Rapid and large-scale purification and characterization of renin from mouse submaxillary gland

Lectin chromatography of extrarenal renin protein in human plasma and tissues: Potential endocrine function via the renin receptor

Secretion of prorenin from extrarenal tissues comprises approximately half of the renin protein in plasma; its origin is unknown. The discovery of a prorenin/renin receptor that activates vascular tissue kinases raises interest in this otherwise inactive component. We have studied its glycosylation as this may distinguish it from renal renin. The binding of renin protein (active and prorenin) in human plasma and tissues to concanavalin (Con A) and wheat germ lectins was deployed. Immunoradiometric and enzyme kinetic assays were applied to column fractions. Mannosylated renin protein binds to Con A and has been shown to be taken up by human vascular and hepatic cells on mannose-6-phosphate receptors, possibly as a clearance mechanism. But the other binding sites of prorenin/renin that elicit a cellular phosphorylation response are apparently independent of glycosylation. The tissues examined (kidney, adrenal, ovary) each contain high proportions of Con A binding renin, but the plasma of normal resting males and females contain mainly non-binding renin, the proportion increasing as renal renin secretion decreases. The extreme of this relationship is seen in anephric patients and in some normal women on oral contraceptives with suppressed renal renin, in whom plasma renin is entirely non-binding to Con A. Conversely, when renal renin secretion was stimulated, the increased plasma active renin bound to Con A. However, extrarenal tissues containing exclusively Con A non-binding renin protein, and hence potential sources of anephric plasma renin protein, were not identified, but are unlikely to include adrenal or female reproductive tract. The findings are consistent with the view that normal human plasma contains a considerable amount of amannosylated prorenin of extrarenal origin that escapes hepatic clearance and has a longer half-life than renal renin. This plasma renin form would be expected to be activated in association with the recently described renin/prorenin aspartyl protease receptor and to participate in local pathophysiological processes.

Renin and kallikrein in connecting tubule of mouse

BACKGROUND

The observation of renin expression in connecting tubule, a segment that also expresses tissue kallikrein (KLK-1), raises two questions. Are the genes expressed in the same or in different cells of connecting tubule? Does this topography support the hypothesis that KLK-1 activates prorenin or is it more likely that it affords coordinated gene regulation?

METHODS

Renin and KLK-1 were examined by immunostaining and in situ hybridization. Renin activation by KLK-1 was investigated in vitro. In vivo, excretion of prorenin and active renin was compared in mice homozygous for targeted inactivation of KLK-1 (TK(-/-)) and normal littermates (TK(+/+)).

RESULTS

Using in situ immunostaining for renin and in situ hybridization for KLK-1 mRNA, we found that connecting tubule cells expressing renin also expressed KLK-1. We confirmed in vitro activation of prorenin by KLK-1, but found no difference in the ratio of active renin to prorenin in urine of TK(-/-) and TK(+/+) animals. Compared to TK(+/+) controls, TK(-/-) mice exhibited significantly lower 24-hour excretion of prorenin (5.05 +/- 1.16 mg Ang I/hour vs. 9.39 +/- 1.96 mg Ang I/hour, P < 0.05) and active renin (1.98 +/- 0.25 mg Ang I/hour vs. 3.58 +/- 0.39 mg Ang I/hour, P < 0.05), with no difference in either urine volumes or plasma renin concentrations.

CONCLUSION

Direct interaction between renin and KLK-1, not ruled out in vitro, is not supported in vivo. By contrast, lower excretion of active renin and prorenin in TK(-/-) compared to TK(+/+) suggest coordinated regulation of the two proteins in their participation to collecting duct function.

Hypertension in the (mRen-2)27 Rat Is Not Explained by Enhanced Kinetics of Transgenic Ren-2 Renin

Enhanced efficiency of the reaction between transgenic Ren-2 mouse renin and endogenous rat angiotensinogen has been suggested as 1 mechanism that contributes to the accelerated hypertension and increased tissue angiotensin of the (mRen-2)27 transgenic rat. This was tested in a study conducted at pH 7.4 in vitro that compared the kinetic constants of purified mouse Ren-2 and rat renin (each at 100, 75, 50, and 25 pmol/L) reacting with physiologic concentrations of rat angiotensinogen (0 to 4 μmol/L). Under these conditions, the kinetic constants for Ren-2 ( K m , 1.8 μmol/L; K cat , 0.07/s; and K cat / K m , 0.04 L · μmol −1 · s −1 ) were not different from rat renin. However, Ren-2 renin acting on its homologous mouse angiotensinogen was confirmed as being much slower. We conclude that hypertension in the Ren-2 rat is not related to renin kinetics. Other mechanisms are considered, with reference to human essential hypertension.

