Irazabal, Maria V

Abstract Chronic kidney disease (CKD) is a public health concern that affects over 200 million people worldwide and is associated with a tremendous economic burden. Therefore, deciphering the mechanisms underpinning CKD is crucial to decelerate its progression towards end-stage renal disease (ESRD). Renal tubular cells are populated with a high number of mitochondria, which produce cellular energy and modulate several important cellular processes, including generation of reactive oxygen species (ROS), calcium homeostasis, proliferation, and apoptosis. Over the past few years, increasing evidence has implicated renal mitochondrial damage in the pathogenesis of common etiologies of CKD, such as diabetes, hypertension, metabolic syndrome (MetS), chronic renal ischemia, and polycystic kidney disease (PKD). However, most compelling evidence is based on preclinical studies because renal biopsies are not routinely performed in many patients with CKD. Previous studies have shown that urinary mitochondrial DNA (mtDNA) copy numbers may serve as non-invasive biomarkers of renal mitochondrial dysfunction. Emerging data also suggest that CKD is associated with altered expression of mitochondria-related microRNAs (mitomiRs), which localize in mitochondria and regulate the expression of mtDNA and nucleus-encoded mitochondrial genes. This review summarizes relevant evidence regarding the involvement of renal mitochondrial injury and dysfunction in frequent forms of CKD. We further provide an overview of non-invasive biomarkers and potential mechanisms of renal mitochondrial damage, especially focusing on mtDNA and mitomiRs.

Significance Statement Efficacy of rituximab (RTX) in ANCA-associated vasculitis (AAV) in patients with severe renal involvement (eGFR<30 ml/min per 1.73 m 2 ) has not been addressed in clinical trials. This observational study did not find statistically significant differences between RTX and cyclophosphamide (CYC) for remission-induction therapy or any apparent benefit from the addition of plasma exchange (PLEX) to standard remission-induction therapy for patients with AAV and severe renal involvement. Although our analyses suggest that the benefits and risks of these therapeutic choices (RTX versus CYC with and without PLEX) are balanced, a randomized, controlled trial is needed to confirm these findings. Background Treatment of patients with ANCA-associated vasculitis (AAV) and severe renal involvement is not established. We describe outcomes in response to rituximab (RTX) versus cyclophosphamide (CYC) and plasma exchange (PLEX). Methods A retrospective cohort study of MPO- or PR3-ANCA–positive patients with AAV (MPA and GPA) and severe kidney disease (eGFR <30 ml/min per 1.73 m 2 ). Remission, relapse, ESKD and death after remission-induction with CYC or RTX, with or without the use of PLEX, were compared. Results Of 467 patients with active renal involvement, 251 had severe kidney disease. Patients received CYC ( n =161) or RTX ( n =64) for remission-induction, and 51 were also treated with PLEX. Predictors for ESKD and/or death at 18 months were eGFR <15 ml/min per 1.73 m 2 at diagnosis (IRR 3.09 [95% CI 1.49 to 6.40], P =0.002), renal recovery (IRR 0.27 [95% CI 0.12 to 0.64], P =0.003) and renal remission at 6 months (IRR 0.40 [95% CI 0.18 to 0.90], P =0.027). RTX was comparable to CYC in remission-induction (BVAS/WG=0) at 6 months (IRR 1.37 [95% CI 0.91 to 2.08], P =0.132). Addition of PLEX showed no benefit on remission-induction at 6 months (IRR 0.73 [95% CI 0.44 to 1.22], P =0.230), the rate of ESKD and/or death at 18 months (IRR 1.05 [95% CI 0.51 to 2.18], P =0.891), progression to ESKD (IRR 1.06 [95% CI 0.50 to 2.25], P =0.887), and survival at 24 months (IRR 0.54 [95% CI 0.16 to 1.85], P =0.330). Conclusions The apparent benefits and risks of using CYC or RTX for the treatment of patients with AAV and severe kidney disease are balanced. The addition of PLEX to standard remission-induction therapy showed no benefit in our cohort. A randomized controlled trial is the only satisfactory means to evaluate efficacy of remission-induction treatments in AAV with severe renal involvement.

