Renalase, a new secretory enzyme responsible for selective degradation of catecholamines: achievements and unsolved problems

Proteomic profiling of renal tissue of normo- and hypertensive rats with the renalase peptide RP220 as an affinity ligand

Renalase (RNLS) is a recently discovered protein that plays an important role in the regulation of blood pressure by acting inside and outside cells. Intracellular RNLS is a FAD-dependent oxidoreductase that oxidizes isomeric forms of β-NAD(P)H. Extracellular renalase lacking its N-terminal peptide and cofactor FAD exerts various protective effects via non-catalytic mechanisms. Certain experimental evidence exists in the literature that the RP220 peptide (a 20-mer peptide corresponding to the amino acid sequence RNLS 220-239) reproduces a number of non-catalytic effects of this protein, acting on receptor proteins of the plasma membrane. The possibility of interaction of this peptide with intracellular proteins has not been studied. Taking into consideration the known role of RNLS as a possible antihypertensive factor, the aim of this study was to perform proteomic profiling of the kidneys of normotensive and hypertensive rats using RP220 as an affinity ligand. Proteomic (semi-quantitative) identification revealed changes in the relative content of about 200 individual proteins in the kidneys of hypertensive rats bound to the affinity sorbent as compared to the kidneys of normotensive animals. Increased binding of SHR renal proteins to RP220 over the normotensive control was found for proteins involved in the development of cardiovascular pathology. Decreased binding of the kidney proteins from hypertensive animals to RP220 was noted for components of the ubiquitin-proteasome system, ribosomes, and cytoskeleton.

The search for potential hypotensive peptides in the amino acid sequence of human renalase and their identification in proteolytic fragments of this protein

Renalase (RNLS) is a secretory protein discovered in 2005. It plays an important role in the regulation of blood pressure. Studies by two independent laboratories have shown that administration of purified recombinant RNLS reduced blood pressure in experimental animals. However, the mechanisms of the antihypertensive effect of RNLS still remain unclear, especially in the context of the shift in the catalytic paradigm of this protein. In addition, there is growing evidence that endogenous plasma/serum RNLS, detected by enzyme immunoassay, is not an intact protein secreted into the extracellular space, and exogenous recombinant RNLS is effectively cleaved during short-term incubation with human plasma samples. This suggests that the antihypertensive effect of RNLS may be due to peptides formed during proteolytic processing. Based on the results of a bioinformatics analysis of potential RNLS cleavage sites (Fedchenko et al., Medical Hypotheses, 2022; DOI: 10.1016/j.mehy.2022.110895), a number of short peptides have been identified in the RNLS sequence that show similarity to fragments of known peptide inhibitors of angiotensin-converting enzyme. Some of them were found as a part of larger RNLS peptides, formed during RNLS cleavage by chymotrypsin and, and to a lesser extent, by trypsin.

The effect of renalase-derived peptides on viability of HepG₂ and PC3 cells

Renalase (RNLS) is a recently discovered protein, which plays different roles inside and outside cells. Intracellular RNLS is a FAD-dependent oxidoreductase (EC 1.6.3.5), while extracellular RNLS lacks its N-terminal peptide, FAD cofactor, and exhibits various protective effects in a non-catalytic manner. Certain evidence exists, that plasma/serum RNLS is not an intact protein secreted into the extracellular space, and exogenous recombinant RNLS is effectively degraded during short-term incubation with human plasma samples. Some synthetic analogues of the RNLS sequence (e.g. the Desir's peptide RP-220, a 20-mer peptide corresponding to the RNLS sequence 220-239) have effects on cell survival. This suggests that RNLS-derived peptides, formed during proteolytic processing, may have own biological activity. Based on results of a recent bioinformatics analysis of potential cleavage sites of RNLS (Fedchenko et al., Medical Hypotheses, 2022) we have investigated the effect of four RNLS-derived peptides as well as RP-220 and its fragment (RP-224) on the viability of two cancer cell lines: HepG₂ (human hepatoma) and PC3 (prostate cancer). Two RNLS-derived peptides (RP-207 and RP-220) decreased the viability of HepG₂ cells in a concentration dependent manner. The most pronounced and statistically significant effect (30-40% inhibition of cell growth) was observed at 50 μM concentration of each peptide. In the experiments with PC3 cells five of six RNLS-derived peptides had a significant impact on the cell viability. RP-220 and RP-224 decreased cell viability; however, no concentration dependence of this effect was observed in the range of concentrations studied (1-50 μM). Three other RNLS-derived peptides (RP-207, RP-233, and RP-265) increased viability of PC3 cells by 20-30%, but no concentration-dependence of this effect was found. Data obtained suggest that some RNLS-derived peptides may influence the viability of various cells and manifestation and direction of the effect (increase of decrease of the cell viability) is cell-type-specific.

