Pathogenesis Of Polycystic Kidney Disease Research Articles

Netrin-1 increases epithelial cell proliferation and promotes renal cyst formation by activating Rac2 in collecting duct cells

Despite recent advances in our understanding of the pathogenesis of polycystic kidney disease (PKD), the underlying molecular mechanisms involved in cystogenesis are not fully understood. Common features of PKD are excessive epithelial cell proliferation and fluid-filled cyst formation in the kidney, leading to loss of kidney function. We recently demonstrated that netrin-1 is upregulated in primary human PKD cystic cells and in the kidneys of rodent models of PKD. Moreover, overexpression of netrin-1 in tubular epithelium increases cell proliferation (p<0.01) and induces renal cyst development (p<0.0001), while decreasing netrin-1 reduces cyst growth (p<0.01) and improves kidney function (p<0.05). However, the underlying mechanism by which netrin-1 induces cystic cell proliferation is unknown. We hypothesize that netrin-1 increases cystic epithelial cell proliferation by activating Ras-Related C3 Botulinum Toxin Substrate 2 (Rac2) in collecting duct (CD). 4-week-old male tubular overexpressed netrin-1 transgenic mice (NTN-1 Tg6) and 8-week old Pkd1RC/RC mice were randomized to receive vehicle or the specific Rac2 inhibitor EHT 1864 (20 mg/kg/48hr i. p; n=4-5/group) for 4 weeks. Blood and kidneys were collected for biochemical, histological, and Western blot analysis. Renal co-localization of Rac2 with CD specific marker Auaphorin-2 in kidney of human and mouse PKD was assessed by immunofluorescence staining and protein expression was measured by Western blot analysis. Renal Rac2 activity was measured using Rac2 activation kit. Cystic index were measured using H&E staining. Cell proliferation was measured using MTT assay and renal function was measured using BUN assay kit. Rac2 is upregulated in the CD of both human PKD and Pkd1RC/RC mice (p<0.01) compared to controls. Moreover, overexpression of netrin-1 activates Rac2 in the cystic kidney (p<0.001) and in human cystic cells (p<0.05). Overexpression of Rac2 increases cell proliferation and phosphorylation of ERK in CD cells (p<0.01). Inhibition of Rac2 reduces netrin-1-induced CD cell proliferation (p<0.01) and cyst growth (p<0.01) in both netrin-1 transgenic (NTN-1 Tg6) and Pkd1RC/RC mice. Our results demonstrate that overexpression of netrin-1 increases cystic epithelial cell proliferation via activating Rac2 in CD cells and contributes to cyst growth. Future studies will be carried out to dissect the downstream signaling mechanism of netrin-1/Rac2 mediated cell proliferation cyst formation in PKD. This work is supported by Intramural grant award (IGPP00043) from Augusta University to R. Mohamed; National Institute of Health (1P01HL134604-01) to J.C. Sullivan. This is the full abstract presented at the American Physiology Summit 2024 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.

고양이 다낭성신장질환의 유전학적 연구 및 발병기전에 대한 고찰

Autosomal-dominant polycystic kidney disease (ADPKD) is a progressive genetic disease in which multiple small and large fluid-filled sacs (cysts or cysts) are formed in one or both kidneys. Polycystic kidney disease in cats is classified as an autosomal dominant genetic disease and has been found to be caused by mutations in the PKD1 gene that is coding a unit of mechanosensitive calcium channel, polycystin 1. It shows that humans and cats share a genetic cause for polycystic kidney disease. In this paper, we try to understand the pathogenesis of polycystic kidney disease through the genetic mutations and protein functions of feline polycystic kidney syndrome reported so far, and discuss the direction of genetic research that needs to be performed in the future.

Overexpression of notch signaling in renin cells leads to a polycystic kidney phenotype.