Significance Statement Accurate prediction of risk for disease progression is crucial for clinical management of autosomal dominant polycystic kidney disease (ADPKD). The Mayo imaging classification of ADPKD uses height-adjusted total kidney volume (htTKV) and age to identify patients at highest risk. Because the current Mayo classification applies only to patients with typical diffuse cystic disease (class 1) and poorly predicts eGFR decline for the remaining 5%–10% of patients with atypical morphology (class 2), imaging-based risk modeling remains unresolved. The authors report an expanded imaging classification model in which use of a recalculated htTKV value that excludes prominent exophytic cysts improved prediction for eGFR trajectory. Using a recalculated htTKV may allow inclusion of class 2 patients in the Mayo classification of ADPKD and reclassification of class 1 patients with prominent exophytic cysts. Background The Mayo Clinic imaging classification of autosomal dominant polycystic kidney disease (ADPKD) uses height-adjusted total kidney volume (htTKV) and age to identify patients at highest risk for disease progression. However, this classification applies only to patients with typical diffuse cystic disease (class 1). Because htTKV poorly predicts eGFR decline for the 5%–10% of patients with atypical morphology (class 2), imaging-based risk modeling remains unresolved. Methods Of 558 adults with ADPKD in the HALT-A study, we identified 25 patients of class 2A with prominent exophytic cysts (class 2Ae) and 43 patients of class 1 with prominent exophytic cysts; we recalculated their htTKVs to exclude exophytic cysts. Using original and recalculated htTKVs in association with imaging classification in logistic and mixed linear models, we compared predictions for developing CKD stage 3 and for eGFR trajectory. Results Using recalculated htTKVs increased specificity for developing CKD stage 3 in all participants from 82.6% to 84.2% after adjustment for baseline age, eGFR, BMI, sex, and race. The predicted proportion of class 2Ae patients developing CKD stage 3 using a cutoff of 0.5 for predicting case status was better calibrated to the observed value of 13.0% with recalculated htTKVs (45.5%) versus original htTKVs (63.6%). Using recalculated htTKVs reduced the mean paired difference between predicted and observed eGFR from 17.6 (using original htTKVs) to 4.0 ml/min per 1.73 m 2 for class 2Ae, and from −1.7 (using original htTKVs) to 0.1 ml/min per 1.73 m 2 for class 1. Conclusions Use of a recalculated htTKV measure that excludes prominent exophytic cysts facilitates inclusion of class 2 patients and reclassification of class 1 patients in the Mayo classification model.

Chronic kidney disease (CKD) remains a worldwide public health problem associated with serious complications and increased mortality rates. Accumulating evidence indicates that elevated intracellular levels of reactive oxygen species (ROS) play a major role in the pathogenesis of CKD. Increased intracellular levels of ROS can lead to oxidation of lipids, DNA, and proteins, contributing to cellular damage. On the other hand, ROS are also important secondary messengers in cellular signaling. Consequently, normal kidney cell function relies on the “right” amount of ROS. Mitochondria and NADPH oxidases represent major sources of ROS in the kidney, but renal antioxidant systems, such as superoxide dismutase, catalase, or glutathione peroxidase counterbalance ROS-mediated injury. This review discusses the main sources of ROS and antioxidant systems in the kidney, and redox signaling pathways leading to inflammation and fibrosis, which result in abnormal kidney function and CKD progression. We further discuss the important role of the nuclear factor erythroid 2-related factor 2 (Nrf2) in regulating antioxidant responses, and other mechanisms of redox signaling.