Elevated Levels of Renalase, the β-NAD(P)H Isomerase, Can Be Used as Risk Factors of Major Adverse Cardiovascular Events and All-Cause Death in Patients with Chronic Kidney Disease

BACKGROUND

Renalase is an enzyme and a cytokine involved in cell survival. Since its discovery, associations between it and both cardiovascular and kidney disease have been noted. Recognizing this, we conducted a study in which we followed patients with chronic kidney disease.

MATERIAL AND METHODS

The study involved 90 CKD patients with varying stages of the disease and 30 healthy controls. Renalase was measured with an ELISA kit, and patients were followed-up after a median of 18 months. During the follow-up, we asked about the occurrence of MACE, all-cause mortality and the need for dialysis initiation.

RESULTS

In CKD subgroups, RNSL correlated with all-cause death only in the HD group (Rs = 0.49, p < 0.01). In the whole CKD population, we found a positive correlation of RNSL concentration and both MACE occurrence (Rs = 0.38, p < 0.001) and all-cause death (Rs = 0.34, p < 0.005). There was a significant increase in MACE occurrence probability in patients with elevated renalase levels (>25 μg/mL).

CONCLUSIONS

Elevated renalase levels can be used as a risk factor of MACE in patients with CKD, but its long-term utility needs further research. High renalase levels are a risk factor of death among CKD patients. In HD patients, all deaths were observed among patients with >30 μg/mL; this level could be used as a "red flag" marker in future studies.

A new method for quantitative determination of renalase based on mass spectrometric determination of a proteotypic peptide labelled with stable isotopes

RATIONALE

Renalase is a recently discovered kidney secretory protein, which is considered as an important component involved in blood pressure regulation. Although altered levels of renalase have been detected in plasma and urine of patients with various kidney diseases, there is certain inconsistency of changes in the renalase levels reported by different laboratories. The latter is obviously associated with the use of the ELISA as the only available approach for quantitative analysis of renalase. Thus there is a clear need for the development of antibody-independent approaches for renalase quantification.

METHODS

We have developed a new method for quantitative determination of human renalase, which is based on mass spectrometric detection of a proteotypic peptide containing С-terminal ¹³ C¹⁵ N-labelled lysine. It corresponds to a tryptic peptide of human renalase, which has been previously detected in most mass spectrometric determinations of this protein.

RESULTS

Using the labelled peptide H-EGDCNFVAPQGISSIIK-OH, corresponding to positions 100-116 of the human renalase sequence, as an internal standard and recombinant human renalase we have generated a calibration curve, which covered the concentration range 0.005-50 ng/mL with a limit of quantitation of 5 pg/mL. Using this calibration curve we were able to detect urinary renalase only after enrichment of initial urinary samples by ammonium sulfate precipitation (but not in untreated urine).

CONCLUSIONS

Results of our study indicate that quantitative determination of renalase based on mass spectrometric detection of a proteotypic peptide labelled with stable isotopes gives significantly lower values of this protein in human urine than those reported in the literature and based on the ELISA.

