Soluble (Pro)Renin Receptor Level in Patients with Severe Obesity Is Associated with Visceral Adiposity and Is Involved with Insulin Resistance and Renal Injury.

INTRODUCTION: High soluble (pro)renin receptor (s[P]RR) level in circulation is reported in obese patients; however, it is unclear which body composition components are responsible for it. In this study, the authors examined blood s(P)RR levels and ATP6AP2 gene expression levels in visceral and subcutaneous adipose tissue (VAT, SAT) in severely obese patients who underwent laparoscopic sleeve gastrectomy (LSG), with the aim of clarifying the relationship with body composition and metabolic factors. METHODS: Seventy five cases who underwent LSG between 2011 and 2015 and were postoperatively followed-up for 12 months at the Toho University Sakura Medical Center were included in the analysis of the cross-sectional survey at baseline, and 33 cases were included in the analysis of the longitudinal survey during the 12 months after LSG. We evaluated body composition, glycolipid parameters, liver/renal function, as well as serum s(P)RR level and ATP6AP2 mRNA expression level in VAT and SAT. RESULTS: The mean serum s(P)RR level at baseline was 26.1 ng/mL, this value was considered higher than values in healthy subjects. There was no significant difference in the expression level of ATP6AP2 mRNA between VAT and SAT. At baseline, multiple regression analysis for the association between s(P)RR and variables identified that visceral fat area, HOMA2-IR, and UACR showed the independent relationships with s(P)RR. During the 12 months after LSG, body weight, serum s(P)RR level showed a significant decrease (from 30.0 ± 7.0 to 21.9 ± 4.3). Multiple regression analysis for the association between the change in s(P)RR and variables showed that changes in visceral fat area, and alanine transaminase were independently related to the change in s(P)RR. CONCLUSION: This study showed that blood s(P)RR level was high in severely obese patients, decreased with weight loss by LSG, and was associated with visceral fat area in both pre- and postoperative changes. The results suggest that blood s(P)RR levels in obese patients may reflect the involvement of visceral adipose (P)RR in insulin resistance and renal damage mechanisms associated with obesity.

Serum soluble (pro)renin receptor level as a prognostic factor in patients undergoing maintenance hemodialysis.

The (pro)renin receptor [(P)RR)] is a multifunctional protein that is cleaved to generate the soluble (P)RR [s(P)RR], reflecting the status of the tissue renin-angiotensin system and/or activity of the (P)RR. The serum s(P)RR level is associated with arteriosclerosis, independent of other risk factors, in patients undergoing hemodialysis (HD). This study was conducted to investigate whether the s(P)RR level was associated with new-onset cardiovascular events or malignant diseases and poor prognosis in patients undergoing HD. Overall, 258 patients [70 (61-76) years, 146 males] undergoing maintenance HD were prospectively followed up for 60 months. We investigated the relationships between s(P)RR levels and new-onset cardiovascular events/ malignant diseases and mortality during the follow-up period using Cox proportional hazard analyses. The cumulative incidence of new-onset cardiovascular events (P = 0.009) and deaths (P < 0.001), but not of malignant diseases, was significantly greater in patients with higher serum s(P)RR level (≥ 29.8 ng/ml) than in those with lower s(P)RR level (< 29.8 ng/ml). A high serum s(P)RR level was independently correlated with cardiovascular mortality (95% CI 1.001-1.083, P = 0.046). The serum s(P)RR level was associated with cardiovascular events and mortality, thus qualifying as a biomarker for identifying patients requiring intensive care.

Urinary soluble (pro)renin receptor excretion is associated with urine pH in humans.

The (pro)renin receptor [(P)RR] binds to renin and its precursor prorenin to activate the tissue renin-angiotensin system. It is cleaved to generate soluble (P)RR and M8-9, a residual hydrophobic truncated protein. The (pro)renin receptor also functions as an intracellular accessory protein of vacuolar-type H+-ATPase, which plays an essential role in controlling the intracellular vesicular acid environment. Thus, in the kidney, (P)RR may play a role in transporting H+ to urine in the collecting duct. Although blood soluble (P)RR has been recognized as a biomarker reflecting the status of the tissue renin-angiotensin system and/or tissue (P)RR, the significance of urinary soluble (P)RR excretion has not been determined. Therefore, this study aimed to investigate the characteristics of urinary soluble (P)RR excretion. Urinary soluble (P)RR excretion was measured, and its association with background factors was investigated in 441 patients. Relationships between changes in urine pH due to vitamin C treatment, which reduce urine pH, and urinary soluble (P)RR excretion were investigated in 10 healthy volunteers. Urinary soluble (P)RR excretion was 1.46 (0.44-2.92) ng/gCre. Urine pH showed a significantly positive association with urinary soluble (P)RR excretion, independent of other factors. Changes in urine pH and urinary soluble (P)RR excretion due to vitamin C treatment were significantly and positively correlated (ρ = 0.8182, p = 0.0038). These data showed an association between urinary soluble (P)RR excretion and urine pH in humans, suggesting that (P)RR in the kidney might play a role in urine pH regulation.