Effects of dietary sodium and genetic background on angiotensinogen and Renin in mouse

Elements of a renin-angiotensin system expressed along the entire nephron, including angiotensinogen secreted by proximal tubule and renin expressed in connecting tubule, may participate in the regulation of sodium reabsorption at multiple sites of the nephron. The response of this tubular renin-angiotensin system to stepwise changes in dietary sodium was investigated in 2 mouse strains, the sodium-sensitive inbred C57BL/6 and the sodium-resistant CD1 outbred. Plasma angiotensinogen was not affected by sodium regimen, whereas plasma renin increased 2-fold under low sodium. In both strains, the variation in urinary parameters did not parallel the changes observed in plasma. Angiotensinogen and renin excretion were significantly higher under high sodium than under low sodium. Water deprivation, by contrast, induced significant activation in the tubular expression of angiotensinogen and renin. C57BL/6 exhibited significantly higher urinary excretion of angiotensinogen than did CD1 animals under both conditions of sodium intake. The extent to which these urinary parameters reflect systemic or tubular responses to challenges of sodium homeostasis may depend on the relative contribution of sodium restriction and volume depletion.

Angiotensinogen concentrations and renin clearance : implications for blood pressure regulation

Renin (REN) requires seconds to convert angiotensinogen (AGT) to angiotensin I. We tested the hypothesis that this long catalytic cycle might indicate an influence of AGT concentrations on REN clearance. We studied 2 transgenic rat (TGR) strains for human (h) AGT; one strain has hAGT values approximately 7-fold higher than the other (68+/-18 versus 10+/-4 microg angiotensin I/mL). hREN (30 000 pg) was bolus-infused into both lines and into nontransgenic controls. The terminal half-life (T1/2beta) was increased (130 versus 82 minutes) and the metabolic clearance rate (MCR) was decreased (0.83+/-0.29 versus 2.2+/-0.66 microL. min(-1). g(-1)) in the high hAGT strain compared with the low hAGT strain. The difference was not related to volume of distribution at steady state. Infused hREN blocked with remikiren resulted in T1/2beta and MCR values that were not different from control values. Infused unblocked and blocked radiolabeled hREN was distributed similarly in the hAGT TGR strains. Infused mouse REN, which cannot convert hAGT, had similar T1/2beta and MCR values in hAGT TGR. Measuring REN with direct radioimmunoassay or by enzyme kinetic assay gave similar results. We next crossed homozygous hAGT TGR from both strains with homozygous hREN TGR. Heterozygous offspring from the low hAGT TGR strain had plasma REN activity, hREN concentration, and rat AGT values that were no different from those of their parents. However, TGR offspring with high hAGT values had massively elevated plasma REN activity and hREN concentration as well as elevated blood pressure, even though both the hREN and rREN genes are downregulated. We conclude that increased AGT concentrations decrease REN MCR and increase REN T1/2beta. The REN-AGT complex may stabilize plasma REN concentration and regulate plasma REN activity independent of renal REN secretion and angiotensin II-mediated feedback. These effects could augment angiotensin I generation and influence blood pressure. The notion that AGT is merely a passive substrate reservoir for REN should be revised.

Elements of a paracrine tubular renin-angiotensin system along the entire nephron

The renin-angiotensin system is a major regulator of body sodium, predominantly through the actions of intrarenal angiotensin II of unclear origin. We show that polarized epithelium of the proximal tubule synthesizes and secretes angiotensinogen at its apical side and that the protein can be detected in urine as a function of dietary sodium. Furthermore, we demonstrate that renin is expressed and secreted in a restricted nephron segment, the connecting tubule, also in a sodium-dependent fashion. A paracrine renin-angiotensin system operating along the entire nephron may contribute to long-term arterial pressure regulation by integrating distant tubular sodium-reabsorbing functions.