Relationship between Renalase Expression and Kidney Disease: an Observational Study in 72 Patients Undergoing Renal Biopsy

The relationship between the levels of renalase and changes in proteinuria, hypertension, renal function, renal tubular epithelial cell apoptosis and B-cell lymphoma-2 (Bcl-2) expression was investigated in patients (chronic nephritis, primary nephrotic syndrome or other kidney disease) that underwent renal biopsy. The study group comprised 72 patients undergoing renal biopsy. Patient profiles and renal function were collected. Concentrations of renalase and Bcl-2 were measured by immunohistochemistry. Tubular injury was detected by periodic acid Schiff staining (PAS) and renal tubular epithelial cell apoptosis was assessed by TUNEL assay. The expression of renalase was significantly lower in renal biopsy specimens than in normal kidney tissues. There was a positive linear relationship between renalase and some serum and cardiac indices; a negative correlation was found between age, eGFR, Ccr and 24-h urinary protein. Renal tubule injury index and tubular epithelial cell apoptosis index showed a negative linear correlation with renalase. The results showed that renalase probably increased the expression of Bcl-2. By two independent samples t-test, renalase levels were significantly increased in the non-hypertension group than in the hypertension group. One-way ANOVA showed that renalase expression was higher in samples with Lee's grade III than in those with Lee's grade V. The expression of renalase was significantly decreased in patients who underwent renal biopsy, and was also associated with blood and renal function. The research proved that renalase may reduce renal tubular injury and apoptosis of renal tubular epithelial cells through the mitochondrial apoptosis pathway, finally achieving the purpose of delaying the progress of renal failure.

The enzyme: Renalase

Within the last two years catalytic substrates for renalase have been identified, some 10 years after its initial discovery. 2- and 6-dihydronicotinamide (2- and 6-DHNAD) isomers of β-NAD(P)H (4-dihydroNAD(P)) are rapidly oxidized by renalase to form β-NAD(P)⁺. The two electrons liberated are then passed to molecular oxygen by the renalase FAD cofactor forming hydrogen peroxide. This activity would appear to serve an intracellular detoxification/metabolite repair function that alleviates inhibition of primary metabolism dehydrogenases by 2- and 6-DHNAD molecules. This activity is supported by the complete structural assignment of the substrates, comprehensive kinetic analyses, defined species specific substrate specificity profiles and X-ray crystal structures that reveal ligand complexation consistent with this activity. This apparently intracellular function for the renalase enzyme is not allied with the majority of the renalase research that holds renalase to be a secreted mammalian protein that functions in blood to elicit a broad array of profound physiological changes. In this review a description of renalase as an enzyme is presented and an argument is offered that its enzymatic function can now reasonably be assumed to be uncoupled from whole organism physiological influences.

Increased serum renalase in peritoneal dialysis patients: Is it related to cardiovascular disease risk?

BACKGROUND

Renalase, with possible monoamine oxidase activity, is implicated in degradation of catecholamines; which suggests novel mechanisms of cardiovascular complications in patients with chronic kidney diseases. Epicardial adipose tissue (EAT) has been found to correlate with cardiovascular diseases (CVD) in dialysis patients. The present study aimed to evaluate the association of serum renalase levels with EAT thickness and other CVD risk factors in peritoneal dialysis (PD) patients.

METHODS

The study included 40 PD patients and 40 healthy controls. All subjects underwent blood pressure and anthropometric measurements. Serum renalase was assessed by using a commercially available assay. Transthoracic echocardiography was used to measure EAT thickness and left ventricular mass index (LVMI) in all subjects.

RESULTS

The median serum renalase level was significantly higher in the PD patients than in the control group [176.5 (100-278.3) vs 122 (53.3-170.0)ng/ml] (p=0.001). Renalase was positively correlated with C-reactive protein (r=0.705, p<0.001) and negatively correlated with RRF (r=-0.511, p=0.021). No correlation was observed between renalase and EAT thickness or LVMI. There was a strong correlation between EAT thickness and LVMI in both the PD patients and the controls (r=0.848, p<0.001 and r=0.640, p<0.001 respectively).

CONCLUSIONS

This study indicates that renalase is associated with CRP and residual renal function but not with EAT thickness as CVD risk factors in PD patients.

