Urinary prostasin: a possible biomarker for renal pressure natriuresis in black adolescents

Increased urinary excretion of the epithelial Na channel activator prostasin in patients with primary aldosteronism

OBJECTIVES

Prostasin is a glycosylphosphatidylinositol-anchored serine protease that is released in urine and is involved in epithelial Na channel activation. A direct association between urinary prostasin (u-prostasin) concentration and activation of the aldosterone-driven pathway has been suggested; however, in previous studies on primary aldosteronism, a semiquantitative evaluation, rather than a precise quantification, of prostasin was performed. We aim to investigate if u-prostasin concentrations are higher in patients with primary aldosteronism than in patients with essential hypertension and whether u-prostasin measurements could be a useful marker for diagnosing primary aldosteronism in hypertensive patients.

METHODS

A total of 62 primary aldosteronism and 56 essential hypertension patients were enrolled. Biochemical and hormonal parameters were measured by applying routine laboratory methods, and u-prostasin levels were assessed by ELISA.

RESULTS

Primary aldosteronism patients had higher u-prostasin levels than did essential hypertension patients. Prostasin levels were positively correlated with the aldosterone-to-renin ratio and inversely correlated with plasma K and urinary Na levels. In the highest concentration quartile, u-prostasin levels were associated with a several-fold higher probability of primary aldosteronism diagnosis in hypertensive patients. Receiver operating characteristic curve analysis showed that prostasin was specific but poorly sensitive as a diagnostic marker for primary aldosteronism.

CONCLUSIONS

The study shows that an elevated u-prostasin concentration in humans is a specific marker for primary aldosteronism, which involves the classical model of epithelial Na channel activation. There was no statistically significant difference in prostasin concentrations among patients with different primary aldosteronism subtypes. Studies with a larger series of patients are necessary to clarify the clinical usefulness of the prostasin assay.

Urinary prostasin excretion is associated with adiposity in nonhypertensive African-American adolescents

BACKGROUND

Metabolic abnormalities in obesity can overstimulate the renal epithelial sodium channel (ENaC) and subsequently lead to blood pressure (BP) elevation. Prostasin, a membrane-bound/secretive serine protease, is thought to activate ENaC via the proteolytic cleavage of the channel. Our specific aim was to explore whether there is a relationship between adiposity and urinary prostasin excretion at the population level.

METHODS

In 271 African-American adolescents, urinary prostasin concentrations were determined by enzyme-linked immunosorbent assay and normalized by urinary creatinine.

RESULTS

Urinary prostasin excretion increased in the overweight/obese group (n = 110, 38.2 ± 4.0 ng/mg) vs. the normal-weight group (n = 161, 20.7 ± 1.2 ng/mg, P = 0.03). Urinary prostasin excretion was significantly correlated with BMI percentiles (r = 0.14, P = 0.02), waist circumference (r = 0.13, P = 0.05), total body fat mass (r = 0.20, P < 0.01), and percentage body fat (r = 0.23, P < 0.01). Urinary prostasin excretion was also correlated with plasma aldosterone (r = 0.11, P = 0.05) and systolic BP (SBP; r = 0.15, P = 0.02), but the significances disappeared after adjustment of any of the adiposity variables.

CONCLUSION

Our data for the first time suggest that adiposity plays a role in urinary prostasin excretion, and its associations with aldosterone and BP appear to be modulated by adiposity. Whether urinary prostasin excretion is a biomarker/mechanism underlying obesity-related hypertension deserves further investigations.

A genome-wide methylation study on essential hypertension in young African American males

Objective

There is emerging evidence from animal studies suggesting a key role for methylation in the pathogenesis of essential hypertension. However, to date, very few studies have investigated the role of methylation in the development of human hypertension, and none has taken a genome-wide approach. Based on the recent studies that highlight the involvement of inflammation in the development of hypertension, we hypothesize that changes in DNA methylation of leukocytes are involved in the pathogenesis of hypertension.

Method & Results

We conducted a genome-wide methylation analysis on 8 hypertensive cases and 8 normotensive age-matched controls aged 14–23 years and performed validation of the most significant CpG sites in 2 genes in an independent sample of 36 hypertensive cases and 60 normotensive controls aged 14–30 years. Validation of the CpG sites in the SULF1 gene was further conducted in a second replication sample of 36 hypertensive cases and 34 controls aged 15.8–40 years. A CpG site in the SULF1 gene showed higher methylation levels in cases than in healthy controls in the genome-wide step (p = 6.2×10⁻⁵), which was confirmed in the validation step (p = 0.011) for subjects ≤30 years old but was not significant for subjects of all ages combined (p = 0.095).

Conclusion

The identification of a difference in a blood leukocyte DNA methylation site between hypertensive cases and normotensive controls suggests that changes in DNA methylation may play an important role in the pathogenesis of hypertension. The age dependency of the effect further suggests complexity of epigenetic regulation in this age-related disease.