Mouse and rat plasma renin concentration and gene expression in (mRen2)27 transgenic rats

The (mRen2)27 transgenic rat [TGR(mRen2)27] is said to have low plasma levels of active renin. We used a direct radioimmunoassay (RIA) for mouse submaxillary renin, as well as an indirect enzyme-kinetic assay based on the generation of angiotensin I with modification of the pH optimum, to measure rat and mouse plasma renin activity (PRA), plasma renin concentration (PRC), and plasma prorenin in TGR before and after lisinopril. The relationship between rat PRC and % rat kidney extract was steepest at pH 6.0 and flat at pH 8.5, whereas the relationship between mouse PRC and purified mouse renin was steepest at pH 8.5 and flat at pH 6.0. Mouse PRC was highly correlated with direct RIA measurements (r = 0.93). PRA before lisinopril was little influenced by pH, whereas the increase with lisinopril was greatest at pH 6.5. PRC before lisinopril was fourfold higher at pH 8.5 compared with that at pH 6.0. Lisinopril increased both PRC values but reversed the pH dependency. Prorenin was fourfold higher at pH 8.5 compared with that at pH 6.0 and decreased slightly with lisinopril. Renal renin concentration was higher at pH 6.0 than at pH 8.5. With lisinopril, renal renin concentration increased at both pH values. Mouse PRC was not changed by lisinopril. Ribonuclease protection assay showed both rat and mouse renin gene expression in the kidney, which increased with lisinopril. Thus TGR have circulating active rat and mouse renin and prorenin. The notion that TGR are a "low renin" model should be revised.

Gene targeting in mice reveals a requirement for angiotensin in the development and maintenance of kidney morphology and growth factor regulation

Elevated levels of endogenous angiotensin can cause hypertensive nephrosclerosis as a result of the potent vasopressor action of the peptide. We have produced by gene targeting mice homozygous for a null mutation in the angiotensinogen gene (Atg-1-). Postnatally, Atg-1- animals show a modest delay in glomerular maturation. Although Atg-1- animals are hypotensive by 7 wk of age, they develop, by 3 wk of age, pronounced lesions in the renal cortex, similar to those of hypertensive nephrosclerosis. In addition, the papillae of homozygous mutant kidneys are reduced in size. These lesions are accompanied by local up-regulation of PDGF-B and TGF-beta1 mRNA in the cortex and down-regulation of PDGF-A mRNA in the papilla. The study demonstrates an important requirement for angiotensin in achieving and maintaining the normal morphology of the kidney. The mechanism through which angiotensin maintains the volume homeostasis in mammals includes promotion of the maturational growth of the papilla.

Hypertension in the transgenic rat TGR(mRen-2)27 may be due to enhanced kinetics of the reaction between mouse renin and rat angiotensinogen

The transgenic rat TGR(mRen-2)27, in which the Ren-2 mouse renin gene is transfected into the genome of the rat, develops severe hypertension with high adrenal renin and low kidney renin. These animals express both mouse and rat renin. To investigate the cause of hypertension in the TGR rat, we compared the kinetics of mouse renin acting on mouse and rat angiotensinogens. The optimum pH of the renin reaction in the Sprague-Dawley rat was 6.5, whereas the optimum pH of the reaction in the TGR rat was approximately 8.5. The optimum pH of the renin reaction in the DBA mouse was 6.0. Purified mouse Ren-2 renin acting on rat angiotensinogen showed a pH profile similar to that for the renin reaction in the TGR rat. The angiotensinogen concentration in pooled plasma from eight DBA mice was 104.5 ng angiotensin I/mL and was clearly lower than that in Sprague-Dawley rats (772.4 +/- 37.3 ng angiotensin I/mL, n = 4). The reaction of purified mouse Ren-2 renin with rat angiotensinogen was 10 times faster than with mouse angiotensinogen. Plasma renin activity in DBA mice increased dramatically on addition of rat angiotensinogen (from 253.4 +/- 66.7 to 225,000 +/- 48,000 ng angiotensin I/mL per hour). Intravenous injection of 2 or 10 microL of DBA mouse plasma into the nephrectomized Sprague-Dawley rat increased the mean arterial pressure of the rat by 27.7 +/- 4.7 and 61.8 +/- 2.7 mmHg, respectively, whereas injection of 200 microL of Sprague-Dawley rat plasma did not change the mean arterial pressure of the rat.(ABSTRACT TRUNCATED AT 250 WORDS)

Comparative studies on species-specific reactivity between renin and angiotensinogen

