Citations

Vascular abnormalities are the most important non-cystic complications in Polycystic Kidney Disease (PKD) and contribute to renal disease progression. Endothelial dysfunction and oxidative stress are evident in patients with ADPKD, preserved renal function, and controlled hypertension. The underlying biological mechanisms remain unknown. We hypothesized that in early ADPKD, the reactive oxygen species (ROS)-producing nicotinamide adenine dinucleotide phosphate hydrogen (NAD(P)H)-oxidase complex-4 (NOX4), a major source of ROS in renal tubular epithelial cells (TECs) and endothelial cells (ECs), induces EC mitochondrial abnormalities, contributing to endothelial dysfunction, vascular abnormalities, and renal disease progression. Renal oxidative stress, mitochondrial morphology (electron microscopy), and NOX4 expression were assessed in 4- and 12-week-old PCK and Sprague-Dawley (wild-type, WT) control rats (n = 8 males and 8 females each). Endothelial function was assessed by renal expression of endothelial nitric oxide synthase (eNOS). Peritubular capillaries were counted in hematoxylin–eosin (H&E)-stained slides and correlated with the cystic index. The enlarged cystic kidneys of PCK rats exhibited significant accumulation of 8-hydroxyguanosine (8-OHdG) as early as 4 weeks of age, which became more pronounced at 12 weeks. Mitochondria of TECs lining cysts and ECs exhibited loss of cristae but remained preserved in non-cystic TECs. Renal expression of NOX4 was upregulated in TECs and ECs of PCK rats at 4 weeks of age and further increased at 12 weeks. Contrarily, eNOS immunoreactivity was lower in PCK vs. WT rats at 4 weeks and further decreased at 12 weeks. The peritubular capillary index was lower in PCK vs. WT rats at 12 weeks and correlated inversely with the cystic index. Early PKD is associated with NOX4-induced oxidative stress and mitochondrial abnormalities predominantly in ECs and TECs lining cysts. Endothelial dysfunction precedes capillary loss, and the latter correlates with worsening of renal disease. These observations position NOX4 and EC mitochondria as potential therapeutic targets in PKD.

Autosomal dominant polycystic kidney disease (ADPKD) is the most common genetic cause of end-stage renal disease (ESRD). The treatment options for ADPKD are limited. We observed an upregulation in several IGF-1 pathway genes in the kidney of Pkd1 RC/RC mice, a model of ADPKD. Pregnancy-associated plasma protein A (PAPP-A), a metalloproteinase that cleaves inhibitory IGF binding proteins (IGFBPs), increasing the local bioactivity of IGF-1, was highly induced in the kidney of ADPKD mice. PAPP-A levels were high in cystic fluid and kidneys of humans with ADPKD. Our studies further showed that PAPP-A transcription in ADPKD was mainly regulated through the cAMP/CREB/CBP/p300 pathway. Pappa deficiency effectively inhibited the development of cysts in the Pkd1 RC/RC mice. The role of PAPP-A in cystic disease appears to be regulation of the IGF-1 pathway and cellular proliferation in the kidney. Finally, preclinical studies demonstrated that treatment with a monoclonal antibody that blocks the proteolytic activity of PAPP-A against IGFBP4 ameliorated ADPKD cystic disease in vivo in Pkd1 RC/RC mice and ex vivo in embryonic kidneys. These data indicated that the PAPP-A/IGF-1 pathway plays an important role in the growth and expansion of cysts in ADPKD. Our findings introduce a therapeutic strategy for ADPKD that involves the inhibition of PAPP-A.

Heterogeneity of lymphatic vessels during embryogenesis is critical for organ-specific lymphatic function. Little is known about lymphatics in the developing kidney, despite their established roles in pathology of the mature organ. We performed three-dimensional imaging to characterize lymphatic vessel formation in the mammalian embryonic kidney at single-cell resolution. In mouse, we visually and quantitatively assessed the development of kidney lymphatic vessels, remodeling from a ring-like anastomosis under the nascent renal pelvis; a site of VEGF-C expression, to form a patent vascular plexus. We identified a heterogenous population of lymphatic endothelial cell clusters in mouse and human embryonic kidneys. Exogenous VEGF-C expanded the lymphatic population in explanted mouse embryonic kidneys. Finally, we characterized complex kidney lymphatic abnormalities in a genetic mouse model of polycystic kidney disease. Our study provides novel insights into the development of kidney lymphatic vasculature; a system which likely has fundamental roles in renal development, physiology and disease.