Polycystic kidney disease (PKD) is an inherited disorder that results in large kidneys, numerous fluid-filled cysts, and ultimately end-stage kidney disease. PKD is either autosomal dominant caused by mutations in PKD1 or PKD2 genes or autosomal recessive caused by mutations in the PKHD1 or DZIP1L genes. While the genetic basis of PKD is known, the downstream molecular mechanisms and signaling pathways that lead to deregulation of proliferation, apoptosis, and differentiation are not completely understood. The Notch pathway plays critical roles during kidney development including directing differentiation of various progenitor cells, and aberrant Notch signaling results in gross alternations in cell fate. In the present study, we generated and studied transgenic mice that have overexpression of an intracellular fragment of mouse Notch1 ('NotchIC') in renin-expressing cells. Mice with overexpression of NotchIC in renin-expressing cells developed numerous fluid-filled cysts, enlarged kidneys, anemia, renal insufficiency, and early death. Cysts developed in both glomeruli and proximal tubules, had increased proliferation marks, and had increased levels of Myc. The present work implicates the Notch signaling pathway as a central player in PKD pathogenesis and suggests that the Notch-Myc axis may be an important target for therapeutic intervention.

Non-coding RNAs as potential biomarkers and therapeutic targets in polycystic kidney disease.

Polycystic kidney disease (PKD) is a significant cause of end-stage kidney failure and there are few effective drugs for treating this inherited condition. Numerous aberrantly expressed non-coding RNAs (ncRNAs), particularly microRNAs (miRNAs), may contribute to PKD pathogenesis by participating in multiple intracellular and intercellular functions through post-transcriptional regulation of protein-encoding genes. Insights into the mechanisms of miRNAs and other ncRNAs in the development of PKD may provide novel therapeutic strategies. In this review, we discuss the current knowledge about the roles of dysregulated miRNAs and other ncRNAs in PKD. These roles involve multiple aspects of cellular function including mitochondrial metabolism, proliferation, cell death, fibrosis and cell-to-cell communication. We also summarize the potential application of miRNAs as biomarkers or therapeutic targets in PKD, and briefly describe strategies to overcome the challenges of delivering RNA to the kidney, providing a better understanding of the fundamental advances in utilizing miRNAs and other non-coding RNAs to treat PKD.

Non-cell-autonomous activation of hedgehog signaling contributes to disease progression in a mouse model of renal cystic ciliopathy.

Polycystic kidney disease (PKD) is a ciliopathy characterized by fluid-filled epithelial cysts in the kidney. Although it is well established that the primary cilium is essential for hedgehog (HH) signaling and HH signaling is abnormally activated in multiple PKD models, the mechanism and function of HH activation in PKD pathogenesis remain incompletely understood. Here we used a transgenic HH reporter mouse line to identify the target tissue of HH signaling in Arl13f/f;Ksp-Cre mutant kidney, in which the cilia biogenesis gene Arl13b is specifically deleted in epithelial cells of the distal nephron. In addition, we used a co-culture system to dissect cross-talk between epithelial and mesenchymal cells in the absence of expanding cysts. Finally, we treated Arl13bf/f;Ksp-Cre mice with the GLI inhibitor GANT61 and analyzed its impact on PKD progression in this model. We found that deletion of Arl13b in epithelial cells in the mouse kidney, in vivo, led to non-cell-autonomous activation of the HH pathway in the interstitium. In vitro, when co-cultured with mesenchymal cells, Arl13b-/- epithelial cells produced more sonic hedgehog in comparison to cells expressing Arl13b. Reciprocally, HH signaling was activated in mesenchymal cells co-cultured with Arl13b-/- epithelial cells. Finally, whole body inhibition of the HH pathway by GANT61 reduced the number of proliferating cells, inhibited cyst progression and fibrosis and preserved kidney function in Arl13bf/f;Ksp-Cre mice. Our results reveal non-cell-autonomous activation of HH signaling in the interstitium of the Arl13bf/f;Ksp-Cre kidney and suggest that abnormal activation of the HH pathway contributes to disease progression.

The Less Well-Known Little Brothers: The SLC9B/NHA Sodium Proton Exchanger Subfamily-Structure, Function, Regulation and Potential Drug-Target Approaches.