The renin-angiotensin system (RAS) is the most important regulator of electrolyte homeostasis and blood pressure. Our recently generated transgenic mice carrying either the human renin (hREN) or human angiotensinogen (hANG) genes did not develop hypertension but dual gene strains obtained by cross-mating separate lines of mice exhibited a chronically sustained increase in blood pressure, suggesting the presence of species-specific reactivity between renin and angiotensinogen. In order to examine this specificity, the present study was designed to perform a strictly comparative study on hydrolysis of hANG by hREN and mouse submandibular renin (mREN) in vitro by using pure proteins. The recombinant hANG (rhANG) and the synthetic human-type tridecapeptide (hTDP), Asp-Arg-Val-Tyr-Ile-His-Pro-Phe-His-Leu-Val-Ile-His, corresponding to the N-terminal sequences of hANG, were used to determine the species specificity of recombinant hREN (rhREN) and mREN. While hTDP was cleaved by both rhREN and mREN with similar Km and with the same order of kcat, rhANG was cleaved by mREN with 16.7-fold higher Km and with 28.2-fold lower kcat than by rhREN. These results showed that kcat/Km value of mREN for rhANG was 468-fold lower than that for rhREN acting on rhANG.

Sheep hypothalamus contains a non-angiotensin ligand for type 1 and type 2 angiotensin II receptors

1. The aim of this study was to determine whether the brain contains an alternative ligand for angiotensin II (AII) receptors. 2. A radioreceptor assay based upon bovine cerebellar membranes (Type 2 AII receptors) was used to monitor the partial purification of an AII-like material from sheep hypothalami. 3. This material displaces 125I-[Sar1, Ala8]-AII from both type 1 (rat adrenal capsular membranes) and Type 2 AII receptors in a manner parallel to that of AII. It has a size of approximately 30,000 Da, is strongly cationic, is stable to boiling but is destroyed by trypsin. It is not recognized by AII antisera. 4. These data provide direct evidence for a non-angiotensin endogenous ligand for brain AII receptors. This novel ligand may play a role in the regulation of blood pressure and other actions mediated by brain AII receptors.

Synthesis of human angiotensinogen (1-17) containing one of the putative glycosylation binding sites and its hydrolysis by human renin and porcine pepsin

The N-terminal heptadecapeptide of human angiotensinogen (Asp-Arg-Val-Tyr-Ile-His-Pro-Phe-His-Leu-Val-Ile-His-Asn-Glu-Ser-Thr-NH2 ), with the C-terminal carboxyl group amidated, was synthesized in order to study the role of Asn-Glu-Ser, a putative carbohydrate binding site, on the hydrolysis by human renin. The synthesis was performed by fragment condensation using the Honzl and Rudinger azide procedure. In our conditions for azide segment condensation, histidine racemization was demonstrated to be negligible for most of the condensation reactions. Human renin liberates angiotensin I from h-angiotensinogen (1-17)-NH2 with a Km value of 3.4 x 10(-5) M, at pH 7.3 and 37 degrees being similar to h-angiotensinogen (1-13), an analog without the carbohydrate binding site. However, the Vmax value of 4.1 x 10(-9) mol/G.U. min is one order of magnitude higher. Porcine pepsin was demonstrated to cleave preferentially Leu10-Val11 bond and, surprisingly, His9-Leu10 as well.

The renin-angiotensin system: an overview of its intracellular function

The enzyme renin has been purified and characterized by structural analysis. Pure renin protein was used to produce a specific antibody to renin, which was useful in demonstrating the presence of a specific renin in many tissues other than kidney. Further, in these cells angiotensins I and II and converting enzyme all were found to coexist with renin by immunohistochemical studies, indicating the local production of renin, angiotensinogen and angiotensins in these cells. Angiotensin II produced in the cultured cells was secreted to the outside of the cells. Secretion of angiotensin II from the angiotensin-producing cells was demonstrated with perfused mesenteric artery. The secretion of angiotensin II from the vascular beds was inhibited by converting enzyme inhibitors, and was stimulated by the adrenergic beta-agonist isoproterenol. These studies demonstrate local production and controlled secretion of angiotensin II and define its physiologic role.