Introduction Autosomal dominant polycystic kidney disease (ADPKD) is characterized by progressive development and enlargement of bilateral renal cysts, and the majority of renal complications including organ failure arise mainly as a consequence of the cystic burden along with associated inflammation and fibrosis. Abnormal epithelial cell proliferation, along with the inability to maintain planar cell polarity, underlies cyst formation and enlargement. Therefore, processes that stimulate renal cell proliferation have the potential to generate the cystic phenotype. Interestingly, an increased nuclear factor (erythroid‐derived 2)‐like 2 (Nrf2) response has been shown to direct cancer cells into an anabolic mode that favors cellular proliferation, and has been associated with renal cyst formation in experimental and human fumarate hydratase deficiency. However, the Nrf2 response has not been described in ADPKD. We hypothesized that early ADPKD presents with an elevation in the Nrf2 response that favors cellular proliferation and contributes to cystogenesis. Methods We sought to longitudinally characterize the Nrf2 response and association with cystogenesis and fibrosis in a slow progressive mouse model of ADPKD ( Pkd1 RC/RC ) and its wildtype controls (n=6 males, 6 females per group). Urine and plasma samples were collected at 30, 60, 120, and 180 days for chemistries and metabolic profiles, and cystic index (CI), and total kidney volume (TKV) were determined from abdominal MRI. Nrf2 levels and related response enzymes, as well as cell proliferation and fibrosis were analyzed using western‐blots, immunofluorescence, and assay kits. Results At 30 days, Pkd1 RC/RC mice presented increased CI (Figure ) and TKV/BW. However, serum creatinine and fibrotic markers were not different compared to controls. Pkd1 RC/RC mice exhibited elevated Nrf2 expression and immunoreactivity early on that declined as ADPKD progressed from 30 to 180 days (Figure ) and correlated directly with cell proliferation (R 2 =0.693, p<0.05) and inversely with fibrotic markers (R 2 =0.672, p<0.05). Conclusions Our study shows longitudinal changes in the Nrf2 response in Pkd1 RC/RC mice that are associated with cystogenesis early on and renal fibrosis at later stages of the disease. These findings have significant implications for the treatment of human ADPKD, and suggest that Nrf2 modulators might represent an advantageous intervention for the disease Support or Funding Information NIDDK R21 DK118391, R25‐DK101405, NIDDK P30 DK090728 A) Representative H&E‐stained kidney mid‐sections from Wild Type (WT) and Pkd1 RC/RC mice at 1 month. Pkd1 RC/RC mice presented increased cystic index (CI) from early stages of the disease. CI is calculated as % of cyst area within the total kidney section. B) Longitudinal levels of Nrf2 activation in WT and Pkd1 RC/RC mice. Pkd1 RC/RC mice exhibited elevated Nrf2 levels early on that declined as the disease progressed. Nrf2 activation is calculated from nuclear extracts by colorimetric assay. Figure 1

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.

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.

While zebrafish embryos in the first five days after fertilization are clear and amenable to optical analysis, older juveniles and adults are not, due to pigmentation development and tissue growth. Thus other imaging methods are needed to image adult specimens. NMR is a versatile tool for studies of biological systems and has been successfully used for in vivo zebrafish microscopy. In this work we use NMR microscopy (MRM) for assessment of zebrafish specimens, which includes imaging of formalin fixed (FF), formalin fixed and paraffin embedded (FFPE), fresh (unfixed), and FF gadolinium doped specimens. To delineate the size and shape of various organs we concentrated on 3D MRM. We have shown that at 7 T a 3D NMR image can be obtained with isotropic resolution of 50 μm/pxl within 10 min and 25 μm/pxl within 4 h. Also, we have analyzed sources of contrast and have found that in FF specimens the best contrast is obtained by T 1 weighting (3D FLASH, 3D FISP), whereas in FFPE specimens T 2 weighting (3D RARE) is the best. We highlight an approach to perform segmentation of the organs in order to study morphological changes associated with mutations. The broader implication of this work is development of NMR methodology for high contrast and high resolution serial imaging and automated analysis of morphology of various zebrafish mutants.