The SLC9 gene family encodes Na+/H+ exchangers (NHEs), a group of membrane transport proteins critically involved in the regulation of cytoplasmic and organellar pH, cell volume, as well as systemic acid-base and volume homeostasis. NHEs of the SLC9A subfamily (NHE 1–9) are well-known for their roles in human physiology and disease. Much less is known about the two members of the SLC9B subfamily, NHA1 and NHA2, which share higher similarity to prokaryotic NHEs than the SLC9A paralogs. NHA2 (also known as SLC9B2) is ubiquitously expressed and has recently been shown to participate in renal blood pressure and electrolyte regulation, insulin secretion and systemic glucose homeostasis. In addition, NHA2 has been proposed to contribute to the pathogenesis of polycystic kidney disease, the most common inherited kidney disease in humans. NHA1 (also known as SLC9B1) is mainly expressed in testis and is important for sperm motility and thus male fertility, but has not been associated with human disease thus far. In this review, we present a summary of the structure, function and regulation of expression of the SLC9B subfamily members, focusing primarily on the better-studied SLC9B paralog, NHA2. Furthermore, we will review the potential of the SLC9B subfamily as drug targets.

Single Gene Mutations in Pkd1 or Tsc2 Alter Extracellular Vesicle Production and Trafficking.

Simple SummaryExtracellular vesicles shed from primary cilia may be involved in renal cystogenesis. The disruption of the Pkd1 gene in our cell culture system increased the production of EVs in a similar way that occurs when the Tsc2 gene is disrupted. Disruption of the primary cilia depresses EV production, and this may be the reason that the combined Kif3A/Pkd1 mutant mouse has a less severe phenotype than the Pkd1 mutant alone. We initiated studies aimed at understanding the renal trafficking of renally-derived EVs and found that single gene disruptions can alter the EV kinetics based on dye tracking studies. These results raise the possibility that EV features, such as cargo, dose, tissue half-life, and targeting, may be involved in the disease process, and these features may also be fertile targets for diagnostic, prognostic, and therapeutic investigation.Patients with autosomal dominant polycystic kidney disease (ADPKD) and tuberous sclerosis complex (TSC) are born with normal or near-normal kidneys that later develop cysts and prematurely lose function. Both renal cystic diseases appear to be mediated, at least in part, by disease-promoting extracellular vesicles (EVs) that induce genetically intact cells to participate in the renal disease process. We used centrifugation and size exclusion chromatography to isolate the EVs for study. We characterized the EVs using tunable resistive pulse sensing, dynamic light scattering, transmission electron microscopy, and Western blot analysis. We performed EV trafficking studies using a dye approach in both tissue culture and in vivo studies. We have previously reported that loss of the Tsc2 gene significantly increased EV production and here demonstrate that the loss of the Pkd1 gene also significantly increases EV production. Using a cell culture system, we also show that loss of either the Tsc2 or Pkd1 gene results in EVs that exhibit an enhanced uptake by renal epithelial cells and a prolonged half-life. Loss of the primary cilia significantly reduces EV production in renal collecting duct cells. Cells that have a disrupted Pkd1 gene produce EVs that have altered kinetics and a prolonged half-life, possibly impacting the duration of the EV cargo effect on the recipient cell. These results demonstrate the interplay between primary cilia and EVs and support a role for EVs in polycystic kidney disease pathogenesis.

Afferent Renal Nerve Activity is Proportionately Increased with Cystic Progression in a Preclinical Model of Autosomal Recessive Polycystic Kidney Disease