Membrane-anchored serine proteases in health and disease

Serine proteases of the trypsin-like family have long been recognized to be critical effectors of biological processes as diverse as digestion, blood coagulation, fibrinolysis, and immunity. In recent years, a subgroup of these enzymes has been identified that are anchored directly to plasma membranes, either by a carboxy-terminal transmembrane domain (Type I), an amino-terminal transmembrane domain with a cytoplasmic extension (Type II or TTSP), or through a glycosylphosphatidylinositol (GPI) linkage. Recent biochemical, cellular, and in vivo analyses have now established that membrane-anchored serine proteases are key pericellular contributors to processes vital for development and the maintenance of homeostasis. This chapter reviews our current knowledge of the biological and physiological functions of these proteases, their molecular substrates, and their contributions to disease.

Obesity related methylation changes in DNA of peripheral blood leukocytes

BACKGROUND

Despite evidence linking obesity to impaired immune function, little is known about the specific mechanisms. Because of emerging evidence that immune responses are epigenetically regulated, we hypothesized that DNA methylation changes are involved in obesity induced immune dysfunction and aimed to identify these changes.

METHOD

We conducted a genome wide methylation analysis on seven obese cases and seven lean controls aged 14 to 18 years from extreme ends of the obesity distribution and performed further validation of six CpG sites from six genes in 46 obese cases and 46 lean controls aged 14 to 30 years.

RESULTS

In comparison with the lean controls, we observed one CpG site in the UBASH3A gene showing higher methylation levels and one CpG site in the TRIM3 gene showing lower methylation levels in the obese cases in both the genome wide step (P = 5 × 10(-6) and P = 2 × 10(-5) for the UBASH3A and the TRIM3 gene respectively) and the validation step (P = 0.008 and P = 0.001 for the UBASH3A and the TRIM3 gene respectively).

CONCLUSIONS

Our results provide evidence that obesity is associated with methylation changes in blood leukocyte DNA. Further studies are warranted to determine the causal direction of this relationship as well as whether such methylation changes can lead to immune dysfunction.

The cutting edge: membrane-anchored serine protease activities in the pericellular microenvironment

The serine proteases of the trypsin-like (S1) family play critical roles in many key biological processes including digestion, blood coagulation, and immunity. Members of this family contain N- or C-terminal domains that serve to tether the serine protease catalytic domain directly to the plasma membrane. These membrane-anchored serine proteases are proving to be key components of the cell machinery for activation of precursor molecules in the pericellular microenvironment, playing vital functions in the maintenance of homoeostasis. Substrates activated by membrane-anchored serine proteases include peptide hormones, growth and differentiation factors, receptors, enzymes, adhesion molecules and viral coat proteins. In addition, new insights into our understanding of the physiological functions of these proteases and their involvement in human pathology have come from animal models and patient studies. The present review discusses emerging evidence for the diversity of this fascinating group of membrane serine proteases as potent modifiers of the pericellular microenvironment through proteolytic processing of diverse substrates. We also discuss the functional consequences of the activities of these proteases on mammalian physiology and disease.

Regulation of sodium transport by ENaC in the kidney

PURPOSE OF REVIEW

The amiloride-sensitive epithelial sodium channel (ENaC) plays a major role in the regulation of sodium transport in the collecting duct and hence sodium balance. This review describes recent findings in the regulation of ENaC function by serine proteases in particular and other regulatory aspects.

RECENT FINDINGS

Regulation of ENaC occurs at many levels (biophysical, transcriptional, post-translational modifications, assembly, membrane insertion, retrieval, recycling, degradation, etc.). Recent studies have recognized and delineated proteolytic cleavage, particularly of the alpha and gamma subunits, as major mechanisms of activation. Release of peptide fragments from these two subunits appears to be an important aspect of activation. These proteolytic mechanisms of ENaC activation have also been demonstrated in vivo and strongly suggested in clinical circumstances, particularly the nephrotic syndrome. In the nephrotic syndrome, filtered plasminogen may be cleaved by tubular urokinase to yield plasmin which can activate ENaC. In addition to these mechanisms, regulation by ubiquitination and deubiquitination represents a pivotal process. Several important deubiquitinating enzymes have been identified as important in ENaC retention in, or recycling to, the apical membrane. New aspects of the genomic control of ENaC transcription have also been found including histone methylation.

SUMMARY

The mechanisms of regulation of ENaC are increasingly understood to be a complex interplay of many different levels and systems. Proteolytic cleavage of alpha and gamma subunits plays a major role in ENaC activation. This may be particularly clinically relevant in nephrotic syndrome in which plasmin may activate ENaC activity.

Prostasin inhibits cell invasion in human choriocarcinomal JEG-3 cells

Controlled invasion of the uterine wall by the trophoblast cells is pivotal for the successful pregnancy, and various kinds of protease are involved in this process. Serine protease prostasin has been shown to participate in the proteolytic activation of epithelial sodium channel as well as cleavage of epidermal growth factor receptor extracellular domain in human epithelial cells. Its physiological significance in human placentation has been suggested but not validated. In the present study, we found that prostasin was expressed at a relatively high level in human placenta trophoblasts in early pregnant weeks. In the in vitro cultured human choriocarcinomal JEG-3 cells, treatment with functional antibody against prostasin led to promotion in cell invasion capability, as well as increase in the production of MMP-2, MMP-26, TIMP-1, and TIMP-4. Our data indicated that this serine protease may function as an invasion suppressor in human trophoblast, participating in the invasion-restrictive regulation of trophoblasts to avoid their over-penetration into the uterine wall.