Towards understanding the polycystins

Autosomal dominant polycystic kidney disease (ADPKD) is a very common inherited disease caused by mutations in PKD1 or PKD2 genes characterized by progressive enlargement of fluid-filled cysts and loss of renal function [1]. Previous studies proposed a role for human polycystin-1 in renal morphogenesis acting as a matrix receptor in focal adhesions and for polycystin-2 as a putative calcium channel [2, 3]. The genome of Caenorhabditis elegans contains 2 new members of the polycystin family: lov-1, the homolog for PKD1; and pkd-2, the homolog for PKD2 [4; this paper]. Mutation analysis in C. elegans showed similarly compromised male mating behaviors in all single and double lov-1 and pkd-2 mutants, indicating their participation in a single genetic pathway. Expression analysis localized LOV-1 and PKD-2 to the ends of sensory neurons in male tails and to the tips of CEM neurons in the head, consistent with functions as chemo- or mechanosensors. Human and C. elegans PKD1 and PKD2 homologs, transfected into mammalian renal epithelial cells, co-localized with paxillin in focal adhesions suggesting function in a single biological pathway. Based on the role of polycystins in C. elegans sensory neuron function and the conservation of PKD pathways we suggest that polycystins act as sensors of the extracellular environment, initiating, via focal adhesion assembly, intracellular transduction events in neuronal or morphogenetic processes.     

Autosomal dominant polycystic kidney disease: molecular genetics and pathophysiology

In autosomal dominant polycystic kidney disease (ADPKD), the precise steps leading to cyst formation and loss of renal function remain uncertain. Pathophysiologic studies have suggested that renal tubule epithelial cells form cysts as a consequence of increased proliferation, dedifferentiation, and transition to a secretory pattern of transepithelial-fluid transport. Since the cloning of two genes implicated in ADPKD, there has been an explosion of information about the functions of the gene products polycystin 1 and 2. In this review, we discuss what is known of the functions of the polycystins and how this information is providing important insights into the molecular pathogenesis of ADPKD.     

Molecular complexes formed with polycystins

Polycystins are a family of novel transmembrane proteins with at least six members already identified in humans. Defects in polycystins-1 and -2 are responsible for nearly all cases of autosomal-dominant polycystic kidney disease (ADPKD), a major cause of end-stage renal failure. With the progress made in elucidating the genetic basis of ADPKD, the challenges are to understand the functions of polycystins and to delineate the biochemical and cellular mechanisms of cyst development and progression. In this review, we summarize the recent advances in our knowledge of the functions of polycystins with emphasis on the molecular composition of polycystin protein complexes in the kidney.     

Autosomic dominant polycystic kidney disease and metformin: Old knowledge and new insights on retarding progression of chronic kidney disease

Autosomal dominant polycystic kidney disease (ADPKD) is the most common congenital kidney disorder, generally caused by mutations in the PKD1 and PKD2 genes, coding for polycystins 1 and 2. Its pathogenesis is accompanied by alterations of the cAMP, mTOR, MAPK/ERK, and JAK/STAT pathways. ADPKD is clinically characterized by the formation of many growing cysts with kidney enlargement and a progressive damage to the parenchyma, up to its complete loss of function, and the onset of end-stage renal disease (ESRD). The current aim of ADPKD therapy is the inhibition of cyst development and retardation of chronic kidney disease progression. Several drugs have been recently included as potential therapies for ADPKD including metformin, the drug of choice for the treatment of type 2 diabetes mellitus, according to its potential inhibitory effects on cystogenesis. In this review, we summarize preclinical and clinical evidence endorsing or rejecting metformin administration in ADPKD evolution and pathological mechanisms. We explored the biology of APDKD and the role of metformin in slowing down cystogenesis searching PubMed and Clinical Trials to identify relevant data from the database inception to December 2020. From our research analysis, evidence for metformin as emerging cure for ADPKD mainly arise from preclinical studies. In fact, clinical studies are still scanty and stronger evidence is awaited. Its effects are likely mediated by inhibition of the ERK pathway and increase of AMPK levels, which are both linked to ADPKD pathogenesis.     