Significance Statement The lack of rapidly progressive murine models reflecting the more severe end of the spectrum of autosomal recessive polycystic kidney disease (ARPKD) inhibits progress to understanding ARPKD pathogenesis. Defects in primary cilia have been implicated in polycystic kidney disease, but their potential role is poorly understood. The authors generated and characterized new mouse and rat models of ARPKD and autosomal dominant polycystic kidney disease (ADPKD) and investigated the interaction between causative genes for these two conditions. Their digenic models demonstrated a synergistic interaction that better reflects the early-onset disease characteristic of ARPKD. Analysis of mRNA expression in the models highlighted different disrupted pathways, but with a commonality of dysregulated mechanisms associated with primary cilia. These models may improve understanding of ARPKD and preclinical testing for this disease. Background Autosomal recessive polycystic kidney disease (ARPKD) and autosomal dominant polycystic kidney disease (ADPKD) are genetically distinct, with ADPKD usually caused by the genes PKD1 or PKD2 (encoding polycystin-1 and polycystin-2, respectively) and ARPKD caused by PKHD1 (encoding fibrocystin/polyductin [FPC]). Primary cilia have been considered central to PKD pathogenesis due to protein localization and common cystic phenotypes in syndromic ciliopathies, but their relevance is questioned in the simple PKDs. ARPKD’s mild phenotype in murine models versus in humans has hampered investigating its pathogenesis. Methods To study the interaction between Pkhd1 and Pkd1 , including dosage effects on the phenotype, we generated digenic mouse and rat models and characterized and compared digenic, monogenic, and wild-type phenotypes. Results The genetic interaction was synergistic in both species, with digenic animals exhibiting phenotypes of rapidly progressive PKD and early lethality resembling classic ARPKD. Genetic interaction between Pkhd1 and Pkd1 depended on dosage in the digenic murine models, with no significant enhancement of the monogenic phenotype until a threshold of reduced expression at the second locus was breached. Pkhd1 loss did not alter expression, maturation, or localization of the ADPKD polycystin proteins, with no interaction detected between the ARPKD FPC protein and polycystins. RNA-seq analysis in the digenic and monogenic mouse models highlighted the ciliary compartment as a common dysregulated target, with enhanced ciliary expression and length changes in the digenic models. Conclusions These data indicate that FPC and the polycystins work independently, with separate disease-causing thresholds; however, a combined protein threshold triggers the synergistic, cystogenic response because of enhanced dysregulation of primary cilia. These insights into pathogenesis highlight possible common therapeutic targets.

Background and objectives Intracranial aneurysm rupture is the most devastating complication of autosomal dominant polycystic kidney disease. Whether selective or widespread intracranial aneurysm screening is indicated remains controversial. Design, setting, participants & measurements Records of 3010 patients with autosomal dominant polycystic kidney disease evaluated at the Mayo Clinic between 1989 and 2017 were reviewed. Those who had presymptomatic magnetic resonance angiography screening were included. Results Ninety-four intracranial aneurysms were diagnosed in 75 of 812 (9%) patients who underwent magnetic resonance angiography screening. Sex, age, race, and genotype were similar in the groups with and without aneurysms; hypertension and history of smoking were more frequent in the aneurysm group. Twenty-nine percent of patients with aneurysms compared with 11% of those without aneurysms had a family history of subarachnoid hemorrhage ( P <0.001). Most aneurysms were small (median diameter =4 mm; range, 2–12 mm); 85% were in the anterior circulation. During a total imaging follow-up of 469 patient-years, de novo intracranial aneurysms were detected in five patients; eight intracranial aneurysms grew (median =2 mm; range, 1–3 mm). During a total clinical follow-up of 668 patient-years, seven patients had preemptive clipping or coil embolization; no intracranial aneurysms ruptured. During a total clinical follow-up of 4783 patient-years in 737 patients with no intracranial aneurysm detected on the first magnetic resonance angiography screening, two patients had an intracranial aneurysm rupture (0.04 per 100 person-years; 95% confidence interval, 0 to 0.10). The rate of intracranial aneurysm rupture in large clinical trials of autosomal dominant polycystic kidney disease was 0.04 per 100 patient-years (95% confidence interval, 0.01 to 0.06). Conclusions Intracranial aneurysms were detected by presymptomatic screening in 9% of patients with autosomal dominant polycystic kidney disease, more frequently in those with familial history of subarachnoid hemorrhage, hypertension, or smoking. None of the patients with and two of the patients without aneurysm detection on screening suffered aneurysmal ruptures. The overall rupture rate in our autosomal dominant polycystic kidney disease cohort was approximately five times higher than that in the general population.