Comparative analysis of expression of genes encoding enzymes of catecholamine catabolism and renalase in tissues of normotensive and hypertensive rats

Comparative analysis of expression of genes encoding enzymes of catecholamine catabolism (monoaminbe oxidases A and B (MAO A and MAO B) and catechol-O-methyl transferase (COMT)) and renalase has been carried out in tissues of normotensive Wistar-Kyoto (WKY) rats and spontaneously hypertensive rats (SHR). Among investigated tissues the highest level of mRNA of genes encoding key enzymes of catecholamine catabolism (MAO A, MAO B, COMT) was found in the heart of WKY rats. In SHR the mRNA levels of these genes were lower (p<0.05-0.01), however, no similar changes were observed in the tissues studied in dependence of hypertension. The relative mRNA levels of the studied genes normalized versus actin mRNA significantly varied. In heart and kidney the relative level of COMT mRNA significantly exceeded the relative levels of both MAO A mRNA and MAO B mRNA. In the brain differences in mRNAs of MAOA, MAOB, and COMT were less pronounced. However, in all examined tissue the renalase mRNA level was much (at least 10-20-fold) lower than any other mRNA studied. Taking into consideration known correlations between mRNAs and corresponding protein products reported in the literature for many genes these results suggest that in the case of any catalytic scenarios proposed or even proved for renalase this protein cannot contribute to catecholamine degradation. It is also unlikely that the products of renalase reaction, b-NAD(P)+ and hydrogen peroxide, can exhibit a hypotensive effect due to low expression of the renalase encoding gene.

[The history of renalase from amine oxidase to a a-NAD(P)H-oxidase/anomerase]

Renalase is a recently discovered secretory protein, which plays a certain (still poorly understood) role in regulation of blood pressure. The review summarizes own and literature data accumulated since the first publication on relanase (2005). Initial reports on FAD-dependent amine oxidase activity of this protein were not confirmed in independent experiments performed in different laboratories. In addition, proposed amine oxidase activity of circulating extracellular renalase requires the presence of FAD, which has not been detected either in blood or urinary renalase. Moreover, renalase excreted into urine lacks its N-terminal peptide, which is ultimately needed for accommodation of the FAD cofactor. Results of the Aliverti's group on NAD(P)H binding by renalase and weak diaphorase activity of this protein stimulated further studies of renalase as NAD(P)H oxidase catalyzing reaction of catecholamine co-oxidation. However, physiological importance of such extracellular catecholamine-metabolizing activity (demonstrated in one laboratory and not detected in another laboratory) remains unclear due to existence of much more active enzymatic systems (e.g. neutrophil NAD(P)H oxidase, xanthine oxidase/xanthine) in circulation, which can perform such co-oxidation reactions. Recently a-NAD(P)H oxidase/anomerase activity of renalase, which also pomotes oxidative conversion of b-NADH isomers inhibiting activity of NAD-dependent dehydrogenases, has been described. However, its possible contribution to the antihypertensive effect of renalase remains unclear. Thus, the antihypertensive effect of renalase still remains a phenomenon with unclear biochemical mechanim(s) and functions of intracellular and extracellular (circulating) renalases obviously differ.

Effects of salt intake and potassium supplementation on renalase expression in the kidneys of Dahl salt-sensitive rats

Renalase is currently the only known amine oxidase in the blood that can metabolize catecholamines and regulate sympathetic activity. High salt intake is associated with high blood pressure (BP), possibly through the modulation of renalase expression and secretion, whereas potassium can reverse the high salt-mediated increase in blood pressure. However, whether potassium could also modulate BP through renalase is unclear. In this study, we aim to investigate how salt intake and potassium supplementation affect the level of renalase in rats. Eighteen salt-sensitive (SS) and 18 SS-13BN rats were divided into six groups, receiving normal salt (0.3% NaCl), high salt (8% NaCl) and high salt/potassium (8% NaCl and 8% KCl) dietary intervention for four weeks. At the end of experiments, blood and kidneys were collected for analysis. mRNA level of renalase was measured by quantitative real-time PCR and protein level was determined by Western blot. We found that mRNA and protein levels of renalase in the kidneys of SS and SS-13BN rats were significantly decreased (P < 0.05) after high salt intervention, whereas dopamine in plasma was increased (P < 0.05) compared with rats received normal salt, suggesting that salt may induce salt-sensitive hypertension through inhibition of renalase expression. We also found increased mRNA level and protein level of renalase, decreased catecholamine levels in plasma, and decreased BP in SS rats treated with high salt/potassium, compared with that of the high salt SS group. Taken together, the salt-induced increase and potassium-induced decrease in BP could be mediated through renalase. More studies are needed to confirm our findings and understand the underlying mechanisms.

