applying real-time quantitative PCR and microarray analysis we studied expression of four candidate genes (hsp70, angiotensinogen, Na/K-ATPase-alpha and 5-aminolevulinic acid synthase (ALAS)) in gill, kidney and liver tissues. Genes involved in osmoregulative processes (Na/K-ATPases-alpha and angiotensinogen) showed highly plastic but similar expression in the two populations dependent on environmental salinity. However, we observed a unique sixfold up-regulation of hsp70 in kidney tissue of flounder from the North Sea following long-term acclimation to Baltic salinities. Similarly, significant differences between North Sea and Baltic flounders in expression of ALAS in response to different salinities were found in gill and liver tissue. These findings strongly suggest that gene expression in flounders is shaped by adaptation to local environmental conditions. This identification of adaptive differences in high gene flow marine organisms adds a new dimension to our current understanding of evolutionary processes in the sea and is of paramount importance for identification, protection and sustainable management of marine biodiversity.