Polycystic kidney disease (PKD) is the most common genetic cause of kidney failure, though the mechanisms underlying cyst formation and disease progression remain unclear. Innervation of the kidney contributes to the pathology of other cardiorenal dysfunction, including hypertension and chronic kidney disease ‐ frequent complications of PKD. In previous studies, we demonstrated renal denervation (RDNX), either total or afferent‐targeted (sensory) nerve ablation, reduced cystogenesis in a rat model of autosomal recessive PKD, thus highlighting a role for renal afferent nerves in PKD renal cystogenesis. To further elucidate this novel relationship, we aimed to quantify the renal afferent nerve activity (ARNA) in the adult PCK rat compared to non‐cystic controls. We hypothesized that ARNA would be elevated in the PCK rat compared to controls, and ARNA would directly correlate with renal cystic severity.To address our hypothesis, we conducted direct afferent renal nerve recordings in 10‐week‐old PCK (n=15; 11M/4F) and age‐matched Sprague‐Dawley controls (SD; n=14; 6M/8F). Multiunit nerve recording was performed under isoflurane anesthesia by isolating and placing a renal nerve bundle on an iridium bipolar electrode, which was then encased in silicone. The nerve bundle was severed proximal to the electrode to isolate afferent renal nerve activity (ARNA). Following a 10‐minute stabilization period, resting ARNA was recorded for 10 minutes. To permit comparison between animals, resting ARNA was normalized to a maximal stimulus, achieved by renal pelvic perfusion of 50 µM capsaicin. Finally, electrical noise was isolated by sectioning the distal end of the nerve bundle. Recordings were rectified and integrated over 50 ms. ARNA was expressed as a percentage of maximal ARNA. Following nerve recording, kidneys were collected, formalin fixed, and embedded in paraffin for histologic analysis of renal cystic index (CI). Kidneys were stained with Masson’s Trichrome and analyzed using ImageJ, and CI was quantified by normalizing cystic area to the total kidney area. Data presented as mean ±SEM.Resting ARNA was higher in PCK (22.7±4.2%) rats compared to non‐cystic SD controls (7.4±1.3%; Figure 1). Overall, PCK rats had an average CI of 8.7±0.7%. No sex differences in ARNA between male and female PCK rats were detected; however, CI was higher in male PCK rats (9.5±2.3%) compared to female PCK (6.3±1.9%). Further analysis of ARNA versus cystic index revealed a direct correlation between ARNA and renal cystic severity (F=5.9; R=0.61; p<0.05; Figure 2).These findings support our hypothesis that ARNA is elevated in the PCK rat. Importantly, ARNA is directly correlated with cystic progression in this model. To our knowledge, this study is the first to directly measure ARNA in this model of ARPKD, as well as to compare ARNA to cyst severity. These findings, combined with our previous studies, lead us to conclude that increased ARNA may directly contribute to the progression of PKD in this model. Presently, these data are limited to single endpoint observations. We are currently conducting additional studies to further dissect the temporal relationship between ARNA and renal cyst development. Our future studies will investigate the stimuli amplifying ARNA in a continued effort to parse the role of this novel neural‐renal axis in the pathogenesis of PKD.

Netrin-1 Overexpression Induces Polycystic Kidney Disease: A Novel Mechanism Contributing to Cystogenesis in Autosomal Dominant Polycystic Kidney Disease

Despite recent advances in understanding the pathogenesis of polycystic kidney disease (PKD), the underlying molecular mechanisms involved in cystogenesis are not fully understood. This study describes a novel pathway involved in cyst formation. Transgenic mice overexpressing netrin-1 in proximal tubular cells showed increased production and urinary excretion of netrin-1. Although no cysts were detectable immediately after birth, numerous small cysts were evident by the age of 4 weeks, and disease was accelerated along with age. Surprisingly, cyst formation in the kidney was restricted to male mice, with 80% penetrance. However, ovariectomy induced kidney cyst growth in netrin-1-overexpressing female mice. Cyst development in males was associated with albuminuria and polyuria and increased cAMP excretion in netrin-1 transgenic mice. Netrin-1 overexpression significantly increased extracellular signal-regulated kinase and focal adhesion kinase phosphorylation and vimentin expression. Interestingly, p53 expression was increased but in an inactive form. Furthermore, netrin-1 expression was increased in cystic epithelia and urine of various rodent models of PKD. siRNA-mediated suppression of netrin-1 significantly reduced cyst growth and improved kidney function in netrin-1 transgenic mice and in two genetic animal models of PKD. Together, these data demonstrate that netrin-1 up-regulation induced cyst formation in autosomal dominant PKD.

First Author Spotlight.

First Author Spotlight.