Background and objectives In the 3-year Tolvaptan Efficacy and Safety in Management of ADPKD and Its Outcomes (TEMPO) 3:4 and 1-year Replicating Evidence of Preserved Renal Function: an Investigation of Tolvaptan Safety and Efficacy in ADPKD (REPRISE) trials, tolvaptan slowed the decline of eGFR in patients with autosomal dominant polycystic kidney disease at early and later stages of CKD, respectively. Our objective was to ascertain whether the reduction associated with the administration of tolvaptan is sustained, cumulative, and likely to delay the need for kidney replacement therapy. Design, setting, participants, & measurements One hundred and twenty-eight patients with autosomal dominant polycystic kidney disease participated in clinical trials of tolvaptan at the Mayo Clinic. All had the opportunity to enroll into open-label extension studies. Twenty participated in short-term studies or received placebo only. The remaining 108 were analyzed for safety. Ninety seven patients treated with tolvaptan for ≥1 year (mean±SD, 4.6±2.8; range, 1.1–11.2) were analyzed for efficacy using three approaches: ( 1 ) comparison of eGFR slopes and outcome (33% reduction from baseline eGFR) to controls matched by sex, age, and baseline eGFR; ( 2 ) Stability of eGFR slopes with duration of follow-up; and ( 3 ) comparison of observed and predicted eGFRs at last follow-up. Results Patients treated with tolvaptan had lower eGFR slopes from baseline (mean±SD, −2.20±2.18 ml/min per 1.73 m 2 per year) and from month 1 (mean±SD, −1.97±2.44 ml/min per 1.73 m 2 per year) compared with controls (mean±SD, −3.50±2.09 ml/min per 1.73 m 2 per year; P <0.001), and lower risk of a 33% reduction in eGFR (risk ratio, 0.63; 95% confidence interval, 0.38 to 0.98 from baseline; risk ratio, 0.53; 95% confidence interval, 0.31 to 0.85 from month 1). Annualized eGFR slopes of patients treated with tolvaptan did not change during follow-up and differences between observed and predicted eGFRs at last follow-up increased with duration of treatment. Conclusions Follow-up for up to 11.2 years (average 4.6 years) showed a sustained reduction in the annual rate of eGFR decline in patients treated with tolvaptan compared with controls and an increasing separation of eGFR values over time between the two groups.

The failure of the polycystins (PCs) to function in primary cilia is thought to be responsible for autosomal dominant polycystic kidney disease (ADPKD). Primary cilia integrate multiple cellular signaling pathways, including calcium, cAMP, Wnt, and Hedgehog, which control cell proliferation and differentiation. It has been proposed that mutated PCs result in reduced intracellular calcium, which in turn upregulates cAMP, protein kinase A (PKA) signaling, and subsequently other proliferative signaling pathways. However, the role of PKA in ADPKD has not been directly ascertained in vivo, although the expression of the main regulatory subunit of PKA in cilia and other compartments (PKA-RIα, encoded by PRKAR1A) is increased in a mouse model orthologous to ADPKD. Therefore, we generated a kidney-specific knockout of Prkar1a to examine the consequences of constitutive upregulation of PKA on wild-type and Pkd1 hypomorphic ( Pkd1 RC ) backgrounds. Kidney-specific loss of Prkar1a induced renal cystic disease and markedly aggravated cystogenesis in the Pkd1 RC models. In both settings, it was accompanied by upregulation of Src, Ras, MAPK/ERK, mTOR, CREB, STAT3, Pax2 and Wnt signaling. On the other hand, Gli3 repressor activity was enhanced, possibly contributing to hydronephrosis and impaired glomerulogenesis in some animals. To assess the relevance of these observations in humans we looked for and found evidence for kidney and liver cystic phenotypes in the Carney complex, a tumoral syndrome caused by mutations in PRKAR1A. These observations expand our understanding of the pathogenesis of ADPKD and demonstrate the importance of PRKAR1A highlighting PKA as a therapeutic target in ADPKD.