Characterization of recombinant human prorenin and renin

A cell line that secretes substantial quantities of recombinant human prorenin was prepared by transfecting Chinese hamster ovary cells with a gene encoding preprorenin. The prorenin was purified to homogeneity and was found to have a single amino terminus, reflecting cleavage after a typical 23 amino acid signal sequence. The purified inactive prorenin was not a substrate for active renin and was not capable of self-activation. Prorenin could be converted to renin by addition of exogenous protease, and deglycosylation of the prorenin did not alter the sensitivity to protease activation. The enzymatic activity of deglycosylated renin was kinetically identical to that of the native protein. Multimilligram quantities of recombinant human renin and prorenin were purified, providing suitable material for studies directed toward greater understanding of the function of these proteins and for structural studies such as x-ray diffraction for use in design of renin inhibitors.

Role of N-linked oligosaccharides attached to human renin expressed in COS cells

One or both of two putative N-glycosylation sites (at asparagine-5 and -75) of human renin was eliminated by amino acid replacement of the asparagine residue with an alanine residue using site-directed mutagenesis. The three glycosylation-deficient renins (Asn-5, Asn-75, Asn-5 and -75 mutants) were expressed in COS cells and secreted into the conditioned media. The secreted amounts of the three mutants were different from one another, although the mutant and wild-type renins had practically the same specific activity. An Asn-5 and -75 mutant which did not contain any glycosylation sites was unstable in the medium, suggesting that the N-linked oligosaccharides play an important role in stabilization of human renin.

Characterization of N-linked oligosaccharides attached to human renin expressed in COS cells

To study the role of N-linked oligosaccharides attached to human renin, we generated three kinds of glycosylation-deficient renins in which one or both of two putative N-glycosylation sites was eliminated by amino acid replacement using site-directed mutagenesis. Examination of the three mutant renins (Asn-5 to Ala, Asn-75 to Ala, and both Asn-5 and -75 to Ala) expressed in COS cells demonstrated that both putative sites were certainly glycosylated with heterologous N-linked oligosaccharides. Moreover, the oligosaccharide chain attached at Asn-5 was different from that attached at Asn-75 in its molecular size. In addition, the secreted amount of the three mutant renins were different from one another, although the mutant and wild-type renins had practically the same specific activity. Our results suggest that the N-linked oligosaccharides have no effect on the enzymatic activity, but play an important role in stable secretion of human renin.

Modified peptides which display potent and specific inhibition of human renin

A new class of angiotensinogen analogues which contain heteroatom-methylene and retro-inverso amide bond replacements was synthesized and evaluated for renin inhibition. Selected compounds in the series were specific for renin over other aspartic proteinases, and the most potent inhibitor demonstrated hypotensive activity in a salt depleted monkey.

Multiple forms of immunoreactive renin in human pituitary tissue

Immunoreactive renin was demonstrated in pituitary tissues of postmortem human subjects with different diseases. The specific immunoreactive renin activity comprised the majority of the tissue renin-like activity (mean, 83%), indicating the absence of nonspecific actions of proteases such as cathepsin D. We used three pituitary specimens with high levels of the specific renin activity for further biochemical characterization of the enzyme. Small differences were found in the molecular mass (45 K, 42 K and 37 K), binding to concanavalin A-Sepharose, and isoelectric points (pI) (4.72, 4.78, 4.86, 5.06, 5.28 and 5.44). These results seem to be interpreted as evidence for the presence of specific renin in the human pituitary with microheterogeneity.

Structure of mouse submaxillary gland renin

To determine the structural basis for the highly specific action of renin, structural features of the active site and the complete amino acid sequence of mouse submaxillary gland renin were determined. A rapid method was developed for a large scale purification of renin from mouse submaxillary gland. The active site of renin was shown to consist of 2 aspartyl residues, 2 tyrosyl residues and one arginyl residue, the structures analogous to the active site of pepsin and other acid proteases. Renin was found to consist of one heavy chain (Mr = 31,036) and one light chain (Mr = 5,458) connected by a disulfide bridge. Amino acid sequences of these chains were determined using overlapping peptides generated by cleavage with cyanogen bromide, trypsin, Staphylococcus aureus protease and Lysobacter enzymogenes endoproteinase Lys-C. Sequences involving 2 catalytically essential aspartyl residues 32 and 215, characteristic to acid proteases, were found identical with pepsin, penicillopepsin and chymosin. The sequence of L-chain was homologous with carboxyl terminal region of porcine pepsin in 46% of amino acid residues. H-chain showed 41% homology with 284 residues on the amino-terminal side of the porcine pepsin molecule. Residues identical in renin and acid proteases are distributed throughout the length of the molecules, suggesting a similarity in their overall structure.