Establishment of the induced pluripotent stem cell line PLAFMCi006-A from peripheral blood mononuclear cells of polycystic kidney disease patients with PKD2 gene mutation

Polycystic kidney disease (PKD) caused by PKD2 mutation is an important type of autosomal dominant PKD. In this study, peripheral blood mononuclear cells from a patient with PKD2 polycystic kidney disease were reprogrammed to obtain induced pluripotent stem cells (iPSCs). After stable amplification, the pluripotency of the iPSCs was determined by identifying their cell-surface markers, their expression of pluripotency-related genes, and their ability to form teratomas with three germ layers in vivo. The establishment of the iPSC line could provide a basis for a kidney-like organ model of human PKD caused by PKD2 mutation for use in studying the pathogenesis of PKD along with relevant screening and testing intervention drugs.

Rapamycin treatment correlates changes in primary cilia expression with cell cycle regulation in epithelial cells

Primary cilia are sensory organelles that regulate cell cycle and signaling pathways. In addition to its association with cancer, dysfunction of primary cilia is responsible for the pathogenesis of polycystic kidney disease (PKD) and other ciliopathies. Because the association between cilia formation or length and cell cycle or division is poorly understood, we here evaluated their correlation in this study. Using Spectral Karyotyping (SKY) technique, we showed that PKD and the cancer/tumorigenic epithelial cells PC3, DU145, and NL20-TA were associated with abnormal ploidy. We also showed that PKD and the cancer epithelia were highly proliferative. Importantly, the cancer epithelial cells had a reduction in the presence and/or length of primary cilia relative to the normal kidney (NK) cells. We then used rapamycin to restore the expression and length of primary cilia in these cells. Our subsequent analyses indicated that both the presence and length of primary cilia were inversely correlated with cell proliferation. Collectively, our data suggest that restoring the presence and/or length of primary cilia may serve as a novel approach to inhibit cancer cell proliferation.

Metalloproteinase PAPP-A regulation of IGF-1 contributes to polycystic kidney disease pathogenesis.

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 Pkd1RC/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 Pkd1RC/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 Pkd1RC/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.

Discoidin Domain Receptor 1 (DDR1) tyrosine kinase is upregulated in PKD kidneys but does not play a role in the pathogenesis of polycystic kidney disease.

Tolvaptan is the only drug approved to slow cyst growth and preserve kidney function in patients with autosomal dominant polycystic kidney disease (ADPKD). However, its limited efficacy combined with significant side effects underscores the need to identify new and safe therapeutic drug targets to slow progression to end stage kidney disease. We identified Discoidin Domain Receptor 1 (DDR1) as receptor tyrosine kinase upregulated in vivo in 3 mouse models of ADPKD using a novel mass spectrometry approach to identify kinases upregulated in ADPKD. Previous studies demonstrating critical roles for DDR1 to cancer progression, its potential role in the pathogenesis of a variety of other kidney disease, along with the possibility that DDR1 could provide new insight into how extracellular matrix impacts cyst growth led us to study the role of DDR1 in ADPKD pathogenesis. However, genetic deletion of DDR1 using CRISPR/Cas9 failed to slow cyst growth or preserve kidney function in both a rapid and slow mouse model of ADPKD demonstrating that DDR1 does not play a role in PKD pathogenesis and is thus a not viable drug target. In spite of the negative results, our studies will be of interest to the nephrology community as it will prevent others from potentially conducting similar experiments on DDR1 and reinforces the potential of performing unbiased screens coupled with in vivo gene editing using CRISPR/Cas9 to rapidly identify and confirm new potential drug targets for ADPKD.

Polycystic kidney disease.

Cystic kidneys are common causes of end-stage renal disease, both in children and in adults. Autosomal dominant polycystic kidney disease (ADPKD) and autosomal recessive polycystic kidney disease (ARPKD) are cilia-related disorders and the two main forms of monogenic cystic kidney diseases. ADPKD is a common disease that mostly presents in adults, whereas ARPKD is a rarer and often more severe form of polycystic kidney disease (PKD) that usually presents perinatally or in early childhood. Cell biological and clinical research approaches have expanded our knowledge of the pathogenesis of ADPKD and ARPKD and revealed some mechanistic overlap between them. A reduced 'dosage' of PKD proteins is thought to disturb cell homeostasis and converging signalling pathways, such as Ca2+, cAMP, mechanistic target of rapamycin, WNT, vascular endothelial growth factor and Hippo signalling, and could explain the more severe clinical course in some patients with PKD. Genetic diagnosis might benefit families and improve the clinical management of patients, which might be enhanced even further with emerging therapeutic options. However, many important questions about the pathogenesis of PKD remain. In this Primer, we provide an overview of the current knowledge of PKD and its treatment.