常染色体显性多囊肾病的预后评估及治疗

常染色体显性多囊肾病(autosomal dominant polycystic kidney disease, ADPKD)患病率为1‰~2‰, 属于罕见病, 临床主要表现为双侧肾囊肿且逐渐发展, 肾脏体积进行性增大, 肾功能逐步降低。PKD1基因突变约占81%, PKD2基因突变约占10.5%~22%。血管加压素(arginine vasopressin, AVP)和环磷酸腺苷(cyclic adenosine monophosphate, cAMP)信号通路在ADPKD囊肿发展过程中发挥重要作用。近年来发表的梅奥风险评估模型和PROPKD(predicting renal outcome in polycystic kidney disease)评分是ADPKD较好的预后评估模型, 已成为临床医生决策的重要依据。通过拮抗AVP受体, 抑制cAMP通路的托伐普坦已成为ADPKD首个特异治疗药物, 可有效抑制总肾脏体积的增长和保护肾功能。药物的长期安全性仍需进一步研究。     

Molecular genetics of autosomal dominant polycystic kidney disease

Autosomal dominant polycystic kidney disease (ADPKD) is a common Mendelian disorder, occurring in approximately 1 in 1000 births and accounting for 8% to 10% of cases of end-stage renal disease (ESRD). Mutations of 2 genes, PKD1 and PKD2, account for the disease in approximately 80% to 85% and 10% to 15% of families respectively. The gene products (polycystin 1 and 2) of PKD1 and PKD2 are plasma membrane proteins and components of a novel signalling pathway that regulates epithelial cell growth and differentiation. Significant inter- and intrafamilial renal disease variability in ADPKD has been well documented and is influenced by both germline and somatic genetic events. Specifically, genetic locus heterogeneity and 2 rare Mendelian syndromes have been shown to strongly influence the variability of interfamilial renal disease, and as-yet-unknown genetic and environmental factors likely modify both inter- and intrafamilial renal disease severity. Furthermore, individual cyst formation in ADPKD represents an aberration of monoclonal growth triggered by somatic PKD1 or PKD2 mutations within individual epithelial cells. Current studies are in progress to identify major genetic and environmental modifiers of renal disease variability. A thorough knowledge of these determinants will allow better patient risk assessment and development of mechanism-based therapy in ADPKD.     

Genetic mechanisms and signaling pathways in autosomal dominant polycystic kidney disease

Recent advances in defining the genetic mechanisms of disease causation and modification in autosomal dominant polycystic kidney disease (ADPKD) have helped to explain some extreme disease manifestations and other phenotypic variability. Studies of the ADPKD proteins, polycystin-1 and -2, and the development and characterization of animal models that better mimic the human disease, have also helped us to understand pathogenesis and facilitated treatment evaluation. In addition, an improved understanding of aberrant downstream pathways in ADPKD, such as proliferation/secretion-related signaling, energy metabolism, and activated macrophages, in which cAMP and calcium changes may play a role, is leading to the identification of therapeutic targets. Finally, results from recent and ongoing preclinical and clinical trials are greatly improving the prospects for available, effective ADPKD treatments.     

The isolated C-terminus of polycystin-1 promotes increased ATP-stimulated chloride secretion in a collecting duct cell line

Cyst expansion in autosomal dominant polycystic kidney disease (ADPKD) requires accumulation of fluid into the cyst lumen, which is probably driven by aberrant chloride secretion by the cyst lining epithelium. Extracellular ATP is a potent stimulus for chloride secretion in many epithelial systems, and provides a plausible mechanism for secretion in ADPKD. Therefore the link between polycystin-1 and ATP-stimulated chloride secretion was investigated in the M1 cortical collecting duct cell line. M1 cells were stably transfected with a glucocorticoid-inducible cytoplasmic C-terminal polycystin-1 construct fused to a membrane expression cassette. Induction of fusion protein expression was associated with augmentation of ATP-stimulated transepithelial chloride secretion. After nystatin-induced permeabilization of the basolateral membrane, it was determined that expression of the polycystin fusion protein modulated an ATP-responsive apical chloride conductance. It is concluded that up-regulation of ATP-stimulated chloride secretion might play a significant role in cyst expansion in ADPKD.     