Soluble (pro)renin receptor increased by hypoxia maintains oxidative metabolism in trophoblasts.

Elevated soluble (pro)renin receptor (s(P)RR) concentration in maternal blood is associated with gestational hypertension and preeclampsia. Placenta has abundant expression of (P)RR, and the binding of (P)RR with pyruvate dehydrogenase E1 beta subunit (PDHB) is reported to maintain oxidative metabolism. Thus, we hypothesized that placental hypoxia may increase (P)RR, and the increased (P)RR may preserve PDHB expression. Expression and functional analyses were performed using human placental trophoblast cells, mainly JAR cells. (P)RR co-immunoprecipitated and showed co-immunofluorescence with PDHB mainly in the mitochondria. Hypoxia treatment significantly increased intracellular s(P)RR protein expression, but secreted s(P)RR in the culture medium was decreased by hypoxia. Hypoxia treatment did not alter PDHB expression or activity in the basal condition, but when (P)RR was knocked down by siRNA, PDHB protein and activity were reduced by hypoxia. Acetyl-CoA, the product of PDH activity, was significantly reduced by hypoxia treatment with (P)RR siRNA. S(P)RR is generated from full-length PRR when cleaved by specific proteases. Protease inhibitor experiments suggested furin and site 1 protease as the enzymes generating s(P)RR in JAR cells, and only when treated by site 1 protease inhibitor, PF429242, PDHB protein showed a significant trend to decrease with hypoxia. In JAR cells, hypoxia increased intracellular s(P)RR, and (P)RR preserved the expression and function of PDHB during hypoxia. (P)RR may help maintain oxidative metabolism and efficient energy production during placental ischemia in hypertensive disorders of pregnancy.

Elevated (Pro)renin Receptor Expression Contributes to Maintaining Aerobic Metabolism in Growth Hormone Deficiency.

CONTEXT: Growth hormone deficiency (GHD) leads to obesity and may induce tissue hypoxia. As (pro)renin receptor [(P)RR] is reported to contribute to the aerobic metabolism by stabilizing pyruvate dehydrogenase (PDH), it may play a substantial role in GHD. OBJECTIVE: We aimed to investigate serum soluble (P)RR [s(P)RR] concentration, the origin of s(P)RR, and significance of (P)RR in GHD. DESIGN SETTING AND PARTICIPANTS: Serum s(P)RR concentration was examined in 72 patients with pituitary diseases, including 32 patients with severe GHD (SGHD) and after GH replacement in 16 SGHD patients. Leptin-deficient ob/ob obese mice were treated with pegvisomant, a GH receptor antagonist, to explore the source of elevated serum s(P)RR in GHD. Adipocytes were cultured with 5% O2 to examine the effects of hypoxia. RESULTS: Serum s(P)RR concentration was higher in patients with SGHD than in those without SGHD. Obesity was the important determinant of s(P)RR concentration. Serum s(P)RR concentration significantly decreased after GH replacement in SGHD patients. (P)RR mRNA expression was increased specifically in the adipose tissue (AT) of pegvisomant-treated obese mice compared with that of control obese mice. Hypoxia in cultured adipocytes increased (P)RR expression without affecting the PDH E1 ß subunit (PDHB) expression; however, with (P)RR knockdown by small interfering RNA, hypoxia significantly decreased the expression of PDHB. CONCLUSION: GHD patients showed increased serum s(P)RR concentration, possibly caused by obesity and hypoxia. (P)RR expression in AT of GHD patients may be elevated to help maintain aerobic metabolism under hypoxia. Thus, the elevated serum s(P)RR level may reflect hypoxia in ATs.