NHA2 promotes cyst development in an invitro model of polycystic kidney disease.

Significant and selective up-regulation of the Na+ /H+ exchanger NHA2 (SLC9B2) was observed in cysts of patients with autosomal dominant polycystic kidney disease. Using the MDCK cell model of cystogenesis, it was found that NHA2 increases cyst size. Silencing or pharmacological inhibition of NHA2 inhibits cyst formation invitro. Polycystin-1 represses NHA2 expression via Ca2+ /NFAT signalling whereas the dominant negative membrane-anchored C-terminal fragment (PC1-MAT) increased NHA2 levels. Drugs (caffeine, theophylline) and hormones (vasopressin, aldosterone) known to exacerbate cysts elicit NHA2 expression. Taken together, the findings reveal NHA2 as a potential new player in salt and water homeostasis in the kidney and in the pathogenesis of polycystic kidney disease. Autosomal dominant polycystic kidney disease (ADPKD) is caused by mutations in PKD1 and PKD2 encoding polycystin-1 (PC1) and polycystin-2 (PC2), respectively. The molecular pathways linking polycystins to cyst development in ADPKD are still unclear. Intracystic fluid secretion via ion transporters and channels plays a crucial role in cyst expansion in ADPKD. Unexpectedly, we observed significant and selective up-regulation of NHA2, a member of the SLC9B family of Na+ /H+ exchangers, that correlated with cyst size and disease severity in ADPKD patients. Using three-dimensional cultures of MDCK cells to model cystogenesis invitro, we showed that ectopic expression of NHA2 is causal to increased cyst size. Induction of PC1 in MDCK cells inhibited NHA2 expression with concordant inhibition of Ca2+ influx through store-dependent and -independent pathways, whereas reciprocal activation of Ca2+ influx by the dominant negative membrane-anchored C-terminal tail fragment of PC1 elevated NHA2. We showed that NHA2 is a target of Ca2+ /NFAT signalling and is transcriptionally induced by methylxanthine drugs such as caffeine and theophylline, which are contraindicated in ADPKD patients. Finally, we observed robust induction of NHA2 by vasopressin, which is physiologically consistent with increased levels of circulating vasopressin and up-regulation of vasopressin V2 receptors in ADPKD. Our findings have mechanistic implications on the emerging use of vasopressin V2 receptor antagonists such as tolvaptan as safe and effective therapy for polycystic kidney disease and reveal a potential new regulator of transepithelial salt and water transport in the kidney.

A cleavage product of Polycystin-1 is a mitochondrial matrix protein that affects mitochondria morphology and function when heterologously expressed

Recent studies have reported intrinsic metabolic reprogramming in Pkd1 knock-out cells, implicating dysregulated cellular metabolism in the pathogenesis of polycystic kidney disease. However, the exact nature of the metabolic changes and their underlying cause remains controversial. We show herein that Pkd1ko/ko renal epithelial cells have impaired fatty acid utilization, abnormal mitochondrial morphology and function, and that mitochondria in kidneys of ADPKD patients have morphological alterations. We further show that a C-terminal cleavage product of polycystin-1 (CTT) translocates to the mitochondria matrix and that expression of CTT in Pkd1ko/ko cells rescues some of the mitochondrial phenotypes. Using Drosophila to model in vivo effects, we find that transgenic expression of mouse CTT results in decreased viability and exercise endurance but increased CO2 production, consistent with altered mitochondrial function. Our results suggest that PC1 may play a direct role in regulating mitochondrial function and cellular metabolism and provide a framework to understand how impaired mitochondrial function could be linked to the regulation of tubular diameter in both physiological and pathological conditions.