Renalase does not catalyze the oxidation of catecholamines

It is widely accepted that the function of human renalase is to oxidize catecholamines in blood. However, this belief is based on experiments that did not account for slow, facile catecholamine autoxidation reactions. Recent evidence has shown that renalase has substrates with which it reacts rapidly. The reaction catalyzed defines renalase as an oxidase, one that harvests two electrons from either 2-dihydroNAD(P) or 6-dihydroNAD(P) to form β-NAD(P)(+) and hydrogen peroxide. The apparent metabolic purpose of such a reaction is to avoid inhibition of primary dehydrogenase enzymes by these β-NAD(P)H isomers. This article demonstrates that renalase does not catalyze the oxidation of neurotransmitter catecholamines. Using high-performance liquid chromatography we show that there is no evidence of consumption of epinephrine by renalase. Using time-dependent spectrophotometry we show that the renalase FAD cofactor spectrum is unresponsive to added catecholamines, that adrenochromes are not observed to accumulate in the presence of renalase and that the kinetics of single turnover reactions with 6-dihydroNAD are unaltered by the addition of catecholamines. Lastly we show using an oxygen electrode assay that plasma renalase activity is below the level of detection and only when exogenous renalase and 6-dihydroNAD are added can dioxygen be observed to be consumed.

Human urinary renalase lacks the N-terminal signal peptide crucial for accommodation of its FAD cofactor

Renalase is a recently discovered secretory protein involved in the regulation of blood pressure. Cells synthesize all known isoforms of human renalase (1 and 2) as flavoproteins. Accommodation of FAD in the renalase protein requires the presence of its N-terminal peptide. However, in secretory proteins, such peptides are usually cleaved during their export from the cell. In the present study, we have isolated human renalase from urinary samples of healthy volunteers and human recombinant renalases 1 and 2 expressed in Escherichia coli cells. In these proteins, we investigated the presence of the renalase N-terminal peptide and the FAD cofactor and performed computer-aided molecular analysis of the renalase crystal structure to evaluate possible consequences of removal of the N-terminal peptide. In contrast to human recombinant renalase isoforms 1 and 2 containing non-covalently bound FAD and clearly detectable N-terminal peptide, renalase purified from human urine lacks both the N-terminal signal peptide and FAD. The computer-aided analysis indicates that the removal of this peptide results in inability of the truncated renalase to bind the FAD cofactor. Thus, our results indicate that human renalase secreted in urine lacks its N-terminal peptide, and therefore catalytic activities of urinary renalase reported in the literature cannot be attributed to FAD-dependent mechanisms. We suggest that FAD-dependent catalytic functions are intrinsic properties of intracellular renalases, whereas extracellular renalases act in FAD- and possibly catalytic-independent manner.

