The prorenin receptor (PRR), a recently discovered component of the renin-angiotensin system, is expressed in the nephron in general and the collecting duct in particular. However, the physiological significance of nephron PRR remains unclear, partly due to developmental abnormalities associated with global or renal-specific PRR gene knockout (KO). Therefore, we developed mice with inducible nephron-wide PRR deletion using Pax8-reverse tetracycline transactivator and LC-1 transgenes and loxP flanked PRR alleles such that ablation of PRR occurs in adulthood, after induction with doxycycline. Nephron-specific PRR KO mice have normal survival to ∼1 yr of age and no renal histological defects. Compared with control mice, PRR KO mice had 65% lower medullary PRR mRNA and protein levels and markedly diminished renal PRR immunofluorescence. During both normal water intake and mild water restriction, PRR KO mice had significantly lower urine osmolality, higher water intake, and higher urine volume compared with control mice. No differences were seen in urine vasopressin excretion, urine Na(+) and K(+) excretion, plasma Na(+), or plasma osmolality between the two groups. However, PRR KO mice had reduced medullary aquaporin-2 levels and arginine vasopressin-stimulated cAMP accumulation in the isolated renal medulla compared with control mice. Taken together, these results suggest nephron PRR can potentially modulate renal water excretion.

IMPORTANCE Malignant head and neck paragangliomas (HNPGLs) are rare entities, and there are limited data regarding optimal treatment recommendations to improve clinical outcomes. OBJECTIVE To classify succinate dehydrogenase (SDH) germline mutations associated with malignant HNPGLs, evaluate time from diagnosis to identification of malignant tumor, describe locations of metastases and the functional status of malignant HNPGLs, and determine the role of selective neck dissection at the time of initial surgical resection. DESIGN, SETTING, AND PARTICIPANTS A retrospective cohort study was completed of patients diagnosed with paragangliomas on various sites on the body at an academic tertiary cancer hospital between the years 1963 and 2018. A subanalysis of HNPGLs was also completed. Data regarding diagnosis, gene and mutation, tumor characteristics and location, and treatments used were reviewed between February 2017 and March 2018. MAIN OUTCOMES AND MEASURES Mutations of SDH genes associated with benign and malignant HNPGLs, treatments used, time to the discovery of malignancy, and location of metastasis. RESULTS Of the 70 patients included in the study, 40 (57%) were male, and the mean (SD) age was 47 (21.1) years. Of patients with tumors isolated to the head and neck, 38 (54%) had benign HNPGLs, which were associated with mutations in the genes SDH subunit B (SDHB) (n = 18; 47%), SDH subunit C (n = 2; 5%), and SDH subunit D (n = 18; 47%). Among those with malignant HNPGLs, all but 1 patient had mutations in SDHB (n = 5; 83%); 1 patient had no mutation associated with their disease. The average age at diagnosis for malignant HNPGLs was 35 years, while benign tumors were diagnosed at an average age at 36 years. All patients with malignant disease underwent surgery. Four patients were found to have metastasis at the time of selective neck dissection. Among patients with malignant HNPGLs, 5 (83%) were treated with adjuvant radiation, and 1 (17%) was treated with adjuvant chemotherapy. CONCLUSIONS AND RELEVANCE Malignant HNPGLs are rare entities that are difficult to diagnose and are typically identified by the presence of regional or distant metastasis. The results of this study found the prevalence of malignant HNPGLs to be 9%. These data suggest that it is beneficial to perform a selective neck dissection at the time of tumor excision. All patients with malignant HNPGLs but 1 had SDHB mutations.

The role of intranephron angiotensinogen (AGT) in blood pressure (BP) regulation is not fully understood. Previous studies showed that proximal tubule‐specific overexpression of AGT increases BP, whereas proximal tubule‐specific deletion of AGT did not alter BP. The latter study may not have completely eliminated nephron AGT production; in addition, BP was only assessed on a normal salt diet. To evaluate this issue in greater detail, we developed mice with inducible nephron‐wide AGT deletion. Mice were generated which were hemizygous for the Pax8‐rtTA and LC‐1 transgenes and homozygous for loxP‐flanked AGT alleles to achieve nephron‐wide AGT disruption after doxycycline induction. Compared to controls, AGT knockout (KO) mice demonstrated markedly reduced renal AGT immunostaining, mRNA, and protein levels; unexpectedly AGT KO mice had reduced AGT mRNA levels in the liver along with 50% reduction in plasma AGT levels. BP was significantly lower in the AGT KO mice compared to controls fed a normal, low, or high Na+ intake, with the highest BP reduction on a low Na+ diet. Regardless of Na+ intake, AGT KO mice had higher plasma renin concentration (PRC) and markedly reduced urinary AGT levels compared to controls. Following angiotensin‐II (Ang‐II) infusion, AGT KO mice demonstrated an attenuated hypertensive response despite similar suppression of PRC in the two groups. Taken together, these data suggest that nephron‐derived AGT may be involved in Ang‐II‐dependent hypertension, however, a clear role for nephron‐derived AGT in physiological BP regulation remains to be determined.

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It is unknown if intrarenal generation of angiotensinogen (AGT) is important in blood pressure (BP) regulation. Previous studies showed that proximal tubule-specific overexpression of AGT increases BP, while proximal tubule-specific deletion of AGT using the KAP promoter-Cre transgene did not alter BP. The latter study may not have completely eliminated nephron AGT production; in addition, BP was only assessed on a normal salt diet. To evaluate this issue in greater detail, we developed mice with inducible nephron-wide AGT deletion. Mice were generated which were hemizygous for the Pax8-rtTA and LC-1 transgenes and homozygous for loxP flanked AGT alleles to achieve nephron-specific AGT disruption after doxycycline induction. Adult Pax8-rtTA/LC-1/floxed AGT mice at 3 months of age were treated with doxycycline 2 mg/ml in drinking water for 11 days and studied 4 weeks after treatment. Blood pressure (recorded via telemetry) and metabolic balance studies were determined during 5 days of normal, high and low Na diets. Compared to controls, AGT knockout (KO) mice demonstrated significantly lower systolic, diastolic, and mean BPs on all three diets (N=4 each group). The BP reduction was most evident on a low Na diet (mean BP 107 ± 2 mmHg in controls and 88 ± 13 mmHg in AGT KO). Plasma renin concentration was higher in the AGT KO mice as compared to controls on all three diets. There were no detectable differences in weight, urine volume, urine osmolality or urine Na excretion between the controls and KO mice on all three diets, however due to variability, small differences in these parameters may not have been detected. Taken together, these data suggest that nephron AGT may contribute to BP regulation and this is most evident during low Na intake.