Polycystin-1, the PKD1 gene product, is in a complex containing E-cadherin and the catenins

Autosomal dominant polycystic kidney disease (ADPKD) is a common human genetic disease characterized by cyst formation in kidney tubules and other ductular epithelia. Cells lining the cysts have abnormalities in cell proliferation and cell polarity. The majority of ADPKD cases are caused by mutations in the PKD1 gene, which codes for polycystin-1, a large integral membrane protein of unknown function that is expressed on the plasma membrane of renal tubular epithelial cells in fetal kidneys. Because signaling from cell-cell and cell-matrix adhesion complexes regulates cell proliferation and polarity, we speculated that polycystin-1 might interact with these complexes. We show here that polycystin-1 colocalized with the cell adhesion molecules E-cadherin and alpha-, beta-, and gamma-catenin. Polycystin-1 coprecipitated with these proteins and comigrated with them on sucrose density gradients, but it did not colocalize, coprecipitate, or comigrate with focal adhesion kinase, a component of the focal adhesion. We conclude that polycystin-1 is in a complex containing E-cadherin and alpha-, beta-, and gamma-catenin. These observations raise the question of whether the defects in cell proliferation and cell polarity observed in ADPKD are mediated by E-cadherin or the catenins.     

Therapies to slow polycystic kidney disease

Advances in the understanding of cystogenesis and availability of animal models orthologous to human autosomal dominant polycystic kidney disease (ADPKD) and recessive polycystic kidney disease (ARPKD) will likely facilitate the development of treatments for these diseases. Proteins mutated in ADPKD and ARPKD, as well as in several animal models, are localized to renal primary cilia. These are thought to have a sensory function and contribute to the regulation of the intracellular calcium ([Ca2+]i). It seems likely that the maintenance of a differentiated renal epithelial phenotype, characterized by controlled fluid secretion and cell proliferation, requires precise functional coordination of cAMP and Ras/Raf/MEK/ERK signaling by [Ca2+]i. [Ca2+]i alterations, linked to genetic defects causing polycystic kidney disease, may hinder negative feedback mechanisms that control cAMP and Ras/Raf/MEK/ERK signaling, and result in increased fluid secretion and cell proliferation. cAMP levels, Raf kinase activities and ERK phosphorylation are increased in polycystic kidneys. There is also evidence of abnormal cross-talk between cAMP and MAPK pathways, that can be reproduced in wild-type cells by altering [Ca2+]i. While cAMP inhibits Ras-Raf-1-stimulated phosphorylation of ERK in normal kidney cells, it markedly increases B-Raf kinase activity and ERK phosphorylation in polycystic kidney cells. Treatment strategies should probably be aimed at increasing [Ca2+]i, inhibiting Ras/Raf/MEK/ERK signaling or lowering cAMP in the distal nephron and collecting duct. Vasopressin is the major adenylyl cyclase agonist in the collecting duct principal cells via a V2 receptor. OPC31260, a V2 receptor antagonist, lowers renal cAMP and markedly inhibits cystogenesis in four animal models of polycystic kidney disease, three of which are orthologous to human diseases (PCK rat, ARPKD; pcy mouse, adolescent nephronophthisis; Pkd2WS25/- mouse, ADPKD). The renal selectivity and safety profile of this class of drugs make it an excellent candidate for clinical trials.     

Modifier effect of the Glu298Asp polymorphism of endothelial nitric oxide synthase gene in autosomal-dominant polycystic kidney disease

Autosomal-dominant polycystic kidney disease (ADPKD) is one of the most common monogenic diseases. It is characterized by a substantial variability in the severity of renal phenotype, primarily assessed by the age at end-stage renal disease (ESRD). The role of modifier genes has been shown in various hereditary diseases, including ADPKD. The gene coding for the endothelial nitric oxide synthase (NOS3) is considered to have a modifier effect on the severity of ADPKD, even if there are studies among different populations that have shown contradictory results. In this study, we investigated the influence of one of the most studied polymorphisms of the NOS3 gene, the Glu298Asp polymorphism, on the age at ESRD in ADPKD. We analyzed a total of 100 ADPKD unrelated patients and 107 healthy cohorts from the Greek population. ADPKD patients were classified into two subgroups: patients with early (rapid progressors) and late (slow progressors) age at ESRD. The results suggested that the Glu298Asp polymorphism of NOS3 gene is associated with the onset age of ESRD. The distribution of C/T alleIes is significantly different between rapid and slow ADPKD progressors leading to the conclusion that the T allele of the Glu298Asp polymorphism of NOS3 gene is associated with earlier progression to ESRD in ADPKD patients.     