The catalytic function of renalase: A decade of phantoms

Ten years after the initial identification of human renalase the first genuinely catalytic substrates have been identified. Throughout the prior decade a consensus belief that renalase is produced predominantly by the kidney and catalytically oxidizes catecholamines in order to lower blood pressure and slow the heart has prevailed. This belief was, however, based on fundamentally flawed scientific observations that did not include control reactions to account for the well-known autoxidation of catecholamines in oxygenated solutions. Nonetheless, the initial claims have served as the kernel for a rapidly expanding body of research largely predicated on the belief that catecholamines are substrates for this enzyme. The proliferation of scientific studies pertaining to renalase as a hormone has proceeded unabated despite well-reasoned expressions of dissent that have indicated the deficiencies of the initial observations and other inconsistencies. Our group has very recently identified isomeric forms of β-NAD(P)H as substrates for renalase. These substrates arise from non-specific reduction of β-NAD(P)(+) that forms β-4-dihydroNAD(P) (β-NAD(P)H), β-2-dihydroNAD(P) and β-6-dihydroNAD(P); the latter two being substrates for renalase. Renalase oxidizes these substrates with rate constants that are up to 10(4)-fold faster than any claimed for catecholamines. The electrons harvested are delivered to dioxygen via the enzyme's FAD cofactor forming both H2O2 and β-NAD(P)(+) as products. It would appear that the metabolic purpose of this chemistry is to alleviate the inhibitory effect of β-2-dihydroNAD(P) and β-6-dihydroNAD(P) on primary metabolism dehydrogenase enzymes. The identification of this genuinely catalytic activity for renalase calls for re-evaluation of much of the research of this enzyme, in which definitive links between renalase catecholamine consumption and physiological responses were reported. This article is part of a Special Issue entitled: Physiological enzymology and protein functions.

[Computer modelling of monoaminoxidases]

The article summarized results of studies on active site structures of monoamine oxidases (MAO) performed in the Institute of Biomedical Chemistry (Russia) by computer modelling approaches. MAO, catalyzing the reaction of oxidative deamination of major neurotransmitter monoamines, exists in two highly homologous forms, MAO A and MAO B, distinguished by substrate specificity and inhibitor selectivity. The development of approaches for active site modelling of these enzymes (with unknown three-dimensional structures) started from analysis of relationship between the geometrical sizes of rigid indole and isatin derivatives and their inhibitory activity. These studies resulted in molding of the active site structures of MAO A and MAO B. These molds reflect the sizes and shapes of active sites of these enzymes. These mold models have been used for virtual screening of molecular databases for new inhibitors. The models obtained at different stages of MAO investigations have been compared with recently appeared three-dimensional structures of MAO A and MAO B.

Renalase mRNA levels in the brain, heart, and kidneys of spontaneously hypertensive rats with moderate and high hypertension

Background

Renalase is a recently discovered secretory protein involved in regulation of arterial blood pressure in humans and animals. Results of animal experiments from independent laboratories indicate that administration of human recombinant renalase decreases blood pressure and some genetically predisposed hypertensive rats have lowered renalase levels.

Material/Methods

The levels of renalase mRNA expression in brain hemispheres, heart, and kidneys of spontaneously hypertensive rats (SHR) with moderate (140–180 mm Hg) or high (>180 mm Hg) hypertension and of control Wistar-Kyoto (WKY) rats were analyzed using real-time PCR.

Results

Spontaneously hypertensive rats with high hypertension (>180 mm Hg) had a lower renalase mRNA level in brain hemispheres, and higher heart and kidney renalase mRNA levels compared with control WKY rats. In SHR with a moderate increase in arterial blood pressure (140–180 mm Hg), the tissue renalase mRNA changed in the same direction but did not reach the level of statistical significance as compared with control rats.

Conclusions

The results indicate that the development of hypertension in SHR is accompanied by altered expression of the renalase gene in the examined organs as compared with control WKY rats. The brain and peripheral tissues renalase mRNA levels demonstrate opposite trends, which are obviously crucial for impaired regulation of blood pressure in SHR.