Deletion of Pkd1 in renal stromal cells causes defects in the renal stromal compartment and progressive cystogenesis in the kidney

Autosomal dominant polycystic kidney disease (ADPKD), caused by PKD1 and PKD2 gene mutations, is one of the most common genetic diseases, affecting up to 1 in 500 people. Mutations of PKD1 account for over 85% of ADPKD cases. However, mechanisms of disease progression and explanations for the wide range in disease phenotype remain to be elucidated. Moreover, functional roles of PKD1 in the renal stromal compartment are poorly understood. In this work, we tested if Pkd1 is essential for development and maintenance of the renal stromal compartment and if this role contributes to pathogenesis of polycystic kidney disease using a novel tissue-specific knockout mouse model. We demonstrate that deletion of Pkd1 from renal stromal cells using Foxd1-driven Cre causes a spectrum of defects in the stromal compartment, including excessive apoptosis/proliferation and extracellular matrix deficiency. Renal vasculature was also defective. Further, mutant mice showed epithelial changes and progressive cystogenesis in adulthood modeling human ADPKD. Altogether, we provide robust evidence to support indispensable roles for Pkd1 in development and maintenance of stromal cell derivatives by using a novel ADPKD model. Moreover, stromal compartment defects caused by Pkd1 deletion might serve as an important mechanism for pathogenesis of ADPKD.

B-type natriuretic peptide overexpression ameliorates hepatorenal fibrocystic disease in a rat model of polycystic kidney disease

Polycystic kidney disease (PKD) involves progressive hepatorenal cyst expansion and fibrosis, frequently leadingto end-stage renal disease. Increased vasopressin and cAMP signaling, dysregulated calcium homeostasis, andhypertension play major roles in PKD progression. Theguanylyl cyclase A agonist, B-type natriuretic peptide (BNP), stimulates cGMP and shows anti-fibrotic, anti-hypertensive, and vasopressin-suppressive effects, potentially counteracting PKD pathogenesis. Here, we assessed the impacts of guanylyl cyclase A activation on PKDprogression in a rat model of PKD. Sustained BNP production significantly reduced kidney weight, renal cystic indexes and fibrosis, in concert with suppressed hepatic cystogenesis invivo. Invitro, BNP decreased cystic epithelial cell proliferation, suppressed fibrotic gene expression, andincreased intracellular calcium. Together, our data demonstrate multifaceted effects of sustained activation ofguanylyl cyclase A on polycystic kidney and liver disease. Thus, targeting the guanylyl cyclase A-cGMP axis may provide a novel therapeutic strategy for hepatorenal fibrocystic diseases.

Far Upstream Element-Binding Protein 1 Binds the 3' Untranslated Region of PKD2 and Suppresses Its Translation.

Autosomal dominant polycystic kidney disease pathogenesis can be recapitulated in animal models by gene mutations in or dosage alterations of polycystic kidney disease 1 (PKD1) or PKD2, demonstrating that too much and too little PKD1/PKD2 are both pathogenic. Gene dosage manipulation has become an appealing approach by which to compensate for loss or gain of gene function, but the mechanisms controlling PKD2 expression remain incompletely characterized. In this study, using cultured mammalian cells and dual-luciferase assays, we found that the 3' untranslated region (3'UTR) of PKD2 mRNA inhibits luciferase protein expression. We then identified nucleotides 691-1044, which we called 3FI, as the 3'UTR fragment necessary for repressing the expression of luciferase or PKD2 in this system. Using a pull-down assay and mass spectrometry we identified far upstream element-binding protein 1 (FUBP1) as a 3FI-binding protein. In vitro overexpression of FUBP1 inhibited the expression of PKD2 protein but not mRNA. In embryonic zebrafish, FUBP1 knockdown (KD) by morpholino injection increased PKD2 expression and alleviated fish tail curling caused by morpholino-mediated KD of PKD2. Conversely, FUBP1 overexpression by mRNA injection significantly increased pronephric cyst occurrence and tail curling in zebrafish embryos. Furthermore, FUBP1 binds directly to eukaryotic translation initiation factor 4E-binding protein 1, indicating a link to the translation initiation complex. These results show that FUBP1 binds 3FI in the PKD2 3'UTR to inhibit PKD2 translation, regulating zebrafish disease phenotypes associated with PKD2 KD.