Background and objectives To evaluate the growth pattern of kidney cyst number and cyst volume in association with kidney size, demographics, and genotypes in autosomal dominant polycystic kidney disease. Design, setting, participants, & measurements Kidney cyst number and cyst volume were measured from serial magnetic resonance images, giving a maximum follow-up of 14.23 years, from 241 patients with autosomal dominant polycystic kidney disease (15–46 years old at baseline). The growth pattern was analyzed, in association with sex, age, height-adjusted total kidney volume, and genotype, using linear mixed models of repeated measurements and tests of interactions with age (as a time-dependent covariate) to assess rates of change over time. Models were also fit using Irazabal class. Genotypic groups were characterized as either ( 1 ) PKD1 truncating, PKD1 nontruncating, and PKD2 plus patients with no mutation detected; or ( 2 ) in combination with PKD1 mutation strength groups. Results Imaging and genetic data were collected (at least one visit) for 236 participants. The mean height-adjusted total cyst number increased exponentially over time from a baseline value of 762 to 1715 at the last clinic visit, while the mean height-adjusted total cyst volume increased exponentially from 305 to 770 ml. Height-adjusted total kidney volume, height-adjusted total cyst number, and height-adjusted total cyst volume were all highly correlated over time. Female participants and participants with larger height-adjusted total kidney volume at baseline showed smaller rates of change in the log of height-adjusted total cyst number and cyst volume. PKD1 was associated with significant increases in both cyst number and volume at a given age, but genotype did not significantly affect the rate of growth. Conclusions Both height-adjusted total cyst number and height-adjusted total cyst volume increased exponentially and more than doubled over 14.23 years of follow-up. Compared with PKD2 plus no mutation detected, PKD1 was associated with a greater cyst number and volume at a given age, but no significant difference in the rate of growth.

Objectives Pancreatic lesions in autosomal dominant polycystic kidney disease (ADPKD) are primarily cysts. They are increasingly recognized, with isolated reports of intraductal papillary mucinous neoplasia (IPMN). Methods Retrospective study to determine prevalence, number, size, and location of pancreatic abnormalities using abdominal magnetic resonance imaging (MRI) of genotyped ADPKD patients (seen February 1998 to October 2013) and compared with age- and sex-matched non-ADPKD controls. We evaluated presentation, investigation, and management of all IPMNs among individuals with ADPKD (January 1997 to December 2016). Results Abdominal MRIs were examined for 271 genotyped ADPKD patients. A pancreatic cyst lesion (PCL) was detected in 52 patients (19%; 95% confidence interval, 15%–23%). Thirty-seven (71%) had a solitary PCL; 15 (28%) had multiple. Pancreatic cyst lesion prevalence did not differ by genotype. Intraductal papillary mucinous neoplasia was detected in 1% of ADPKD cases. Among 12 IPMN patients (7 branch duct; 5 main duct or mixed type) monitored for about 140 months, 2 with main duct IPMNs required Whipple resection, and 1 patient died of complications from small-bowel obstruction after declining surgical intervention. Conclusions With MRI, PCLs were detected in 19% and IPMNs in 1% of 271 ADPKD patients with proven mutations, without difference across genotypes. Pancreatic cyst lesions were asymptomatic and remained stable in size.

Background: Fifty percent of patients with autosomal dominant polycystic kidney disease (ADPKD) present hypertension (HTN) early on, which increases to nearly 100% at end-stage, and is associated with faster renal functional decline. Endothelial dysfunction (ED) accompanied by oxidative stress (OS) precedes the development of HTN, but the mechanisms responsible remain unknown. The aim of this study was to determine whether NADPH oxidase (NOX4) and mitochondrial dysfunction contribute to OS and ED preceding HTN in early ADPKD. Methods: We prospectively measured plasma levels of homocysteine (Hcy), 8-isoprostane, NOX4 and the mtDNA genes COX3 and ND1 in young normotensive (without BP medication) ADPKD patients, and age-matched healthy volunteers (HV) (n=10, each). Total kidney volume (TKV) and Renal Blood Flow (RBF) were evaluated by MRI. Results: BP levels were higher in ADPKD, and HtTKV was twofold higher in ADPKD vs. controls. eGFR and RBF were similar between the groups (Table). Plasma Hcy, 8-isoprostanes and NOX4 were higher in ADPKD, and correlated directly with HtTKV (p<0.05, Figure), but the correlation with RBF was not significant. Plasma mtDNA copy number were lower in ADPKD compared to controls, and correlated inversely with HtTKV(R 2 0.397 and 0.392 respectively). Conclusion: Early ADPKD is associated with elevation in Hcy, 8-isoprostane, and NOX4 levels, and decreased mtDNA copy numbers, which precede the reduction in RBF and the development of HTN, and are associated with disease severity. NOX4 and mitochondrial abnormalities may contribute to oxidative stress, endothelial dysfunction, and possibly the development of HTN and disease progression in ADPKD.