Renalase is an α-NAD(P)H oxidase/anomerase

Renalase is a protein hormone secreted into the blood by the kidney that is reported to lower blood pressure and slow heart rate. Since its discovery in 2005, renalase has been the subject of conjecture pertaining to its catalytic function. While it has been widely reported that renalase is the third monoamine oxidase (monoamine oxidase C) that oxidizes circulating catecholamines such as epinephrine, there has been no convincing demonstration of this catalysis in vitro. Renalase is a flavoprotein whose structural topology is similar to known oxidases, lysine demethylases, and monooxygenases, but its active site bears no resemblance to that of any known flavoprotein. We have identified the catalytic activity of renalase as an α-NAD(P)H oxidase/anomerase, whereby low equilibrium concentrations of the α-anomer of NADPH and NADH initiate rapid reduction of the renalase flavin cofactor. The reduced cofactor then reacts with dioxygen to form hydrogen peroxide and releases nicotinamide dinucleotide product in the β-form. These processes yield an apparent turnover number (0.5 s(-1) in atmospheric dioxygen) that is at least 2 orders of magnitude more rapid than any reported activity with catechol neurotransmitters. This highly novel activity is the first demonstration of a role for naturally occurring α-NAD(P)H anomers in mammalian physiology and the first report of a flavoprotein catalyzing an epimerization reaction.

Construction of the coding sequence of the transcription variant 2 of the human Renalase gene and its expression in the prokaryotic system

Renalase is a recently discovered protein, involved in regulation of blood pressure in humans and animals. Although several splice variants of human renalase mRNA transcripts have been recognized, only one protein product, hRenalase1, has been found so far. In this study, we have used polymerase chain reaction (PCR)-based amplification of individual exons of the renalase gene and their joining for construction of full-length hRenalase2 coding sequence followed by expression of hRenalase2 as a polyHis recombinant protein in Escherichia coli cells. To date this is the first report on synthesis and purification of hRenalase2. Applicability of this approach was verified by constructing hRenalase1 coding sequence, its sequencing and expression in E. coli cells. hRenalase1 was used for generation of polyclonal antiserum in sheep. Western blot analysis has shown that polyclonal anti-renalase1 antibodies effectively interact with the hRenalase2 protein. The latter suggests that some functions and expression patterns of hRenalase1 documented by antibody-based data may be attributed to the presence of hRenalase2. The realized approach may be also used for construction of coding sequences of various (especially weakly expressible) genes, their transcript variants, etc.

Renalase's expression and distribution in renal tissue and cells

To study renalase's expression and distribution in renal tissues and cells, renalase coded DNA vaccine was constructed, and anti-renalase monoclonal antibodies were produced using DNA immunization and hybridoma technique, followed by further investigation with immunological testing and western blotting to detect the expression and distribution of renalase among the renal tissue and cells. Anti-renalase monoclonal antibodies were successfully prepared by using DNA immunization technique. Further studies with anti-renalase monoclonal antibody showed that renalase expressed in glomeruli, tubule, mesangial cells, podocytes, renal tubule epithelial cells and its cells supernatant. Renalase is wildly expressed in kidney, including glomeruli, tubule, mesangial cells, podocytes and tubule epithelial cells, and may be secreted by tubule epithelial cells primarily.

Renalase, hypertension, and kidney - the discussion continues

Hypertension and cardiovascular complications are very common in chronic kidney disease (CKD). Overactivation of sympathetic nervous system is also widely recognized in CKD. Renalase may play an important role in the control of blood pressure (BP) by its regulatory function of catecholamine metabolism. Renalase could be synthesized not only by the kidney but also by cardiomyocytes, liver, and adipose tissue. It probably exerts a hypotensive action, at least in animal models. Whether it metabolizes catecholamines remains to be proved. Another issue that remains to be resolved is the relationship between renalase and renal natriuresis and phosphaturia. In this review, the updated experimental and clinical data on renalase are presented and possible interactions with the endothelium are discussed. Renalase is "a new postulated therapeutic target." Proof of concept studies are needed to define the pathophysiological link between the kidney, sympathetic tone, BP, and cardiovascular complications.