Macrophage migration inhibitory factor promotes cyst growth in polycystic kidney disease

Autosomal dominant polycystic kidney disease (ADPKD) is characterized by renal cyst formation, inflammation, and fibrosis. Macrophages infiltrate cystic kidneys, but the role of these and other inflammatory factors in disease progression are poorly understood. Here, we identified macrophage migration inhibitory factor (MIF) as an important regulator of cyst growth in ADPKD. MIF was upregulated in cyst-lining epithelial cells in polycystin-1–deficient murine kidneys and accumulated in cyst fluid of human ADPKD kidneys. MIF promoted cystic epithelial cell proliferation by activating ERK, mTOR, and Rb/E2F pathways and by increasing glucose uptake and ATP production, which inhibited AMP-activated protein kinase signaling. MIF also regulated cystic renal epithelial cell apoptosis through p53-dependent signaling. In polycystin-1–deficient mice, MIF was required for recruitment and retention of renal macrophages, which promoted cyst expansion, and Mif deletion or pharmacologic inhibition delayed cyst growth in multiple murine ADPKD models. MIF-dependent macrophage recruitment was associated with upregulation of monocyte chemotactic protein 1 (MCP-1) and inflammatory cytokine TNF-α. TNF-α induced MIF expression, and MIF subsequently exacerbated TNF-α expression in renal epithelial cells, suggesting a positive feedback loop between TNF-α and MIF during cyst development. Our study indicates MIF is a central and upstream regulator of ADPKD pathogenesis and provides a rationale for further exploration of MIF as a therapeutic target for ADPKD.     

Expression and cellular localisation of renal endothelin-1 and endothelin receptor subtypes in autosomal-dominant polycystic kidney disease

The major factors influencing the rate of progression of chronic renal disease in autosomal-dominant polycystic kidney disease (ADPKD) are unknown and there are currently no effective treatments for slowing the progression of chronic renal failure in ADPKD patients. As a first step in investigating the potential role of endothelin-1 (ET1) and its receptors (ETA and ETB) in the pathophysiology of progression in ADPKD, we have studied their expression and cellular localisation in ADPKD kidney. Immunoreactive ET1 was detected in cyst epithelia, mesangial cells and vascular smooth muscle cells suggesting continuing ET1 synthesis in the cystic kidney. Compared to healthy controls, ETA mRNA was 5-10-fold higher in ADPKD cystic kidney. In cystic kidney, neo-expression of ETA receptors was found overlying glomeruli and cysts and markedly increased in medium-sized renal arteries by microautoradiography. This is the first study to demonstrate a specific upregulation of ETA receptors in human renal disease. Future studies should address whether ETA selective antagonists may be effective in slowing renal disease progression in ADPKD.     

Autosomal dominant polycystic kidney disease: recent advances in pathogenesis and treatment

Autosomal dominant polycystic kidney disease (ADPKD) is a common genetic disorder affecting 1 in 1,000 people in the general population and accounts for up to 10% of all patients on renal replacement therapy. Numerous fluid-filled epithelial cysts arise from different nephron segments as spherical dilatations or small out-pouchings, enlarge progressively and eventually become disconnected from the rest of the renal tubule. The development of cysts is accompanied by destruction of the renal parenchyma, interstitial fibrosis, cellular infiltration and loss of functional nephrons. ADPKD is not only a kidney disease but also a systemic disorder associated with intracranial arterial aneurysms, cardiac valvular defects, colonic diverticulosis and cyst formation in other organs such as the liver, spleen and pancreas. The identification of PKD1 and PKD2 together with the drive to elucidate the functions of their encoded proteins, polycystin-1 (PC1) and polycystin-2 (PC2), has led to an explosion of clinical and scientific interest in this common disorder. The aim of this review is to highlight recent advances in our understanding of ADPKD pathogenesis which are leading to exciting new treatment strategies.     