Impact of renal denervation on renalase expression in adult rats with spontaneous hypertension

The aim of this study was to investigate the impact of renal denervation on the blood pressure, plasma renalase content and expression of renalase and tyrosine hydroxylase (TH) in the kidney of spontaneous hypertensive (SH) rats and to explore the mechanism of renal denervation involved in lowering blood pressure. SH rats (n=48) were randomly assigned to baseline, surgery (renal denervation), sham and control groups. WKY rats matched in age (n=12) served as the baseline control group. All rats were housed until they were 12 weeks old. The rats in the baseline group and the WKY group rats were sacrificed, and blood and kidney were collected for examination. In the renal denervation, sham and control groups, the blood pressure was continuously monitored. One and six weeks after renal denervation, 6 rats in each group were sacrificed, and blood and kidney were collected for examination. ELISA was employed to measure the plasma renalase, and western blot analysis was performed to detect the expression of TH and renalase in the kidney. Compared with the WKY rats, SH rats in the baseline group had significantly increased blood pressure and markedly elevated TH protein expression (P<0.05), but dramatically reduced plasma renalase content and protein expression of renalase in the kidney (P<0.05). One week after surgery, the mean arterial pressure and TH protein expression in the surgery group was lowered compared with the baseline group and dramatically reduced when compared with the sham and control groups (P<0.05). In the surgery group, renalase levels were markedly increased compared with the baseline, sham and control groups (P<0.05). Six weeks after renal denervation, the mean arterial pressure and TH levels in the surgery group were significantly increased while the renalase content and expression were markedly reduced compared with those at week 1, however, there were no marked differences among the surgery, sham and control groups (P>0.05). Moreover, no pronounced differences in the above variables were found between the sham and control groups at any timepoint (P>0.05). Renal denervation can lower blood pressure, which may be attributed to the suppression of sympathetic nerves, increase in plasma renalase content and renalase expression in the kidney.

Mass spectrometry detection of monomeric renalase in human urine

Renalase is a recently discovered secretory protein, which is suggested to play a role (which still remains elusive) in regulation of blood pressure. Earlier it was purified from urine of healthy volunteers by means of ammonium sulfate fractionation and subsequent affinity chromatography (Xu et al. (2005) J. Clin. Invest., 115, 1275). The resultant purified preparation of renalase contained 2 proteins with molecular masses of 35 and 67-75 kDa. The authors believed that the latter represents a dimerization (aggregation) product of the 35 kDa protein. In this study we have detected relanase in urinary samples of 2 of 6 volunteers only after immunoaffinity enrichment of urinary samples subjected to ammonium sulfate precipitation. Electrophoresis of the purified preparation also demonstrated the presence of 2 proteins with molecular masses of 35 and 66 kDa, respectively. Mass spectrometry analysis of these proteins identified 35 and 66 kDa proteins as renalase and serum albumin, respectively. Thus, our results do not support suggestion on formation of renalase dimers and they indicate that urinary renalase excretion significantly varies in humans.

FAD-binding site and NADP reactivity in human renalase: a new enzyme involved in blood pressure regulation

Renalase is a recently discovered flavoprotein that regulates blood pressure, regulates sodium and phosphate excretion, and displays cardioprotectant action through a mechanism that is barely understood to date. It has been proposed to act as a catecholamine-degrading enzyme, via either O(2)-dependent or NADH-dependent mechanisms. Here we report the renalase crystal structure at 2.5 Å resolution together with new data on its interaction with nicotinamide dinucleotides. Renalase adopts the p-hydroxybenzoate hydroxylase fold topology, comprising a Rossmann-fold-based flavin adenine dinucleotide (FAD)-binding domain and a putative substrate-binding domain, the latter of which contains a five-stranded anti-parallel β-sheet. A large cavity (228 Å(3)), facing the flavin ring, presumably represents the active site. Compared to monoamine oxidase or polyamine oxidase, the renalase active site is fully solvent exposed and lacks an 'aromatic cage' for binding the substrate amino group. Renalase has an extremely low diaphorase activity, displaying lower k(cat) but higher k(cat)/K(m) for NADH compared to NADPH. Moreover, its FAD prosthetic group becomes slowly reduced when it is incubated with NADPH under anaerobiosis, and binds NAD(+) or NADP(+) with K(d) values of ca 2 mM. The absence of a recognizable NADP-binding site in the protein structure and its poor affinity for, and poor reactivity towards, NADH and NADPH suggest that these are not physiological ligands of renalase. Although our study does not answer the question on the catalytic activity of renalase, it provides a firm framework for testing hypotheses on the molecular mechanism of its action.