多囊蛋白-1 LRR-WSC区单克隆抗体的制备及其在免疫组织化学诊断中的应用

目的 用杂交瘤技术制备抗多囊蛋白-1 LRR-WSC区单克隆抗体，检测多囊蛋白-1在肾组织和肾细胞株中的分布和定位。方法 用多囊蛋白-1 LRR-WSC区融合蛋白PCI-e免疫BALB／c小鼠，将其脾细胞与骨髓瘤细胞株SP2／0进行细胞融合，间接酶联免疫吸附试验(ELISA)筛选出阳性克隆，有限稀释法将杂交瘤细胞株单克隆化，间接ELISA法和免疫印迹法(WB)鉴定抗体的特异性。用制备的抗多囊蛋白-1 LRR-WSC区单克隆抗体，免疫组织化学和免疫细胞化学法检测多囊蛋白-1在不同肾组织和肾细胞株中的分布。结果 细胞融合后经筛选和克隆得到的杂交瘤细胞株经WB分析表明，该细胞株分泌的单克隆抗体能特异地与多囊蛋白-1 LRR-WSC区结合。免疫组织化学显示，多囊蛋白-1主要分布于正常肾组织的远端肾小管和集合管，在胎肾囊肿组织中表达于近端肾小管，在人常染色体显性多囊肾病(ADPKD)肾囊肿组织中，表达于囊肿衬里上皮细胞，同时在ADPKD肾囊肿衬里上皮细胞系和猪近端肾小管细胞株(LLC-PK1)中也发现了多囊蛋白-1的表达。结论 本实验成功制备了抗多囊蛋白-1 LRR-WSC区的单克隆抗体，该抗体对深入研究ADPKD的发病机制具有重要意义。多囊蛋白-1在肾组织中的表达模式对肾小管的形态发生、维持肾小管结构的完整性非常重要。     

肾脏总体积对常染色体显性多囊肾病病情进展和预后评估价值的Meta分析

目的 采用Meta分析的方法,探讨肾脏总体积(TKV)对常染色体显性遗传性多囊肾病(ADPKD)病情进展及预后判断的价值.方法 运用计算机检索Cochrane Library、PubMed、Embase、中国知网(CNKI)等数据库,检索ADPKD患者TKV 和病情进展及预后判断相关的文献,检索期限为各数据库建库至20...     

Polycystic liver and kidney diseases

There have been remarkable advances in research on polycystic liver and kidney diseases recently, covering cloning of new genes, refining disease classifications, and advances in understanding more about the molecular pathology of these diseases. Autosomal dominant polycystic kidney disease (ADPKD) is the most common hereditary disease affecting kidneys. It affects 1/400 to 1/1000 live births and accounts for 5% of the end stage renal disease in the United States and Europe, and is caused by gene defects in the PKD1 or PKD2 genes. Compared to ADPKD, polycystic liver disease (PCLD) is a milder disease and does not lower life expectancy. Both diseases are usually adult-onset diseases. Defects in genes, which code the hepatocystin and SEC63 proteins, have just recently been found to cause PCLD. It now seems that ADPKD is caused by malfunction of the primary cilia, a cell organ sensing fluid movement, and that PCLD is a sequel from defects in protein processing. Autosomal recessive polycystic kidney disease (ARPKD) belongs to a group of congenital hepatorenal fibrocystic syndromes. All ARPKD patients have a gene defect in a gene called PKHD1, the protein product of which localizes to primary cilia. We summarize the present clinical and molecular knowledge of these diseases in this review.     

Hepatic cysts in autosomal dominant polycystic kidney disease

Hepatic cysts are one of several extrarenal manifestations of the ADPKD gene. Several factors, including age, gender, pregnancy, the degree of renal cystic disease, and the extent of renal functional impairment, may modify the expression of hepatic cystic disease. With advances in medical care, such as improvement in the management of end-stage renal disease, hemodialysis, and renal transplantation, patients with ADPKD will experience an increased life expectancy. As a result, complications associated with hepatic cysts may become more common, and physicians may encounter an increasing number of patients with ADPKD who have infected hepatic cysts. Several issues in the management of this complication remain unresolved, but the article by Telenti and associates in this issue of the Proceedings addresses some of the critical issues that physicians who are responsible for the care of these patients will certainly confront in future years.